SEASONAL DISTRIBUTION OF THE PLANKTON OF THE WOODS HOLE REGION : : : : By Charles J. Fish
From BULLETIN OF THE BUREAU OF FISHERIES, Volume XLI, 1925
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SEASONAL DISTRIBUTION OF THE PLANKTON OF THE WOODS HOLE REGION oo
By CHARLES J. FISH, Ph. D., General Assistant, U. S. F. S. Albatross
Pd Contribution from the U. S. Fisheries Biological Station, Woods Hole, Mass. & CONTENTS Page Page FALrOuuction see eee we Sacre a SS AL 91 | General discussion of plankton—Contd. Methodsti) om. atiitanaliaveriata: 9 93 Crustacea—Continued. NOG Fit OT eee are Sa et a 96 Copepoda =e 22 tases oe 141 Salinity and density _-...-__--2--+--_- 98 Cimipedia= 5a eee 147 Wewiperavuress 6 caer sa cuee Seen 100 EAT bUTOSETS Cae ee 149 General discussion of plankton_-_--_-_--_- 101 Cumaces's=s2 ier ee aes 152 Diatoms and other plants________- 104 Schizopoda and Stomatopoda-_ 152 Proto zOae MUR e el SR Le 121 Macrura ss: Sites pee ewer 155 Coelenteratasss222+-s22bue 2 ete 123 BrachyUrass eer. pe eee ee 159 Annulata and Vermes_--_--------- 130 Pyenogonida and Xiphosura___ 161 INGO EC 2 SS Se Se eee ee aoe 136 Chordatas === Ste sam abe ese ee 162 Pichinodermataesa= 225 = seen 138 Bis Lak Set cee eee ae meee re 164 CruStaCede mre ee ree He eet 139) |) General conclusions==== === "=== -- == 172 iPhyllopoda sl: Sean! Sy. iees 139) PBiblicsraphy=222 saa= ee eee 176 Ostracod assis 4S: bette 140 INTRODUCTION
In the plankton section of the report of the Conseil Permanent International pour l’Exploration de la Mer, published in September, 1922, it was pointed out that greater attention should be paid to the seasonal variation and range of marine plankton. As early as 1880, Prof. S. F. Baird remarked to Commander Z. L. Tanner, after the initial cruise of the United States Fish Commission steamer Fish Hawk, that ‘the profitable study of useful sea fishes can not be prosecuted without a knowledge of their food, the food of their food, their respective friends and foes, the habitat of the several species, and their means of passing from one region to another in the embryonic as well as in the adult stage. The temperature, currents, and specific gravity, also, should be studied in connection with the migra- tions and habits of pelagic forms.’’ Since that time only one area of the Atlantic coast of the United States has been investigated with the object of completely surveying and determining the distribution of the plankton, currents, salinity, and temperature. The interesting results of these investigations, which were
91
99 BULLETIN OF THE BUREAU OF FISHERIES
carried on by Dr. H. B. Bigelow, are published in a series of bulletins from the Museum of Comparative Zoology at Cambridge, Mass., and a more complete account of these investigations and explorations is now in process of publication.
It has long been known that Woods Hole occupies a unique position on the Atlantic coast. It is the northern limit of many southern forms and the southern limit of many northern forms. Oceanic animals, also, are often carried into this pocket on the coast by the southerly winds and strong tides that prevail in the summer months. For that reason Woods Hole was selected as an ideal location for the study of plankton and the interrelationships of the various pelagic faunas.
Under “‘plankton’’ I have included all animals occurring in surface collections, whether free-swimming or carried by currents. Such a broad definition includes a great many benthonic forms carried from their natural habitat by storms or high winds, but in a littoral region one can not always decide accurately which species have been accidentally carried to the surface and which are free-swimming.
The present paper is the result of a continuous investigation of the plankton in Great Harbor, Woods Hole, Mass., covering a period of two years. The purpose was to make an exhaustive qualitative study of the plankton of this region, the seasonal distribution of the various species, their interrelationships, and the general factors governing their distribution.
The investigation consisted of three parts: (1) An examination of plankton samples taken daily during the years 1899 and 1900 in Great Harbor by the late Vinal N. Edwards, collector for the United States Fish Commission; (2) a survey of all records of surface collections of previous years; and (3) examination of living material taken daily in surface collections in Great Harbor, observations on tem- perature, salinity, and other factors governing the seasonal distribution of the plankton, and a survey of the general geography of the region as a factor affecting plankton distribution.
The first part of the investigation occupied the entire time of the author during the year 1921-22 and was carried on in the biological laboratory at Brown Uni- versity. Many of the fragile animals had become disintegrated during the 22 years in which the material had remained untouched, and the preservatives in some of the samples had evaporated. Over 200 vials remained intact, however, and offered ample material for study.
The second part of the work involved much time and proved to be a very tedious task. The results, however, were very important, as they covered the daily records of surface collections extending over a period of 15 years—1893 to 1907, inclusive. ‘The larval fish and celenterates taken during this time had been carefully identified by Vinal N. Edwards. Diatoms, copepods, amphipods, annelids, and other planktonic forms were recorded as groups, the relative abundance for each day bemg carefully noted. Complete records of the weather, wind, and temperature for most of this period were available and proved indispensable in explaining peculiarities in the seasonal distribution of many species. This part of the work was done by Marie D. P. Fish, who aided me in the study of the larval fish also.
The final part of the work was carried on from June 22, 1922, until December 31, 1923, at the laboratory of the United States Bureau of Fisheries at Woods Hole,
PLANKTON OF THE WOODS HOLE REGION 93
Mass. From June 22, 1922, until May 1, 1923, observations were made daily at the same spot where all my previous material had been taken. Fortunately a series of collections had been made by R. A. Goffin during the spring of 1922. From these I was able to trace the first appearance of the summer species. From May 1 to December 1, 1923, the collections were made three times a week, except during the interval from August 22 to October 4. The records for the past summer are therefore not as complete as those of 1922, although they serve as a basis for com- parison.
A kind invitation from Dr. P. S. Galtsoff to assist him in his monthly surveys of Long Island Sound from September, 1922, to August, 1923, made possible valuable observations on the distribution of certain pelagic organisms, particularly the diatoms, in relation to their presence at Woods Hole.
It is a pleasure to express my especial gratitude to Prof. A. D. Mead and Prof. R. M. Field, of Brown University, who furnished me helpful assistance and guidance throughout my work. I am especially indebted to Marie D. P. Fish for her careful tabulation of Vinal N. Edwards’s records of surface collections and temperatures collected over a period of 15 years. I am indebted to Dr. P.S. Galtsoff, who made possible my observations on salinity at Woods Hole and the plankton of adjacent regions, and I wish also to express thanks to Dr. Henry B. Bigelow, Dr. Hugh M. Smith, Dr. Paul Bartsch, Dr. Albert Mann, and Prof. A. E. Verrill, for helpful
advice and criticism rendered at various times during the progress of my work.
METHODS
My first plans provided for daily observations on temperature of the air and water (surface and bottom), salinity, oxygen, wind, weather, sea, transparency, vertical hauls, and surface and bottom collections with plankton nets of No. 2 and No. 20 bolting cloth. Because of the amount of time required to identify the many species of zooplankton and phytoplankton it was found desirable to discontinue certain of these observations. The following schedule was finally adopted:
1. Daily temperatures of surface water and air.
2. Salinity (at certain periods) and density.
3. Daily meteorologic observations on wind, weather, sea, etc.
4, Vertical hauls at weekly intervals with No. 20 net.
5. Daily surface hauls with No. 2 and No. 20 nets. (Later, No. 20-net hauls were reduced to twice a week except during the diatom maxima.) Nets 3 feet by 12 inches with a brass bayonet-lock bucket on bottom were used.
The temperature was taken each day at the time of setting the plankton nets. A series of observations later proved conclusively that at all times the bottom temperature at my station is exactly the same as that of the surface (Table 2,p.101). Bottom observations then were made only during periods of rapidly declining or rising temperatures.
For a period extending over four months salinity was determined daily by titration with nitrate of silver. When these could not be made at once, they were preserved in the standard ‘‘citrate of magnesia” bottles of the sort used for that
94 BULLETIN OF THE BUREAU OF FISHERIES
purpose by the United States Bureau of Fisheries. After it was found that there were usually no important variations observations were made only on certain occasions to indicate the influx of Gulf Stream and other ocean water. Had it been possible continuation of the daily tests would have been very desirable.
Observations on the condition of the weather, sea, wind, and sky were taken daily. These factors are of great importance, particularly the winds, in determining the distribution of planktonic animals.
Vertical hauls were made weekly, but they yielded rather disappointing results. The water is only 11 feet deep at low tide, and for that reason a very small net of the Birge type, with a special bucket, was adopted. The material collected was centrifuged for two minutes at about 1,000 revolutions per minute in a graduated glass tube, and the result measured in cubic centimeters. The figures obtained are not included in this report because I did not have time to make individual counts of the various species, and the total mass was meaningless, bemg made up of diatoms, dinoflagellates, particles of dirt and detritus, larval copepods, larval mollusks, and an occasional adult copepod. All the large planktonic forms had successfully evaded the net as it was being drawn to the surface, and the resulting mass did not give a fair estimate of the amount of plankton in the water at the time. To get these various-sized animals, a series of nets of at least 10 different meshes would be necessary, and even with these there would be so much overlapping that the results would be of little value. The pump has not succeeded in overcoming this difficulty in the case of the marine plankton. On eight occasions during the past year I centrifuged over 100 samples taken by pump in Long Island Sound, and invariably the deposit contained a larger proportion of small forms and a smaller proportion of large forms than did the vertical hauls made at the same time. A successful anit of accurately determining the real volume of marine zooplankton as well as of phytoplankton is yet to be devised.
The most valuable results were obtained with surface nets. The waters are so churned up in Great Harbor that there was no difference in the collections taken at the surface and those taken at the bottom, except that the latter often contained more sand and small detritus. For that reason the bottom hauls were discontinued.
The daily routine of plankton collecting and investigation, consisted of three parts. First, the nets were suspended from the end of the dock by means of pulleys attached to outlying piles in such a position that one was suspended in a northerly direction and the other in a southerly one (fig. 1, p. 97).
When the nets were hauled the contents were emptied into a flat glass dish entirely covered with black paint except for a small area at one corner. A tight- fittmg top completely shut out all light except in the corner over the clear glass. A light placed at this end caused all the Crustacea, larval annelids, and, in fact, most of the free-swimming planktonic organisms that are positively phototropic to crowd at the lighted corner, where they could be picked out individually with a pipette or drawn out in bunches with a long glass tube and deposited in a watch glass or petri dish for examination. A second collection was then made from the detritus in the bottom, consisting of dead organisms and any forms that had not been attracted to the light. Finally, the last bit of sediment, after all the rest of the tow had been poured into a silk bag to be strained, was placed in a dish. This
PLANKTON OF THE WOODS HOLE REGION 95
was often found to contain large numbers of small mollusks, ostracods, and Foram- inifera.
After the living specimens had been observed they were killed with a 2 per cent solution of formalin and reexamined. The species not readily identified were placed in separate watch glasses and subjected later to a more careful examination with a higher-power lens. For a general examination of zooplankton a binocular microscope with low-power lenses (Nos. 55, 40, and 24) is very satisfactory. Smaller forms were mounted on slides and examined with a compound microscope.
Several samples of phytoplankton were placed in watch glasses and examined alive. This made possible a rapid survey of a large amount of material. Next some of the material was mounted on slides, with barium mercuric iodide as a mount- ing medium, and examined with a higher-power lens.
The common species were tabulated daily on charts, records being made of the rarer specimens. If these began to appear frequently, they were given a place on the chart. This method proved to be very simple and convenient. The material was later put in 2 per cent formalin and labeled for future reference.
The direction of the currents in Great Harbor during the flood tide (fig. 1, p. 97) was determined in two ways. The first method was very simple, consisting of observations made while great masses of broken ice were floating through the passage during the spring months. The results obtained in this way could be checked up as often as desired. The second method was used to determine the smaller currents near shore, and the course of the back eddy along the shore of Nonamesset. This was accomplished by placing large quantities of shavings in the water on a calm day and plotting the courses which they took. The resultsmay not be entirely accurate in minute details, but they show the general movements of the water in the harbor during flood tide.
The combined results of my observations on material of 1899-1900 and those of Mr. Edwards have been plotted on quadrille paper. The charts based on the work of the past two years are on Keuffel and Esser No. 334D graph paper.
A great difficulty presented itself when I started to assemble my results. In qualitative work the greatest amount of material possible is essential, and the only way to obtain this is by surface towing, which obviously does not lend itself to any accurate measurement. Hven if figures could be secured the daily variation in the winds and tides is so great at Woods Hole that the results would be more confusing than helpful. One can state when the first specimen of a species appears and when its season ends, and the fact that the numbers may be increasing daily can also be seen, but to present this information in a satisfactory manner is difficult.
The plan finally adopted consisted of the use of four categories—very scarce, scarce, abundant, and very abundant. These served as calibrating points from which the seasonal distribution of a species could be plotted in a fairly accurate manner. Of course, the basis for measuring the abundance of copepods was not the same as that for the diatoms; 500 of the former might be considered abundant, while the same number of diatoms would be considered very scanty. Again, 50 specimens of the oceanic annelid, Tomopterus, would be considered abundant, but 50 specimens of a common copepod would be thought scarce. The measure- ment, therefore, is relative; that is, the symbol given to a particular animal for a
96 BULLETIN OF THE BUREAU OF FISHERIES
particular day indicates its relative abundance for that day compared with its abundance for all the preceding days or weeks since its appearance and is not to be compared with that of the species of any other phylum. To eliminate as far as possible the confusion arising from daily variation, three-day averages were used in plotting the points on the charts. There may be objections to my method of presenting the data in graphic form where definite figures were not available. However, I feel that the seasonal variation can best be shown in this way, and that any method which sim- plifies the work and makes it more easily understood is justifiable. The symbols used on the charts are as follows: V.A., very abundant; A., abundant; S., scarce; V. S., very searce; and JN., none.
LOCATION
All material for the present investigation, with the exception of a few observa- tions made in Vineyard Sound, was obtained from the water at the end of the Bureau of Fisheries dock at Woods Hole, Mass. ‘This spot was selected, first, because it offered such excellent possibilities for qualitative plankton investigation, and, second, because the bottom fauna, whose larvee make up a large percentage of the summer plankton, had already been carefully surveyed.
The location is an exceptionally fortunate one for an investigation of seasonal distribution, although impossible for a study of diurnal migration. On the flood tide the local current rushing through the narrow passage of Woods Hole sometimes reaches a speed of 8 miles an hour. Figure 1 shows that one of the three main branches of this current heads directly for the Fisheries dock. Here it divides, one half turning to the south and the other to the north. By placing nets at the two ends of the dock one hour after the tide has turned to flood and hauling them one hour before the ebb it is possible to have a strong current of water passing through the nets continuously for four hours. More material can be collected in this way than would be possible in several hours’ towing from a boat. To deter- mine the complete pelagic fauna of a region, the largest possible number of daily samples are needed. Even then many scarce forms probably pass through their seasonal cycle without once being observed in surface collections.
Another advantage of the position of this particular station is the uniformity of the plankton both during the day and during the night. Extended observations showed that the mixture of the waters during the flood tide so churns up the plankton that there is almost no difference between the hauls of the day and those taken in the evening. I know of but two exceptions to this statement. These are the amphipods and certain annelids, which remain under rocks in the daylight and emerge after dark. Then they are picked up by the strong currents and appear in the greatest numbers in evening collections. As these are not true pelagic animals, they do not seriously affect the problem. Thus, the collections made at any time showed equally well the representative plankton for that day.
The features of the coast adjacent to Woods Hole have much to do with its fauna. It has long been thought that the arm of Cape Cod to the east constitutes a barrier that changes the course of the cold northern ocean current and deflects it away from the continent. Not all oceanographers agree as to the above, but even
97
PLANKTON OF THE WOODS HOLE REGION
Fia, 1.—Currents of Great Harbor, Woods Hole, Mass., during flood tide.
, nets,
Light shaded area, shallow water; Scale in statute miles
black area,
land
; +, rocks; @, location of plankton
98 BULLETIN OF THE BUREAU OF FISHERIES
if this is not true, Verrill and subsequent authors, including Bigelow (1914-1922), found that the coastal water temperatures north and east of Cape Cod were very much lower in summer than those south of it. None of the planktonic animals common north of the cape appear south of itinsummer. In winter, however, the cape does not form a barrier for the neritic plankton, which often appears at Woods Hole in great abundance.
The Gulf Stream lies about 85 nautical miles off the Massachusetts coast, just beyond the end of the Continental Shelf. Between this warm area and the mainland there is a broad belt extending from the north. Some consider this to be a continuation of the Labrador current and attempt to explain faunal distribution on that basis. Others consider it to be mainly a contrast belt between the warm littoral zone and the Gulf Stream. According to the latter viewpoint, the Labrador current does not extend south of Newfoundland. No matter which theory is correct it is evident that this broad belt is affected on one side by the southerly winds and on the other by the unusually strong tides of this region. Any forms, then, that have blown in from the Gulf Stream will be carried farther mland by the moving water. This peculiar alliance of wind and tide probably explains why much tropical plankton, which is taken so often in this locality, occurs at no other points along the coast.
Woods Hole also forms the northern limit of most of the southern boreal pelagic animals. Many copepods and celenterates, of which Mnemeopsis is a striking example, occur often in Great Harbor but never farther north along the coast. Thus, it is clearly evident that Woods Hole is a very unsatisfactory spot to work out the characteristic pelagic fauna of the north Atlantic coast region, for not only northern and southern boreal types appear with the littoral plankton at certain seasons, but the Gulf Stream and other oceanic forms are likely to be carried in at any time. Again, the swift currents rushing through the passage produce local peculiarities in the plankton. However, if we desire to study the conditions at Woods Hole as a special problem and try to understand the conglomeration of faunas, their interrelations, and the factors governing their appearance and dis- appearance it becomes highly interesting and instructive.
SALINITY AND DENSITY
The salinity at Woods Hole normally varies comparatively little throughout the year. No streams of importance empty into Great Harbor, and as all the larger rivers of Buzzards Bay are situated at the upper end the salinity of the southern area is not sufficiently different from that of the sound to have any appre- ciable effect on the plankton.
Titrations made almost daily from July until October, 1922, during the flood tide (Table 1) indicate that the water entering Great Harbor is of a slightly lower salinity than that of Vineyard Sound, found by Bigelow (1915) to be 32.2 per mille in August, 1913, and by Sumner (1913) to be 32.2 per mille in August, 1906. In 1922 the average salinity at the Fisheries dock for late July and August was 31.57 per mille, and for September and early October, 31.03 per mille.
PLANKTON OF THE WOODS HOLE REGION 99
TaBLE 1.—Salinity of surface water at Woods Hole from July to October, 1922
Degree Degree Degree Degree Degree Degree Date of Date of Date of Date of Date of Date of
salinity salinity Salinity salinity salinity salinity July 27_ 31.53 || Aug. 6_---| 30.30 || Aug.16_._| 31.58 |] Aug. 27 31.85 || Sept. 8__ 31. 22 || Sept. 24 31. 40 July 28__- 46 || Aug. 7 31.20 || Aug.17_--| 31.53 || Aug. 28 31.31 || Sept. 9 31.18 || Sept. 27 31. 44 July 29_ 31.62 || Aug.8__._| 31.29 }| Aug.18.-_) 31.82 |) Aug. 29 31. 49 || Sept. 10 31. 33 || Sept. 29__| 31.40 July 30. 31.31 ug.9_---| 32.01 }| Aug.19-__| 31.60]} Sept. 1 31.36 || Sept.11__} 31.02] Sept. 30__| 31.62 July 31 31.31 |} Aug.10---| 32.01]; Aug.20_-_| 31.65 |] Sept. 2 31. 36 || Sept. 12 31. 06 =.--|/ 30.88 Aug. 1 31.31 || Aug. 11 31.73 |} Aug.21-__| 31.85 || Sept.3 31. 09 || Sept. 13 31.15 || Oct. 2-_--| 31535 Aug. 2__-- 31. 56 |} Aug. 12 31. 82 || Aug. 22_ 31.85 || Sept. 4 30. 91 |} Sept. 14 318) || Oct onens 31.35 Aug. 3----] 31.71 || Aug. 13. 31. 53 || Aug. 23_ 31.85 || Sept. 5 31.18 |} Sept. 16_-] 31.15 ]| Oct. 10__ 31.49 Aug. 4... 31. 64 |} Aug. 14 31. 60 |} Aug. 24_ 31.65 || Sept. 6__ 31. 04 |} Sept. 17_- 31. 06 || Oct. 11_ 31.20 Aug. 5.. 31.46 |} Aug. 15 31. 67 |} Aug. 25_ 31.71 |} Sept. 7 31. 49
After southerly winds a slight increase in salinity usually can be noted. This would naturally be expected, for the outlying waters always have a higher salinity— in the case of the Gulf Stream upwards of 35 per mille. It was to determine to what extent this influx of ocean waters takes place after storms that the titrations were made in Great Harbor. They covered the period when most tropical oceanic animals appear in the plankton. The results showed that very little change takes place even during hard southerly winds unless they extend over a long period of time. ‘This is probably due to a dilution resulting from a mixture with the fresher waters of the southern part of the bay. Marked changes may have occurred in Vineyard Sound but were not evident farther inland.
On August 6 and 7 a heavy southwest storm took place, reaching its height on the second day. During this time the wind blew continuously and much Sargassum was noticed in the sound. A slight increase in salinity from 31.29 to 32.01 per mille on August 9 and 10, followed by a gradual decline, was the only evidence of outside water, and this was below the usual average for theSound in August. However, this again may have represented a mixing of the bay water with that of a higher salinity than is usually found in the sound.
Hard southerly winds extending over a long period of time replace the waters of the region to such an extent that the dilution by bay water is hardly noticeable except after a hard rain or a period of melting snow. This was shown by the density records during the spring of 1922. Figures 2 and 3 give the daily variation in the density at Great Harbor, taken by Mr. Hamblin at the Fisheries dock at 12 o’clock noon. As these unfortunately have no relation to the tides, they can only indicate in a general way the conditions existing at any particular time. Standard hydrometers, certified by the Bureau of Standards, were used, the error being probably not greater than + 0.0001.
The density in shallow waters is governed by two factors, temperature and salinity, the comparative influence of each being clearly shown in Figures 2 and 3. A comparison of Figures 2 and 3 with Figures 4 and 5 indicates the effect of the temperature. Durmg the warmest seasons a minimum density is found, and during the coldest months it reaches its highest pot. Were there no change in the salinity the curve would rise and fall evenly, corresponding to the rise and fall in the temperature of the water. The sudden increase or decrease in the curve at any particular time is due to an increase or decrease in salinity. As previously
100 BULLETIN OF THE BUREAU OF FISHERIES
stated, there are no rivers in the immediate vicinity of Great Harbor, although melting snow and hard northerly winds cause the sudden appearance of waters of comparatively low density. Prevailing southerly winds extending over a long period of time cause high density. In the spring of 1922 (fig. 2), combined with the usual low temperature, the density almost equaled that of ocean water and remained that way until the middle of May.
The effect of melting snow shows clearly (fig. 2) in the first week of April, 1922, and (fig. 3) on January 2 and 3, 1923. On the latter dates 2 marked increase in the number of diatoms was also noticeable. The greatest change took place on March 31, when the density dropped from 1.0260 to 1.0244 in one day. A heavy snowstorm had occurred on March 30, followed by rain and snow on March 31 and April 1. The rapid rise took place during a period of constant hard southwesterly winds. The extreme point reached on April 9 (1.0270), accompanied by a drop of 1° in temperature, is impossible to explain on the basis of local conditions. Southerly winds prevailed, but were not unusually strong. Some hydrographical change beyond the limits of the immediate region must have accounted for it.
It is probable that the salinity plays little or no part in the seasonal distribution of the planktonic animals of this region. The fresh waters of the upper bay no doubt form a barrier for the oceanic species and the brackish water forms probably do not go far out to sea. Such conditions, however, are not found in this immediate region.
TEMPERATURE
The subject of the temperature at Woods Hole and adjacent regions is so fully discussed by Sumner in his report that only the particular conditions existing in Great Harbor during the past two years need be considered here.
Figures 4 and 5 show the variations in the temperature of the air and water for the years 1922-23, inclusive, to December 31. The figures were obtained from the records taken daily at 8 a. m. by Mr. Hamblin, of the Bureau of Fisheries. This hour was selected because it eliminates the temporary midday rise of surface temperature typical of all shallow water. Figure 6 was compiled by Sumner to show the mean average temperature of the air and water for a period of five years. A comparison of this chart with that of the past year shows many important points. The fact that Sumner’s chart is based on noon records must be considered, although it probably had little effect on the water curve. The highest point on this curve is on August 12, when the mean temperature was slightly over 71° F. The highest point reached in 1922 was 71° F., on August 8. The curve for 1922 agrees well with that of the average temperature for other years. The lower point of the latter (30° F.) was reached only once, on February 19. In 1922 the curve fell below this on two occasions (January 25 and February 17-19), and reached it on February 4.
During the spring of 1923 very unusual conditions prevailed. The tempera- ture went below 30° F. on January 29, and never rose above this point until March 14. Throughout this period the temperatures fluctuated between 28.5 and 29° F., reaching 28° F. on February 24. This unusually cold water, occurring for such an extended period, accounts for certain peculiarities in the plankton of the present
JANUARY. FEBRUARY. MARCH. APRIL. MAY. JUNE. JULY. AUGUST. SEPTEMBER. OCTOBER NOVEMBER. DECEMBER.
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MAY. JUNE. JULY. AUGUST. SEPTEMBER OCTOBER Is ~ 3s sor s 10 is bd 35 905 $ ro is 3s yr ‘Ss » 35 pet s to ts bed s yr to s ~ ie aa peeed ues Let por eel na eaea hs Baga l Seinibesd alice =i asa seed ea oe! ad posed bSeSd ba bee +} +t ba! Basal alec | | BES Desi Bee ent CI nee ee te Son SSIES ‘ieee pipet — eb eres peered - 4 be! feaed ba oi “kes bobad Dose!
for each day of the year 1922,
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Fic. 6.—Diagram showing mean air and water temperatures at Woods Hole, Mass., for each day of the year, 1902 to 1906, inclusive. The less regular line represents air temperature and the more regular line water temperature
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PLANKTON OF THE WOODS HOLE REGION 101
spring. The warmest months were July and August; the coldest were January, February, and March.
The strong currents rushing through the “Hole” on the flood tide churn the water to such an extent that any change in the temperature of the air affects the bottom water as quickly as it does that of the surface. Table 2 gives a series of temperature observations taken when the temperature was suddenly rising or fall- ing. These show the result of the mixing of the waters.
TaBLe 2.—Surface and bottom temperatures taken at Woods Hole in 1922-28
°C. at °C. at °C.at | °C. at
Date surface | bottom Date surface | bottom Fi Ge ee 20.2 20} Allee 19200 woes ieee Tne ole 3 3 RU yrds 9 20 ee eee 21,2 PB OY hoa Diets tala Kt ae ee 1 1 July 31, 1922___- ao 22 22 Dec. 19, 1922___ o4 =a —0.5 —0.5 Aug. 13, 1922____ 20.5 20.5 || Mar. 19, 1923_____ 2 2 Aug. 14, 1922____ 21.8 21.8 |] Mar. 20, 1923_____ = —il Aug. 15, 1922_ 22 22 Mar. 21, 1923__ a ibis 1.5 Sept. 6, 1922____ 22 22 War 82291925 Sea ROLES SEE as 2 2 Sept. 7, 1922____ 2 ass 21.4 214 via 2351923 eee eames ewan ne sees ae 0.3 0.3 Benes 922 = S 2 ae Sas es ee ee 20. 4 20. 4
GENERAL DISCUSSION OF PLANKTON
Marine plankton at Woods Hole falls naturally into two great groups—the oceanic and the neritic—each of which has quite distinct characteristics.
The oceanic plankton consists for the most part of adult animals existing throughout life as a part of the pelagic fauna. The only immature forms normally occurring are the young of these oceanic species. Occasionally larval animals from the neritic plankton are blown out in offshore winds, but this does not occur often. However, it would be impossible to draw a line denoting the boundary between the two types. There exists a broad intermingling area into which each species extends to a point where external conditions form a natural barrier. As all forms are not subject to the same conditions, this wide intermingling zone results.
The neritic plankton, in contrast to the oceanic, consists for the most part of immature forms which in adult life are not a part of this community. There are, of course, many truly pelagic animals common to the littoral zone, but these are usually greatly outnumbered by the temporary intruders, except during the winter and spring months, when the larval forms reach their minima at the same time that many copepods and Sagitte have their maxima.
Figure 7 illustrates in a general way the constituent parts of the zooplankton at Woods Hole at different times during the year. It will be noticed that the summer and winter plankton are made up of representatives from the same groups. The great difference in the relative abundance of these in the two seasons will be discussed later.
The influx of oceanic species occurs both in summer and winter, although the number of different forms occurring in the colder months is comparatively small. During the summer, however, swarms often appear. Great masses of Sargassum, with its many inhabitants—Physalia and other floating forms—often fill the waters of the Sound after a southeast storm or a continued hard wind. Wheeler noticed
102 BULLETIN OF THE BUREAU OF FISHERIES
that such copepods as Pontella meadii and Anomalocera patersoni appeared in the tow only after this weather. Dr. H. M. Smith attributes the presence of prac- tically all of the small tropical fish that are taken each year in the Sound and at Katama Bay to southerly winds. The floating Sargassum offers shelter for these animals after they have been passively transported up from the south, and as the weeds are blown inland the fish accompany them. During the winter months such winds are fatal, but in summer the broad expanse of water extending from the coast reaches a temperature as high as that of the stream. Here any forms
Variation in the constituent parts of the plankton at Woods Hole during the year
PLANKTON Summer Spring and fall Winter Temporary Constant Many | ‘ oéelenterates " Permanent Temporary Temporary Permanent
Usual Ocean Larval Benthos, Benthos, Benthos, Few Larval Ocean Usual neritic forms nekton adults carried carried larvée nekton forms neritic adults blow (fish and lar- by cur- by cur= of (fish) blow adults
and lar- in and vée (ad- rents and rents and Benthos in and lare) vae squid) ults on- on float- on float- and free- vae ly in ing ob- ing ob- swimming breeding jects jects adults season) Fig. 7
carried out of their caurses can exist very well until the temperature drops in the fall, when all perish.
The shallow waters of the immediate region, sheltered as they are by the arm of Cape Cod, respond very quickly to changes of weather, heating rapidly and cool- ing suddenly. In summer Buzzards Bay is warmer than Vineyard Sound, the maximum temperature occurring at the head of the bay, the minimum around Cuttyhunk. Such conditions continue through August and into October. With the sudden drop in air temperature the bay water responds immediately and results im an exact reversal of the conditions found in August. At this time the water of
PLANKTON OF THE WOODS HOLE REGION 103
the bay becomes colder than that ofthe Sound. That has an important effect on the plankton of Woods Hole, for as long as the bay remains warmer than outside waters all animals carried into it will survive and be carried through the passage during the flood tides. As soon as the temperature drops in the bay the tropical forms entering it will perish and not return to the Sound. Such a condition is very noticeable in the fall, when all Gulf Stream forms suddenly disappear from the plankton of Great Harbor, although they may be taken in abundance in the Sound or at Katama Bay throughout October and November. The arrival of southern forms is usually noted as soon at Woods Hole as in the Sound.
In some parts of the eastern Atlantic a great many animals having a double breeding season are found. These forms appear in the spring and again in the fall. At Woods Hole examples of this group are limited to one phylum—the Ceelenterata. Figure 26 (p. 124) shows clearly that almost all Hydromedusz common to this region have been taken both in spring and fall, the spring swarm being the largest and lasting for the longest time. The Scyphomeduse rarely have this double period- ical appearance. During the past year, however, early ephyre of Aurelia flavidula were taken in November and again in April. The Ctenophora have been taken in small numbers throughout the winter, but usually swarm in the fall and early spring.
I know of no permanent planktonic animals at Woods Hole having this biannual distribution. Certain copepods are most abundant in the fall or spring, but never at both seasons. Such forms are also plentiful in the winter and have been included in the winter plankton. Two species of importance belong to this group— Tortanus discaudata from December to June and Pseudodiaptomus coronatus from August to January.
Under normal conditions the zooplankton, although varying considerably in its constituent parts, is always abundant at Woods Hole. The dominant winter or summer form of one year may be totally absent the next, but some other species usually takes its place. During the winter of 1899 and 1900 Temora longicornis formed the greater part of the plankton, while in the fall of 1922 and the spring of 1923 hardly an adult specimen was found, the dominant species that year being Pseudocalanus elongatus. In the winter of 1923 the temperature of the water re- mained so high that neither of these winter species had appeared by December 29. Centropages hematus and Acartia bifilosa constituted the bulk of the collections. Temperature and weather conditions, no doubt, determine to what extent the north- ern forms pass south of Cape Cod and enter local waters. Almost no cold-water species were found in the early winter of 1923. Such diatoms as Rhizosolenia alata, Skeletonema costatum, and Dityliwm brightwelli appeared rarely or not at all, and even the cod apparently sought deeper water, for no young were taken in surface collections.
Normal diatom maxima have no noticeable effect on the larger planktonic forms. When the unusually large swarms of phytoplankton appear, however, the zooplankton decreases rapidly and may even totally disappear for a time. Such conditions are often found during the summer maxima of Rhizosolenia semispina. Usually the winter maxima do not affect the largerforms. In the winter of 1922-23 the phytoplankton and zooplankton were both abundant at the same time. At
104 BULLETIN OF THE BUREAU OF FISHERIES
this time Rhizosolenia alata was the dominant diatom. In 1923-24 Nitzschia serrata occurred in such abundance that the zooplankton disappeared almost entirely from November 16 until February 1. During this period top and bottom collections in the shallow water of the bay and sound yielded nothing but diatoms. The zoo- plankton was found to be fairly abundant in the deeper waters at the western end of the Sound. As soon as the diatoms declined in numbers the larger forms returned to the shallow water. Figures 8 and 9 show the relative abundance of the zooplank- ton and phytoplankton in 1922 and 1923.
DIATOMS AND OTHER PLANTS
The diatoms of this locality may be divided into two great groups—the pelagic and the bottom forms. In certain parts of Great Harbor the bottom diatoms are very abundant, and often large numbers occur in surface collections after storms or particularly strong winds. As no fresh-water streams of importance are found in the vicinity of Woods Hole to carry the various chemicals needed for diatom pro-
e ~ ° Q
goad 2 é¢2é
Dese
j 5 2 3 Vode 22) GBR B08 (See 1 i Vea re iH eH Aa iH Se: Se : it) VoSe Ht V.S. i it De Lo Fic. 8.—Relative abundance of zooplankton and Fic. 9.—Relative abundance of zooplankton and phyto- phytoplankton in surface collections from May plankton in 1923. , zooplankton; —-.e=—=, phyto-
to December, 1922. —.— phytoplankton
. zooplankton; plankton
duction, much essential material must be carried through the “ Hole” from Buzzards Bay by the strong currents. For that reason bottom diatoms were found to be more abundant in eddies and pockets about the entrance of the bay than elsewhere in Great Harbor and not scattered about evenly on the bottom in shallow water, as might otherwise be expected.
Together with the dinoflagellates, the pelagic diatoms make up the greater part of the phytoplankton of the region. On all but two occasions the former were far outnumbered by the latter. In every haul made during the year with a No. 20 net diatoms were found. They had regular seasonal variations which were very similar to those of previous years (figs. 10 and 11). There is a regularity in the quantita- tive variation as well as in the qualitative. The maximum of one year may be larger, smaller, earlier, or later than that of another, but the basic characteristics of the rhythm remain for the most part unchanged. An exception to this rule is
PLANKTON OF THE WOODS HOLE REGION 105
found in the appearance of certain oceanic forms, which will be discussed later. Extremely unusual physical factors may even eliminate a part of the cycle, but as soon as normal conditions are restored the progression continues as before. Such was the case in December, 1923, during an unusually warm period (fig. 11). Al- though quantitatively the winter diatom maxima remained approximately the same as in the previous year, qualitatively it was very different (fig. 10).*
To understand the seasonal distribution we must know something of the nature of the various forms that enter Great Harbor. The individual species of neritic phytoplankton are much more widely distributed than the zooplankton, and factors governing their appearance and disappearance are for the most part quite different. As in the case of land plants, the diatoms are able to form organic substances from
° 3 o
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Absa’ sidan Bape 8 2 8 ld As Veh if is att f iH Ht Se co is Het z Ee HH HI +H HH Se Vee EHH Ht V.3. is i Bar: iH # = i i ih} tt Ne ie —
Fic. 10.—Seasonal distribution of most abundant Fic. 11.—Seasonal distribution of most abundant diatoms diatoms occurring in surface collections from occurring in surface collections of 1923. Rhizosolenia ex- June to December, 1922. Rhizosolenia ex- cluded. ———, Chzetoceros; —---—, Corethron valdivie; cluded. , Cheetoceros; —e—, Corethron —eco—, Ditylium brightwelli; -------- , Leptocylindrus valdivie; ——, Ditylium brightwelli; -----, danicus; —-e —, Nitzschia seriata; —-—-—-, Skeletonema Leptocylindrus danicus; —---—, Nitzschia costatum
Seriata; —-»e+«—, Skeletonema costatum
the various inorganic chemicals. Together with the littoral marine flora they form the basic source of food supply in thesea. Since all plankton animals are consumers and depend solely on the organic materials produced by the plants, the importance of the diatoms and the necessity for information regarding the sources of their production can not be overestimated.
Obviously the two fundamental necessities for diatom growth are sunlight and food material. Secondary factors, such as temperature, salinity, necessary resting periods, etc., limit the geographical and seasonal distribution of certain species but do not usually affect the group as a whole. Physical conditions fatal to one species may be particularly favorable to another. Sunlight limits the vertical range of the species to the narrow zone penetrable by the light (photic zone). This usually does not form a limiting factor of production in local waters or littoral plankton in general.
1 See paragraph 1, page 113. 8242°— 257, 2
106 BULLETIN OF THE BUREAU OF FISHERIES
It is of extreme importance in ocean waters, however. Food material is the domi- nant governing factor for all diatoms. The supply of the substances not common to all sea water arises from two sources—outwash from the land and the replacing of chemicals by the breaking down of the organic substances in the sea. For this reason diatoms are much more abundant in the coastal waters, particularly near the mouths of large rivers (Table 3). No doubt the large amount of disintegrating material often found in coastal water (Bigelow, 1914) after a diatom decline forms an important item in the replacement of essential chemicals such as silicic acid and nitrates, but in comparison with the source of supply from the land it must be rather small. Conversely, in the open ocean it probably forms the most important source in regions where the land areas exert little or no influence. In this respect the oceanic and coastal conditions are widely different.
TaBLE 3.—Disiribution of diatoms in Long Island Sound in early March, 1923. Volume determined from vertical hauls
Locality Date | Volume | Depth (8505 Meters
MPnTOgS RN GCE er seeter eet Hee Se ee ease eNe 22d Aa eee ee em Mar. 5 4 5 Hempstead Harbor_ A Edn 6 5 Matinicock Point__- idol 2.5 5 Cold Epune Harbor 2.5 5 Pecks Ledge________ 4.5 5 Pine Creek Point_____- a 4 5 Off Bridgeport Harbor-------- Bes Lae Riek rae a Base 8 5 Stratfordjront eee oe aie —_ a Eee 20 5 Housatonic River, near breakwater_ Redo 12 5 New Haven\iHarboro.) = 92-22 ote a oh nee 2 ee a ae do 10 5 Stations inside of Harbor No. 1__- Mar. 7 8 5 Stations inside of Harbor No. 2___ Laidol= 6.5 5 Stations inside of Harbor No. 3__- edo 6.5 5 Bive-fathomenOck es mae it Geek Tree ee et ee eae a ee ee ee ee |e do-___- 7 5 Sachem Head-_-_-___ _-do_- 10.5 5
ammonasset Point _-do__ 8.5 5 Falkner Island _-- dos 2 5 Gardiners Bay--- Mar. 8 5 5 Little Peconic Ba’ .-do_ 1 5 Hortons Point_-__ me dows 4.5 5 HMAtOMMRO Iter see eee ee oe ee ee Mar. 9 3.3 5 iMid-Sound positions 40-59-o4N7i/o~23—1 On Wie eee nee oe anne eee aaa _-do. 4 5
In the ocean, where uniform physical conditions often exist to comparatively deep water, Nathansohn (1909) found that the diatoms are most abundant in localities where the greatest amount of vertical circulation takes place. (Gran, 1912, gives maximum abundance often as deep as 50 meters and large numbers at 100 meters.) Large quantities of organic material are constantly sinking to the deeper water, and the decomposition of dead plants and animals at these levels sets free the nutri- tive substances, which are returned to the photic zone in the ascending currents. In anticyclonic systems like that of the Sargasso Sea, where little or no vertical cir- culation takes place, the diatoms were found to be very scanty. Nathansohn’s (1909) theory, no doubt, does not apply to all conditions found in the sea, but remains as the best explanation of the source of production of oceanic diatoms. Ocean currents, which themselves change according to the seasons, cause the diversity of high sea plankton in fixed geographical positions. The occurrence of certain species far beyond the limits of their natural range is usually attributed to currents.
In the coastal waters an entirely different condition of affairs exists. Over the deeper parts of the neritic zone plant life usually is limited to a very thin surface
PLANKTON OF THE WOODS HOLE REGION 107
layer, which is differentiated from the deeper water masses by a lesser density and higher temperature. In seasons when there is great outwash from the land the neritic diatoms often form great swarms. In localities where upwelling or vertical circulation takes place under these conditions the surface layers, with their flora, are blown away from the shore and replaced by infertile water drawn up froni the bottom layers. The outwash of this fertile water is very favorable to the offshore plankton but causes a diminution of diatoms near the coast, the few that were not carried out having adverse conditions to combat. An inshore wind, on the other hand, heaps up the surface waters and is conducive to luxuriant plant growth. Repeated investigations (Gran, 1912; Nathansohn, 1909; Leder, 1917) of this prob- lem have confirmed the belief that often the rapid appearance and disappearance of diatom maxima is notso much a biological question as a hydrographical one. Gran and Nathansohn in 1909 observed, ‘‘We find an intensive plant life, and conse- quently also an intensive animal life, everywhere at the surface of the sea where an influx of water masses takes place, which has not, or at least has not immediately previous, served as a source of nourishment for phytoplankton.”
Sometimes a diatom society is found in summer in the lower strata, with its higher density and lower temperature, which was present in the surface waters earlier in the spring. Such conditions are common among the zooplanktonic forms and are occasionally found among the diatoms. Miss Ogilvie found the same dia- toms in the lower strata off the south coast of Ireland in August as were present at the surface from January to April. This is an indication that certain neritic forms, which are apparently periodical in their occurrence, might remain as permanent members of the plankton if conditions of existence were more uniform. This is interesting in view of the fact that many investigators have considered that a resting period (spore formation) is a necessary part of the existence of truly littoral species.
It is impossible in local waters accurately to determine the real relationship of the local conditions of existence and the development of the diatoms, because the currents often cause variations much greater than those actually due to conditions of existence. Gran (1912), realizing this, substituted a study of the rate of growth as a measure of production in place of quantitative chemical analysis of food mate- rials present in the water. In the vicinity of Woods Hole, where the currents are unusually strong, the production would have to take place at an extremely high rate in order to maintain itself were it not for the many “‘pockets”’ of quiet water which are supplied with abundant land outwash. In certain less protected sections of the coast this may be an important factor in the sudden disappearance of certain species. As soon as the rate of production declines the species is unable to maintain itself, and this inability to replace the numbers carried away by the currents may cause the maxima to disappear long before the food supply is exhausted.
In dealing with the conditions of production it is very important to know just where the production of floating forms takes place before attempting to explain their appearance or disappearance. Two theories are now held. One contends that all production of pelagic neritic diatoms takes place off the coasts, the sudden swarming in inland’rivers and small bays being the result of tides and winds. The second theory is that production also takes place within certain limits in inland waters. To be sure, winds may blow quantities of diatoms into open harbors and
108 BULLETIN OF THE BUREAU OF FISHERIES
small bays, but this does not explain the conditions as they are often found. Since Woods Hole is a particularly unfortunate location to observe the factors of diatom production, I shall cite results obtained in Long Island Sound in 1922 and 1923.
The first indication of local production was the variation in the species of pelagic diatoms found in the different harbors and river mouths along one shore. Had winds carried them there, one would expect to find the same species in all the harbors. This was not the case except during the greatest swarms, when the Sound seemed filled with a single species. In succeeding cruises it was noted that the volume of phytoplankton in the vertical hauls taken at the mouths of rivers and in harbors connected with inland streams was much greater than that of the mid- Sound or harbors containing no land outwash. Table 3 (p. 106) shows the centri- fuged volume, in cubic centimeters, taken with a Hensen medium-sized vertical net at various points in the Sound. The predominant species was Skeletonema costatum. A strong west wind had prevailed for several days before the collections were made. Had the distribution of diatoms resulted from this they should have occurred most abundantly along the southeast shore near the eastern end. The table clearly shows that the greatest swarms occurred at the mouths of the rivers and harbors where the most land drainage is carried into the waters. The salinity is low in all parts of the Sound, and for that reason the diatoms do not penetrate far into the mouths of the rivers and harbors. No great tides sweep the Sound at any place except at the ‘‘race,” and even there Galtsoff found that 8 miles is the maximum distance that the water is carried in a single tide.
Another source of evidence can be found in Peck’s (1896) report on diatom collections in Buzzards Bay. His stations were laid in two lines, one at right angles to the other, extending the length and width of the bay. A series of observa- tions at various points along these courses showed that the greatest abundance of diatoms occurred at the two inshore stations. The other two ends of the courses were located in Vineyard Sound and the rapids at Woods Hole, and therefore are not considered. He concluded from these records that there was a shallow area of diatoms surrounding all the shores of Buzzards Bay. A glance at Figure 12 will show that the two inshore points he selected (indicated by A) were near the mouths of the greatest harbors of the entire Bay. The large rivers at the head of the Bay empty their waters near Peck’s north station, while the waters of the Acushnet and Nasketucket Rivers join at the point of his western station. Undoubtedly Peck would have found his hauls less rich if he had selected spots along the eastern shore.
A noticeable characteristic of neritic plankton flora is the variety of diatoms that is usually found in every swarm. One or two species predominate, but the many other species occurring in smaller numbers make up the so-called “diatom society.” Allen, in 1920, made the following statement:
Detailed study of the records has clearly shown the important fact that when there is an increased production of the most prominent forms there is also increased production of the less prominent forms and an increase in the number of different forms. Such facts naturally lead to the assumption that conditions favorable to high productivity of diatoms‘ the sea affect a large number of forms in the same way. They also lead to the inference that determination of the
species that shall lead in production is due largely to the biological factors, such as rapid multi- plication and vigorous development.
PLANKTON OF THE WOODS HOLE REGION 109
As most rules have exceptions, so, too, an exception to this rule is often found at Woods Hole during the summer months when the oceanic diatom (Rhizosolemia semispina) occurs in such abundance that almost every other form of animal and plant life disappears for a time. The occurrence of this interesting species will be discussed later.
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191904 ‘onrtaHna O
= > 2 4 = > 7
quVAINIa
punog present, pus Avg spivzzng jo deyjw—'zt “ot
The diatom spores are no doubt at all times exceedingly numerous in local waters and are carried about by the currents and winds. When conditions become favorable for those already present or those transported to a harbor or river mouth
110 BULLETIN OF THE BUREAU OF FISHERIES
where rich food material has been washed from the land, the spores germinate and increase rapidly in numbers. The development will continue until the food supply is exhausted or other unfavorable conditions arise. In discussing spore formation in diatoms Gran (1912) stated:
When we subsequently find the same species once more in abundance, we have every reason for surmising that the resting spores on the bottom were the principal source from which these forms have been derived. Ability to form resting spores must be of the utmost importance for the existence of the species in coastal waters. The chief difference between coastal seas and the ocean, so far as hydrographical conditions are concerned, lies in the extreme and rapid changes in such fundamental conditions of existence as salinity and temperature in coastal waters. Rest- ing spores, therefore, must be the means by which many species continue in coastal seas, not- withstanding the fact that there conditions of existence are favorable only for a limited portion of the year. The Arctic diatoms, for instance, which sometimes are to be found in the plankton of the Skager-Rak, are very easily affected by a rise in temperature, but their development takes place during the winter months from February to April, when the temperature is at its minimum. In the summer they are not to be seen, but their resting spores are then most probably on the bottom. In the same way a whole series of warmth-loving species pass through the winter as resting spores and are to be found along our shores only in the warmest months of summer and
autumn.
As in the case of the littoral pelagic fauna, the winter diatom flora throws an interesting light on the effect of the arm of Cape Cod on the winter forms in local waters. In summer the cold waters north of the cape form a barrier for southern neritic plankton. Samples taken by Bigelow in August, 1922, in Massachusetts Bay, contained the same diatoms as those which appeared in Woods Hole in greatest abundance in December. No doubt many of the northern diatoms are carried south in the summer, but the sudden rise in temperature apparently is sufficient to cause them to form resting cells or die. The effect of a slight change of tempera- ture was evident at the end of March, 1923, when the winter forms suddenly disap- peared. In winter, on the contrary, those carried south find a favorable climate with a supply of food material that has accumulated since the disappearance of the summer forms. Together with local winter neritic species they form a maximum the extent of which depends upon the supply of silicates, nitrates, etc., in the water, and remain until the food is exhausted or the temperature becomes unfavorable. Tn this way the arm of Cape Cod forms a southern barrier for northern littoral plank- ton only in summer and not at all times, as in the case of many benthonic species.
If this assumption were based upon the neritic diatoms alone, it could hardly hold, because, combined with the evidence of the existence of diatom spores in all coastal waters, the factor of temperature alone could explain the condition, and trans- portation by currents around Cape Cod would not be necessary. However, as the most abundant species (Rhizosolenia alata) north of the cape in August was a truly oceanic form and proved to be the first to appear in large numbers at Woods Hole, I think it justifiable to attribute it to the currents, just as in the case of the northern copepods appearing about the same time which were certainly transported in that manner.
None of the so-called “pulses” which Allen observed on the Pacific coast occurred at Woods Hole in 1922 or 1923. The seasonal curves rose and fell evenly. On April 3, 1913, Bigelow found the waters of Massachusetts Bay filled with dia- toms. These were not evenly distributed but appeared as brownish-colored bands
PLANKTON OF THE WOODS HOLE REGION 111
alternating with clear areas. It may be that patches like these formed the pulses of which Allen speaks, for his collections were on the open coast and taken from the end of a wharf past which the belts of uneven abundance would drift.
The seasonal variation of the diatom maxima and the appearance of oceanic species in local waters can be understood best by considering the geographical position of Woods Hole as compared with other areas of the eastern and western Atlantic. Steuer (1911) found that in general the maxima of the various species,
ee ee ee
Karajakfjord in Greenland ‘Nerth European Coast
Skager Ralc
Fic. 13.—Schematic diagram of the seasonal distribution of the diatom maxima in the northern and southern parts of the eastern Atlantic. After Steuer
both neritic and oceanic, is closely related to temperature, and thus varies according to the latitude. It has long been known that on both the European and American coasts the most luxuriant diatom growth does not take place in the warmest months even as far north as Norway and Newfoundland.
At Karajakfjord, in Greenland, Vanhéffen (1897) found only one maximum, from May until the beginning of September. South of this there occurs the typical spring and fall maxima, which retreat farther and farther from the warmest seasons as one approaches the Tropics. Steuer (1903) found that this constant succession of diatom maxima toward the south necessarily leads to the assumption that some- where in the south there will be a meeting of the two maxima in winter, and this was found to occur in the Adriatic Sea by Leder (1917), Steuer (1903), Stiasny (1908), and Gran (1909) (fig. 13). A smaller maximum was also found to occur in June and July. Conditions on the American coast are surprisingly similar to those of the eastern Atlantic (fig. 14).
ee re ee
Bay of Femdy
Massachusetts Bay
Vineyard Sound and Buzzards Bay
Long Island Sound
Fig. 14.—Schematic diagram of the seasonal distribution of the diatom maxima on the western Atlantic coast
Observations in eastern Canadian waters by Bailey, MacMurrich, and Fritz show that the greatest maxima occur in the spring and fall. Bigelow (1917) com- mented on the similarity of the diatom distribution in the Gulf of Maine and that of the North Sea, Irish Sea, and Skager-Rak. He also found a great maxima in Massachusetts Bay in April and early May, 1913, and a smaller one in September, 1915, and one in late August, 1922.
The striking effect of the arm of Cape Cod on the plankton is again evident here, for within 20 miles of latitude of Massachusetts Bay conditions similar to those of the Mediterranean and Adriatic Seas are found in Buzzards Bay. Here and throughout the shallow waters south of Cape Cod a rich winter diatom plankton
112 BULLETIN OF THE BUREAU OF FISHERIES
Pa gi tmociget ahs nly & Bret ath te Sala tay nt SE Hs VoAo -E
Ae : =
HEH
gestae
iaspane
Baa
Se + ; 7
VS.
He: Fie. 15.—Occurrence of Rhizosolenia in surface collections from May to December, 1922.
setigera; , Rk. shrubsolei; —-—--——, R. alata genuina; . R. alata gracillima; 009000000, R, styliformis; —ccem, R, fereensis
22 4 8 3 Vode A. pre Se VoSe We
Fic. 16.—Occurrence of Rhizosolenia in surface collections of 1923.
starts usually in November and continues until March, reaching a maximum in December. This compares very closely with the maxima found year after year at Trieste. Corresponding to the short summermaximum of thatregion, a summerswarm occurs also at Woods Hole, starting usually in July and remaining until September. A compari- son of the seasonal distribution and breeding sea- sons of the zooplankton of the two regions shows that theconditions at Trieste are of amore south- erly nature than in this region, although it is farther north. Its relation to the Mediterranean makes the reason for this obvious. The summer maximum is very variable, because the local neritic species play a minor part, the greater part consisting of a single oceanic form (Rhizo- solenia semispina). Obviously, conditions be- yond the limits of the adjacent coast have much to do with the appearance of thisform. In 1922 and 1923 it was particularly abundant (figs. 15
June Jule Auge Sepe Octe Nove Dece
, Rhizosolenia semispind; -s-smc-e-e, Fe. setigera;
———, F, shrubsolei; mom, FR, alata genuina; 000000, R, styliformis; tt++++++, R. calcar avis; mmeemm, Fe. delicatula
PLANKTON OF THE WOODS HOLE REGION
Actinoptychus undulatus Asterionella japonica Bacteriastrum delicatulum Belleroché& malleus Biddulphia alterans Biddulphia favus Biddulphia biddulphiana, Biddulphia rhombus Corethron valdivide Ditylium brightwelli Grammatophora marina Grammatophora serpentina Guinardia flaccida Leptocylindrus danicus Licmophora flavellata Licmophora lyngbyei Nitzschia closterium Nitzschia paradoxa Nitzschia seriata Paralia sulcata Rhabdonema adriaticum Skeletonema costatum Stephanopyxis appendiculatus ‘Striatella unipunctate Synedra gallionii Synedra undulata Thalassiothrix Jongissima Thalassiothrix nitzschioides Distephanus speculum Dictyocha fibula Cerataulina bergonii
Fie. 17.—Distribution of diatoms and Silicoflagellata in 1922 (excluding Cheetoceros and Rhizosolenia)
Je
JUL
Auge
Sepe
Octe
NoVe
Dece
113
114 BULLETIN OF THE BUREAU OF FISHERIES
and 16), filling the waters of the bay and the eastern part of Vmeyard Sound. ‘The seasonal distribution of diatoms in Long Island Sound in 1922-23, during the winter months, was found to be very similar to that of Woods Hole except that the swarms appeared slightly later. d¢ 48 3 8 Aetinoptyehns undulatus cae OFaeeeaeoewenaecatversereee :
Febo
Jule Auge Sepo Octe Nove, DeGs
Asterionella japonica Bacteriastrum delicatulum H Be eeseeeeceeet Biddulphia alterans t cf H i oH He Biddulphia favus H EEE EEE Biddulphia granulata Het : Biddulphia biddulphiana HE Biddulphia vesicvlosa H Ee Corethron valdiviae : HH Dityliwm brightwelli ¥ragilaria crotonensis Grammat ophora marina Grammatophora serpentina Guinardia flaccida Hyalodiscus stelliger i rth Leptocylindrus danicus Ht Liomophora flavellata PSSASEEER PEPE : BEECH oEtoet ete Licmophora lyngbyei GSESSHESHECREEHSEE : Melosira borreri : Eo Nitzschia closteriun + Nitzsohia longissima H Nitzschia paradoxa Sete ts Nitzschia seriata ose aissetts E : \ Paralia sulcata cof sie Sa Rhabdonema adriaticun : Skeletonema costatun strate Striatelle mipunctata = Synedra gallionii Synedra undulata Thalassiosira decipiens Thalassiosira hyalina Thalassiosire nordenskiolaiijsie Thalassiothrix frauenfeldii eaubedady PeEeeee Thalassiothrix longissima ; EEEEEREEEE i Thalassiothriz nitzschioidest= Distephams speculun —
Dictyocha fibula { H Cerataulina bergonil +
Cyolophora tenuis Ht
aL :
Fra. 18.—Distribution of diatoms and Silicoflagellata in 1923 (excluding Chsetoceros and Rhizosolenia)
The pelagic diatoms of the Woods Hole region may be grouped under three headings—tychopelagic, oceanic, and neritic. The tychopelagic group is made up of semi-bottom forms, which often occur in coastal waters in enormous numbers. They are carried about by the winds and tides, usually without relation to any
PLANKTON OF THE WOODS HOLE REGION 1135)
particular season (figs. 17 and 18). The following common tychopelagic forms appeared in the surface collections of the past year: Actinoptychus undulatus, Bid- dulphia alterans, B. favus, B. granulata, B. biddulphiana, B. rhombus, B. vesiculosa, Hyalodiscus stellager, Melosira borreri, and Paralia sulcata. All of these species are temperate forms.
The oceanic and neritic diatoms that have a distinct periodicity in occurrence may be grouped according to the latitudes in which they are distributed. This method, originated by Cleve, has been used by almost all planktonologists. The various groups into which Cleve divided the characteristic plankton diatoms are represented at Woods Hole by the following species:
Boreal Arctic___.-._..-___- Cheetoceros mitra. Nitzschia closterium. Thalassiosira hyalina. nordenski6ldii. North Temperate_________- Chetoceros danicum. debile. diadema. sociale. teres. Leptocylindrus danicus. Liemophora flavellata. Nitzschia longissima. Rhizosolenia feeroeensis. setigera. . Skeletonema costatum. Stephanopyxis appendiculatus. Synedra, gallionii. Thalassiosira, decipiens. Thalassiothrix nitzschioides. South Temperate__________ Asterionella japonica. Bacteriastrum varians. Cheetoceros cinctum. contortum. didymum. laciniosum. lorenzianum. schiittii. Ditylium brightwelli. Fragilaria crotonensis. Grammatophora marina. serpentina. Guinardia flaccida. Nitzschia paradoxa. Rhabdonema adriaticum. Rhizosolenia calear avis. delicatula. shrubsolei. Striatella unipunctata. Synedra undulata. cbropical¥s:< 425), “Savina e Bellerochea malleus. Rhizosolenia ealear avis. shrubsolei.
Neritic_--------
116 BULLETIN OF THE BUREAU OF FISHERIES
iBorealltAc.ctichee eee eee Cheetoceros atlanticum. boreale. criophilum. decipiens. Nitzschia seriata. Rhizosolenia hebetata (semispina), Thalassiothrix longissima. emperates. == aot See ss Cheetoceros densum. peruvianum. willei. Rhizosolenia alata f. genuina. f. gracillima. Thalassiothrix frauenfeldii.
Oceanie__-==_2__
TEropical 2 =. = et ee Cheetoceros coarctatum. ‘ peruvianum. Antarctic. <eeeees Sea eel Corethron valdivie.
In 1922 the summer swarm was composed almost entirely of members of the genus Rhizosolenia (figs. 15 and 16). Rhizosolenia semispina and R. shrubsoler appeared about June 15, followed in July by R. setigera. The latter two species were never as numerous as the former. &. semispina increased rapidly until July 5, when the swarms literally filled the waters of the bay and sound, clogging even the coarsest plankton nets with a slimy brown ooze. Shortly after this it began to decline, disappearing about September 9. The 1923 maximum was very similar, except that the two minor species terminated their season earlier than in the previous year, while &. semispina declined more slowly, remaining in small numbers through- out the fall and early winter.
The occurrence of this species at Woods Hole during the summer months is rather interesting. It is a northern oceanic form, known from both the Arctic and Antarctic regions, and was found by Ostenfeld (1913) to thrive best in the areas of the North Atlantic where cold currents seek southward. It is particularly abun- dant in the spring in the region of the Labrador Current about Newfoundland and Nova Scotia. Bigelow (1917), m July, 1914, found a large maximum off Marthas Vineyard, at the time when the great swarms appear in local waters. In 1923 the author found them extending from Cape Cod along the eastern side of Marthas Vineyard to Nantucket and in Vineyard Sound as far as Menemsha Bight. None were found at the western end of the Sound or in the waters about No Man’s Land. This indicates that they enter the region from the northeast, as would be expected. Miss Ogilvie (1923) found a maximum in July, 1920, off the south coast of Ireland.
The summer maximum at Woods Hole, then, is not wholly dependent upon local conditions. Either of the two neritic species, Rhizosolenia shrubsolei and R. setigera might dominate if hydrographical conditions prevented the appearance of R. semispina. The abundance of the latter species will depend partly on the num- bers blown into the bay and sound and partly upon the food material present there. Although it is a northern form it must have an extremely broad temperature range, because its distribution in Buzzards Bay in 1923 showed conclusively that great production was taking place there at a time when the temperature was ranging from 19 to 21° C.
PLANKTON OF THE WOODS HOLE REGION iy)
As the numbers of Rhizosolenia semispina diminished in the late summer of 1922, Chetoceros (fig. 19) increased, but lasted for only a short time. Another diatom (Corethron valdivie) then became very i abundant and reached its maximum about Sep- # 8 tember 20 (fig. 10, p. 105). A rapid decline took z place after this, followed by another Cheetoceros increase. In 1923 Corethron appeared on Sep- tember 21, reaching its maximum on November 3 (fig. 11,p.105). All available records for Coreth- ron show it to have its flowering season in the 3. fall. In European waters Ostenfeld (1913) re- ports it to be most abundant in autumn. Ogilvie (1923) found it abundant on the south coast of Treland in July, 1920, and in August and No- vember, 1921. Fritz (1921) records it from the Bay of Fundy in October, 1916, and in September and October, 1917. We
The winter maximum at Woods Hole consists Fic. 19.—Occurrence of the more abundant spe- usually of a greater variety of abundant species: 968 of Chetoc’tos from ai aan than that of the summer. In 1922 many species © didymum; —.—, ©. laciniosum; ——, appeared suddenly about November 8. As the ©?) ~-— @ sociale season progressed different forms predominated on different days, but all were usually abundant. At first Rhizosolenia alata f. genuina, a temperate oceanic
Sepeo Oote Nove Dece
VeSe
Br Sect cree ant Ng) Le oy eZ) inns nies KOS SSL IRnNG EPS EPRE ease va el nen bass maM Glzen TUR: ean SE VeAe
Ae
Sa
VeSe
Ne
Fia. 20.—Occurrence of the more abundant species of Cheetoceros in surface collections of 1923. ----.-, , Chetoceros decipiens; —, C. didymum; —eeo—, C. laciniosum; —»—, C. schuitlii; —-—=, C. sociale
118 BULLETIN OF THE BUREAU OF FISHERIES
species, proved to be the most conspicuous form (fig. 15). Later this was replaced by Leptocylindrus danicus and Skeletonema costatum. Both of these species are north temperate neritic forms, which are supposed by Ostenfeld to exist all the year round on the bottom, being carried up among the plankton in the flowering season and during high winds. The distribution at Wood Hole appears to substantiate this very well (figs. 10 and 11, p. 105). The winter flowering
e » e @ e e co ta¥4) Qe + > tS) ‘3 S ) S) e) o a) <= “A io) & (=)
C.boreale Cecontortum Cecoarctatum Cedanicum Cedebile €edensum Cediadema C.didymum €elaciniosum C.lorenzianum Ceperuvianun Ceschuttii Cesociale Cewillei Cemitra C.spenov. Cecriophilum C.decipiens Fic. 21.—Distribution of Cheetoceros from June to December, 1922
season is evident, and the scattered occurrence throughout the year can be best explained by Ostenfeld’s theory. Although very similar to tychopelagic forms, these two species differ in that they multiply greatly while members of the plankton. Other abundant members of the 1922-1923 winter society were Ditylium brightwelli, Thalassiothrix nitzschioides, Rhizosolenia setigera, R. shrubsolei, and Chetoceros sociale, all of which are neritic species (figs. 10, 11, etc.). Two oceanic forms
PLANKTON OF THE WOODS HOLE REGION 119
(Witeschia seriata and Chetoceros decipiens) were fairly numerous 4t times but always played a minor rdle.
As previously stated, unusual physical factors may cause great variation in the time when the maxima appear as well as in the constituent parts. Such was the case in the winter of 1923 (figs. 4 and 5, p. 100), when, after an unusually warm season, although quantitatively the winter diatom maximum was approximately the same as in the previous year, qualitatively it was very different. Rhizosolenia alata, the first dominant species to appear in the 1922 swarm, occurred only as scattermg forms in 1923; while Nitzschia seriata, a rather scanty form in 1922, out- numbered all others during the entire winter maximum by more than 1,000,000: 1 (fig. 11, p. 105). Certain other members of the 1922 maximum, of which Ditylium brightwelli is an example, did not appear at all.
Te y
5 . . e a =. a -o y a. Fe 5 eh es
G.atlantious C.boreale Cecinctum C.coarctatmn C.contortum C.criophilum C.decipiezs
Cedensun Codiadems C.didymun C.laciniosun C.lorenziamm Ceperuvianom Ceschuttii Cesociale C.teres C.willei Cospenove
Fic. 22.—Distribution of Chetoceros in 1923
The absence of Rhizosolenia alata (excepting scattering forms) might have been caused by the extremely mild weather of the early winter. However, as it is a com- mon oceanic species there are many other factors which may have affected it. Certainly the unusual temperature influenced the neritic forms. During the short time when the temperature was normal in the early fall (fig. 11) many species— Chxtoceros didymum, Skeletonema, Leptocylindrus, etc. (figs. 21 and 22)—appeared and began their normal flowering season. When the unusual temperature condi- tions continued, however, they declined and remained as scattering forms or dis- appeared; but one species, Rhizosolenia setigera, which has an extremely wide tem- perature range (fig. 16), apparently thrived with Nitzschia during the period.
Nitzschia seriata is an Arctic oceanic species which often appears in large numbers off the Norwegian coasts. It is very variable in occurrence, being present
120 BULLETIN OF THE BUREAU OF FISHERIES
some years and entirely absent in others. In all areas investigated it forms its greatest maxima in the spring. In the spring of 1923 it reached its maximum in January, remaining throughout March. The following winter it arrived slightly earlier and increased rapidly, swarming early in November (figs. 10 and 11, p. 105). Throughout the winter season it remained as the most dominant species.
The distribution of diatoms during the past year may have been unusual. Certainly two seasons’ changes are not sufficient from which to draw conclusions. However, as all available records for past years seem to indicate similar summer and winter maxima, it is probable that yearly variations will be in the date of the appearance of these same species and not so much in the species themselves. Winds May carry in unusual oceanic species, but these may be considered accidental visi- tors whose appearance again can not be predicted. The following diatoms appeared in surface collections of the past year:
Actinoptychus undulatus (Bailey).
Asterionella japonica, Cleve.
Bacteriastrum varians, Lauder.
Bellerochea malleus (Brightwell).
Biddulphia alterans (Bailey).
B. biddulphiana (Smith).
B. favus (Ehrenberg).
B. granulata, Roper.
B. rhombus (Ehrenberg).
B. vesiculosa (Agardh).
Cerataulina bergonii, Peragallo.
Cheetoceros atlanticum, Cleve.
. boreale, Schiitt.
. cinctum, Gran.
. coarctatum, Lauder.
. contortum, Schiitt.
. criophilum, Castracane.
. danicum, Cleve.
debile, Cleve.
. decipiens, Cleve.
densum, Cleve.
diadema (Ehrenberg).
didymum, Ehrenberg.
. laciniosum, Schiitt.
lorenzianum, Grunow.
. mitra (Bailey).
peruvianum, Brightwell.
. schiittii, Cleve.
. sociale, Lauder.
. teres, Cleve.
. willei, Gran.
Corethron valdivie, Karsten.
Cyclophora tenuis, Castracane.
Ditylium brightwelli (West).
Fragilaria crotonensis (M. Hd- wards).
Grammatophora marina, Kiitz- ing.
aeaaaneaaqaanaaaaaaaaaa
G. serpentina, Ehrenberg.
Guinardia flaccida (Castracane).
Hyalodiscus stelliger, Bailey.
Leptocylindrus danicus, Cleve.
Liemophora flavellata, Smith.
L. lyngbyei (Kiitzing).
Melosira borreri, Greville.
Nitzschia closterium, Smith.
N. longissima (Brebisson).
N. paradoxa, Grunow.
N. seriata, Cleve.
Paralia suleata (Ehrenberg).
Rhabdonema adriaticum, Kiitzing.
Rhizosolenia alata f. genuina (Gran).
R. alata f. gracillima (Cleve).
R. calear avis, Schultze.
R. delicatula, Cleve.
R. feerceensis, Ostenfeld.
R. hebetata var. semispina (Hensen).
R. setigera, Brightwell.
R. shrubsolei, Cleve.
R. styliformis, Brightwell.
Skeletonema costatum (Gre- ville).
Stephanopyxis appendiculatus, Ehrenberg.
Striatella unipunctata (Lyngbye).
Synedra gallionii, Ehrenberg.
S. undulata (Bailey).
Thalassiosira decipiens (Grunow).
T. hyalina (Grunow).
T. nordenskidldii, Cleve.
Thalassiothrix frauenfeldii (Gru- now).
T. longissima, Cleve and Grunow.
T. nitzschioides, Grunow.
PLANKTON OF THE WOODS HOLE REGION 121
After southerly storms during the summer Vineyard Sound is often filled with floating Sargassum bacciferum (Turner). This is a tropical plant from the Gulf Stream, which is usually accompanied by a community of pelagic animals. As it has never been known to reproduce in the region, it is probable that all die in the fall when the temperature of the water drops. Although not true oceanic plankton, this plant must be mentioned, for many pelagic forms enter Woods Hole attached to it. A local species (Sargassum filipendula Agardh) is commonly found attached to rocks and piles below the low-water mark in the harbor, but this has no relation to the plankton.
PROTOZOA
. The protozoa were omitted in the present investigation, with the exception of the large forms that at times were numerous enough to form an important part of the plankton. Unless special methods are used UF 3 no real estimate of the abundance of the many B 3 minute organisms of this phylum can be made. Lohmann (1911) showed that at least 50 percent a. of the living forms entering the finest silk nets available pass through the meshes and escape. It Ha is very possible to grow cultures of protozoa, as _ 5, SHEE Peck has already done at Woods Hole, but it was not my purpose to create artificial complexes, so that method was not employed. It is of value, 4,5, however, in obtaining many of the rarer species.
Certain of the larger protozoa were very abundant at times, particularly Ceratium tripos, Peridinium depressum, P. oceaniewm, and several Te feat RULER Ae of species of the genus Tintinnopsis. The distribu- Protozoa in surface collections from June to tion of these animals often appears to be very December 102, ———) Ceratium Here
definitely related to that of the plants. Duringa So00ccc, Peridinium depressum: — - — heavy diatom maximum very few of the larger aioe BBS 0 ey EGTA EOL 2 C —... —, Peridinium oceanicum var. oblongum forms appear, particularly the dinoflagellates. It may be that as soon as the plants have exhausted their food supply and disappeared the protozoa that utilize the nitrates and not the silicates increase rapidly. Just why they should follow immediately after the diatoms is a puzzle, but it is clearly noticeable and can readily be seen by comparing Figures 15, 16, 23, and 24. Thus, after the great Rhizosolenia semispina maximum of the summer, Ceratiwm tripos swarmed, followed closely by C. macroceros and C. fusws in smaller numbers. These would have reached a maximum earlier, I believe, had it not been for the influx of Corethron valdime, which came in September, 1922 and 1923. For that reason their normal high point was never reached. Throughout November and December, 1922, they declined as the winter diatom maximum increased, disappear- ing shortly before the diatoms ceased in April. This may have been caused by the gradual rise in temperature at that time. Within three days after the bulk of the diatoms disappeared two species of pro- tozoa fairly swarmed in the plankton. The most abundant of these was an unidenti- 8242°—25}——3
Aug. Sepe Oot
Ne
122 BULLETIN OF THE BUREAU OF FISHERIES
fied species of the genus Tintinnopsis, although the other (Peridiniwm depressum) was also taken in great numbers. Hundreds of the thimblelike cups of Tintinnopsis could be seen at one time in the field of the microscope. Certain other forms were noticed at different periods throughout the year, but they never formed an im- portant part of the plankton.
A second species of Peridinium (Peridinium oceanicum var. oblongum) had a maximum in the fall of both years. This is a much smaller form than P. depressum and was never present in such large numbers. In 1922 it appeared on July 9, reaching its maximum late in August and disappearing about Spetember 15. In 1923, as in the case of almost all the planktonic forms of that season, the period was later, commencing about September 2 and remaining until November 20. :
ee | on Ce ae eee e a aS » °o c Lh og Deaton 8 Bie We
Se
VeSe
He Fic. 24.—Occurrence of most abundant forms of Protozoa in surface collections of 1923. —-—-—.,, Ceratiwm tripos; -------= 4 C. macroceros; —-eee—, C. fusus; —-.e—, Peridiniwm depresswm; -e-.-e-0-.— , P. oceanicum var. oblongum; ———,
Tintinnopsis sp
During the fall maximum of Ceratium the water fairly blazed with light when disturbed. They caused the net to gleam like a lantern, and often bottom forms not normally taken at the surface were attracted to it.
An interesting radiolarian (Heterophrys sol) also occurred in the fall. During September and October, 1922, the numbers gradually increased until they became exceedingly abundant, often being found in bunches of 20 or 30 specimens. Afterthe 26th of October the number rapidly diminished until November 1, when the last one was seen. None appeared in the collections of 1923.
Of the Silicoflagellata, Distephanus speculum and Dictyocha fibula occurred as scattering individuals throughout the year except in the warmest months. Diste- phanus was most abundant from November, 1922, to March, 1923, and Dictyocha appeared from September to May. Many Foraminifera appeared, usually after a storm. These, however, sank quickly to the bottom again and were rarely taken
.
PLANKTON OF THE WOODS HOLE REGION 123
in surface collections in calm weather. Some six species were distinguished, but positive identification was impossible because there was not sufficient literature available at the time.
The following protozoa were identified from the surface collections of 1922-23:
Acineta tuberosa, Ehrenberg. March 4, 1923. Ceratium fusus (Ehrenberg). See Figures 23 and 24. C. longipes (Bailey). February to June, 1923.
C. macroceros (Ehrenberg). See Figures 23 and 24. C. tripos (Miller). See Figures 23 and 24.
Dictyocha fibula, Ehrenberg.
Distephanus speculum, Heckel.
Glenodinium compressa, Calkins. March 4, 1923. Gonyaulax tricantha, Jérgensen. April 21, 1923. Gymnodinium gracile, Bergh.
Heterophrys sol, Ehrenberg.
Peridinium depressum, Bailey. See Figures 23 and 24. P. oceanicum var. oblongum, Aurivillius. Figures 23 and 24. Tintinnopsis davidofi, Daday. October 14, 1922. Tintinnopsis sp. See Figures 23 and 24.
BS; g Ble Cee yecrray orcs emer im ae a” | Bongainvillia superoiliaris Gemmaria oladophora Obelia spe Podoooryne fulgurans Hi Podocoryne carnea rH Stomotooa apiceata ce Hotopleura ovhracea Hybooodon prolifer H ;
Lizsia grata Syncoryne mirabilis
Syncoryne producta Turritopsis mutricula ilercertium campanula Tiaropsis diademata Dysmorphosa fulgurans Bougainvillia carolinensis Dipurena strangulatsa
Fic. 25.—Occurrence of Hydromedusz in surface collections from June, 1922, to December, 1923 CGLENTERATA
One hundred and sixty species of ccelenterates were recorded from the Woods Hole region by Sumner. Of these, 132 were Hydrozoa, 5 were Scyphoza, and 8 were Ctenophora. Thirty-eight species are listed in the tow records of Vinal N. Edwards for the years 1893-1907. Figures 25, 26, and 27 show the maximum occurrence of the more common species, while in Table 4 the rarer forms, together with the particular dates of appearance, are noted. The records of the more common Seyphomeduse and ctenophores are also recorded on individual charts.
The diagrams show clearly that there are definite seasons of occurrence for the various species of ccelenterates. In most cases the species have a long spring maximum and also a short one in the fall. Such a semiannual appearance is not
124
BULLETIN OF THE BUREAU OF FISHERIES
Syncoryne mirabilis | epee at}
Hybocodon prolifer
Turritopsis nutricula,
Podosoryne fulgurans
Lizzia grata
Bougainvillia superciliaris| | | | | | games| | SRReReREE
Bongainvillia carolinensis SES
Nemopsis bachet
Tima formosa
imaeepere diademata
Epenthesis folleata
Obelia sp.
Zygodactyla groenlandica
Agiantha digitalis
Lirlope seutigera ERES (SREEEE Ieee es a fn eae [dae
to 1907
cyanea Pleurobrachia Bolina
Mnemeopsis
Beroe
Fic. 27.—Maximum seasonal distribution of Seyphomedusz and Ctenophora, based on records of the years 1893 to 1907. See
individual charts for Aurelia, Pleurobranchia, and Mnemeopsis
PLANKTON OF THE WOODS HOLE REGION 125
common among marine animals. Bougainvillia superciliaris, Hybocodon prolifer, Nemopsis bachei, Tiaropsis diademata, Podocoryne fulgurans, and Tima formosa are examples of Hydromedusz having double seasonal distribution. However, hardly a single species that occurs normally in the spring has not also been taken in small numbers in the fall. With the exception of Podocoryne carnea none of the summer visitors have this biannual appearance.
A regular progression of the more common species of Medusz can usually be noticed in the spring. Hybocodon prolifer appears first, followed closely by Syn- coryne mirabilis and Lizzia grata. In early July, as these species reach the end of their season, Podocoryne carnea and P. fulgurans appear, followed in August by Dipurena strangulata and Bougainvillia carolinensis. The summer and fall species always occur in smaller numbers than the spring forms. Certain forms appear to be distributed throughout the year. Hpenthesis folleata has been recorded for almost every month.
a a
Baa on Cue a igen ae ns Eee a aa Aurelia Cyanea, Dactylometra 4 Pleurobrachia Mnemiopsis
Fic. 28.—Occurrence of Seyphomedusz and Ctenophora in surface collections from June, 1922, to December, 1923
Three species of Scyphomeduse are taken frequently in surface collections (fig. 28). The most common (Aurelia flavidula) appears usually in March, April, and May, although ephyre have been taken from August to October.
Taste 4.—Occurrence of uncommon Hydromeduse in surface towings
Species Date Abundance mictopleura ochraceaes-22-- 2-2 ee PAIGE OS 19048 2 ee ee eect Few. Corymorpha pendula---_- Aprs2siandi20M1g05 88 oa ee tt Many. Stomotoca apicata__-____ Apr. 27, May 1, and Aug. 15, 1903___._-___.__-__.------- Few. Staurostoma laciniata-_-- Apr. 9, 1906---______- Do.
Eutima mira--____-_---- Oceania languida_______- Genus Clytia (probably May 16, 1905_-_____ ay Rhegmatodes tennuis-_- pelaSentnclandel 440076 tos Soe octane anos Many. Melani Ghaconica sees ee ihe ee ee a Apr. 24, 25, and 30, and May 2, 1906_____-_-_---_---_---- Few.
Every year in Waquoit Bay immense swarms of strobelias and ephyre of Aurelia appear before the ice leaves. They also occur in varying abundance in all local protected coves and shallow bays where eel grass (Zostera marina) grows in abundance. The young apparently rests on the bottom during the ebb tide, rising with the flood tide. During this period the water is often filled with them, while a few hours later none may be seen. In the spring of 1923 ephyre were particularly numerous at Waquoit Bay, although only a single specimen appeared in my collec- tions from Great Harbor. By April the meduse had increased in size, varying
126 BULLETIN OF THE BUREAU OF FISHERIES
from 1 to 3 inches in diameter. Shortly after this they disappeared. The disap- pearance probably took place when all strobilization had stopped and the currents carried the meduse away. Occasionally at a later date swarms of large adults have been seen in Vineyard Sound or Buzzards Bay. No adults were noted during the past summer (1923) in local waters, although large swarms of mature Aurelia were seen on two occasions in neighboring localities—Mount Hope Bay on July 14, and at the entrance of Oyster Bay in early August.
It is difficult to understand how the planule get back into the harbors (particu- larly Waquoit Bay) in such large numbers when apparently no adults remain in the region. The eggs can not be deposited before the medusz leave in the summer because the ani- mals are not mature at the time. I have never
1895 seen a Mature specimen in Waquoit Bay. There seem to be but two possibilities—either enough 1896 adults remain in the bay until the breeding season (perhaps on the bottom) to repopulate it or the mange planule are drifted in by the tide. I believe that 1898 the first assumption is more probable; that is, that sufficient adults remain to restock the waters even 1899 though none may,be seen at the surface. The dif- ficulties besetting the second possibility make it 1900 almost impossible except under rare conditions when Vineyard Sound is filled with adult Aurelia 2002 at the correct time. Jn the first place the medusa 1902 are entirely at the mercy of the winds and tides. They may be widely scattered in coastal waters i903 or piled together in great banks, as described by Hargitt and Agassiz. The latter author consid- Lele ered that the animals gathered together in the ache breeding season, but this is not probable. After storms large numbers of disks, mmus lobes and none tentacles, of both Aurelia and Cyanea are often found at the surface in local waters. All are de- 1907 stroyed before winter arrives. As the sexes are
Fic. a) Ouse of Aurelia flavidula during separate in Aurelia it is largely a Matter of chance Line are Skea So! whether fertilization takes place at all, because the adults: are likely to be widely separated before reaching sexual maturity. Under these conditions it would hardly be possible for the species to maintain itself, because it is apparently beset with more difficulties than the cod and has a proportionately much smaller number of eggs. Therefore, the few adults that remain in the bays may serve to maintain the species during seasons when fertilization in the open waters is impossible, while a fortunate gathering of adults during the breeding season May account for the enormous swarms present in certain years. This dependence on a chain of circumstances to bring the sexes together at the right time probably goes far to explain the irregularities in this and allied neritic species.
PLANKTON OF THE WOODS HOLE REGION 127
Cyanea capillata appears commonly in spring and fall, but not in as great numbers as Aurelia. On April 14, 1923, the first specimen appeared. Throughout May and early June specimens varying from 10 to 50 mm. could be seen daily at the surface in Great Harbor, often in large numbers. Alexander Agassiz observed great numbers of Cyanea at the surface between 4 and 5 a. m. at Provincetown. “By 7 a. m. all had returned to deeper waters, although not a breath of air had disturbed the surface.’’ A variation in abundance was clearly noticeable in local waters during the past year, but the vertical migration did not affect the whole group, Some specimens occurring at the surface throughout the day. Their numbers increased rapidly, however, during the flood tide. It may be that Agassiz’s observa-
1698 1699 | 1900 } 1901 1902 1903 | 1904 | 1905 |_|
1906
1907
Fig. 30.—Occurrence of Cyanea capillata during successive years, 1893 to 1907
tions could be explained on that basis. Unfortunately no records of the tide were given.
Dactylometra quinquecirra occurs occasionally in Vineyard Sound and Buzzards Bay, although in very small numbers. In Narragansett Bay it is usually very abundant in September and October. On August 8, 1923, a single specimen was taken in Lackeys Bay, and several days later a few were observed in Vineyard Sound. George Gray records large numbers taken on several occasions, together with Salpa democratica-mucronata, off Nonamesset Island at the mouth of Great Harbor. This species is known to be nocturnal, and for this reason the local appear- ance may be greater than the records indicate because very little night collecting -
128 BULLETIN OF THE BUREAU OF FISHERIES
has been done except from the Fisheries dock. This species appears to prefer the relatively impure water of bays and rivers, rarely being taken in coastal waters. Ctenophora present a very difficult problem to anyone attempting to determine seasonal distribution. They are found scattered throughout the year in many places. In this region the limits of the seasonal appearance are very definite, although the abundance varies greatly. Pleurobrachia pileus (figs. 27,28, and 31)
Fic. 31.—Occurrence of Pleurobrachia pileus during successive years, 1893 to 1907
appears in late December and remains until the latter part of May. The occur- rence during 1923 was very scattered. For a few weeks in December, 1922, they were abundant in all collections and then diminished gradually until February. From February until April few were seen, but on April 1 many appeared and remained throughout the month. In certain seasons immense swarms occur. During the latter part of April, 1895, Mr. Edwards often noted that the nets filled in a few minutes with these jelly-like organisms.
PLANKTON OF THE WOODS HOLE REGION 129
Mnemiopsis leidyi appears in smaller numbers at Woods Hole. In Long Tsland Sound there is a very large fall maximum in August and a large winter maximum in December and January. They are rarely found in Buzzards Bay in large numbers, and were taken in only 3 years during the 15 for which the author has records. During the past year a single specimen appeared on December 11 and three on December 15. Cape Cod is, no doubt, the northern limit of this species, and its appearance in local waters depends upon the winds. Specimens taken this spring were stragglers from the winter maximum of more southern waters. No remnants of the fall maximum found their way into Great Harbor in 1922 (figs. 27, 28, and 32).
Bolina alata has been taken at Woods Hole in September by Mr. Edwards. Agassiz described it as being one of the commonest species in Massachusetts Bay, but rare south of Cape Cod. None was seen in Great Harbor during the past year.
Beroe cucumis is usually very rare in this region, although Mr. Gray found it abundant on one or two occasions in late April and May. It is a northern form
ha ieilicfiaile Sate eeabet| oh 1908 LE gt ei vo eno elles on alc a
Fic. 32.—Occurrence of Mnemiopsis leidyi during successive years, 1893 to 1908 whose appearance in local waters is accidental, depending upon strong easterly winds. The following celenterates appeared during the”years 1922 and 1923:
Hydromeduse: Hydromeduse—Continued. Bougainvillia carolinensis Syncoryne mirabilis, Agassiz. (McCrady). S. producta, Hargitt. B. superciliaris, Agassiz. Tiaropsis diademata, Agassiz. Dipurena strangulata, MeCrady. Turritopsis nutricula, McCrady.
Ectopleura ochracea, Agassiz. Gemmaria cladophora, Agassiz. Hyboezodon prolifer, Agassiz. Lizzia grata, Agassiz. Melicertum campanula, Agassiz.
Scyphomeduse: Aurelia flavidula, Peron and Lesueur. Cyanea, capillata, Eschscholtz. Dactylometra quinquecirra (Desor).
Obelia sp. Ctenophora: Podocoryne carnea, Sars. Mnemiopsis leidyi, Agassiz. P. fulgurans (Agassiz). Pleurbrachia pileus (Fabricius)
Stomotoca apicata (McCrady).
130 BULLETIN OF THE BUREAU OF FISHERIES
Ceelenterates recorded from 1893 to 1907 were:
Hydromeduse: Hydromedusze—Continued. Aglantha conica, Hargitt. Staurostoma laciniata (Agassiz). A. digitalis, Miller. Stomotoca apicata (McCrady). Bougainvillia carolinensis (Mc- Synocoryne mirabilis, Agassiz. Crady). Tiaropsis diademata, Agassiz. B. superciliaris, Agassiz. Tima formosa, Agassiz. Clytia (probably C. bicophora), Turritopsis nutricula, McCrady. Agassiz. Zygodactyla grcenlandica (Peron and Corymorpha pendula, Agassiz. Lesueur).
Ectopleura ochracea, Agassiz. Epenthesis folleata, McCrady. Eutima mira, McCrady. Hybocodon prolifer, Agassiz. Liriope scutigera, McCrady.
Scyphomeduse: Aurelia flavidula, Peron and Lesueur. Cyanea capillata, Eschscholtz Dactylometra quinquecirra (Desor).
Lizzia grata, Agassiz. Ctenophora: Hi. Nemopsis bachei, Agassiz. Beroe cucumis, Fabricius
Obelia sp. Bolina alata, Agassiz.
Oceania languida, Agassiz. Mnemiopsis leidyi, Agassiz. Podocoryne fulgurans (Agassiz). Pleurobrachia pileus (Fabricius).
Rhegmatodes tenuis, Agassiz. ANNULATA AND VERMES
The free-swimming annelids may be grouped under three headings—true pelagic adults, benthonic adults swimming during their breeding season, and the early larval stages of all marine Polycheta. A fourth group may be added in this case to include the bottom forms carried by strong currents during storms.
Of the true pelagic annelids only one species occurs frequently in the waters of Buzzards Bay and Vineyard Sound, although Moore (1903) has described two other types from this region. Tomopteros helgolandica is taken from December to April at Woods Hole. During seasons when southerly winds are prevalent they have been taken in considerable abundance. The greatest number recorded was in 1906, when many specimens were taken almost daily throughout April until May 2. During the spring of 1923 there were almost no winds from the south, and as a result oceanic forms have been rare. One specimen of Tomopteros appeared on February 5, that being the only specimen taken during the year.
Benthonic annelids often appear at the surface in great numbers, particularly in the evening, during their breeding season. In the groups where the sexual products are discharged directly into the water the active period is comparatively short, sometimes lasting less than a week. ‘This occurs in the various species of the family Nereide. The adults swarm at certain definite places, usually along sandy beaches or protected harbors, and literally fill the water with cloudy masses of eges and sperm.
From July 20 to 24, 1922, Nereis ambata swarmed in immense numbers at the surface in the eel pond. A few were noticed at other spots along the shore, but none appeared in the daily surface collections. On April 1, 1923, the beach at Nobska Point was the scene of a swarming of NV. virens. On many occasions during the first two weeks of April ripe males were seen swimming among the Fucus about
PLANKTON OF THE WOODS HOLE REGION 131
the Fisheries dock. In this case, as in the case of NV. limbata, free-swimming larvee appeared in great numbers in the tow, but few adults were taken. The usual swarming season for N. limbata ranges from June to September. A few adults of NV. pelagica were taken during the year, but none of these contained ripe sex products. The breeding season of this species is in August and September. Platynereis megalops is also commonly taken at the surface from July to September. Although the young were taken on several occasions, but one adult appeared in the collections
July, 1922
August Jane, 1923
September October November December November Decenber
Amphitrite ornata Arabella opalina Autolytus cornutus Autolytus ornatus” Autolytus alexandri Autolytus emertoni Autolytus varians _ Autolytus longisetosis Dodecacera concharum Harmothoe imbricata Ichthyobdella rapax Lepidonatus squamatus Iarval Lesquamatus Lumbrineris tenuls Magelona rosea ~ Nereis limbata
Nereis pelagica Nereis virens Nephthys bucera Odontosyllis lucifera Odentosyllis spe Paedophylax dispar Phyllodoce catenula Phyllodoce gronlandica Platynereis megalops Podarke obscura
Spio setosa- Telepsavus larvae Tomopterus helgolandica | Unidentified larvae stoi
Fic. 33.—Occasional occurrence of annelids in surface collections from June, 1922, to May, 1923. @, single specimen taken
of the past two summers. All of the members of this family undergo extensive physical changes in adapting themselves for pelagic life during the breeding period. The anterior, nonsexual part remains the same, but in the posterior, sexual region the parapoda become broad and flat and the chete increase greatly in length. In this form the worm is known as Heteronereis and is able to swim very rapidly.
In contrast to the Nereide stand the families Syllide and Hesionide. The different species of Autolytus carry their eggs and swim about for varying lengths
132 BULLETIN OF THE BUREAU OF FISHERIES
of time, often occurring for periods of more than four months. For the greater part of the year they remain attached to hydroids and algz on rocks and piles as nonsexual individuals. In this form they are not free-swimming and their occasional appearance in surface collections is accidental. In the breeding season certain of these nonsexual individuals develop eggs in the posterior part of the body (posterior to the gizzard), while others develop sperm. Strobilization then occurs, and sexual individuals, which immediately become pelagic, are broken off. The females that break off carry clusters of eggs in a pouch on the ventral side. The stolons are either male or female, the two sexes never developing from the same stalk. Occasionally chains of five or six worms, which have not yet separated, may be seen at the surface. Free-swimming males and male chains are usually more abundant than the females. Alexander Agassiz fully described this alteration of generations in 1862. The sexual species of Autolytus are highly phosphorescent and are often extremely numerous in the tow.
Podarke obscura is a very characteristic member of all evening surface collec- tions of the summer. On calm, dark nights swarms of them appear at the surface in protected harbors. The first specimen taken in 1922 appeared on July 6, the last on September 27. In the strong currents about the collecting station the occurrence of Podarke was more scattering than is usual, although many were carried into the nets during both day and night. In daylight, however, the number was much smaller, because at that time the adults seek protection under rocks and among the Fucus.
Larvel annelids appear in the plankton at all seasons of the year. During the early spring they form almost the only representatives of the benthos in the tow. A very small percentage of the species has been worked out, and for that reason it has been impossible to identify a large number of the larval forms that were taken during the past year. Larval Nereis were very abundant during April and May in 1899, 1900, and 1923. These spring forms probably were Nereis virens. Another large increase in the latter part of October in each of the years recorded may have been WN. limbata, although the date is rather late for this species. Such conclusions must remain as mere speculation until further data on the breeding seasons can be obtained. This can readily be realized if one considers that there are six species of the family Nereide represented at Woods Hole, and larval Nereidi- formia have been taken in every month of the year except September.
Two very characteristic larval annelids appear each year in large numbers. The first occurs in late July and continues throughout October. Fewkes has described it from Newport as a species of the genus Telepsavus. His identification is doubt- ful, however, for no adult of the species has been recorded from this section of the Atlantic coast. In 1922 it appeared first on July 26 and continued to be taken until October 25. The second larve (Lepidonatus squamatus) appeared first on Decem- ber 19. Throughout the spring it was taken daily in large numbers. The season lasted until the last of April. This fact is rather unusual for Sumner records the breeding season as late April, May, and June. An adult female of this species taken on February 2, 1923, was filled with ripe eggs. During May and June, 1922,
PLANKTON OF THE WOODS HOLE REGION 133
no larve appeared in the surface collections. From these observations the breed- ing season is seen to be much more extended than has hitherto been supposed.
Occasionally postlarval forms occur after northeast storms. As these are not true free-swimming larve they are listed with adults taken under similar conditions. During the past year several nonplanktonic annelids have been taken. Certain of these may swim freely in their breeding season, but the occurrence in the collec- tions was so scattering that I have not considered it as normal. Dodecacera con- charum offers a peculiar problem. Scattered specimens, often quite numerous, varying from 15 to 20 mm. in length, appeared from July 16 to August 15, 1923. The presence of these immature specimens over such an extended period of time could hardly have been accidental, and yet Dodecacera is known to be a truly benthonic annelid.
Comparatively few leeches have been taken from the Woods Hole region. Sumner records five species, all of which were taken from fish. One species (Ich- thyobdella rapax) appeared twice in the surface collections of 1922-23—once on January 20 and once on April 7. Both occurrences were during the breeding season of the winter flounder (Pseudopleuronectes americanus). Former records give the summer flounder as its host, but it is highly probable that it will be found on both species.
The following annelids were taken in 1922-23:
Amphitrite ornata (Leidy). Nereis pelagica, Linnzeus. Arabella opalina (Verrill). N. virens, Sars.
Autolytus cornutus, Agassiz. Nephthys bucera, Ehlers.
A. ornatus, Verrill. Odontosyllis lucifera, Verrill.
A. alexandri, Agassiz. O. sp.
A. emertoni, Verrill. Pedophylax dispar, Webster. A. varians, Verrill. Phyllodoce catenula, Verrill. A. longisetosis, Agassiz. P. grénlandica, Oersted. Dodecacera concharum, Oersted. Platynereis megalops (Verrill). Harmothée imbricata, Malmgren. Podarke obscura, Verrill. Ichthyobdella rapax, Verrill. Spio setosa, Verrill. Lepidonatus squamatus, Leach. Telepsavus larve?
Lumbrineris tenuis, Verrill. Tomopterus helgolandica, Greef. Magelona rosea, Moore. Unidentified larve of several species. Nereis limbata, Ehlers.
Sagitta is the only true pelagic representative of the phylum Vermes found in this region. It usually appears in December and remains until June. In listing the Sagittz of past years no attempt was made to distinguish between Sagitta elegans and S. serrodentata. The former is more littoral and northern in its distribution, while the latter is a southern oceanic form often occurring in the Gulf Stream. During the spring of the present year (1923) no specimens of S. serrodentata were taken. This may be explained by the fact that the prevailing winds have been from the north and comparatively few oceanic forms of any sort have found their way in. However, since S. serrodentata forms such an unimportant part of the outside plankton, its presence in the region of Woods Hole is, no doubt, so rare that the distribution curve of Sagitta for any year can be considered to be the seasonal variation of S. elegans. A sudden appearance after July and before November
134 BULLETIN OF THE BUREAU OF FISHERIES
would probably follow a southwest wind, and in this case the species might be S. serrodentata, although deep-water collections off the coast in warm weather often reveal large numbers of S. elegans. Such a condition may have taken place in August 1903 (see fig. 35). On August 4, 1922, one specimen of 8. serrodentata was taken and another on August 5.
In the 16 years that S. elegans has been recorded, with one or possibly two excep- tions, none appeared before November or remained after July. The usual time of appearance is December. In 1899 a few were taken on December 23, and in 1898 many suddenly appeared on December 12. In 1922 two specimens were found on October 4, one on October 5, two on October 10, and gradually increased from then until early December, when large numbers appeared. The highest point is usually reached in February. During this month they swarm.
It is interesting to compare these results with those of Dr. H. B. Bigelow (1914) in Massachusetts Bay. In late December he found S. elegansin the tow. Through-
e
a 4 s ‘oO
Rive Biacifinwpitiod Mies co Bines
Ne Fig. 34.—Occurrence of Sagza evegans in surface collections from June, 1922, to December, 1923. , distribution in 1922; —.—, distribution in 1923
out January and February the numbers increased until they formed the bulk of the plankton. Occasionally 8. serrodentata was taken, but always S. elegans was by far the most abundant. When the water began to grow warmer in early March, the numbers fell off rapidly, so that on March 4 only 12 specimens were taken. The last Sagittee appeared on April 14. This is merely additional evidence of the similarity of plankton north and south of Cape Cod in winter.
In March and April, 1923, swarms of S. elegans with ripe eggs were abundantin Great Harbor. During the latter part of April large numbers of eggs appeared and, together with the eggs of the mollusk Littorina litorea, made up the greater part of the tow. On May 2 the first young were observed. These increased rapidly in number and were very abundant throughout May and June. The last specimen was
PLANKTON OF THE WOODS HOLE REGION 135
taken on July 18, although the numbers had been very small since June 20. In August, 1923, large numbers of small Sagittz of the spring brood were taken off No Man’s Land in deep water.
Many species of Platyhelminthes and Nemathelminthes have been recorded from surface collections, but these have been accidental in occurrence and, with the exception of certain early larve, do not form a part of the littoral plankton. Most members of the phylum, excluding internal parasites, live among the marine plants
1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 Ff 1905
1906
1907
Fig. 35.—Occurrence of Sagitta elegans im surface collections during successive years. Broken lines indicate scattering occurrence
and detritus on muddy bottoms or on piles. Some forms like the rotifers, of which a few marine genera occur at Woods Hole, swim about freely, but even these are not a part of the open-water plankton. Only one rotifer (Synchexta triopthalma Lauter- born) was observed during the past year, and this was seen but once.
Often in summer planarians appeared, but no attempt was made to identify them. One species, however (Microstomum davenporti Graff), was taken in the harbor on
136 BULLETIN OF THE BUREAU OF FISHERIES
two occasions, August 5 and 16, and in the Sound on August 18 and September 21. A single specimen of Nectonema agile Verrill was found among much detritus after a hard wind on July 11.
MOLLUSCA
Gastropod larve are found throughout the year in all surface collections from inshore waters. There is considerable doubt as to the percentage of forms whose early stages are free-swimming. Many species, such as Busycon canaliculatum (Say) and Buccinum undatum Linnzus, secrete cases in which the young pass their early stages, emerging in the form of the adults. Others deposit eggs in jelly- like masses attached to the underside of rocks and on marine plants. Littorina palliata (Say) is an example of this type. Still other forms, such as L. rudis Maton, are viviparous. The eggs of all of these are never found floating, and the young normally do not appear in the plankton. Certain young after emerging from the egg cases may accidentally be carried along by the currents. This probably explains the presence of many species taken during the summer and fall.
A fourth group of gastropods no doubt contribute the bulk of the planktonic larve. This group, of which Lnttorina litorea and Lacuna vincta are examples, discharge their eggs directly into the sea water. In these two species each egg is especially adapted for floating by a surrounding ring of jelly, which gives the appear- ance of the trench helmets worn by the American soldiers in the late war. This device serves also as a means of protection. The eggs and free-swimming larvz are found in great numbers from March until July. This is also the breeding season of Littorina litorea in English waters, according to Tattersall, who made extended observations upon that species. Lacuna vincta also swarms in February and March, some eggs having been found as early as December by Sumner. The eggs of this species may be distinguished by a light greenish tinge. In March of the present year (1923) great numbers of Littorina eggs appeared daily and in- creased throughout April. None were found in collections of the previous June. There was a maximum of eggs identical to those of Littorina in the fall, which the author has not been able to identify. There can be little doubt that this floating condition explains the rapid expansion of Littorina litorea after it was once estab- lished on the western Atlantic coast.
An interesting adaptation to pelagic existence is found in a larval vitrinellid, the species of which I have been unable to ascertain. Shortly after the nucleus has formed, a broad shield grows out as an extension of the shell. This shield appears like the wide brim of a straw hat and enables the larva to float. Later, as older specimens showed, the shield is lost and the young mollusk sinks to the bottom. It is an interesting adaptation and has never before, to my knowledge, been noted.
In the summer of 1922 Dr. Paul Bartsch kindly aided me in identifying the gastropod larve that appeared during June, July, and August. The many forms often bear no resemblance to the adults, but are identified by comparing the nuclear whorls. These never change and offer an excellent means of identification. The nucleus is now used as a basis for classification among adult mollusks also.
PLANKTON OF THE WOODS HOLE REGION 137
Apparently none of the larger gastropods have free-swimming stages, the bulk of the summer forms coming from those minute species that live on the floating Fucus and Sargassum. The following gastropods were distinguished in surface collections of 1922:
Littorina litorea (Linnzus). Tritonofusus stimpsoni (Morch). Bittium alternatum, Say. Triphoris nigrocinctus, Stimpson. Astyris lunata (Say). Lacuna vincta, Montagu. Skenea planorbis, Fabricius. A vitrinellid genus (?). A combellid, probably Anachis avara
(Say).
But one Nudibranch mollusk has been recorded by Edwards from surface collections. This species (Facelina bostoniensis (Couthouy)) appears each spring, often in large numbers. This year it appeared on January 21 and continued to be taken until May. Upon examination many females were found to contain dozens of small larvee, which were very similar in form to the adults. Four other species were represented by single specimens taken during the year—Elysiella catula (Agassiz), June 1; Doto coronata (Gmelin), September 6; Alderia harvardi- ensis (Agassiz), March 29; and family Dotonidz, November 8.
Clione limacina (Phipps), a pteropod, is often taken in large numbers around Marthas Vineyard. It is a member of the oceanic plankton and is occasionally blown into Great Harbor during southern storms. The author has five records of its appearance in surface collections. The first four—September 10, 1888, March 20, 1896, April 28, 1911, and May 2, 1911—were taken by V. N. Edwards; the fifth, on May 3, 1918, by R. A. Goffin. Another pteropod (Heterofusus retro- versus (Fleming)) had been recorded once in local waters (Sumner, 1913a). A single specimen was taken in Great Harbor on January 12, 1924.
The larval Pelecepoda present a most difficult problem to the plankton investi- gator. The early larve all look alike and can be distinguished, with any degree of certainty, only by careful measurements. During the summer the author was able to make few such measurements and for that reason the results are very in- complete. The late larval stages are more easily distinguished. J. Stafford’s excellent paper on bivalve larve made the identification of these forms a rather simple matter. At this stage, however, the bivalves sink to the bottom and are taken in much smaller numbers.
The most common pelecepods of this region live in the shallow waters of pro- tected bays and harbors. For that reason they are quickly affected by the increase in temperature during the spring. The length of time required for the ripening of the gonads is not known, but many larve of Mytilus edulis were found early in June, 1922. Later in July larve of a slightly different shape were noted. These proved to be the young of both Venus mercenaria and Mya arenaria. Many Pecten larve were taken near Block Island in September, but none appeared at Woods Hole. Mya, Venus, and Mytilus remained throughout the summer and until late in the fall. By August 10 Mytilus had almost acquired the adult shape and appeared less frequently in the collections, although many were taken through- out November and December. By this time the larve had long since passed the
§242°—25;——4
(138 BULLETIN OF THE BUREAU OF FISHERIES
swimming stage and were carried into the nets by the strong currents. No oyster larvee were noted during the summer of 1922.
Of the Amphineura one species (Chztopleura apiculata Carpenter) was taken on September 23, 1922. The larva was at that time in a late stage of development, the shell measuring 1.2 mm. in length. However, the free-swimming period had not ceased, for the little animal continued to float about in a watch glass for several hours.
Throughout the latter part of May and June the eggs of Loligo pealit Le Sueur are found in great abundance. Scattering young forms appeared on June 2, 1922, and increased rapidly until July 11, when the largest number was taken. On clear, calm days small schools of these little cephalopods could be seen swimming at the surface in much the same manner as the adults. Such schools were particularly common about the fish traps, where large numbers of adults are frequently captured.
° ° ° ° ° e > .) i= > VA 2 E : g 4 % 8 E a f = é Q e 7 had 8 7 2 8s Woke Ae i a. | | 5. A. ab istese i YeS SEE : V8 i t HH Tm Ne + $ Fic. 36.—Occurrence of larval forms of Loligo Fic. 37.—Occurrence of Phyllopoda in surface col- pealii in surface collections of 1922 and 1923. lections from May to December, 1922. —,—, , distribution in 1922; ______-, » dise Podon intermedius; , LEvadne nord. tribution in 1923 manni; -------- , L. tergestina
In August there was a decrease in the abundance. This continued throughout that month and early September. Two specimens were taken in October and one on November 20. The last occurrence is rather surprising, because no young forms had been seen since October 18, and then only one specimen was found. In 1899 the last specimen was taken on October 24. In 1923 the season jasted from June 26 until October 16 (fig. 36).
ECHINODERMATA
Practically all of the echinoderms of the Woods Hole region have a free-swim- ming stage. A few holothurians and one starfish (Henricia sanguino lenta (Miiller)), are viviparous, but these are uncommon forms. In certain years great numbers of the larvz of Asterias have been taken in surface towings. None were found in collections of 1898-99 nor during 1922, although Asterias is known to breed through- out the summer months in this region. In 1923 a single brachiolaria of Asterias
PLANKTON OF THE WOODS HOLE REGION 139
appeared on July 16, it being the only specimen taken that year. In Narragansett Bay the season is usually completed in a few weeks in late June; after that hardly a ripe adult can be found. As four species of Asterias have been recorded from Woods Hole it is probable that all do not breed at the same time. This might account for the extended breeding season.
A specimen of Leptosynapta inhzrens (Miller), 20 mm. long, was taken on September 19 after a hard northeast storm. This was not a free-swimming form and would not normally occur in surface collections.
CRUSTACEA PHYLLOPODA
Two species of marine Phyllopoda (Podon leuckarti arid Evadne nordmanni) have been recorded from the Atlantic coast of the United States. D. L. MacDonald records three species from St. Andrews, New Brunswick, two of which (E. spinifera Miller and Podon finmarchichus) have never since been taken. As the name of the original describer does not appear on the list, I am unable to find any other record of P. finmarchichus. This name is not given in any available literature on the subject. E. spinifera is a southern form that has not appeared in this region during the past year.
Two species of Hyadne were taken at Woods Hole in abundance during the summer of 1922. Hvadne tergestina, new to this region, appeared on May 20, be- coming very numerous by July 1. During the summer diatom maximum the num- bers decreased but rose again in September. After that they declined until Novem- ber, the last bemg recorded on November 15.
Ewadne nordmanni appeared shortly after FE. tergestina, but never became abundant in the summer months (fig. 37, p. 188). In October they increased and reached their highest point about November 1, at a time when EL. tergestina was fast disappearing. Throughout December they declined rapidly and disappeared about January 20. £. nordmanni is easily distinguished by its pinkish color as well as its different appendage formula. J. tergestina is usually quite colorless and very transparent.
Podon intermedius was first recorded from the western Atlantic by MacDonald at St. Andrews, New Brunswick. This species appeared in the surface collections of Great Harbor on May 27, 1922, and increased rapidly, reaching a high point in the last week of June. The numbers declined during the period of the diatom swarms, but rose again, reaching the peak in the middle of September. Another diatom maximum in early October reduced the number a second time, but they once more rose and remained until the last of the month. During November P. intermedius became scarcer and disappeared about December 15. In general, the season is the same for the various species. Evadne nordmanni has the longest occurrence. The distribution of P. intermedius in 1923 was very similar to that of the previous year, except that it arrived later (fig. 38).
No specimens of Podon leuckarti (Sars) were taken during the past year, and a careful search through the collection of 1899 and 1900 failed to show any, although
140 BULLETIN OF THE BUREAU OF FISHERIES
Pratt and Sharpe recorded them as occurring in great abundance. No specimens . have been placed in the National Museum, and as Sharpe’s collections were lost I have been unable to find any identified material. It seems strange, however, that a species not recorded from the region appeared in such great abundance, while the common form was absent during those three years.
On July 28, 1923, Podon polyphemoides appeared in the surface tow. No specimens of this species had been observed in the collections of the previous year or in 1899 to 1900. The season was very short, lasting less than four weeks. The last specimen was taken on August 22. At the mouth of New Haven Harbor in Long Island Sound, August 1 to 3, 1923, swarms of this species were observed. They .
i
Apre Sepa Oate
e .) oO Saye
ae Re ae
ry Jane) Fede
Ae
Se
VeSe
Ne
Fic. 388.—Occurrence of Phyllopoda in surface collections of 1923. ———, Podon intermedius; —eoe—, P. polyphemoides; —.—, Hvadne nordmanni; -------- , £. tergestina
were so numerous that a surface tow of 15 minutes yielded 80c. c. of P. polyphemoides and almost nothing else.
The following phyllopods appeared in the surface collections of 1922-23: Podon intermedius Lilljeborg, P. polyphemoides (Leuckart), Evadne nordmanni Loven, and E. tergestina Claus.
OSTRACODA
With few exceptions the ostracods are not true planktonic animals. None of the Woods Hole species belong in the pelagic group, although many appear in sur- face collections after storms or hard winds, along with particles of sand, Foramini- fera, and other bottom forms.
Cushman found that, excepting one specimen, all species of the Myodocopa taken in the survey of Vineyard Sound and Buzzards Bay came from the “Gut of Canso,” directly across the harbor from the fisheries station.
PLANKTON OF THE WOODS HOLE REGION 141
In the collections of the past year one of this tribe (Cylindroleberis mariz) appeared with greater frequency than any other one species, even though the Podocopa are much more abundant at certain spots in Great Harbor. This instance shows how easily wrong conclusions may be made in the study of littoral plankton if the bottom fauna is not clearly understood. It illustrates, also, an important point about the fauna of the harbor. The bottom forms dwelling here are so dis- tributed that they are protected from the rushing currents, although they are able to derive benefit from the food material carried by these waters. For that reason, even under unusual conditions, the benthos occurring in surface collections proba- bly is transported from Buzzards Bay. This is quite evident in the case of amphi- pods where the distribution is very well understood. Even the animals of the “Gut of Canso” are carried away rarely, and the ostracods become dislodged only when the hydroids and Fucus, to which they attach themselves, are torn from their - bases.
The following ostracods were taken in 1922-23: Sarsiella americana Cushman, Cylindroleberis mariz (Baird), C. zostericola Cushman, Loxoconcha impressa (Baird), Cythereis emarginata Sars, and genus Cythereis (several species).
COPEPODA
Together with the Phyllopoda and an occasional euphausid or hyperid, the Copepoda form the only truly pelagic Crustacea of the local plankton. Except in the seasons of diatom maxima, they are always present in abundance. Farran found that whenever a species is present in sufficient numbers a distinct periodicity in its occurrence is noticeable. This is true at Woods Hole. Although copepods are always present in varying numbers, certain species are continually disappearing and being replaced by others. The copepods of Great Harbor may be divided roughly into two great groups—the summer community and the winter community.
The summer forms may arise from three sources: (2) Annual appearance of local coastal species common to the region, (b) the young of these common forms, appearing often in large numbers during the breeding season, (c) southern oceanic forms blown in by winds from the Gulf Stream during the warm weather.
The first of these sources accounts for most of the summer species. These may again be grouped under two headings: (1) True pelagic species and (2) bottom forms appearing after hard winds. The most typical summer pelagic species are Acartia tonsa and Centropages typicus. These form the bulk of the summer copepod fauna. Later in the fall Pseudodiaptomus coronatus reaches its maximum and outnumbers all other forms. This, however, is not a true summer species, but serves as a connection between the warm and cold water copepods. Tortanus dis- caudata serves in a similar capacity in the spring and early summer. Benthonic adults of the family Harpacticide are often taken in surface collections. These are usually found among bottom plants and alge but are capable of swimming quite as well as the Gymnoplea. The most common summer Copepoda are Acartia tonsa, Centropages typicus, Pseudodiaptomus coronatus, Labidocera estiva, Oithona similis, O. brevicornis, Alteutha depressa, Parategastes sphzricus, Amphiascus obscurus, Ilyopsyllus sarsi, and Dactylopusia vulgaris.
142 BULLETIN OF THE BUREAU OF FISHERIES The young of the summer copepods never appear in large numbers, as in the case of winter breeders, and only three species—Acartia tonsa, Pseudodiaptomus coronatus, and Centropages typicus—were identified. The third summer group varies considerably in different seasons. If the prevailing winds through June, July, and August are from the south, great numbers
of Gulf Stream forms may appear. Such was the case in 1922, and for that reason several species new to this coast were
fade jae Sensis taken. The common annual visitors also Ves 2 Bostorducr sob wit dente Gd. & a Se Se TS. ; Ws. B. n ‘ Fic. 39.—Occurrence of species of Acartia in sur- face collections from June to December, 1922. Fic. 40.—Occurrence of species of Acartiain surface collec- tions of 1923. —.—, Acartia tonsa; ———, A. bifilosa;
——, Acartia tonsa; ------, , immature A. tonsa; —-—, A. bifilosa; —.—, A. clausii
appeared in abundance. The southerly winds did not continue in the fall, however,
and the result was that the usual tropical fish and ccelenterates were not observed at Katama Bay and in Vineyard Sound.
No doubt these conditionsa ffected cope-
, A. clausii; —-——, A. longiremus
< . ° a ° ° . Bea ee aaa aS 5 pods as well. As an illustration of this Ae Microsetella rosea appeared in great 1a eg Be See ee Be SHE SEES asi ae 8. Se : : - 4% ae aE + v.3 Ne : ry Fic. 41.—Occurrence of Pseudodiaptomus coro- matus and Tortanus discaudata in surface col- Fic. 42.—Occurrence of Pseudodiaptomus coronatus and Tor- lections from June to December, 1922. : tanus discaudata in surface collections of 1923. ee P. coronatus; —.—, T. discaudata coronaius; ——.«—, T. discaudata.
numbers on September 2 in vertical hauls taken off Block Island. Later during this - month (fig. 46, p. 145) scattering specimens were observed at Woods Hole. Much larger numbers would probably have been found here if hard south winds had
PLANKTON OF THE WOODS HOLE REGION 143
prevailed. The summer forms from the Gulf Stream taken in 1922-23 were Pontella pennata, P. meadii, Anomalocera patersoni, Microsetella rosea, Setella gracilis, and Thawmaleus claparedii.
No distinct division can be made dividing the summer forms from the winter ones. Figures 40, 42, 44, etc., show clearly how much the seasonal distributions of the various species overlap each other. Certain forms, such as Centropages hematus, appear as early as August and remain until May. As the breeding season is in December and January, they are considered to be true cold-water forms.
The winter copepods may roughly be divided into four groups: (a) Those northern species that remain in deep water or north of Cape Cod during the sum- mer, entering this region every winter in great numbers, (6) the young of the winter species, (¢) northern oceanic forms occasionally finding their way in, @) Har- pacticide, usually acci- dental members of the
he
%.5:
V.S.
Fic. 43.—Occurrence of Centropages in surface collections from June to
December, 1922. ———, Cenitro- Be
pages typicus; ==-==, C. hematus; Fic. 44—Occurrence of Centropages in surface collections of 1923. —e—, C. hematus (immature ———, Centropages typicus; , C. hematus;i—eeo—, C. typicus forms) (immature form); —.—, C. hematus (immature form)
plankton, but in a few cases rising to the surface during the breeding season.
Three copepods are usually characteristic of all winter plankton—Pseudo- calanus elongatus, Temora longicornis, and Centropages hematus. During the years 1922 and 1923 almost no specimens of Temora appeared. This is very unusual, for all samples of past years taken at this season are literally filled with them. As they appear in the greatest numbers in February, March, and April, the unusually cold weather of the spring of 1923 (fig. 5, opp. p. 100) may have affected them as it has many of the other animals. The young of Pseudocalanus and Centropages became so abundant in January and February that they far out- numbered the adults, a condition which was never found among summer forms. A few immature Temora were noted, but their appearance was not common.
Northern species are sometimes plentiful in the waters of Vineyard Sound and often appear in surface collections in Great Harbor. Calanus finmarchicus is the most common of these cold-water forms. Metridia lucens, Eurytemora herdmant, and £. hirwndoides were taken often during the spring of 1924. No other northern copepods to my knowledge have ever been recorded from Woods Hole.
144 BULLETIN OF THE BUREAU OF FISHERIES
Members of the family Harpacticide sometimes appeared during the winter months. Only one species (Tachidws brevicornis) had a definite free-swimming period. Egg-bearing females were taken in towings throughout the spring, often in great abundance. This, apparently, was the only one of the group that had a pelagic period during the year. Others may have been free-swimming but did not occur in sufficiently large numbers to indicate it.
4 gq. & Bini non onl Comantiahede
a
Se
ves.
Ne Fic. 45.—Occurrence of Pseudocalanus elongatus in surface collections from June, 1922, to December, 1923.
«-.---, distribution of adults in 1922; —_— —, distribution of immature specimens in 1922; ————, dis tribution of adults in 1923; —. —, distribution of immature specimens in 1923
The winter forms collected during the past year were as follows:
Pseudocalanus elongatus. Acartia clausii. Calanus finmarchicus. A. longiremus. Centropages hematus. A. bifilosa.
Temora longicornis Tortanus discaudata. Eurytemora herdmani. Microsetella norvegica. E. hirundoides. Idya furcata.
Metridia lucens. Tachidius brevicornis.
Over 50 species of parasitic copepods have been recorded from Woods Hole. Often they are taken in surface collections, but they do not home form a part of the plankton except in their larval stages. None appeared in 1922. In 1923 a male Caligus schistonyx was taken.
Three lists of free-swimming copepods have been made for this region. Wheeler recorded 30 species, but most of these were taken in the vicinity of the Gulf Stream and are extralimital. Sharpe recorded 60 species in 1911, of which only 23 occurred at Woods Hole. Twelve others were quoted from Williams’ s report on Narragan- sett Bay, and the remainder were taken from Wheeler’s list. Summer, in 1911, compiled 25 (plus 12) species from the combined data of Wheeler and Sharpe, no new additions being made.
PLANKTON OF THE WOODS HOLE REGION 145
During the past year 42 species of free-swimming copepods appeared in the surface collections taken from the end of the Fisheries dock. Of these, 19 belong to the tribe Gymnoplea and 22 to the tribe Podoplea. In Sharpe’s list 12 species from this region belong to the Gvmnoplea. The list for this tribe. I believe, is
July Sept Apre
g g
June Augs Octe Nove Dece Jane Feb.
falanus finmarchious Psendocalanus elongatus Immature P.elongatus ff : ; : Paracalanus parvus Centropages typicus = s oo Centropeges hematus : Immature Cehematus femora longicornis. Eurytemora herdmani : t Eurytemora hirundoides Metridia lucens P.coronatus
Iabidocera destiva Pontella meadii Anomalocera patersont Acartia tonsa
Acartia clausii : Acartia longiremis Acartis bifilosa Tortams discandata Oithona similis Hicrosetella rosea Microsetella norvegica HEH Setella gracilis Seine
Thaumsleus claparedii
Harpacticus chelifer HH
Harpacticus uniremis Altentha depressa fener Parategastes sphaericus Idya furcata f Dactylopusia vulgaris Tachidius brevicornis Asphiascus obscurus Parawestwoodia minuta
Longipedia coronatus Tlyopsyllus sarsi
Fic. 46,—Occurrence of Copepoda in surface collections from June, 1922, to May, 1923. (Oithona brevicornis is not distinguished from 0. similis)
now fairly complete. The Podoplea, however, have scarcely been touched and will, no doubt, yield many more species when carefully studied. Twelve species taken in 1922-23 are new to the Woods Hole region. I have not listed as new any forms previously recorded from Narragansett Bay.
146
BULLETIN OF THE BUREAU OF FISHERIES
June Jule
Alteutha depressa Anomalocera patersoni Calanus finmarchious Caligus schistonyx Burytemora herdmani Halithalestris croni Harpacticus chelifer Iabidocera sestiva Tiyopsyllus sarsi Oithona brevicornis Oithona similis Paracalanus parvus Parategastes sphaerious Pontella meadii Pontella pennata fachidius brevicornis femora longicornis
Sep. Octe Nove Dece
Fic. 47.—Occurrence of certain copepods in surface collections from May to December, 1923
The following Copepoda were taken during 1922-23;
Tribe GyMNOPLEA
Family Calanide:
Calanus finmarchicus (Gunnerus). Pseudocalanus elongatus (Boeck). Paracalanus parvus, Claus.1
Family Centropagide:
Family Pontellide:
Centropages typicus, Kroyer.
C. hematus (Lilljeborg).
Temora longicornis (Miller).
Eurytemora herdmani, Thompson Scott.
E. hirundoides (Nordquist).
Metridia lucens, Boeck.
Pseudodiaptomus coronatus, Williams.
and
Labidocera <estiva, Wheeler.
Pontella meadii, Wheeler.
P. pennata, Wilson.!
Anomalocera patersoni, Templeton.
Acartia tonsa, Dana.
A. longiremis (Lilljeborg) .1
A. bifilosa, Giesbrecht.!
Tortanus discaudata Scott).
Acartia clausii, Giesbrecht.
(Thompson and
Tribe PopoPLEA
Family Cyclopide: Oithona similis, Claus. O. brevicornis, Giesbrecht.1 Hermanella sp. Family Harpacticide: Microsetella rosea, Dana.! M. norvegica, Boeck. Setella gracilis, Dana.! Thaumaleus claparedii.! Harpacticus chelifer (Miller). Alteutha depressa, Baird. Harpacticus uniremis, Kréyer. Parategastes spzericus (Claus). Idya fureata (Baird). Dactylopusia vulgaris, Sars. Laophonte sp. A.? L. sp. B.? Tachidius brevicornis (Miller). Amphiascus obscurus, Sars.! Parawestwoodia minuta, Claus.! Longipedia coronata, Claus. Tiyopsyllus sarsi, Sharpe. Asellopsis sp. Halithalestris croni (Kroyer). Family Caligids: Caligus schistonyx, Wilson.
1 New to Woods Hole.
2 Both differing distinctively from Z. longicaudata Boeck. New to Woods Hole.
PLANKTON OF THE WOODS HOLE REGION 147 CIRRIPEDIA
At certain seasons of the year barnacle larvee are very abundant in the plank- ton. In both the nauplius and “cypris” stages they swim freely, although as a rule the “cyprids” settle on the Fucus soon after the metamorphosis and are not taken in large numbers in surface collections. At such times often thousands can be taken in a single sweep of a hand net drawn through the Fucus near the water’s edge. The nauplii of the three species of Balanus are so much alike that even the most careful identification is often rather uncertain. However, the difference . in the breeding periods makes the identification easy in the field, although in certain years the seasons of Balanus crenatus and B. eburneus overlap.
Balanus crenatus is not as abundant in the immediate vicinity of Great Harbor as are the other species of the genus, and for that reason the larve occur in much smaller numbers in surface collections. The breeding season starts early in June and generally continues until the middle of July. In 1922 (fig. 48) the first larvae
BS Bog Bote Bo shoes Bg
3 ye ae oS USE Ne See I ve ae +H 4 zs 8. Se 5 VeSe Ved. Be Ne Fia. 48.—Occurrence of barnacle larve in surface Fie. 49.—Occurrence of barnacle larve in surface collections collections from June to December, 1922. of 1923. , Balanus balanoides nauplii; ----- = 12) —-—, Balanus balanoides; -------, B. balanoides ‘‘cyprids’; —-—-—, B. crenatus; —-»—, crenatus; ——»«—, Chihamalus stellatus; ” B. eburneus; +, Chthamalus stellatus
B. eburneus; 4-, Lepas sp.
appeared on July 2; the last on July 16. They were abundant on only one day— July 13. After this a single specimen was taken on July 15 and one on July 16. It is possible that nauplii may have occurred after August 1, when fairly large num- bers of B. eburneus suddenly appeared. However, as an interval of 15 days elapsed between the two periods, the possibility of a stray B. crenatus nauplius being present would probably be so small that it need not be considered. In 1923 the first speci- men appeared on June 29 (fig. 49). Scattered nauplii and ‘‘cyprids” were taken until July 23. Off Coney Island, N. Y., swarms of early nauplii (no doubt B. crenatus) were taken on June 12, 1923.
Balanus eburneus is usually found in August, although the nauplii seldom form an important part of the surface collections. This may be due to the fact that the summer plankton is particularly rich and the barnacles, therefore, are greatly outnumbered. It is certain, however, that they never appear in such swarms as does B. balanoides.- The first nauplii in 1922 (fig. 48) appeared on August 1, scat-
148 BULLETIN OF THE BUREAU OF FISHERIES
tering individuals being taken until November 12, when the last specimen was ob- served. In 1923 the first nauplii appeared on August 12 (fig. 49).
Balanus balanoides appeared first on December 16, 1922 (fig. 48). By January 1 great numbers filled the tow. An examination of adults at this time showed that almost every specimen was filled with young and all seemed to be at exactly the same stage of development. In 1923 the first nauplii appeared on December 7 (fig. 49). On February 8, 1923, the first ‘‘cypris larve” appeared. These were at all times far less abundant that the nauplii. Throughout February and March they continued to appear, declining in April, although a few specimens were found in every haul. In certain parts of Long Island Sound, on March 5 and 6, the “eypris larve”’ were exceedingly abundant. The season in 1899 and 1900 coin- cided exactly with that of 1922 and 1923.
A comparison of this locality with other places along the coast is necessary in order to understand the relative position of Woods Hole. In Massachusetts Bay Bigelow found nauplii of Balanus balanoides throughout March and early April, 1913. Nauplii swarmed off Boon Island on April 5 of the same year. By April 9 large numbers of the “cyprids” with few nauplii were observed, while collections of seven days later revealed only “‘cyprids.”” These were most numerous from April 25 to 30, when they formed the bulk of the macroplankton, and con- tinued to appear as scattered forms until the middle of May, when all had practi- cally disappeared.
In early March swarms of Balanus were found in the “cypris stage” among the Fucus along the shores of upper Narragansett Bay. Some were already attached. In Newport Harbor the author found large numbers of nauplii from January 25 to 81, 1922.. The largest swarm appeared on January 30. On March 4 of the same year “cyprids” literally filled the waters in the harbor of Bristol, R. I. It was not possible to carry on further observation in this locality, so the duration of the season was not determined. The author has taken nauplii in upper Narragansett Bay in large numbers in late January.
From these records it appears that the breeding season in Narragansett Bay and vicinity is somewhat later than at Woods Hole. This may be because the water responds more quickly to sudden drops in air temperature and retards the developing eggs. As one goes farther north the season grows later. Thus, Dr. Bigelow found that the breeding time starts in March in Massachusetts Bay and terminates quickly, due to the apparent rapid development of the larye. In Newfoundland the breeding season of this species is in June and July.
Chthamalus stellatus, although quite abundant locally, appeared in very small numbers in the plankton on only two days in 1922—-August 15 and 16. No “cyprid larvee’”’ were found. In 1923 a single specimen was taken on July 23.
A single nauplius of Lepas appeared in the collections on September 30, 1922. This larva often occurs locally, although the adults are not real residents of the region but are blown in by southerly winds and often appear in great numbers on floating logs and Sargassum. During such seasons the larve of several species are frequently found.
PLANKTON OF THE WOODS HOLE REGION ¥ 149 ARTHROSTRACA
Twenty-seven species of Amphipoda were taken in surface hauls during the past year. But one of these (Luthemisto bispinosa), belongs to the pelagic family Hyperiide. Young specimens were found on five occasions in January. The adults, which are often parasitic in Aurelia and Cyanea, are usually seen after southerly winds, when the medusz are blown into the harbor. All other amphipods belong to the benthos. During the breeding season, however, some species swim at the sur- face, both in daytime and at night, and are often taken in the tow in large numbers. Thus, the bottom forms may be divided into three groups, viz: (1) Those that swim during the breeding season, (2) those that are carried by the currents, and (3) those forms that for some reason other than the breeding season are attracted to the surface.
$ a & 3 <_ a 3 a a a. 7 2 $ eeauas Ss. Se 5 = sti . rad VoSe VeS. FH if ; Ret top : sestis, aortas Pee fee Pract it bs Seenss> Et 5 Pee E lr Ee uo Fic. 50.—Occurrence of amphipods in Fic. 51.—Occurrence of amphipods in surface collections of 1923. Free- surface collections from June to De- swimming period during breeding season. , Calliopius lxvius- cember, 1922. Free-swimming pe- culus; —-ese—, C. lzviusculus (young); --------, , Monoculodes riod during the breeding season. edwardsi; —-—-——, Batea secunda; —.» —, Gammarus annulatus . Batea secunda; ——ec.—, Monoculodes edwardsi; —« -—, Gam- marus annulatus; ------=-<, , Callio- pius leviusculus; —-—, Stenothoé cypris
In the first group there are two very conspicuous summer breeders. These can be found in Figure 52, designated by a long line. Certain forms, like Caprella, appear to have such a season, but this is caused by another condition. They live on hydroids, and as many of these are found floating after every strong wind the amphipods attached to them will float long after other forms have sunk again to the bottom. Of the summer forms Batea secunda and Stenothoé cypris are very noticeable. At times hundreds of specimens were taken in a single haul, many of the females carrying eggs or early embryos.
On November 6, 1922, Monoculodes edwardsi started breeding (fig. 50). Many were taken throughout December and on a few occasions in January, the last occurring on January 21. About the middle of December two other species (Cal- hopius leviusculus and Gammarus annulatus) suddenly appeared in abundance. The former often swarmed at the surface in large numbers, and individuals could
150 BULLETIN OF THE BUREAU OF FISHERIES
be seen darting about in the water around the Fisheries dock throughout the spring months. G. annulatus reached its maximum after Calliopius had started to decline, although the collections of April often contained many specimens of both species. Verrill records great swarms of Calliopius far out at sea during this season. On one occasion they were found to be very abundant in the Gulf Stream.
After heavy northeast or southeast storms great numbers of amphipods are often found in the tow. At such times, however, many species usually appear. This condition characterizes the group and contrasts it with the first group, where
June July Auge Septe Octe NOVe Dece Jane Feb. Mare Apre
g
Corophium cylindricun Caprella geometrica Amphithoe longimana Amphithoe rubricata Gammarus locusta Pontogenia inermis Unciole irrorata C.mucronatus
Stenethoé cypris
Batea secumda Elasmopus laevis Ptilocheirus pinquis ‘Caprella linearis
Paraphoxus spinosus Ampelisca compressa Ampelisca spinipes Byblis serrata : Synchelidium spe Hensgeaedl ue aduas Jassa marmorata Ampelisca macrocephala Monooulodes edwardsi EEEE
Calliopius laeviusculus PEE Gammarus annulatus Grubia compta Tryphosa pinguis Enthemisto bispinosa Euthemisto rubricornis
Fic. 52.—Occurrence of amphipods in surface collections from June, 1922, to May, 1923
one or two species make up tne entire amphipod representation. These conditions are particularly obvious in summer. On July 24, 1922, after a hard northeast storm, seven species of amphipods and two species of isopods were taken in one day’s collection. Such heavy offshore winds carry the surface waters out and cause an upwelling of bottom waters, carrying many of the bottom animals with them.
The third group appeared onlyinsummer. It was made up of the same species as the second group, but these occurrences were the result of different causes. Throughout the summer and particularly after the great diatom maximum the water was extremely phosphorescent. At such times the net appeared like a ball
PLANKTON OF THE WOODS HOLE REGION any
of fire as it swayed back and forth in the current. As the amphipods are positively phototropic, many, no doubt, are attracted by the light and are drawn into the net. Another factor as well may influence these collections which were always found more abundant at night. Experiments have shown that many amphipods rise to the surface at night and go down in the daylight. If this is true for many of the species, we should expect to find them more abundant in surface collections taken in the evening. How much effect this really has upon the plankton hauls I do not know, but I offer it as a possible explanation. I found no conditions in winter that could have resulted from such causes. Possibly the evening migrations do not take place during the cold season.
The following amphipods were taken in surface collections during 1922 and 1923:
Euthemisto bispinosa (Beeck). Tryphosa pinquis (Boeck). Paraphoxus spinosus, Holmes. Ampelisca spinipes, Boeck.
A. macrocephala, Lilljeborg.
A. compressa, Holmes.
Byblis serrata, Smith. Stenothoé cypris, Holmes. Monoculodes edwardsi, Holmes. Calliopius leviusculus (Kréyer). Pontogenia inermis (Kréyer). Batea secunda, Holmes. Gammarus locusta (Linnzus). G. annulatus, Smith.
Carinogammarus mucronatus (Say). Elasmopus levis (Smith). Ptilocheirus pinquis, Stimpson. Amphith6e rubricata (Montagu). A. longimana, Smith.
Jassa marmorata, Holmes. Grubia compta (Smith). Ericthonius rubricornis, Stimpson. Corophium cylindricum (Say). Unciola irrorata, Say. Synchelidium sp.
Caprella linearis, Linnzus.
C. geometrica, Say.
The Isopoda, with the exception of certain parasites, do not normally form a part of the plankton. ‘They are most abundant in surface collections in summer. This is because numbers of Idothea and allied genera are found on floating Sargassum and Fucus, which, when carried into the nets or forced by them, often deposit many of their passengers. In winter this condition does not exist and few species are taken. On one occasion in the spring of 1900 many adult Cirolana concharum appeared in the tow. No doubt these were floating on a piece of wood or a dead fish which may have been carried into the net.
The most interesting by far of the isopods taken during the summer were four minute species of the family Bopyride, which are parasitic on copepods. These occurred in large numbers at certain times. Two species were found on Acartia tonsa, one on Centropages typicus, and one on Labidocera xstiva. They were most abundant from July to October, one specimen appearing unattached on December 20. None of the winter copepods seemed to be infested. No species have been recorded from this coast, and as a paper on these forms, now in the course of publication in England, is not yet completed, it was decided to wait for it before attempting to identify these isopods.
The following species were taken in 1922-23:
Idothea baltica (Pallas).
I. phosphorea, Harger.
I. metallica, Bose.
Edotea triloba (Say).
Circolana concharum (Stimpson).
Tanais cavolinii, Milne Edwards. Chiridotea czca (Say). Leptochelia savignyi (Kréyer). Erichsonella filiformis (Say). Family Bopyride, four species.
152 BULLETIN OF THE BUREAU OF FISHERIES CUMACEA
The Cumacea occupy a place in the plankton similar to that of the amphipods. Large numbers are often taken at the surface during the breeding season, the females carrying eggs or larve. This particular group differs from the Arthrostraca in the length of the breeding season. Females of two species (Diastylis sculpta and Cyclaspis variens) were found carrying eggs at various times between July and January, although both species were most abundant in September and October. Females of Oxyurostylis smithi were also found with eggs on October 19. With the exception of the greater number taken during the breeding season, no particular time can be given for the occurrence of Cumacea in the plankton. They are found to be most abundant usually after astorm. D.quadrispinosa, which is reported to be abundant in this region, was not taken during the past year. The following forms were taken in 1922-23: Cyclaspis variens Calman, Leptocuma minor Calman, Oxyurostylis smithi Calman, Diastylis polita Smith, and D. sculpta Sars. :
SCHIZOPODA AND STOMATOPODA
The larval stages, and often the adults (Neomysis americana) of the Myside, at certain times of the year are very characteristic members of the Woods Hole plankton. The euphausiids, however, are “outside” forms and appear with other oceanic plankton only after southwest winds.
The Myside, living among the eelgrass in shallow water, are not true pelagic animals, but an occasional adult may be carried into the net at any time. Certain species apparently never swim freely during the breeding season. Heteromysis formosa and a species of the genus Erythrops (new to the region) are examples of this type. The former species has been recorded for every month of the year. Neomysis americana, on the contrary, has a definite pelagic period and swarms in surface waters from December to April, inclusive. The larve appeared during the last week of April in 1899 and 1900 and continued in small numbers until July, the young being liberated in the form of the adults. In 1923 the first adult appeared on May 17.
Adult euphausiids have been recorded at various times by Edwards, but none are permanent inhabitants of this region. Their occurrence will be better under- stood when the distribution of the various species off the coast is more fully worked out. Five species from the surface collections of 1898, 1899, 1922, and 1923 were identified. On December 12, 1898, after a hard southwest storm, two Thysanoéssa inermis and one T. longicaudata were taken. There may be something in the occurrence of the former species to give a clue to its distribution. Zimmer gives it a wide range. It is a cold-water form, extending from the Vineyard Sound to the Gulf of Maine in the North Atlantic, always being found within the 50-fathom line. Records made to date seem to indicate a northerly migration throughout the summer months. The specimens recorded from Woods Hole were taken on December 12. The Albatross found scattered individuals in the deeper parts of Vineyard Sound in late July and August. Bigelow found it most abundant north of Cape Ann in early July and on German Bank in August, with minor centers of abundance off Penobscot Bay and in the northeast corner of the Gulf during the
PLANKTON OF THE WOODS HOLE REGION U3}
same month. Just as a northerly movement takes place in summer a southerly one is noticeable in late fall and winter. More complete data will be necessary to verify these statements, but it is evident that this species is most likely to be taken at Woods Hole from late fall until early spring.
The young of Thysanoéssa longicaudata in the late “ cyrtopia”’ stage were com- paratively abundant from May 10 to June 24, 1899. From this data it would seem that the adults enter the shallow waters during the breeding season of May and June. Bigelow found them abundant only in the center of the Gulf of Maine during the fall. This species, according to Zimmer, is also a cold-water form. It oceurs occasionally in Vineyard Sound and quite frequently out beyond the Gulf Stream. As the young have never been taken since 1899, it is probable that the occurrence is not annual, but was due to unnatural conditions. Figure 53 gives the seasonal distribution for that year.
One specimen of Huphausia krohnit was taken on June 22, 1899, and another on November 9, 1922. Off the Atlantic coast they were taken in abundance in July and August. This is asouthern species and may be expected to enter Vineyard Sound in the summer months. A single specimen of EH. tenera Se appeared on October 30, 1923.
A battered specimen of the genus Thysano- poda was taken’on June 23, 1922. The condi- tion of the carapace made a determination of the species impossible. This was unfortunate be- cause, although three species are recorded from the western Atlantic, each has been taken on only one occasion. Thysanopoda xqualis (H. J. Hansen) was recorded nearest the Woods Hole region. N..
; A single specimen of Meganyctiphanes BO Se Hee ea ene eR cae ts Th jtonneece vegrea, taken April 25, 1906, was found in the tongicaudata in surface collections of 1898 and surface collections of Mr. Edwards. This is a 18%: (One adult on December 12, 1898) very common boreal Atlantic species, and it is surprising that more have not been taken in Great Harbor.
The following Schizopoda were taken in surface collections at Woods Hole: Thysanoéssa inermis (Kroyer), T. longicaudata Kroyer, Euphausia krohnit Brandt, Meganyctiphanes norvegica (Sars), Thysanopoda sp., and Euphausia tenera Hansen.
Seven species of stomatopod larve have been recorded from the Woods Hole region, although but two species of adults occur here. Most of the larve are East Indian forms carried north by the Gulf Stream. The various members of the order are known to have an extremely long pelagic life with many larval stages. This, no doubt, accounts for the tropical larve occasionally appearing in Great Harbor. The larval Squillide are of two forms—the Alima and the Erichthus form. All the species recorded locally, with the exception of Chloridella, belong to the latter form.
Adult Chloridella empusa (Say) are rather scarce in the immediate vicinity of Woods Hole, and for that reason the larve are not abundant in the plankton.
8242°—25}—_5
154 BULLETIN OF THE BUREAU OF FISHERIES
In 1899 a single specimen was taken on August 7. None were observed in 1922. Figure 54 shows that the normal season is in August. Edwards’s earliest record was in 1895, when several specimens were taken in August. His largest captures were made in 1905, when many appeared on October 21 and 22. Heretofore adults of Chloridella have been comparatively plentiful, but during the past few years they have gradually disappeared until they are now very rarely found. This explains the absence of larve in surface collections of recent years. The Erichthus larve of Lysiosquilla armata wate NS SPA. le, (Pa Smith are among the most common on the south-
A 2 2 o 8 § em coast of New England. They are usually found farther from the coast than Chloridella, probably because the adults are found in moder- ately deep water. Chloridella empusa is found on the muddy bottoms of bays and rivers. Vinal Edwards took 12 specimens of Lysiosquilla larve off Gay Head on September 12, 1902. Two speci- mens were taken in the same locality on August 15 and one on August 25, 1923, in Muskeget Channel.
Krichthus larve of two species of the genus Odontodactylus are recorded by R. P. Bigelow from this region. One was taken off Nantucket October 8, 1883, and the other at Woods Hole | | August 22, 1876. One of these appears to be the
r | ~| | | same as that incorrectly identified by S. I. Smith pce tl (1874) as the larva of Chloridella empusa. His specimens were taken in Vineyard Sound on
i | } August 11. In 1923 two specimens of Smith’s
i [ | | | |e species appeared in surface collections from Great Bee Pt Harbor on August 21 and three on August 22.
Bigelow considers these larvee to be West Indian forms carried north in the Gulf Stream. Considering conditions existing during the past summer, this appears to be questionable. In 1922, when tropical plankton was abundant in loeal waters, none were found. In 1923 no Gulf Stream plankton or fish were taken, either in Vineyard
_ Sound or Katama Bay. If hrs: stomatopod larvee
hea, Shear ani nt wag are from the south, they are apparently the only
years from 1893 to 1907 tropical forms that found their way into shallow water this year. This seems hardly possible.
On July 17, 1908, Edwards found over 2,000 Erichthus larve in the stomach of a small mackerel taken at Woods Hole. Upon examination the author found them to be the young of the species of Odontodactylus figured by Smith. The specimens were for the most part entire and were probably found not far from Great Harbor. As one fish was able to capture more than 2,000, they must have
EEE Ee ai RL A Oa i
1907 8
PLANKTON OF THE WOODS HOLE REGION 155
been extremely abundant. It is difficult to see how such large numbers could have remained together in the long journey from the West Indies (where they never form a very considerable part of the plankton) to our coast and then not be scattered by the strong winds, which were necessary to blow them in. It is more probable that they are the young of an unknown species of the genus Odontodactylus inhabit- ing the deeper waters off the New England coast, possibly beyond the range of
e e o e e e e er VE uEe Wis awe oie takes a az) =) << m (o) a A
Vohe
Ae
Se
VeS
Fic. 55.—Occurrence of larval Macrura in surface collections of 1922.
, Pagurus; ee eee, Crago Septemspinosus; ——« —=_ Palzmonetes vulgaris; —-coe—, Naushonia crangonoides; ——e—= Hippolyte zostericola; eeeeeee, Callianassa stimpsont
Lysiosquilla armata. Two unidentified species of Erichthus larve were taken by Verrill off Marthas Vineyard in August. One he suggests to be the larva of Pseudo- squilla ciliata Miers. Both species were no doubt southern forms.
r MACRURA
The Macrura form a very important part of the summer plankton. None of the members of this group are pelagic in adult life except some of the Caridea during the breeding season, but in all the larve are planktonic.
156 BULLETIN OF THE BUREAU OF FISHERIES
Usually the first larvee to appear in the spring are those of Crago septemspinosus, but the spring of 1922 was unusually cold and for that reason none occurred during April. On April 21 several adult females bearing eggs were taken at the surface. This is characteristic of the species. In Narragansett Bay, on May 7, 1922, great numbers of adult females bearing eggs, as well as a few young, were taken in surface collections on a bright sunny day. Bumpus found young forms appearing in March at Woods Hole, while Thompson observed them as late as September 19. The first young were seen on February 1 in 1900. After this none were taken until April 3. From that day on they were abundant, declining in July and August. On October 17 the last specimen was taken. In 1922 the first of this species was noted on May 15, and great numbers were taken throughout July and early August. During the latter month there was a rapid decline, and none were taken from August 27 until October 29. On this date four specimens appeared. Scattered individuals were found in almost every haul until December 13, when a single Crago, 10 mm. long, occurred. In 1923 the first larvee appeared on May 9 and the last, a specimen 6 mm. long, was taken on December 13. The maximum was reached early in July. All
oO > s a = 3
"=
Auge Sept. Oct.
Nove Dec.
> 4
AEre
f E
Crago septemspinosus Palaemonetes vulgaris Hippolyte zostericola Homarus americanus Upogebia affinis Callianassa stimpsoni
Naushonia crangonoide: Emerita talpoida Eupagurus spe
Fic. 56.—Occurrence of larval Macrura in surface collections of 1923
available records indicate that the normal season starts early in April, reaches its maximum in June or July, and usually ends in November.
Palemonetes vulgaris appears usually much later than Crago (figs. 55 and 56). Bumpus found females with early eggs on June 20. Throughout July and August the larve are very abundant, but all breeding ceases by September, according to Thompson. In 1899 larval Palemonetes appeared suddenly in great numbers in the tow of June 15. Scattered specimens had been taken for a few days previous. From June until September 18 young in all stages of development were very abund- ant. From this date they declined rapidly and had practically disappeared by September 28, few specimens occurring after this. A single postlarval individual was taken on October 31. The first larvee appeared on June 25, 1922: A gradual increase continued until the middle of July, when the maximum abundance was reached, followed by a gradual decline through August and September, late stages being taken throughout the month of October. The early larve are rarely found after the middle of September, however. In 1923 the first specimen was taken on July 16; the last on August 22.
PLANKTON OF THE WOODS HOLE REGION 157
Hippolyte zostericola was observed first in collections taken in the second week of July, 1922. Earlier records show that the young may occur at any time after July 1. The season is much more extended than that of either Crago or Palz- monetes, for very young specimens are often abundant throughout October. Scat- tering older larve were taken in November, the last appearing on November 18.
Figure 55 shows the distribution of this species, which reached its maximum in September, 1922. In 1923 four early larve were taken on July 26. One late larval stage (4 mm.) appeared on Decem- ber 13 and one on December 17.
Only three adults, including the type speci- men, of the rare species Naushonia crangonoides have been found. Two of these were taken on the island of Naushon and one on the smaller of the Weepecket Islands. The distribution is much broader than has been supposed, however, because numerous larve appeared in surface collections from Katama Bay on the seaward side of Marthas Vineyard. Although the larval forms are never exceedingly abundant in the surface collections of Great Harbor, they occurred regularly in small
numbers in almost every tow taken during the
breeding season. ‘The first specimens appeared on July 8, and the last were taken on September 19, 1922. The greatest numbers were found on July 24, although the average abundance was higher around August 1 (fig. 55). Figure 56 shows the distribution in 1923.
In spite of the fact that Homarus americanus breeds in great abundance in all the deeper waters of the region, larval forms are rarely taken in the plankton. During the summer of 1922 none were found in Great Harbor, although a single speci- men appeared in surface collections from Vineyard Sound on July 24. As this larva was in rather a late stage, no doubt it had been clinging to the floating weeds, which were abundant in the net. The few captures of past years (fig. 57) were, with one exception, made during June and July. This appears to be the normal maximum season for
1894
1895
1896 1897 1898
1899
1900 1901 1902
1903
1904
| - EERE ESS SERS ESGRHUoASBe oes
1905
Fiq. 57.—Occurrence of larval forms of Homarus americanus in surface collections of successive years, 1893 to 1907
the species in this region. <A
specimen taken on September 12, 1902, probably resulted from heavy winds, which were prevalent that year. On June 26, 1923, one was found after a hard southwest wind. A natural conclusion in the matter is that the larval lobsters under normal conditions do not form a part of the surface plankton but remain
158 BULLETIN OF THE BUREAU OF FISHERIES
near the bottom. Storms and strong currents may carry them to the upper strata, but the fact that they usually appear on only one or two days a year at the most indicates that their presence there is not normal.
Certain other Macrura were found occasionally in summer surface collections. Emerita talpoida was first taken on July 22, 1922, and continued to appear in small numbers until September 1, when four appeared, the greatest number found on any one day. Invariably these larve when placed in a watch glass would cast their shells and acquire the adult form within 24 hours. It was interesting to observe the little creatures as they labored continuously to dig into the glass bottom of the dish. After a time they would drop exhausted but could be made to resume their activity by disturbing the surface of the water.
Upogebia affinis was taken twice in August, 1922. In English waters larve of this genus are extremely numerous, but such is not the case at Woods Hole. The adults are not uncommon in this region, and in some years the larval forms may occur in greater numbers. In 1923 they were fairly abundant. The first specimen appeared on July 20; the last on October 25. The largest numbers were taken in early August. :
The transparent larve of Callianassa stimpsoni Smith are frequently found in surface collections. Like Upogebia they are never found in abundance, although small numbers can usually be taken throughout July and August. In 1922 the first specimen appeared on July 16. After that scattered individuals were taken until the middle of August. The first larvee were observed on July 26, 1923. From August 12 to 15 they were unusually numerous but soon declined again. The last specimen was taken on October 4.
The young of the many species of Paguride found in this region are always present in large numbers throughout the summer months. They are very similar to the larve of various Caridea but may be distinguished by the cephalothorax, which is drawn out in two points on the posterio-ventral margin. M. T. Thompson (1903) made a careful study of this group and described the development of the interesting larve. The early stages of the various species are almost identical, and in the case of the two most abundant forms—Pagurus longicarpus Say and P. annulipes (Stimpson)—it is impossible to distinguish them apart. Thompson found that P. longicarpus has the longest breeding season, extending from May until mid-September. Other species with eggs were found at different times during the summer. On April 8 of the present year (1923) two second-stage larve appeared. This is unusually early and far antedates any records for the region. No other specimens occurred during the month. On May 8, 1922, a single larva was taken. After this scattering forms appeared until June 1, when they became very abundant. Together with all other macroplanktonic animals they decreased during the summer diatom maximum (see figs. 15 and 55). In September the swarms appeared for a short time but soon declined, the last one disappearing on November 9. The first Glaucothoé was seen on July 13. After this scattering forms appeared throughout the summer, although they never were as abundant as the zoée. Their distribution in 1923 is shown on Figure 53.
PLANKTON OF THE WOODS HOLE REGION 159
The following Macrura were taken in the surface collections for 1922-23:
Crago septemspinosus (Say). Homarus americanus, Milne-Edwards. Palzmonetes vulgaris (Say). Emerita talpoida (Say).
Hippolyte zostericola (Smith). Upogebia affinis (Say).
Naushonia crangonoides, Kinglsey. Pagurus sp.
Callianassa stimpsoni, Smith. BRACHYURA
Larval crabs are always present in the summer plankton in large numbers and form very important food for many fish. As few of the zoée had been worked out, they were a source of much trouble until the many forms were finally identified. The development of the various species will be taken up in a later paper.
All the crabs of this region have free-swimming larval stages, although certain species are seldom taken in surface collections. The megalops are found in smaller numbers than the zoée. Investigation showed that in this stage the young crab
is usually found among the eelgrass and een nara parece rs . a = a n lo} Fucus. Itcanswimaswellasthezoéa 4... seroratus but remains closer to the bottom. camer borealis After hard winds large numbers were ™221pes ccellatus Tallinectes sapidus 3 2 4 2 2: Carcinides métnas a < C -) = Libinia spe Polyonyz macrocheles (Gibbes) Heteroorypta gramilata Pinngtheres ostreun (Say) ari Pelia mtica Pinnixa scayana Stinpson ft Heopanope texana sayi sone som ee Poiyeays masochle Ovalipes ocellatus (Herbst) = Pimiza chébtopterana Carcinides maénas (Linnaeus) SESS SHH! Pinniza sayana Planes minutus (Linnaeus) Seeeeteees Pimnotheres maculatus Uca pugnax (Smith) a5 Oca spo Dea pugilator (Bosc) SS @yas coarctatus Leach Fic. 58.—Brachyura occurring rarely in surface Fig. 59.—Occurrence of larval forms of Brachyura in surface collections of 1922. Eggs of Planes minutes collections of 1923. No observations were made from (Linnaeus) from an adult taken in the tow August 22 to September 18. Megalops of Hyas coarctatus were hatched in the laboratory Leach were obtained from Muskeget Channel on August 25
often taken in the nets. The megalops transforms into the “young crab” stage in a single molt. The ‘‘young crabs” are very rarely found swimming, except in the species Pinniza chextopterana and P. sayana. These have no megalops stage but change directly from the zoéa into a young crab, which may be compared with the megalops of other species, for they swim about in much the same manner and are often very abundant in the plankton.
The zoéz of Uca were rarely taken at the surface. Megalops appeared on only two occasions, after storms. This seems very strange, because Uca is probably the most abundant crab found in this region. Hymen reports the zoé as being very abundant in the surface collections at Beaufort, N. C., at all times during the summer. I believe that the fiddler crabs of this region have a very short larval period in which the zoée as well as the megalops remain at or near the bottom. Carcimides mznas larve may have similar habits, in this locality at least, for zoéz were taken on only three days in October, 1922, and on one occasion in 1923 (figs. 58 and 59).
160 BULLETIN OF THE BUREAU OF FISHERIES
The females of Pinnotheres maculatus are commensal in Mytilus. The males swim freely about and were often taken during the breeding season but never after. Young males in all stages of development were frequently seen swimming. The young of this species formed one of the most abundant members of the plankton from July 6 to November 1, 1922 (see fig. 60). P. ostrewm has similar habits but is not as common as P. maculatus.
The unusual larve of Polyonyx macrocheles occurred scatteringly from July 26 to October 29, 1922. These peculiar zoéz differ from all other forms im the great length of the rostrum. On July 16, 1892, a sample of towings from Taunton River, Mass., was found to contain swarms of this species. Hardly anything else appeared. Faxon found the zoéx swarming at the mouth of Massachusetts Bay in August, 1878.
The adults are exceedingly rare. Agassiz found Ss Sylore one adult at Newport under a stone, and Doctor Tennent collected one on Devil’s Foot Island in a Chetopterus tube. G. Gray reports that several were found in Chetopterus tubes at Woods Hole in 1922. In 1923 the zoéx were taken from July 20 until August 22 (see fig. 59).
The various species of crabs have definite breeding seasons, which often overlap each other. Cancer irroratus appears first, followed closely by Neopanope texant say? (fig. 62). In 1922 the first zoéa, of Cancer was observed on May 10. None appeared during April of the present year (1923), although many females bearing late eggs were taken on April 10 in lobster pots. Figures 60, 61, and 62 show the breeding seasons of the most abundant species taken in 1922, while the scarcer
Fic. 60.—Occurrence of common grapsoid larve forms appear on Figure 58. et ca i min ste amen ec In 1922 another zoéa, almost identical to that of C. irroratus, was first found on Septem- ber 8 and continued until October 31. This was undoubtedly C. borealis, although the megalops were smaller than those of C. aroratus, a smaller speciés. Adult specimens of C-. borealis taken at No Man’s Land on August 31, 1923, con- tained ripe eggs. The first larve appeared in Great Harbor on October 4; the last on October 28 (fig. 59). The following brachyuran larve were taken at Woods Hole in 1922 and 1923.
E
Jule
VA.
Cancer irroratus, Say. Pelia mutica (Gibbes).
C. borealis, Stimpson. Neopanope texana sayi (Smith). Ovalipes ocellatus (Herbst). Polyonyx macrocheles (Gibbes). Callinectes sapidus, Rathbun. Pinnotheres ostreum, Say. Carcinides menas (Linnzus). Pinnixa sayana, Stimpson. Libinia emarginata, Leach. P. chetopterana, Stimpson.
L. dubia, Milne-Edwards. Pinnotheres maculatus, Say. Eurypanopeus depressus (Smith). Uca pugnax (Smith).
Planes minutus (Linnzus). U. pugilator (Bosc).
Heterocrypta granulata (Gibbes).
PLANKTON OF THE WOODS HOLE REGION 161
PYCNOGONIDA AND XIPHOSURA
Pyenogonids are not pelagic animals, but live on hydroids and among the alge, occurring in surface collections only when the objects to which they are attached float into the nets. For this reason they are usually taken during the summer months. Only one specimen appeared in collections made after October 1. That was on March 29 of the present spring (1923), when a single Pallene brevirostris Johnston was observed. This species is very abundant in the im- mediate region of Woods Hole and occurred almost daily during July and August. Females carrying eggs were found on August 21. On October 1, 1922, a male of Tanystylum orbiculare Wilson appeared. This was the only member of the species taken during the past year. A specimen of an unidentified genus new to the
ry e g §
Jule Octe
g Vode
e e o s e Bk BR ee 2.8 8 Vode Ae A Se s vV.S oh V.S. Ne Ne Fic. 61.—Occurrence of common larve of the tribe Fig. 62.—Occurrence of common laryz of the tribe Oxyrhyncha in surface collections of 1922. —-.—=, Cyclometopa in surface collections of 1922. ——, Libinia emarginata and ZL. dubia, species not dis- Cancer irroratus; —~—-, Neopanope texana sayi; tinguished; ———, Pelia mutica —.—, Callinectes sapidus
region appeared in August, 1922, and on July 23, 1923, a single Anoplodactylus lentus Wilson.
Limulus polyphemus deposits eggs on sandy shores below the low-tide line. There are not many such spots about the bay in the vicinity of the “Hole,” and for that reason few young are carried into Great Harbor. In certain localities, such as the sand flats at Duxbury, Mass., and Cold Spring Harbor, L. I., great numbers of the young forms in the so-called “trilobite” stage swim about at the surface. However, heavy shells prevent these animals from being very active members of the plankton, and consequently they are usually taken only in calm, shallow water. When disturbed, they become motionless and sink to the bottom,
162 BULLETIN OF THE BUREAU OF FISHERIES
where it is almost impossible to distinguish them from the sand. None were taken in the surface collections of 1922; in fact, they are recorded only twice by Edwards in 15 years. In 1899 a few were taken on July 11 and again on July 12. In 1904 several appeared on August 9. On August 14, 1923, a single specimen was taken. As these are the only times that they have been seen here, it is probable that they are usually absent in surface collections except after northeast storms, when specimens may be transported from Buzzards Bay. The specimen taken in 1923 appeared after a hard northeast wind.
CHORDATA
After a storm on J uly 16, 1922, a postlarval Balanoglossus aurantiacus (Girard) was taken. On September 9 and 11 of the same year a single acidian larva, 1 mm. in length, appeared. They were the only representatives of this phylum seen during the year, excepting the Appendicularia, which at times appeared in great abundance. There were two species of the latter, one occurring during the summer and fall and
aS ca i i b 5 4 0 a + NS 8 Oy ‘ s Z g iso 8 3 tsi ch oo °o o Ae Se VeoSe Ne — ms Fic. 63.—Occurrence of Appendicularia in surface collections from June, 1922, to December, 1923. —.—,
distribution in 1922; , distribution in 1923
the other in winter, the seasons almost overlapping. Both belong to the genus Oikopleura. On several days in the latter part of July, 1922, single specimens were noted. In August the number increased until they became very abundant. Throughout September, October, and November they grew scarcer, rapidly disap- pearing in December (see fig. 63).
During October and November the ‘‘ Haus,” characteristic of Oikopleura, was taken. At times the tow contained hundreds of these pink “‘ Hiauser,’’ each filled with copepods. One, on October 24, 5 mm. in length, was found to contain exactly 100 copepods; 97 of these were Acartia tonsa, 2 were Centropages hematus, and 1 was Labidocera zstiva. The contents of all had been removed, leaving only the outer transparent shell. Lohmann found that this ‘“‘Haus” was often so delicate that the most minute organisms, which normally pass through the finest nets, were captured. In some forms the mesh gradually becomes finer toward one end. Undoubtedly those taken in my collections were not complete, for the wall mesh was compara-
PLANKTON OF THE WOODS HOLE REGION 163
tively coarse and both ends were broken. Lohmann gives 17 mm. as the average length of the “‘Haus” of Ovkopleura albans Loeck. It is difficult to understand how copepods could be induced to enter such a small opening. Possibly, as in O. albans, the complete “‘Haus” is made up of two compartments—one of coarse and the other of fine mesh. The currents of water produced by the movement of the animal’s tail cause microorganisms to collect in the fine mesh. This tich food center may attract
. the copepods, which § r 5 Fi 3 a & 3 é 3 é crowd into the outer ol anes < 5 5&5 2 8 6 B& @B
opening. The re- i993 | moval of the soft partsof thecopepods 1894 was no doubt the work of protozoa. I have observed them completely clean out a decapod megalops jg97 in two days. The difficult thing to im- 1898 agine, however, is how so many cope- 1899 pods could get into such a small amount 1900 fie of space. Lohmann found that a new “Haus” is secreted every six hours. This fact accounts 1993 for the great number taken. 1904 Only one species (Oikopleura _longi- 1905 cauda (Vogt), listed by Pratt as Appendi- 1906
pestis ee al noe [ela a Fe NG OPN el )
corded from the Fia. 64.—Occurrence of Appendicularia during successive years. No record was made region. Neither after 1904
member of the genus taken this year contains the ‘‘Kapuze” characteristic of Pratt’s species. The winter form agrees very closely with, and probably is, O. van- hoffent Lohmann, while the summer form has many of the characteristics of O. dioica Fol. At the time lack of sufficient literature prevented a final determination, and the preserved forms are not in a sufficiently good state of preservation to be iden-
tified positively.
164 BULLETIN OF THE BUREAU OF FISHERIES
In records of past years (fig. 64) the overlapping of fall and winter species shows very clearly. The winter type often appears as late as April, but disappears as soon as the temperature of the water rises. In 1894 and 1896 appendicularians appeared in large numbersin June. Thisis very unusual and may have been caused by an influx of Gulf Stream water. ;
Swarms of Salpa democratica-mucronata Forskil blew ashore at Menemsha Bight in Vineyard Sound on January 11, 1901. None are recorded from surface collections in Great Harbor, but they may be expected at any time during that month after hard southwest winds.
FISH
Ehrenbaum states (in his excellent volume on the ‘“‘Eier und Larven von Fischen”’) that the young stages of all fish, even those belonging to the bottom dwellers, are usually true planktonic forms during and often after their larval period.
From the standpoint of the planktonologist, fish of the Atlantic coast may be grouped roughly under two headings—those that have pelagic larve and those that have not. The latter group, of which Opsanus tau (Linneus) is a striking example, contains very few members and does not enter into the plankton problem.
The first group is of great importance. A division may again be made here to separate those fish having pelagic eggs from those having demersal ones. No relationship exists between the condition of egg laying and the habits of the fish ~ or between the various species of fish having these habits. Bottom-living forms, such as Gadus callarias and Tautoga onitis, have pelagic eggs while Clupea harengus, a surface dweller, has demersal ones. As a rule, most of the larger fish of this region belong to the group having buoyant eggs, the demersal group being composed of such small forms as Ammodytes, Pholis, Apeltes, Cyprinodon, Lucania, Fundulus, and Menidia. As many investigators have shown, special adaptations enable both types of eggs to have the best possible chance to survive.
In order to overcome the many difficulties besetting pelagic life, fish with buoyant eggs extrude enormous numbers of ova. These are small, translucent, and practically invisible against the bright sky, which forms the background. A very few species have pelagic eggs, which float together in a gelatinous membrane, often many feet in length. Such a condition is characteristic of Lophius piscatorius. The incubation period of pelagic eggs is comparatively short, largely governed by the temperature of the water. The young fish hatch in a very immature con- dition, and these, too, are translucent except for the eyes and scattering yellow and black chromatophores. For several days they are quite helpless, and undoubtedly during this period enormous numbers are destroyed. Later they become very lively, darting about and feeding ravenously on copepods. It is interesting to note that the eggs become translucent just before spawning. During development they are rather opaque, and the yolk is deeply colored.
Demersal eggs are laid in bunches on the sea bottom or attached to plants by fine threads. Here, again, there are special adaptations for fertilization and pro- tection. Contrasted with the former group, where the females outnumber the males, McIntosh found that fish of this group are mostly males. This condition
PLANKTON OF THE WOODS HOLE REGION 165
he believed to be necessary, for the milt rises and is likely to be lost before the eggs can be fertilized. The eggs are usually quite opaque and heavily laden with yolk. By being grouped in large bunches they are not so easily preyed upon by the bottom- feeding animals, although no doubt many are lost in this way. The eggs are com- paratively fewer in number and have a longer incubation period.
Young fish of this group are often just as numerous in surface collections as those hatching from pelagic eggs, for they usually hatch in a much more advanced stage, thus greatly reducing the mortality.
Gadus callarias and Pholis gunnellus, characteristic members of the spring plank- ton, are excellent representatives of these two groups. The former emerge from the
e eo
E z Pautogolabrus adspersus pF Tautoga onitis
Prionotus carolinus Stenotomus chrysops
Jule Sepe Octe NOVe Dece
Brevoortia tyrannus Syngnathus fusous Spheroides maculatus Lophopsetta maculata Merluccius bilinearis Poronotus triacanthus | ‘Menidia menidia notata ‘ Urophysis spe SBue wea : -Leptocephalus Elops ? Rhinonems cimbrius
Heplatessoides
Myoxocephalus aeneus 7? Microgadus tomcod
Fic. 65.—Occurrence of fishes in surface collections from June to Decemper, 1922
egg in a helpless condition and for some time are tossed about at the mercy of the waves as delicate little transparent larve. (The black chromatophores arrange themselves in vertical bands and may camouflage the young fish in much the same way that similar designs served to protect our ships during the late war.) The other species (Pholis gunnellus) is never found in an entirely helpless condition. The young, which are much farther advanced than those of the cod when they appear in surface collections, are always very lively and swim rapidly toward the light when placed in a glass tray. (The larval cod were always dead when removed from the nets.) Copepods were always found in the intestines of even the smallest specimens. This is further evidence of the activity of this species in its very early pelagic existence. The eggs are laid on the bottom in a compact mass and are guarded by the adult fish until hatched.
166 BULLETIN OF THE BUREAU OF FISHERIES
In summer the most abundant larve are Tautogolabrus adspersus and Tautoga onitis. Both have pelagic eggs and appear in June, remaining until August. During this time the eggs are often very numerous, appearing like masses of minute bubbles on the surface in the examining dish.,
Mr. Edwards took 34 species of larval fish in the 15 years recorded in Figures 67 to 81. During the past year 20 species were identified. Of the summer forms all but one (leptocephalus of Elops?) are common to this region. The leptocephalus is not that of an eel but of a true fish, as the tail is well developed and forked. I have placed it in the genus Elops because that is the only common southern fish recorded from this region that has a leptocephalus stage.
Of the winter larve all were of species breeding in the region except Gadus cal- larias. This is a northern species common off southern New England, the adults of which never enter the immediate region. As the nearest important spawning
“Tautogolatrus adspersus Tautoga onitis Prionotus carolims Stenotoms ‘chrysops Brevoortia tyrannus Syngnathus fusous Spheroides maculatus Lophopsetta maculata Meplucoius bilinearis Poronotus triacanthus Menidia menidia notate Fholis gunnellus
Gadus callarias . Byoxocephalus aeneus ? Microgadts tomcod Anmodytes americanus Poamericanus
Fic. 66.—Occurrence of fishes in surface collections of 1923
grounds are on Nantucket Shoals, the appearance of early larve at Woods Hole probably results from southerly or easterly currents. Postlarval forms, usually about 20 mm. in length, find their way into this region and are often taken in May (fig. 67) in large numbers, depending upon the season. Still later postlarval stages (40 to. 50 mm.) are always present in the shallow coastal waters in May and June. Many were taken within the boat basin at the Fisheries dock on May 24, 1923, with a fine net. During this period they are destroyed in large numbers by Loligo pealit. A school of over 200 of these squid, all about 5 inches in length, seined in Great Harbor, were found to be feeding entirely upon young cod. Several specimens were observed with a young fish protruding from the beak and one or more others held securely in the tentacles.
In 1923 early larval stages of cod appeared in small numbers in the tows of January, February, and early March. Surface collections made in Vineyard Sound at various times during this period showed that they were present there also, but likewise in small numbers. Just