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
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By CHARLES J. FISH, Ph. D.,
General Assistant, U. S. F. S. Albatross

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Contribution from the U. S. Fisheries Biological Station, Woods Hole, Mass.
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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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} | +t tot to ae
eta eosaaeed iti eed
wd Posed Eee ee fever} ert
1.0260 |}.
i poset i ate} — Poteet eee 1 1.0260
+ cy j— mee t+ aoe t—-| eee
= Lert ttt tied ssl +
A il tere — ward boa tts +
1.0255 Seas
Cars es ae ie 7 BSSe4 Fa BS BS tt 1.0255
i Le ty atte is Bae Dawes eee Eee +
d rt bette tan tote Wt wes peaes eeu bi Peed based
IAIN ES RAs bee} bee beret er ee + + eaaws bese’ t+
pe St aa teases ioe jean
fees -
1,0245 aes Toth 1.0245
et Lt t+ {. 1bessd essa
Peel ieee Pewee Deseu Pecsd beeea |
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peep a otto te +
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bend beeed beees ts + poet 1. 4 te bossa
— poeta fot e+ tH —- a
eat DSA EN rel eens ed ie ak bie [|
| SS Dated Doe Pawerd Baaiea Hees ttt ttet beeeet
1,0235 oat ee ae 1,0235
ised 2 esha Teeateos Leased el iSeetaaes ?
oe ent cc tt — oat ee + +++ ze =
ot aioe baert ery} Le et+t 1+
1,0230 ~— [ea | 1.0230
fee beet te Leet Leeeet
pened pease on {
1,0225 - 1,0225
L- posed beerd mmr ++ and baees +
[Sa] eal nena |
t+ Lt toe
1,0220 —— 1,0220
ie |} peeed
— ema iseed es
| ot

8242°—

(Face p, 100.) No. 1

Fic, 2—Diagram showing density of water at Woods Hole, Mass., for each day of the year 1922, Observations made at 12 o'clock noon, Density at the temperature in situ

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E22] 0083) Pag PSE i

No. 3

DECEMBER.
(Face p. 100.)

af

NOVEMBER.

15

OCTOBER
OA |B A Vee a EES

DESI. bee

SEPTEMBER.
15

os

a
Uh

CTE ate TT
AH ENEIE Ieee Hae idl i

Density at the temperature in situ

AUGUST.
15

Observations made at 12 o'clock noon.

JULY.

23,

“|
|
el

., for each day of the year 19:

JUNE.

LH ARHTHanaiiiiil

CT
z HET . He |

25

Fic. 3.—Diagram showing density of the water at Woods Hole, Mass.

APRIL
15

Hee

Ue

MARCH.

FEBRUARY.

JANUARY

ae a eae

UNKDEREOULTEROATONTEER

ry

1.0271
1.0265

1.0261
1.0255

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30°

25°

20°

10°

10

JANUARY.

as. (92)_- 35) is

FEBRUARY.

fo 1s

19°

5

MARCH

114

Fic 4.—Diagram showing tempersture of air and water at Woods Hole, Ma

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
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eel na eaea hs Baga l Seinibesd alice =i asa seed ea
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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,

Tho less regular line represents air temperature and the more regular line water temperature.

Readings are in Fahrenheit, and observations were made at 8 a. m,

NOVEMBER.

fo = 0

Eg

yor

8242°—257.

DECEMBER.

Sm i ws 4

1s° 19

(Face p. 100.) No. 3

»

1s”

70°

65°

55

50°

2°

a Poet
poe dt

f
id
}

‘ ‘

Pacem! on

h Shinn

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75°

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70

65

55

JANUARY.

SEPTEMBER.

NOVEMBER. DECEMBER.
3 = s 10 15 ead psiss Jo Lt ed to iS 0 to s @
ail ++ _ Lt on Ea te at
PSEA bene ee
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| x pes Le L ie bagi heaes
2 12°13)
ane°being fin 4Ahi2® as%s°17VAB ? 17°} hs? 6° 37°
Fia. 5.—Diagram showing temperature of alr and water at Woods Hole, Mass., for each day of the year 1923. The less regular line represents air temperature and the more regular line water temperature. Readings are in Fahrenheit and observations were made at § a. m. —25t (Face p. 100.) No, 4

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SEPTEMBER. OCTOBER NOVEMBER. DECEMBER.

AUGUST.

JULY.

ee es

JUNE.

MAY.

APRIL.

MARCH.

FEBRUARY.

JANUARY

Te tallies
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HE IRESUSEC CHIU NERELLAZEG TERA ESERLSTARIADEEIOSEEIOELS Ht

5

(Pace p. 100.) No.

ihe

8242°—25

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

i
23
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Hitt

PetHETH

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SU SaGSTUAEREEIEENG))

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t

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

a

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.

=

wem BEDLORD

Aha,
oh,
COVIW 1D2HNON

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 what effect the artificial conditions created by
the hatchery had is not known, but probably the 351,000,000 larvee liberated during

PLANKTON OF THE WOODS HOLE REGION

Anguilla rostrata
brevoortia tyrannus

Anchovia brownii

Apeltes quadracus

Microgadus tomcod

Sanne Seeea 4

Gadus*callarias

[Cael Pa AG
se a a A

Fic. 67,—Maximum seasonal distribution of fishes not common in surface collections, based on records of the
years 1893 to 1907

Brosmius brosme

Hmm
HRESCOEoR
mem | | TT Tt |
oo

oma! | | | tT

| louie | [|
ete et fa

Fic. 68.—Occurrence of Pholis gun-
nellus during successive years, 1893
to 1907

Fic. 69.—Occurrence of Yautogola-
brus adspersus during successive
years, 1893 to 1907

167

168 BULLETIN OF THE BUREAU OF FISHERIES

the spring less than a mile from the collecting station increased the surface catch
somewhat. Itis barely possible that all early specimens taken may have originated
from that source. Their absence in records of past years, combined with their
total absence during the early spring of 1924 (when no larval cod were liberated at
Woods Hole), seems to substantiate this possibility. It must be remembered,
however, that the unusually warm weather existing during the early part of the
past winter apparently prevented the adult fish from spawning on their usual
grounds, and for that reason no eggs were available at the hatchery. The cod
may have sought deep areas so far from the coast that the early forms, which were
never abundant in this region anyway, could not be transported into these waters.
Fishermen reported that they had never known the cod catch to be so small on the
southern New England grounds as during the early winter of 1923. They were
totally unable to supply the Woods Hole station with any spawning fish. The
usual fall school which annually enters Narragansett Bay also failed to appear.
It will be interesting to learn whether the postlarve appear as usual in May, 1924.

In Figure 67 and Table 5 several fish taken rarely in past years are listed.
Most of these are southern forms and occur only in the summer when the Gulf
Stream inhabitants are blown in. Lactophrys trigonus, Cryptacanthodes maculatus
Anarhichas lupus, and Seriola zonata are representatives of this fauna.

TaBLE 5.—Fishes very rarely taken in surface collections

Species Date Abundance

mentoce gees conger-_-
Osmerus mordax--____
Poronotus triacanthus_

Lactophrys iieonus Sy eas

Cyclopterus lumpus---______ ee mene 5
Cryptacanthodes Seatac _.| Apr. 22; 23, 25, and 26, 1907 wee he Mea 0 Do.
Anarhichas lupus___--______ _.-| May 1 and 2; 1899, and June 3 and 5, 189! Few.
Rhinonemus cimbrius-______________ Apr. 1, 27, 28, and 30, 1900; June 2, By 4, .. and 6, 1906; and July 17, 1906_| Very many.
Lophius piscatorius-_-_--__-.-_--.--- Tune 10, 1899 Few.
Pseudopleuronectes americanus---__- Apr. 13, 1897

Limanda ferruginea? __-| Jan. 4, 1908_____

Seriola zonata>_. 3222: Aug. 30, 1907

DaEnIA DHS pseudoharengus_-_-_______ Noiliyal3; “1896-. — - 2-20. -- 5-2. Se ee eee

The remaining figures show clearly that the fish have a definite breeding
season within certain limits, usually determined by temperature. Temperature chart
for the spring of 1923 (fig. 5, opp. p. 100) indicates how unusually cold the water
was. The result was that many of the fish, as well as other larval forms, did not
appear. The approximate temperature throughout the breeding season of each
common species may be found by comparing the individual figures with Figures
4,5, and 6. This particular temperature, however, must not be regarded as the
complete governing factor. At some time earlier in the year a rise or fall in tempera-
ture caused the ovaries and testes to ripen. When the sex products have com-
pletely matured they will be extruded within certain limits irrespective of tempera-
ture. After this extrusion the immediate temperature then plays its part. Cod
eggs have been made to hatch in 9 days or 64 days by varying the temperature of
the water.

PLANKTON OF THE WOODS HOLE REGION 169

Fic 72.—Occurrence of Ammodytes americanus during
successive years, 1893 to 1907

Fic. 70.—Occurrence of Tau-
toga onitis during succes-
Sive years, 1893 to 1907

Fic. 71.—Occurrence of Myorocephalus zxneus during
successive years, 1893 to 1907

Fic. 73.—Occurrence of Pollachius
virens during successive years, 1893
to 1907

8242°—25}——_6

170 BULLETIN OF THE BUREAU OF FISHERIES

As the salinity of Woods Hole is not noticeably different from the outer waters,
it probably plays no part in the distribution of the larval fish of this region. The
governing factors are, then, temperature and food, if we omit the effect of winds
and currents, which at times may influence the distribution greatly.

The abundance of food has a powerful effect on the lives of the young fish.
Given favorable temperatures, the larve will develop rapidly and in great numbers
if food is plentiful. If food is scanty, few larval fish will be found. During the
winter and spring months copepods make up practically the entire food of the
young forms. The most abundant copepods during colder weather are usually
Temora longicorns and Pseudocalanus elongatus. No doubt both of these species
contribute equally to the food supply. As the spring of 1923 was exceptionally
cold, Temora did not appear. Scattering forms were taken during the winter, but
never more than three or four specimens on any one day. Out of 200 examinations
of stomach contents of larval fish this spring not a single Temora was found.
Pseudocalanus elongatus and Centropages hematus were very plentiful, particularly
the former, and these constituted their food, the bright red color of the Pseudo-
calanus showing clearly through the thin walls of all the young fish collected.

The summer fishes have a much greater variety of food and for the most part
do not limit their menu to Copepoda, although Acartia tonsa and Centropages typicus
are eaten in great numbers. A young puffer (Spheroides maculatus), 3.5 mm. in
length, examined on June 28, 1922, was found to contain 12 Littorina litorea, 9
Venus mercenaria, and 2 Deuntia tonsa. Often a young fish was taken with a large
copepod or phyllopod protruding from its mouth.

The relationship of the larval fish to its food supply is therefore very close,
and one must determine it accurately in order to understand the distribution of
a species. Such a study was attempted at the Plymouth laboratory by Doctor
Lebour, who obtained some interesting results. More extended observations will
be necessary before the relationship of the many factors can be clearly understood.

The following forms were taken in surface collections of 1922-23:

Tautogolabrus adspersusi@Walbaum)—_--=----2 1 £2) Pach ee ae ee eee Cunner.
Tautoga, onitis (limn seus): Vee oe a Ee eit ee Tautog.
Prionotusiesrolinus:(@iimmcens) ene ee 2 ee ee Sea Robin.
Stenotomusichrysopsy@Linn-eus) 22 - = 2222 2 Pa ee eee ee Scup.
Brevoortia: tyrannus! (atrobe) seta. - 2 Bee ie eee Menhaden.
Syngnathusifuscus;storerss- eee ae be ee ee eee Pipefish.
Spheroides maculatus (Bloch and Schneider) ___________________________=____ Puffer.
Hippoglossoides platessoides (Fabricius) -_--________-__---- ee Sand dab.
Merluccius bilinearis.(Mitehill) 24 "222 3 eee eee Whiting.
Poronotus tricamthus- (Peck) mee ee ae errr ictal ee ell eee rested eae Butterfish.
Menidia;menidiatno tata (Vintec kant) ses eee eee ae ee ee eee Silversides.
Pholis: gunnellus; Giimnssus)). a ee ee Sea op makes, SRL ree pede Rock eel.
Urophycis.-) #240 5 ks eek 2 2 ee Hake.
Gadus callarias Minnseus! ot) oe 0) De ee ee ee es. ye ee eee Cod
Leptocephalus, Elops?

Microgadusitomcodi@Walbaura) rs So ee ee ee Oa ean = eae tes Tomcod.
IMiyoxocepballus me neush (vite brill) eye tee eee a eee ee ee Eye fee eee Sculpin.
ophopsebbasmna cls tars Vinita) ys eee rene ee ae yn en ene ne Sy SE Window-pane.
FRET OMe 3a SKE La fo EL cea (ELL 1 22 1) ee Rockling.

AmModytes;AMericanus; De Uaiyates = ee eee A nee ee Sand launce.

PLANKTON OF THE WOODS HOLE REGION Wal

Fic. 74.—Occurrence of Urophycis sp. during successive years,
1893 to 1907

Fie. 75.—Occurrence of Steno-
tomus chrysops during suc-
cessive years, 1893 to 1907

Fic. 77.—Occurrence of Syngnathus

Fic, 76.—Occurrence of Clupea harengus during successive years, 1893 to fuscus during successive years, 1893
1907 to 1907

LA2 BULLETIN OF THE BUREAU OF FISHERIES

The following fish were taken in surface collections of 1893 to 1907:

Anguilla rostrata (Lesueur). Pholis gunnellus (Linneus).
Leptocephalus conger (Linnzus). ‘ Cryptacanthodes maculatus Storer.
Clupea harengus Linnzus. Anarhichas lupus Linnzus.

Brevoortia tyrannus (Latrobe). Prionotus carolinus (Linnzeus).
Anchovia brownii (Gmelin). Pollachius virens (Linnzus).

Osmerus mordax (Mitchill). Microgadus tomcod (Walbaum).

Apeltes quadracus (Mitchill). Gadus eallarias Linnzeus.
Syngnathus fuscus Storer. Urophycis sp.

Menidia menidia notata (Mitchill). Rhinoneumus cimbrius (Linnzus).
Ammodytes americanus De Kay. Brosmius brosme (Miiller).

Poronotus tricanthus (Peck). Lophius piscatorius Linnzeus.
Stenotomus chrysops (Linnzus). Pseudopleuronectes americanus (Walbaum).
Tautogolabrus adspersus (Walbaum). Hippoglossoides platessoides (Fabricius).
Tautoga onitis (Linnzus). Lophopsetta maculata (Mitchill).
Lactophrys trigonis (Linnzus). Pomolobus pseudoharengus (Wilson).
Spheroides maculatus (Bloch and Schneider). Seriola zonata (Mitchill).
Myoxocephalus eneus (Mitchill)?. Limanda ferruginea (Storer)?.

Cyclopteras lumpus Linnzus.

GENERAL CONCLUSIONS

I shall not attempt to summarize all the conclusions arrived at during the
past year. For the most part these have been taken up under the various subjects
and in the discussion on plankton. The following are some of the more general
conclusions concerning the nature of the plankton and the physical factors affecting
its distribution, resulting from a 2-year study of the Woods Hole pelagic fauna:

1. Woods Hole is an excellent location for the study of the seasonal distribution
of plankton.

2. It is impossible to investigate diurnal distribution in Great Harbor. The
current rushing through the passage during the flood tide mixes the water so com-
pletely that the distribution of plankton remains the same at all times. The entire
body of water is affected at the same time, even during periods of sudden heating
or rapid cooling of the air.

3. No great amount of fresh water enters Woods Hole. The salinity averages
about 31.5. For this reason titrations are of importance in determining the
presence of ocean water.

4. As in the case of the benthonic animals, the plankton of this region is made
up of a complex of faunas. It forms the northern limit of many southern species,
the southern limit of many northern species, and a pocket where oceanic animals
blown in by strong southerly winds are deposited.

5. The tropical species appear gradually in Great Harbor in the summer, but
stop suddenly in the fall. This is because the temperature of the water in Buzzards
Bay rises higher than that of the coastal waters in summer but responds quickly to
the falling temperature of the air and by fall becomes much colder. Animals
carried into this region in summer survive, but in the fall the lower temperature
proves fatal and few live to be carried through the passage back into the deeper
waters. However, members of this group may be taken throughout the fall in
Vineyard Sound, where the decline in temperature is not so rapid.

PLANKTON OF THE WOODS HOLE REGION

Auge

Fic. 78.—Occurrence of Prionotus car-
olinus during successive years,
1893 to 1907

Fic. 79.—Occurrence of
Spheroides maculatus
during successive
years, 1893 to 1907

Fic. 80.—Occurrence of
Hippoglossoides plates-
soides during succes-
sive years, 1893 to 1907

Fic. 81.—Occurrence of Menidia menidia notata
during successive years, 1893 to 1907

174 BULLETIN OF THE BUREAU OF FISHERIES

6. The arm of Cape Cod forms a permanent northern barrier for the southern
neritic plankton but only a summer barrier for northern pelagic species.

7. The proportion of benthonic animals occurring in the plankton of this
region is much greater than that found in normal littoral plankton. After north-
east storms Buzzards Bay types predominate; after southerly storms Vineyard
Sound types are most plentiful. This is particularly noticeable in the case of
amphipods.

8. No correct impression of the relative abundance of the local benthonic
fauna can be obtained from surface collections unless the distribution of each of
these animals in the bay and sound is completely understood.

9. A distinct periodicity in the occurrence of all the common animals of the
region is clearly noticeable. The succession of species remains almost the same
each year, the only variation being in the time of their appearance and disappear-
ance.

10. The planktonic animals of the region, with one exception, may be placed
in two general groups—the summer community and the winter community. The
ceelenterates are the exception. For the most part these have a long spring maxi-
mum and a short one in the fall.

11. The pelagic diatoms exert a very great influence on the zooplankton. When
the greatest maxima appear most of the zooplanktonic forms disappear. There
are possibly two reasons for this. First, the common species having these swarm-
ing periods do not form the food of the zooplankton so far as I have been able to
determine. During the maxima of the larger diatoms the smaller members of this
group which are eaten by pelagic animals disappear, causing a scarcity in the
food supply. This may account for the similarity in the time of disappearance of
the larger forms and the small diatoms. Second, the great numbers of the diatoms
filling the water apparently cause conditions unfavorable for animal life of any
sort. The macroplankton seems to be literally choked out. This, however, is
hardly probable, and is offered merely as a possible explanation.

12. Conditions favoring the increased production of one species of diatoms
are also favorable for many others, provided that one does not become so abundant
that almost all others disappear. The summer maximum often exemplifies the
latter condition. The winter swarm usually consists of many species in which
various forms predominate at different times.

13. My observations on the distribution of pelagic diatoms lead me to disagree
with the theory that all production takes place in deeper waters off the coast, the
species occurring in the littoral waters being the result of winds and tides. Such
factors no doubt account for the distribution of the various species, but the quan-
titative distribution can not always be explained on that basis.

All evidence points clearly to the fact that great production of floating diatoms
takes place at the mouths of rivers where the largest amount of drainage from the
land is emptied into the coastal waters. Peck’s observations in Buzzards Bay also
indicate that the greatest swarms are found where the greatest outwash from the
land occurs. Buzzards Bay is a great reservoir in which pelagic diatoms accumu-
late and multiply, and as a result the swarms carried into Great Harbor are often
exceedingly large.

PLANKTON OF THE WOODS HOLE REGION 175

14, Temperature is the dominant factor in governing the seasonal distribution
of all local pelagic animals. It also determines whether oceanic species entering
the region shall perish at once or live long enough to become an important factor
in the local fauna. Three general conditions cause the appearance of the pelagic
animals—winds, tides, and the food supply. Salinity forms barriers in some locali-
ties, but not at Woods Hole. Once introduced into the region, the organisms remain
until the temperature becomes unfavorable or the food supply is exhausted, and
then they must leave or perish. Food is also an important factor in causing the
disappearance of a species during a period of favorable physical conditions. This
is probably the limiting factor of the summer diatom season. Temperature governs
the breeding seasons of all planktonic and benthonic animals of this region. The
temperature prevailing at the time of the extrusion of the eggs is not often the im-
portant factor, for the eggs are usually thrown off as soon as ripe, provided the
conditions are not too unfavorable. After the eggs have been deposited in the
waters the existing temperature plays a part in determining whether the incubation
period will be long or short. The determination of an early or a late breeding
season, then, depends upon the temperature at some previous date when a warming
or cooling of the water started the development of the sex products. This fact
must be considered when interpreting the appearance of certain larve in the
plankton.

15. Reactions to changes of temperavire are tur one cuvse part More evident
among planktonic animals than among benthonic forms. Bottom dwellers, par-
ticularly sessile forms, in order to maintain themselves must be able to withstand a
great range of temperature. Unusually low temperatures often kill large numbers,
but as a rule both the larve and adults are extremely hardy. This is not true in the
case of planktonic forms. Certain species, such as Calanus finmarchicus, although
preferring cold water, are able to stand sudden rising or falling temperatures and
appear to survive as well in water of 22° C.as at 0° C. Most pelagic animals, how-
ever, particularly the phytoplankton, disappear as soon as the temperature condi-
tions become unfavorable. 2

16. The annual distribution of the diatom maxima of the American coast is
very similar to that of the eastern Atlantic waters in that the seasons of the greatest
swarms retreat farther and farther from the warmest months as one approaches the
Tropics. A similarity in the seasonal variation in Kuropean and American waters
of the same latitude is particularly noticeable, conditions at Woods Hole correspond-
ing to those in the Adriatic Sea. The great effect of the arm of Cape Cod on the
local plankton is again evident here, for within 20 miles of Massachusetts Bay,
with conditions similar to the Norwegian Sea, conditions comparable to those of the
Mediterranean and Adriatic Seas are found in Buzzards Bay.

17. The distribution of the plankton of the western Atlantic coast is little
understood, and the number of animals new to the region taken during the past
year indicates that most of the eastern Atlantic coast pelagic species probably will
be found here also.

176 BULLETIN OF THE BUREAU OF FISHERIES

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PLANKTON OF THE WOODS HOLE REGION 177

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é

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PLANKTON OF THE WOODS HOLE REGION 179

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