PLANKTON OF THE WOODS HOLE REGION 
121 
After southerly storms during the summer Vineyard Sound is often filled with 
floating Sargassum hacciferum (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 Jilipendula 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 
no real estimate of the abundance of the many 
minute organisms of this phylum can be made. 
Lohmann (1911) showed that at least 50 per cent 
of the living forms entering the finest silk nets 
available pass through the meshes and escape. It 
is very possible to grow cultures of protozoa, as 
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, 
however, in obtaining many of the rarer species. 
Certain of the larger protozoa were very 
abundant at times, particularly Ceratium tripos, 
Peridinium depressum, P. oceanicum, and several 
species of the genus Tintinnopsis. The distribu- 
tion of these animals often appears to be very 
definitely related to that of the plants. During a 
heavy diatom maximum very few of the larger 
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, Ceratium tripos 
swarmed, followed closely by C. macroceros and C. fusus in smaller numbers. 
These would have reached a maximum earlier, I believe, had it not been for the 
influx of Corethron valdivise, 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 imidenti- 
8242°— 25t ^3 
Fig. 23. — Occurrence of most abundant forms of 
Protozoa in surface collections from June to 
December, 1922. , Ceratium tripos; 
, C. macroceros: , C. fusus: 
o o o o o o o , Peridinium depressum: 
Tintinnopsis sp.; — . — , Heterophrys sol: 
— ... — , Peridinium oceanicum var. ohlongum 
