PLANKTON" OF THE GULF OF MAINE 
383 
PHYTOPLANKTONIC COMMUNITIES 
Although our studies in the Gulf of Maine are in their infancy, as compared 
with the intensive surveys that have been made in north European waters, they 
have progressed sufficiently to give a general idea of the groups of microscopic 
plants primarily concerned, and of their seasonal alterations; and although periodic 
or sporadic fluctuations are to be expected in the composition of the pelagic com- 
munities, the seasonal cycle here outlined and the accompanying charts, based on 
our tow-net hauls, are offered with some confidence as representing what may be 
called the basic status of the phytoplankton of the Gulf of Maine. 
It is necessary to select some arbitrary starting point in describing the general 
seasonal succession of diatoms, peridinians, and other groups, though necessarily 
this is an artificial one because the planktonic cycle is uninterrupted from year’s 
end to year’s end. Perhaps the most convenient is the status late in February or 
during the first days of March, when the phytoplanktonic community falls to its 
lowest ebb over the Gulf of Maine as a whole, just prior to the vernal awakening 
that takes place in the sea as well as on the land. Unfortunately our data for the 
open gulf at this season are not all that could be desired, for although the Albatross 
made a general planktonic survey of the gulf between the 22d of February and the 
24th of March in 1920, this, as it proved, did not altogether forestall the earliest 
flowerings of diatoms. But from this cruise, added to winter tow nettings made in 
1912 and 1913 (Bigelow, 1914a), and during December to January, 1920-1921, 
and from the counts of diatoms tabulated by Fritz (1921), it is safe to assert that when 
the temperature of the gulf is at its minimum for the year, just prior to the first 
trace of spring warming, its offshore waters as a whole and the estuarine tributaries 
of the Bay of Fundy 23 support only a very scanty phytoplankton, in which peridinians 
(p. 407) and oceanic diatoms mingle (fig. 104), except that vernal flowerings of dia- 
toms are already under way locally along its northwestern shore and over the western 
part of Georges Bank. In 1920 this description applied to the entire basin of the 
gulf as well as to the eastern part of Georges Bank, at least up until the middle of 
March. But flowerings of diatoms, resulting in local swarms so dense as to be the 
most spectacular event in the yearly planktonic cycle, were already under way along 
a narrow coastal zone between Cape Ann and Cape Elizabeth by the first week of 
that month (stations 20059 and 20060), and their future expansion was foreshadowed 
even thus early in the season by the fact that diatoms in small numbers had replaced 
the peridinians as far east along the coast as Mount Desert Island, on the one hand 
(stations 20056 and 20058), and bulked about as large as the peridinians in a very 
sparse phytoplankton off Gloucester on March 1, on the other (station 20050; genera 
Coscinodiscus and Thalassiosira) . On March 4, 1913, diatoms dominated near this 
last locality, and on March 5, 1920 (station 20061), we found a pure diatom plankton 
with only an occasional peridinian; but on both these occasions the total catch of 
phytoplankton was still very scanty. As April 3 (Bigelow, 1914a, p. 405) is the 
earliest date when we have found diatoms in great abundance at the mouth of Mas- 
23 No planktonic data are yet available for other inclosed wafers or harbors around the gulf at this season. 
