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 tliis 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 " 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 200G0) , 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- 



" No planktonic data are yet available for other inclosed waters or harbors around the gull at this season. 

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