PLANKTON OF THE GULF OF MAINE 397 



Diatoms may also be expected to flower on one part of Georges Bank or another 

 at any season from late winter to midsummer, but nothing is known of their status 

 there in autumn or early winter. 



Fish (1925) has pointed out that the waters just west of the barrier of Cape Cod 

 show quite a different seasonal cycle — namely, rich diatom plankton throughout the 

 winter, usually with a brief summer maximum, but with few diatoms in spring — this 

 seasonal distribution corresponding to the Mediterranean, as that of Massachusetts 

 Bay and of the Gulf of Maine generally does to the diatom cycle of the North Sea, 

 Irish Sea, and Skager-Rak. Thus, as Fish (1925, p. Ill) emphasizes, the same 

 relationship between the seasonal succession of diatom maxima and the latitude and 

 temperature obtains in the western side of the North Atlantic as in the eastern. 



Peridinians dominate the phytoplankton of the open gulf throughout the summer 

 and autumn, but they become very scarce, actually as well as by contrast, during the 

 flowering period of the diatoms. The latter are much the more important group of 

 the two in estuarine situations, where they occur in greater or less abundance through- 

 out the year instead of dwindling almost to the vanishing point between their flower- 

 ing periods. Peridinians, on the other hand, are seldom more than a very minor 

 constituent of the plankton in estuarine situations. 



Finally, before turning to the quantitative records, I may point out that the 

 Gulf of Maine diatoms are chiefly of local origin — that is, that they are produced 

 in the gulf itself and are not immigrants thither from elsewhere. For the western 

 center of dispersal this may be taken as proved; and while the chain of evidence 

 favoring the endemic origin of the diatom plankton of the Nova Scotian side of the 

 gulf is not so complete, there is nothing in our records to suggest that it receives any 

 important accessions from the east around Cape Sable. On the contrary, none of the 

 hauls made east of the cape during March, 1920, June, 1915, or July and August, 

 1914, have yielded diatoms in any abundance; nor are the diatoms of the eastern 

 side of the gulf more Arctic in their affinities than those of the western, as might be 

 expected if the Nova Scotian current were responsible for their presence there, but 

 rather the reverse. 



QUANTITATIVE DISTRIBUTION OF THE PHYTOPLANKTON 



When the study is undertaken of the plankton of an ocean area previously 

 virgin cround in this respect, a general qualitative and seasonal survey is the first 

 task. Until we know what groups of organisms are the chief constituents of the 

 pelagic community, at what seasons they reach their maximum abundance, and 

 have outlined their temporal and geographic fluctuations in general, it is difficult to 

 plan counts of the actual numbers in which they occur, to yield results commen- 

 surate with the vast amount of labor entailed. For this reason our hauls in the Gulf 

 of Maine have so far been made with the ordinary horizontal nets of appropriate 

 mesh, but I believe that with the information now at hand the time is ripe for more 

 intensive quantitative studies of the phytoplankton of the offshore waters of the 

 gulf, such as Fritz (1921) has undertaken for the St. Andrews region. 



In north European waters this stage has long been passed, and since the time 

 when Henson (1887) first focused scientific attention on the productivity of the 

 hi<di seas, quantitative determinations innumerable of marine and fresh-water 



