PLANKTON OF THE GULF OF MAINE dyO 



tows on a line across the mouth of the bay (stations 10337 to 10339), where it had 

 dominated the phytoplankton a month earlier. 



Bailey (1917, p. 101) also records an abundance of diatoms (Skeletonema) near 

 Grand Manan Island in the Bay of Fundy in early September, and Dr. McMur- 

 rich's lists show a rather pronounced maximum of diatoms (chiefly Thalassiothrix) 

 at St. Andrews in September and October, 1916. But during the season of 1917, 

 when Fritz's (1921) counts located the vernal maximum in late April and early 

 May at St. Andrews, with a period of scarcity for diatoms in June, the second 

 maximum fell in July, followed by a sudden diminution in the number of diatoms in 

 August, with much smaller numbers in September. The wide fluctuations in her 

 counts at the same locality on different dates in July and August is an instructive 

 illustration of the streaky way in which shoals of diatoms often occur. Note 

 especially an increase from 632,000 on July 23 to 7,186,000 on August 2, falling to 

 14,900 on the 8th. It is more likely that the net chanced to hit a streak of diatoms 

 on the occasion of the rich catch, which a haul made shortly previous or later might 

 have missed, than that an active flowering culminated during the two-weeks interval. 



It is dangerous to generalize from a small number of hauls, especially for a 

 tide-swept locality, but it seems that a secondary maximum of diatoms is to be 

 expected sometime during the late summer or early autumn both in Massachusetts 

 Bay and in Passamaquody Bay, and therefore probably all along the coast line in 

 estuarine situations; one, however, which is less abundant than the vernal flowering 

 and likewise less regular in the date of its occurrence. 



Little change has been noted in the general composition of the phytoplankton 

 of the Massachusetts Bay region during the period November-January, Ceratium 

 dominating. Hauls off Gloucester on November 20, December 4, and December 23, 

 1912, yielded a scanty plankton, chiefly Ceratium, with few diatoms (Bigelow, 

 1914a, p. 404). In 1920 the several species of diatoms that are most abundant from 

 spring to early autumn had practically vanished from the whole coastal belt between 

 Cape Cod and the mouth of the Bay of Fundy by December and January; but by 

 contrast the diatom genus Coscinodiscus apparently has a flowering period in mid- 

 winter, for it rivalled Ceratium at all the stations occupied by the Halcyon off the 

 western and northern shores of the gulf from December 28, 1920, to January 9, 

 1921, dominated locally off the Merrimac Kiver (station 10442), and was the 

 most numerous diatom genus (though dominated by the peridianians) in the eastern 

 side of the basin, in the Fundy deep, and off western Nova Scotia at this time (stations 

 10499 to 10502). 



Judging from the midwinter data just outlined and from our experience during 

 the first days of March in 1920 and 1921, peridinians are predominant and diatoms — 

 except for Coscinodiscus — fall to a very low ebb out at sea in the Gulf of Maine dur- 

 ing the later winter. Fritz (1921) found only very small numbers at St. Andrews 

 from November until the middle of March, compared with the tremendous flower- 

 ings of spring. But diatoms may be a considerable element, quantitatively, in the 

 plankton here and there along the open coast even in midwinter, as was the case off 

 Gloucester on January 16 and in Ipswich Bay, a few miles north of Cape Ann, on 

 January 30 in 1913, on which occasions our towings yielded about as great a bulk 



