PLANKTON OF THE GULF OF MAINE 459 



coast, according to Gran (1902, p. 17), Phseocystis reaches its maximum after the 

 diatoms have passed their apex of abundance, with a monotonous Phseocystis plank- 

 ton succeeding them for a very short period. Apparently it bears much the same 

 temporal relationship to the vernal diatom flowerings in Massachusetts Bay, but 

 in the western basin farther offshore it seems that Phssocystis precedes instead of 

 succeeds the greatest seasonal abundance of diatoms. 



The records of the International Committee point to May as the month in which 

 Phseocystis is at its maximum in the North Sea — that is, about the same season as 

 in the Gulf of Maine. Judging from the general geographic distribution of Phseocys- 

 tis, the latter is probably its most southerly center of abundance in the western side 

 of the North Atlantic, but the optima of temperature and salinity for this alga can 

 not be established for American waters until more records are available. It may, 

 however, be of interest to note that the Gulf of Maine collections (being from water 

 of 3 to 4.5°) have been well within the temperature limits of Ph. pouchetii in European 

 waters. But the salinity in which we have found it (31.43 to 32.45 per mille) is far 

 less than the mean of the European records, which is given by Ostenfeld (1910) as 

 about 34.8 per mille for pouchetii and as 34. S9 per mille for globosa, though the former 

 also occurs at the mouth of the Baltic in waters less saline than those of the Gulf of 



Maine. 



HALOSPH/ERA 



The unicellular pelagic alga Halosphsera viridis Schmidt 73 has been found at many 

 of our stations, sometimes in considerable numbers, though it is not sufficiently 

 prominent in the Gulf of Maine to have received a local vernacular name as it has 

 in the Mediterranean (Steuer, 1910, p. 2). Halosphsera was first detected in the 

 gulf in 1915, when it was widely distributed over the eastern basin of the gulf in 

 May (stations 10269, 10270, 10271, 10272, and 10273), though nowhere abundant, 

 and occurred locally off Mount Desert in June (stations 102S4 and 10286) ; also at one 

 station (10310) in August. It was likewise found across the whole breadth of the 

 continental shelf south of Nova Scotia in June (stations 10291, 10293, 10294, and 

 10296), and off Shelburne in September (station 10313); likewise on German Bank 

 on September 2 of that year (station 10310) and in the Massachusetts Bay region 

 early and late in October (stations 10322, 10336, and 10337). During the spring 

 cruises of the Albatross in 1920 Halosphsera was detected at some thirty stations in 

 the gulf widely distributed both in time and space (stations 20044, 20045, 20048, 

 20054, 20057, 20064, 20067, 20069, 20070, 20072, 20073, 20074 to 20076, 20078 to 

 20080, 20086, 20097, 20098, 20100, 20105, 20112, 20120, 20123, 20124, 20126, and 

 20129). These records, combined, suggest that Halosphsera attains its maximum in 

 the gulf late in the spring, practically disappearing again in midsummer, 74 though it 

 has been described as plentiful at that season in the colder waters about Cape Breton, 

 Nova Scotia (Wright, 1907). Doctor McMurrich found Halosphsera in late spring 

 and early summer (April 17 to July 6) at St. Andrews, winch corresponds to the 

 May-June maximum in the open Gulf of Maine. 



™ Identification according to Lemmcrmann, 1908, p. 21. 



"Our failure to find Halosphasra previous to 1915 was probably due to the fact that most of our stations in previous years were 

 in late July and August when Halosphsera is rare in the Gulf of Maine. 



