PLANKTON OF THE GULF OF MAINE 89 



southeastern corner of the gulf, where vertical hauls have yielded only 25 to 65 cubic 

 centimeters per square meter on four visits (March 11, 1920, station 20064; April 17, 

 1920, station 20112; June 25, 1915, station 10298; and July 23, 1914, station 10225), 

 although made in depths of from 200 to 340 meters, and the coastal zone east of 

 Penobscot Bay would seem to be the least productive. 



Recapitulating for the Massachusetts Bay region, the zooplankton is at its 

 scantiest some time in March, earlier or later according to the forwardness of the 

 season; it increases very rapidly in amount during May, reaches its annual maximum 

 of abundance late in May or early in June, when there may be from 10 to 20 times 

 as much animal life in the water (200 to 300 cubic centimeters per square meter) as 

 in March, and wanes in August. A second well-marked pulse is noticeable in Sep- 

 tember, culminating in October, after which the plankton diminishes once more. 

 Our experience during the cold months of 1912 and 1913 (Bigelow, 1914a) was that 

 a moderate amount of zooplankton is to be found in the bay throughout the winter, 

 but that it suddenly declines almost to the vanishing point late in February or 

 early in March. 



The plankton passes through a corresponding quantitative cycle throughout 

 the entire coastal zone from Massachusetts Bay to the mouth of the Bay of Fundy; 

 but although the waters east of Cape Elizabeth are as barren as the region from 

 the Isles of Shoals to Cape Cod in early spring, they are never as productive of 

 zooplankton as is the latter in late spring and early summer, and, consequently, 

 the difference between the seasons of maximum and of minimum abundance of 

 plankton is not as great. 



The fact that the northern corner of the eastern basin proved extremely barren 

 on April 20, 1920 (station 20100), whereas we have found an abundant animal 

 plankton there in summer, suggests that this region, like Massachusetts Bay, is the 

 site of a wide seasonal fluctuation, with a brief period of barrenness in spring coin- 

 cident with the vernal flowerings of diatoms. This applies likewise to the shallows 

 off Cape Sable and over the eastern part of Georges Bank, where the zooplankton is 

 extremely plentiful in midsummer but sparse in March. 



So far as our experience goes, the seasonal fluctuation in the amount of plank- 

 ton present is widest in the neighborhood of the Isles of Shoals, with a range of 

 from practically nil to upwards of 300 cubic centimeters per square meter. The 

 coastal belt along the outer islands east of Penobscot Bay illustrates the opposite 

 extreme. Here the catches of the vertical nets may be but little larger (25 to 30 

 cubic centimeters per square meter) in summer (the richest season) than in spring, 

 and we have only once made a reasonably productive vertical haul in this zone (70 

 cubic centimeters per square meter at station 10098). 



The quantitative fluctuations are also comparatively narrow from season to 

 season, or at least no pronounced impoverishment takes place in spring, in the deep 

 waters of the western basin, so that the plankton of that part of the gulf is classed as 

 "rich," not "scanty," the year around, as shown by the following table. 



