PLANKTON OF THE GULF OF MAINE 399 



This depends somewhat on the shapes of the plant cells, smooth ones naturally 

 fitting together much more closely than setose or irregular cells or chains (Michael, 

 1921, p. 564). Unfortunately, measurements of volume have little value as a 

 measure of the phytoplankton for tow nettings containing appreciable proportions 

 of larger organisms (e. g., copepods), unless these be painstakingly picked out. 

 Nevertheless, even the most critical supporter of more rigorous methods must 

 allow a certain value to estimates of the volume of plankton, at least for comparative 

 purposes, especially when diatoms are flowering, for as a rule there is then very little 

 else in the water. At their worst horizontal hauls tell whether the plankton is com- 

 paratively rich or scanty, as between stations where similar hauls are made; and 

 when prosecuted over a period of years, as has been done near the Isle of Man 

 under the leadership of Professor Ilerdman, 30 very instructive results may be 

 expected. Because of their inherent inaccuracy, however, they can not be used 

 as a measure of the absolute amount of plankton present in the water, nor even as 

 a basis of comparison between different areas, unless the requirements of hauls of 

 uniform duration, at uniform speed, and with nets of uniform type be rigorously 

 adhered to. 



In midwinter the production of phytoplankton in the inner parts of the gulf is 

 so low that the volumes recorded in December, 1920, and January, 1921, ranged 

 only from 0.5 to 6.5 cubic centimeters; 31 but toward the end of February or early in 

 March of 1920 the vernal flowerings of diatoms on the southwestern part of Georges 

 Bank, on the one hand, and in the immediate vicinity of Cape Elizabeth, on the 

 other, were responsible for catches of phytoplankton 40 to 200 times as great as in 

 the center of the gulf or along its northern and eastern coast, where the catches made 

 during the March cruise of the Albatross in 1920 were often too small to measure 

 (fig. 108). During April of that year, the month when the diatom flowerings attain 

 their maximum abundance in the two sides of the gulf, the amount of vegetable 

 matter present in the surface waters of the Cape Elizabeth region in the west and 

 from the shallows off Cape Sable out to Browns Bank on the east is so much larger 

 still, without any corresponding augmentation in the central or northern part of 

 the gulf, that, allowing for the clogging of the nets, which I have repeatedly empha- 

 sized, it is not out of bounds to claim plankton volumes a thousandfold greater in 

 the most productive regions than in the more barren localities (fig. 109). Two 

 successive stations located 25 miles west of Cape Sable, where the volume of plankton 

 increased from less than 1 cubic centimeter to at least 380 cubic centimeters (actually, 

 no doubt, much more) during the three-weeks interval between March 23 and 

 April 15 of that spring, is a notable illustration of the rapidity with which the pelagic 

 flora augments in quantity when diatoms are flowering actively. The plankton 



* See especially Herdman, Scott, and Dakin, 1910. 



!1 The volumes here listed are the total yields of surface hauls of one-half hour's duration with a No. IS bolting-silk net 14 centi- 

 meters in diameter, not the amounts in any given volume of water or below any given areas of seasurface. They, therefore, are not 

 absolute measures, though comparable one with another. Since the unavoidable errors preclude accuracy, measurements have 

 been only to the nearest cubic centimeter, and all the larger volumes should be regarded as too small because of the clogging of the 

 net already alluded to. Probably none of the volumes of 200cubic centimeters or more represent much more than half tbe amount 

 of plankton that was actually present in the horizontal column of water through which the net was dragged, but through a part 

 of which it failed to fish after its meshes were clogged. 



75S9S— 2G 26 



