PLANKTON OF THE GULF OF MAINF. 403 



May 4, 1915 (station 10267) that every interstice of the fine net was clogged and its 

 silken bag transformed into a cone of slime almost impervious to water after a few- 

 minutes submergence at a locality where a net of the same specifications took oidy 

 5 cubic centimeters of phytoplankton on March 24, 1920, and 50 cubic centimeters on 

 April 18 of that year. Even a coarse (No. 5 silk) net, 24 centimeters in diameter, 

 yielded over 2,000 cubic centimeters, mostly diatoms of one species, after 20 minutes' 

 towing, though a large part of the phytoplankton must have escaped through it. 



Perhaps I should remark in passing that while very rich catches are the rule 

 throughout the areas occupied by the flowerings of diatoms during these periods of 

 abundance, considerable local variations in the volumes of plankton present in the 

 water arc to be expected from place to place, for instead of being uniformly and evenly 

 distributed, "the congregations of diatoms are often so streaky that one can actually 

 see the net pass through alternate bands of brownish diatoms and of clear water 

 (Bigelow, 1914a, pp. 405 and 407). 33 Conceivably it might miss the productive spots 

 altogether, and very likely this happened off Cape Ann on April 9, 1920 (station 

 20091), when the catch of phytoplankton was very small though diatoms were then 

 extremely abundant (200 + cubic centimeters) both south and north of the cape a few 

 miles away. In the deeper waters offshore, however, the phytoplankton is much more 

 evenly distributed, and it may even approach perfect uniformity over large areas in 

 the open sea. 



The duration of the flowering season of the diatoms determines the period during 

 which large volumes of phytoplankton (say upwards of 50 cubic centimeters per haul) 

 are to be expected anywhere in the Gulf of Maine. After the diatoms pass the peak 

 of their abundance the amount of phytoplankton rapidly diminishes, and from that 

 time forward, as copepods, Sagittas, and other animals form an increasing proportion 

 of the catch, measurements of its volume become less and less instructive. 



In Massachusetts Bay the phytoplankton attains its maximum abundance (as 

 measured by volume) by the last half of April, diminishing again so suddenly that 

 the amount taken among the copepods during the first week in May, 1920 (after the 

 brief swarming of Phseocystis had come to an end), was hardly measurable. And 

 while large volumes may be expected in the western basin until well into May (p. 338), 

 the volume of phytoplankton taken there in the standard haul on June 26, 1915, 

 after diatoms had practically disappeared, was less than 3 cubic centimeters (station 

 10299). 



Near land, east of Penobscot Bay, where diatoms persist more or less throughout 

 the summer (p. 396), we have occasionally made large catches in August, notably in 

 1912, when Asterionella (p. 431) occurred in such abundance that although the net 

 came back aboard filled to the brim with several liters of slimy brown diatom soup 

 (Bigelow, 1914, p. 133), its yield was only a part of what was actually present in the 

 water through which it was drawn. In fact, this has been the richest haul of phyto- 

 plankton ever recorded for the Gulf of Maine. 



In most parts of the gulf where the spring diatom flowering is a short-lived 

 phenomenon, its dissipation leaves but little vegetable plankton in the water; nor does 

 the augmentation of peridinians, characteristic of late spring and early summer, 



3 * This has often been remarked by previous students. 



