PLANKTON OF THE GULF OF MAINE 



41 



Similarly, the spring cruise of 1920 suggests that S. elegans may be expected to 

 rival the copepods in abundance over a large part of Georges Bank in February, 

 March, and April, just as it does in July; for it was a large element in the catch at a 

 station on the southwest part of the bank on February 22 (station 20046), on the 

 northeast part on April 17, and had been so plentiful at a third station on the eastern 

 part of the bank on March 11 (station 20066) that the "glass worms," with a great 

 abundance of haddock eggs, dominated the catch (fig. 19). In short, Georges 

 Bank is apparently a center of abundance for S. elegans throughout the year (p. 310), 

 and the presence of a shoal of large Limacina retroversa on the northern part of the 

 bank on March 11, 1920 (station 20065), reproduced our experience of July 20, 

 1914, though the exact localities in question were about 80 miles apart. 



Late in the winter and early in the spring the scanty zooplankton of the gulf is 

 chiefly composed of fully adult animals, a fact made evident by the predominantly 

 large size of its calanoid copepods and Sagittae, giving the catches a distinctive aspect 

 when compared with those of July or August. The recrudescence which charac- 

 terizes the advance of spring results primarily from the local propagation of its 

 several component groups, not of replenishment by immigrants from any extra- 

 limital source. This has been proved by repeated observations. 



In Massachusetts Bay this vernal augmentation is earliest apparent at stations 

 close in to the land, in the shape of a sudden appearance of hosts of copepod nauplii 

 (figs. 27 and 28). This event commences some time late in March off the mouth of 

 Boston Harbor, for we found few nauplii there on the 5th of that month in 1920 

 (station 20062), but an abundance of them on the 5th of April (station 20089), 

 besides many copepods in the older larval stages. As the season advances this 

 vernal wave of reproduction on the part of the copepods spreads seaward; and the 

 nauplii appeared in multitudes at the mouth of the bay during the last half of April, 

 1920, where we had found only an occasional copepod — egg, nauplius, or juvenile — 

 on March 1 or April 9. In 1920 the swarms of larval copepods, together with the 

 various other larvas that appear about the same time, produced a decided increase 

 in the volume of animal plankton present in the water of the Massachusetts Bay 

 region by the first week in May. This was our experience in 1913, also, when W. W. 

 Welsh found the water in Gloucester Harbor reddened for areas of about a square yard, 

 several yards apart, with what proved to be swarms of copepod nauplii and young 

 copepods on May 3. The peak of production of copepods, however, is so soon 

 passed in Massachusetts Bay that our nets brought back proportionally more of 

 the older juveniles and fewer nauplii off Gloucester on May 16, 1920, than 12 days 

 earlier, while the hauls off Magnolia, Mass., on May 17, 1913, yielded only a few 

 copepod nauplii but an abundance of the later stages (chiefly Calanus, with some 

 Eurytemora), besides many crab larvce in the zcea stage. 



The vernal replenishment of the zooplankton follows much the same course in 

 the coastal belt immediately north of Cape Ann as in Massachusetts Bay, with a few 

 copepod nauplii among the swarming diatoms off the mouth of the Merrimac 

 River as early as March 4 in 1920 (station 20060). The nauplii were again noted 

 there on April 9, and on May 7 hauls made close by with the closing net yielded 



