PLANKTON OF THE GULF OF MAINE 49 



The winter plankton of 1920-1921 differed from that of 1912-1913 in the rarity 

 of the amphipod genus Euthemisto, both species of which not only occurred regularly 

 dining December, January, and February, 1912 and 1913, but usually in consider- 

 able numbers. Sagitta elegans, though it occurred regularly, was also far less 

 numerous in the midwinter of 1920-1921 than at that season in 1912-1913, when it 

 was an important factor in the tows made in Massachusetts Bay from December 

 untd February. Whether these differences were actually the result of annual fluctua- 

 tion in the stock of these two animals present or whether both are normally more 

 abundant in Massachusetts Bay and its vicinity than in other parts of the gulf in 

 winter remains to be learned. 



Other features of the winter plankton of the gulf worth mention are that the 

 buoyant eggs of the American pollock (PollacTiiusvirens) appear in great numbers from 

 November until February over its restricted breeding grounds; that cod eggs are to 

 be expected throughout the winter (Bigelow and Welsh, 1925, p. 424) if the nets be 

 towed near where the fish are spawning — seldom otherwise or in large numbers; and 

 that some few copepods (probably Calanus) continue to reproduce right through the 

 cold season, for their nauplii were detected at most of our December- January 

 stations of 1920 and 1921, most plentifully in Massachusetts Bay. Euthemisto, too, 

 must breed then (though probably in small numbers) to account for very young 

 specimens taken off Gloucester on December 29, 1920. In this connection I may 

 also call attention to numbers of large Calanus hyperboreus (5 per cent of all the cope- 

 pods) among a very rich catch of C. finmarchicus in the western basin on December 

 29, 1920 (station 10490, p. 304), and of Stephanomia bells in the eastern basin and 

 in the shoal water off Yarmouth (Nova Scotia), which was nearly barren otherwise, 

 on January 5. On the other hand, the arrow-worm Sagitta serratodentata vanishes 

 from the gulf sometime during late winter, our latest seasonal record of it being for 

 January 16, 1913 (off Gloucester). 



Judging from the tow-net hauls made during 1913, the zooplankton of the 

 Massachusetts Bay region continues decidedly uniform in composition throughout 

 January and February, when the successive hauls reproduced one another with 

 monotonous regularity, until early in March, when the quantity of animal plankton 

 present in the water decreased to its annual minimum (p. 39) coincident with the 

 vernal augmentation of vegetable plankton described elsewhere (p. 385), a change 

 soon followed by the wave of reproduction on the part of the copepods which I 

 have just discussed. It may safely be assumed that this is equally true of the 

 northeastern part of the gulf, for although, unfortunately, we have no plankton records 

 from its outer waters during the period January 9 to February 22, Doctor McMurrich 

 found Calanus jinmarchic us and Pseudocalanus, with Temora longicornis and the neritic 

 copepod genus Acartia, the chief animal constituents of tow-net catches during this 

 season of the year at St. Andrews. 



The seasonal planktonic cycle in the deep waters of the gulf below 100 meters 

 calls for separate discussion, because the Euchseta community is largely below 

 the reach of the wide fluctuations of temperature to which the inhabitants of the 

 shoaler strata of the gulf are subject. Data on this for the early winter consist of 

 two tow-net hauls, one from 240 meters in the western basin, December 29, 1920 



