PLANKTON OF THE GULF OF MAINE 61 



Judging from our cruise during the spring of 1915, they reach their greatest 

 abundance and their widest dispersal in the gulf some time in May. The localities 

 of capture, with what data are available on the currents at that season, suggest that 

 after they have once passed Cape Sable their general line of drift is westward toward 

 the center of the gulf, not northward along the west coast of Nova Scotia, which is 

 the route followed by most visitors from the south (e. g. by Sagitta serratodentata), 

 and that they keep near the surface. 



Alexander Agassiz's (1S65) discovery of Mertensia and of Ptychogena in Massa- 

 chusetts Bay in early autumn, of Mertensia in abundance at Eastport, Me., in the 

 early sixties of the past century, and Fewkes's (1888) record of the latter as plentiful 

 there in the summer of 1885 and at Grand Manan in July and August, 1886, are 

 contrary to our experience during the period 1912 to 1915; nor does Doctor McMur- 

 rich mention Mertensia at all in his plankton lists for St. Andrews. It is probable 

 that such an abundance of Mertensia and its presence in the inner part of the gulf 

 so late in the season were the visible evidence of a greater influx of northern water 

 past Cape Sable than has taken place at any time during the past decade, and that 

 this inflow turned more northward toward the Bay of Fundy. Unfortunately, 

 however, no record was taken of the temperatures of the gulf during the years in 

 question, and, conversely, no collections were made of the plankton during the 

 abnormally cold summer of 1884. 



The group of northern animals that better resist high temperature is repre- 

 sented in our catches with some frequency by the two calanoid copepods Calamus 

 hyperboreus and Metridia Tonga, occasionally by a third large copepod, Gaidius 

 tenuispinis, and regularly by the naked pteropod Clione limacina (p. 125). The 

 status of each of these in the gulf is discussed below. I need only add here, of 

 Metridia longa, that while it reaches the gulf chiefly as an immigrant with the Nova 

 Scotian water, it is able to survive there for a considerable period and to thrive 

 "amazingly in their wanderings," says Willey (1921, p. 194), speaking of the species 

 at St. Andrews, in the Bay of Fundy, " if we may judge from their store of oil." Prob- 

 ably, as he suggests, most of them perish eventually in the gulf without leaving de- 

 scendants, and thus, though the animals concerned are diametrically opposite in 

 faunal origin, the distributional status of this copepod within the gulf is analogous 

 to that of Sagitta serratodentata , the specimens that penetrate the gulf as driftage from 

 the north, surviving there long enough to scatter far and wide and to be picked up 

 in the tow net, still flourishing though far from Cape Sable and long after they have 

 passed by it. 



Metridia longa can not be looked upon as a regular annual visitor to the gulf, 

 for while it has been taken at many stations in some years, in others it has been 

 sought in vain (p. 247). There is some evidence that in the years when it passes 

 west of Cape Sable in greatest number it succeeds in breeding to some extent in 

 the gulf, and the result of its longevity there, coupled with this local reproduc- 

 tion, is that in its years of plenty it becomes so widely distributed that the locality 

 records do not mirror its lines of immigration and of dispersal. For further dis- 

 cussion of this point see page 249. 



