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Charles J. Fish 



vicinity of the south channel had attained late nauplius stages by mid- April in 1932, 

 when eggs but no larvae were found in the eastern basin. No evidence of propagation 

 was found farther east off Halifax at this time, or in the inner Gulf west of Mt. Desert 

 where the first evidence of local production was found in late May and June. As in 

 the outer region, and corresponding to Calanus finmarchicus (Fish, 1936 a), Pseudo- 

 calanus minutus (Fish, 1936 b) and Oithona similis (Fish, 1936 c), a progressive delay 

 to the eastward in the time of spawning was evident in the inner coastal area after 

 the species had become established there in 1932. This is indicated in Fig. 4 showing 

 early nauplii limited to the eastern Gulf at a time when late nauplii, presumably the 

 western crop, dominated everywhere. By September, propagation had largely ceased 

 in the Gulf, both in 1931 and 1932 (Table II). 



Although the progressive delay to the eastward in the time of spawning, and the 

 relatively small numbers of adults and larvae in the New Brunswick region of the Bay 

 of Fundy (Figs. 2 and 4) indicate that Microsetella responds in a general way to the 

 limiting factor of low temperature, in a manner characteristic of the boreal zooplankton 

 population, there is evidence that it can reproduce at somewhat lower temperatures 

 than Calanus and Pseudocalanus. In Frenchman's Bay in 1930 (Table I) M. norvegica 

 propagated successfully in large numbers during July and August at surface tempera- 

 tures averaging from 11 °-l 3 -5 ° C. and was the only pelagic copepod (with the exception 

 of Temora longicornis) found developing in those waters. An abundant population 

 of offshore species dominated by Calanus and Pseudocalanus (adults and late cope- 

 podite stages) was present in the lower levels of Frenchman's Bay throughout the 

 summer of 1930, but their eggs and larvae rarely appeared in the collections. 



Table IV 



Relative abundance of adults of Oithona similis and Microsetella norvegica in the 



Gulf of Maine and Bay of Fundy in 1931 and 1932. April-June: mean numbers per 



minute. August-September : mean numbers per cubic metre. .• no observations 



It would appear, therefore, that although Microsetella and its nauplii ordinarily 

 provide a less abundant supply of food for summer larval plankton feeders in the 

 Gulf of Maine and Bay of Fundy than Oithona they do appreciably supplement the 

 latter stock in those waters and seem to be of particular significance in areas like 

 Frenchman's Bay and the adjacent turbulent coastal region eastward from Mt. Desert 

 where low surface temperatures prevent successful summer propagation of the more 

 dominant Gulf zooplankton species. 



