Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 242-249. 



Observations on the biology of Microsetella norvegica * 



By Charles J. Fish 

 Narragansett Marine Laboratory, University of Rhode Island 



Summary — Microsetella norvegica is one of two microcopepod species which appear significant in 

 the natural economy of certain western Atlantic boreal waters. During the winter months it extends 

 its range southward at least as far as the latitude of Chesapeake Bay. North of Cape Cod in the 

 Gulf of Maine region it is widespread with a tendency to form concentrations of limited area. 



Propagation in 1932 began in March in the outer area between Georges Bank and Cape Cod and 

 gradually expanded as the season progressed until it reached a peak in the Gulf along a band seaward 

 of the 100 metre curve from Casco Bay to the Bay of Fundy. 



There is evidence of three and possibly four generations between March and September. As in other 

 endemic pelagic species there was a progressive delay to the eastward in the time of spawning, but 

 unlike most of these Microsetella was found propagating successfully at low summer temperatures, 

 averaging 1 1 °-13-5° C, in the turbulent eastern (Frenchman's Bay) area. 



INTRODUCTION 



There has been increasing recognition of the importance of adult and larval micro- 

 copepods in the natural economy of both coastal and open ocean waters. Because of 

 their small size and frequent preference for subsurface levels they cannot be repre- 

 sentatively sampled with nets of the mesh most frequently used for zooplankton, and, 

 consequently, are commonly much more important members of the pelagic population 

 than published records indicate. 



One member of this group, 0///io/jfl5/m///5Claus,whichWiLSON( 1941) has concluded 

 to be the most widely distributed and numerous of all copepods, is also one of the 

 most prolific in western Atlantic boreal coastal waters where its young provide an 

 abundant source of food for larval plankton feeders in midsummer (Fish, 1936 c). 



Relatively little attention has so far been accorded Microsetella norvegica Boeck, 

 a second and even smaller (0-3-0 -5 mm) microcopepod species, also endemic in boreal 

 coastal waters. Although widespread, it has not been reported to be particularly 

 abundant in north European coastal areas (Ruud, 1929; Stormer, 1929; Wiborg, 

 1954) or south of Cape Cod in the western Atlantic (Fish, 1925; Deevey, 1952). 



Table I 

 Mean numbers o/ Microsetella norvegica in Frenchman'' s Bay. Number per cubic metre. 



Upper 50 metres 



1930 



July 10 

 July 18 

 August 1 

 August 7 

 August 14 



Adults-Copepodites 



Nauplii 



208,360 

 293,467 

 248,850 

 152,820 

 295,460 



404,720 



195,567 



169,523 



92,850 



93,600 



* Narragansett Marine Laboratory Contribution No. 1 1 . 



242 



