EGG-PRODUCTION AND FEEDING BY COPEPODS PRIOR TO THE SPRING BLOOM OF PHYTOPLANKTON IN FRAM STRAIT, GREENLAND SEA

Reproductively active Calanus hyperboreus (Krøyer) and C. glacialis Jaschnov were captured in the upper 100 m of Fram Strait (77° to 79°N) in late winter 1987. There was no evidence of a phytoplankton bloom; chlorophyll a concentrations were uniformly low (<0.1 mg m-3), and nitrate concentrations were uniformly high (>11.3 mg-at m-3). Gut-fullness measurements indicated that females were ingesting very little. The maturation state of gonads of both C. hyperboreus and C. glacialis indicated that 75% of females were in a ripe condition consistent with observed egg laying. The lipid content of females laying eggs was reduced in both species compared to that of females not laying eggs. In C. hyperboreus the reduction was 39% and in C. glacialis it was 44%. All the evidence suggests that both C. hyperboreus and C. glacialis were laying eggs in late winter by using lipids stored previously; they were not relying on ambient concentrations of phytoplankton. The daily rate of egg laying by C. glacialis using lipids in late winter exceeded the rate reported for summer when ambient food supplies have been shown to be necessary. It is suggested that individuals, spawned well in advance of the spring bloom of phytoplankton, may comprise a major portion of the annual recruitment to the entire population of C. glacialis in this area, and that their life cycle can be completed within 1 yr. Neither Metridia longa (Lubbock) nor C. finmarchicus (Gunnerus) laid eggs during this study. © 1990 Springer-Verlag.