SEASONAL CYCLES IN POPULATION ABUNDANCES AND EGG-PRODUCTION RATES IN THE PLANKTONIC COPEPODS CENTROPAGES-TYPICUS AND ACARTIA-CLAUSI

Laboratory studies on the seasonal cycling of egg production rates for Centropages typicus and Acartia clausi did not reflect seasonal changes in densities for these species at sea. Maximum egg production rates occurred from autumn to spring when population abundances at sea were low. In late spring, an increment in population numbers was followed by a drastic decline in egg deposition which continued into summer. The percentage loss due to mortality, calculated using egg data and total number of copepodid stages CIII and CIV recorded at sea ̃2 weeks later, indicated greatest mortality (80-99%) from eggs to copepodids during periods of high breeding intensity. These results suggest that high and low density phases in population numbers may be the outcome of variations in reproductive potential and survival rates of eggs and immature stages rather than reproductive potential per se. © 1990 Oxford University Press.