SEASONAL PATTERNS IN GONAD MATURATION, SEX-RATIO AND SIZE IN SOME SMALL, HIGH-LATITUDE COPEPODS - IMPLICATIONS FOR OVERWINTERING TACTICS

Seasonal changes in gonad maturation. sex ratio and size are described for field populations of the marine calanoid copepods Pseudocalanus acuspes (Giesbrecht. 1881) and Acartia longiremis Lilljeborg in Balsfjorden, northern Norway. Reproductive populations of both species were present from March to September. Beginning in August, gonads in P.acuspes late copepodites and A.longiremis adult females switched to an undeveloped resting state. Dormancy was terminated in late winter, several weeks before the vernal bloom. Small samples of Pseudocalanus minutus (Boeck) indicated both an earlier induction and termination of the overwintering phase in this species. Overwintering populations of P.acuspes copepodite stage V were dominated by males. but sex ratios evened out at the time of spring moulting and mating. Juvenile males were larger than the females, except after the vernal bloom and in early summer. The findings are discussed in relation to seasonal life history tactics.