REPRODUCTION OF CALANUS-GLACIALIS UNDER ICE IN SPRING IN SOUTHEASTERN HUDSON-BAY, CANADA

In situ egg production rates of Calanus glacialis Jaschnov females caught under the ice cover of southeastern Hudson Bay, Canada, between early April and mid-June 1986 were measured by direct observations and by an egg-ratio method in order to investigate the role of ice microalgae and under-ice phytoplankton production in copepod reproduction. Egg production commenced, although at low rates, in early May, about 3 wk after the onset of measurable concentrations of ice microalgae at the ice-water interface. Egg production increased to about 12-eggs female-1 d-1 in early June, after the ice cover began to melt. The time taken by immature adult females to reach maturity in the field was estimated to be ca. 3 wk (between late April and mid-May) by visual evaluation of gonad maturity in preserved females. In the laboratory, females caught on 10 April and maintained in saturating concentrations of the diatom Thalassiosira weissflogii took only a few days to produce eggs at high rates, indicating C. glacialis was food-limited during the ice algal bloom at the interface. We suggest that ice algal grazing changes the timing, relative to high food concentrations in the water column, of reproduction in C. glacialis by promoting oogenesis and oocyte maturation.