Coupling between ice microalgal productivity and the pelagic, metazoan food web in southeastern Hudson Bay: a synthesis of results

Abstract

A multidisciplinary study of the ice algal production cycle in southeastern Hudson Bay in spring, 1986, provided an exceptional opportunity to observe trophic interaction between ice algae and metazoan zooplankton. During the ice algal bloom, females of the biomass-dominant copepod species, Calanus glacialis and Pseudocalanus spp. (predominantly P. minutus), grazed at night near the ice-waste interface. Feeding activity of these copepods significantly increased after the start of ice melt in mid-May when ice algae were released in large quantities into the water column. Copepod egg production was negligible during the ice algal bloom, then increased by approximately two orders of magnitude by mid-June. While changes in Calanus productivity can be attributed to increases in female-specific egg production rates alone, Pseudocalanus productivity was also substantially augmented by the appearance in late May of females of a second species, P. newmani. The data are consistent with the hypothesis that the major sources of nutrition for copepod production during this period are scdimenting ice algae (during and immediately after the bloom at the ice-water interface) and diatoms seeded from the interfacial layer and actively growing in the water column (in late May and Junnc). Larvae of Arctic cod and sand lance, the yolk-sac stages of which were found in samples immediately after the onset of ice melt, were in a good position to feed on the resulting high concentrations of copepod nauplii in mid-June. These results therefore suggest a strong coupling between the ice algal production cycle and production cycles in the pelagic food web in this region.