DISTRIBUTION, REPRODUCTION AND DEVELOPMENT OF CALANUS SPECIES IN THE NORTHEAST WATER IN RELATION TO ENVIRONMENTAL-CONDITIONS

The vertical and horizontal distribution of mesozooplankton biomass an d its composition, together with the reproduction and development of t he three dominant herbivorous copepods Calanus finmarchicus, C. glacia lis and C. hyperboreus, were studied in the Northeast Water between th e end of May and end of July, 1993. Biomass varied between 0.15 and 10 .6 g m(-2) and was lower on the shallow banks. Highest biomass was fou nd on the shelf slope and in the entrances to Belgica and Westwind Tro ughs. There was no seasonal trend during the study period. Among the z ooplankton taxa, copepods were dominant, with 84% biomass of all other taxa, followed by chaetognaths with 14%. The large Calanus species ma de up 91% of copepod biomass. The most abundant species, C. glacialis, inhabited areas of low current speeds on Belgica and Ob Bank, C. hype rboreus dominated shelf slope and trough stations, while C. finmarchic us was most abundant in the Return Atlantic Current along the shelf sl ope and also eastern Belgica Trough. C. glacialis was the only Calanus species spawning during this period, but young copepodites of the oth er species were also abundant. Egg production of C. glacialis was at a maximum by our arrival and continued to at least mid August. Accordin g to the results from starvation experiments, its egg production was f uelled by food uptake, but was decoupled from phytoplankton chlorophyl l until July, indicating ice-algae and microzooplankton as an alternat ive food source. Only when the polynya approached its maximum extent w as a close relationship to phytoplankton established. Due to both spat ial and temporal heterogeneity of the occurrence of young copepodite s tages it was impossible to follow the growth of cohorts of development al stages. Herbivorous carbon requirements estimated from egg producti on rates were mostly less than one third of the phytoplankton stock. F rom egg production and the distribution of young stages, the outer Wes twind Trough seems to be the centre of biological activities. This may be related to the formation of young ice in winter in this area, whic h was found to carry a large mass of under-ice algae, High biomass but low production in Belgica Trough indicate this as an advective and ex patriated community of C. finmarchicus and C. hyperboreus, where grazi ng is negligible, at least during early summer.