Winter studies on zooplankton in Arctic seas: the Storfjord (Svalbard) and adjacent ice-covered Barents Sea

Zooplankton was sampled in the Storfjord and ice-covered Barents Sea during March 2003. Environmental conditions represented a typical winter situation with low air temperatures, close pack ice, and extremely low chlorophyll concentrations. Polar water dominated the hydrographic regime in the upper layers. Zooplankton distribution reflected spatial variability of hydrography. The copepods Pseudocalanus spp., Oithona similis, Microsetella norvegica together with gastropod larvae were most numerous. Biomass averaged for the entire water column varied from 3.3 to 14.3 mg dry mass m(-3), Calanus glacialis and Parasagitta elegans contributed most, followed by C. finmarchicus, Oithona similis, and Pseudocalanus spp. Various holoplankters showed reproductive activity, especially cyclopoid copepods and chaetognaths. A few C. glacialis females laid eggs in situ, but when fed diatom cultures rapidly increased their egg production. Meroplankton including larvae of nudibranchia, bivalvia, ophiuroida, polychaeta, and bryozoa were also present. Our data demonstrate that the pelagic community of the seasonally ice-covered Barents Sea was not in a sleeping state at the end of the winter, but in addition to dormant stages, a portion of mainly omnivorous and several carnivorous species was reproducing.