Microzooplankton composition under the sea ice and in the open waters in Terra Nova Bay (Antarctica)

The aim of this study was to describe the microzooplankton composition under the sea ice in the Ross Sea (Antarctica) and its possible role as seed for the open-water community. We compared the under-sea-ice data to the communities present in the ice-free waters and at the retreating ice edge in order to test the hypothesis that the microzooplankton composition and abundance depend on the temporal development of the ecosystem. In December 2011, microzooplankton were sampled through two boreholes in sea ice, and 1 month later, in nearby stations that had been free from ice for a short time. The data from these samples were compared with a previous campaign (January 2011) when all of the area had been free of ice for a longer period. Our data indicate that under the sea ice the communities were very different from those of the ice-free waters, both in terms of abundance and diversity, with the prevalence of heterotrophic dinoflagellates and aloricate ciliates. Tintinnids were almost absent below the sea ice, and their abundance increased during the sampling at the intermediate depths. The present study provides evidence for the effect of the environment on the microzooplankton distributions, and indicates that the microzooplankton presence mainly depends on the sampling period. The community under the sea ice appears not to seed the open water community once the ice has retreated. The presence of the ice appears to influence the whole water-column production, which might thus not feed the deeper communities. The most important constraint appears to be the time that has lapsed from the presence of ice cover to the ice-free period.