Microzooplankton community composition in the winter sea ice of the northern Weddell Sea

Sympagic microzooplankton were studied during late winter in the northern Weddell Sea, for diversity, abundance and carbon biomass. Ice-cores were collected on an ice floe along three dive transects, and sea water was taken from under the ice through the central dive hole from which all transects were connected. The areal and vertical microzooplankton distributions in the ice and water were compared. They showed high abundance (max 1183 ind. L-1) and biomass (max 28 µg C L-1) in the ice-cores, and were low in the water, below sea ice (maxima, 19 ind. L-1; 0.15 µg C L-1, respectively). The highest amounts were found in the lower 10-cm section of ice cores. The microzooplankton community within sea ice comprised mainly aloricate ciliates, foraminifers and micrometazoans. In winter, microzooplankton represent an important fraction of the sympagic community in the Antarctic sea ice, providing a food supply for the upper levels of the trophic web. They can potentially also control microalgal production, and can contribute to particulate organic carbon concentrations when released into the water column due to ice melting in spring. Continued reduction of the sea ice might undermine these roles of microzooplankton, leading to reduction or completely loss in diversity, abundance and biomass of these sympagic protists.