Population dynamics of an ice-associated diatom, Thalassiosira australis Peragallo, under fast ice near Syowa Station, East Antarctica, during austral summer

A clear shift from vegetative cells to auxospores and resting spores in Thalassiosira australis was observed in the water column and sinking fluxes under the fast ice near Syowa Station in the austral summer of 2005/2006. This is the first report of the auxosporulation by T. australis in situ. Resting spores were also observed in the sediment even before new spore formation, suggesting that T. australis can overwinter in the sediment. Heterotrophic dinoflagellates ingested and digested vegetative cells and auxospores but did not digest resting spores, suggesting a high tolerance of resting spores to grazing by heterotrophic dinoflagellates. We discuss the possible life history and overwintering strategy that T. australis uses in an Antarctic coastal area to cope with the unpredictable timing of sea ice growth and decay.