Species composition and ecology of dinoflagellates from the Southern Ocean near South Georgia

Dinoflagellates were identified and counted from preserved vertical net haul samples collected from a station grid centred on South Georgia in austral summer 1981 –1982. All species were scarce in comparison with diatoms, the dominant large-celled microplankton. Dinophysis antarctica Balech was the most abundant and widespread species. Maximum dinoflagellate numbers were found at stations forming a belt to the south and west of the island. Whilst previous analysis of diatom community composition had revealed distinct species associations, no differences in species composition between this region and areas of low dinoflagellate abundance could be resolved. Since both heterotrophic and photoautotrophic taxa were found in the samples, it is difficult to identify environmental features which could act on most of the dinoflagellate taxa. The large-scale pattern of dinoflagellate distribution may reflect the pattern of water circulation along the edge of the South Georgia continental shelf.