Annual succession of marine protozoans in the arctic with emphasis on winter dynamics

The succession of pelagic ciliates and heterotrophic dinoflagellates was investigated in Disko Bay, West Greenland, from April 1996 to June 1997. In terms of biomass they contributed equally. Their annual distribution was bimodal with maxima in May/June and August. Summer levels were similar to those reported at lower latitudes. Winter dynamics were different. Due to 2 mo of polar darkness, food concentrations for ciliates and heterotrophic dinoflagellates were below threshold concentrations for growth. Nonetheless, small populations persisted throughout the winter. Both protozoan groups had a concentration of ~0.25 x 103 cells l-1. The succession patterns showed that all individual species peaked at different times during the summer months. However, diversity of the winter community was not different from that observed during summer. Even in the polar winter, the autotrophic ciliate Myrionecta rubra and the obligate mixotrophic ciliate Laboea strobila were recorded. Different strategies for winter survival of protozoans are discussed.