Contribution of different algae groups to their total biomass and infusoria biomass in under ice water

Samples of under ice water were collected at 4 stations not far from the White Sea Biological Station of the Zoological Institute RAS (Chupa Inlet, Kandalaksha Bay) in April 2002. For the first time it was shown that in winter numerous phototrophic and heterotrophic flagellates together with diatoms inhabited water column under sea ice. Abundance and biomass of these small algae was comparable with similar summer data. Biomass of algae in 2-40 m layer in early April 2002 exceeded 300 mg C/m2, increasing up to 0.69-2.9 g C/m3 just under ice. Sinking of the algae was insignificant, may be due to active grazing in the thin upper layer of the water column. High abundance of heterotrophic flagellates and dinoflagellates may indicate importance of the microbial food chain. From obtained data it may be concluded that the vegetation season, as well as the season of high activity of nano- and microheterotrophs starts in the White Sea far earlier, than it was supposed before.