Distribution and Relationship between Heterotrophic Organisms and Viruses on the East Siberian Sea Shelf

The distribution of heterotrophic bacteria, viruses, and heterotrophic nanoflagellates was studied in the shelf waters of the East Siberian Sea along the meridional transect from the Kolyma River delta in September. The production of heterotrophic bacteria and their mortality as a result of protozoan grazing and lysis of viruses were also determined. The patterns of the spatial distribution of microorganisms and viruses varied: the number of bacterioplankton decreased with increasing distance from the Kolyma delta, while, on the contrary, its size and biomass increased to the shelf areas with negative water temperatures. The highest abundance and biomass of virioplankton were recorded at the extreme southern and northern stations of the transect and the abundance and biomass of heterotrophic nanoflagellates increased from the south to the north. The studied shelf waters were characterized by a high concentration of fine-textured detrital particles, and, as a consequence, a relatively large number of viruses attached to detritus. The mortality of heterotrophic bacterioplankton accounted for most of its daily production. Protozoan grazing was the main cause of bacterial mortality that significantly exceeded their mortality due to viral lysis.