Heterotrophic Nano- and Microplankton in the Kara Sea in Autumn

Based on the obtained and all available literature data, it has been shown that the abundance of heterotrophic flagellates in the Kara Sea at the end of the season is relatively stable in different years, while in other Arctic seas (East Siberian and Chukchi seas) the values of this indicator are 1.5–2 times higher. The indicators of the abundance of heterotrophic nanoflagellates in bottom water vary to a much lesser extent than in the water column. The abundance of heterotrophic nanoflagellates in the bottom water of the bays of the Novaya Zemlya archipelago is significantly lower than in the same biotopes in the eastern and western parts of the Kara Sea. Most organisms are free-living forms. About a third of protozoa are associated with detrital particles. The ratio of the biomass of heterotrophic flagellates to that of bacteria more than doubles in the layer of bottom water and in the upper layer of sediments compared to the water column. For the water column of the Kara Sea, the calculated value of grazing of bacterioplankton by flagellates does not exceed 2% of their biomass. The ratio of the eaten biomass of bacterioplankton to the biomass of consumers in most cases decreases with depth.