Structure of the Biotic Component in the Rybinsk Reservoir Ecosystem: Importance of Heterotrophic Bacteria (Review)

The total biomass of the biotic component of the ecosystem has been determined and the contribution of the main ecological groups—autotrophic and heterotrophic organisms from different habitats—to its formation has been estimated in a large plain meso-eutrophic reservoir (Rybinsk Reservoir, Upper Volga). Particular attention is paid to the role of heterotrophic bacteria in the structure and functioning of the biota in the reservoir. The total biomass of the biotic component of the ecosystem is 71536 t C, which is 5.2% of the total organic carbon in the reservoir. Higher aquatic plants make the largest contribution to the formation of the biomass in the reservoir. Their biomass, including epiphyton, was 6.0 and 1.9 times larger than the biomass of plankton and benthos, respectively. Heterotrophic bacteria, most of which inhabit bottom sediments, rank second in respect to their contribution to the total biomass. The comparison of the total primary production of all phototrophic organisms and the carbon demand of heterotrophic bacteria indicates the importance of allochthonous organic matter in the functioning of the reservoir ecosystem.