[Relations between Bacterioplankton, Heterotrophic Nanoflagellates, and Virioplankton in the Littoral Zone of a LarRe Plain Reservoir:. ImDact of Bird Colonies.]

Interactions of the main components of microbial planktonic food web (bacteria, heterotrophic nanoflagellates, and viruses) were studied in a protected overgrown littoral zone of the Rybinsk Reservoir (Upper Volga).. The effect of bird colonial, settlements (the Laridae family) on these processes was deter- mined. The following systems exhibited significant negative correlations: "heterotrophic nanoflagellates- large rod-shaped bacteria" ("predator-prey"), "viruses-bacteriophages-bacterial products" ("parasite-. host") and "heterotrophic nanoflagellates-viruses-bacteriophages." Relations between biotic factors con- trolling bacterial development were more pronounced outside the zone affected by colonial bird settlements. Near the bird colony the role of viruses in mortality of planktonic bacteria increased. Reproduction of bacte- rial cells accelerated in response to the increase in feeding activity of heterotrophic nanoflagellates. Viruses- bacteriophages and heterotrophic nanoflagellates probably eliminate different targets until medium-sized cells become predominant in the bacterial community. Then heterotrophic nanoflagellates consume bacterial cells infected with viruses.

[Activity and growth efficiency of heterotrophic bacteria in Rybinsk Reservoir].

The active fraction, production, and respiration of heterotrophic bacteria are determined to assess their growth efficiency and their role in the carbon cycle in the pelagic zone of Rybinsk Reservoir in summer. The greater part of organic substances assimilated by bacteria is mineralized to CO2. It has been established that the essential part of the constructive and energy metabolism of bacteria is supported by the input of allochthonous substances. Bacterioplankton, producing the biomass at their expense, performs functions similar to the functions of phytoplankton, and substantially supports the structural and functional organization of the planktonic food web in the reservoir.

[Structure of heterotrophic plankton in the littoral zone of the plain reservoir under effect of hydrophilic birds].

The eutrophic effect of products of vital activity of colonies of hydrophilic birds on the community of heterotrophic plankton in shallow parts of the plain reservoir is shown. The strongest effect of birds is observed in a protected part of the reservoir. Specific changes in some characteristics of zooplankton as distinct from the response to the anthropogenic effect are found.