Relations between bacterioplankton, heterotrophic nanoflagellates, and virioplankton in the littoral zone of a large plain reservoir: Impact of bird colonies

Abstract

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.