Diversity and Community Dynamics of Heterotrophic Flagellates in the Littoral Zone of a Large Plain Reservoir

— Over four years in the spring–summer period, the species composition and the community structure of planktonic heterotrophic nanoflagellates (HNF) were studied in different types of littoral waters of the Rybinsk Reservoir (Upper Volga), including those affected by the vital activity of colonial birds. A total of 105 species and forms of HNF from 13 large taxa and a group of uncertain taxonomic position were identified. The taxa Choanoflagellida and Chrysomonadida were represented by the largest number of species in all the littoral zones studied. Fewer species of HNF were recorded in the littoral zone affected by the bird colonies than in areas outside the zones of their influence. The maximum number of species (81) was recorded in the protected overgrown littoral zone, and the minimum (48 species), in the open littoral zone near the heron colony. In the entire littoral area, 35 species were common. Among them, three species ( Bodo designis, Paraphysomonas imperforata, and Spumella sp. 1) had a high frequency of occurrence (≥50%). However, the basis of the diversity of the GNF was formed by the species, the frequency of occurrence of which was less than 20%. However, the species the frequency of which was ≤20% were the basis for the diversity of HNF. They made up more than half of the species list in all habitats. The dominant complex of the littoral communities in the reservoir was represented by 19 species.