Peculiarities of distribution of zooplankton in the overgrowing small reservoir

Our studies concerned a small plane water reser- voir in the middle taiga subzone of the Komi Re- public. A large diversity and quantity of zooplank- ton was revealed. The distribution of zooplankton throughout the water area of the reservoir was relatively regular and depended on the nature of its constituent biotopes. Three zooplankton com- plexes were identified. Two of them are typical for the relatively warm summer period. The plankton complex with domination of immature forms of Cyclopoida juv. with subdominants Mesocyclops leuckarti, Polyarthra euryptera, Bosmina (E.) cf. longispina, and Ceriodaphnia pulchella developed in the deep-water areas during this period. Shal- low-water areas overgrown with microphytes were dominated by a complex of Bosmina (E.) cf. longispina, Sida crystallina with subdominants Ceriodaphnia pulchella, Polyphemus pediculus, and juvenile Cyclopoida. By composition, both complexes were similar to the communities inhabiting the sublittoral and littoral zones of the lakes in the study region. The absence of the pelagic complex as such is due to the small size of the water reservoir. In colder summer period, regardless of the type of biotopes, the whole aquatorium was dominated by Daphnia cristata.The flow of plankton organisms with flood waters favored the appearance in the watercourse located in its lower reaches, of untypical zooplankton species Limnosida frontosa, Diaphanosoma brachyurum, Leptodora kindtii, etc., most of which, however, did not distribute downstream. Besides, abnormally high zooplankton abundance and biomass was observed in this section of the river due to mass development of copepods.Distribution of plankton organisms in the river coves was associated with the nature of overgrowth and distribution of macrophyte communities. For example, in the Dendel Cove where thickets were sparse and dominated by semi-submerged and submersed aquatic vegetation, plankton was more diverse and its abundance and biomass were higher (by 1.5 and 1.8 times, correspondingly) than those in the Nyuvchim Cove with dominating thick-growing Typha latifolia, Elodea canadensis, and Potamogeton perfoliatus.