Zoobenthos and zooplankton in small rivers of the Kobra River basin (National park “Koygorodsky”)

The studies were carried out on two small rivers – tributaries of the Kobra River (the Volga River basin), located on the territory of Koygorodsky National Park. The structure, quantitative development of zoobenthos and fauna of benthic invertebrates were studied. Hydrobiological sampling was carried out in June – July 2021. Standard methods were used for sampling. 87 species and taxa of a higher rank of invertebrates were found in the benthic fauna. The most diverse were caddisflies (21), mayflies (21), stoneflies (13) and oligochaetes (12 species). Quantitative development of the zoobenthos of the Kobra River basin is comparable to the average for the rivers of the Vyatka River basin as a whole and was 19 thous. ind./m2 and 74.6 g/m2 in the Suran River, and 14.1 thous. ind./m2 and 19.2 g/m2 in the Mytets River. The chironomids played a leading role in benthic invertebrate communities, and accounted for an average of 26.3–33.4% of the total zoobenthos abundance. Mayfly larvae and leeches dominated in the Suran River by biomass, as well as molluscs and caddisflies – in the Mytets River. The maximum quantitative characteristics were noted on the reaches of both rivers. The development of benthos was much poorer on the riffles. Three rare species from the orders of mayflies, stoneflies and dragonflies were identified. Zooplankton in the small tributaries of the Kobra River was studied using standard methods: in the Suran River on the early June and in the Mytets River – on the end of the July 2021. Plankton fauna was represented by 28 taxa, rotifers and copepods prevailed. Plankton species diversity, abundance and biomass were lower in the Suran River (the beginning of the vegetation season), which indicated the processes of zooplankton formation. The above indicators were higher in the middle of the summer season in the Mytets River, and indicated the stability of plankton communities. The presented data significantly expand the understanding of the biodiversity of aquatic ecosystems in the southern taiga zone.