Long-term variability of quantitative indices of zooplankton in the western part of the Northern Caspian

The Northern Caspian Sea is an area of the Caspian Sea characterized by high productivity and is the main feeding ground for representatives of the ichthyofauna. Animal plankton is of particular interest as a group of invertebrate organisms, the most mobile and sensitive to various external (abiotic) influences. It is on this group of animals that the ongoing research will focus. The northern part of the Caspian Sea differs sharply from the central and southern parts of the Caspian Sea in terms of hydrological and hydro-chemical regimes. The level of development of planktonic communities in the Northern Caspian Sea is formed under the influence of a complex of factors, the main of which is the volume of river runoff and, as a result, changes in the hydrochemical conditions of the aquatic habitat. The abundance and biomass of animal plankton are one of the main parameters characterizing the spatial, temporal and trophic structures of aquatic ecosystems. Their interannual fluctuations are reflected in the subsequent trophic chains of the reservoir – pelagic fish, primarily Caspian sprats. The analysis of the dynamics of the abundance, biomass and structure of zooplankton over a number of years – from 2011 to 2022 – is presented, which allows us to assess the functioning of the ecosystem of the Caspian Sea. The results of long-term studies of the zooplankton community can be included in the mathematical model of the reservoir and used to predict the current state of the Caspian Sea.