Effects of eutrophication on the long-term dynamics of juvenile fish communities

Abstract

The article reveals the patterns of the temporal dynamics of juvenile fish communities under conditions of eutrophication of water bodies. The study was conducted in the reservoirs of the nature reserve “Dniprovsko-Orilsky”. Ichthyological sampling was carried out according to standard methods used in the study of the quantitative and qualitative composition of fish communities. During the study period, representatives of 38 species of juvenile fish were established in the surveys. Numbers of fish communities showed temporal patterns and differed significantly between habitat types. At presence of the general temporary trends of abundance, each of types of biotopes is characterized by the features of temporary dynamics. The highest level of abundance was characteristic of the channel part of the Dnieper River. Lake ecosystems of the Dnieper River floodplain were characterized by a much lower level of fish abundance. Among lake ecosystems, the highest number of juvenile fish communities was established for the reservoirs of the Taromsky ledge. The highest biomass was established for the channel part of the Dnieper River. The biomass of juvenile fish communities was significantly lower in the lacustrine water bodies. Species diversity of juvenile fish communities statistically reliably depends on habitat type and year as a categorical variable. The number of species increases with the growth of community abundance up to a certain level, after which there is an exit to a plateau: the growth of abundance is not accompanied by a significant increase in the number of species in the community. Biotopes can be divided into three groups according to the level of diversity. It has been substantiated that the establishment of protected areas and the maintenance of a fish conservation regime within them is an important factor in stabilizing the temporal dynamics of abundance, diversity and sustainability of fish populations over a much larger area than the territory of the reserve itself. Young fish communities are a sensitive indicator of the temporal dynamics of the ecological state of water bodies and respond both to the negative impact of anthropogenic activities and to positive measures of protection of biological diversity in protected areas.