LONGTERM ZOOPERIPHYTON COMMUNITIES CHANGE IN KANIV RESERVOIR (RIVER DNIPRO BASIN)

Abstract

This study examines long–term changes in zooperiphyton in the upper part of the Kaniv Reservoir. Community composition was compared using data obtained in the 1970s and in recent years. The analysis demonstrated that in the past in areas with a natural temperature regime, communities were dominated by the bivalve mollusk Dreissena polymorpha Pallas. In contrast, in areas affected by heated water discharges from the Trypilska Thermal Power Plant (TPP), bryozoans prevailed, primarily Plumatella emarginata. Currently, communities dominated by dreissenids (D. polymorpha and D. bugensis Andr.) are considered climax, they prevail on experimental substrates after extended (multi–month) exposure. However, in recent years, the typical succession of gradual dreissenid development has been interrupted by growth of bryozoans, mainly P. fungosa. In 2024, the invasive bryozoan species Pectinatella magnifica. Leidy was first recorded in the Kaniv reservoir. This species has a highly aggressive life strategy, as its colonies practically eliminated dreissenid settlements on experimental substrates. The establishment and potential further spread of this species in the reservoir basin may pose a threat of new biological obstructions in water supply systems of power plants, which is particularly undesirable during wartime. The study using the experimental substrate method at two localities within a right–bank bay of the reservoir differing in trophic status showed that under mesotrophic conditions dreissenid–dominated communities form, whereas under polytrophic conditions bryozoans dominate throughout the entire growing season. In such environments, mostly the mobile colonies of Cristatella mucedo Cuvier were dominating. It is suggested that the identified bryozoans species should be attributed to organisms with higher saprobity indices than is currently believed. The experimental substrate method should be considered important not only for studying successions in aquatic ecosystems, but also as an effective tool for early detection of bio–hazards in water supply systems. Over the past years, zooperiphyton has undergone significant changes, including shifts in community dominants and the emergence of an invasive, potentially hazardous species.