This study examines long-term changes in the Black Sea ecosystem, including the warming of its waters amid anthropogenic pollution and eutrophication. The aim of the study is to describe structural shifts in water masses and biotopes, as well as to assess alterations in key ecosystem components. Through the analysis of multi-year hydrological datasets, mathematical modelling, and hydrological studies, it has been demonstrated that a comprehensive understanding of the Black Sea's ecosystem changes requires consideration not only of climate warming, anthropogenic pollution, and eutrophication but also of chronological changes in water mass structure and associated biotopes. Ongoing deoxygenation is reducing the habitat layer for cold-water species, while warming has already caused the disappearance of the cold intermediate layer - with which these species are associated - dissolving it into surrounding waters at temperatures around 9°C. Further warming of surface waters may lead to the degradation of cold-water species assemblages that form the trophic foundation of the Black Sea's current ecosystem. A significant transformation is expected due to the increasing dominance of warm-water and eurythermic species.
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