On ecosystem-based regions in the Baltic Sea

Maintenance of diversity of life in the sea and supporting sustainable use of marine resources require an ecosystem approach. The principles of differentiation of large geographical units on the ecosystem basis that could be applied in research and for the assessment and management of ecosystems and resources in the Baltic Sea have not been satisfactorily formulated up to now.Long-term data series collected by the authors and literature sources were used to subdivide the Baltic Sea into regional ecosystem units. Ten regions (Kattegat, Belts and the Sound, Arkona, Southwest, Eastern and Northwest of the Baltic Proper, Gulf of Riga, Gulf of Finland, Bothnian Sea, Bothnian Bay) were differentiated, some of them including sub-regions. They were grouped into three macroregions (the Transition Area, Baltic Proper and Large Gulfs). Hydrodynamic and geomorphological characters and the areas of local populations of organisms developed as a result of adaptation of species to their habitats constituted the main basis of the division. Circular cyclonic density-dependent currents in the deeps facilitate levelling of the conditions and integrate ecosystems in the regions. They are also responsible for the establishment of the regional depots of nutrients. The nutrients for the biological production are supplied mainly via the zones of intense vertical mixing (high-energy zones) to the euphotic layer. The regions differ in essential environmental conditions. In the process of adaptation to their habitats fishes (herring Clupea harengus membras, sprat Sprattus sprattus balticus, cod Gadus morhua callarias, flounder Platichthys flesus trachurus etc.) and other organisms have developed infraspecific units. The ecosystems and infraspecific units of exploited species should be assessed and managed separately if their vital parameters significantly differ from one another.