DISTRIBUTION OF ALIEN ZOOBENTHIC SPECIES ON THE SHELF OF THE BLACK SEA

Abstract

The number of alien species in the zoobenthos of the Black Sea increased up to 65 species. Depending on the scale of their distribution in the Black Sea, non-native zoobenthos species are combined into three groups: 1) 5 species have spread in the entire sea, 2) 35 species were found in several areas, and 3) 25 species were found only in one of the areas of the sea. Six areas of the Black Sea shelf have been identified (Varna - Burgas, Danube, Northwestern, Crimean, Caucasian and Anatolian) in accordance with the seasonal and annual values of the thermohaline characteristics. The zoobenthos differed not only in quantity, but also in the composition of non-native species between the six areas of the shelf. The results of multivariate statistical analysis revealed a low level of similarity between these areas of the Black Sea shelf. The greatest similarity in the composition of alien species of zoobenthos was observed for the Danube region with the Varna and Burgas bays, which border each other. The species composition of the alien species of the Caucasian shelf was more similar to the Varna - Burgas and Danube areas than to the neighboring Crimean and Anatolian areas. Spatial gradients of temperature and salinity form hydrological fronts of water masses, which are a kind of ecological barriers and can limit the natural exchange of alien species between shelf areas.