Distribution of Alien Zoobenthic Species on the Black Sea Shelf

摘要

The number of alien species in the zoobenthos of the Black Sea increased to 65 species. Depending on the scale of their distribution in the Black Sea, nonnative zoobenthos species are combined into three groups: (1) five species have spread over the entire sea shelf, (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 nonnative species. 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 zoobenthos species was observed for the Danube region to 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 barrier and can limit the natural exchange of alien species between shelf areas.