Taxonomic composition and seasonal dynamics of density of phytoplankton, heterotrophic bacteria, ciliates, holoplankton, meroplankton and zoobenthos of mud bottom sediments were studied in 2010–2011 in the Liman ‘Zmeinoe Ozero’. Twelve non-native species of fauna were recorded, that penetrated into the Liman with ships' ballast water (established species – 6, cryptogenic species – 2, casual species – 4). The basic ‘groups of risk’ of invasions are tintinnids infusorians, neritic species of copepods and spionid polychaetes. The attempt to define the degree of vulnerability of the recipient ecosystem to biological invasions is made on the basis of an energy balance method. The prognosis of biological pollution of the north-eastern Black Sea by ships' ballast waters was executed.
