Introduced Species

Abstract

Five species of diatom algae, ten species of epiphyte-fouling algae, seven species of plankton invertebrates, 21 benthic organisms and three species of fish were introduced during last 100 years and established in the Caspian Sea. In addition, a minimum of 18 species penetrated into the Caspian but did not get established. A very fortunate introduction of two species of invertebrates, polychaetous worms Nereis diversicolor and the bivalve mollusk Abra ovata, into an empty ecological niche became a classic example of successful acclimatization and has obtained worldwide recognition. Just after the opening of the Volga–Don Canal 19 species from the fouling community were introduced in the Caspian Sea, but now planktonic organisms (15 species) predominate among nonindigenous species. On one hand, this is explained by the fact that most of the possible fouling has already penetrated into the Caspian; on the other hand, a new way of organism delivery—with ballast waters—has appeared. The introduced species represented by a small number of species occupy the dominating position by biomass in communities of phytoplankton, zooplankton, benthos, and fouling. All introductions were accompanied by a considerable rearrangement of communities, which was manifested in changes of indices. The most impressive example is the introduction of comb jelly Mnemiopsis leidyi causing the most serious changes in the whole ecosystem.