ISSN 2075-1117, Russian Journal of Biological Invasions, 2012, Vol. 3, No. 4, pp. 255–280. © Pleiades Publishing, Ltd., 2012. Original Russian Text © T.A. Shiganova, E.I. Musaeva, T.A. Lukasheva, A.N. Stupnikova, D.N. Zas’ko, L.L. Anokhina, A.E. Sivkovich, V.I. Gagarin, Yu.V. Bulgakova, 2012, published in Rossiiskii Zhurnal Biologicheskikh Invasii, 2012, No. 3, pp. 61–99. 255 INTRODUCTION In the 20th century, especially in its second half, the species composition of flora and fauna in the Black Sea underwent significant changes under the influence of various climatic and anthropogenic factors. A global factor is also that nonindigenous species spontane- ously invade or are intentionally introduced into the Black Sea. Among the Ponto-Caspian seas, the Black Sea is most densely connected to the World Ocean via channels and through accelerated shipping. In addi- tion, the modern Black Sea, as the other seas, is influ- enced by the applied activity of humans. As a result, its flora and fauna are modified owing to spontaneous invasion of alien organisms during ship voyages, delib- erate introduction of commercial species, spontane- ous penetrations of new organisms along with delibe- rate species, unauthorized releases of aquarium spe- cies, and penetration and distribution of alien species along newly built canals joining water bodies previ- ously separated from each other. Among the listed vec- tors of penetrations, the most common is invasion of new species with ballast water either after special bal- last tanks are constructed (in Russia, they have been produced since 1980s) or as a part of biofouling cenoses. In the second half of the 20th century, many marine and brackish-water species were accidentally or intentionally introduced into the Black Sea. As a result, the Black Sea became a recipient water body for a large number of alien species of different origin. There have been abnormalities in the functioning of the Black Sea’s ecosystem since 1970s, which resulted in naturalization of many of these alien species. According to the inventory of alien species carried out from 1900 until now, 156 species have established in the Black Sea basin (including limnetic species), or even 161 species if doubtful species are considered. In addition, another 222 Mediterranean species were registered only in the Bosporus region and not included in the composition of alien species. There are still no data on the naturalization of 37 species which have been found recently. These species are also not listed as established (Shiganova, 2009). Until the 1980s, naturalization was mainly observed in temperate-water species. Owing to a rise of the water surface layer temperature in the Black Sea, some warm-water Mediterranean species began to intensely invade its area through the Lower Bosporus Stream (an example showing how thermophilic organ- isms penetrate northward). Previously, the Mediterra- nean species were mainly found in the Bosporus region. They were the most numerous among the rep- resentative of bottom cenoses (zoobenthos and mac- rophytes). Their further distribution was prevented by the lower salinity level in the main part of the Black Sea, the hydrogen sulfide zone under the oxygen-con- taining surface level, and low winter temperatures. Thus, the majority of the Mediterranean species that penetrated into the Black Sea and did not invade the area beyond the Bosporus region are not included in the list of established species of the Black Sea. The Bosporus region is a kind of intermediate “acclimati- zation water basin” allowing naturalization of the Mediterranean species in the Black Sea. Nevertheless, the number of these species has increased during the last decades both in the coastal regions of the south- Increase in Findings of Mediterranean Nonnative Species in the Black Sea T. A. Shiganova a , E. I. Musaeva a , T. A. Lukasheva b , A. N. Stupnikova a , D. N. Zas’ko a , L. L. Anokhina a , A. E. Sivkovich a , V. I. Gagarin a , and Yu. V. Bulgakova a a Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia e-mail: shiganov@ocean.ru b Shirshov Institute of Oceanology, Southern Branch, Russian Academy of Sciences, Gelendzhik-7, Krasnodar krai, Russia Received May 10, 2011 Abstract—Data from our investigations and other publications on the Mediterranean species records in the Black Sea are summarized in the article. The number of such findings has increased in the last decades both in the southern Black Sea, where these species have always occurred, and in the other areas of the Black Sea owing to a rise of the water surface layer temperature and more intense shipping. The vectors of species pen- etrations, their possibility of establishment, and their role played in the ecosystem are discussed. DOI: 10.1134/S2075111712040042 Keywords: Mediterranean species, Black Sea, northward expansion, ballast water