There are 1966 animal species found in the Black Sea. These include some Mediterranean animal species for which it is believed that it is not possible to adapt fully to the living conditions in the Black Sea.

There are 1966 animal species found in the Black Sea. These include some Mediterranean animal species for which it is believed that it is not possible to adapt fully to the living conditions in the Black Sea.

 

Fish and mammals pass actively from the Sea of Marmara into the Black Sea. Some of them stay forever here and preserve their abilities to reproduce, while others enter only for a limited period of time to find food, after which they go back to the Sea of Marmara to reproduce. The Black Sea is inhabited by approximately 180 species of fish and three species of dolphins. The endangered monk seal lived here till the last quarter of the 20^th century.

Plankton sea organisms, which may not swim, flow with the sea currents. They enter with the current coming from the Bosporus, after which, a large part of them joins the surface sea currents. Thus, they disseminate in the different parts of the sea. In the Black Sea, the Mediterranean sea bottom fauna has gradually occupied the whole shelf zone. It is irregularly distributed but we can distinguish three fauna regions:

 

Because of the fact that temperatures in the Black Sea are comparatively lower than those in the Mediterranean, it is inhabited by more cold-hardy Mediterranean species, most of which are species of North Atlantic origin. Thus, for example, from all sponges living in the Black Sea  82.8 % are from the North Atlantic, while only 17.2 % are Mediterranean endemites.

Because of the connection the Black Sea had in the past with the Caspian Sea, there are a number of Caspian relicts. The greatest number of autochthonous species are seen among crustaceans, worms, mussels, snails and fish. About 80 % of the relict fauna is originates from the sea. It is assumed that it is a distant relative of the fauna from the ancient Tethys Ocean.