Status of alien species in the Mediterranean and Black Sea

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Mediterranean Sea (Figure 19). Ship transportation is the main vector for the alien species with ballast
tanks and hull fouling. Meanwhile, after the opening of the Suez Canal, some species pass to the
Eastern Mediterranean Sea from the Red Sea. It is called lessepsian migration (Por, 1978). Some
commercial species have been intentionally introduced, like the Japanese oyster Crassostera gigas or
the venerid Ruditapes philippinarum, which have also been established in the Mediterranean Sea.
Accidentally introduced Caulerpa taxifolia has also spread around the Mediterranean. All these alien
species dispersed over the Mediterranean have changed marine biodiversity and fisheries in this
unique sea.
The present Mediterranean fauna and flora are a mixture of the Mediterranean and Red Sea biota
components due to the Suez Canal. It is possible to call the eastern Mediterranean Sea a lessepsian
province after this biotic change. Nevertheless, a total of 10 000 to 12 000 marine species have been
recorded in the Mediterranean Sea and this rich biodiversity represents 8–9 percent of the total number
species in the world’s seas (EEA, 2006). It should be noted that the deep sea part of the Mediterranean
Sea is still poorly studied and more potential species may be discovered in the next years if the
research intensity is increased in the region, particularly in the deep basins.
3.2 Main vectors for alien species in the Mediterranean Sea
The main vectors for alien species in the Mediterranean Sea can be described as follows:
a) shipping, ship’s ballast waters, tank sediments, hull fouling, and marine debris;
b) straits: the Kerch and the Turkish Straits System for the Black Sea species and the Gibraltar
Strait for the Atlantic species. These straits also play an important role for the introduction of
the Black Sea originated alien species, such as Liza haematocheila, Mnemiopsis leidyi and
Rapana venosa, and the Atlantic originated alien species, respectively.
c) the Suez Canal: one of the major vectors for the Indo-Pacific originated species or lessepsian
species,
d) intentional or unintentional introduction by humans: this introduction is generally for
aquaculture or aquarium; and
e) besides these main vectors, aquarium, fish baits and other minor vectors should also be
considered.
According to Streftaris et al. (2005), shipping, although it contributed more than aquaculture as a
vector, appears to have had a less significant role (20 percent) in the Mediterranean than the Suez
Canal (52 percent). Galil (2008a) reported 558 and Galil (2009) 573 species from the Mediterranean
Sea. However, this number was estimated as thousands by Por (2009).