Origin and vectors of introduction of exotic molluscs in Greek waters

Exotic species of macrophytes, invertebrates and fish have become increasingly prominent in most coastal habitats in the Mediterranean Sea, the Greek waters included, over the last decades. It is well established that the introduction of non-indigenous species has significant ecological as well as economic impact in the Mediterranean Sea. A review of the exotic molluscan records in Greek waters revealed a total of 26 species (16 Gastropoda, 10 Bivalvia). Nine species are of Indo-Pacific and Erythrean origin, and are already well established in the Eastern Mediterranean. The occurrence of these species in the Greek Seas is attributed to progressive penetration through the Suez Canal, the so-called Lessepsian migration. Four species, namely the gastropods Nerita sanguinolenta, Haminoea cyanomarginata, Melibe fimbriata and the bivalve Pseudochama corbieri, are Red Sea endemic and Indo-Pacific biota, which have been first sighted in Greek waters and to date have a limited distribution in the entire Mediterranean. Another four species, the gastropods Crepidula fornicata and Polycerella emertoni and the bivalves Petricola pholadiformis and Mya arenaria, which originate from the Atlantic and occur in ports/lagoons, may have entered via shipping and/or aquaculture. The gastropods Strombus persicus and Rapana venosa and the bivalves Anadara demiri and Crassostrea gigas are of Pacific, Indian Ocean or Persian Gulf origin and the vector of their introduction, though not documented, is presumed to be shipping or aquaculture. The rate of molluscan introductions in Greek waters is increasing exponentially with time : 13 out of the 26 species have been recorded since 1990, and further studies may reveal many more.