Alien species in the Mediterranean Sea by 2012. A contribution to the application of European Union’s Marine Strategy Framework Directive (MSFD). Part 2. Introduction trends and pathways

More than 60 marine non-indigenous species (NIS) have been removed from previous lists and 84 species have been added,bringing the total to 986 alien species in the Mediterranean [(775 in the eastern Mediterranean (EMED), 249 in the central Mediterranean(CMED), 190 in the Adriatic Sea (ADRIA) and 308 in the western Mediterranean (WMED)]. There were 48 new entriessince 2011 which can be interpreted as approximately one new entry every two weeks. The number of alien species continues toincrease, by 2-3 species per year for macrophytes, molluscs and polychaetes, 3-4 species per year for crustaceans, and 6 speciesper year for fish. The dominant group among alien species is molluscs (with 215 species), followed by crustaceans (159) and polychaetes(132). Macrophytes are the leading group of NIS in the ADRIA and the WMED, reaching 26-30% of all aliens, whereas inthe EMED they barely constitute 10% of the introductions. In the EMED, molluscs are the most species-rich group, followed bycrustaceans, fish and polychaetes. More than half (54%) of the marine alien species in the Mediterranean were probably introducedby corridors (mainly Suez). Shipping is blamed directly for the introduction of only 12 species, whereas it is assumed to be themost likely pathway of introduction (via ballasts or fouling) of another 300 species. For approximately 100 species shipping is aprobable pathway along with the Suez Canal and/or aquaculture. Approximately 20 species have been introduced with certaintyvia aquaculture, while >50 species (mostly macroalgae), occurring in the vicinity of oyster farms, are assumed to be introducedaccidentally as contaminants of imported species. A total of 18 species are assumed to have been introduced by the aquarium trade.Lessepsian species decline westwards, while the reverse pattern is evident for ship-mediated species and for those introduced withaquaculture. There is an increasing trend in new introductions via the Suez Canal and via shipping.