Invading European Seas: Assessing pathways of introduction of marine aliens

Assessing pathways of introduction of marine alien species is essential to identify management options and evaluate management decisions to regulate and prevent new introductions. By critically reviewing related information in scientific/grey literature and online resources, 1369 alien marine species in European seas were identified, of which 1257 were linked to the most probable pathway(s)/vector(s) of introduction. Based on their reported year of introduction, trends in the numbers of introduced species per pathway/vector were assessed on a decadal basis and invasion patterns were described for each pathway. The trend of new introductions of alien species in Europe has been increasing, with more than half of the species probably being introduced by shipping. Marine and inland corridors (primarily because of the Suez Canal) were the second most common pathway of introduction followed by aquaculture and aquarium trade. Aquaculture was the only pathway for which there was a marked decrease in new introductions during the last decade, presumably due to compulsory measures implemented at a national or European level. Introductions via all the other pathways have been increasing, aquarium trade being the pathway with the most striking observed increase. Many more species are expected to invade the Mediterranean Sea through the Suez Canal, as it has been continuously enlarged and the barriers for the invasion of Red Sea species have been substantially decreased. In addition to the existing regulations on aquaculture, the implementation of appropriate management measures on shipping and aquarium trade, e.g. the implementation of the Ballast Water Management Convention, awareness raising among aquarium hobbyists, and also implementation of a stricter legislative framework on the import of non-native aquarium species, could reverse the increasing trend in new introductions.