Globalisation in marine ecosystems: the story of non-indigenous marine species across European seas

The introduction of non-indigenous species (NIS) across the major European seas is a dynamic non-stop process. Up to September 2004, 851 NIS (the majority being zoobenthic organ- isms) have been reported in European marine and brackish waters, the majority during the 1960s and 1970s. The Mediterranean is by far the major recipient of exotic species with an average of one introduction every 4 wk over the past 5 yr. Of the 25 species recorded in 2004, 23 were reported in the Mediterranean and only two in the Baltic. The most updated patterns and trends in the rate, mode of introduction and establishment success of introductions were examined, revealing a process similar to introductions in other parts of the world, but with the uniqueness of migrants through the Suez Canal into the Mediterranean (Lessepsian or Erythrean migration). Shipping appears to be the major vector of introduction (excluding the Lessepsian migration). Aquaculture is also an important vector with target species outnumbered by those introduced unintentionally. More than half of immigrants have been estab- lished in at least one regional sea. However, for a significant part of the introductions both the establishment success and mode of introduction remain unknown. Finally, comparing trends across taxa and seas is not as accurate as could have been wished because there are differences in the spatial and taxonomic effort in the study of NIS. These differences lead to the conclusion that the number of NIS remains an underestimate, calling for continuous updating and systematic research.