Abstract
Non-native marine species are both witnesses to, and players in, a rapidly changing world. Their establishment in new environments raises a paradox : how do they manage to settle permanently in habitats where they have not evolved ? Yet this paradox is only apparent. The recurrence of introduction events, often linked to the boom in international maritime trade, is a key factor in their establishment. Ports, where commercial shipping and pleasure boating are concentrated, are hot spots for the introduction of non-native species. Archetypal urban marine habitats, they are also invaluable natural laboratories for observing the evolutionary processes at work in these species : interbreeding between genetically distinct populations, mosaic genetic structuring resulting from local and long-distance dispersal, emergence of ecotypes resulting from hybridization between native and introduced species. These are all dynamics which, without dispersal due to human activities, would have remained very rare, if not impossible. In the marine environment, for example, biological invasions, maritime transport and coastal urbanization - all major facets of globalization - interact closely, fostering the emergence of new ecological interactions and new evolutionary lineages.
