Non-indigenous species in Northern Europe and the Great Lakes-St. Lawrence River: the importance of geographic origin

Ecosystems all over the world are continuously invaded by new species, which become non-indigenous species (NIS) in the new location. Increasing ship traffic raises the chances for relocations of aquatic species to new regions since shipping is identified as the major transport vector. This dissertation focused on NIS from the North and Baltic Seas and the Great Lakes-St. Lawrence River region. Both regions are connected via frequent transatlantic ship traffic and highly invaded by well documented NIS. Comparing origins of established aquatic NIS in both regions revealed that the systems are highly invaded by species that originate from the Ponto-Caspian region which consists of the Black, Azov and Caspian Seas. Further, observed numbers of established NIS in the two regions were compared to expected numbers of NIS from major donor regions based on the available species pool from donor regions, frequency of shipping transit, and an environmental match between donor and recipient regions. It was discovered that Ponto-Caspian taxa colonized both regions in much higher numbers than expected (Chapter I). A comprehensive study of seven life history traits for each NIS in both regions revealed that certain traits such as dormancy, regeneration and r-strategy are potentially beneficial for invasion success (Chapter II). Global warming as part of a predicted climate change might become a hazard for the survival of some native species, especially in coastal zones which is the habitat of amphipods. Environmental tolerance towards changing temperatures was investigated in three amphipod species and the results revealed that the Ponto-Caspian species Pontogammarus maeoticus has a higher temperature tolerance, especially towards rising temperatures, compared to Gammarus oceanicus, which is native to the Baltic Sea (Chapter III). Hence, with predicted global warming Ponto-Caspian species might be able to compete against native species in the Baltic Sea