Neobiota may have a competitive advantage over native species due to a lack of enemies as predators or pathogens. In the North Sea region, it has been assumed that no parasites are to be found in marine introduced species. In an attempt to test this assumption, we investigated introduced molluscs for metazoan parasites near the island of Sylt (Wadden Sea): the Pacific oyster Crassostrea gigas, the American razor clam Ensis americanus and the American slipper limpet Crepidula fornicata.No natural infection was found in the gastropod C. fornicata but we found native trematodes infesting tissues of the bivalve C. gigas and E. americanus [1]. These results implicate that introduced bivalves are not necessarily free of detrimental parasites but can serve as hosts in complex parasitic life cycles [2]. Introduced species may thus affect parasite populations by influencing the fate of infectious stages which either end in dead end hosts or complete their life cycle by adding new linking hosts. Furthermore, parasite burdens are diverted providing probably a relief for native host species [1].Future studies should consider these implications to arrive at a better understanding of the interplay between the introduced species and pathogens.References[1] Krakau M, Thieltges DW and Reise K (2006) Native parasites adopt introduced bivalves of the North Sea. Biological Invasions 8 (4): 919-925[2] Thieltges DW, Krakau M, Andresen H, Fottner S and Reise K (2006) Macroparasite community in molluscs of a tidal basin in the Wadden Sea. Helgoland Marine Research, Online First. DOI: 10.1007/s10152-006-0046-3