Status van de Toegeknepen korfmossel Corbicula fluminalis (O.F. Müller, 1774) in Nederland

After their introduction in the second part of the 1980s, both the Prosperity clam Corbicula fluminalis (O.F. Müller, 1774) and the Asian clam Corbicula fluminea (O.F. Müller, 1774) rapidly spread in the Netherlands, especially in the Rhine distributaries and in the river Meuse. However, more recently the Prosperity clam has been reported from a few locations only, while this is not the case for the Asian clam. Our own observations including those from members of the Netherlands’ Malacological Society and a search in databases with monitoring results of national and regional water management authorities, including the website https://observation.org, pointed out that in the period 2010-2017 living specimens of the Prosperity clam were found in small numbers at twelve locations, of which six were located in the Rhine distributaries. The reason for the decline of the species is unclear. Differences between both clams in reproduction strategy and habitat preference are suggested. That the Prosperity clam is still present in the Netherlands could be the result of drift from upstream areas in the Rhine and Meuse basins, since ten of the locations where the Prosperity clam was found are situated in either the rivers themselves or in waterbodies directly connected to them. Our conclusion is that the species should be considered as ‘rare’ in the Netherlands.