The invasive Corbicula species (Bivalvia, Corbiculidae) and the sediment quality in Flanders, Belgium

Corbicida species, C. fluminea and C. fluminalis (Bivalvia, Corbiculidae) started to invade the Belgian section of the river Meuse, and some of the connected canals in the early 1990s. During 1999 and 2000, sediment samples from 33 watercourses in Flanders, Belgium were collected and analysed. The clam was found in six watercourses. C. fluminea was present in all of the six watercourses, whereas C. fluminalis was found only in three canals. Overall, the density of Corbicula species averaged around 200 individuals/m(2), except for four places connected with the river Meuse where the density was higher than 1000 individuals/m(2). In 63\% of the invaded sites, the clam was the most abundant taxon. Most of the sites (89\%) colonised by Corbicula species were (slightly to heavily) polluted by organic contaminants and heavy metals. However, no correlation between the clam density or proportion and the quality of the sediment was observed. Including Corbicula species in the Biotic Sediment Index calculation altered biological sediment quality classification in 52\% of the cases. The results show that colonisation of Corbicida species in Belgium is continuing to expand.