Abstract. The Asiatic clam Corbicula fl uminea invaded the river Rhine in the Netherlands and Germany in the 1990s. It was fi rst recorded in Switzerland (Basel) in 1995. We examined the distribution of the clam at 76 sites along the bank of the river Rhine, in three fi rst order tributaries (Wiese, Birs, Ergolz) and in the Canal de Huningue in the region of Basel (Switzerland, Germany and France) in 2003. C. fl uminea was found in the river Rhine and in the Canal de Huningue, which obtains water from the river Rhine. C. fl uminea was recorded 22 km upstream of Basel, but not any further. This indicates a mean upstream spread of 2.4 km per year. It had not yet colonized any of the fi rst order tributaries examined. The clam was most abundant on fi negrained substrates (sand) with slowly fl owing, shallow water. This fi nding was confi rmed by a substrate choice experiment in the river Rhine. Our results show that the spread of C. fl uminea in the river Rhine does not stop where cargo shipping ends. Passive dispersal by waterfowl and recreational boating may facilitate further upstream spread. C. fl uminea might be less successful in colonizing rivers with rapid current such as fi rst order tributaries. These are assumed to serve as refuges for native molluscs.
The spread of alien molluscs is a serious threat to native biodiversity in fresh waters. Alien freshwater molluscs may deplete the resources of native species and alter the physical structure of the habitat through their shell mass. These changes might have both positive and negative effects on native community members. We investigated the native macroinvertebrate community in relation to the densities of four alien mollusc species (Corbicula fluminea, Dreissena polymorpha, Potamopyrgus antipodarum and Lithoglyphus naticoides) in a sandy flat of Lake Neuchâtel, Switzerland. The habitat examined was dominated by these alien mollusc species. The abundance of the alien molluscs did not directly impact the native community assembly. However, C. fluminea and D. polymorpha influenced the composition and diversity of native macroinvertebrates by transforming the sandy substratum into a partly hard substratum habitat. Substantial differences in community composition between shallow (\3.5 m) and (C5 m) deep sites were recorded. At shallow sites, the abundance of D. polymorpha was significantly reduced as a result of depth-selective feeding of ducks. A controlled shell decay study revealed that shells of alien molluscs (C. fluminea, D. polymorpha) persist for a longer period in the sediment than those of native molluscs. Consequently, shells of alien molluscs have a long-lasting impact by modifying the sandy habitat. This form of ecosystem engineering favours the occurrence of several native taxa, but is disadvantageous for other taxa with specific habitat requirements, and thus can be regarded as an indirect impact of competition.
Research on the ecology and impacts of the zebra mussel (Dreissena polymorpha) has developed in parallel with the long history of their spread across Europe and to North America. There is less scientific knowledge however about the quagga mussel (Dreissena rostriformis bugensis). The recent spread of both zebra and quagga mussels to the Western states of the USA, has spurred on dreissenid research. The 17th International Conference on Aquatic Invasive Species (ICAIS), was held in San Diego, California in September 2010. This special edition of Aquatic Invasions includes topical research presented at ICAIS and also extra subsequent papers on ecology, risk assessment and control of various aquatic invasive species in different parts of the globe.
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