The impact of an introduced bivalve (Corbicula fluminea) on the benthos ofa sandy stream

1. The effect of an exotic, burrowing bivalve (Corbicula fluminea) on the b enthic fauna of a sandy-bottomed stream was assessed by field and laborator y experiments. Corbicula differs from other freshwater, non-native bivalves in that it both filter- and pedal-feeds and thus has the potential to infl uence the streambed community in different ways. 2. In the field, cages were used to vary the abundance of Corbicula in the streambed. Increasing abundance of Corbicula was negatively associated with the abundance of benthic bacteria and flagellates but had no apparent effe ct on other protists or meiofauna. 3. In the laboratory, we compared the effect of Corbicula on the benthic co mmunity when the bivalves were able both to filter- and pedal-feed with tha t when they were able only to filter-feed. Bivalves restricted to filter-fe eding were placed in sediment lacking benthic fauna and organic matter, the n the benthos in nearby natural sediment was compared with the community pr esent when Corbicula was able to move freely through the sediment and both to filter- and pedal-feed. Corbicula able to pedal-feed were again associat ed with a decreased abundance of benthic flagellates and bacteria, as well as diatoms.