Filtration and Respiration Rates of Two Unionid Species and Their Impact on the Water Quality of a Lowland River

Abstract

As a consequence of their filter-feeding activity, mussels produce a zone around them that is depleted in suspended particles. As the inhalant and exhalant openings of freshwater mussels are generally situated adjacent to each other, this effect may deteriorate the efficiency of filter feeding in standing waters (O’Riordan 1993; Lenihan et al. 1996). In running waters, however, water is permanently mixed by turbulent flow, so that no vertical food gradients may be produced. Therefore, streams and rivers are favourable habitats for freshwater mussels, which may there dominate the total biomass of benthic invertebrates. In streams and small rivers in the uplands of Europe, the great populations of unionid mussels that once lived there are mostly extinguished. However, in the lowlands there are still plankton-rich lake outlets or larger rivers, where this rich nutritional resource is exploited by large populations of unionid mussels of the genera Unio, Anodonta and Pseudanodonta (Unionidae) (Kasprzak 1986). In these type of streams, a second aspect favours mussel colonization, which is the absence of catastrophic spates, which may affect mussel populations in the uplands through the mobilization of bed sediments, and physical abrasion or cracking of the shells.