Vodní měkkýši Malé Bečvy (Česká republika) [Aquatic molluscs of the Malá Bečva River (Czech Republic)

Abstract

This paper brings a review of a malacological survey of Malá Bečva River (Central Moravia, Czech Republic). Malá Bečva is a canal 18 km long and approximately 7 m wide, which runs from the Bečva River near Troubky and flows into the Mostěnka stream (influent to the Bečva River) in altitude 190 m. Aquatic molluscs sites were studied in 2007 at 9 sites. Altogether 23 species of aquatic molluscs (9 gastropods, 14 bivalves) were found. Except non-native species Potamopyrgus antipodarum, which is rare in Moravia, only the occurrence of common and widespread gastropods was documented, while research based on bivalves provided more interesting results. Large populations of three endangered species Unio crassus, Pisidium amnicum, and P. moitessierianum were documented. Population of Unio crassus was estimated at 5000-20000 individuals. This species and also Pisidium amnicum occurred only in the upper part of the Malá Bečva River from Troubky to Chropyně. Aquatic malacofauna of this part showed similarity with Strhanec Canal, which is canal of the Bečva River situated less than 10 km upstream of the Malá Bečva River. Bivalves Unio tumidus, Sinanodonta woodiana, Sphaerium rivicola, S. corneum and also Anodonta cygnea and Pseudanodonta complanata occur only downstream of Chropyně. This change of the malacofauna is probably caused by high nutrient tributary flows into the Malá Bečva River near Chropyně.