Distribution patterns and habitat characterization of aquatic Mollusca in the Weidlingbach near Vienna, Austria
Zieritz, A.; Waringer, J.
A total of 186 aquatic Gastropoda (plus 271 empty shells) and 141 Bivalvia (plus 182 empty shells) were caught from October 2003 to August 2004 at the Weidlingbach, a fourth order tributary of the Danube near Vienna, Austria, using quantitative sediment sampling and a catch-per-unit-effort (CPUE) approach at 15 sampling stations from source to mouth. The catch comprised 5 gastropod and 2 bivalve species with the neozoon Potamopyrgus antipodarum (Gray, 1843), together with Radix labiata (Rossmässler, 1835), accounting for 92.6 % of total gastropods; the peaclam Euglesa personata Malm, 1855 was the most abundant Bivalvia species. Snails were most abundant in summer/autumn and strongly diminished during the winter months, whereas mussels maintained stable populations throughout the year. On the microhabitat scale, P. antipodarum significantly preferred boulder and poorly-sorted gravel sediment at current velocities from 10 to 20 cm 1, whereas R. labiata was most abundant at boulders and gravel at 30 to 40 cm. Among mussels, Euglesa casertana (Poli, 1791) preferred habitats with finer and better-sorted sediments and lower current velocities than E. personata. P. antipodarum, R. labiata and Ancylus fluviatilis O. F. Müller, 1774, were most common at higher stream order sites near the mouth characterized by high discharge and coarse sediments densely overgrown by filamentous green algae. The two Euglesa species and Bythinella austriaca (Frauenfeld, 1857), on the other hand, were most abundant near the source at low order sites with low discharge, heavy moss stands and fine, detritus-rich sediments. Mollusc species richness increased in a downstream direction.