Vilken preferens har tjockskalig målarmussla (Unio crassus) för bottensubstrat och vattenhastighet i Storån, Östergötland?
The thick shelled river mussel (Unio crassus) has a fragmented distribution in southern Sweden. It is a threatened and protected species. In both the Swedish red list and the IUCN Red List of Threatened Species Unio crassus is classified as Endangered (EN). Causes for this classification are for instance differentiated bottom substrate and deterioration in water quality. In this study, habitat preferences of Unio crassus were investigated to assist in future restoration work. The environmental parameters that were used to characterize the habitat in sites with or without Unio crassus were water depth, bottom substrate, water velocity, slope, and shading. In this thesis I focused in bottom substrate and water velocity. Sites with Unio crassus had finer bottom substrate and lower water velocity than sites without (t>2.54, p<0.05, t-test). Most of the sites with Unio crassus had a bottom substrate with a size <4 mm and a water velocity around 0.3-0.5 m/s. These two variables were correlated with each other. When the water velocity was higher, the bottom substrate was coarser. These results are in line with other studies, showing that if the bottom substrate is either too coarse or too fine, it could impact Unio crassus. Too coarse bottom substrate probably results in difficulty in burrowing and too fine most likely results in interfering with respiration and feeding. Earlier studies indicate that the water velocity can have a greater impact on unionids than bottom substrate. Because of the correlation between bottom substrate and water velocity it is not easy to disentangle the importance of each factor.