Invasive zebra mussel (Dreissena polymorpha) threatens an exceptionally large population of the depressed river mussel (Pseudanodonta complanata) in a postglacial lake

Freshwater mussels are in decline worldwide, with the depressed river mussel Pseudanodonta complanata being one of the rarest and most endangered species in Europe. Invasive mussels are suspected to be an important factor of decline, but there is little information on their interaction with native species.
This study analysed densities, depth distribution and individual sizes and weights in one of the largest known populations of P. complanata in Europe in relation to the co-occurring invasive zebra mussel Dreissena polymorpha and other mussel species, using a systematic transect analysis.

P. complanata was the dominant unionid species in Lake Siecino reaching densities of up to 26 ind. m-2, with half of the specimens found at a water depth of 2.0 – 4.0 m. Densities were highest on sandy substrates in areas of underwater currents. In contrast, 67% of native U. tumidus were found at depths < 1 m, indicating different habitat preference.
 In the study area, 91% of P. complana...