• Energy Research

During 2009–2011, 50 points of the Daube River Basin were surveyed. In 23 of them, seven species of Unionidae were recorded: U. pictorum, U. tumidus, U. crassus sensu lato, A. anatina, A. cygnea, P. сomplanatа and S. woodiana, which is an invasive species. Th e index of occurrence of freshwater mussels in general was 100 % in the Lower Danube River (5 study areas), 42 % in Tisa River (31 study areas), 33.3 % in Seret River (3 study areas), 36 % in Prut River (11 study areas). Th e index of occurrence of species was rather low: 24 % of A. anatina, 22 % of U. tumidus, 22 % of U. crassus, 16 % of U. pictorum, 14 % of P. complanata, 14 % of S. woodiana, and 2 % of A. cygnea. U. crassus was not found in the Lower Danube river, while A. cygnea was found only there outside the main watercourse. Th e invasive species S. woodiana occurred in the Lower Danube River and in the sub-basin of Tisa River (with 83 % and 20 % frequency, respectively. Th e mean values of population densities ranged from 1.00 (A. cygnea) to 6.14 ind./m2 (S. woodiana), and the mean biomass varied from 1.14 (P. сomplanatа) to 797.54 g/m2 (S. woodiana).