Assessment of the distribution and population characteristics of Musculium lacustre Müller, 1774 (Mollusca, Bivalvia, Sphaeriidae) in anthropogenically altered aquatic landscapes of the northern right bank of the Dnipro River in Ukraine

Abstract Today, the rapid disappearance of bivalves in European water bodies is a matter of serious concern. The state of study of mollusks of the family Sphaeriidae in Europe, including Ukraine, is considered insufficient, which does not allow to assess their resources, develop measures for protection and restoration of their numbers. The paper assesses the distribution and frequency of occurrence of the small bivalve Musculium lacustre Müller, 1774 (Mollusca, Bivalvia, Sphaeriidae) in the anthropogenically altered aquatic landscapes of the northern right bank of the Dnipro River of Ukraine. This species is considered to be quite eutopian, but in the surveyed region it shows a clear tendency to decrease the frequency of occurrence and population density of individuals. The reason for this situation is the disappearance of typical habitats due to the transformation of rivers into a system of ponds and reservoirs as a result of dam construction and pollution. Out of 232 sites analyzed, M. lacustre was found in the Pripyat sub-basin in only 5 sites, and in the Teteriv basin (Middle Dnipro sub-basin) in only 2 sites (the frequency of occurrence in these sub-basins is 4% each, and the overall figure for the sampling area is 3%. The maximum population density was 21 in the Hnylopyat River, 11 in the Gusak River, and 1-3 ind./m 2 in other sampling sites, although according to literature data, in the last century it could reach several thousand per m 2 in Ukraine. Found in rivers and streams, it prefers flowing areas.