Species composition in assemblages of the family Unionidae Rafinesque, 1820 (Mollusca: Bivalvia) as an indicator of ecological changes in water bodies of Central Polissia, Ukraine

Though Ukraine is one of the countries with insufficient water supply, the northern region of central Polissia has a dense river network. The region’s major rivers – Teteriv, Sluch, Ubort, and Uzh – have undergone significant anthropogenic change. Water pollution has adversely affected their fauna, including the Unionidae (Mollusca: Bivalvia). This study has monitored these changes, and was conducted in two stages. A total of 78 sites with habitats typical for the Unionidae were examined; 45 in 1998–2013, of which 24 were resampled in 2019–2020, and a further 33 were sampled at the same time. Six native species generally characteristic of Ukraine (Unio pictorum Linnaeus, 1758, U. tumidus Philipson, 1788, U. crassus Philipsson, 1788, Anodonta anatina Linnaeus, 1758, A. cygnea Linnaeus, 1758, and Pseudanodonta complanata Rossmassler, 1835) were recorded. While nearly all sites examined in 1998–2013 held some unionids, by 2019–2020, they were recorded in only 62.5% out of the total number of sites in Sluch River basin, 80% in Teteriv River, 40% in Ubort River, and 62.5% in Uzh River. The species richness at sites where unionids were recorded had also declined. Pseudanodonta complanata, recorded in every surveyed basin in 1998–2013, was not observed at any of the sites examined in 2019–2020. In 23 out of the 24 re-examined sites, the extinction of one or more Unionidae species was recorded. It is evident that the role of these large mussels as ecosystem engineers is being compromised.