Predictors of Distribution and Diversity of Rare, Protected, and Endangered Freshwater Mollusks in Rivers With Various Land Use in the Context of Environmental Changes

Rivers face multiple stressors that act on biodiversity. In view of global environmental changes, river modifications, deforestation, and pollution, their natural parts are of highest importance in maintaining the biodiversity of mollusks. The study addresses the predictors of rare mollusk species, as they serve as ecological indicators of ecosystem quality and drivers of ecosystem pollution in agricultural, urban, and forest catchments. Analyses of environmental predictors and mollusk distribution were provided, and the model of multivariate canonical correspondence analysis was constructed. The pH of the water was relatively high, indicating alkaline conditions, whereas conductivity was low, indicating no salty influences in river basins. The study revealed the occurrence of species globally threatened (EN), vulnerable in Europe (VU), least concern species (LC), or legally protected in Poland, for example, <i>Unio crassus, Anodonta cygnea</i>, and <i>Unio tumidus</i>. Mollusks showed a high positive association with 13 predictors that reflected the variety of substrates, river and water parameters, and debris. As shown by CCA results, they also avoided rivers in urban catchments. The results provide new data for managing areas, and the specifics are easy to extrapolate to other contexts. Mollusks occurrence in freshwaters has decreased dramatically, placing them among the most threatened animals on Earth. Overall, this study highlights the complex interactions between environmental conditions and mollusk diversity.