The Balkan region is inhabited by hundreds of endemic freshwater molluscs, mainly small hydrobiids, and is considered a hotspot of global biodiversity. On the other hand, data about their distribution as well as data about distribution of more common and widespread molluscs have been still sparse and complete inventories of the mollusc communities of many areas are missing. The river Cetina is the largest river in the Adriatic part of Croatia. Aquatic non-marine molluscs of this river were studied in 2009, 2018-2022 and 2024. The quantity of distributional data were obtained thus the main objective of this study was to summarize and analyse recent distributional data on freshwater and brackish molluscs with special focus on endemic or threatened species. In total 35 aquatic molluscs were found at 26 sites at Cetina including its the biggest tributary Ruda. Mollusc communities at individual sites were usually composed of 5-15 species. Molluscs Theodoxus fluviatilis, Holandriana holandrii, Bithynia tentaculata, Radomaniola spp., Emmericia patula, Stagnicola fuscus, Physa fontinalis, Ancylus fluviatilis, Euglesa casertana and E. subtruncata were the most often recorded taxons found at least at half of studied sites. Notable is the occurrence of gastropods Dalmatinella simonae, Horatia klecakiana, Islamia sp. and several species of genus Radomaniola. No bivalves from the family Unionidae were found in the main stream of Cetina or Ruda. Numerous populations of non-native gastropod Potamopyrgus antipodarum in Cetina were found. The most serious impact is the change in the water regime caused by the construction of dams, which most likely had an impact on changes in the mollusc communities.
Luboš Beran (Thu,) studied this question.