Apennine spring fens support diverse and biogeographically distinctive mollusc assemblages compared with Alpine fens

Alkaline spring fens are biodiversity hotspots supporting species-rich mollusc assemblages, including habitat specialists and glacial relicts. While fen malacofauna is well studied in the Carpathians and Alps, comparable data from southern European mountains remain scarce. We analysed mollusc assemblages from 23 alkaline spring fen plots in the Northern and Central Apennines and compared them with 31 fen sites from the western and central-eastern Alps using standardized quantitative sampling. We recorded 61 species, including nine aquatic taxa. Local species richness did not differ significantly among regions, despite the small extent and isolation of Apennine fens. Richness increased in warmer sites and those with more mineral-rich groundwater, but decreased with elevation. By contrast, fen-specialist richness was higher under colder conditions. Community composition was driven mainly by temperature, with additional regional differentiation reflecting historical and biogeographic factors. Alpine fens more frequently supported cold-adapted glacial relicts, including Vertigo genesii , Pupilla alpicola , and Columella columella , absent from the Apennines. Conversely, the Northern Apennines hosted the southernmost known populations of the late-glacial relict Vertigo geyeri , while the Central Apennines contained isolated populations of Vertigo angustior and Euconulus alderi . Apennine spring fens are therefore important refugial habitats of high conservation value.