Water mites (Acari: Parasitengona: Hydrachnidia) as inhabitants of groundwater-influenced habitats - considerations following an update of Limnofauna Europaea

Following an update of the survey of the European water mite fauna (Acari: Hydrachnidia) last published by K. Viets (1978), we confirmed the occurrence of 970 species. Based on the evaluation of these data, new bibliography and our own unpublished data, the main habitat preference is determined for each species. The resulting ecological data are analysed with a main focus on species inhabiting groundwater-influenced habitats. No other invertebrate group includes a similarly high share of species with a particular relationship to spring habitats: about one fifth of the European Hydrachnidia has a preference for spring habitats, a total number of 137 (14%) is crenobiontic (living exclusively in springs). The following topics are addressed: (1) the significance of spring habitats for the diversity of water mites − percentage of crenobionts/crenophiles at different geographical latitudes; (2) regional stenotopy − intraspecific differences in habitat preference between populations at different latitudes; (3) communities colonizing springs vs. hyporheic − similarities and differences; (4) evolution of crenobiosis in water mites − potential governing factors; (5) endangered species − direct and indirect anthropogenic threats to the natural diversity of water mites.