The nature of biodiversity in hypogean waters and how it is endangered

The specialised aquatic hypogean, i.e. stygobiotic, fauna has been recognis ed in some regions moderately rich. Slovenia, the broader Dinaric region, a nd Europe are particularly rich with about 7-8% of all Metazoa and about 40 % of Crustacea species being stygobionts. The hypogean biotic diversity is in general predominantly a crustacean diversity. The high number of stygobi ont Crustacea-Malacostraca species can be explained by the near absence of Insecta as well as by their high endemicity and sometimes additional specia lisation, i.e. the spatial and ecological partition of the environment by t he species. Although one cave system may exceptionally shelter up to 40 sty gobiont species, they are distributed there into separate associations. Amo ng more than 2000 described stygobiontic Malacostraca species, which includ e close to 950 Amphipoda, the species numbers within some genera are very h igh (e.g. Niphargus with 275 spp.). With 10 orders represented the higher t axonomic diversity of stygobiont Malacostraca matches that of fresh waters or the sea. Comparison of some faunas shows that the limiting factors for b iodiversity might be the lower ecological diversity of habitats and restric ted food resources underground, both brought about to a high degree by the darkness and absence of plants. Being K-strategists, stygobionts are endang ered by any sudden changes in their environment. In the case of an increase d food input by modest organic pollution, they can be outcompeted by energe tically demanding but competitively stronger recent immigrants from surface .