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

Abstract

The specialised aquatic hypogean, i.e. stygobiotic, fauna has been recognised in some regions moderately rich. Slovenia, the broader Dinaric region, and 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 stygobiont Crustacea–Malacostraca species can be explained by the near absence of Insecta as well as by their high endemicity and sometimes additional specialisation, i.e. the spatial and ecological partition of the environment by the species. Although one cave system may exceptionally shelter up to 40 stygobiont species, they are distributed there into separate associations. Among more than 2000 described stygobiontic Malacostraca species, which include close to 950 Amphipoda, the species numbers within some genera are very high (e.g. Niphargus with 275 spp.). With 10 orders represented the higher taxonomic diversity of stygobiont Malacostraca matches that of fresh waters or the sea. Comparison of some faunas shows that the limiting factors for biodiversity might be the lower ecological diversity of habitats and restricted food resources underground, both brought about to a high degree by the darkness and absence of plants. Being K-strategists, stygobionts are endangered by any sudden changes in their environment. In the case of an increased food input by modest organic pollution, they can be outcompeted by energetically demanding but competitively stronger recent immigrants from surface.