High biodiversity in hypogean waters and its endangerment - The situation in Slovenia, the Dinaric Karst, and Europe

Of approximately 12,600 aquatic animal species, registered in 1978 in Europ e, more than 200 were facultative cave dwellers, approximately 1,000 specie s (in 1998 already 2,000 taxa) or 8%, were specialized stygobionts. More th an half are Crustacea. The relatively high number of crustacean hypogean sp ecies is rendered possible mainly by (1) the absence of their insect compet itors as well as (2) spatial partition due to the small distribution areas of most stygobionts. Slovenia, with approximately 200 taxa in its 20,000 km (2), has the highest density, and the Dinaric area with nearly 400 taxa in its only 153,400 km(2) has the highest absolute number of stygobiont taxa k nown in the world. The situation is similar for terrestrial cave faunas. The crustacean diversity is mostly a result of ecological and morphological diversification within a few genera (e.g., Niphargus, Proasellus, Monolist ra). However, higher taxa (families, orders) are well represented. Besides some non-specialized newcomers to hypogean habitats, some ubiquitous specie s (e.g., Asellus aquaticus, Synurella ambulans) possess a number of isolate d hypogean populations that are troglomorphic to varying degrees. Hypogean species are endangered by urbanization and other uses of the sensi tive karst landscape. Although a slight organic pollution of the energy poo r cave waters is favourable to their inhabitants, it may enable invaders fr om the surface to outcompete troglomorphic specialists in sinking rivers. C onservation of cave species is very demanding, since it requires protection of the whole drainage areas on the surface.