SPECIES RICHNESS OF MICROCRUSTACEA IN SUBTERRANEAN FRESH-WATER HABITATS - COMPARATIVE-ANALYSIS AND APPROXIMATE EVALUATION

Among terrestrial biomes the groundwater domain is generally considere d to be a species poor environment. This view results, mainly, from th e large geographic scale faunistic surveys (tens and hundreds of kilom etres) and the traditionally coarse spatial scale (i.e. macroscale lev el) of ecological analysis. This view has been challenged by MARGALEF (1993) who suggests that high diversities are to be expected in the su bterranean environment comparable to those found in the deep sea becau se of environmental similarities, e.g. low energetic resources. During the last twenty years long-term ecological research on much smaller s cales, i.e. metres to hundred metres for interstitial media, a mesosca le approach, or kilometre size for karat systems was carried on. Long- term projects on limnic subsurface systems have shown that the species richness (SR) of the microcrustacea (Harpacticoida, Cyclopopoida, Ost racoda) is much higher than previously considered. Details on Harpacti coida of the alluvial bedsediments of a Pyreneean brook, the Lachein, and on Ostracoda of the alluvial sediments of the Danube plain (the ph reatic zone), near Vienna, are presented. The SR values of the interst itial microcrustacea obtained through investigations at a mesoscale le vel are comparable to those of karstic and/or surface freshwater benth ic water systems they are lower than those of the deep-sea data sets f or equivalent crustacean groups at a similar scale of investigation. F rom the data presented we infer the following points: (a) The subterra nean waters are much more rich in species than earlier accepted, at le ast for some organismic groups like the microcrustacean cope pods and ostracods. (b) Hence, to describe the still unknown fauna it is approp riate to sample the subsurface waters at an ecological scale. (c) Only studies during long-term ecological projects and with intensive, quan titative, sampling programmes allow a correct evaluation of the subter ranean faunal diversity. (d) The species richness of a given subsurfac e site is strongly dependent on the structure of the habitats and the functioning of the underlying ecosystems. (e) Finally we consider the rationale for the protection of the subterranean faunal diversity.