SUMMARY1. Using species distribution data from 111 aquifers distributed in nine European regions, we examined the pairwise relationships between local species richness (LSR), dissimilarity in species composition among localities, and regional species richness (RSR). In addition, we quantified the relative contribution of three nested spatial units -aquifers, catchments and regions -to the overall richness of groundwater crustaceans. 2. The average number of species in karst and porous aquifers (LSR) varied significantly among regions and was dependent upon the richness of the regional species pool (RSR). LSR-RSR relationships differed between habitats: species richness in karstic local communities increased linearly with richness of the surrounding region, whereas that of porous local communities levelled off beyond a certain value of RSR. 3. Dissimilarity in species composition among aquifers of a region increased significantly with increasing regional richness because of stronger habitat specialisation and a decrease in the geographic range of species among karst aquifers. Species turnover among karst aquifers was positively related to RSR, whereas this relationship was not significant for porous aquifers. 4. The contribution of a given spatial unit to total richness increased as size of the spatial unit increased, although 72% of the overall richness was attributed to among-region diversity. Differences in community composition between similar habitats in different regions were typically more pronounced than between nearby communities from different habitats. 5. We conclude by calling for biodiversity assessment methods and conservation strategies that explicitly integrate the importance of turnover in community composition and habitat dissimilarity at multiple spatial scales.

We examined taxonomic and geographic patterns of the obligate groundwater fauna (i.e. stygobiotic fauna) by assembling in a distributional data base all species occurrences reported from France since 1805. A simulated annealing algorithm was used to identify conservation targets. Until the 60s, biological surveys were restricted to caves but the proportion of sampling sites in unconsolidated sediments increased from 1 to 16% over the last 40 years. A total of 380 species and subspecies in 40 families were collected, 70% of which being restricted to France. As observed in other temperate regions, the stygobiotic fauna was dominated by crustaceans (65% of species) and molluscs (22%). The cumulative number of species did not level off over time, clearly showing that biodiversity was underestimated. Temporal trends in the cumulative number of obligate groundwater and surface water species suggested that groundwater comprised more crustaceans than surface freshwater. Endemism was high although the geographic range size of species increased as distributional data accumulated. Of 380 species, 156 were known from a single 400-km 2 cell, among which 73% were located in the southern third of France. The distribution map of species richness changed dramatically over time, indicating that the location of richness hotspots was sensitive to sampling effort. Less than 2% of the French landscape was needed to capture 60% of known species. Thus, a large proportion of species could be protected by focusing habitat conservation efforts on a few complementary species-rich aquifers located in distinct regions.

De nombreuses données existent sur la faune aquatique souterraine de France mais elles sont encore dispersées. Depuis 2002, un effort a été entrepris pour rassembler sous la forme d'une base de données, les informations disponibles concernant la distribution de cette faune aquatique souterraine de France. Un premier bilan en est présenté dans cet article. La base comprend actuellement 381 espèces et sous-espèces correspondant à plus de 5700 enregistrements. Cette diversité place la faune française parmi l'une des plus riches faunes aquatiques souterraines d'Europe. Le bilan réalisé montre que l'état actuel des connaissances est très hétérogène en fonction du groupe zoologique considéré et de la région étudiée. La base de données sera utilisée pour identifier les régions à forte de biodiversité (richesse spécifique, endémisme) et les aires françaises de conservation prioritaires. Elle permettra également de formuler et de tester différentes hypothèses sur l'origine et les facteurs responsables de la biodiversité aquatique souterraine.