Obligate groundwater fauna of France: diversity patterns and conservation implications

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-km² 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.