Summary 1. The spatial patterns of groundwater biodiversity in Europe remain poorly known, yet their knowledge is essential to understand local variation in groundwater assemblages and to develop sound conservation policies. We explore here the broad‐scale distribution of groundwater biodiversity across Europe, focussing on obligate subterranean species. 2. We compiled published distributional data of obligate subterranean aquatic taxa for six European countries (Belgium, France, Italy, Portugal, Slovenia and Spain), and conducted a detailed biological survey of six regions (one in Belgium, two in France, one in Italy, one in Slovenia and one in Spain). Based on this data set, we mapped spatial patterns of biodiversity in Europe on a cell grid with 0.2 × 0.2 ° resolution. 3. As of mid‐2006, the total number of described stygobiotic species in the six countries was 930 and the total number of genera with at least one described stygobiotic species was 191. The total number of sampling sites where at least one stygobiont had been collected was 4709, distributed in 1228 of the 4668 grid cells covering the study area. 4. Groundwater stygobiotic biodiversity was dominated by Crustacea with 757 species in 122 genera. Insects were represented by only two species of a single genus of dytiscid beetles restricted to south‐eastern France. 5. The geographic distribution of stygobionts was extremely heterogeneous. Stygobionts were recorded in 26% of the 4668 grid cells and only 33 cells had more than 20 stygobiotic species. These 33 ‘hot‐cells’ of groundwater species richness clustered in seven hotspots. 6. Endemicity was very high, with 43% of the total number of stygobiotic species restricted to a single cell, i.e. <500 km2. 7. Hotspots defined by rarity, number of genera, number of genera with only one species known in Europe, or number of monospecific genera differed markedly in ranking from those based on species richness. However, a core of four hotspots emerged in all cases: one stretching across Slovenia and northeastern Italy, one in the French Pyrenees, one in the Cévennes in southern France and one in the Rhine River valley in northeastern France. 8. Unevenness in stygobiont distribution cannot be explained solely by unevenness in sampling effort. This is indicated in particular by the fact that our comprehensive sampling survey roughly matched the level of taxonomic richness of the studied regions based on previously published information. 9. With sampling effort continuing, a twofold or higher increase in species richness can be expected in several Mediterranean areas, with a potential to discover up to 50% more new species than are currently known in the region.
SUMMARY1. The Pleistocene glaciations during the Quaternary appear to have resulted in an impoverished groundwater fauna in northern Europe. Re-colonisation may have occurred either through long-distance dispersal from unglaciated southern areas or from local refugia. 2. The Belgian groundwater fauna was sampled at multiple sites, and its habitats characterised, to assess whether the composition of present-day stygobiotic assemblages can be attributed to either of these mechanisms. 3. A total of 202 sampling sites were selected in four hydrogeographic units of the Meuse River catchment. Sites were equally divided among the saturated and unsaturated zones of fractured aquifers (karst) and within the hyporheic and phreatic zones of porous aquifers. Seventeen environmental parameters were determined in parallel. 4. More than 140 species were recorded, including representatives of the Amphipoda, Cladocera, Copepoda, Hydrachnidia, Isopoda, Oligochaeta, Ostracoda, Mollusca, Syncarida and Nematoda. Thirty stygobiont species were identified, of which 10 species were new to the Belgian fauna, raising the total number of stygobiotic species in Belgium to 41. 5. The frequency of occurrences of stygobiotic species was always low, with 37% of the sampled sites lacking stygobionts. A few species were exclusive to one hydrological zone, although no statistically significant differences were detected in species richness at any of the four hierarchial levels considered (Meuse catchment = region, hydrogeographic units, aquifer type and hydrological zone). 6. Overall, results suggest that the stygobiotic fauna of Belgium is species-poor and mostly comprises widely distributed species with broad ecological tolerances. This supports the view that eurytopic species re-colonised the area by long-distance dispersal from refugia in southern Europe. The virtual absence of endemic species further suggests that the scenario of an ancient fauna that survived in local refugia is of minor importance.
Four previously unknown hypogean species of cyclopoid copepods were collected in cenotes and wells of the Yucatán Peninsula, Mexico. Diacyclops chakan sp. n. and D. puuc sp. n. differ from their congeners in combining 3-segmented swimming legs, 11-segmented antennules, and legs 1–4 endopodite segment 2 all with 2 setae. Species of Diacyclops rarely occur in tropical regions, and the Diacyclops described here are only the second and third species recorded from Mexico. The benthic D. puuc was found in the large underground reservoir of a cenote. Diacyclops chakan was encountered in such large open subterranean water basins, but more frequently and abundantly in wells.
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