Our knowledge of the biodiversity of the Southern Ocean (SO) deep benthos is scarce. In this review, we describe the general biodiversity patterns of meio-, macro- and megafaunal taxa, based on historical and recent expeditions, and against the background of the geological events and phylogenetic relationships that have influenced the biodiversity and evolution of the investigated taxa. The relationship of the fauna to environmental parameters, such as water depth, sediment type, food availability and carbonate solubility, as well as species interrelationships, probably have shaped present-day biodiversity patterns as much as evolution. However, different taxa exhibit different large-scale biodiversity and biogeographic patterns. Moreover, there is rarely any clear relationship of biodiversity pattern with depth, latitude or environmental parameters, such as sediment composition or grain size. Similarities and differences between the SO biodiversity and biodiversity of global oceans are outlined. The high percentage (often more than 90%) of new species in almost all taxa, as well as the high degree of endemism of many groups, may reflect undersampling of the area, and it is likely to decrease as more information is gathered about SO deep-sea biodiversity by future expeditions. Indeed, among certain taxa such as the Foraminifera, close links at the species level are already apparent between deep Weddell Sea faunas and those from similar depths in the North Atlantic and Arctic. With regard to the vertical zonation from the shelf edge into deep water, biodiversity patterns among some taxa in the SO might differ from those in other deep-sea areas, due to the deep Antarctic shelf and the evolution of eurybathy in many species, as well as to deep-water production that can fuel the SO deep sea with freshly produced organic matter derived not only from phytoplankton, but also from ice algae.

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SUMMARY1. A possible conservation strategy to minimise the risk of groundwater biodiversity loss due to human activities consists in designing a network of reserve areas at the continental scale that collectively include most groundwater species. To this end, we compared the efficiency of three area selection methods (species richness hotspots, endemism hotspots and complementarity) and examined the influence of spatial constraints (reduced extent and increased aggregation of reserve areas) on the representation of 1059 groundwater species in six European regions. 2. Presence data from a data base elaborated as part of a European initiative on groundwater biodiversity, the PASCALIS project, were referenced onto 4675 grid cells (0.2 by 0.2°). Complementary performed much better than traditional selection methods for maximising species representation in a reserve network arbitrarily limited to 10% of all the cells containing groundwater fauna. It captured 155 more species than areas selected on richness and 77 more species than areas selected on endemism hotspots. 3. Representing species in a specified proportion of their area of occupancy (i.e. 100%, 50% and 10% of the area of occupancy of species occurring in 1, £10, and >10 cells, respectively) required inclusion of 46% of the cells containing groundwater fauna. The reserve network needed to achieve this level of coverage may be too large and fragmented to be implemented and managed in practice. 4. Reduction of the reserve areas to 10% of the landscape containing groundwater fauna and their aggregation into a smaller number of cell clusters resulted in a more realistic reserve network that represented 73.8% (782 species) and 59.1% (274 endemics) of the total number of species and endemics, respectively. 5. We propose several research priorities to improve the design of effective groundwater reserve networks in Europe: (i) devising sampling strategies that reduce uncertainties in the placement of reserves and increase the number of alternative reserve networks and (ii) shifting from a grid-cell selection approach to an aquiferselection approach that incorporates species representation targets, minimum space requirement and also socio-economic costs related to the vulnerability of aquifers and degree of human activity in the catchment.

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.

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