Spatial distribution of stygobitic crustacean harpacticoids at the boundaries of groundwater habitat types in Europe

The distribution patterns of stygobitic crustacean harpacticoids at the boundaries of three differentgroundwater habitat types in Europe were analysed through a GIS proximity analysis and fitted toexponential models. The results showed that the highest frequency of occurrences was recorded inaquifers in consolidated rocks, followed by the aquifers in unconsolidated sediments and, finally,by the practically non-aquiferous rocks. The majority of the stygobitic harpacticoid species werenot able to disperse across the boundaries between two adjacent habitats, with 66% of the speciesoccurring in a single habitat type. The species were not evenly distributed, and 35-69% of themoccurred from 2 to 6 km to the boundaries, depending on the adjacent habitat types. The distributionpatterns were shaped by features extrinsic to the species, such as the hydrogeological properties ofthe aquifers, and by species' intrinsic characteristics such as the preference for a given habitat typeand dispersal abilities. Most boundaries between adjacent habitat types resulted to be "breaches",that is transmissive borders for stygobitic harpacticoids, while others were "impermeable walls", thatis absorptive borders. Our results suggest that conservation measures of groundwater harpacticoidsshould consider how species are distributed within the different groundwater habitat types and attheir boundaries to ensure the preservation of species metapopulations within habitat patches andbeyond them.