Abstract
The distribution patterns of stygobitic crustacean harpacticoids at the boundaries of three different groundwater habitat types in Europe were analysed through a GIS proximity analysis and fitted to exponential models. The results showed that the highest frequency of occurrences was recorded in aquifers 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 were not able to disperse across the boundaries between two adjacent habitats, with 66% of the species occurring in a single habitat type. The species were not evenly distributed, and 35–69% of them occurred from 2 to 6 km to the boundaries, depending on the adjacent habitat types. The distribution patterns were shaped by features extrinsic to the species, such as the hydrogeological properties of the aquifers, and by species’ intrinsic characteristics such as the preference for a given habitat type and dispersal abilities. Most boundaries between adjacent habitat types resulted to be “breaches”, that is transmissive borders for stygobitic harpacticoids, while others were “impermeable walls”, that is absorptive borders. Our results suggest that conservation measures of groundwater harpacticoids should consider how species are distributed within the different groundwater habitat types and at their boundaries to ensure the preservation of species metapopulations within habitat patches and beyond them.
Highlights
The distribution patterns of stygobitic crustacean harpacticoids at the boundaries of three different groundwater habitat types in Europe were analysed through a GIS proximity analysis and fitted to exponential models
Stygobitic harpacticoids were not evenly distributed among groundwater habitat types: 147 species were exclusive of consolidated rocks (CONS), 43 of unconsolidated sediments (UNCONS), and 45 of non-aquiferous rocks (NonAQ)
Zagmajster et al.[36] highlighted that stygobitic crustacean assemblages across Europe are almost entirely replaced within a distance of less than 500 km, but in this case, there was the constraint of the cell size (500 k m2), and the downscaled interpretation remains challenging
Summary
The distribution patterns of stygobitic crustacean harpacticoids at the boundaries of three different groundwater habitat types in Europe were analysed through a GIS proximity analysis and fitted to exponential models. The majority of the stygobitic harpacticoid species were not able to disperse across the boundaries between two adjacent habitats, with 66% of the species occurring in a single habitat type. Our results suggest that conservation measures of groundwater harpacticoids should consider how species are distributed within the different groundwater habitat types and at their boundaries to ensure the preservation of species metapopulations within habitat patches and beyond them. Stygobites are known to be more sensitive to pollutants and temperature increase than their surface-water r elatives[6,7] In this regard, Mammola et al.[8] have recently drawn up a manifesto to bring to light the urgency to better manage quality and quantity of the groundwater resource and conserve its unique biodiversity, being these two aspects inextricably associated. The boundaries between groundwater habitat types may be considered both tangible (structures that can be identified in nature) and relict (arisen from forces no longer operating in the area under study)[26,27]
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