Biogeography and relevant ecological drivers in spring habitats: A review on ostracods of the Western Palearctic

Springs are relevant environments from an ecological point of view. The microhabitat-mosaic structure of these ecotones often harbors high biodiversity. Due to the temperature stability of permanent springs and to the persistence over geological time scales of their aquifers, these environments may act as refugia and as potential speciation sites for aquatic fauna. In this study, we review the current knowledge on the diversity and distribution of ostracods associated with ambient springs in the Western Palearctic area, and on the ecological factors that have been reported to affect their occurrence. Literature mining revealed 37 papers, allowing to gather information on 92 ostracod taxa belonging to 31 genera, found in 612 springs out of a total of 743. More detailed information available from 20 studies carried out in the Central-Eastern Alps and Northern Apennines allowed us to conduct a focus study on a more restricted geographic area. Several species have very low frequency, occurring in just one or two springs. Rare or endemic species were frequent, whilst only one non-native species (Chlamydoteca incisa) was found. Species richness varied from 1 to 9, and it was greater in pool springs than in flowing springs and seepages. Correspondence analysis on the presence-absence data unveiled biogeographical patterns in spring ostracod community composition. The variation in community composition was partly organised along altitudinal, latitudinal, water-temperature, and conductivity gradients, and spring typologies affected assemblage structure as well. Springs are important areas for biodiversity conservation at the continental and regional scale. Nevertheless, relatively few investigations have dealt with the human impacts on springs and their biota, and conservation guidelines are largely missing.