Climatically induced temperature instability of groundwater-dependent habitats will suppress cold-adapted Clitellata species

Groundwater-dependent ecosystems are recognized as biodiversity hotspots, being, apart many negative human impacts, highly threatened also by ongoing climate warming. Clitellata (Annelida) are dominant invertebrates of permanent fauna in spring habitats, representing a heterogeneous group including both specialized cold-stenothermic and ubiquitous eurythermic species. Therefore, they seem to be a good model group to compare the effects of local springwater temperature (recorded in situ by data loggers) and mesoclimate (i.e., local) air temperature. By the analysis of clitellate assemblages at 41 isolated Western Carpathian spring fens, we found that their species composition was significantly driven by mesoclimate air temperature and springwater temperature independently of other important environmental variables (i.e., water mineralization, oxygen content, and total organic carbon). The effect of various environment-related and temperature-related variables on the number of clitellate species was analyzed separately for two categories, that is, substrate dwellers (endobenthic species) and surface-active (epibenthic) species. The decrease of the number of species with the increasing amount of inorganic particles <500 µm in substrate was observed in the substrate dwellers. Mesoclimate air temperature had no significant effect on the number of species of substrate dwellers. However, water temperature, specifically its daily fluctuation, turned out to have a strong effect. Only the sites with no or moderate fluctuation were inhabited by cold-stenotherm spring specialists and cold-water species. In contrast, no significant response to any temperature parameter was found for the number of surface-active species, which was driven only by other environmental variables. Our results suggest that climatically induced increase in temperature fluctuation of spring waters can result in notable reduction of cold-adapted clitellate species (mainly the family Lumbriculidae) at the expense of eurythermic species. Such a scenario predicts compositional changes leading to clitellate assemblages with a dominance of generalist and semi-aquatic species.