Studies on groundwater tardigrades of Lessinian Massif (Northern Italy).

Terrestrial tardigrades require a film of water around the body to conduct an active life. Therefore, in several cases the distinction between freshwater and terrestrial species is unclear as some species can tolerate a wide range of moisture regimes. Less than 6% of species are considered to inhabit permanent freshwater habitats. These species live as epiphyte on aquatic plants, benthic algal mats or among the minute voids of sediments in lotic and lentic waters. Tardigrades are sporadically reported from different groundwater habitats but little data are still available on their ecological affinity for this environment, as well as on their distribution and diversity in groundwater at different spatial scales. A stratified random sampling in both karstic and porous aquifers in the Lessinian Massif (northern Italy) gave the opportunity to asses their distribution patterns on a regional scale and to better define some ecological features of the collected species.Eight tardigrade species were collected in 29 of 129 sampling sites. These sites are located in five hydrogeographic basins in the selected region. Tardigrades were distributed in almost all the groundwater habitats; in saturated porous (wells), in saturated karst (only spring habitats) and in these cases always linked to the presence of unconsolidated sediments, and especially in hyporheic habitats, where they appeared with the highest frequency of occurrence and the highest abundance. They belong to six genera and two families of eutardigrades. Four species belong to typical limnic genera (Pseudobiotus, Thulinius and Dactylobiotus) and are characterized by claws longer than those of moss or soil-dwelling species. One species of Diphascon was already reported from groundwater, while two species of Macrobiotus and one of Hypsibius are easily found in terrestrial habitats. Some species of tardigrades collected in surface hyporheic habitats possess eye-spots. From an ecological point of view, most of them may be considered stygoxene or possibly stygophilous species. The morphological features of these species are similar to those of species living in surface freshwater on in the leaf-litter. This observation highlights the potential role of several habitats located at the interface surface/subsurface environments as potential migration ways for several species to enter groundwater. For the same reason, such a physical continuum and some degree of convergence in habitat features may determine the absence of clear morphological distinction between species living in such interface and those living in true groundwater.This research is partially granted by the EU-Pascalis project and by 60% MIUR from the University of Modena and Reggio Emilia.