The dark side of springs: what drives small-scale spatial patterns of subsurface meiofaunal assemblages?

Springs are amongst the most relevant Groundwater Dependent Ecosystems (GDEs) and are key research environments in freshwater ecology and biology. The strict dependency on ground water of surface spring biodiversity is well known, whereas the biodiversity occurring below the spring is very poorly known. This study analyzes copepod assemblages in the subsurface habitat of a karstic rheo-limnocrenic spring in relation to seventeen environmental parameters. Subsurface copepod assemblages were sensitive to microspatial variation in habitat structure, and species distributions were mostly driven by groundwater flowpath and substratum type, resulting in biologically distinct limnocrenic and rheocrenic sectors at the spring system scale. Habitat patchiness was reflected in differences in the microdistribution of subsurface copepods, stygobiotic assemblages being more sensitive to the measured environmental gradients than non-stygobiotic ones. In spite of the apparent stability of spring environments, copepods, as a target group, performed well as descriptors of sediment texture and hydrodynamics, and may offer relevant information for a better understanding of the potential changes generated by anthropogenic disturbance on these ecosystems.