Understanding benefits and risks of exploiting spring habitats by subterranean animals: insights from a mark-recapture study on the olm (Proteus anguinus)

The olm (Proteus anguinus) is an iconic predator in underground ecosystems, but it also exploits localized spring habitats, characterized by higher trophic abundance and predation risk. This study analyzes the advantages and disadvantages of using springs and caves, with particular attention to population variations. In the classical karst system (NE-Italy), we compared food availability and predator occurrence in 40 springs and 8 caves and monitored 76 P. anguinus individuals through capture-\mark-recapture (CMR) surveys. Individuals captured in springs had a significantly higher Scaled Mass index (SMI) compared to those from caves, with no significant differences in the occurrence of injuries. The greater trophic abundance and diversity in springs, combined with site fidelity, suggests that karst spring ecotones may represent critical foraging areas for stygobionts, such as animals specialized to inhabit groundwater. The results confirm the ecological importance of these karstic springs habitats, which support high biodiversity, species interactions, and serve as key points for studying the adaptive responses of Proteus anguinus and other subterranean species.