Specialized aquatic subterranean communities are probably most species-rich in the thickest epikarst

Stygobionts are aquatic troglobionts, i.e., organisms that are specialized for living in subterranean environment. It has been demonstrated that the epikarst above caves harbors a stygobiont fauna that is as rich as that in deeper caves. The abiotic parameters affecting the aquatic fauna in drip water have been relatively well explored, while aquatic troglobionts alone are not frequently the focus of such studies; consequently, many crucial questions remain insufficiently studied. We hypothesized that the epikarst stygobiont fauna may occur locally in deeper zones of the epikarst, since environmental conditions are more stable there. For this purpose, we studied the composition and annual dynamics of the epikarst stygobiont community from ten water drips in the cave Zguba jama in Slovenia. Copepoda predominated among eight stygobiont taxa. The high total and between-sites dissimilarity of stygobiont communities among the drips was mainly the consequence of species turnover. We found that the greater the distance from the entrance and the ceiling thickness, and the higher the water temperature, the greater was the chance of finding aquatic troglobionts and the higher thier diversity. Our study suggests that locally, owing to specific lithology and geomorphology, epikarst stygobionts can extend from the shallow layers into deeper epikarst layers, where voids with more suitable environmental conditions exists.