Micro-distribution of epikarstic aquifer fauna and its hydrological interpretation: A case study of Velika Pasica Cave in Slovenia

Intensive and long-term monitoring on hydrological parameters has been performed at four permanent dripping sites (VP1VP4) in the Velika Pasica Cave (Slovenia) from 2006 to 2013, in combination with aquatic fauna sampling. Multivariate analytical methods, such as cluster analysis and CCA method, were applied to elucidate the hydrological conditions associated with the spatial distribution of aquatic fauna within the cave and species composition at each dripping site.(1) It was found that hydrological characteristics of these four drip are distinct from each other. (2) By using cluster analysis, 12 species are divided into 4 groups, which correspond to four drips quite well. By employing CCA, the main hydrological parameters are Max and Q, which positively correlate with the first canonical axis and the drip water temperature (temp) which is negatively correlated with the first canonical axis. (3) Seven major species show different affinities to environmental parameters: abundance of Pseudocandona albicans and Speocyclops infernus,concentrating in VP1 samples which are positively correlated with the volume of discharge (Q), while abundance of Morariopsis dumonti and Bryocamptus typhlops, dominant at VP2, are negatively correlated with high discharges (Max); Byocamptus pyrenaicus and Elaphoidella millennii, dominant at VP3,with preferred moderate hydrological conditions, while Moraria varica, dominant at VP4,is positively correlated with drip water temperature. (4) The sum of eigen value by CCA only accounts for 33.8% of total eigen value, which could explain partial of the fauna distribution, but the parts of which cannot be explained due to the unexpected factors, e.g. hydrochemistry, or some stochastic processes. It implies that specific micro-distributions of species among the drips are related to specific environmental parameters.