Fine-scale distribution of hypogean Ostracoda in the interstitial habitats of the Rivers Sava and Rhône

Abstract

The small-scale distributions of three hypogean ostracods were studied in gravel bars in the Rivers Rhône and Sava. Fabaeformiscandona wegelini is widely distributed, whilst Mixtacandona n. sp. and Pseudocandona zschokkei have more localised distributions. In the Sava River (Croatia), the fauna was sampled at depths of between 0.5 and 7 m, and from 0 to 135 m away from the main channel. The River Rhône (France), was sampled a depth of 0.5 m at eight stations along a 1160 m long gravel bar. In both rivers, F. wegelini was most abundant in interstitial habitats fed by superficial waters: close to the channel in the River Sava and in the downwelling area in the River Rhône. The two other species were found in areas fed by groundwaters: in deep sediments and far from the channel in the River Sava and in the upwelling area in the River Rhône. The microdistribution of these hypogean ostracod species is discussed in the context of their larger-scale biogeographical distributions.