BIOGEOGRAPHY OF THE BENTHIC AND INTERSTITIAL LIVING OSTRACODS (CRUSTACEA) OF THE RHONE RIVER (FRANCE)

The biogeography of the ostracod fauna of the River Rhone has been stu died at five sectors along its 320 km length. A total of 648 interstit ial and benthic samples were studied, revealing twenty-six species fro m thirty-nine new localities. Comparison of the faunas of the flood pl ain and the main river channel showed that most species from the main channel were also present in backwater environments. This is probably due to the high ecological diversity of floodplain habitats, coupled w ith the heterogeneity of the main channel and the 'connectivity' betwe en the two systems. Three distinct species assemblages occurred within a longitudinal gradient along the length of the river, which broadly reflected the ecological requirements of their component species. One group exists throughout the length of the Rhone, whilst the two other groups were restricted to its upper or lower reaches respectively. The biogeography of the river's hypogean species is discussed in the cont ext of patterns of recolonization at the end of the last glacial, at r ound 11,000 BP.