First inventory and faunistic particularities of the chironomid populationfrom a 6(th) order section of the sandy River Loire (France)

The chironomid populations of a 40km section of the middle Loire (Tours reg ion) were studied for the first time. Six collections (distributed over the years 1994 to 1996) of pupal exuviae and benthic pupae were made from Apri l to November, in the main river bed, at 4 sites of this potamal zone. A to tal of 12,073 specimens were sorted and 117 species or taxa identified. Thi rty one are new for continental France, in particular Polypedilum acifer TO WNEs and Saetheria reissi JACKSON, two dominant species. Among these, three genera are new: Hayesomyia, Robackia and Saetheria. A new pupal exuvia whi ch has only been noted in the Loire has been recorded: Chironomus Pe23 (LAN GTON 1995). A comparison of the middle Loire chironomid fauna with that of the potamal zones of five large European rivers - Rhone and Garonne (France )- Meuse (Belgium) - Po (Italy) - Rhine (Germany) - confirms the diversity and faunistic originality of the middle Loire using several descriptors suc h as diversity indexes, rarefaction curves, equitability index, distributio n of species abundance, number of "endemic" species and distribution of dom inant species. Causes of the high specific richness observed, as well as ra re species abundance or scarcity, are discussed taking into account functio nal characteristics of the River Loire's potamic parts such as the connecti vity pattern. The relationship between high biodiversity and large, sandy r ivers is also discussed using similar results obtained on two other large s andy rivers: the Po and the Elbe (Germany) rivers.