A survey of the distribution of chironomidae (Diptera, Insecta) of the river rhine by sampling pupal exuviae

Abstract

During the period from 1981-07-23 to 1981-08-10, the River Rhine, from the Alps to the North Sea, was sampled for chironomid pupal exuviae. Samples were also taken from the Grande Canal d'Alsace and from selected tributaries. In all 78 samples were taken, of which 9771 exuviae were examined and 135 taxa identified. A species list is given showing the distribution of taxa between the principal regions of the river (Appendix 1). Samples were also taken to show the ‘within-sample’ and ‘between-sample’ variability, and one pair of samples was used to demonstrate the difference between the two banks of the river below the junction with the Main. The Rhine above the Bodensee has a diverse fauna dominated by Orthocladiinae. The Hochrhein near the entry of the River Aare, and the River Aare itself, also have a diverse fauna, but include many sediment-dwelling Chironominae. Below Strasbourg the fauna changes markedly, losing most of its sediment-dwellers, and shows a great increase of pollution-tolerant species. The fauna generally becomes less diverse and of poorer quality throughout the Oberrhein sections, and faunal changes are demonstrated that are related to the inflow of the Rivers Neckar and Main, Samples from the Mittelrhein gorge and the Niederrhein are generally dominated by two species ofRheotanytarsus and show a progressive reduction of diversity coupled to an increase of pollution-tolerant species. The low proportions of sediment-dwellers in the Niederrhein and the Waal, suggests that the sediments are unsuitable for the support of a normal chironomid fauna.