Waiting for Hydropsyche - Why has only one of at least four local Hydropsyche species returned into the Lower Rhine River?
Engels, S.; Neumann, D.; Löbbel, H.; Brühne, M.
At the beginning of the 20th century, six species of the caddisfly genus Hydropsyche occurred in the Lower Rhine. H. contubernalis, H. angustipennis, H. exocellata and H. pellucidula were among these. After the extinction of the hydropsychid fauna by pollution in the 1960s and early 1970s, H. contubernalis was the first hydropsychid species to reappear in the Lower Rhine, in 1976-1977. However, so far other species such as H. exocellata and H. pellucidula which live in some tributaries of the Lower Rhine have not recolonized the main river. This study establishes a correlation between recolonization of the river by H. contubernalis and the oxygen content in the Lower Rhine. Other aspects, such as tolerance of low oxygen-saturation levels by the larvae and the swarming behaviour of the adults, are described and discussed in the context of continuing absence of other hydropsychid species in the Lower Rhine.