Community structure of larval Chironomidae (Diptera) in a backwater area of the River Danube

Abstract

SUMMARY1. The larval chironomid community was studied quantitatively in three cross‐sections of an impounded area of the River Danube between July 1985 and July 1986.2. Sixty‐six species were identified, most of which belonged to the subfamily Orthocladiinae, but species of the tribe Chironomini were numerically dominant.3. The sections differed distinctly in terms of species number and diversity; a tendency towards increasing species richness and diversity was observed in the upstream sections of the impoundment. Marked fluctuations in these two parameters characterized the area close to the dam; the temporal oscillations in diversity values differed significantly between the sections (ANOVA: P<0.05).4. Clear differences were found between sampling sites in terms of community resilience, the minimum eigenvalue of the community matrix defined as the rate of return of a disturbed system. Longer return times after ‘disturbances’ could be expected at sites further upstream from the dam.5. Temporal persistence of species composition was estimated for each section with Kendal's correlation coefficient from 1985 to 1986. Sites further upstream of the dam illustrated a significantly greater temporal species persistence over time and a smaller degree of fluctuation, compared to the dam area (ANOVA: P<0.05). A significant negative relationship was found between overall persistence and cumulative monthly water discharge, at the dam site (P<0.01).6. Classification of the larval chironomid community gave evidence of generally low spatio‐temporal overlap between species in the impoundment area.