Biodiversity and resource use of larval chironomids in relation to environmental factors in a large river

Larval chironomids were examined at four sites on a cross‐section of the River Danube in Austria between September 1995 and August 1996. The sites differed in hydraulics, sediment composition and habitat stability. 2. Species–accumulation curves, showing the increase in number of species with increasing sampling effort, from three main channel sites were best described by a logarithmic model, suggesting that most of the species occurring at these sites were found. Data from a site connected to a backwater fitted best to a power model, indicating a random assemblage with additional species immigrating from the backwater area. 3. Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 32–91), H′ diversity (1.5–2.3), evenness (0.23–0.28), spatial resource width (0.01–0.06), spatial resource overlap (0.13–0.20), spatial species aggregation (0.60–0.77), temporal community persistence (Kendal's correlation coefficient: 0.47–0.60) and beta‐diversity (6.2–9.7). 4. Redundancy analysis (RDA) was used to relate the community properties and species abundance to environmental factors. Habitat stability was the major factor associated with community structure. Higher sediment turnover led to higher spatial aggregation and, consequently, a decrease in spatial resource width and overlap, and to a decline in larval density and species richness. 5. Species‐abundance patterns agreed well with the log‐normal model. Moderate community persistence and stability of the streambed sediments suggest that the log‐normal model may be a good descriptor for communities of intermediately disturbed habitats, like large rivers, rather than stable habitats.