Spatio-temporal variability of benthic macroinvertebrate community attributes and their relationship to environmental factors in a large river (Danube, Austria)
Fesl, Christian; Humpesch, Uwe H.
The macroinvertebrate community of the riverbed sediments was examined for biodiversity and spatial resource utilization at four sites on a cross-section of the River Danube in Austria between September 1995 and August 1996. The sites differed in water velocity, sediment composition and habitat stability. A species-accumulation curve based on all samples suggested an open community, with 164 species present at the four sites. Of these, 81 species were Chironomidae, 33 species were Oligochaeta and these two groups accounted for some 95 % of the total numbers of macroinvertebrates. Altogether, 93 species occurred at site 1, 82 at site 2, and 71 at site 3. Site 4 had 142 species, of which 47 did not occur at any of the other sites; some (mainly chironomids) possibly immigrate from a neighbouring backwater. Redundancy Analysis (RDA) was used to describe the variation in the relationship between these community attributes, together with total abundances, and environmental factors. The first two RDA-axes separated the four sites with respect to habitat stability and sediment composition; the temporal scale was given by the third and fourth RDA-axes, related to water temperature and flow, respectively. The centroids of the site scores exhibited a clear circular pattern for successive sampling dates, indicating relatively predictable environmental conditions over the year. In general, habitat stability was the major factor associated with community attributes. Lower sediment turnover near the riverbanks coincided with increased densities and decreased species turnover. Highest values for species richness and total abundance occurred at a riverbank site of intermediate stability and greatest sediment heterogeneity, suggesting that the communities were structured by a combination of several factors. Parameters describing resource utilization patterns were only weakly associated with changes in environmental conditions, suggesting that food distribution and/or biotic interactions also influenced community structure.