Community structure and resource use of oligochaetes (Annelida)in relation to hydrophysical factors in a large river

Abstract

The oligochaete community of streambed sediments was examined with respect to 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 hydraulics, sediment composition and habitat stability. At all sites, species-accumulation curves showing the increase in number of species with increasing sampling effort agreed with a logarithmic model, suggesting that most of the present species have been found. Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 30 to 36), H' diversity (0.9 to 1.1), evenness (0.15 to 0.32), spatial resource width (0.01 to 0.05), spatial resource overlap (0.08 to 0.25), spatial species aggregation (0.66 to 0.72), temporal community persistence (Kendal's correlation coefficient: 0.52 to 0.66) and β-diversity (3.6 to 6.1). RDA (Redundancy Analysis) was used to correlate the community properties and species abundance with environmental factors. Habitat stability and sediment heterogeneity were the major factors associated with community structure. Decreasing stability coincided with decreasing densities, species richness and increasing species turnover, whereas sediment composition seemed to fine-tune community structure, coinciding with evenness and spatial resource utilization patterns. Species-abundance patterns agreed well with the log-normal model. Moderate community persistence and stability of the streambed sediments therefore suggest that the log-normal model may be a good descriptor for communities of intermediately disturbed habitats like large rivers rather than stable habitats.