Microhabitat diversity and associated macroinvertebrates in aquatic banks of a large European river

Microhabitats and associated macroinvertebrate communities in aquatic banks of the Upper Rhone River (upstream from Lyon, France) were studied during the autumn of 1985, under low flow conditions. Based on a regular sampling design (one site every 500 m) along 70 km of riverbank, 18 microhabitat types were identified. Mineral microhabitats (from boulders to clay) accounted for 70%; the remainder corresponded chiefly to the microhabitats of aerial or semi-aerial submerged vegetation (27%) and aquatic vegetation (less than 2%). Using various methods, 239 faunistic samples of microhabitat types resulted in the collection of nearly 64 000 organisms representing 133 taxa. A correspondence analysis showed that most of the 18 microhabitat types were on average well characterized by a specific macrofauna. Microhabitats of aquatic vegetation (hydrophytes and algae) contained the richest fauna in terms of both mean specific richness (15.0 and 13.2 per sample, respectively) and mean density (73 125 and 59 475 ind. m−2, respectively). By contrast, mineral microhabitats were faunistically poorer (mean specific richness per sample <6.0, except cobbles; and mean density ≤10405 ind. m−2). The fewest species and lowest density occurred in clay, silt and sand. Estimated mean density of macroinvertebrates in the aquatic banks of the Upper Rhone River was approximately 16 000 ind. m−2. This was four times higher than in deeper sections of the channel at the same season. The aquatic banks of this large European river, with its great diversity of microhabitats, must be taken into account in all macroinvertebrate studies of fluvial systems.