Bernard Cellot

Macroinvertebrate Community Structure and Environmental Characteristics along a Large River: Congruity of Patterns for Identification to Species or Family

In developed countries the longitudinal ecological pattern of large rivers is often strongly influenced by water pollution and flow regulation. The relationship between macroinvertebrate communities and this anthropogenic environment was studied along the French Rhône River. Collected specimens were identified to both family and species level and the results compared. Along the 512 km of this 7th-8th-order river, 10 reaches were chosen for study. Macroinvertebrates were collected 3 times during spring and summer 1991, using 2 techniques, artificial substrates and hand nets Environmental variables (16) were measured and associated with the collected faunistic communities, composed of 73 species or 53 families, depending on the level of identification. The faunistic and environmental structures were compared by means of a co-inertia analysis carried out on the 2 matrices. For the environmental variables and for both families and species, the longitudinal changes were preponderant. The correlation between fauna and environment was very good, as shown by the correlation coefficients r of their F1 scores in the co-inertia analyses: 0.839 and 0.814 for families and species, respectively. For both the fauna and the environment, the ecological pattern of the Rhône River changed downstream of the main city, Lyon, and of the main tributary, the Saône River, where the fauna became poorer. Ephemeroptera and Trichoptera, which were well represented in the Upper Rhône, were replaced by molluscs and lentic groups in the Lower Rhône. The environmental changes in the lower course consisted of higher water mineralisation, increased pollution, and greater flow regulation. Similar patterns were observed at both family and species level, with only a slightly more regular longitudinal change in the upper course at species level. Water pollution was not the only reason for an impoverished fauna in the Lower Rhône, as several taxa found in the upper course were also found in a by-passed section of the lower course. Thus the strong regulation of the Lower Rhône is largely responsible for the limited fauna. The family level of identification gave a meaningful picture of the macroinvertebrate longitudinal pattern of a large river. This family pattern was then compared with that observed in other European large rivers such as the Rhine and the Danube.

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

Microhabitats and associated macroinvertebrate communities in aquatic banks of the Upper Rhône 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 Rhône 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.

Modifications faunistiques engendrées par une faible variation de débit dans une grande rivière

Artificial substrates suspended in the water column and benthic dredging were employed to study the drift of macrofauna and the macrobenthic populations respectively, in a cross section of the Rhône River upstream of Lyon, France. The samples were collected in autumn 1979: first in September under a low flow egime around 400 m3·s−1, then in October during a discharge increase up to 630 m3·s−1.The first factor of correspondence analysis showed a clear cleavage between the two periods, especially for drift communities. The differences are most important in the centre of the stream channel. In October, the water column was invaded by unusual and abundant fauna. This dynamics is due to the increase in number of Crustacea (Gammarus fossarum, Asellus aquaticus), the decrease of some insect larvae (Leuctra fusca, Simuliidae, Baetis fuscatus, stages 1 and 2 of Hydropsyche) and the appearance of typical wetland taxa (some limnophilous Coleoptera and Trichoptera). For some other dominant invertebrates, a modification may occur only in their distribution (stages 3 to 5 of Hydropsyche, Heptagenia sulphurea) while the distribution of Psychomyia pusilla remains the same.These results are discussed with respect to the effects of species biology and the unusual consequences caused by a minor increase in discharge.

Isolation and characterization of the first eight microsatellite loci in Gammarus fossarum (Crustacea, Amphipoda) and cross-amplification in Gammarus pulex and Gammarus orinos

We characterized the first microsatellite markers for Gammarus fossarum. Eight loci gave satisfactory amplification patterns in two stream populations (Southern France) with number of alleles ranging from 2 to 10 and expected heterozygosity from 0.076 to 0.857. We performed cross‐amplification in two closely related gammarid species, Gammarus pulex and Gammarus orinos. Among the eight tested microsatellite loci, four correctly amplified in G. pulex and three in G. orinos.

Environmental and macroinvertebrate dynamics in the Lower Rhone River and a lateral dike field: a study matching two functioning descriptors

Environmental variables and macroinvertebrate communities are studied in two sites of the Lower Rhône River, the main channel and a lateral, occasionally connected dike field. Environmental variables and faunistic communities allow discrimination the two compartments. The environmental and faunistic differences the two sites change over time. The physical and chemical differences are significantly correlated with water discharge of the main channel. The faunistic ones are significantly correlated with the temperature of the dike field water. The connections between the main channel and the dike field could be very important to maintain a high heterogeneity of the habitat, and for recolonization of the main channel after a perturbation.