Traits of benthic macroinvertebrates in semi-natural French streams: an initial application to biomonitoring in Europe

1. The methods used to indicate the biological state of streams are often b ased on taxonomic composition, and the abundance of species or other taxa. This 'taxonomic structure' varies among ecoregions and cannot be applied to wider geographical areas. Therefore, we assessed the species traits of ben thic macroinvertebrates from semi-natural reference sites as a potential be nchmark for large-scale biomonitoring. Our purpose was to assess the stabil ity of community structure, based on the representation of taxa and of trai ts, across large gradients of geology (sedimentary to granitic), altitude ( 65-1982 m), geographical coordinates (0 degrees 48' W to 7 degrees 20' E an d 42 degrees 52' to 48 degrees 44' N), stream order (1-5) and slope (0.5-60 %). 2. We used invertebrate abundance data from the 62 most natural French stre am sites available. These abundance data served to weight the occurrence of 'biological' traits, such as reproductive characteristics, mobility, resis tance forms, food, feeding habits, respiration, and 'ecological' traits, su ch as preferences for temperature, trophic level, saprobity,, biogeographic distribution, longitudinal zonation, substratum and current velocity. 3. Multivariate analyses of taxonomic composition demonstrated a clear site gradient from lowlands to uplands and from calcareous to granitic geology. In contrast, community structure based on both biological and ecological t raits was stable across environmental gradients. 4. The frequency distribution of biological traits indicated that the strea m benthos of the 'reference sites' had a mixture of categories which confir med theoretical predictions for temporally stable and spatially variable ha bitats. A mixture of ecological trait categories also occurred at our refer ence sites. Thus, semi-natural benthic macroinvertebrate communities are fu nctionally diverse. Moreover, we included an initial application of these t raits to a case of slightly to moderately polluted sites to show that the i mpact of humans significantly changes this natural functional diversity. 5. Future studies should focus on the potential for various biological and ecological traits to discriminate different human impacts on the benthic ma croinvertebrates of running waters, and on the integration of this function al application into a general 'reference-condition' approach.