Perspectives for biomonitoring at large spatial scales: a unified measure for the functional composition on invertebrate communities in European running waters

Environmental policies increasingly focus on the enhancement of ecological functions across large geographical areas and thus call for biomonitoring tools that assess these functions at large spatial scales. A potential answer to this call would be to use general biological traits of organisms that indicate ecological functions, as such traits will be comparable among communities even across biogeographic regions that differ in their taxonomic composition. Here, we used benthic invertebrates and European running waters as example to illustrate how multiple biological traits could provide a measure for the large-scale biomonitoring of the functional composition of communities. Our measure considered the relative abundance of 63 categories of 11 biological traits (such as size, reproductive and dispersal potential, food and feeding habits) that indicate various ecological functions. Comparing this measure for 10 most natural French reference regions with 37 other most natural regions/stream types scattered across Europe demonstrated an extremely high spatial and temporal stability of the functional composition of natural invertebrate communities at the European scale. Thus, our functional measure corresponds to a fundamental standard for a large-scale biomonitoring tool, which is the stable and reliable indication of the natural reference state across ecoregions that differ more or less in their taxonomic composition. Applying our functional measure to regulated stream sites below dams (in England, Finland and Spain) and to streams receiving sewage inputs (in Wales, Poland and Sardinia) demonstrated highly significant (p < 10(-6)) differences in the functional composition between the human-impacted and the natural reference communities. In addition, some of the trait categories responded in a consistently contrasting way to each of the two types (regulation, sewage) of human impact. Consequently, our measure for the functional composition of invertebrate communities provides a first unified European baseline for future stream and river management: it was stable in the most natural but otherwise very different running water types across Europe, it safely indicated human impact, and it could potentially discriminate specific types of human disturbances. As all living organisms have multiple biological traits, our approach could serve to generate, for other types of communities and ecosystems, a set of large-scale biomonitoring tools that use similar and perhaps even comparable measures for the functional community composition.