Chironomidae traits and life history strategies as indicators of anthropogenic disturbance
Résumé
In freshwater ecosystems, Chironomidae are currently considered indicators of poor water quality because the family is often abundant in degraded sites. However, it incorporates taxa with a large ecological and physiological diversity and different sensitivity to impairment. Yet, the usual identification of Chironomidae at coarse taxonomic levels (family or subfamily) masks genus and species sensitivities. In this study, we investigate the potential of taxonomic and functional (traits) composition of Chironomidae to de- tect anthropogenic disturbance. In this context, we test- ed some a priori hypotheses regarding the ability of Chironomidae taxonomic and trait compositions to dis- criminate Mediterranean streams affected by multiple stressors from least-disturbed streams. Both taxonomic and Eltonian trait composition discriminated sites ac- cording to their disturbance level. Disturbance resulted in the predicted increase of Chironomidae with higher number of stages with hibernation/diapause and of taxa with resistance forms and unpredicted increase of the proportion of taxa with longer life cycles and few gen- erations per year. Life history strategies (LHS), corre- sponding to multivoltine Chironomidae that do not in- vest in hemoglobin and lack strong spring synchroniza- tion, were well adapted to all our Mediterranean sites with highly changeable environmental conditions. Medium-size animals favored in disturbed sites where the Mediterranean hydrological regime is altered, but the reduced number of larger-size/carnivore Chironomids suggests a limitation to secondary produc- tion. Results indicate that Chironomidae genus and re- spective traits could be a useful tool in the structural and functional assessment of Mediterranean streams. The ubiquitous nature of Chironomidae should be also espe- cially relevant in the assessment of water bodies natu- rally poor in other groups such as the Ephemeroptera, Plecoptera, and Trichoptera, such as the lowland rivers with sandy substrates, lakes, or reservoirs.