Discriminating permanent from temporary rivers with traits of chironomid genera

Abstract

Chironomidae are diverse and present a wide variety of ecological preferences. Thus, they have high potential in establishing reference conditions for river bioassessment and in providing functional information, especially when other macroinvertebrates are poorly represented. However, because of taxonomic difficulties and poor knowledge of traits, they are neglected in bioassessment programmes and kept at coarser taxonomic levels, reducing the discrimination power of invertebrate-based diagnostic tools. Here, we compared the efficiency of Chironomidae at the subfamily and genus levels and their biological traits (Eltonian and morphological) in the distinction between permanent (medium altitude and lowland) and temporary Mediterranean streams. We established a priori predictions on the expected Chironomidae trait categories in each stream type, conferring the best adaptations to particular environmental constraints. Genus composition (not subfamily) and respective trait categories differed among the three stream types. Both biological traits identified differences between stream types. Among Eltonian traits, diapause stages segregated permanent medium altitude from lowland and temporary stream assemblages, reflecting adaptations to temperature and flow regime variations. Substrate relation and size distinguished temporary from permanent stream assemblages, interpreted as an adaptation to unstable sediments and irregular flow regimes. Morphological traits associated with mobility and foraging (e.g. , body setae, Lauterborn sensory organs) discriminated temporary from permanent stream assemblages, reflecting differences in temporal and spatial stream heterogeneity. The use of these morphological characteristics relying on the observation of few characteristics, offers an alternative to the use of Chironomidae Eltonian traits in bioassessment and ecological studies, without a need for high taxonomic expertise.