Influence of flow variability on macroinvertebrate assemblages in an intermittent stream of semi-arid Brazil

Abstract

This study aims to evaluate the effects of variable water flow on macroinvertebrate composition and taxon richness in a semi-arid intermittent stream. Chironomid larvae were the most abundant group of insects in the intermittent stream studied. Nevertheless, their response to flow was similar to the macroinvertebrate fauna as a whole. Macroinvertebrates were more abundant in the late wet phase and in the drying phase. A higher richness was also observed during this period, when new taxa where registered. Discharge, temperature, conductivity and dissolved oxygen were the main variables explaining the variation in richness and density of macroinvertebrate. These variables were also important in explaining the variation in community composition through time. It is suggested that invertebrates cope with the extreme intermittent flows by resilience during variable flows in the wet phase and by resistance during the dry phase. It is however important to notice that frequently high discharges drive the community to lower richness and densities, whereas the resistance during the dry phase is characterized by a taxonomic shift resultant from the survival of the few taxa that supports the initial desiccation and the opportunism of colonizing predaceous taxa overcoming non-resistant taxa.