Effects of intermittent stream flow on macroinvertebrate community composition and biological traits in a naturally saline Mediterranean stream

Abstract

As saline streams are geographically widespread in arid and semiarid regions, flow intermittence frequently occurs as another stressor factor apart from salinity. Rambla Salada is a temporary naturally saline stream with an intermittent reach upstream. This stream is an ideal scenario to study the effects of intermittent stream flow on macroinvertebrate community composition and biological traits in a naturally saline Mediterranean stream. This study analysed three sites with different hydrological regimes (one intermittent and two perennials). Flow intermittence exerted low pressure on the macroinvertebrate composition and biological traits which led to the loss of drought-intolerant species and taxa rather than acting as a selective force to promote desiccation-resistant taxa. Macroinvertebrate community at the intermittent site was a subset of the community found in perennial sites, and the presence of flier taxa at this site helped avoid flow cessation. These minor changes have consequences to assess the ecological quality of these saline temporary streams in the context of the Water Framework Directive, given the major differences revealed by some indices between the intermittent and perennial sites as the former obtained lower values due to the presence of few desiccation-intolerant species, which significantly increased the value of those biological indices.