Habitat‐oriented sampling of macroinvertebrates affects the determination of ecological status in temporary mediterranean river systems

Inter‐annual and annual variation in precipitation levels in Mediterranean temporary river systems strongly influence riverine flow regimes and as a result habitat' availability for biological assemblages. Under‐sampling of less well‐presented microhabitats in such changeable, dynamic systems can result in information loss leading to misclassification of Water Framework Directive (WFD) compliant ecological status, with serious consequences for Programmes of Measures in River Basin Management Plans. This paper compares two benthic macroinvertebrate sampling protocols tested in intermittent Mediterranean streams (n = 40) in the Algarve region of southern Portugal. The officially adopted WFD compliant European assessment system for the ecological quality of rivers using benthic macroinvertebrates, a composite sampling protocol, focuses sampling a greater area of the most representative microhabitats at a given sampling site (proportional habitat sampling). A non‐proportional habitat sampling protocol was applied to test the assumption that taxa may have preference for different microhabitats and that this could influence classification of ecological status. Variation was detected in the levels of similarity in the structure and the composition of the benthic macroinvertebrate community within sampling sites and rivers, based on material collected using the two collection methods. Ecological index scores and biotic metrics were higher when the non‐proportional oriented sampling protocol was utilized resulting in a ‘good ecological status’ classification at sites that had been classified as ‘Bad’ using the official WFD, Decision tree analysis results indicated that changes in the area of individual microhabitats sampled among protocols was the principal driver behind differences in ecological status derived. The results indicate that more realistic classifications could be achieved in intermittent Mediterranean rivers when considering and sampling less well‐represented microhabitat types (non‐proportional sampling) rather than distributing sampling effort by the proportion of the dominant habitat present as currently used for the WFD protocol. The application of the non‐proportional microhabitat‐based approach, which accounts for selective preferences of some benthic macroinvertebrate taxa, would ensure that a greater proportion of a given site community contributes to the assessment. Copyright © 2014 John Wiley & Sons, Ltd.