Benthic macroinvertebrate communities of intermittent streams in the middle reaches of the Guadiana Basin (Portugal)

The Guadiana River has an irregular hydrological regime, with severe drough ts and floods, but little is known about how aquatic fauna respond to these natural events. Macroinvertebrate data and environmental information were collected at seven sites from three tributaries in the middle reaches of th e Guadiana River, approximately every 3 months from April 1995 to April 199 7. Despite considerable annual variation in discharge (related to duration of flood and drought periods), the number of macroinvertebrates found was c onsistently high. Diptera represented the major proportion of the benthic f auna (73.2%) followed by Ephemeroptera (10.3%), Coleoptera (4.1%) and Trich optera (3.1%). Canonical correspondence analysis (CCA) was used to evaluate the relationships between taxa density and habitat variables. Generally, P lecoptera and Ephemeroptera were found in the upstream sampling sites. Wide r and deeper sites were associated with the presence of Diptera and were le ast diverse. High values for both the Shannon-Wiener diversity index and th e average score per taxon were usually found at upstream sites where Epheme roptera and Plecoptera predominated. The data suggest that macroinvertebrat es have a great capacity to recover rapidly from severe drought periods, bo th in terms of taxonomic diversity and number of individuals.