Longidutinal distribution of benthic macroinvertebrates in the Moulouya River (Morocco)

The longitudinal distribution of benthic macroinvertebrates has been studied along the Moulouya River, one of the three permanent large rivers of Morocco. The study was carried out in May and June 1994 on 19 sites : 12 along the main channel and 7 on springs or important tributaries. Taxonomic richness and species richness (mainly Mollusca, Ephemeroptera, Plecoptera, Coleoptera and Trichoptera) showed similar patterns with a maximum downstream. Biotypologic analysis by C.A. performed on 68 species distinguished four sections : i) the upper Moulouya, including springs and mountain tributaries with crenobialrithral species, ii) a transitionnal zone, iii) the very homogeneous section of the middle Moulouya plus downstream zones of tributaries despite water pollution and characterized by eurytopic-thermophilous species, and finally iv) the lower Moulouya characterized by potamic-limnophilous species downstream from two successive impoundements. On this basis, the study of functional feeding groups showed that only the lower Moulouya did not correspond to the predictions of the River Continuum Concept. The discontinuity in the lowermost section was due to both regulation effects (discharge and streambed width reductions) and to a more abundant riparian vegetation.