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

The longitudinal distribution of benthic macroinvertebrates has been studie d along the Moulouya River, one of the three permanent large rivers of Moro cco. 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 richn ess and species richness (mainly Mollusca, Ephemeroptera, Plecoptera, Coleo ptera and Trichoptera) showed similar patterns with a maximum downstream. B iotypologic analysis by C.A. performed on 68 species distinguished four sec tions : i) the upper Moulouya, including springs and mountain tributaries w ith crenobialrithral species, ii) a transitionnal zone, iii) the very homog eneous section of the middle Moulouya plus downstream zones of tributaries despite water pollution and characterized by eurytopic-thermophilous specie s, and finally iv) the lower Moulouya characterized by potamic-limnophilous species downstream from two successive impoundements. On this basis, the s tudy of functional feeding groups showed that only the lower Moulouya did n ot correspond to the predictions of the River Continuum Concept. The discon tinuity in the lowermost section was due to both regulation effects (discha rge and streambed width reductions) and to a more abundant riparian vegetat ion.