Longitudinal ecological zonation in four Algerian streams

This hydro-biological survey on benthic invertebrates was carried out in the most important hydrographic network of the Mitidja plain,Oued El Harrachbasin, Algeria. Results revealedecological zonation taking into account the taxonomic richness and the relative abundance of different zoological groups, and allowed distinguishing abundant, ubiquitous and permanent taxa as well as the existence of a spatiotemporal faunistic gradient. These preliminary results allowed highlightingtaxonomically the “upstream invertebrate fauna”, the “ubiquitous invertebrate fauna” and the “downstream invertebrate fauna”. Consequently, it appearedthat Plecoptera, Hemiptera, Coleoptera are characteristic to the upstream area during the whole year in most of the sampling sites, whereas Diptera, Oligochaeta and Hydracarina are more abundant in the downstream area but in less density in the middle stream. On the other hand, the longitudinal evolution approach was considered in order to evaluate the inter-site distribution. According to the trophic levels, the classification between the various communities was investigated taking into account the concepts of the "Food Functional Group" and "The River Continuum Concept".