Variabilité structurelle des peuplements de macro-invertébrés benthiques dans le bassin versant de la Soummam (Algérie, Afrique du Nord)

Abstract

Summary. — Structural variability of benthic macro-invertebrate communities in the watershed of the Soummam (Algeria, North Africa). — The spatio-temporal distribution and structure of benthic invertebrate communities has been studied in a catchment area of northern Algeria (the watershed of Soummam). The samples were collected over two seasons (spring and summer) in 2005 and 2006 with some additional ones in 2007. They were obtained in 34 stations located at elevations between 20 m and 1100 m a. s. l. Community variability was analysed in terms of space (taxonomic variability in the three parts of the Soummam catchment area) and time (seasonal variation between spring and summer). In the Soummam catchment area, two types of large-scale factors (altitude and slope) govern the distribution of benthic macro-invertebrates by acting on the flow velocity and nature of the substrate. Changes in current speed affect the nature of the substrate which in turn affects the structure of the benthic macro-invertebrate fauna. Five groups of taxa were determined by their density : 56.4 % of taxa have a number of individuals less than 50 per m2, 25.5 % between 50 and 500 per m2, 14.1 % between 500 and 2500 per m2, 2.4 % between 2500 and 5000 per m2, and 1.8 % of taxa with numbers higher than 5000 per m2. This structure shows slight differences between the three parts of Soummam catchment area.