Abundance, diversity and community structure of macroinvertebrates in an Algerian stream : the Sébaou wadi

We investigated the abundance, diversity and community structure of mayflies (Ephemeroptera), stoneflies (Plecoptera) and blackflies (Diptera : Simuliidae) in the Sébaou basin (Algeria). Fifty-five species were collected (i.e. 22 mayflies, 14 stoneflies and 19 blackflies species) in 18 sampling sites located in both main streams and tributaries of the Sébaou river (Great Kabylie, North Algeria). Analysis of species diversity of the three considered taxa showed an altitudinal gradient with maximal diversity in the piedmont and low altitude mountain areas (from 200 to 500 m), which provided the most heterogeneous habitats to the benthic fauna. In contrast, the low diversity of the lowland sites was due to high water temperatures, reduced summer discharge and anthropogenic disturbances. In the same way, the low diversity of the high mountain areas can be attributed either to low water temperatures or high fluctuation in daily temperature. Three species assemblage groups are revealed, the first two are related to an upstream-downstream gradient, with headwater sites characterised by stoneflies species and middle stream sites by a high mayfly and blackfy diversity and abundance. The third group was identified as spring sites characterised by a low abundance and occurrence of stonefly species. Both altitudinal species diversity gradient and species assemblage of the Sébaou wadi were different from European and temperate areas, revealing that the accentuated North African Mediterranean climate could induce changes to both species and community structure. These results provide insights to the influence of some environmental features on aquatic insect species distribution and community structure in North African streams.