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

We investigated the abundance, diversity and community structure of mayflie s (Ephemeroptera), stoneflies (Plecoptera) and blackflies (Diptera: Simulii dae) in the Sebaou 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 Sebaou river (Great Ka bylie, North Algeria). Analysis of species diversity of the three considere d taxa showed an altitudinal gradient with maximal diversity in the piedmon t and low altitude mountain areas (from 200 to 500 m), which provided the m ost heterogeneous habitats to the benthic fauna. In contrast, the low diver sity of the lowland sites was due to high water temperatures, reduced summe r discharge and anthropogenic disturbances. In the same way, the low divers ity of the high mountain areas can be attributed either to low water temper atures or high fluctuation in daily temperature. Three species assemblage g roups are revealed, the first two are related to an upstream-downstream gra dient, with headwater sites characterised by stoneflies species and middle stream sites by a high mayfly and blackfly diversity and abundance. The thi rd group was identified as spring sites characterised by a low abundance an d occurrence of stonefly species. Both altitudinal species diversity gradient and species assemblage of the S ebaou wadi were different from European and temperate areas, revealing that the accentuated North African Mediterranean climate could induce changes t o both species and community structure. These results provide insights to t he influence of some environmental features on aquatic insect species distr ibution and community structure in North African streams.