ENVIRONMENTAL FACTORS INFLUENCING THE COMPOSITION AND DISTRIBUTION OF MAYFLY LARVAE IN NORTHERN ALGERIAN WADIS (REGIONAL SCALE)

Relationships between the assemblage structure of mayflies (Insecta: Ephemeroptera) and habitat conditions in wadis were explored in 87 localities of the North Algeria with 17 environmental variables and presence / absence data on Ephemeroptera species. The objective of this work is to (1) identify the environmental variables driving the composition of mayfly assemblages at the regional scale; (2) define the ecological preferences of mayflies species collected along environmental gradients, using recently developed statistical tools, including Outlying Mean Index Analysis (OMI) and (3) describe the assemblages of species that occur in similar habitats. 27 species of Ephemeroptera were recorded, about half of the entire Algerian mayfly fauna. Species richness is high (SR > 10), in spring, at stations located in mountain rivers (Blidean Atlas, Djurdjura) between altitude 300 to 600m. Water mineralization and altitude are the most important parameters which affected the abundance of Algerian mayfly species (North Algeria). In less extent, precipitation, substrate size, organic pollution and riparian vegetation explain also this distribution. However dissolved oxygen, pH and hydraulic factors (current velocity, depth) seem to be secondary. Baetis rhodani, Caenis luctuosa, Ecdyonurus rothschildi and Baetis pavidus are the most tolerant species against the considered variables. Rhithrogena sp. (RTol = 0.39) is characterized by narrow habitat tolerance. As for Habrophlebia gr. fusca and Alainites sp., they are linked to the headwaters (altitude), Labiobaetis neglectus and Cloeon dipterum to heavily mineralized waters (Cl and Mg). Cheleocloeon dimorphicum, Choroterpes (Ch.) atlas and Procloeon gr. bifidum occur in warm waters and Cloeon gr. simile is able to tolerate salty waters (high conductivity). Finally, Caenis pusilla, Acentrella sinaica and Ecdyonurus rothschildi, despite their narrow marginality, prefer the covered sites with coarse substrate and tolerate light pollution.