Heterogeneity of periphyton in French Mediterranean rivers

The ecological niche of periphytic algae can be characterized by a long list of environmental variables: hydrology, substratum, light, water chemistry, temperature, other biota (Rott, 1991). In the French Mediterranean area, all the watercourse types are represented; we investigated permanent or intermittent, natural or perturbed streams, large rivers or brooks and tricklets flowing out on limestone or crystalline massifs. Most of studies are based on samples of periphyton from natural substrata (e.g. pebbles, cobbles, sand, silt and clay and macrophytes), but also some from artificial substrata. We also sampled simultaneously measurements of water quality and other relevant environmental variables. All investigations in Mediterranean area show the high sensibility of periphyton reacting quickly to environmental parameters; it is shown by a heterogeneous pattern of colonization at different levels.