Species associations in lotic macroinvertebrates and their use for river typology. Example of the Adour-Garonne drainage basin (France)

We analysed the regional distribution of 147 lotic invertebrate species fro m four insect orders - Ephemeroptera, Plecoptera, Trichoptera, Coleoptera - Elmidae and Hydraenidae - EPTC - in the whide Adour-Garonne drainage basin (South -Western France, Surface = 116 000 km(2)). The aim of this work was to provide a stream classification based on characteristic species assembl ages. The faunal data (species occurrence) were recorded at 252 sampling si tes, and studied using factorial analysis. Using dynamic cluster analysis, it was possible to classify the data without prior knowledge. Six zones wer e characterised within the drainage basin, along with their theoretical spe cies assemblages. The main interest of our results is that the stability of such theoretical assemblages may be used to define representative and/or r eference sites for biological surveillance, as changes in reference assembl ages can be considered as a biological indicator of environmental changes i n streams from a given region or longitudinal section.