Comparison between the fish communities of lakes, reservoirs and rivers: can natural systems help define the ecological potential of reservoirs ?
Résumé
The European Water Framework Directive (WFD) aims at improving the ecological status of continental waters, including man-made water bodies. Thereby it raises the question of the reference conditions for reservoirs. A number of limnologists consider reservoirs as intermediate systems between lakes and rivers. Hence, the aim of this study is to contribute to the implementation of the WFD by comparing the fish communities across these three types of ecosystems. This was achieved using fish sampling data from 21 natural lakes, 50 reservoirs and 549 river stations. The lists of occurring species are very similar between lakes and reservoirs, and appear as a subset of the species occurring in rivers. Lakes and reservoirs are also very similar in terms of common and rare species. Conversely, the comparison of community structures (summarised by correspondence analysis axes) supports the hypothesis of an intermediate position of reservoirs between lake and river systems. This latter result could reflect the effect of large-scale processes undergone by freshwater ecosystems whatever their type and the non-independence of water bodies within their catchments, particularly when considering the communities of highly mobile organisms like fishes. Although the major conservation concerns are about natural systems, artificial ones should also be considered in monitoring and assessment programs in order to allow efficient catchment-scale management policies.
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