The eastern part of the Morbihan gulf (south Brittany, France) is a confined area, where the anthropic actions (dredging, urban and agricultural inputs...) are increasingly significant. Other biotic and abiotic factors, in particular the climatic fluctuations and the introduction of exotic species, have an impact on the benthic ecosystem and modify the equilibrium between species within the assemblages. The use of ecological groups and the biotic indices method allows to detect the first signs of disturbance of the assemblages. In 1961, the macrofauna assemblages were poor in number of species and densities. They were dominated by sensitive species, mainly bivalve molluscs. Therefore, they seemed to be in a normal state. In 1995, the assemblages were much richer and reached very high densities. The dominance of tolerant and, especially, opportunistic species mainly Polychaetes, signifies that hypertrophic conditions are settled. Intermediate data (1969 and 1975) allow to well appreciate this 35-years evolution. |
