During an environmental monitoring programme after the Amoco-Cadiz and the Tanio oil-spills, beaches in the north-west coasts of Brittany were visited annually (1982-1986).Regrouping the benthic fauna according to the ecological groups, enabled their utilization as biological indicators.
The organic carbon and nitrogen analysis in the sediment used along with the biotic index showed that fine sand beaches were distributed in three categories separating the perturbated, unbalanced and the normal stations. C : N ratios in spite of their relative precision appeared to be around 6-7 for the normal stations but >15 for the unbalanced and heavily perturbated stations.
