The composition of the echinoderm, mollusc and decapod assemblages associated with a Posidonia oceanica meadow located close to a fish-farmvaried with distance from the cages Three ecological zones were identified. The intermediate zone II (40-160m from the cages) had a higher species richness and abundance than either zones I (nearest the cages) and III (320m from the cages), probably due to the higher production resulting from a moderate level of nutrient enrichment at intermediate distances from the source of pollution.