LAUSR

Abstract This study assessed the environmental impact of the cage culture of cobia (Rachycentron canadum) off the coast of Recife, northeastern Brazil. Fifteen thousand juveniles were reared in four 1200 m3 floating cages for 9 months and fed with a 42% protein commercial feed. Sampling campaigns were held at the beginning, during and after harvest (February, August and December of 2011, respectively). Seven sampling stations were established transverse to the coastline, and a control was placed 200 m to the southeast of the cages. Local hydrodynamics had an important role in dispersing the farming residues, which favored dispersion northeastwards. The area of direct impact of settling particles was estimated to be from 10 to 129 m from the cages. A significantly higher concentration of total nitrogen in the intermediate and final sampling campaigns and lower dissolved oxygen levels in the final sampling were observed. Significant changes in the structure of the macrobenthic community (decreased diversity and evenness parallel to an increase in density) reinforce that a process of organic enrichment took place in the area surrounding the fish farm. These changes, however, occurred only in a temporal, not spatial, fashion and were likely due to the organic enrichment of sediment by wastes from fish farming.