1. Introduction
The eutrophication of coastal waters caused by anthropic
activities has become a common problem in many countries. This
process contributes to an increase in primary productivity and
often generates undesirable changes in the structure and function
of aquatic ecosystems. In recent decades, eutrophication caused by
intensive aquaculture has become a constant concern for government
authorities, owing to the large amount of residues produced
by this activity. These wastes (mostly fecal material and uneaten
food) increase water nutrients, in particular nitrogen and phosphorous
(Beveridge 1996).
One of the main environmental concerns in aquatic animal
cultivation is the direct discharge of wastewaters into coastal
waters. Wastewater pollutants promote organic enrichment, sedimentation
and toxicity. This set of factors results in the deterioration
of coastal ecosystems and consequent loss of biodiversity
(Chopin et al. 2001). Although water is the major recipient of dissolved
residues from aquaculture, a considerable portion of the
solid material is retained inside the ponds, discharge canals or in
the vicinity of the farms (Funge-Smith and Briggs 1998). Both the
culture medium and coastal habitats where the activity is practiced