The challenge of sustainable aquaculture: effects on the environment of the Patos Lagoon Estuary

Abstract

Over the last ten years, catches of the pink shrimp Farfantepenaeus paulensis by artisanal fishermen in the Patos Lagoon Estuary (southern Brazil) have been decreasing. This has created economic and social problems for approxi-mately 3500 families, who rely on this activity as their main source of income. In an attempt to solve these problems, the Mariculture Laboratory of the University of Rio Grande (FURG) has developed a technological package for the pen culture of this species in the estuarine area. This culture system requires low investment, is easy to manage and allows fishermen to continue their normal activities. This study evaluates the influences that this culture may have on the macrobenthic communities surrounding the enclosures. The experiment was carried out around a 0.3 ha pen placed in the estuarine area adjacent to Marinheiros Island (Rio Grande county). This area has a central channel over 5 meters deep and shallow areas less than 1.5 meters deep near the shore, where the pen was installed. Two linear transects were carried out in opposite directions parallel to the shoreline, starting from the edge of the pen. Monthly water and sediment samples were collected 5, 15, 30 and 100 m from the pen to evaluate oxygen consumption, chlorophyll-a, total phosphorus and total nitrogen concentrations. Characterization of the macrobenthic community revealed the presence of Laeonereis acuta, Nephtys fluviatilis, Neanthes sp., Kalliapseudes schubartii, Callinectes sap-idus, Erodona mactroides, Heleobia australis, Heteromastus similis and isopods. Significant differences in the diversity and abundance of the species were detected between the samples, especially at the closest point to the pen, where more H. similis specimens were found. No significant differences in oxygen consumption, total nitrogen or total phos-phorus concentrations were found between the sampled points. These results demonstrate that this kind of culture system does not influence water quality in the surrounding area. The higher abundance of H. similis near the pen (1m) demonstrated a very limited impact on the macrobenthic community. Organic matter accumulation zones created by the presence of the pen might favor the presence of H. similis, which is a deposit feeder. This result could become more significant if the culture conditions are intensified or more pens are installed.