Seacage aquaculture in a World Heritage Area: The environmental footprint of a Barramundi farm in tropical Australia

The fate of aquaculture wastes from a seacage farm within a pristine mangrove environment was studied. Seasonal and tidal differences were most important in determining water quality within receiving waters and obscured any nutrient enrichment effect by the farm. Farm wastes added significantly to the N budget status of the creek system, but overall water quality conformed to Queensland EPA Water Quality standards. Mangrove trees throughout the creek system contained ¹⁵N signatures traceable to aquaculture feeds, but the footprint of the farm itself was best indicated by the ratio of Zn:Li in sediments. The creek became hypoxic (<2 mg l⁻¹) during wet season low tides. Consequently, we recommended monitoring of water-column oxygen concentrations to warn of hypoxic conditions threatening to fish health, as well as Zn:Li ratios in sediment accumulation zones to determine the area of influence of the farm.