Biofiltering and uptake of dissolved nutrients by Ulva armoricana (Chlorophyta) in a land-based aquaculture system

Abstract

An on-land flow-through cultivation system was designed for the macroalgal species Ulva armoricana (Chlorophyta) to reduce the environmental impact of aquaculture effluent in coastal ecosystems as part of an integrated aquaculture system. The macroalgae was cultured in various enriched media at a stocking density of 500 kg wet weight/pond. Overall, U. armoricana was able to remove a greater percentage of inorganic nitrogen in the double fertilizer ratio. The total dissolved phosphate was higher in standard seawater. U. armoricana showed preference for bioaccumulation, with ranges as follows: zinc (9.908 - 32.942 mg.kg-1); copper (1.893 - 5.927 mg.kg-1); cadmium (0.254 - 1.500 mg.kg-1); and lead (none detected). Apart from the presence of cadmium (Cd), the algal biomass produced at the end of the experiment was of a relatively good quality with limited heavy metal contamination so that U. armoricana could be successfully used as a plant stimulant but not as part of a feed formulation for livestock and for the food industry. This study showed that U. armoricana can effectively be used as a biological filter for dissolved nutrient uptake from aquaculture effluents. The prospect of better management practices, based on the utilization of Ulva mariculture designs, bodes well for the aquaculture industry.