Sargassum henslowianum as a potential biofilter in mariculture farms of a subtropical eutrophic bay

Abstract

Abstract Mariculture has caused negative environmental impacts on the marine ecosystem in Dapeng Cove, Daya Bay, South China Sea. In this study, the brown macroalgae Sargassum henslowianum was introduced into fish and oyster farms as a biofilter to evaluate its bioremediation potential. We examined the temporal dynamics of seaweed growth, tissue nutrients (N and P), and heavy-metal contents (Cu and Zn) over a 100-day culture period (December 2012 to March 2013). The thalli of seaweed grown in the fish farm suffered greater from fouling and predation than those grown in the oyster farm. The specific growth rates by wet weight of S. henslowianum for the first three culture periods were all significantly higher in the oyster farm (at 6.30, 6.90, and 2.18% d−1) than the rates in the fish farm (at 2.77, 4.19, and −1.16% d−1). The tissue nutrients and heavy-metal contents of the seaweed at both sites all varied significantly with time. The estimated N bioaccumulation efficiency of seaweed at the oyster farm increased with time (from −34.44 to 62.91 mg thallus−1 d−1) until late February, but values for the seaweed at the fish farm (−4.70 to 7.19 mg thallus−1 d−1) increased only until late January. N bioaccumulation efficiency was significantly higher for seaweed in the oyster farm than for seaweed in the fish farm up to February 23; similar trends were found for the P, Cu, and Zn bioaccumulation efficiencies. We conclude that large-scale cultivation of S. henslowianum in the oyster farms of Dapeng Cove should be the first choice to alleviate eutrophication and improve water quality, and the seaweed biomass should be harvested by late February, allowing it to accumulate the optimum amount of nutrients and heavy metals from the water column.