Assessment of nutrient cycling in an intensive mariculture system

Rapid mariculture expansion has raised concerns about coastal eutrophication. This study assesses nutrient cycling in Sansha Bay, China, a eutrophic semi-enclosed bay with intensive mariculture. A two-endmember mixing model showed significant additions of dissolved inorganic nitrogen (DIN; 6.9 ± 4.1 μmol L^-1) and phosphorus (DIP; 0.45 ± 0.29 μmol L^-1) in May 2020, mainly from mariculture. Estimated N and P inputs from fish farming were 7789 ± 361 tons and 1497 ± 91 tons in spring, respectively, with N mainly in dissolved form and P in particulate form. And, trash fish feed caused higher nutrient release than formulated feed. Of the feed input, 52.8 ± 4.7 % of DIN and 33.0 ± 3.7 % of DIP were released into environment, exceeding riverine input and offshore exchanges. Co-culturing kelp and oysters removed 1079 ± 11 tons of N and 156 ± 8 tons of P. Therefore, adjusting feed types and planning co-cultivation strategies could alleviate eutrophication resulting from mariculture expansion.