P/Ca in coral skeleton as a geochemical proxy for seawater phosphorus variation in Daya Bay, northern South China Sea

► We examine the reliability of coral P/Ca proxy in a distinctive eutrophic regime. ► Coral P/Ca was primarily a function of TP sw rather than PO4sw. ► The signal of P/Ca includes not only phosphate, but also organic phosphorus. ► Form of skeletal P, analytical methods and distinctive nutrient regime can explain our findings. ► Total P in corals may be more efficient P proxy in eutrophic environments.