Migration patterns and pollution assessment of heavy metals in seawater, sediments, and marine organisms in the Xisha coral reef ecosystem of the South China Sea.

Pollution and protection of coral reef ecosystems have long been a focus of research. In this study, concentrations of heavy metals (HMs, including Cu, Pb, Zn, Cr, Cd, As, and Hg) were analyzed in seawater, surface sediments, and major marine organisms collected from the area surrounding the Xisha Islands in the South China Sea (SCS). Multiple assessment approaches, including the Risk Quotient (RQ), Index of Geo-accumulation (Igeo), Nemerow Comprehensive Pollution Index (NCPI), Pollution Load Index (PLI), Bioconcentration Factor (BCF), and Biomagnification Factor (BMF), were applied to evaluate HM pollution levels and trophic transfer. The marine environment of the Xisha coral reef area exhibited relatively low levels of HM contamination. Elements such as Cd and As tended to bioaccumulate in benthic organisms (bivalves), while Hg showed marked biomagnification in large predatory organisms. The primary factors controlling HM pollution were identified as the dilution effect of high-rate calcareous biogenic sedimentation and anthropogenic sources, including vessel traffic.