Impact of dredging on macrobenthic communities and ecological quality in South Korean shellfish farms

Dredging is widely used to improve sediment conditions in shellfish aquaculture areas, but its ecological effects are often difficult to distinguish from natural temporal variability. This study evaluated sediment chemistry, macrobenthic communities, and ecological quality status (EcoQS) before and after dredging in two South Korean shellfish farming bays. Environmental drivers were examined using multivariate analyses, and EcoQS was assessed using five benthic indices and one composite index. The two bays showed contrasting responses. In Gangjin Bay, dredging coincided with clear changes in macrobenthic community composition and EcoQS under elevated organic matter and Pb-related sediment risk. In Yeojaman Bay, stronger hydrodynamic exchange, lower organic enrichment, and temporal variability appeared to moderate the detectable effects of dredging. Metals and organic matter-related variables were important correlates of macrobenthic variation. M-AMBI and the composite index showed stronger relationships with environmental gradients than most single indices. Mean sediment Pb in Gangjin Bay and Zn in Yeojaman Bay exceeded national threshold criteria. Dredging effects in shellfish farms are bay-specific and should be interpreted in conjunction with sediment characteristics, metal contamination, hydrodynamic conditions, and temporal variability. Site-adapted monitoring integrating sediment chemistry, macrobenthic communities, and a multi-index EcoQS assessment is recommended for sustainable shellfish farm management.