Disturbance of benthic topography and macrofauna community by sand mining in EEZ of the South Sea of Korea

초록

Sand mining in offshore area has rapidly increased due to rising global demand for construction resources. However, the environmental impacts of anchor suction dredging on the continental shelf including the Exclusive Economic Zone (EEZ) remain poorly understood. In this study, we conducted long-term monitoring (2013-2023) in four sand mining sectors on the continental shelf of the South Sea of Korea, a region characterized by deep waters (similar to 80 m) and limited terrestrial sediment supply. To evaluate geomorphological changes and benthic community responses to sand mining, particularly targeting the sediment composition, depth, current velocities, and benthic macrofauna communities, were investigated. Our results suggest that the seabed after sand mining is predominantly composed of sand (average: 89.8 %) with minor variations in sediment composition. Sand mining conducted in 2019 has resulted in an increase of water depth by 1-2 m within mining pits, which persisted for at least 29 months due to the slow benthic current velocities and a limited supply of terrestrial sediments. The number of species and abundance of the benthic macrofauna rapidly increased right after sand mining, but gradually decreased over time during the mining events. However, during the three years of long cessation period of sand mining, the relative taxonomic distinctness remained lower than that in the non-mining areas. The early dominance of polychaetes after sand mining reflects unstable benthic community that has not fully recovered. These findings underscore the need for management strategies that regulate and monitor sand mining with specific targets of amounts, areas, and periods of sand mining, considering the recovery of benthic communities in offshore marine ecosystems.

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