Oyster aquaculture enhances marine carbon sequestration by driving phytoplankton-derived particulate organic carbon

Coastal mariculture, particularly filter-feeding bivalve aquaculture, offers a promising approach to promote sequestered marine carbon and mitigate climate change. However, a mechanistic understanding of how bivalve farming regulates regional particulate organic carbon (POC) dynamics remains limited. Through year-round field monitoring in a representative oyster farming area in southern China, we found that culture modes (water depth and culture stage) significantly influenced the capacity and efficiency of oyster carbon sequestration. Shallow cultivation (1 m) promoted a 174 % greater carbon sequestration content than deepwater cultivation (5 m), and the carbon sequestration rate observed during the early farming stage was 30 % higher than that in the later cultivation phase. Unlike in non-culture areas, POC dynamics in oyster culture areas were strongly regulated by farming activities and environmental conditions (physical environments and nutrients), with patterns shifting across culture stages. Living POC community, dominated by plankton, exhibited seasonal rather than depth-related shifts. Importantly, during the later cultivation phases, a synergistic interaction between oysters and phytoplankton-derived POC potentially contributes to ecosystem-level carbon sequestration and nutrient cycling. These findings refine the understanding of feedback mechanisms between cultured bivalves and phytoplankton and provide a scientific basis for optimizing blue carbon strategies in coastal mariculture.