Stage-Specific Drivers of Carbon-Sequestration Dynamics in <i>Porphyra</i> Mariculture and Responses to Global Warming

Seaweed mariculture represents a promising blue-carbon strategy, but its carbon-sequestration dynamics and resilience to warming remain insufficiently constrained. Here, we conducted a comprehensive field assessment at a representative <i>Porphyra</i> (nori) mariculture farm in coastal China, where we monitored multisphere carbon pools across the water-column, sediments, atmosphere, and biomass. Multivariate statistical analysis and machine-learning models were used to identify stage-specific drivers and project carbon-pool responses under multiple warming scenarios. Our results demonstrate that <i>Porphyra</i> cultivation delivers substantial carbon-sequestration benefits, as it significantly enhances atmospheric CO₂ sequestration and sedimentary carbon burial. Concurrently, the system consistently releases dissolved organic carbon (DOC), of which 48-54% was transformed into long-lived refractory DOC. High-temporal-resolution monitoring reveals highly dynamic carbon pools across cultivation stages, with dominant controls on net sequestration shifting from inorganic-carbon uptake and hydrodynamics during early growth to biologically mediated processes at peak biomass. Simulations across climate-change scenarios indicate that although inorganic pools were more temperature-sensitive than organic pools, changes across all major pools under projected warming over the coming decades remain within 5%, underscoring strong resilience to warming. Together, these process-based insights support the integration of macroalgal mariculture into blue-carbon action plans and carbon-offset initiatives.