The photosynthetic uptake of inorganic carbon from Pyropia seaweed aquaculture beds: Scaling up population-level estimations

Seaweed aquaculture beds (SABs) contribute positively to CO₂ removal (CDR) worldwide. Among cultivated seaweed species, Pyropia represents approximately 8% of the global seaweed production and has the capacity to sequester a significant amount of carbon from the surface layer of the coastal ocean. In this study, we evaluated the carbon uptake efficiency of Pyropia SABs by measuring their photosynthetic rates. Pyropia individuals were collected from Pyropia SABs on the south and west coasts of South of Korea from December to March (cultivation period) in 2016 to 2019, and the photosynthetic light response curves (P-E curves) were measured. Oxygen-based photosyntheses were converted into carbon-based photosynthetic rates using theoretical photosynthetic quotients. Pyropia thallus consumed an average 37 mg C g⁻¹ww d⁻¹, with a high ratio of gross primary production to respiration (P/R ratio; 5–14). To quantify the carbon uptake potential in the coastal areas of South Korea during the cultivation period, we extrapolated the carbon uptake rates using the estimated biomass, total area of Pyropia SABs, and meteorological irradiance data. The highest carbon uptake rate (2143 kt C month⁻¹) was observed in the Southwestern Sea of South Korea in December. Considering all productivity data from the entire cultivation period, approximately 6789 kt C was taken up by the Pyropia SABs. Therefore, our study indicates a significant potential to mitigate climate change by reducing greenhouse gas emissions using Pyropia SABs.