WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2025 77 The current discussion on expanding blue carbon is meaningful because, for the first time, the international community is institutionalizing ecosystems outside the previous guidelines. Tidal flats, seaweeds, and marine sediments have been virtually excluded from national reduction policies. Still, through this discussion, their carbon storage function is being reviewed, and the first steps are being taken to recognize them as institutional sinks by establishing quantitative standards and technical systems. It is not a simple conceptual expansion but a structural shift from scientific validation and institutionalization to policy use. The role of marine ecosystems is now entering a new phase, proven by data and standards rather than mere potential. Tidal Flats Without Photosynthesis, Proven by Data Tidal flats have been recognized as iconic marine ecosystems, but they are not internationally acknowledged as carbon sinks. Due to their lack of vegetation, they have not been considered blue carbon ecosystems, such as mangroves and seagrass beds, and have been excluded from the IPCC criteria. In recent years, however, South Korea has been at the forefront of the discussion by scientifically quantifying the carbon storage capabilities of tidal flats and presenting them to the international community. Professor Khim Jong-Seong of Seoul National University’s School of Earth and Environmental Sciences stated at the ‘Our Sea Our Life Book Concert’ on April 16 that “Korean researchers were the first to scientifically prove the carbon absorption capacity of tidal flats, which was previously little known.” He analyzed sediment samples from tidal flats across Korea and quantitatively demonstrated how tidal flats absorb and store carbon dioxide. He explained, “At the IPCC-62, an outline of the blue carbon methodology, including tidal flats, was finalized, and if it is officially adopted by the Session later this year, it will be a significant turning point.” According to the Seoul National University Blue Carbon Project Group’s paper, “Sediment Organic Carbon Storage in Tidal Flats of the Korean Peninsula” (2021, Science of the Total Environment), Korea’s tidal flats store more than 13 million tons of organic carbon and absorb up to 490,000 tons of CO2 annually (Figure 2). Regions with higher mud content, such as the West Coast, exhibited greater storage capacity, and clay content was closely correlated with organic carbon levels. This research scientifically supports that tidal flats are not just exposed to tides but serve as long-term carbon storage. Professor Kwon Bong-Oh of Kunsan National University’s Department of Marine BioResources emphasized, “Photosynthesis by microalgae and sedimentation co-occur on the mudflat surface, allowing long-term CO2 storage. Although the structure differs from traditional vegetationbased blue carbon, its function is sufficiently proven.” If tidal flats are included in the IPCC guidelines, Korea could be recognized as a leading country in the entire process, from scientific validation to the proposal of international standards. It would signal a new chapter in ocean-based carbon mitigation strategies beyond simply adding a new sink. Seaweeds: A Carbon Forest Created by Photosynthesis Seaweed is one of the fastest-growing plant organisms in the ocean, fixing CO2 through photosynthesis and playing a key role in the organic carbon cycle of marine ecosystems (Figure 3). In Korea, the Marine Forest Creation Project has focused on large brown algae communities to enhance carbon absorption. According to the Korea Fisheries Resources Agency (FIRA), since 2009, approximately 347 km² of marine forests have been established, absorbing around 117,000 tons of CO2 annually. Seaweed carbon absorption is measured mainly through two methods. First, the amount of oxygen produced during photosynthesis is indirectly estimated. Dissolved oxygen (DO) in seawater, generated as seaweed fixes CO2, is measured over time and converted to CO2 absorption using an ‘inorganic carbon conversion factor,’ with quantification adjusted for seasonal photosynthesis rates. The second method is sediment-based analysis. Samples of the sediment around the seaweeds are taken and analyzed for organic carbon content, sedimentation rate, and density, and the amount of biogenic organic matter left behind by the seaweeds during their growth is estimated to be fixed on the seabed. These two methods work in parallel, and Korea is currently establishing a measurement, reporting, and verification system that meets international standards. A FIRA official explained, “Seaweed communities can be created both naturally and artificially, and their growth area and cycle can be managed, making them suitable for institutionalization.” He added, “Currently, seaweed-based sea forests meet five of the FIGURE 2. South Korea's tidal flats store 1,300 tons of organic carbon and can absorb 260,000 tons of carbon dioxide annually. FIGURE 3. Schematic diagram of total carbon uptake of sea forests. (Source: Korea Fisheries Resources Agency). (CONTINUED ON PAGE 78)
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