Seaweeds represent a promising blue carbon resource, capable of rapidly absorbing carbon dioxide through photosynthesis and contributing meaningfully to annual carbon sequestration. In this study, we quantified the carbon reduction potential of seaweed blooms and surrounding sediments by evaluating photosynthetic efficiency, carbon content in seaweed tissues, and organic carbon concentrations across different sediment depths in six tidal flats along the Korean coast. The estimated CO₂ uptake by seaweeds ranged from 0.02 to 4.2 Mg CO₂ ha⁻¹, while sediments showed values between 23 and 732 Mg CO₂ ha⁻¹. These results indicate that both seaweed blooms and adjacent sediments are important contributors to carbon sequestration, with sediments displaying particularly high carbon storage potential.
The dominant bloom species varied regionally, reflecting seasonal physiological differences and species-specific carbon storage capacities. On Jeju Island, where seaweed blooms persist year-round, seaweeds stored substantial amounts of carbon regardless of vegetation coverage, and sediment organic carbon content was exceptionally high. In contrast, tidal flats on the western coast, though lower in organic carbon content, exhibited considerable carbon sequestration due to their broad areal extent.
Overall, the blue carbon storage potential of seaweeds per unit area was comparable to, or even greater than, that of other major blue carbon ecosystems such as mangroves, salt marshes, and seagrasses. These findings emphasize the significant role of seaweed ecosystems and associated sediments in carbon storage and highlight the need for continued research and certification efforts to recognize them as valuable blue carbon sinks.