Blue carbon is an essential component for achieving net-zero emissions and meeting the goals of the Paris Climate Agreement. This study focuses on the subtropical Mao-ao Bay in the northeastern Taiwan, evaluating the potential of carbon sequestration by investigating the primary productivity of phytoplankton and benthic macroalgae throughout the year of 2023. The results indicated that the carbon emission factors of photosynthetic organisms in Mao-ao Bay range from -0.2290 to -0.7705 gCO₂e m^-2 d^-1 (negative values denote the long-term sequestration of CO₂), with an average of -0.4437 ± 0.2421 gCO₂e m^-2 d^-1. This carbon sink is equivalent to 1.62 tonCO²e ha^-1 yr^-1. Seasonal variations revealed stronger carbon sequestration in the winter, possibly due to boosted inorganic nutrient supply from better water mixing. Furthermore, increasing the coverage of benthic macroalgae could significantly enhance the contribution to coastal blue carbon.

blue carbon,primary production,phytoplankton,macroalgae