Implementation of blue carbon offset crediting for seagrass meadows, macroalgal beds, and macroalgae farming in Japan

The "blue carbon" concept and the role of blue carbon stored in shallow coastal ecosystems in mitigating climate change have attracted attention worldwide. In addition to typical blue carbon ecosystems, such as mangroves, tidal marshes, and seagrass meadows, macroalgal beds and macroalgae farming are also gaining recognition as potential blue carbon sinks. Effective policies and methodologies are important for the conservation and expansion of blue carbon sinks, as well as the consequent reduction of atmospheric carbon dioxide (CO2). One of the most effective methods is carbon offset credit schemes. However, to date, almost all credit schemes have been implemented for mangroves and saltmarshes. None has been implemented for seagrass meadows, macroalgal beds, and macroalgae farming, although their CO2 uptake potentials are large. Here, we review three blue carbon offset credit projects for seagrass meadows, macroalgal beds, and macroalgae farming implemented in Japan. We show the blue carbon offset crediting projects of (1) Yokohama City, the first in the world; (2) Fukuoka City, the second such project in Japan; and (3) the first Japanese national governmental demonstration project. Furthermore, we highlight their characteristics by comparing them with the other blue carbon offset projects. Finally, we discuss the need to accelerate blue carbon offset credit projects and related initiatives in the future.