[A-CG40] Coastal Ecosystems 2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG40-10] Seasonal variations in the carbon metabolism of kelp and Sargassum seaweed

*Kenta Watanabe¹, Hirotada Moki¹, Masakazu Hori², Tomohiro Kuwae¹ (1.Port and Airport Research Institute, 2.Japan Fisheries Research and Education Agency)

Keywords:Seaweed beds, Carbon dynamics, Blue carbon, Dissolved organic carbon

Vegetated coastal ecosystems contribute to the global carbon budget through their carbon metabolism including photosynthesis, respiration, and organic carbon (OC) production. The restoration, preservation, and creation of these habitats are attracting attention as one of the negative emission activities because they have a potential to sequester atmospheric CO₂ in the ocean. Seaweed beds are the most dominant vegetated habitats in coastal waters also in Japan. Because seaweed inhabits on hard substrata, a large proportion of OC produced by them are exported to outside of the habitats and not stored inside the habitats. Although the export and the subsequent fate of dissolved OC (DOC) contribute substantially to carbon flows driven by seaweeds, the seasonal variations have little been understood. In this study, we measured monthly the rate of DOC release, photosynthesis, and respiration by seaweeds (kelp and Sargassum seaweeds) by field bag experiments. We conducted DOC degradation experiments to assess the recalcitrance of DOC produced by seaweeds. Our results show that there are seasonal variations in net primary production and DOC release rate, which would be related to the biomass changes. We will also present the variations in the recalcitrance of DOC and annual carbon flows by seaweed metabolism.