[A-CG56] Coastal Ecosystems-2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG56-P04] Macroalgal metabolism and carbon budgets affect atmospheric CO₂ uptake in a temperate Sargassum bed

*Kenta Watanabe¹, Goro Yoshida², Masakazu Hori², Yu Umezawa³, Hirotada Moki¹, Tomohiro Kuwae¹ (1.Port and Airport Research Institute, 2.National Research Institute of Fisheries and Environment of Inland Sea, 3.Tokyo University of Agriculture and Technology)

Keywords:macroalgal bed, CO2 sink, metabolism, blue carbon, carbon dynamics

Macroalgal beds are considered to be one of the vegetated coastal ecosystems (i.e., blue carbon ecosystems) that act as atmospheric CO₂ sinks. Macroalgal metabolisms and carbon budgets affect CO₂ sequestration by macroalgal beds, but its relationships are still poorly understood. In this study, we investigated air–water CO₂ exchange and budgets of dissolved inorganic carbon, total alkalinity, and dissolved organic carbon (DOC) in a temperate Sargassum bed during the productive winter. We estimated the metabolism of macroalgae and carbon budgets by using a field-bag method, a degradation experiment, and mass balance modelling over a diurnal cycle. Our results showed that macroalgal metabolism and carbon budgets affected atmospheric CO₂ uptake in and around the Sargassum bed. The macroalgal metabolism formed water with low CO₂ and high DOC that was then exported offshore. This export process potentially promotes CO₂ uptake in and around macroalgal beds.