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

[ACG40-02] Coral Bleaching simulation in the Sekisei Lagoon, Okinawa, Japan, based on a coupled hydrodynamic–biogeochemical–polyp-scale coral bleaching model

*Takashi Nakamura¹, Toshihiro Miyajima², Tomihiko Higuchi², Sylvain Agostini³, Ikuko Yuyama⁴, Hiroyuki Fujimura⁵ (1.School of Environment and Society, Tokyo Institute of Technology, 2.Atmosphere and Ocean Research Institute, The University of Tokyo, 3.Shimoda Marine Research Center, University of Tsukuba, 4.Yamaguchi University, 5.University of the Ryukyus)

Keywords:coral bleaching, 2016, numerical simulation, Sekisei Lagoon, coral polyp model

To elucidate the mechanism responsible for coral bleaching and to project the status of coral communities in the future, a coral bleaching model was developed based on a reef-scale three-dimensional hydrodynamic–biogeochemical model coupled with a polyp-scale coral bleaching model.
The polyp-scale bleaching model was developed by incorporating the dynamics of photoinhibition, reactive oxygen species (ROS), and zooxanthella density based on a previously developed coral polyp model by Nakamura et al. (2013). The polyp-scale bleaching model was coupled with reef-scale hydrodynamic-biogeochemical model based on the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System (Warner et al., 2010) with model coupling framework by Nakamura et al. (2018). We also developed a hydrodynamic model of the Sekisei Lagoon area which is down-scaled from the global and regional ocean analysis/reanalysis products by a multi-nested approach based on the COAWST Modeling System, and conducted 26-year (1994 to 2020) high spatiotemporal resolution hindcast simulation in and around the Sekisei Lagoon area (The results are shown here: http://www.nakamulab.mei.titech.ac.jp/yaeyama_hindcast_simulation). Coral bleaching simulation in the Sekisei Lagoon area was conducted based on the Sekisei Lagoon hydrodynamic model with the coral bleaching model.
In 2016, mass-bleaching events had occurred worldwide, and corals in the Sekisei Lagoon had also been heavily damaged through the bleaching event. Therefore, we conducted a bleaching simulation in 2016 and successfully reproduced the mass-bleaching event by this bleaching model. Bleaching simulations were also conducted for the other years, and the results were compared with the observed bleaching ratio in and around the Sekisei Lagoon taken through the Monitoring Sites 1000 project by Ministry of the Environment, Japan. In this result, it is confirmed that the bleaching situation was reasonably reproduced by this bleaching model.