Presentation Information
[O03-P03]Seawater anomalies and widespread coral bleaching along subtropic to temperate Japan coast during the fourth global coral bleaching event★Invited Papers
*Kurihara Haruko1, Hiroya Yamano2, Sayaka Yasunaka3, Nina Yasuda2, Chuki Hongo4, Masako Nakamura5 (1.University of the Ryukyus, 2.Tokyo University, 3.Tohoku University, 4.Wakayama Prefectural Nanki Kumano Geopark Center, 5.Tokai University)
Keywords:
Climate Change,Coral,Bleaching,Ocean warming,Coastal Kuroshio current
Coral reef ecosystems are among the most diverse and productive marine ecosystems, hosting more than 25% of all marine species, despite covering less than 1% of the ocean. Coral reefs also provide critical ecosystem services, including coastal protection from natural disasters, as well as benefit to human such as food provision, fisheries, tourism and medicines (Beck et al. 2018, Hoegh-Guldberg et al. 2019, Li et al. 2023). However, coral reefs are among the most threatened marine ecosystems under climate change. Corals bleaching, a phenomenon in which corals loss their symbiotic dinoflagellate algae (Symbiodiniaceae), resulting in reduced growth and increased mortality, is primary driven by extreme temperature stress. Mass coral bleaching events caused by thermal stress are now observed worldwide and are expected to become more severe and frequent with ongoing global warming and the intensification of marine heatwaves (Hughes et al. 2017; Sully et al. 2019).
During 2023-2034, the combination of long-term climate-drive warming and a strong El-Nino-Southern Oscillation (ENSO) event resulted in record-breaking global temperature (Peng et al. 2025). This unprecedented ocean warming triggered the fourth global coral bleaching event, which began in the Caribbean subsequently expanded to the Southern Hemisphere (Reimer et al. 2024).
In this study, we evaluated sea surface temperature anomalies and Degree Heating Weeks (DHW) along the coast of Japan influenced by the Kuroshio and Tsushima warm Currents in 2024. DHW is an index suggested to predict coral bleaching risk and is calculated as the cumulative weekly positive temperature anomalies when sea surface temperature exceeds the maximum mean monthly climatology by at least 1 °C. In addition, we assessed coral bleaching prevalence at two subtropical reef sites (Ishigaki and Okinawa Island), and six non-reef temperate sites extending up to 35 °N along the Japanese coast.
We found that the maximum monthly mean (MMM) temperature reached the highest value in the past 43 years at five sites out of the six examined sites. The DHW index also reached record-high values at all sites over the same period, exceeding 8.0 °C weeks at all locations and reaching a maximum of 19.10 °C weeks. Previous studies have shown that the DHW values greater than 4.0 °C weeks are associated with the onset of coral bleaching, while values exceeding 8.0 °C weeks result in widespread mass bleaching and coral mortality. Consistent with this, in situ observation revealed mass coral bleaching at both subtropic reef and temperate sites, with the exception of Tateyama. At temperate sites, scleractinian corals including species that have recently expanded their distributions poleward exhibited extensive bleaching. However, while most bleached corals in particularly shallow reef areas at subtropical sites suffered high mortality, the majority of corals at temperate sites recovered following bleaching.
Here we further discuss the potential future impacts of climate change on coral distribution and coastal ecosystems, as well as the implication to human society.
During 2023-2034, the combination of long-term climate-drive warming and a strong El-Nino-Southern Oscillation (ENSO) event resulted in record-breaking global temperature (Peng et al. 2025). This unprecedented ocean warming triggered the fourth global coral bleaching event, which began in the Caribbean subsequently expanded to the Southern Hemisphere (Reimer et al. 2024).
In this study, we evaluated sea surface temperature anomalies and Degree Heating Weeks (DHW) along the coast of Japan influenced by the Kuroshio and Tsushima warm Currents in 2024. DHW is an index suggested to predict coral bleaching risk and is calculated as the cumulative weekly positive temperature anomalies when sea surface temperature exceeds the maximum mean monthly climatology by at least 1 °C. In addition, we assessed coral bleaching prevalence at two subtropical reef sites (Ishigaki and Okinawa Island), and six non-reef temperate sites extending up to 35 °N along the Japanese coast.
We found that the maximum monthly mean (MMM) temperature reached the highest value in the past 43 years at five sites out of the six examined sites. The DHW index also reached record-high values at all sites over the same period, exceeding 8.0 °C weeks at all locations and reaching a maximum of 19.10 °C weeks. Previous studies have shown that the DHW values greater than 4.0 °C weeks are associated with the onset of coral bleaching, while values exceeding 8.0 °C weeks result in widespread mass bleaching and coral mortality. Consistent with this, in situ observation revealed mass coral bleaching at both subtropic reef and temperate sites, with the exception of Tateyama. At temperate sites, scleractinian corals including species that have recently expanded their distributions poleward exhibited extensive bleaching. However, while most bleached corals in particularly shallow reef areas at subtropical sites suffered high mortality, the majority of corals at temperate sites recovered following bleaching.
Here we further discuss the potential future impacts of climate change on coral distribution and coastal ecosystems, as well as the implication to human society.