Under the Rising Heat: Coral Bleaching Across Japan in 2024

Under the Rising Heat: Coral Bleaching Across Japan in 2024 | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Under the Rising Heat: Coral Bleaching Across Japan in 2024 Fabian Gösser, Ayaka Umeda Paul, Jue Alef A. Lalas, Joseph D. DiBattista, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8699206/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Japan spans one of the world’s widest latitudinal ranges of zooxanthellate coral ecosystems, from tropical reefs in the southern Ryukyus to marginal temperate coral communities along the Pacific coast of Honshu. While high-latitude coral populations have often been viewed as potential thermal refugia, the 2024 global bleaching event provided a rare opportunity to assess their vulnerability under extreme heat stress. Using daily satellite-derived sea surface temperature (SST) and Degree Heating Week (DHW) information from NOAA Coral Reef Watch, combined with field-verified bleaching observations, we mapped the spatial extent and severity of thermal stress across Japanese coral habitats from ~ 24°N to 34°N. Maximum SST frequently exceeded 31°C in tropical and subtropical regions and surpassed 30°C at temperate sites, with all surveyed locations reaching DHW Alert Level 3. Bleaching was confirmed from southern Iriomote and Okinawa, to high-latitude sites in Kochi and Shikinejima, demonstrating elevated summer temperatures now affect corals far beyond the traditional subtropical range. Repeated bleaching since the 1990s has contributed to declining coral cover and shifts toward stress-tolerant and non-coral benthic communities on many southern subtropical reefs, whereas temperate coral populations remain constrained by episodic disturbances, storm impacts, thermal variability, and winter cold spells. The 2024 Global Coral Bleaching Event shows, Japanese mainland coral communities are not insulated from heat stress and their role as climate refugia needs reconsideration. Our findings highlight the exceptional latitudinal extent of the 2024 Global Coral Bleaching Event in Japan and emphasize the need for integrated, climate-adaptive conservation strategies across Japanese coral ecosystems. Coral bleaching High-latitude reefs Degree Heating Weeks Thermal refugia Figures Figure 2 Figure 4 Full Text Additional Declarations No competing interests reported. Supplementary Files JapanbleachingSupplementaryfiles.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8699206","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":625067886,"identity":"91f761fb-06b0-4044-8d50-3f64c15c3873","order_by":0,"name":"Fabian Gösser","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAklEQVRIiWNgGAWjYBAC9gYehgNIfBsgZmw8gF0xBPAcQNWSBtLSQFALMjgMJvFrYT978MDPHQx2/eztjz983HPebm37YaAtNTbROLXw5CUc7D3DkDyz54yZ5Ixnt5O3nUkEajmWltuAQ4s9Q47BAd42hmSDGzlszDwHbiebHQBqYWw4jFMLD/8bg4N/QVruP3/8+c+Bc8lm5x8S0CKRY3AYaIudwQ0GA2mGAwfszG4QskXiXcJh2TaJBMmeHDPJngPJCWY3gLYk4PELD3/u4Y9v22zs+dmPP/7w44Cdvdn59IcPPtTY4NQCBRKJMAUQRgJ+5WBgj8EYBaNgFIyCUQADABTJZ05Kw3tWAAAAAElFTkSuQmCC","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":true,"prefix":"","firstName":"Fabian","middleName":"","lastName":"Gösser","suffix":""},{"id":625067887,"identity":"fde9f485-1b8d-4312-9c58-83514f8baa2c","order_by":1,"name":"Ayaka Umeda Paul","email":"","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":false,"prefix":"","firstName":"Ayaka","middleName":"Umeda","lastName":"Paul","suffix":""},{"id":625067888,"identity":"f863c93a-534f-492b-9a69-9adb8d0222c4","order_by":2,"name":"Jue Alef A. 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This site is frequently visited for a research project, with the same entry point. The pictures may not show the exact same position, but they should only differ by a few meters.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8699206/v1/3d42684af45aef081c7d0a4e.png"},{"id":107869108,"identity":"be41cb8d-2d6b-4a18-9628-d0a93294a33a","added_by":"auto","created_at":"2026-04-27 07:36:07","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":3015408,"visible":true,"origin":"","legend":"","description":"","filename":"JapanbleachingSupplementaryfiles.docx","url":"https://assets-eu.researchsquare.com/files/rs-8699206/v1/2b1c668477dc3718e11f0a0f.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Under the Rising Heat: Coral Bleaching Across Japan in 2024","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Coral bleaching, High-latitude reefs, Degree Heating Weeks, Thermal refugia","lastPublishedDoi":"10.21203/rs.3.rs-8699206/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8699206/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eJapan spans one of the world\u0026rsquo;s widest latitudinal ranges of zooxanthellate coral ecosystems, from tropical reefs in the southern Ryukyus to marginal temperate coral communities along the Pacific coast of Honshu. While high-latitude coral populations have often been viewed as potential thermal refugia, the 2024 global bleaching event provided a rare opportunity to assess their vulnerability under extreme heat stress. Using daily satellite-derived sea surface temperature (SST) and Degree Heating Week (DHW) information from NOAA Coral Reef Watch, combined with field-verified bleaching observations, we mapped the spatial extent and severity of thermal stress across Japanese coral habitats from ~\u0026thinsp;24\u0026deg;N to 34\u0026deg;N. Maximum SST frequently exceeded 31\u0026deg;C in tropical and subtropical regions and surpassed 30\u0026deg;C at temperate sites, with all surveyed locations reaching DHW Alert Level 3. Bleaching was confirmed from southern Iriomote and Okinawa, to high-latitude sites in Kochi and Shikinejima, demonstrating elevated summer temperatures now affect corals far beyond the traditional subtropical range. 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Our findings highlight the exceptional latitudinal extent of the 2024 Global Coral Bleaching Event in Japan and emphasize the need for integrated, climate-adaptive conservation strategies across Japanese coral ecosystems.\u003c/p\u003e","manuscriptTitle":"Under the Rising Heat: Coral Bleaching Across Japan in 2024","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-24 11:13:49","doi":"10.21203/rs.3.rs-8699206/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e334fbc6-70ad-4adc-ae5d-9096fde991b2","owner":[],"postedDate":"April 24th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-28T22:24:47+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-24 11:13:49","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8699206","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8699206","identity":"rs-8699206","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}