Satellite-based analysis of an unverified mass coral bleaching event on the Great Barrier Reef in 2021
Spady, Blake L., Skirving, William J., Geiger, Erick F., Cantin, Neal E., Liu, Gang, De La Cour, Jacqueline L., Mumby, Peter J., Norrie, Andrew, and Manzello, Derek P. (2025) Satellite-based analysis of an unverified mass coral bleaching event on the Great Barrier Reef in 2021. Coral Reefs, 44 (4). pp. 1275-1285.
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Abstract
The Great Barrier Reef (GBR), Australia, has experienced more frequent heat stress events since the region’s first recorded mass coral bleaching event in 1998. Seven confirmed mass coral bleaching events have occurred on the GBR, including five events since 2016. Due to the large scale of the GBR, comprehensive visual bleaching surveys are challenging, particularly as heat stress events accumulate more frequently in remote regions. One such event lacking extensive bleaching surveys occurred on the northern GBR in 2021, suggesting a need for alternative monitoring options. Satellite-based heat stress monitoring products recorded significant bleaching-level heat stress (4 °C-weeks) on 67% of the northern GBR in 2021, comparable in extent to previously confirmed events. Here, we demonstrate a strong correlation between satellite-based heat stress metrics and mass bleaching on the GBR, and indicate that the GBR has likely experienced at least eight mass bleaching events from 1998 to 2024, three of which were consecutive events affecting the northern GBR from 2020 to 2022. In-water surveys and time-series observations of individual corals at Lizard Island confirm partial and fully bleached corals (> 50% coral cover bleached) were common in shallow and deep habitats in 2021. From 1998 to 2015, there were two widespread bleaching events; this increased to one event every 1.5 years from 2016 to 2024, indicating that the GBR is approaching an annual bleaching scenario. As heat stress events become more common, bleaching thresholds from satellite-based monitoring products remain accurate and should continue to be used to predict and understand the potential impacts from thermal stress to reef ecosystems.
| Item ID: | 87879 |
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| Item Type: | Article (Research - C1) |
| ISSN: | 1432-0975 |
| Keywords: | Coral reefs, Degree Heating Week, Heat stress, Mass bleaching, Remote sensing, Sea surface temperature |
| Copyright Information: | © The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. |
| Date Deposited: | 06 Mar 2026 04:58 |
| FoR Codes: | 31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 100% |
| SEO Codes: | 18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180504 Marine biodiversity @ 100% |
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