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ORIGINAL RESEARCH article

Front. Mar. Sci.
Sec. Coral Reef Research
Volume 11 - 2024 | doi: 10.3389/fmars.2024.1438087

Optimization of thermal stress thresholds on regional coral bleaching monitoring by satellite measurements of sea surface temperature

Provisionally accepted
Bailu Liu Bailu Liu 1,2,3Shawna A Foo Shawna A Foo 4Lei Guan Lei Guan 1,3,5*
  • 1 College of Marine Technology, Faculty of Information Science and Engineering, Ocean University of China, Qingdao, China
  • 2 The University of Sydney, Darlington, New South Wales, Australia
  • 3 College of Marine Technology, Sanya Oceanographic Institution, Ocean Univisity of China, Sanya, China
  • 4 School of Life and Environmental Sciences, The University of Sydney, Darlington, New South Wales, Australia
  • 5 Laboratory for Regional Oceanography and Numerical Modeling, Qingdao Marine Science and Technology Center,, Qingdao, China

The final, formatted version of the article will be published soon.

    Coral bleaching events have become more frequent in recent years due to the impact of widespread marine heatwaves. The Coral Reef Watch (CRW) program, part of the National Oceanic and Atmospheric Administration (NOAA), assesses bleaching risk by considering measures of daily coral heat stress (Hotspot, HS) and accumulated heat stress (Degree Heating Week, DHW). However, there is a mismatch between coral bleaching alerts through satellite monitoring and records of coral bleaching in the South China Sea (SCS) and its surrounding seas, where operational HS and DHW thresholds appear too conservative. Through comparison with field records of bleaching events in the SCS, this study examined the optimization of the DHW under a fixed or variable HS threshold, evaluating the accuracy of coral bleaching monitoring through a range of evaluation indices, including the Peirce Skill Score (PSS) and the Area Under the Curve (AUC). Our results show that when the DHW index was calculated based on the current operational HS threshold (1 °C), reducing the DHW threshold from 4 °C to 1.86 °C-weeks significantly improved PSS from 0.17 to 0.66, and AUC from 0.58 to 0.83. Further, by optimizing both HS and DHW, evaluation statistics were further improved, with the PSS increasing to 0.71 and the AUC increasing to 0.85. While both methods could significantly optimize the operational bleaching alert level for the SCS, the results suggest that optimization of both the HS and DHW thresholds is better than optimizing DHW alone. As marine heatwaves become more frequent, accurately predicting when and where coral bleaching is likely to occur will be critical to improving the estimation of regional coral stress due to climate change and for understanding coral reefs’ response to recurrent bleaching events.

    Keywords: Coral bleaching monitoring, South China Sea, sea surface temperature, Degree heating week, thermal stress

    Received: 25 May 2024; Accepted: 11 Nov 2024.

    Copyright: © 2024 Liu, Foo and Guan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Lei Guan, College of Marine Technology, Faculty of Information Science and Engineering, Ocean University of China, Qingdao, China

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