Temperature patterns and mechanisms influencing coral bleaching during the 2016 El Niño

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Under extreme heat stress, corals expel their symbiotic algae and colour (that is, ‘bleaching’), which often leads to widespread mortality. Predicting the large-scale environmental conditions that reinforce or mitigate coral bleaching remains unresolved and limits strategic conservation actions1,2. Here we assessed coral bleaching at 226 sites and 26 environmental variables that represent different mechanisms of stress responses from East Africa to Fiji through a coordinated effort to evaluate the coral response to the 2014–2016 El Niño/Southern Oscillation thermal anomaly. We applied common time-series methods to study the temporal patterning of acute thermal stress and evaluated the effectiveness of conventional and new sea surface temperature metrics and mechanisms in predicting bleaching severity. The best models indicated the importance of peak hot temperatures, the duration of cool temperatures and temperature bimodality, which explained ~50% of the variance, compared to the common degree-heating week temperature index that explained only 9%. Our findings suggest that the threshold concept as a mechanism to explain bleaching alone was not as powerful as the multidimensional interactions of stresses, which include the duration and temporal patterning of hot and cold temperature extremes relative to average local conditions.

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Fig. 1: Indo-Pacific scale and severity of coral bleaching during the 2016 El Niño/Southern Oscillation event.
Fig. 2: Effect of environmental variables on coral bleaching.

Data availability

Data are available at the Knowledge Network for Biocomplexity (https://knb.ecoinformatics.org) via https://doi.org/10.5063/F1WQ024C.

Code availability

R code is available on GitHub: https://github.com/WCS-Marine/2016-bleaching-patterns


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T.R.M. and N.A.M. received support from the John D. and Catherine T. MacArthur Foundation and the Sustainable Poverty Alleviation from Coastal Ecosystem Services (SPACES) NE-K010484-1 project. E.S.D. was supported by a Banting Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada and the John D. and Catherine T. MacArthur Foundation. Data collection in the Solomon Islands was supported by the Wallace Research Foundation, and the Waitt Foundation supported data collection in Fiji. Maldives data collection was supported by IUCN and USAID. M.M.M.G. received support from the French National Research Agency under the STORISK project (no. ANR-15-CE03-0003). Data collection in Zanzibar was partly supported by the NORHED project coordinated by the State University of Zanzibar (SUZA). The Tiffany & Co. Foundation and the John D. and Catherine T. MacArthur Foundation supported data collection in some Western Indian Ocean reefs. V.J.P. received support from the DST-INSPIRE Faculty Programme, and Z. Tyabji and S. Chandrasekhar assisted V.J.P. with data collection in the Andaman Islands. R.A. received funding support from the Pew Marine Fellowship and an Intramural Project from the Spanish National Research Council (CSIC-201330E062). S.A.K. was funded by the VILLUM Foundation (no. 10114). A.T.H. received funding from the Carnegie Corporation of New York. Indonesia data collection was supported by the John D. and Catherine T. MacArthur Foundation and Margaret A. Cargill Philanthropies. We thank the following people for assistance with data collection: A. Baird, A. Halford, R. J.-L. Komeno, C. Miternique, A. dan Muhidin, E. Muttaqin, E. Montocchio, C. Muhando, S. Pardede, N. Summers and S. Yadav.

Author information

T.R.M., E.S.D. and J.M.M conceived the study with the support of all the authors. T.R.M led the manuscript writing, with the help of E.S.D. and J.M.M. E.S.D., J.M.M., S.D. and T.R.M. conducted all the analyses. All the other authors contributed data, edited and approved the manuscript.

Correspondence to Tim R. McClanahan.

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