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. 2022 Aug;28(15):4509-4522.
doi: 10.1111/gcb.16083. Epub 2022 Feb 2.

Present and future bright and dark spots for coral reefs through climate change

Shannon Sully  1 , Gregor Hodgson  2   3 , Robert van Woesik  1
Affiliations

Present and future bright and dark spots for coral reefs through climate change

Shannon Sully et al. Glob Chang Biol. 2022 Aug.

Abstract

Marine heatwaves can cause coral bleaching and reduce coral cover on reefs, yet few studies have identified "bright spots," where corals have recently shown a capacity to survive such pressures. We analyzed 7714 worldwide surveys from 1997 to 2018 along with 14 environmental and temperature metrics in a hierarchical Bayesian model to identify conditions that contribute to present-day coral cover. We also identified locations with significantly higher (i.e., "bright spots") and lower coral cover (i.e., "dark spots") than regionally expected. In addition, using 4-km downscaled data of Representative Concentration Pathways (RCPs) 4.5 and 8.5, we projected coral cover on reefs for the years 2050 and 2100. Coral cover on modern reefs was positively associated with historically high maximum sea-surface temperatures (SSTs), and negatively associated with high contemporary SSTs, tropical-cyclone frequencies, and human-population densities. By 2100, under RCP8.5, we projected relative decreases in coral cover of >40% on most reefs globally but projected less decline on reefs in Indonesia, Malaysia, the central Philippines, New Caledonia, Fiji, and French Polynesia, which should be focal localities for multinational networks of protected areas.

Keywords: bright spots; climate change; coral cover; coral cover projections; coral ecology; hierarchical Bayesian model.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

FIGURE 1
FIGURE 1
Modern global percent coral cover. The locations of 2949 survey sites and their percent coral cover measured during the years 1997–2018
FIGURE 2
FIGURE 2
Model parameter coefficients of modern coral reefs globally. The relationships between the percentage of coral cover in each survey and the environmental variables are displayed within a Bayesian framework with mean values (circles) and 95% credible intervals (the thin black horizontal lines) as well as 50% credible intervals (the thick black horizontal lines) from 7714 Reef Check surveys at 2949 sites in 76 countries from 1997 to 2018. Blue dots show a positive association with percent coral cover, red dots show a negative association with percent coral cover, and white dots show no significant association with percent coral cover (95% credible interval crosses zero dashed line)
FIGURE 3
FIGURE 3
The sites of modern global coral reef “bright spots” and “dark spots” from 1997 to 2018. Gray dots are the survey sites where the measured percent coral cover was within 1.5 standard deviations (30% total coral cover) of expected coral cover. Yellow dots are the survey sites where the measured percent coral cover was at least 1.5 standard deviations greater than the expected percent coral cover. Dark circles are the survey sites where the observed percent coral cover was less than 1.5 standard deviations less than the expected percent coral cover
FIGURE 4
FIGURE 4
Projected absolute change in percent coral cover at Reef Check sites globally. The difference between modern (1997–2018) expected percent coral cover and future expected percent coral cover at Reef Check sites globally. Change in percent coral cover: (a) by the year 2050 for RCP4.5, (b) by the year 2100 for RCP4.5, (c) by the year 2050 for RCP8.5, and (d) by the year 2100 for RCP8.5
FIGURE 5
FIGURE 5
Projected relative change in percent coral cover at Reef Check sites globally. The relative difference between modern (1997–2018) expected percent coral cover and future expected percent coral cover at Reef Check sites globally. Relative change in percent coral cover: (a) by the year 2050 for RCP4.5, (b) by the year 2100 for RCP4.5, (c) by the year 2050 for RCP8.5, and (d) by the year 2100 for RCP8.5
FIGURE 6
FIGURE 6
Absolute and relative change in future global percent coral cover under Representative Concentration Pathways (RCPs) 4.5 and 8.5 in 2100. (a) Absolute change under climate change scenario RCP4.5, (b) relative change under RCP4.5, (c) absolute change under RCP8.5, and (d) relative change under RCP8.5
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