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Abstract Marine heatwaves are increasing in frequency and duration, threatening tropical reef ecosystems through intensified coral bleaching events. We examined a strikingly variable spatial pattern of bleaching in Moorea, French Polynesia following a heatwave that lasted from November 2018 to July 2019. In July 2019, four months after the onset of bleaching, we surveyed > 5000 individual colonies of the two dominant coral genera,PocilloporaandAcropora, at 10 m and 17 m water depths, at six forereef sites around the island where temperature was measured. We found severe bleaching increased with colony size for both coral genera, butAcroporableached more severely thanPocilloporaoverall. Acroporableached more at 10 m than 17 m, likely due to higher light availability at 10 m compared to 17 m, or greater daily temperature fluctuation at depth. Bleaching inPocilloporacorals did not differ with depth but instead varied with the interaction of colony size and Accumulated Heat Stress (AHS), in that larger colonies (> 30 cm) were more sensitive to AHS than mid-size (10–29 cm) or small colonies (5–9 cm). Our findings provide insight into complex interactions among coral taxa, colony size, and water depth that produce high spatial variation in bleaching and related coral mortality.
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Local habitat heterogeneity rivals regional differences in coral thermal tolerance
Abstract Variable temperature regimes that expose corals to sublethal heat stress have been recognized as a mechanism to increase coral thermal tolerance and lessen coral bleaching. However, there is a need to better understand which thermal regimes maximize coral stress hardening. Here, standardized thermal stress assays were used to determine the relative thermal tolerance of three divergent genera of corals (Acropora,Pocillopora,Porites) originating from six reef sites representing an increasing gradient of annual mean diel temperature fluctuations of 1–3 °C day−1. Bleaching severity and dark-acclimated photochemical yield (i.e.,Fv/Fm) were quantified following exposure to five temperature treatments ranging from 23.0 to 36.3 °C. The greatest thermal tolerance (i.e.,Fv/Fmeffective dose 50) was found at the site with intermediate mean diel temperature variability (2.2 °C day−1), suggesting there is an optimal priming exposure that leads to maximal thermal tolerance. Interestingly,AcroporaandPocilloporaoriginating from the least thermally variable regimes (< 1.3 °C day−1) had lower thermal tolerance than corals from the most variable sites (> 2.8 °C day−1), whereas the opposite was true forPorites, suggesting divergent responses across taxa. Remarkably, comparisons across global studies revealed that the range in coral thermal tolerance uncovered in this study across a single reef (< 5 km) were as large as differences observed across vast latitudinal gradients (300–900 km). This finding indicates that local gene flow could improve thermal tolerance between habitats. However, as climate change continues, exposure to intensifying marine heatwaves is already compromising thermal priming as a mechanism to enhance coral thermal tolerance and bleaching resistance.
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- Award ID(s):
- 1923743
- PAR ID:
- 10498806
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Coral Reefs
- Volume:
- 43
- Issue:
- 3
- ISSN:
- 0722-4028
- Format(s):
- Medium: X Size: p. 571-585
- Size(s):
- p. 571-585
- Sponsoring Org:
- National Science Foundation
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