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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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Coral Community Composition Linked to Hypoxia Exposure
ABSTRACT Tropical reef ecosystems are strongly influenced by the composition of coral species, but the factors influencing coral diversity and distributions are not fully understood. Here we demonstrate that large variations in the relative abundance of three major coral species across adjacent Caribbean reef sites are strongly related to their different low O2tolerances. In laboratory experiments designed to mimic reef conditions, the cumulative effect of repeated nightly low O2drove coral bleaching and mortality, with limited modulation by temperature. After four nights of repeated low O2, species responses also varied widely, from > 50% bleaching inAcropora cervicornisto no discernable sensitivity ofPorites furcata.A simple metric of hypoxic pressure that combines these experimentally derived species sensitivities with high‐resolution field data accurately predicts the observed relative abundance of species across three reefs. Only the well‐oxygenated reef supported the framework‐building hypoxia‐sensitiveAcropora cervicornis, while the hypoxia‐tolerant weedy speciesPorites furcatawas dominant on the most frequently O2‐deplete reef. Physiological exclusion of acroporids from these O2‐deplete reefs underscores the need for hypoxia management to reduce extirpation risk.
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- PAR ID:
- 10552011
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 30
- Issue:
- 10
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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