Impact of ocean warming on coral thermal tolerance (ANCHOR)

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Climate change affects coral reef ecosystems at an unprecedented scale, with a global increase of the frequency, intensity, and duration of heat stress events, resulting in escalating rates of coral bleaching (i.e., loss of their photosynthetic algal endosymbionts) and mortality. Thermally tolerant corals will most likely be the main reef builders and ecosystem sustainers of future reefs, but we do not know how the predicted increase in sea surface temperatures will affect their ability to respond to even hotter summer maxima. Here, we propose to determine if and how putative 'stress resilient' corals can adjust their thermal tolerance thresholds, or alternatively if those thresholds are genetically fixed. We propose to conduct a long-term warming experiment (following the IPCC RCP-2.6 and 4.5 trajectories) interspersed with short-term heat stress assays that mimic summer maxima. The new standardized Coral Bleaching Automated Stress System (CBASS) will be used to determine the progression of corals’ thermal thresholds over time and assess if any possible acclimation is lost upon return to baseline conditions. The genomic and genetic underpinnings of thermal tolerance in the investigated coral colonies will be characterized via their gene expression and microbial community composition. Our results could uncover critical processes underlying coral thermal tolerance thresholds and how organisms respond to acute heat stress events in a warming world, to ultimately better forecast the impact of climate change on coral reefs of the future.