RAPID: Does life-long acclimatization to temperature variability promote coral climate resilience?

Coral reefs are in serious danger, with relentless ocean warming currently considered the greatest threat to reef survival. Sustained temperatures just 1°C above a coral’s typical summer maximum can lead to coral bleaching – the breakdown of symbiosis between the coral and its endosymbiotic algal partner. Coral bleaching can often lead to coral death, and marine heatwaves causing mass coral bleaching have increased from a single mild event in the last century to as many as five per decade in modern times. Remarkably, thermally variable habitats provide a glimmer of hope that heatwave-resilient coral populations may exist, as exposure to high daily temperature variability can ‘prime’ reef-building corals to better withstand heat stress. This project investigates the effects of the most extreme marine heatwave to occur on the southern Great Barrier Reef to understand whether the elevated coral bleaching thresholds due to priming equate to coral community resilience against bleaching during a heatwave. The work enhances our understanding of how priming influences coral responses to heat stress, the ecological relevance of current priming benefits in a warming ocean, and the physiological properties of corals that may promote heat tolerance. Broader impacts of this project include research support and training for several early career scientists as well as informing local, regional, and global action from stakeholders in making conservation and management decisions, particularly surrounding ecosystem intervention and restoration. For the 500 million people who rely on coral reefs for food, tourism, and coastal protection, a better understanding of how diverse coral communities develop thermal tolerance and withstand the increasing threat of marine heatwaves supports more effective conservation and management of coral reef ecosystems in a changing climate. It has become increasingly important to identify heat-tolerant coral populations capable of surviving intensifying marine heatwaves. This project tests the hypothesis that life-long exposure to daily temperature fluctuations improve the ability of corals to cope with the additional heat stress associated with severe marine heatwaves. This research advances understanding of the priming exposure (e.g., magnitude of diel thermal variability) most beneficial for bleaching resistance and survival and the physiological properties that promote this resilience across biological scales. Specifically, this project: (i) compares coral community bleaching resilience (i.e. prevalence and severity) during this heatwave with a decade of seawater temperature, coral demography, species composition, and benthic cover data, and (ii) compares the gene expression and physiology of three genera of corals (Acropora, Pocillopora, and Porites) across six sites with different maximum diel temperature fluctuations (2.4–7.7°C/day). This research advances understanding of the mechanisms underlying coral community resilience to heat stress and enables more effective conservation and management of coral reef ecosystems during the extreme heatwaves accompanying changing climate. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.