How diversity in heat tolerance can help protect coral reefs

Adjacent corals at Lizard Island on the Great Barrier Reef show varying degrees of bleaching. Photo by Melissa Nagle
New research from Southern Cross University has discovered previously unrecorded diversity in the heat tolerance of corals in Australia’s Great Barrier Reef, raising hope that the corals’ own genetic resources may hold the key to helping them recover and adapt.
In a study published September 23 in the journal Communications Earth and Environment, researchers measured the bleaching thresholds of more than 500 colonies of table coral (Acropora gracilis) using a portable experimental system that was deployed at sea on 17 reefs across the Great Barrier Reef.
The research was led by Southern Cross University PhD student Melissa Naugle and carried out by a team from Southern Cross University, the Australian Institute of Marine Science (AIMS), the University of Queensland and the New Caledonia Development Institute as part of the Coral Reef Restoration and Adaptation Programme (RRAP).
“We found heat-tolerant corals on nearly every reef we studied, highlighting that corals across the Great Barrier Reef may harbor important genetic resources for conservation and restoration,” Naugle said.
“This is important news for corals, who are experiencing their fourth global mass bleaching event in the Great Barrier Reef and unprecedented increases in summer ocean temperatures. Naturally occurring changes in heat tolerance are essential to help corals adapt to climate change and for any restoration plans to be successful.”
These findings are substantiated in another recent study by co-author Hugo Dennis, also a PhD student at Southern Cross University, who also found wide variation in the heat tolerance of different coral species.
The results of this study have important implications for the future of coral reefs.
“Differences between individual corals drive natural selection to produce future generations of more resilient corals,” said co-author Dr. Line Bay, Senior Principal Research Scientist and Research Program Director at AIMS.
“Having a firm understanding of these changes is crucial for understanding how corals adapt to a warming climate.”


The experimental system used to test bleaching thresholds for over 500 coral colonies at sea. Courtesy of AIMS Joanna Harford (Australian Institute of Marine Science).
“This study highlights the existence of naturally heat-tolerant corals that can be targeted by RRAP for large-scale reef restoration and protection efforts to protect this important ecosystem from rising ocean temperatures already locked in by climate change,” said Dr. Cedric Robillo, Executive Director of the Coral Reef Restoration and Adaptation Program.
“Heat tolerance mutations could be useful for restoration programs such as breeding, which could accelerate adaptation and produce offspring that are better suited to warmer waters, but this will depend on the extent to which the observed heat tolerance mutations are linked to heritable genetic variation,” said co-author Dr Emily Howells, Senior Research Fellow at Southern Cross University and Project Leader for the Coral Reef Restoration and Adaptation Programme.
The most heat-tolerant corals were identified from this study and are now being used in selective propagation trials through the Coral Reef Restoration and Adaptation Program.
This study investigated not only the extent of variation in coral thermal tolerance but also the underlying causes of that variation.
“In this paper, we explore many of the environmental influences that shape thermal tolerance, including temperature history, nutrient concentrations, and the symbiotic algae that live within coral tissue,” Naugle said.
The study found that environmental factors such as ocean temperature are important in influencing heat tolerance, but there was a large amount of variation in heat tolerance that could not be explained by environment alone, which is likely due to genetic differences between individual corals.
“We then analyze the DNA sequence data from these individuals to identify genetic variants associated with heat tolerance, which will help us understand the adaptive capacity of natural coral populations and inform breeding studies,” Naugle said.
“While restoration activities such as breeding may increase coral populations, reducing greenhouse gas emissions is paramount to giving coral reefs the best possible future.”
Further information: Heat tolerance varies widely among reef-building coral species on the Great Barrier Reef, Communications Earth & Environment (2024). DOI: 10.1038/s43247-024-01649-4
Courtesy of Southern Cross University
Source: How diversity in heat tolerance helps protect coral reefs (September 23, 2024) Retrieved September 23, 2024 from https://phys.org/news/2024-09-diversity-tolerance-coral-reefs.html
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