Genetic Diversity Offers Hope for Coral Reef Recovery

A recent study by Southern Cross University found that corals on the Great Barrier Reef display unexpectedly high levels of heat tolerance, indicating that their genetic diversity could be key to their survival and recovery. The findings have been published in Communications Earth and Environment.

Researchers assessed the bleaching thresholds of more than 500 colonies of the table coral Acropora hyacinthus using a portable experimental system deployed across 17 reefs along the Great Barrier Reef.

As part of the Reef Restoration and Adaptation Program (RRAP), Melissa Naugle, a Ph.D. candidate at Southern Cross University, led a team of researchers from these institutions as well as the Australian Institute of Marine Science (AIMS), the University of Queensland, and the Research Institute for Development in New Caledonia.

We found heat-tolerant corals at almost all the reefs that we studied, highlighting how corals across the entire Great Barrier Reef may hold genetic resources that are important for protection and restoration.

Melissa Naugle, Ph.D. Candidate and Study Team Lead, Southern Cross University

“This is important news for corals, which are experiencing the 4th global mass bleaching event and unprecedented summer sea temperatures on the Great Barrier Reef. Naturally occurring heat tolerance variation is crucial for corals to adapt to climate warming and for the success of restoration initiatives,” adds Melissa Naugle.

These findings were further supported by a recent study conducted by co-author and fellow Southern Cross University PhD candidate Hugo Denis, who also observed significant variation in heat tolerance in different coral species.

The findings of this study will significantly impact future coral reefs.

Differences between individual corals is the fuel for natural selection to produce future generations of more tolerant corals.

Dr. Line Bay, Study Co-Author, Senior Principal Research Scientist and Research Program Director, Australian Institute of Marine Science

Bay continued, “Developing a solid understanding of this variation is crucial to understanding how corals will adapt to climate warming.”

This work highlights the availability of naturally heat-tolerant corals that can be targeted by RRAP, as a large-scale reef restoration and conservation effort, to protect this critical ecosystem from warming ocean temperatures that are already locked in from climate change.

Dr. Cedric Robillot, Executive Director, Reef Restoration and Adaptation Program, Southern Cross University

Dr. Emily Howells, Study Co-Author and Senior Research Fellow at Southern Cross University and Project Lead in the Reef Restoration and Adaptation Program, said: “Heat tolerance variation can be useful for restoration programs such as selective breeding, which may accelerate adaptation to produce offspring better suited to warmer waters. Though, this outcome depends on how much of the heat tolerance variation we observe is tied to heritable gene variants.”

Through the Reef Restoration and Adaptation Program, the most heat-tolerant corals identified in the study are currently being used in a selective breeding trial.

The research not only assessed the extent of heat tolerance but also investigated the factors contributing to this variation.

“In this paper, we explored many of the environmental influences that shape heat tolerance, like thermal history, nutrient concentrations, and the symbiotic algae that live inside coral tissue,” said Melissa. 

While environmental factors, such as sea temperatures, significantly influenced heat tolerance, a considerable variation remained unexplained by these factors, suggesting that genetic differences among individual corals likely play a crucial role.

Melissa concluded, “Next, we’ll analyze DNA-sequencing data from these individuals to identify gene variants associated with heat tolerance. This can help us understand the adaptation potential of natural coral populations and inform selective breeding work. While restoration initiatives like selective breeding may strengthen coral populations, reducing greenhouse gas emissions is most crucial to give coral reefs the best future possible.”

Journal Reference:

Naugle, S, M., et al. (2024) Heat tolerance varies considerably within a reef-building coral species on the Great Barrier Reef. Communications Earth & Environment. doi.org/10.1038/s43247-024-01649-4