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A unique stress experiment has aligned deoxygenation stress with the natural night-day cycle of the common coral reefs that form the Great Barrier Reef. Credit: Morgan Bennett-Smith
The deoxygenation of the oceans is now recognized as the main threat to the future global survival of the coral reef.
Oxygen is life, in or out of the water, and this raises concerns that dwindling ocean oxygen reserves are adding further environmental stress to already highly vulnerable coral reef ecosystems. Although the twin effects of ocean warming and acidification are well studied, until now there has been limited understanding of how the growing threat of ocean deoxygenation can affect the ability of corals to function and ultimately form coral reefs. .
A unique deoxygenation-reoxygenation stress experiment provided researchers at the University of Technology Sydney (UTS), the University of Konstanz and the University of Copenhagen with insights into how corals handle deoxygenation stress and the key genes that probably drive the varying susceptibility to stress that commonly results in coral bleaching.
The study, published in Biology of global change found that, like other animals and humans, corals have a similar and sophisticated response to low oxygen levels or hypoxia. The response is commonly triggered during oxygen-free exercise and cancer growth in humans
“Ocean deoxygenation is potentially a greater and more immediate threat to coral reef survival than ocean warming and acidification,” said lead author and UTS PhD candidate Rachel Alderdice.
“Coral reefs are increasingly exposed to low oxygen events due to climate change and localized pollution often caused by nutrient runoff.
“The extent to which corals are at risk for future decline in bottom ocean oxygen levels depends on their hypoxia sensing and response systems, so being able to identify this gene response system is significant and exciting,” Ms Alderdice, of the UTS Climate Change Cluster (C3) Future Reefs Research Program, said.
The unique stress experiment aligned deoxygenation stress with the natural night-day cycle of the common coral reefs that form the Great Barrier Reef. Transcriptomics RNA sequencing revealed key expressed genes that help keystone species such as Acropora tenuis respond to and tolerate low oxygen levels.
However, the research also revealed that not all corals appeared to be equally sensitive to hypoxia.
“We found that those bleached corals had delayed and less effective programming of their genetic response system to hypoxia than the unbleached coral. Differences in programming skills for this key genetic system can be key to understanding what determines corals’ ability to tolerate environmental stress and ultimately how to more accurately predict the future for coral reefs, “the University of Constance and senior author, Dr Christian Voolstra said
The researchers say that identifying such “ common switch ” stress genetic repertoires could provide a new means of identifying genes of interest to guide new diagnostics for better reef coral management or as a target for efforts to selective breeding of “ coral reef restoration ” aimed at increasing stress resistance corals.
Co-author Associate Professor David Suggett, who leads UTS C3’s Future Reefs Research Program, said, “A key concern we have right now is whether corals and reefs are already suffering the effects of sub-O2 stress. lethal. We were so concerned about uncovering the effects of ocean warming and acidification, we forgot about deoxygenation, despite its life-sustaining role and that oxygen is a property of the ocean that we can measure well. “
“This work confirms our recent analysis that continued ocean deoxygenation will play a vital role in shaping the future of our coral reefs, and yet another reason to urgently address climate change,” he said.
Reference: November 16, 2020, Biology of global change.
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