Genes help some coral cope with low oxygen

Low oxygen levels in the ocean prevent coral from respiring properly and could be as much of a threat to the world’s reefs as ocean acidification and rising temperatures, researchers say.

And it’s happening now. “Coral reefs are increasingly being exposed to low oxygen events due to climate change and localised pollution often caused by nutrient run-off,” says Rachel Alderdice, from Australia’s University of Technology Sydney (UTS).

There is some good news, but it comes with a qualification.

In a recent study, Alderdice, UTS colleagues and researchers from Denmark and Germany found that some coral species are genetically equipped to overcome stress from hypoxia (an absence of sufficient oxygen). But only some.

Acropora tenuis, a common coral on Australia’s Great Barrier Reef, is more resistant than others to bleaching, for example, but Acropora selago, is more likely to bleach when stressed.

“We found those corals that bleached had a delayed, less-effective programming of their hypoxia response gene system compared to the non-bleached coral,” says Christian Voolstra from the University of Konstanz, a co-author of a paper in the journal Global Change Biology.

“The differences in programming abilities for this key gene system may be fundamental to understanding what dictates corals’ capacity to tolerate environmental stress – and ultimately how to more accurately predict the future for coral reefs.”

The findings came after the team examined RNA transcripts produced by coral under oxygen stress to see what genes were used to combat hypoxia. RNA transcripts reflect the genes that are being used at a certain time or in response to a certain condition, so the researchers determined which genes were being “switched on” when the coral didn’t have enough oxygen.

These genes were used in a stress response system called the hypoxia‐inducible factor (HIF)‐mediated hypoxia response system (HRS). HIF-HRS helped overcome low oxygen levels in A. tenuis and protected the coral from bleaching.

These genes also provide new ways of diagnosing and managing stressed coral, the researchers say, and can be used to select strong coral for breeding to repopulate some parts of the reef.

Surprisingly, some of the HIF-HRS genes made heat-shock proteins, which are commonly used for overcoming high temperatures. This suggests the genes that help coral breath in low oxygen could also help overcome other stresses caused by climate change.