Stony coral: NMR and climate resistance

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  • Published: Jun 15, 2017
  • Author: David Bradley
  • Channels: NMR Knowledge Base
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Credit where it's due

Stylophora pistillata, a well-studied stony coral common in the Indo-Pacific. Credit: Kevin Wyman/Rutgers University

2D nuclear magnetic resonance (NMR) spectroscopy and ultra-high-resolution 3D imaging have been used to investigate a well-known and previously well-studied stony coral of the Indo-Pacific to reveal that it precipitates minerals through a biologically driven process. The findings suggest that this particular species may be more resistant to climate change than first thought.

"For stony corals, we're fairly confident that the acidification issue is exaggerated," suggests Paul Falkowski of Rutgers University. "They’re more resilient than we give them credit for." He and his colleagues have demonstrated using various techniques how these creatures rely on proteins to help them create their rock-hard skeletons. These creatures are not quite as susceptible to the effects of acidification of the oceans, driven by rising atmospheric carbon dioxide concentrations and global warming, as is of increasing concern with regards soft corals.

"The bottom line is that corals will make rock even under adverse conditions," Falkowski says. He leads the Environmental Biophysics and Molecular Ecology Laboratory at Rutgers University-New Brunswick and adds that, "They will probably make rock even as the ocean becomes slightly acidic from the burning of fossil fuels."

Stony silence

Falkowski's post-doctoral researcher and lead author on the paper in the journal Science associated with this work, Stanislas Von Euw, used a materials science approach and tapped several high-tech imaging methods to show that corals use acid-rich proteins to build rock-hard skeletons made of calcium carbonate minerals.

"What we're showing is that the decades-old general model for how corals make rock is wrong," Falkowski adds. "This very careful study very precisely shows that corals will secrete proteins, and the proteins are what really forms the mineral and the proteins are very acidic, which will surprise a lot of people."

Corals are largely colonial organisms that harbour hundreds to hundreds of thousands of polyps, each an individual animal. Reefs built by stony, shallow-water coral species are among the world's most diverse ecosystems and incredibly important to thousands of species of fish and other sea life. Additionally, thousands of human communities rely on reefs for food, protection, jobs, and tourism, according to the US National Oceanic and Atmospheric Administration. Unfortunately, one of the threats of climate change is perceived as the demise of corals. The long-term environmental prognosis is not good for many species of coral that are susceptible to the often deadly bleaching caused by rising sea temperatures, nutrient pollution, and physical destruction of coral reefs. Moreover, carbon dioxide emissions are directly linked to oceanic acidification and reduced availability of calcium carbonate which these creatures use to maintain their structures.

Rocky resistance

There have been two main hypotheses regarding how stony corals construct their skeletons. One relies on largely physical and chemical processes while the other assumes a biologically driven mechanism. The Rutgers team in studying Stylophora pistillata have shown that coral "stone" is precipitated through a biological process.

"As far as I know, we were unique in the world in using a coordinated set of techniques to understand the ultrastructure of coral skeletons," Falkowski adds. In addition to NMR spectroscopy, the team also used Raman imaging and spectroscopy, and scanning helium ion microscopy. The data reveal how random nanoparticles are deposited in coral microenvironments enriched in organic material. The nanoparticles accumulate to form the stony structures composed of calcium carbonate, in the form of aragonite. The NMR spectra specifically showed that acid-rich proteins in the corals are the main drivers. Moreover, these proteins function at a pH of about 8.5 to 7. The ocean normally has a pH of 8.1 or 8.2 and climate change forecasts suggest that this figure might drop to 7.8. Even at that level, these stony corals will still be able to make rock, the team suggests.

Related Links

Science 2017, 356, 933-938: "Biological control of aragonite formation in stony corals"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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