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Scientists Pinpoint How Corals Build Their Bony Structures

Stony coral play a role in their own growth that may help them survive in increasingly acidic seas. | Ryan McMinds/ Flickr/ CC BY 2.0

Corals rely on their own proteins to help create their rock-hard skeletons, according to a finding that contradicts a theory that the structures are created solely by a more passive chemical process, a new study reveals. The results , published in the 2 June issue of Science, suggest that the skeletal growth of corals may not be as negatively impacted by increasingly acidic seas as previously expected.

Corals are tiny marine invertebrates that typically live in colonies, secreting calcium carbonate to form a hard skeleton. These iconic creatures are increasingly threatened by climate change — most notably by related increases in seawater temperature. Surveys show that 29% of corals in Australia's Great Barrier Reef died in 2016, for example, largely due to warmer ocean temperatures in the region.

As part of a warming climate, the amount of dissolved carbon dioxide in the surface ocean also increases. This in turn boosts the acidity of the water and produces chemical conditions in the ocean that absorb some of the carbonate that marine organisms need to grow their skeletons and shells.

"Fortunately, based on our new work to understand coral reef development, we think that increasing ocean acidity, while it does impact many other marine organisms negatively, may not make it significantly harder for corals to deposit their calcium carbonate skeletons," said Paul Falkowski of Rutgers University, the study's lead author.

To date, scientists have struggled to pinpoint the underlying processes of coral skeletal development. Particularly contested has been just how the "rocky" bones of corals are created — through environmentally-dependent chemical reactions or in a controlled manner using proteins produced by the coral. Falkowski said that it has been traditionally difficult to determine the true process for a number of reasons, including a lack of information about the full scope of coral proteins and an inability to grow and observe coral specimens in sufficient detail.

A magnified calcification center on coral, surrounded by microsized argonite crystals. | Viacheslav Manichev and Stanislas Von Euw/ Rutgers University

Using an array of advanced imaging techniques, Falkowski and colleagues gained an unprecedented look into the formation of coral skeletons. They observed the clear progression of structural development, where small "balls" of magnesium-rich carbonate evolve into aragonite fibers. The imaging reveals that a set of highly acidic proteins actively drive this process.

"It is really remarkable how, at the smallest scale, we can observe how corals control the production and arrangement of their carbonate fibers to form a macroscopic biologically produced 'rock,'" said Falkowski.

Next his team plans to image the individual proteins within the coral skeleton, in an attempt to understand the spatial arrangement of the proteins and their potential role in the formation of the "rock."

Falkowski noted that because the corals catalyze the formation of carbonates with highly acidic proteins, they will still have the ability to form skeletons as the ocean acidifies.

"Corals make reefs — which are extremely important ecological environments that harbor extremely diverse groups of animals and microbes in shallow tropical and subtropical marine oceans around the globe," he said. "If corals can calcify in the face of ocean acidification that helps ensure that the base of these key ecosystems will survive human pollution of the atmosphere from the emission of carbon dioxide due to burning fossil fuels."


Michelle Hampson

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