Certain coral colonies regulate themselves, survive ocean acidification

A species of corals living in a dynamic reef system could protect itself from the impact of ocean acidification, claim scientists from the ARC Centre of Excellence for Coral Reef Studies, or Coral CoE.

Ocean acidification, one of the greatest long-term challenges facing reefs, is caused by rising carbon dioxide, or CO2. This condition reduces corals' ability to form their skeletons and build reef structures.

Researchers discovered that coral colonies of P. cylindrical, which thrive in Heron Island lagoon on the Great Barrier Reef, have a unique way of solving the problem. The team from University of Western Australia and the University of Queensland detail their findings in the journal Proceedings of the National Academy of Sciences.

“Our research shows that some corals living in dynamic reef systems have the ability to maintain a nearly constant pH within their calcifying fluid, regardless of the pH of the surrounding environment. This enables them to continue to form their calcium carbonate skeleton even under relatively low pH conditions,” said Lucy Georgiou, the study’s lead author.

Her co-author, Professor Malcolm McCulloch, claims that the findings indicate physiological controls on the pH of the coral’s calcifying fluid despite large declines in the highly dynamic environment. He said that previous mesocosm experiments conducted under constant conditions of pH and temperature indicated a partial dependence of the corals' calcifying pH on the external seawater.

With the regulatory mechanism, corals are able to grow at a relatively constant rate, which may mean they are more resilient to the effects of ocean acidification in such environment than previously thought. To study the colony in its natural environment, the researchers used the innovative Free Ocean Carbon Enrichment, or FOCE, technique, which simulates the impact of ocean acidification.

The team warned though that while their findings are positive, it’s not yet known if the adaption is specific to certain species or if it is limited to colonies in dynamic reef systems. Georgiou said this is most likely to apply on corals from reefs such as Heron Island lagoon, where temperature and pH fluctuations vary greatly on daily to seasonal basis.

For their next steps, the team hopes to explore if P. cylindrica colonies from more stable environments also have the ability to adapt and if they can be as resilient to increased acidity. They also need to explore the impact of rising sea temperature on the corals' ability to maintain its internal pH, Georgiou said.

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