Falling ocean pH levels means rising threats for coral reefs

The rate of acidification in coral reef ecosystems is more than three times faster than in the open ocean, say a team of Southern Cross University biogeochemists.

Led by recent graduate Dr Tyler Cyronak, the results highlight how coral reefs may be acidifying faster than expected.

The University’s Centre for Coastal Biogeochemistry Research has published its results, ‘Enhanced coral reef acidification driven by regional biogeochemical feedbacks’ by Dr Tyler Cyronak, Associate Professor Isaac Santos, Associate Professor Kai Schulz, and Professor Bradley Eyre, in the latest edition of the Geophysical Research Letters journal.

Ocean acidification, or the lowering of the ocean pH due to anthropogenic inputs of carbon dioxide, has been well documented in the open ocean. However, this research looked back at studies done in coral reefs since the 1960s and found that the rate of acidification in coral reef ecosystems was more than three faster than in the open ocean.

The researchers developed a model based on previous work at Heron Island in the Great Barrier Reef to determine what the potential causes of this rapid increase in carbon dioxide were. “Our model demonstrated that small changes in the biogeochemistry, or the way coral reefs breathe carbon dioxide, could be to blame,” said Dr Cyronak.

Heron Island in the Great Barrier Reef  Photo by Christian Wild

Heron Island in the Great Barrier Reef
Photo by Christian Wild

“During the day coral reefs take up carbon dioxide because photosynthesis is dominant and at night they release carbon dioxide through respiration. Small changes to this natural daily cycle can have a big impact on the average acidity of coral reef waters.” Professor Bradley Eyre, director of the Centre for Coastal Biogeochemistry Research, said the study was significant. “The findings from this study are globally important because coral reefs are under a lot of pressure from climate change,” said Professor Eyre.“Ocean acidification in particular is expected to result in reef loss, which may now be worse than previously expected.” The biogeochemists argue that increased inputs of organic material and nutrients could be responsible. “More organic material can change the ratio of respiration to photosynthesis,” said Associate Professor Kai Schulz “Coral reefs are generally balanced, but if respiration increases it can have a big effect on the average carbon dioxide levels of a reef.”

The news is not all bad for coral reefs, with the scientists offering some hope. “I think there are some positives to these findings,” said Dr Cyronak. “Generally ocean acidification is thought of as a global problem. However, if the pH of a coral reef can be controlled by reducing runoff and terrestrial inputs there may be solutions to help offset the global problem of ocean acidification, or at least the increased threat, on a regional level.”

The work was funded by the Australian Research Council Discovery program.

Sharlene King, Southern Cross University, 12 August 2014. Article.

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