- Increased ocean acidity does not slow down growth of the yellow finger corals around Heron Island, researchers have found.
- This adaptation is most likely a response to the extreme, but natural, fluctuations in temperature and pH that commonly occur in seawater around Heron Island, the authors write.
- This finding is a “step closer to help us understand how corals will cope in future oceans where pH is likely to drop due to human induced rising carbon dioxide levels,” researchers say.
Ocean acidification is troubling for most marine creatures. But some corals may have built-in protection mechanisms that could help them cope with changing ocean chemistry, a new study published this week in the Proceedings of the National Academy of Sciences has found.
Increased acidification of oceans — or lowering of seawater pH — due to carbon dioxide from burning fossil fuels is expected to harm corals by corroding their calcium carbonate skeleton, and slowing their growth.
To see if this is true for the yellow finger corals (Porites cylindrical), a team of scientists from the University of Western Australia and University of Queensland subjected yellow finger coral colonies within some sections of Heron Island in the Great Barrier Reef of Australia to heightened fluctuations in seawater pH levels.
The team found that despite fluctuations in the seawater acidity, the yellow finger corals continued to grow at the same steady rate.
The secret, the researchers discovered, was that these corals maintained an internal pool of “calcifying fluid” at a fixed pH level. This calcifying fluid — where calcium carbonate crystals form giving rise to the coral reef skeleton — seemed unaffected by the external seawater chemistry, and allowed the corals to grow their skeleton at a steady rate.
“We knew corals have some form of internal pH regulation mechanism in relation to the external seawater, but this is the first time we see the mechanism being so strong,” Lucy Georgiou, lead author of the study from the University of Western Australia, told Mongabay.
This adaptation is most likely a response to the extreme — but natural — fluctuations in temperature and pH that commonly occur in the seawater around Heron Island, the authors write. These fluctuations are far more than in many other reef systems, they add.
Oceans are becoming increasingly acidic. The pH of ocean water has fallen by 0.1 pH units since the beginning of the industrial revolution, resulting in a 30 percent increase in acidity, according to the National Oceanic and Atmospheric Administration. In the future, oceans will continue to absorb excess carbon dioxide from the atmosphere, and become more acidic, experts warn.
So the yellow finger corals’ ability to maintain the chemical balance of their calcifying fluid could make them more resilient to future changes in ocean pH levels.
“It a step closer to help us understand how corals will cope in future oceans where pH is likely to drop due to human induced rising carbon dioxide levels,” Georgiou said. “We can now see if other species and corals from less dynamic systems have this ability to adapt to the conditions of Heron Island and lower pH waters.”
But there are still lots of unanswered questions, she added. These include questions such as, “will increasing temperatures impact the internal pH regulation of the coral and how these corals will fair in other reefs if they are transplanted to provide more resilient coral colonies on fragile systems,” she said.
- Georgiou L. et al (2015) pH homeostasis during coral calcification in a free ocean CO2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef. Nature Plants doi/10.1073/pnas.1505586112.