Last updated March 22, 2018 at 11:35 am
Researchers test lab theory on section of Great Barrier Reef – with alarming results.
Experimental plume of acidified seawater and a dye tracer flowing across a coral reef flat in Australia’s Great Barrier Reef. Credit: Aaron Takeo Ninokawa
Ocean acidification makes it harder for corals to grow. As CO2 concentrations in our atmosphere rise, the gas dissolves into the world’s oceans, producing carbonic acid.
In more acid conditions it’s harder for corals to grow by building their carbonate frameworks. Not only is it more difficult to grow, existing structures can also start to dissolve.
What happens when coral reefs are exposed to acidic waters?
This stunting effect on coral growth has been known for a while now, but changes in growth have only ever been measured on individual species in lab conditions, not on actual living reefs.
New research published in Nature does just that – with a research team led by Ken Caldeira and Rebecca Albright carrying out an acidification experiment on a section of the Great Barrier Reef.
Related content: Not just the oceans, freshwater acidification is happening too
Once a day over the course of a month, they dissolved CO2 into seawater, added a tracing dye, and released the acidified water over a section of reef at One Tree Island at low tide. This dropped the pH of seawater from 8.12 to 7.98. Given current trends, we’re likely to see oceans reach this sort of pH by about 2060.
The researchers found that the net rate of community calcification (the difference between new growth, and dissolving of existing structures) dropped by 34 per cent in the area of the reef exposed to the plume of acidified seawater. This is a higher sensitivity than previously reported for coral structures.
“Our findings provide strong evidence that ocean acidification caused by carbon dioxide emissions will severely slow coral reef growth in the future unless we make steep and rapid reductions in greenhouse gas emissions,” said Albright.
Could we give the reef an antacid?
Previously this research team had conducted a similar experiment, instead making seawater more alkaline. They found that this gave the coral a boost in its ability to grow.
In the face of ocean acidification, could artificially increasing the alkalinity of seawater near critical reefs be a last ditch rescue method?
“It’s a viable strategy if you have a small, enclosed area without a lot of water exchange that is of high conversation priority,” said Albright.
“However, this is not a scalable solution to mitigating ocean acification on global coral reefs – the only solution is cutting carbon emissions.”
Keeping track of ocean acidification
Future Reef 2.0 is a $1 million research program run by CSIRO to continue to monitor the Great Barrier Reef and its water chemistry. Samples are being collected along 2,000 km of the Queensland coast.
The project has been in place since 2013, providing critical data to help monitor reef health and growth, and understand where and how acidification is impacting the reef.
