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Coral reefs cannot grow properly in acidic ocean conditions

Coral reefs will struggle to grow by the end of this century if carbon dioxide emissions continue at the current rate. This is the conclusion of experts at the Carnegie Institution For Science, who have analyzed a natural coral reef community after it was exposed to manufactured acidic ocean water.

The same research team previously published a groundbreaking study which provided evidence that ocean acidification is already slowing the growth of corals. They manipulated the sea water of a coral reef community to make it more alkaline, and showed that the coral’s ability to construct itself was improved with less acidity.

For the current study, the team manually adjusted the acidity of ocean water to represent the end-of-century projections of carbon emissions. They flowed the water over a coral community off the coast of Australia.

“Last time, we made the seawater less acidic, like it was 100 years ago, and this time, we added carbon dioxide to the water to make it more acidic, like it could be 100 years from now,” said lead author Ken Caldeira.

The ocean absorbs a massive amount of carbon from the atmosphere. When ocean water is mixed with the carbon dioxide, it produces carbonic acid, which corrodes coral reefs and other aquatic creatures.

Reefs are particularly susceptible to ocean acidification because their skeletons are built by the accumulation of calcium carbonate, and acidity in the surrounding water makes this process more difficult.

“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.

The research team managed to demonstrate how ocean acidification affects coral reefs on an ecosystem scale and not just in a particular individual or species. The study authors explained that this approach is critical in becoming fully aware of the impact that ocean acidity has on corals as well as on the coastal communities that depend on them.

“Coral reefs offer economic opportunities to their surrounding communities from fishing and tourism,” said Caldeira. “But for me the reef is a beautiful and diverse outpouring of life that we are harming with our carbon dioxide emissions. For the denizens of the reef, there’s not a moment to lose in building an energy system that doesn’t dump its waste into the sky or sea.”

The study is published in the journal Nature.

By Chrissy Sexton, Staff Writer

Image Credit: Aaron Takeo Ninokawa of UC Davis

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