Bubbles highlight reef trouble

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This was published 12 years ago

Bubbles highlight reef trouble

By Deborah Smith

THEY are called champagne reefs, but they provide little cause for celebration.

Three coral reefs near Papua New Guinea, which are bathed in bubbles of carbon dioxide from volcanic vents, have provided a unique natural laboratory for the long-term effects of ocean acidification.

Acidification ... Papua New Guinea's coral reefs are being bathed in bubbles of carbon dioxide from volcanic vents.

Acidification ... Papua New Guinea's coral reefs are being bathed in bubbles of carbon dioxide from volcanic vents.

The results suggest the diversity and resilience of coral reef ecosystems will be severely reduced as the pH of oceans declines, due to rising carbon dioxide emissions from the burning of fossil fuels.

An international team co-led by Katharina Fabricius of the Australian Institute of Marine Science studied the three volcanic seeps in Milne Bay.

A team member, Janice Lough, said most volcanic vents are surrounded by hot water, which would complicate results. "The beauty of these ones is that they are cool." As carbon dioxide from the atmosphere dissolves it alters ocean chemistry, reducing the ability of corals and other marine organisms to build their skeletons, shells and other hard structures.

Researchers have tended to rely on studies in the laboratory to understand the possible impact of this effect. But these experiments are often of short duration and it is difficult to simulate factors in the wild.

The reefs where the pH varied naturally, depending on the amount of bubbles present, were a lucky find, Dr Lough said.

The researchers found that coral cover remained constant as pH declined from 8.1 to 7.8 – the change expected if atmospheric carbon dioxide levels increase from 390 ppm to 750 ppm. But branching corals, which provide habitat for many species, were replaced by boulder-like hard corals.

There were fewer soft corals and sponges but more sea grass present as carbon dioxide levels rose. "These champagne reefs are natural analogues of how coral reefs may look in 100 years if ocean acidification conditions continue to get worse," said a team co-leader, Chris Langdon, of the University of Miami.

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Dr Lough said the findings were a serious concern. "We wouldn't want the Great Barrier Reef to look like this."

The study, published in Nature Climate Change, found that reef development ceased at pH 7.7 and would be "catastrophic".

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