Acid Oceans Caused Great Barrier Reef's Growth Rates to Decline by 40 Percent

Could we be heading for a new and grimmer era for coral reefs? An expedition to Australia's Great Barrier Reef has found that coral growth rates have plummeted by 40 percent since the mid-1970s. This could be evidence of a more acidic ocean, which could cause major complications for reefs in the future.

Coral reefs are an important part of the oceanic ecosystem. They provide shelter for young fish and also protect coastlines from erosion and storms. Yet since the beginning of the Industrial Revolution, about one-third of the carbon dioxide released into the atmosphere has been absorbed by the oceans. This causes oceanic waters to become more acidic and can make it harder for animals to form calcium carbonate shells, such as those produced by corals.

Recent studies have actually shown that there's been a reduction in coral growth in the Great Barrier Reef, southern Thailand and the central Red Sea of between 13 percent and 24 percent over the past few decades. Yet because observations of carbonate chemistry trends haven't been well-documented at these sites, it's not possible to confirm that acidification is behind the decline.

In order to better understand how reefs are faring today in comparison to the past, the researchers examined recent growth measurements of a section of Australia's Great Barrier Reef with similar measurements that were taken more than 30 years ago.

In the end, the researchers found that rates of reef calcification were 40 percent lower in 2008 and 2009 than they were during the same season in 1975 and 1976. That said, they couldn't prove that there was a change in the amount of live coral covering the structure over this time period. This means that it's likely that ocean acidification could explain the 40 percent decline.

"Coral reefs are getting hammered," said Ken Caldeira, the team leader, in a news release. "Ocean acidification, global warming, coastal pollution and overfishing are all damaging coral reefs. Coral reefs have been around for millions of years, but are likely to become a thing of the past unless we start running our economy as if the sea and sky matters to us very soon."

The findings are published in the journal Geochimica et Comochimica Acta.