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Ocean acidification is taking a toll on coral reef growth. Can we save the reefs?

Scientists find more evidence that coral reefs are suffering from environmental changes. But, they say it's not too late. 

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    A healthy coral reef in Australia’s Great Barrier Reef.
    Courtesy of David Kline
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Coral reefs host about 25 percent of all marine life. But corals are increasingly struggling to build the immense calcium-carbonate-based structures. Researchers previously found that in Australia's Great Barrier Reef, for example, coral growth rates are down by about 40 percent in the past three decades

The reefs are colorful marine ecosystems that face a number of increasing stressors including pollution, overfishing, increasing water temperatures and changing ocean chemistry. To better understand how to reverse the damage, scientists have been working to isolate the impact of one stressor in particular, ocean acidification, on coral reefs.

Although scientists have long thought that ocean acidification will slow growth rates of coral reefs, a new study suggests it may already be happening. Researchers found that a sort of antacid treatment promoted growth of a coral reef flat in Australia in a new study published Wednesday in the journal Nature

Can we administer a similar procedure to save the reefs globally?

Sure, "you can effectively offset ocean acidification temporarily on a very small scale," study lead author Rebecca Albright tells the Monitor in an interview. Perhaps this could help small, isolated reefs, but such geoengineering solutions would be impossible on a global scale. 

Besides, altering the ocean water chemistry would just be a band-aid, Dr. Albright says. It wouldn't solve the root of the problem.

Like so many environmental challenges today, it ultimately comes back to elevated carbon dioxide emissions.

Here's how it works: Carbon dioxide emissions mostly end up in the Earth's atmosphere, but about 25 percent is absorbed by the world's oceans. As carbon dioxide dissolves into the seawater, it changes the chemistry of that water so as to make it less alkaline. This process uses the carbonate ions that marine organisms also use to build shells and skeletons of calcium carbonate.

Reefs themselves are humongous calcium carbonate structures, formed from the skeletons of coral organisms. So ocean acidification means that there is less material for the organisms to use to amass a reef.

To test the impact of ocean acidification on reefs, the researchers flowed water with added sodium hydroxide to give it a higher pH, and therefore be less acidic, over the coral reef flat. The idea was to expose the coral to water with a chemistry like that of preindustrial times.

Similar studies have been conducted in laboratories with the same results: ocean acidification does indeed slow coral reef growth. But this study was conducted in the ocean, on One Tree Reef in Australia's Great Barrier Reef.

Although cutting carbon emissions is the obvious solution to many scientists, that doesn't mean there's nothing to do in the meantime. 

Remember those other stressors? We can work to reduce those, says Albright. Governments can designate marine ecosystems as protected to reduce pollution and crack down on overfishing in sensitive regions.

As for the carbon dioxide, reducing emissions from burning fossil fuels and other greenhouse gas-producing systems is certainly necessary. But Bärbel Hönisch, a researcher at Columbia University's Lamont-Doherty Earth Observatory who was not part of the study, adds, other things can be done to draw carbon dioxide out of the atmosphere, like planting trees, which absorb carbon dioxide.

Reducing carbon dioxide could help with one of the other stressors too, Dr. Hönisch says in an interview with the Monitor. 

"The corals don't like to be warm," Hönisch says. With global temperatures rising, this is adding stress to the marine system. "If we take the carbon dioxide out of the atmosphere, it would reduce both problems at the same time," she says of the temperature and ocean acidification stressors.

Albright hopes this research will inspire people to make a change. "We don't want people to feel it's too late, we want people to understand the severity of the situation so you feel empowered to act in a responsible way," she says.

"The window is still open, but it's closing rapidly," Richard Aronson, head of the department of biological sciences at Florida Institute of Technology who was not part of the study, tells the Monitor in an interview. "This is the time to fight this out. We need to fight more now than ever before."

So what are we fighting for?

Dr. Aronson says conservation is about preserving quality and diversity of life on Earth. Coral reefs are not just calcium carbonate structures in oceans around the world, they host an incredible amount of marine life.

They also play a large role in the global economy, both supporting a massive amount of the fishing industry and drawing tourists to the reef-rich regions.

Coral reefs also serve as a barrier when large storms sweep towards coastlines. Big waves generated by hurricanes or other storms break over reefs before reaching the shore, so the waves are smaller by the time they reach coastal villages and cities.

As Hollie Putnam, a researcher at the Hawaii Institute of Marine Biology who was not part of the study, tells the Monitor in an email, "Their value is incalculable and their degradation and destruction will be felt globally."

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