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Coral Reef in Palau Thrives in Acidic Waters

One of the main, and overlooked, aspects of pumping over 30 billion tons of carbon dioxide into the atmosphere is ocean acidification. As carbon dioxide levels go up in the atmosphere, greater amounts of carbon dioxide are absorbed by the ocean. They combines with H2O and a Carbonate ion (CO3) to make 2 bicarbonate ions (2 HCO3), pushing the acidity of the ocean down and threatening to destroy the shells of many organisms. While this is certainly dreadful news for oysters, clams and pretty much any hard shelled critter in the seas, corals were seen as the biggest losers of ocean acidification. Not only would their shells dissolve, their algae symbiotes would die off or leave the host.

Before you jump to a conclusion read this recent study by scientists. Cohen says in a place like Nikko Bay, where water is too acidic there were coral everywhere. The bottom is carpeted with fan corals, big boulder-shaped corals, long green tendril-y corals, even squishy corals, all jockeying for position. There are bright, colorful fish too. It’s a parade of life.

“We started taking water samples,” she says, casting back to an earlier visit here. “We analyzed them, and we couldn’t believe it. Of the 17 coral reef systems (around the world) that we’ve been monitoring, this is the most acidic site that we’ve found.”

The higher acidity of the water there was natural, but it defies all expectations. Conventional wisdom is that corals don’t like acidic water, and the water in Nikko Bay is acidic enough that it should keep many of these corals from building up their calcium carbonate skeletons.

Even weirder, Cohen says, is that the acidity goes up as you move from the barrier reefs offshore into Palau’s island bays, and that as that happens, the coral cover and the coral diversity increase as well. From everything we know about corals, Cohen says, this just shouldn’t happen.“There’s something different about Palau.”
That’s what Cohen’s team is trying to figure out — what is it that allows these corals to thrive in such acidic waters?

It’s a distressingly simple process, says oceanographer Katie Shamberger, a member of Cohen’s team: “As we put more and more carbon dioxide in the atmosphere, we end up with more carbon dioxide mixing into the ocean.”

More carbon dioxide in the sea makes the water slightly more acidic. It’s a small increase, Shamberger says, “but it still changes the chemistry of the ocean, and marine organisms are very sensitive to the water surrounding them.”
Organisms like corals. Some scientists have predicted that the growing global acidity could wipe out all the corals on the planet by the end of the century. In Nikko Bay, the water is already as acidic as the entire western Pacific could be by the year 2100. So the team here wants to know whether these reefs might just be the corals of the future — corals that can survive ocean acidification.

The expedition was the researchers’ sixth in Palau. On their dives they collect water in small bottles along with coral samples that they take with a hollow underwater drill that pushes into the corals’ skeletons like a straw pushing into a snow ball. The team corks each hole with a concrete plug, which Cohen says eventually gets covered in new coral tissue.

Cohen’s team examines the cores for growth rates and any signs of strain from the higher acidity. They also search for other clues about what allows these corals to thrive — things like genetic adaptations or unique characteristics of the local environment. Whatever the reason or reasons might turn out to be, Cohen says these reefs should move to the top of the global coral conservation list.

They are the ones that are going to survive climate change, she says, so they need every bit of help they can get. They’re also very important locally. Not only are Palau’s coral reefs a big tourist draw, but like healthy corals around the world, Palau’s provide vital habitat for fish and other sea life, and help protect the shoreline from storms and erosion.