Reefs are fragile and can be good indicators of ocean health, but researchers were surprised to discover a large reef in Palau in the far western Pacific Ocean is thriving in high levels of acidification.

The researchers looked at eight coral reefs in the Palauan archipelago, and found they were extremely healthy even under the acidic conditions, Texas A&M University reported.

"Based on lab experiments and other studies, this is the opposite of what we expected," said researcher Hannah Barkley.

Human-emitted carbon dioxide reacts with water molecules, lowering the ocean's pH in a process called acidification. This process has also been known to remove carbonate ions, which is essential for corals to build their skeletons. The reasons these specific reefs are so healthy despite the acidifications remains a mystery.

"The reefs appear healthy, but they have high levels of bioerosion, which occurs when organisms like mollusks and worms bore into the reef and break it down," said Kathryn Shamberger of Texas A&M University.

"We see coral skeletons that are eaten up and have holes on top and the sides. The coral almost looks like Swiss cheese because of the volume that has been removed," Barkly added.

The researchers believe the acidification in Palau occurs naturally, and is caused by the combination of activities such as the flushing of water through Rock Island lagoons that causes acidification levels to build up over time.

"Ocean acidification is happening in every ocean everywhere on Earth," Shamberger said. "We do know that adding carbon dioxide to the atmosphere from burning fossil fuels and deforestation contribute to higher acidification levels. It is very important for us to understand how coral reefs around the world will respond to continuing ocean acidification and places like Palau with natural acidification provide valuable clues."

The findings were published in a recent edition of the journal Science Advances.