Ocean acidification could cause coral reefs to fall apart

Ocean acidification is threatening the stability of the world’s tropical reefs. Experts at the University of Sydney report that the “glue” that holds the Great Barrier Reef together is being weakened by rising levels of carbon dioxide.

Calcified deposits known as microbialites are formed by microbes that live within reef formations. The deposits bind and stabilize the reef framework, creating a strong scaffold that is used by corals and other reef builders to colonize and grow

The researchers analyzed historical samples from the Great Barrier Reef and found that these calcified scaffolds become thinner and lose their strength as acidity rises and pH levels fall. 

While previous studies have produced some evidence of this phenomenon the past, the current study is the first to show that the destabilizing effects of ocean acidification are impacting reefs worldwide.

“For the first time we have comprehensively shown that the thickness of this geologic ‘reef glue’ correlates with changes in ocean pH and dissolved carbon dioxide,” said study lead author Zsanett Szilagyi.

Looking at the fossil record, the researchers determined that the thickness of reef crusts are a reliable indicator of ocean acidification going back at least tens of thousands of years.

“We haven’t had such a complete and high-resolution record before. And this geologic study shows that as oceans became more acidic, this is reflected in the thickness of these reef crusts,” said study co-author Professor Jody Webster.

In the past, the reef scaffolding was more abundant than the corals and algae that grow on and around them. These crusts display variations in thickness over time, yet continue to serve as the structural support for reefs.

“This means they are really good indicators of changes in environmental conditions of our oceans,” said Professor Webster.

The scientists identified a variation in thickness from 11.5 centimeters 22,500 years ago to about 3 centimeters 12,000 years ago along younger parts of the Great Barrier Reef.

The results of testing from 17 reefs across the globe show that the thinning of reef crusts coincides with pH dropping below 8.2 right up to modern times.

“Previous studies have given us glimpses as to how these microbial crusts respond to changes in their environment. What is new in our study is that we measured more than 700 well-dated microbialite samples from the International Ocean Discovery Program on the Great Barrier Reef and combined this with a meta-analysis of 17 other reef records from around the world,” said Professor Webster.

“This allowed us to assess global-scale changes in microbialite development over the past 30,000 years. And, frankly, the findings are a stark warning sign for the dangers of rapid acidification of oceans.”

The study is published in the journal Marine Ecology .

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By Chrissy Sexton, Earth.com Staff Writer