Coral reef skeleton can survive even in acidic oceans

For the first time, scientists have described the biological process of how corals create their skeletons to form massive and ecologically vital coral reefs in the world’s oceans.

The team at Rutgers Institute of Marine and Coastal Sciences showed how specific proteins produced by corals can form limestone in test-tubes. They also found that the limestone-forming reaction occurs regardless of water-acidity which suggests that corals will survive in coming centuries when the world’s oceans are predicted to become more acidic.

“The good news is that the change in acidity will not stop the function of these proteins, but pollution and rising water temperatures also pose major threads to these essential marine organisms,” said Tali Mass, a postdoctoral researcher and lead author of the study published in Current Biology.

It’s long been known that corals make their external skeletons from a matrix of secreted proteins, but the mechanism behind it was poorly understood.

In this study, the Rutgers team identified over 30 proteins from coral skeletons that might be involved in the process.

They also searched the coral genome for genes that could potentially assist with the production of the skeletal mineral calcium carbonate.

“We produced a draft genome,” said Debashish Bhattacharya, Professor Ecology, Evolution and Natural Resources and Director of the Rutgers Genome Cooperative.

“Basically, that’s a genome that is not yet fully assembled into chromosomes. So, you don’t have the DNA puzzle completely put together, but you have all of the pieces of that puzzle and can figure out what the many pieces – for example, the genes – do in the coral.”

This genome analysis led the researchers to four separate proteins. Their encoding genes were cloned, and expressed in bacteria, then isolated and placed in solutions of seawater at pH 7.6 (the expected future pH of the oceans) and at pH 8.2 ( the pH of today’s seas).

The team then used a scanning electron microscope to examine the proteins which revealed that all had begun to precipitate calcium carbonate crystals in the test tube at both pH levels.

“This work goes a long way toward explaining how coral precipitate calcium carbonate skeletons and clearly shows that the reaction can work at more acidic pH levels. It doesn’t mean that ocean acidification is not a concern, but it does suggest that corals will still be able to form skeletons, and coral reefs will continue to exist,” said Paul Falkowski, Board of Governors Professor of geological and marine science, and co-author of the study.