Besides global warming, burning fossil fuels also cause CO2 levels in the ocean to become higher which causes them to be more acidic. This rising ocean acidity has a negative effect on the ability of corals to build their calcium carbonate skeletons. So much so that it could cause coral reefs to waste away.
But it did make me wonder, how did coral exist millions of years ago when CO2 levels were much higher? And here is my answer:
Jaroslaw Stolarski and his colleagues found that ancient corals were able to alter the way they built their aragonite skeletons to adjust to their increasingly acidic surroundings - opening the door to the possibility that modern corals could do the same under similar conditions.Interesting. Now we just need to toss these corals in the Biosphere, pump in the additional CO2 and see if they can replicate the behavior.
The fossilized corals they studied - belonging to the genus Coelosmilia, which were commonly found during the Cretaceous period - had calcite skeletons, a form of calcium carbonate less susceptible to the corrosive effects of a lower pH (as opposed to aragonite). "We now have many different arguments to prove that these corals were actually made originally out of calcite—and not just aragonite that was transformed after the coral died and become fossilized ... There was great biological variability among the corals, and some of them adjusted perfectly to the prevailing geochemical situation," said Stolarski.
If calcite skeletons were more effective at dealing with an increasingly acidic ocean, why were there still so many aragonite skeletons? According to Stephen Cairns, a research zoologist at the Smithsonian's National Museum of Natural History, it may be because corals evolved the ability to switch their skeletons from one form to the other: "This study has opened the door to the possibility that coral skeletons can potentially change back and forth from aragonite to calcite."