Coral bleaching is destroying reefs all over the world, and scientists have been sounding the alarm about what this may imply about the state of our oceans as the world’s climate warms. But new research from the University of Wisconsin-Madison gives some reason for hope that corals will survive.
The researchers, led by physics professor Pupa Gilbert, have provided evidence that at least one species of coral builds its hard, calcium carbonate skeletons faster and in bigger pieces that previously thought.
“Coral reefs only cover one percent of ocean floors, but they host 25 percent of all marine species, so they’re incredibly diverse and important from a biological point of view,” said Gilbert. “But they’re also economically important for the fishing industry, tourism, and because of their role in providing coastlines with protection from tropical storms.”
Instead of adding material molecule by molecule, at least one coral species, Stylophora pistillata, constructs large chunks of minerals that it adds to its skeleton. The mineral chunks are formed inside the coral’s tissue, which gives it some resistance to the acidifying oceans and provides greater control over how and where their skeletons grow.
Prior to Gilbert’s research, scientists had been unable to distinguish between two competing theories of coral growth. The classical idea was that corals relied on a calcium-rich fluid adding skeletal tissue one molecule at a time. Other evidence showed that the organisms take a more active role by concentrating seawater but still adding to their skeletons one molecule at a time.
Gilbert made her discovery by developing a new way to image the growing portions of coral skeletons to see what the forming structures were made of. They saw particles of unstable, amorphous forms of calcium carbonate at and near the growing surfaces of coral skeletons.
This isn’t to say that the structures are big enough to be seen with the naked eye. Some of the particles were 400 billionths of a meter across, which is 500 times larger than a single calcium carbonate molecule group. The researchers observed that the unstable calcium carbonate precursors crystallized into aragonite, the stable form of calcium carbonate that makes up mature coral skeletons.
If other coral species build their skeletons in a similar way, the oceans may be able to avoid a large-scale crisis in coral skeleton formation that could unravel reef ecosystems.