As the oceans absorb more carbon on a planet increasingly choked by greenhouse gases, scientists worry its reefs — the great storm-deflecting rampart for much of the tropics — will crumble and fall.
But for the first time, a new study by the University of Miami Rosenstiel School of Marine and Atmospheric Science and a team of international scientists has found that at least one soft coral, the shrub-like sea rod found throughout South Florida, the Gulf of Mexico and the Bahamas, is more resilient to ocean acidification fueled by carbon than previously thought. Unlike hard corals and other marine animals with shells that need less acidic water to build calcified skins, corals with interior skeletons like the sea rod can survive.
For marine biologists, it’s a bit of good news in a growing catalog of risks as they race to manage oceans 30 percent more acidic than a century ago.
“We had thought this coral was on the front line,” said co-author Chris Langdon, director of Rosenstiel’s Coral Reefs and Climate Change Laboratory. “It’s reasonable to think this will [apply] to a lot of other things.”
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Corals have been on the planet for two million years, surviving repeated glacial cycles and rising and falling temperatures. But since the 1970s, reefs have disappeared by about 50 percent, hammered by pollution, over-fishing and disease. An outbreak of white pox nearly wiped out elkhorn coral, one of the fastest growing corals and a chief building block for reefs in the Florida Keys, in the 1990s. The coral have not rebounded, even though white pox has disappeared, Langdon said.
“That’s where climate change could be playing a role,” he explained.
With more greenhouses gases in the atmosphere, the chemistry of the oceans is changing as seas absorb more carbon and become more acidic. Higher acidity makes it harder for species that draw calcium from the water to build skeletons. Langdon and others assumed this would affect all corals — adding to stress already caused by pollution and increasing temperatures — and have been racing to find out which corals would be hit hardest.
“It’s sort of like triage,” he said.
Coral are particularly vulnerable because water chemistry can affect both growth and reproduction. To reproduce, corals send out clouds of eggs and sperm for two months during the summer. Fertilized larvae then drift down onto the reef, attach and grow in a cocoon like a butterfly. When they’re ready, they hatch, feeding on tiny plants that grow inside their tissue. But warming oceans have slowed reproduction by almost half. Hotter oceans can also cause the plants inside coral, called zooxanthellae, to die, leaving the coral to starve.
Langdon and other scientists assumed that the sea rod, which is plentiful but grows even more slowly than the elkhorn, would wither in increasingly acidic conditions. To test their theory, they took samples collected from Big Pine Shoals in the Keys and glued them to stands in Langdon’s lab on Virginia Key. For eight weeks, they fed the coral dried fish food and exposed them to rates of acidification projected by the U.N.’s Intergovernmental Panel on Climate Change to occur in the future.
But rather than stop growing or die, the coral continued to build skeletons, they found. Even when they subjected the coral to harsh levels of acidification not expected to occur for nearly 300 years, growth slowed, but the coral survived.
Knowing that the coral will survive allows scientists to predict what reefs may look like under future conditions and come up with ways to better manage them.
“There’s some first-aid things we can do to help the survival of the coral to give them some time, like cutting [carbon] emissions,” Langdon said, along with cutting nutrients from agriculture and sewage.
“Changes humans are causing now are anywhere between 10 and 100 times faster” than the last century, he said. “We need to admit we have a problem.”