Resilience protects corals from hurricanes — and climate change

Many events that humans call disaster rarely are for plants, animals and other organisms, at least in the long term. There are exceptions — like the meteor that killed off the dinosaurs — but usually ecosystems recover from natural events.

Corals, for example, might get beaten up by the turbulent currents of a hurricane that passes through. But new coral colonies form in the months and years afterward, some even originating from pieces of branching coral that had been broken off by the storm. And tropical storms and hurricanes can bring up cool waters from the deep, lowering temperatures around a reef and reducing the threat of coral bleaching (when a coral expels its symbiotic algae, turning itself white).

“Coral reefs have been adapted to the occurrence of hurricanes,” says Yves-Marie Bozec, a coral reef biologist at the University of Queensland in St. Lucia, Australia. “The problem now that coral reefs all over the world are facing is that there are more disturbances that were not here in the past, and that can impair the ability of the reef to recover as it was able to do in the past.”

Those threats include fishing and pollution and — the big one — climate change. Bozec and Queensland colleague Peter Mumby recently created computer simulations to look at the effect of rising temperatures on Caribbean corals. Heat is a big enemy for corals: Warmer temperatures depress growth, and temperature spikes result in bleaching. (Ocean acidification, another outcome of climate change, is also expected to affect coral growth, but Bozec and Mumby haven’t yet factored this into their simulations.) Their study appears November 24 in Philosophical Transactions B.

The researchers found that the gradually rising temperatures act like a form of chronic stress on the corals, and the spikes are an acute event. The bleaching events have the biggest impact, but the rising temperatures — and resulting slower growth — impair the reef’s ability to recover from the temperature spikes. The simulations didn’t incorporate hurricanes, but Bozec says that it’s likely that more stress would make it even more difficult for corals to recover from hurricane damage. “Multiple stresses can have a much, much worse effect,” he says.

Exactly what effect that will be isn’t yet clear. Scientists are still working out how climate change is affecting hurricanes themselves, so it’s difficult to predict such complex future scenarios. Still, “we can reasonably assume that there will be big changes at the community level in terms of dominance of different species,” Bozec says. Some coral species may disappear. Others could adapt and, for example, become more resilient to bleaching.

And that’s the key to any disaster: resilience. It’s what helps a person bounce back from getting their home destroyed in an earthquake, and it’s what helps an ecosystem bounce back from a similarly destructive event. And it’s something that humans can actually help ecosystems like coral reefs to build up, Bozec says: “You can manage the reef at a local scale to try to give to the reef the best chance to recover when faced with these increasing disturbances.” Stopping overfishing, for example, can help take care of the fish, which are an important component of a reef, and add to the reef’s resilience. “There are a lot of disturbances that act very locally,” he says, “and we can do something for that.”