What we can learn from watching video of coral lose its color

Scientists have long warned of coral bleaching events, but few knew the phenomenon could be so violent.

Last week, researchers from the Queensland University of Technology described the first-ever video of coral bleaching in the journal Coral Reefs. They found that under simulated warming conditions, solitary mushroom coral called Heliofungia actiniformis will swell and squeeze, dramatically expelling their algal tenants. The eight-day time-lapse video, which is making the rounds on the internet this week, brings coral to life for viewers who may be more accustomed to thinking about reefs as habitats rather than animals and bleaching as a passive event.

“When you actually show the coral going through these physical efforts, it is a much more vivid way of conveying the science to the public,” says Andréa Grottoli, a professor of earth sciences at Ohio State University, in a phone interview with The Christian Science Monitor. “It adds emotional content to something we know.”

The relationship between coral and algae is a prime example of symbiosis in the animal world. Coral polyps provide a perfect protective home for tiny zooxanthellae algae. In exchange, the photosynthetic algae provide nutrients and color to their (naturally colorless) coral landlords.

But if sea temperatures rise even a few degrees over the normal thermal maximum, corals will begin to expel algae from their bodies and turn white. The whole bleaching process can take as few as 10 days.

“One of the things the video clearly shows is how the ejection of the symbionts is this coordinated, whole animal event,” says Emily Rivest, an incoming assistant professor at the Virginia Institute of Marine Science, in a phone interview with the Monitor. “We didn’t have a detailed understanding of how that beneficial relationship [between coral and algae] breaks down on the mechanical level.”

Algae will return to their hosts if temperatures cool. If the heat doesn’t let up, bleached coral may die. And as climate warming shows no sign of slowing, researchers fear the worst for coral ecosystems.

“Temperature is the single largest stressor facing modern coral reefs, and we are seeing annual bleaching events,” says Dr. Grottoli, who is also head of Ohio State’s Water, Climate and Environment division. “This wasn’t predicted to occur for several decades, but it’s happening now. So that raises the alarm for me.”

Climate change presents a distinctly long-term challenge for conservationists. But marine scientists are already working toward short-term solutions for maintaining coral health.

“The easiest [factors] to control are local sources of stress,” says Dr. Rivest. “Nutrient runoff, sediment runoff from rivers and streams, managing how many fish there are to control algae from overgrowing.”

And by better understanding the mechanics behind bleaching, researchers could target conservation efforts where they count the most.

“There are things that can buy time for coral reefs,” Grottoli says. “We know that reefs that are protected or isolated from human impact tend to recover more quickly from bleaching. And even on bleached reefs, there are some colonies that don’t bleach. So we’re trying to identify what makes those individual corals resilient when other individuals are bleaching.”

In a previous study led by Grottoli, researchers found that coral with higher fat reserves were better able to survive and bounce back from bleaching events. In a different paper, Australian researchers theorized that coral microbiomes could hold clues to saving reef ecosystems.

“The next step is to look through that kind of microbial soup and find which bacteria may be the beneficial ones, understand how they're responding under temperature changes, and what contributions they're making to the coral,” Tracy Ainsworth, a molecular biologist at Australia's James Cook University, told the Monitor's Eva Botkin-Kowacki.