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Oceans and Coasts

Keeping Coral Colorful


Monitoring a Global Coral Bleaching Event

View a slideshow showing the difference between healthy and unhealthy coral and what makes some coral resilient.

Healthy Coral, Sick Coral

Marine scientist Rod Salm narrates an audio slideshow about the risks coral reefs face and what we can do to help.

"By stumbling upon factors that keep coral reefs healthier, especially in the face of climate change, we've been able to take advantage of naturally resilient reefs and use their strength to improve the recovery of coral reef communities everywhere."

- Rod Salm, Conservancy director of marine science and strategies in the Asia Pacific.

For years, it was a mystery. Stumped marine scientists scoured the world’s reefs, examining dead or dying coral. Why, they wondered, were some reefs particularly susceptible to coral bleaching when other nearby reefs remained resilient? And how could they better protect vulnerable reefs?

The answers, it turned out, were right under their face masks.

For more than a decade, The Nature Conservancy’s marine scientists have been at the forefront of coral conservation. During the current global bleaching event, we’re putting our reef resilience principles — which have helped guide marine scientists worldwide for years — to the test and adjusting our methods to better protect coral in the future.

“These resilience ideas have revolutionized the way we go about protecting coral reefs,” says Rod Salm, the Conservancy’s director of marine science and strategies in the Asia Pacific. “By stumbling upon factors that keep coral reefs healthier, especially in the face of climate change, we’ve been able to take advantage of naturally resilient reefs and use their strength to improve the recovery of coral reef communities everywhere.”

The Basis for Bleaching

In 1990, when Salm was developing conservation plans along the coast of Oman, he was one of many scientists worried about coral bleaching. Bleaching occurs when the tiny algae that color corals are ejected due to stress; their host corals turn white and frequently perish. Elevated ocean temperatures are the most common cause of blanched reefs, but other stressors — including storms and freshwater flooding — can also play a role.

Bleaching is one of the biggest threats to the globe’s coral reefs, which shelter a quarter of the world’s marine species and are worth an estimated $375 billion for people. As Salm recently observed while surveying reefs in Mozambique, reefs can bleach and recover — but they can also die, as was the case in Oman in 1990.

Back then, coral mortality due to bleaching approached 95 percent in some areas, but in others, reefs were still thriving. The puzzle persisted through 1998, the worst global bleaching event in history struck. By its end, 16 percent of the world’s reefs had died.

In 1999, Salm made a startling connection. Having recently joined the Conservancy and relocated to the Asia-Pacific region, he was examining bleached coral in the Rock Islands of Palau.

As he swam under an island’s overhang, he noticed that the corals were healthier. The corals beneath his facemask were colorful, but those beneath his swim fins were completely bleached.

Recognition for Resilience

Salm instantly realized that certain factors — like cooler water and shade — created resilient pockets of coral. He also realized naturally robust reefs needed protection if they were to repopulate bleached reefs. And with that revelation, reef resilience conservation — using marine protected areas to preserve vigorous, durable coral and promote overall reef health — was born.

Resilience was presented and met with near-universal approval at the Ninth International Coral Reef Symposium, held in Bali in 2000. That conference attracted enough interest and funding to spark a workshop that Salm convened together with WWF and Honolulu’s The Bishop Museum.

The hypotheses produced at that workshop were then turned into revised principles for designing marine protected areas. The resulting reef resilience principles have since been taught to hundreds of coral reef managers from more than 60 countries through a training program developed by Stephanie Wear, Director of Coral Reef Conservation for the Conservancy’s Global Marine Initiative.

“Since the 2000 symposium where Rod presented his ideas, there has been tremendous growth in the science of reef resilience,” Wear says. “When I go to a coral reef meeting now, the term is on the tip of everyone’s tongue.”

Correcting for Climate

Due in part to the occurrence of another El Niño last year followed by a moderate La Niña earlier this year, oceans have been hot, triggering another significant bleaching event. The bleaching is unfortunate, but it was also expected, and it’s providing reef resilience scientists with a silver lining.

“One of the best ways to gauge the effectiveness of reef resilience is to do monitoring during a bleaching,” says Alison Green, a senior marine scientist with The Nature Conservancy’s Tropical Marine Conservation Program. “That way we can determine which marine protected areas are well-designed and which reefs need additional protection.”

The Conservancy and partners are currently monitoring networks of marine protected areas we’ve helped establish in places like Palau and in the Coral Triangle, Wakatobi National Park and Kimbe Bay. By taking full stock of how well our hypotheses have worked to protect coral, we can recalibrate and improve our reef resilience principles and ensure that the world’s reefs are even better poised to handle the next major bleaching event.

“We have a really long way to go in identifying resilient reefs and protecting them,” Wear of the Global Marine Initiative says. “But we are well on our way, and Rod’s vision is a key reason for that."

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