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Belize Reef Die-Off Due to Climate Change? |
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Brian Handwerk with Lauri Hafvenstein for National Geographic News |
| March 25, 2003 |
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Tim McClanahan, a conservation zoologist with the Bronx, New York-based Wildlife Conservation Society, has studied the coral barrier reefs of Belize for the past decade. McClanahan said he was "hooked" when he noticed that the Belize Barrier Reef System, the world's second largest, showed signs of ill health similar to damaged reefs near densely populated locations like Jamaica. "Why would these reefs out in the middle of the Caribbean, far from land, located near a small country with a small population, not look like they should?" McClanahan recalled. For years, scientists have known that localized human factors such as pollution and overfishing damage coral reefs. But what about the effects of global environmental changes? Many reefs lay close to densely populated countries, making it difficult to distinguish between changes caused directly by humans from those with more widespread origins. When the health of Belize's reefs began to decline, McClanahan and other scientists saw a unique opportunity. "The Belize situation is quite unique, and it suggests global change because the country is small and the pollution and human effects are less than they might be in many other Caribbean countries," McClanahan said. "There's lots of debate about localized human influence versus global, and this reef was one of the best places to test that." Scientists say rising ocean temperatures, increased exposure to ultraviolet radiation, and more frequent and violent storms and weather patterns possibly caused by global climate change have lead to a partial die-off of the reefs known as coral bleaching. Coral Bleaching Coral bleaching—a type of slow death evident when multi-hued coral reefs turn a ghostly, translucent white—is relatively new to Belize. The first mass bleaching occurred in 1995, with an estimated partial mortality of 10 percent of coral colonies, according to a report by the Coastal Zone Management Institute in Belize. In 1997 and 1998, a second mass-bleaching event occurred, coinciding with devastation wrecked by hurricane Mitch. Biologists observed a 48 percent reduction in live coral cover in the Belize reef system. In the past, scientists often attributed bleaching events to local causes: storms, sedimentation, and pollution. But when bleaching began to occur in more remote reefs like Belize, scientists began to revise their assumptions. "This coral bleaching is pretty solidly tied to rising ocean temperatures," said Melanie McField, a Belize-based reef scientist with the World Wildlife Fund, a non-profit environmental organization in Washington, D.C. "It's a fact that global temperatures have risen. There's lots of data and little argument that increased ocean temperatures are the primary agent of bleaching. Ultraviolet light also causes bleaching, and the combination of the two gives you the worst bleaching response." "As for tying overall temperature increases to overall global warming, there is still some debate, but less every year," she said. "I think the majority of scientists agree that global warming is happening and that it's the root cause of these coral bleaching events." If that's the case, the reefs seem destined for increased problems. Global climate change models predict that ocean temperatures will continue to rise in the foreseeable future. Resistance and Recovery Corals often survive infrequent bleaching, but recovery is a slow process during which corals are vulnerable to other threats. "They can become sort of half-dead," said McField. "They don't just live or die. They're strange creatures. They can become partially dead." McField notes that four years ago, disease outbreaks that followed coral bleaching events killed more coral than the bleaching itself. "There are lots of diseases out there waiting to attack the coral when it's a bit weakened," she said. In areas of Belize where live coral cover has died there is still a chance for recovery. Large-scale algae cover, which often overwhelms dying reefs, has not been widespread. This gives biologists hope that the work of other ecosystem actors, such as relatively healthy algae-eating fish populations, may allow coral to recover. "Since the mass bleaching events, Belize's reefs appear to be under a process or recovery," said Nadia Bood, a reef biologist with the Belize-based Coastal Zone Management Institute. "However, recovery is slow and mean live coral cover is still low." "The interesting question will be to see the recovery in the coming years. Some reefs are impacted by coastal development, or located close to major sediment-producing and nutrient-filled rivers. Will those reefs in the areas of greater local human threats recover more slowly than those offshore or those in marine protected areas that have higher fish populations?" McField wonders. "Will either recover at all? These ecological disasters have provided the means for a large-scale experiment, but changes here happen on the scale of decades, which is why long term approaches to science and conservation are required." How to combat such a daunting opponent as global warming? Conservationists say that given the complex factors affecting coral health, much can still be done to aid reefs. "Rather than throwing up our hands and saying 'we can't control that,' we've got to be even more diligent and try even harder to control local impact[s] such as pollution and over-fishing," McField said. Also critical are efforts to better identify the characteristics that make reefs resistant to coral bleaching. It's known that higher current flows cool reefs and remove the toxic products of cellular processes, even more resistant coral species can stave off bleaching. "We have to be prepared for the next bleaching event [and] ready to identify some of these positive things," McField said. "Then perhaps we can build the knowledge we get into the Marine Protected Areas and focus our conservation attention on an area we hadn't before—because that might be the area that survives." In celebration of the 30th anniversary of the UNESCO World Heritage Convention, a multidisciplinary team of conservationists, photojournalists, and new media specialists documented and explored the Belizean Barrier Reef Reserve System. Representatives from EarthWild International, University of California (Berkeley), Nationalgeographic.com, Belize Audubon, Glover's Reef Marine Research Station, and the Wildlife Conservation Society examined universal challenges to conservation and sustainable development and celebrated successes in the preservation of our common natural heritage. More Ocean Stories from National Geographic News Killer Whales—Killing Other Whales Whales Win Right-of-Way in Atlantic Shipping Lanes China's Taste for Turtle Fuels Asian Crisis, Groups Say Belize, UN Try to Save Reefs and Help Fishers New Tech Helps Belize Reef Experts See Big Picture World Heritage Status a Mixed Boon North Atlantic Sharks on Sharp Decline, Experts Say Freshwater Runoff Into Arctic on the Rise, Scientists Say Dead Whale Day? Behind a Phantom Holiday in Alaska Crittercams Provide Insights into Nurse Shark Behavior Human Noise May Disturb Whales' "Love Songs" Do Hammerheads Follow Magnetic Highways in Migration? Ancient Walking Whales Shed Light on Ancestry of Ocean Giants Scientists Mount Assault to Save Endangered Right Whales Study Calls Into Question Global Quotas on Bluefin Tuna Research Expedition Aimed at Halting Loss of Black Coral Related Web site: Glover's Reef Marine Research Station |
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