for National Geographic News
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 bleachinga type of slow death evident when multi-hued coral reefs turn a ghostly, translucent whiteis 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.
SOURCES AND RELATED WEB SITES