For decades, marine scientists have tracked the loss of once-bountiful coral-reefs in the Caribbean Sea. But few have tried to fit the disparate pieces of the coral reef puzzle into a region-wide picture.
Now a team of scientists is publishing what may be the first long-term look at changes in the Caribbean's corals. They find that hard corals - the backbone of reef systems - cover 80 percent less undersea terrain than they did 30 years ago.
Researchers say the losses of coral reefs - the marine equivalent of tropical rainforests in terms of biodiversity - affect the region in several ways. They remove havens for maturing fish and other marine organisms, and destroy buffers that can protect shoreline from the full brunt of storm tides.
But the numbers also impart a ray of hope. They suggest that pollution, overfishing, and tourism are the primary causes of the decline. These local conditions are easier to handle than trying to offset the threats of long-term climate change, notes Dr. Isabelle Côté, a marine ecologist at the Tyndall Center for Climate Change Research in Britain and one of the study's researchers.
According to Roger Griffis, a reef expert at the National Oceanic and Atmospheric Administration, "There have been relatively few studies that have tried to pull this much information together over such a long time period for such a relatively large part of the planet."
The results, published Friday in the journal Science, actually represent a spin-off of efforts to answer a different question. The team was trying to quantify the impact of hurricanes on reefs in the Caribbean.
Researchers examined 65 studies, conducted from 1977 to 1991, involving 263 sites in the region. They initially looked at what happened to the reefs when they were struck by hurricanes. "But to really understand whether hurricanes were leading to declines in coral, we needed a background picture," says Dr. Côté. Only then did the magnitude of the coral-loss problem emerge, stunning the team. Over the years, "people had a feeling that things were going badly," she says. "We've actually put a number on it. And it's much bigger than anyone expected."
After examining the numbers, the team concluded that climate change had less to do with the disappearing coral, than had human-generated problems, such as over-fishing. Côté explains that fledgling colonies of hard coral compete with kelp and other forms of "macro-algae" for sea-floor space. Overfishing has depleted herbivorous species that kept the macro-algae in check. Disease has ravaged populations of sea-urchins, which also ate the macro-algae. Also, poor land-use practices have flushed more silt into rivers that empty into reefs.
This situation is repeating itself in reef zones worldwide. According to the latest Global Reef Monitoring Network annual report, reefs are shrinking. Yet the pace of decline is slowing, thanks to more reef-preservation programs. Dr. Griffis notes that much of this progress can be traced to the US-led International Coral Reef Initiative, launched in 1994, which is the marine equivalent of efforts to save the rain forests.
Among Caribbean islands, tiny Bonaire - just east of Aruba - is considered a pioneer in coral reef preservation. To dive or snorkel among its reefs, tourists pay fees that support monitoring and enforcement. In the US, parts of reefs near the Dry Tortugas have been closed off to tourists. Last year, in a rare move, the International Maritime Organization moved to restrict shipping in the area to limit damage from groundings, waste water discharges, and collisions.
Scientists are now experimenting with transplanting coral from one location to another. They're also installing a global network of "smart" sensors to monitor the conditions at coral reefs. While Côté remains hopeful that the declines can be halted, she warns that additional environmental change could irretrievably weaken the reefs ability to adapt.