Coral Reefs Vanishing Faster Than Rain Forests

Helen Scales
for National Geographic News
August 7, 2007
Coral reefs in the Indian and Pacific Oceans are dying off much quicker than previously thought, a new study shows.

For the last two decades, Indo-Pacific reefs have shrunk by 1 percent each year—a loss equivalent to nearly 600 square miles (1,553 square kilometers). That makes the rate of reef loss about twice the rate of tropical rain forest loss.

The research also revealed that the decline began in the late 1960s—much earlier than had been assumed.

"Twenty or 30 years ago reefs with a high cover of coral were fairly common," said study co-author Elizabeth Selig, a marine ecologist from the University of North Carolina.

"Today there are comparatively few reefs in the Indo-Pacific that we would traditionally think of as being pristine."

The study is the first to conduct a regional, long-term assessment of coral reef health in the Indo-Pacific region, which is home to 75 percent of the world's coral reefs and the greatest diversity of coral and fish. (See coral reef photos.)

Researchers compiled more than 6,000 underwater surveys, which were conducted between 1968 and 2004, in ten subregions of the Indo-Pacific. These included Indonesia, the Philippines, and Australia's Great Barrier Reef. (See a map of the region.)

Each survey measured the percentage of seafloor covered of hard corals—a key indicator of reef health.

"Hard corals are the foundation species of coral reefs," said study co-author John Bruno, a marine ecologist at the University of North Carolina.

"It is like measuring the amount of canopy a rain forest has." (Get rain forest facts, photos, and video.)

A Consistent Pattern

Bruno and Selig found that hard-coral cover on Indo-Pacific reefs currently averages 22 percent—a much lower figure than expected. The percentage is also surprisingly consistent across the region.

"We were amazed that declines in corals were relatively uniform over large areas, despite different areas in the Indo-Pacific having wildly different management practices," co-author Selig said.

The widespread declines may be due to regional or global stressors such as increased sea temperatures, which trigger coral bleaching, she said. (Related: "Global Warming Has Devastating Effect on Coral Reefs, Study Shows" [May 16, 2006].)

"It is also possible that different, smaller-scale threats, [such as] destructive fishing and sedimentation, are causing equivalent declines across the whole region," Bruno added.

The study appeared in this week's online journal PLoS ONE.

Rain Forests of the Sea

Coral reefs are often considered to be the rain forests of the sea due to their high levels of biodiversity, and also because both ecosystems face severe threats from human activities.

"Not only are we losing coral reefs much faster than rain forests, but the [reefs] are already quite rare to begin with," Selig said.

A major obstacle to preventing ongoing reef loss is the difficulty in finding data.

The researchers found it very difficult to track down reef surveys from the 1970s and early 1980s, when scuba diving was still taking off.

"Compared to ecosystems on land, we have had a far shorter time studying coral reefs," Selig said.

The "Blue Water" Problem

Another problem is public perception of the oceans.

"Most people don't dive," Selig said, "and when they see beautiful blue tropical waters, they assume that everything is probably all right."

Selig refers to this as the problem of "blue water."

"It's so hard to persuade people to care when everything still looks so lovely from the surface."

Nancy Knowlton, a marine biology professor at the Scripps Institution of Oceanography in La Jolla, California, said research is a wake-up call.

It also shows that the situation for coral reefs is extremely serious in the Indo-Pacific, and not just the Caribbean, she said.

Scientists have extensively documented the destruction of reefs in the Caribbean, which have suffered heavily for decades from human impacts and devastating coral diseases.

"It was assumed that the Caribbean was the worst case scenario," said Knowlton, who was not involved in the study. "But ignorance is not bliss."

Room for Optimism?

Co-author Bruno thinks there is still room for optimism and that reefs have maintained some resilience to threats from humans.

"Despite the general trend of decline, it seems that some reefs can still recover," he said.

Richard Aronson, a senior marine scientist at the Dauphin Island Sea Lab in Alabama, said that saving coral reefs worldwide means addressing local problems and thinking big.

"As a society we absolutely must address regional and global issues," said Aronson, who is also president of the International Society for Reef Studies.

"Among the most urgent global problems are climate change and other effects of greenhouse-gas emissions, such as acidification of the oceans."

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