In hot water: coral reefs at risk

Animals, Spring, 2002 by Brian Lavendel

In 1850, the U.S. government sent a researcher to southern Florida to see if anything could be done to "get rid" of troublesome coral reefs in the region. The reefs were being blamed for numerous boat groundings and shipwrecks. Fortunately, government officials concluded that instead of trying to remove the reefs, they would erect lighthouses throughout the Florida Keys to keep ships in safe waters.

Today those same reefs--and reefs around the globe--are once again under threat, reports John McManus, marine biologist at the University of Miami and director of the National Center for Caribbean Coral Reef Research. And now the menace comes from a complex series of assaults.

In his more than 20 years studying coral reefs in the Philippines and the Caribbean, McManus says he has witnessed a dramatic decline in the health of coral reef ecosystems. As reports of coral die-offs funneled in from scientists and recreational divers, he grew increasingly troubled. So McManus joined a group of top marine biologists from around the world in coauthoring an unprecedented global study of coral reefs. Reefs at Risk, which was published by the World Resources Institute (WRI) in 1998, concluded that "58 percent of the world's reefs are potentially threatened by human activity."

The world's most biologically diverse marine ecosystems, coral reefs are critical to the health of the oceans. To grasp that fact, McManus explains, one needs to understand coral reefs and their place in the marine ecosystem.

Coral reefs are formed by polyps--which McManus describes as "microscopic jellyfish turned upside-down." The polyps secrete an external skeletal substance similar to concrete. This hard, bony structure not only protects the polyps; it provides shelter for microscopic animals and for fish and invertebrates that feed upon them. These animals in turn provide prey for larger residents, such as grouper and shark. Sea turtles and porpoises are also common around coral reefs, as are open-sea fish, such as tuna, that come to feed.

Yet these remarkable ecosystems occupy only the tiniest sliver of the planet. Scientists estimate that less than 0.2 percent of the ocean floor is covered by coral reefs. If you could sail over the entire surface of the ocean in one year, you'd be sailing over coral reefs a mere 18 hours. And yet these underwater rainforests provide habitat for one-third of all ocean species.

But despite a growing recognition of the problem, the dangers facing coral reefs appear to be looming stronger than ever. In the decade since the Earth Summit in Rio de Janerio, the proportion of coral reefs that have already suffered perilous declines has grown from 10 percent to 27 percent, according to WRI.

Shoreline development is but one threat. When coastal areas are developed, sediment runoff can flow into the water, choking coral reefs. At times, reef structures are mined for sand and limestone to be made into cement for new buildings. Other times, coral reefs themselves are filled in and built upon. Excess nutrients from sewage or fertilizers flow into coastal waters, feeding algae blooms that block sunlight and smother corals. Runoff may also carry pollutants such as pesticides, oil, or heavy metals from industry and roadways.

The list of harms faced by reefs goes on. Unsustainable fishing practices alter coral reef ecosystems. Their natural balance can be disrupted by overharvesting species that clean coral or feed on species that prey on coral. Dredging and long-line fishing and gear can damage fragile corals. Blast fishing--the use of dynamite or other explosives to harvest stunned and dead fish for the seafood trade--obliterates coral structures and communities. Cyanide--which fishermen apply to stun fish for hand collection for the aquarium trade--poisons large areas of sensitive coral.

Even unregulated tourism can pose a threat to reef health. Reefs at Risk notes that "swimmers and divers ... have destroyed coral through trampling, while boat anchors create further damage."

One potential deathly blow to coral reefs is global climate change. Rising sea temperatures may be the cause of widespread "bleaching," a process in which corals turn white and die. Greater frequency and intensity of storms are likely to lead to more physical damage of reefs. "This increase in natural stress levels will leave coral reefs in many parts of the world more vulnerable to human disturbance," according to the report.

The report shocked observers with its blunt analysis of the severity of the dangers faced by coral reefs around the world. It was time, said scientists and public officials, to take steps to safeguard this precious resource.

How important are the reefs? They provide food for millions of people and drive local economies with income from fishing, collecting, snorkeling, and diving. Reefs even protect coastal communities by buffering the wave action of coastal storms and mitigating flooding. The World Wildlife Fund (WWF) estimates that reefs produce an $375 billion in direct and indirect revenues each year.