Warmer seas, more vicious storms, higher ocean levels, and other effects of climate change will push already unhealthy coral reefs past the point of recovery, says a report for WWF.
Coral species around the world, and the complex web of reef life they support, are already stressed by water pollution, coastal development, and overfishing, the report says. Global warming is threatening coral reefs round the world, and recent studies show the prognosis is not good. Ten per cent of the world's reefs are already degraded beyond recognition, 30 per cent are threatened and may be lost in the next 10 years, and another 30 per cent could disappear within the next 20 - 40 years. The report is by David Hopley, former director of the Sir George Fisher Centre at James Cook University in New Queensland, Australia. It is a sad diagnosis for ecosystems that rival Amazon tropical forests in species diversity. Coral reefs are often called cities beneath the sea. A single reef may contain 400 species of corals, and it takes thousands of coral polyps to form a reef colony. Each coral polyp generates a calcium cup in which it lives. Generations of these cups piled one on top of another create the cement-like structures that form coral heads and larger coral reefs. Teeming with exotic marine life, the cracks in a reef are host to more than 1,300 species of fish in the Tropical Pacific. A glass-boat view of the average Philippines reef reveals an oasis of security for blenny, eels, and other animals that inhabit holes in the reef, or angelfish and parrotfish that dart away from predators behind coral branches. It is the solid substrate on which free-floating embryos settle and grow into broad, brilliant sea fans, and it is the refuge for large sea-turtles and sharks. Each reef inhabitant supports a fragile web of life, and today these communities are under pressure on all fronts. In coastal areas, a growing human population creates the demand for development. This brings a surge of rain run-off from denuded areas and increased amounts of rubbish dumped into shoreline waters. In some areas, reefs are even mined for the grit and rubble needed for construction. Hunger and greed drive fishermen to detonate underwater explosives, "dynamite fishing" to feed families and fortunes. Others flush cyanide into the reef from plastic bottles, stunning exotic fish which are later sold to aquarium dealers and pet stores. Meanwhile tourist snorklers and sport divers add to the damage, dragging anchors over coral heads, touching fragile coral polyps, breaking off chunks for trophies of undersea exploits. All of this is, theoretically, controllable. But ocean warming is a more daunting problem, and poses a long-term threat to corals. "Increasingly frequent storms and rising sea levels will leave their mark, but rising sea temperatures are likely to have the most profound impact," says Sue Wells, WWF Marine Programme Manager. Recent outbreaks of reef bleaching are providing a preview of what awaits corals if greenhouse gas emissions continue to go unchecked, and if the earth's — or rather global ocean temperatures, continue to rise. Already this year, WWF researchers report bleaching in the Saba Islands Marine Park in the Caribbean. In the last 10 years, reefs of Costa Rica, Panama, Colombia, and the Galapagos islands have all undergone reef bleaching. Each coral reef is composed of thousands of coral polyps, and each polyp is inhabited by tiny plants called zooxanthellae, which give the coral its bright colour. It is a reciprocal relationship, both organisms need each other to survive. When water temperatures exceed the coral's normal tolerance level, it expels the zooxanthellae, giving the coral the appearance of being bleached. If these partner species don't regenerate, in a short time, the coral eventually dies. No less than 60 major coral bleaching events were reported over the twelve-year period of 1979-1990, compared to the only three recorded events during the preceding 103 years, according to Dr Hopley. In all 60 recent episodes, mass bleaching was triggered by a 1-2 degree centigrade increase in summer temperatures — a change roughly equivalent to the elevated levels researchers predict will occur in the ocean in the next century if global warming continues. More frequent and more deadly tropical storms and hurricanes could also be the result of global warming, according to the report. And if hurricanes like Hugo and Marilyn are common in future, coral reefs may be in for a battering. Damage from these storms, which hit the U.S. Virgin Islands National Park in the Caribbean in 1987 and 1996, nearly destroyed coral ecosystems. Scientists believe that with the storms will become heavier, with longer-lasting rainfall in some areas. The resulting run-off will flush sediment and agricultural chemicals down rivers and into the sea. A sediment plume in Australia's Fitzroy River prompted wide-spread coral deaths around the Keppel Islands. If environmentalists' projections hold true, sea levels will also rise by up to 90 centimetres by the year 2100 as a result of unchecked climate change. While normal growth rates show healthy reefs will be able to keep pace, already stressed reefs will not grow quickly enough. Hopley predicts that in 2100, already endangered reefs in the waters of the Caribbean, southeast Asia, and the eastern Pacific Ocean could be the most hard hit by the effects of climate change. Unfortunately international momentum to set acceptable standards for greenhouse gas emissions to curb global warming have been slow in coming. "Scientists all over the world agree that the global climate system is changing, in part because of our activities. If you want evidence just look around — glaciers worldwide are retreating, Antarctic ice sheets are melting, floods and storms are becoming more severe," said Jonathan Loh, Climate Change and Energy Policy Coordinator for WWF. "And yet governments continue to drag their feet on committing themselves to national targets for reducing greenhouse emissions." For the sake of these tiny coral polyps — and many other creatures — it is up to us to make every effort to limit our contribution to the damage we cause to the global environment. (1,055 words) *Elizabeth Foley is a Press Officer at WWF-International.
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Copyright 1997, The World Wide Fund For Nature