Great barren reefs

 作者:詹悱     |      日期:2019-03-08 04:19:00
By Ian Anderson in Sydney MANY of the world’s coral reefs will be irrevocably damaged by global warming over the next few decades, claims a leading coral expert who has modelled the effect of rising sea temperatures on a phenomenon called coral bleaching. But some coral specialists remain unconvinced, arguing that reef systems are more resilient and can adapt to change. Corals are built by tiny animals called polyps, which are nourished by algae called zooxanthellae. If the water becomes too warm, the zooxanthellae can die—followed swiftly by the polyps, leaving coral bleached and barren. Ove Hoegh-Guldberg, director of the Coral Reef Research Institute at the University of Sydney, says that coral bleaching was first observed in 1979. Since then, there have been six major episodes, with the worst affecting reefs throughout the tropics last year. In a project commissioned by the environmental group Greenpeace, Hoegh-Guldberg has now produced regional reef bleaching forecasts for the next century. He unveiled his predictions this week at the Pacific Science Congress in Sydney, a gathering of researchers from 26 nations bordering the world’s largest ocean. From data on known bleaching events, Hoegh-Guldberg was able to determine the temperature at which bleaching appears to be triggered in different parts of the world. He then used climate models which predict the rise in the temperature of the sea surface for various tropical regions to produce his bleaching forecasts. Although reefs can recover from occasional bleaching events, Hoegh-Guldberg predicts that those in Southeast Asia and the Caribbean could be experiencing it annually within a decade. They will be joined by reefs off Tahiti by 2030 and by Australia’s Great Barrier Reef between 2020 and 2030, he claims. “Even if there is an episode every two years rather than every year, the corals won’t be able to recover,” says Hoegh-Guldberg. The destruction could be delayed if aerosols of smog in the atmosphere have the cooling effect that some climate models predict. But Hoegh-Guldberg argues that this will give a maximum of 50 years’ grace. “Even if you accept the aerosol effect, the end result is still going to be the same,” he says. “It will just take a little longer.” In the long term, Hoegh-Guldberg admits that some corals will be able to adapt to life in warmer seas. But with many species being lost, he says, the reefs’ ecology will be irrevocably altered. “It will be another example of survival of the fittest,” he says. Not everyone agrees with his stark predictions. Terry Hughes, a reef ecologist at James Cook University in Townsville, points to the fossil record which suggests that corals have been subjected to warming trends many times and have survived. “The gloom and doom scenario is overstated,