A ghostly pallor is overtaking the world’s coral reefs. This results when heat-stressed corals expel the algae they rely on for food – and which are responsiblefor their bright and beautiful hues. Death often follows.
Reefs have long been under threat from destructive fishing practices, runoff, coralmining, reckless tourism and coastal development. Now, scientists say, globalwarming is accelerating the destruction.
One of the worst episodes of coral bleaching began last spring, and affected reefsin virtually all the world’s tropical waters.
“In Panama, the bleaching was the most graphic I’ve ever seen,” said NancyKnowlton, a marine biologist with the Smithsonian Institution. “Everything was justbone white.”
Preliminary assessments suggest that the impact will be worst since the only otherknown global-scale bleaching event, in 1998 and 1999, when more than 10 percentof the world’s shallow-water corals died.
Nearly three-quarters of the planet’s reefs are at risk of serious degradation,according to the World Resources Institute. Another analysis, by the Global CoralReef Monitoring Network, found that as much as one-fifth of the reefs have beendegraded beyond recognition or lost.
By midcentury, virtually all reefs will be at risk, scientists fear, not just from local threats or globalwarming, but from an increasingly acidified ocean. Much of the carbon dioxide released to theatmosphere ends up in the oceans, where it forms a weak acid, lowering the pH level of the seas.
A new study offers some of the strongest evidence linking carbon emissions to reef damage. Thestudy examined corals off the coast of Papua New Guinea located near undersea seeps of carbondioxide. The results showed that as acidity rose, coral resilience plunged.
“We must urgently transition to a low-CO2-emissions future or we face the risk of profound losses ofcoral ecosystems,” said Katharina Fabricius, a reef ecologist with the Australian Institute of MarineScience.
The prospects for such a low-carbon transition in the near term seem remote, however. TheInternational Energy Agency says the world’s carbon dioxide emissions reached a record 27.8 billionmetric tons last year.
Coral reefs provide a crucial source of protein for an estimated 500 million people, protectshorelines from tsunamis and storms, and attract tourists that sustain economies.
Many scientists say that confronting local perils such as overfishing is more important than ever. “Ifwe keep local threats low, coral reefs will be able to get over the climate hump,” said Lauretta Burke,a reef biologist.