John Collins Rudolf The New York Times 4 Jun 11;
A ghostly pallor is overtaking the world’s coral reefs.
This draining of color results when heat-stressed corals expel the algae they rely on for food — and which are responsible for their bright and beautiful hues. Death often follows.
Reefs have long been under threat from destructive fishing practices, sediment and nutrient runoff, coral mining, reckless tourism and coastal development. Now, scientists say, global warming is accelerating the destruction.
One of the worst episodes of coral bleaching began last spring and summer, and affected reefs in virtually all the world’s tropical waters, from the Caribbean to the Indian Ocean.
“In Panama, the bleaching was the most graphic I’ve ever seen,” said Nancy Knowlton, a marine biologist with the Smithsonian Institution. “Everything was just bone white.”
Preliminary assessments suggest that the impact will be the most damaging since the only other known global-scale bleaching event, in 1998 and 1999, when more than 10 percent of the world’s shallow-water corals were killed by heat.
Nearly three-quarters of the planet’s reefs are now at risk of serious degradation, according to a report by the World Resources Institute in February. Another analysis, by the Global Coral Reef Monitoring Network, found that as much as one-fifth of the world’s reefs have been degraded beyond recognition or lost entirely.
By midcentury, virtually all reefs will be at risk, scientists fear, not just from local threats or global warming, but from an increasingly acidified ocean. Much of the carbon dioxide released to the atmosphere ends up in the oceans, where it forms a weak acid, lowering the pH level of the seas. Scientists have long speculated that the rising acidity of ocean waters would inhibit the growth of corals.
Now, a new study by an international research team offers some of the strongest observational evidence linking carbon emissions to reef damage. The study examined tropical corals off the coast of Papua New Guinea located near cool, natural undersea seeps of carbon dioxide. The results showed clearly that as acidity rose, coral diversity and resilience plunged.
“This study proves we must urgently transition to a low-CO2-emissions future or we face the risk of profound losses of coral ecosystems,” said Katharina Fabricius, a coral reef ecologist with the Australian Institute of Marine Science who led the research team.
The prospects for such a low-carbon transition in the near term seem increasingly remote, however. Just days before the study was published, the International Energy Agency released new data indicating that the world’s carbon dioxide emissions had reached a record-breaking 30.6 billion tons last year, despite the continuing effects of the global recession.
Coral reefs, which cover barely 0.2 percent of the ocean floor but contain roughly 25 percent of the ocean’s biodiversity, provide a crucial source of protein for an estimated 500 million people, protect shorelines from tsunamis and tropical storms and attract tourists that sustain coastal economies with tens of billions of dollars in annual revenue.
Even as climate change and changing ocean chemistry loom as potentially existential threats to reefs, many scientists say that confronting local perils such as overfishing is more important than ever.
Reef advocates say significant progress has been made in conservation efforts over the past two decades, including major international and national initiatives to create large-scale marine protected zones and local campaigns to educate coastal communities about sustainable fishing, agricultural and development practices.
These efforts must dramatically accelerate if reefs are to survive the added pressures of accumulating carbon emissions, scientists say.
“If we keep local threats low, coral reefs will be able to get over the climate hump,” said Lauretta Burke, a reef biologist.
