Under the sea, coral reefs in Peril

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.

John Collins Rudolf, The New York Times, 4 June 2011. Full article.

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