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The tiny, slimy savior of global coral reefs?

Heat-tolerant algae could help the world's reefs adapt to climate change, researcher says.

By Moises Velasquez-ManoffStaff Writer of The Christian Science Monitor / February 6, 2009

A coral reef on the Palmyra Atoll in the Pacific Ocean, part of a marine preserve established by President George W. Bush.

Jim Maragos, US Fish and Wildlife Service/AP/File

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Miami

Coral reefs, already declining in many areas around the world, face even tougher times ahead, say scientists. Warming and increasingly acidic oceans, combined with other stresses could conceivably spell the end for reefs as we know them, they warn.

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But Andrew Baker, a scientist at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, has a more optimistic view. He thinks that corals have an innate – if limited – capacity to adapt to rising temperatures. And he theorizes that people may be able to help them along.

Earlier this year, Mr. Baker, a 2008 Pew Fellow, launched a project to study the relationship between reef-building coral polyps (a relative of jellyfish) and their symbiotic algae. In exchange for a safe place to live, the algae (called zoo­xanthellae) supply their hosts with energy in the form of sugar. But higher temperatures can cause the coral-algae symbiosis to break down. During a so-called bleaching event, corals lose their algae and, greatly weakened, can die.

Baker hopes to preempt such bleaching events, which have become more frequent in the past 50 years as temperatures have risen globally, by “inoculating” corals with a more heat-resistant strain of algae.

Corals adapt by switching algae

About 10 years ago, Baker noted that some corals naturally hosted a more heat-tolerant strain of algae and could survive much higher ocean temperatures. In the Persian Gulf, for example, where temperatures routinely reach 93 degrees F. – high enough to cause bleaching elsewhere – heat-tolerant al­­gae dominate in corals and the reefs are much more resistant to bleaching. Perhaps more important, certain corals appear to switch to this heartier alga (“clade D’) during warm years.

“There is evidence for what you might call an adaptive response,” says Baker. “The ability to sort of mix and match your symbionts depending on the environment that you’re experiencing, you could imagine would be a huge evolutionary advantage.”

But some think any interference in nature is bad, given the many well-meaning correctives that ended badly. For others, the idea that corals can adjust to higher temperatures by switching algae is debatable: Abundant evidence of stressed and dying reefs around the world suggests otherwise. To this, Baker responds that the absence of evidence shouldn’t be taken as evidence of absence: We don’t know what reefs might look like if they weren’t adapting at all, he says.

More to the point, Baker and others say, even if we stop emitting greenhouse gases tomorrow, it’s too late to avoid a few degrees of warming this century given what’s already in our atmosphere. Even assuming that the fossil fuel puzzle is solved quickly, corals will inevitably face warmer seas. That’s reason enough, Baker says, to research reefs’ ability to adapt and, if possible, try to enhance it.

Why is it important that coral reefs survive? Coral reefs host the most diverse ecosystems in the oceans – or, arguably, anywhere on the planet. Earth has 34 major groups of animals, or phyla. Thirty-two exist in the ocean, compared with just 12 on land. Thirty live on coral reefs. People often call coral reefs the “rain forests of the ocean.” But as Osha Gray Davidson wrote in his 1998 book “The Enchanted Braid,” rain forests might better be called “the coral reefs of the land.”

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