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Overheated corals switch and survive

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If you've ever gone swimming in places like the Sea of Cortez during summer, or even in a sluggish Florida bayou, you've probably noticed how it's possible for ocean water to be too warm. Where you begin to suspect that you may still be sweating, even though you are under water.

Tropical corals suffer from the same problems--but new research suggests they may have begun to deal with them.

Despite corals' longtime affinity for waters languid and warm, the recent, gradual creep of temperatures has led to widely publicized episodes of bleaching and die-off (reeffutures.org has a nice explanation). The problem, it seems, stems from a parting of ways between a coral's two component organisms: a small, reef-building animal related to a jellyfish, and single-celled algae that it shelters in its cells in return for nutrients.

Tragically, cracks appear in this happy arrangement as the temperature rises. The algae (or "zooxanthellae") start to produce toxic waste products. The host has no choice but to eject its guest, and both parties are the sorrier for it. Whole swaths of reef turn a ghostly white.

But recently, scientists working near the Great Barrier Reef found that a coral called Acropora millepora could distinguish between two strains of algae. One strain, originally quite rare on the reef, handled high temperatures ably, allowing corals to stay alive. Three months after a severe bout of bleaching in 2006, the researchers discovered that the heat-tolerant strain had proliferated, spreading to many of the surviving corals, and presumably lending them some protection from future heat waves.

New Scientist tells the story well--though be sure to read all the way to the end, where one expert dourly suggests continued warming may have all corals living on borrowed time. And no one even mentioned the problem of ocean acidification rendering corals unable to build reefs.

(Australian Institute of Marine Sciences/Charlie Veron)

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