It's not a fabulous time to be a coral polyp. Not only are you gagging on pollution and being plagued by algae blooms stimulated by fertilizer runoff, but there's also global warming to deal with... as oceans start absorbing more carbon-dioxide from the air, they become more acidic, making it harder for coral to build their calcium carbonate skeletons. Then, as the world's seawater heats up, zooxanthellae, the single-celled algae that live with, and produce food for, coral polyps start disappearing en masse (or get kicked out by their stressed and confused hosts).

The result? Massive coral bleaching that threatens to pick clean potentially all of the world's coral reefs over the next half-century. It wouldn't be unprecedented: On at least five occasions in the distant past, there wasn't a coral reef to be found anywhere on the planet. The catch is that hundreds of millions of people now depend on the reefs for protection from storms and tidal waves, to say nothing of the multibillion-dollar fishing and tourism industries sustained by reef ecosystems. (Plus, coral can be downright handy—the skeletons are sometimes used as bone substitute in reconstructive surgery.)

So that's the gloom. As a tonic, in the latest issue of New Scientist, Mark Schrope has the scoop on wacky new schemes being hatched as we speak to save the reefs. One solution involves what's basically a buoy attached to a giant plastic tube that extends 100 meters underwater and uses the motion of the ocean to act as a giant pump: "[A]s the buoy drops down into the trough of a wave, the tube also drops, pushing water through a valve at the bottom of the tube. When the next wave lifts the buoy, the valve closes." Basically, these gadgets would pump up seawater from way down under to cool the coasts and stave off bleaching.

It's an idea that's technically feasible, just... really pricey, with a single pump going for $100,000, while save-the-reef funds are rather limited. (A possible financing solution could involve property rights: At the Great Barrier Reef, tour companies are assigned specific sections of the reef, giving them incentive to spend money and keep their areas healthy and clean.) That means, with some trepidation, a few biologists are now looking at Plan B. Namely, there's a particular clade of single-celled zooxanthellae in the Persian Gulf that has so far survived at higher temperatures than what's projected for much of the ocean in 2100. If that species could somehow be transported to coasts around the world and somehow learn to get along with the local coral polyps, we might be able to engineer reefs that can withstand moderate global warming. (Mind you, the reefs in the Persian Gulf would be screwed, since the water there would get hotter still.)

The snag is that no one really understands how coral polyps select which zooxanthellae they want to keep around as symbiotic tenants ("It's one of the black boxes in the field," one biologist tells Schrope), so this sort of bio-engineering has a very low chance of working, and a lot of scientists have qualms about meddling with nature so blatantly. On the other hand, if the alternative involves all the world's reefs dying off, "try anything" might be the new order of the day.

--Bradford Plumer