The tiny, slimy savior of global coral reefs?
Heat-tolerant algae could help the world's reefs adapt to climate change, researcher says.
Jim Maragos, US Fish and Wildlife Service/AP/File
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.
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.”
Half a billion people, probably more, rely directly on coral reef ecosystems for food. And now, at the beginning of what many call the “genomic era,” scientists are seeing the diversity of life on reefs – and biodiversity in general – in a new, utilitarian light. Each unique life form (genome) represents a novel set of solutions to life’s challenges. Now that scientists can isolate and utilize this information directly, ensuring its continued existence takes on added urgency.
'Mining' biodiversity to make money
Gregor Hodgson, executive director of the Reef Check Foundation in Pacific Palisades, Calif., points to new leukemia and pain drugs derived, respectively, from a reef-dwelling sponge and the venom of a reef-dwelling snail. (The revolution in molecular biology itself, driven by rapid gene-sequencing technology, is possible only because of enzymes found in microbes living in a Yellowstone hot springs.)
“This genetic resource is unsurpassed,” says Dr. Hodgson.
But by all accounts, reefs are in crisis. The Global Coral Reef Monitoring Network’s “Status of Coral Reefs of the World: 2008” estimates that, since 1950, the world has lost 19 percent of its reefs. Another 15 percent may disappear within the next 10 to 20 years.
Some Caribbean islands have lost half their coral cover. In 2006, the US National Marine Fisheries Service listed two Caribbean corals – elkhorn and staghorn – as “threatened” under the Endangered Species Act, the first coral species to earn the designation.
“Corals are really in a world of hurt,” says C. Mark Eakin, coordinator of the National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch in Silver Spring, Md. “We need to do everything we can to help.”
Coral reefs colonize 'marine deserts'
Reef-building corals inhabit the equivalent of marine deserts: nutrient-poor waters with lots of sun. But increased nutrients from fertilizer and sewage runoff, among other sources, tip the environment toward favoring algae rather than coral. Chronic overfishing – the removal of grazers that might otherwise keep algal growth in check – also contributes to what oceanographer Jeremy Jackson has dubbed “the rise of slime.” In places like Jamaica – home to some of the Caribbean’s most degraded reefs – seaweed now dominates former coral reefs.
Coral health also depends on healthy intact ecosystems. A disease that decimated Caribbean sea urchins (an algae grazer) in the 1980s has been implicated in a regional reef decline, for example.
On Australia’s Great Barrier Reef, scientists have linked Crown of Thorn starfish outbreaks – they eat coral – to reef degradation as well. Bleaching events inevitably coincide with record-breaking temperatures, particularly 1997-’98 and 2005, the second-hottest and hottest (in the northern hemisphere) years on record, respectively. But observations on remote Pacific atolls indicate that reefs protected from fishing recover much faster after bleaching events than those that aren’t.
Successful attempts to help reefs in coming decades will have to address all these factors, say scientists. That means replacing leaky septic tanks in places like the Florida Keys, say Baker. It means educating fishers to the importance of reef fish to coral health. And it means setting aside no-take marine reserves.
“We’ve really got to be looking outside the box for all sorts of approaches for helping corals get through the series of stresses they’re having to deal with,” says NOAA’s Dr. Eakin. Even extreme proposals like shading reefs or cooling them with water pumped from the ocean depths deserve consideration, he says.
Then there’s Baker’s idea.
For the next three years – half spent in the lab, half in the field – Baker will study under what conditions corals best acquire heat-resistant algae. Will they take it in when heat-stressed and bleached, or before, when still healthy? Should scientists inject it directly, or simply ensure that it’s available in the surrounding water?
How many reefs will get heat-resistant algae?
Whatever the eventual inoculation method, applying it to all reefs everywhere won’t be practical, Baker says. Rather, he foresees choosing a few coral colonies on easily accessible reefs, like the Florida Keys, for treatment. Singling out the largest, oldest colonies will protect corals that produce a disproportionate number of larvae. That, in turn, will enhance the entire reef’s ability to recover after a bleaching event. More likely than widespread treatment of reefs in the wild, however, will be inoculation of corals grown in nurseries for transplantation in the wild.
With heat-resistance already present in greater numbers in their tissues, lab-raised corals will theoretically have a better chance to survive hot years.
Reef Check’s Hodgson thinks Baker’s work is important for what it will reveal about the coral-algae symbiosis, but he warns against meddling in nature. He ticks off a list of unhappy endings: mongooses released in Hawaii to control rats; introduced Bluestripe snapper overrunning Hawaiian reefs; Indo-Pacific scorpion fish stinging their way through Caribbean seas.
“We have a long history of scientists trying to play god with ecology. And almost in every instance it’s been a complete disaster,” he says. Corals switching to heat-tolerant algae “should happen naturally. There shouldn’t be any need to get involved.” (Baker’s aim is to boost populations of algae that are probably already present, not introduce a foreign algal species.)
Others are cautiously optimistic.
“You have to hope that Andrew [Baker] is going to be successful in his goals,” says coral scientist Nancy Knowlton at the Smithsonian Institution in Washington. She recommended Baker for his Pew Fellowship. “On the other hand, it does not alleviate the urgency of having people work extremely hard to reduce carbon dioxide emissions,” she says.
On this, everyone agrees. Attempts to help coral will ultimately be meaningless if the root problem – rising concentrations of atmospheric carbon dioxide – isn’t addressed.
“The idea is to get from here to there without losing all the corals,” Baker says, “so that by the time we start to become a little better stewards of this planet, we still have some reefs left.”