Are Coral Reefs really doomed?
Earlier this month the New York Times published an op-ed by Australian ecologist Roger Bradbury entitled “A World Without Coral Reefs.” Bradbury’s article makes a frightening claim: the planet’s reefs are doomed, sentenced to death by overfishing, pollution, and acidification caused by the ocean’s absorption of carbon dioxide. Instead of preserving the dregs of these “zombie ecosystems,” scientists and conservationists should plan for our reefless future, in which slime will carpet ocean floors and hundreds of millions of people will lack sustenance. The sooner we accept this grim outcome, argues Bradbury, the sooner we can adapt to it.
Bradbury’s message has been greeted by many coral advocates as a welcome dose of realism. “Roger’s editorial is the most powerful piece of writing on coral reefs I’ve seen in a long time, maybe ever,” says marine biologist-turned-filmmaker Randy Olson. “Scientists have to maintain the public’s trust by being honest, and Roger tells the truth instead of clinging to false hope.”
If anything, Bradbury’s op-ed undersold the peril by omitting coral bleaching from the litany of threats. Bleaching is typically caused by increased water temperatures, which induce stressed corals to eject the symbiotic algae that provide nutrients when times are good. Without their algal partners, corals turn a ghostly white, and reefs that remain bleached for too long can perish. Mass bleaching events, such as the die-off that swept Southeast Asia in 2010, are almost certain to occur more frequently in coming years.
Like acidification, warming water is a diffuse danger inflicted by the worldwide burning of fossil fuels. But while carbon emissions represent the greatest existential hazard to corals, many reefs are, at least for now, more damaged by local pressures such as overfishing and agricultural runoff. In the minds of many scientists, the fate of reefs will be determined by whether solving these local, comparatively manageable problems can make corals more resilient against intractable global ones.
For example, studies have suggested that large populations of herbivores like parrotfish, which graze seaweed and so prevent reefs from being engulfed by vegetation, can help corals recover from damage. This revelation has led scientists to advocate for the creation of Marine Protected Areas (MPAs) to safeguard parrotfish from overfishing and, in turn, preserve corals.
But can algae-eating fish fortify reefs against rampant warming and acidification? Probably not: a 2012 study by a trio of American scientists indicated that protected areas haven’t saved reefs from die-offs caused by temperature spikes. “The majority of coral scientists think that creating MPAs will improve coral resilience, but a lot of science suggests that hasn’t worked,” says John Bruno, a marine ecologist at the University of North Carolina and one of the study’s authors.
If interventions such as MPAs won’t save corals from runaway carbon, is there any hope that corals will save themselves? Certain species appear to be capable of adjusting to heat stress, and some, like the Northern Star Coral, can increase the pH of their calcifying fluid – the substance they excrete to form skeletons – under acidic conditions. As researchers wrote in Science in 2011, studies that forecast irreversible demise “may not adequately take account of reef organisms’ capacity for coping with stress and their potential for adaptation.”
Yet relying on acclimation and evolution is foolhardy, as the slow growth rates of many species impede rapid adaptation. “Corals can do some adapting, but the change that’s coming down the road is too great for them to handle,” says Doug Fenner, a reef ecologist at the Department of Marine and Wildlife Resources in American Samoa. “They’re pretty sensitive little animals.”
Coral scientists are unanimous on one point: if humans don’t cease pumping copious amounts of carbon dioxide into the atmosphere, reefs will eventually perish. “I’ve seen reefs that were destroyed by hurricanes bounce back in a decade,” says Fenner, “so I’m convinced that preventing local abuses can buy us some time. But if we don’t reduce CO2, we’re in deep trouble.” According to a 2007 study, reefs begin to erode faster than they grow when atmospheric CO2 exceeds 450 parts per million; our atmosphere already holds 396 ppm, and emissions show no signs of slowing.
Of course, just because we are on pace to turn oceans into hot, acidic dead zones does not mean that we necessarily will. Corals are only damned if civilization fails to stem the CO2 tide, and while Bradbury considers failure a fait accompli, not everyone agrees. “If we can get a handle on greenhouse gas emissions, corals have a chance,” says Bruno, who, it is worth noting, has been described as a pathological optimist. “I don’t think all reefs will die as soon as we cross, say, 400 ppm. I think we have some wiggle room.”
But Bruno’s if is a huge one, and ultimately, whether you think corals are “doomed” comes down to whether you believe society can completely transforming itself in the proximate future. On that point, Randy Olson is pessimistic. “Imagine a truck approaching a cliff at 100 miles per hour,” he says. “Sure, the driver could wake up and slam on the brakes, but that’s not likely.”
Coral’s destiny, like that of so many natural and human systems, is inseparably hitched to the trajectory of climate change. The rest of it – establishing MPAs, mitigating local pollution, praying for evolution to intervene – represents, in all likelihood, a collection of stall tactics that, if we’re extremely proactive and fortunate, will stave off extinction until we’re able to muster the political will to cut carbon. “We know what we need to do, and it’s pretty simple,” says Fenner. “Then again, our society has lots of fixable problems that we never manage to fix.”Tagged in: acidification, coral reef, environment, nature, pollution, Roger Bradbury
Recent Posts on Notebook
- Justin Webb on the medical advances in tackling heart disease
- The Photography Blog: 'Control Order House' by Edmund Clark - Photographing our response to terrorism
- Dementia Awareness Week: Should we keep an open mind to spiritual solutions?
- Hearing loss: An invisible impairment and a preventable disability
- Barking Blondes: When to vaccinate
Latest from Independent journalists on Twitter