The struggle to save Earth's largest life form
Leaf through the latest tomes on the status of coral reefs worldwide and a grim picture emerges. Because of overfishing, soil and nutrient runoff from land, and climate change:Skip to next paragraph
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• A fifth of the reefs - among the planet's most productive habitats - have been destroyed and are not recovering.
• Another quarter face the threat of imminent collapse from human activities.
• Another quarter are said to face long-term collapse.
"If we've learned anything in the last 10 years, it's how to kill a coral reef," says coral ecologist Terry Hughes ruefully.
Those dire facts, drawn from the latest "Global Coral Reef Status Report," however, are serving as a springboard for devising strategies to save the world's coral communities and, by extension, the thousands of marine species that rely on them. The best way to do this, many marine ecologists now maintain, is to focus on a reef's ability to bounce back from hardship. Where ecologists once talked about saving species, habitats, and biodiversity in a tropical reef ecosystem, many now speak of preserving "resilience."
Nowhere is this approach to reef conservation being put through its paces more rigorously than along Australia's Great Barrier Reef - dubbed by some the largest living thing on Earth. In fact, the GBR is a chain of 2,900 reefs stretching some 1,200 miles along Australia's east coast. Slowly expanding its reach as sea levels have risen following the last ice age, the network covers just over 135,000 square miles of coastal ocean.
Beyond its immediate biological value, the reef system represents a ringing cash register for the state of Queensland. Tourism and related activities bring in roughly $1.2 billion (Australian; US$950 million) a year to the region. The reef network also serves as a buffer between the mainland and the high seas that accompany tropical cyclones.
In the past, researchers would study tropical-reef response to single events - such as a hurricane, tropical cyclone, or coral bleaching - to evaluate its ability to bounce back.
"People wrote about these as one-off events," explains Dr. Hughes, a professor at James Cook University in Townsville. "But on longer time frames - from decades to centuries - those are recurrent events. We're now asking: How can this system, on a scale of thousands of kilometers, absorb recurring disturbances without going belly-up? Resilience is about the system absorbing changes" and conservation managers "being proactive in anticipating them."
Calls for this broader approach have been heard for some time. But the need was driven home by virtually back-to-back coral-bleaching events in the summers of 1998 and 2002, during which coastal waters grew unusually warm. Under conditions of high heat and light, the algae that lived in the coral, provided it with food, and gave it its distinctive color underwent a Jekyll-and-Hyde change. The algae became corrosive, eating away at the coral from the inside. In self-defense, the coral expelled the algae - and with it the coral's source of food. The coral turned white and died.
Both bleaching events involved vast tracts of coral, with 2002's event marked as the worst bleaching event on record along the GBR. To many scientists here, these were harbingers of the future as Earth's climate warms - at least in part because of carbon dioxide rising into the atmosphere as humans burn coal, oil, and other fossil fuels.
"Climate change is no longer a future issue for Australians - it's happening," Hughes says.
Even modest sea-surface warming, say 1 or 2 degrees C - the midrange forecast of the Intergovernmental Panel on Climate Change - could prompt large declines in coral communities by 2050, according to Ray Berkelmans and colleagues at the Australian Institute of Marine Science (AIMS) and the US National Oceanic and Atmospheric Administration in a study last year.
The concern: As global warming heats the ocean surface, bleaching events will happen more often, giving reefs less time to recover - all other things being equal, Dr. Berkelmans and others say. Added to that stress, they say, is the destruction that would come from tropical cyclones, which are expected to grow more intense, if not more frequent, as global warming proceeds.
One potential offset to bleaching could be coral's potential for adapting to warmer waters. Some coral communities have been able to survive warmer waters by embracing algae that are more tolerant of heat than their previous tenants, according to a team of scientists led by Andrew Baker, a researcher with the Center for Environmental Research and Conservation at Columbia University in New York. Their findings were reported in the journal Nature last August.