By modeling the effects of climate change on the Great Barrier Reef over the next 50 years, researchers were able to determine a set of local interventions that could delay its decline by up to 20 years, allowing more time for global climate initiatives to take effect.

The study, published Wednesday in Royal Society Open Science, suggests that direct interventions at the ecosystem level are just as essential to extending the life of the world's biggest reef as are efforts to reduce greenhouse gas emissions.

"The Great Barrier Reef is one of the largest, most complex and iconic ecosystems on Earth. It also contributes billions of dollars to the Australian economy every year," said first author Scott Condie, senior principal research scientist at CSIRO Oceans and Atmosphere in Australia. "Unfortunately, climate change is already having a major impact on its health."

These impacts are multifaceted. Increasing ocean temperatures have resulted in coral bleaching, where the animals lose food-producing algae, turn white and, if the stress continues, eventually die. Researchers have estimated that the Great Barrier Reef has lost half of its corals over the last quarter-century. Warming waters also make young corals more likely to be smothered by human-generated sediment, making it more difficult for reefs to maintain their populations.

Despite these devastating losses, coral species are widespread enough that newer research suggests that they are not at immediate risk of extinction. However, because the Great Barrier Reef is host to thousands of other species, the effects of coral losses ripple out into the wider ecosystem. Overheating can kill animals or cause them to migrate to other ecosystems. And stress to corals can trigger outbreaks of harmful species such as the crown-of-thorns starfish, which feeds on coral.

Though the threat to the Great Barrier Reef is tangible, action plans around it tend to focus on general steps to reduce emissions rather than ecosystem-level efforts. But researchers behind the new study say that however important it may be, reducing emissions may not be enough to save the corals because it will take time for the effects to trickle down to the reef.

"Global climate action is essential to saving the Great Barrier Reef. However, this is progressing too slowly for sensitive ecosystems," Condie said. "We are trying to find local interventions that will delay its decline until global action can take effect."

The team focused on interventions that had been suggested in the past but not adequately tested or implemented. These include reducing the population of predatory crown-of-thorns starfish, using artificially generated clouds to shield coral from heat and introducing heat-tolerant corals.  

To test these interventions in an ecologically safe manner, the researchers turned to computer modeling.

"We used diverse information gathered by scientific studies on the Great Barrier Reef over the past 40 years to develop and test a computer model capable of predicting the health of more than 3,700 individual coral reefs that together form the Great Barrier Reef," Condie said.

By introducing the interventions into the model, the team was able to see how these interventions would affect the Great Barrier Reef over the next 50 years. They also modeled what would happen to the reef if no interventions were made.

They found that while the Great Barrier Reef is in serious danger, it is not too late to slow its decline significantly, which would allow time for other climate interventions to be implemented and take effect.

"The most effective combination of interventions may delay decline of the Great Barrier Reef by two decades or more," Condie said. "By 2050, the cover of coral may be double what it would be without any interventions."

The researchers were able to determine this "most effective combination" and identify general trends in the success of interventions, as well.

"The most promising approaches combine multiple interventions deployed across a large proportion of the Great Barrier Reef," Condie said. "Controlling populations of coral-eating crown-of-thorns starfish was an essential element of all successful strategies."

However, the study warns that if no interventions are made, we can expect "precipitous declines" in coral cover over the next 50 years.

"We have a shrinking window of opportunity to halt its decline," Condie said.

The researchers are now testing some of the interventions they modeled on real coral, using these results to refine the models. They hope the fruit of their labor will be a successful plan of action to help save the Great Barrier Reef, one that may also be applicable to corals around the world.

"Coral reefs are distributed throughout the world's tropical coastal seas and nearly all are facing major climate-driven declines," said Condie. "If successful interventions can be identified and tested on the Great Barrier Reef, then similar approaches are likely to assist reefs everywhere."

The study, "Large-scale interventions may delay decline of the Great Barrier Reef," published April 28 in Royal Society Open Science, was authored by Scott A. Condie, Russ C. Babcock, Mark E. Baird, Rebecca Gorton, Alistair J. Hobday and Éva E. Pláganyi, CSIRO Oceans and Atmospheres; Kenneth R. N. Anthony, Australian Institute of Marine Science and University of Queensland; Roger Beeden, Great Barrier Reef Marine Park Authority; Cameron S. Fletcher and David Westcott, CSIRO Land and Water; and Daniel Harrison, Southern Cross University and University of Sydney.