Storms, coral-eating starfish menace Great Barrier Reef
Lauren Morello, E&E reporter
Published: Tuesday, October 2, 2012
Coral cover on Australia's Great Barrier Reef has declined by half over the past 27 years, according to a new study.
Damaging tropical cyclones, the spread of predatory crown-of-thorns starfish and coral bleaching have all taken their toll, say researchers at the Australian Institute of Marine Science, which started long-term monitoring of the reef's health in 1985.
"The Great Barrier Reef is considered the best-managed coral reef in the world," said Katharina Fabricius, a marine ecologist at the institute who contributed to the new study. "So if coral cover on the Great Barrier Reef is going down and nothing else is changing, we are losing a reef that is iconic for Australia and the world."
Crown-of-thorns starfish settle down for a meal of coral. Photo by Katharina Fabricius, courtesy of Australian Institute of Marine Science.
Between 1985 and 2012, the amount of live coral cover on the Great Barrier Reef fell from 28 percent to just 13.8 percent, a 50.7 percent decline, found the research, which was published yesterday in the Proceedings of the National Academy of Sciences.
Fabricius and her co-authors say the best hope to avert that decline and stabilize the reef's coral is working to eradicate outbreaks of the predatory crown-of-thorns starfish, which feeds on living coral.
Just one of the spiky starfish can consume up to 60 square feet of reef cover each year. During periodic outbreaks, when the starfish population booms, their voracious appetite for coral can devastate reefs, which often need 10 to 20 years to recover.
Over the past 27 years, the starfish caused 42 percent of the decline in Great Barrier Reef coral cover, affecting the length of the reef, the study finds.
Storm damage was responsible for 48 percent of the coral loss, mostly in the central and southern sections of the reef. And coral bleaching -- a kind of sudden death that occurs when rising temperatures cause corals to expel the algae that normally live inside them -- caused an additional 10 percent of coral loss, mostly in the northern and central Great Barrier Reef.
Future storms could accelerate destruction
Researchers believe that working to prevent crown-of-thorns outbreaks offers the best hope to stabilize reefs in the face of future storms and continuing climate change, which causes ocean temperatures to rise, increasing the frequency and severity of coral bleaching.
In the absence of the starfish, coral cover on the Great Barrier Reef would increase an estimated 0.89 percent per year, rather than declining 0.53 percent per year as it did during the 1985-2012 study period, the scientists said.
But managing the starfish population isn't easy or cheap. The crown-of-thorns starfish has few natural predators, and the best method scientists have developed for reducing the starfish population is cumbersome and costly: sending trained divers to inject individual starfish with a chemical solution that is not harmful to other marine life.
Ultimately, though, the fate of the Great Barrier Reef depends on working to limit man-made climate change, the researchers said.
Short-term strategies for improving reef health, like reducing the number of crown-of-thorns starfish, can "only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase," the study authors wrote.
Earlier this year, more than 2,600 scientists who study coral reefs signed a statement urging governments to enact better protections for the underwater ecosystems, including efforts to cut the world's greenhouse gas output (ClimateWire, July 10).
If man-made emissions of carbon dioxide continue at the current rate, oceans could become inhospitable for reefs by the end of the century, the scientists said.