A study released today by the Australian Institute of Marine Science shows that the Great Barrier Reef — a Heritage Site frequently held up as one of the world’s most striking coral conservation successes — has experienced considerable decline since 1985, and without intervention, live coral cover is projected to decrease another 5 to 10 percent over the next 10 years.
Mark Eakin, coordinator of NOAA’s Coral Reef Watch program, said the study was important because it encompassed 27 years of data over the whole area of the enormous reef, and its conclusions were a cause for concern and action. What was surprising, he said, is that the research shows a level of decline that he and others had not expected so soon.
“I never considered it untouchable,” he said. “We just looked at it as not having been hit hard yet.”
Over the last 27 years, the study found, coral cover across the 133,000-square mile stretch of the Great Barrier Reef has fallen to 13.8 percent over all, from 28 percent. The study broke down the causes of the decline, attributing 48 percent of coral loss to cyclones, 10 percent to coral bleaching and the remainder — 42 percent — to excessive spawning of destructive crown of thorns starfish. The starfish, believed by researchers to prosper when artificial nutrients increase in oceans, consume and destroy more than their fair share of live coral cover.
The researchers have targeted taking on the starfish problem as the quickest way to address the decline because cyclones and coral bleaching are both associated with the longer-term challenges posed by climate change.
The crown of thorns starfish, a spiny creature that can reach the size of a hubcap, pushes out and widens its stomach, spreading potent enzymes that convert the coral’s live components into a digestible soup. Several population surges have occurred on the Great Barrier Reef over the decades, beginning in the 1960s, prompting action to protect the ecosystem.
But five decades later, scientists still aren’t certain of what causes the boom in the destructive starfish. Higher nutrient levels, from run-off containing sediment and fertilizers, are believed to make possible the survival of larger numbers of starfish larvae than would otherwise reach adulthood. “There is a lot of good scientific rationale,” Dr. Eakin said, but he added that definitive data was harder to find.
He points out that high nutrient levels can, on their own, also harm corals, so taking on the nutrient issue is a logical first step.
The study suggests that if outbreaks of the starfish are brought under control, the coral cover could regrow at a rate of nearly 1 percent a year.
Localized efforts to improve water quality around the Great Barrier Reef by limiting nutrient run-off into the ocean would probably improve reef health and reduce the impact of the starfish, Dr. Eakin said. Outbreaks of invasive species are “something that the reefs may be able to recover from if they aren’t otherwise stressed,” he said.
Perhaps the most sobering aspect of the new research is that it suggests the Great Barrier Reef’s corals are on a similar course to those in the Caribbean –where reef decline is more advanced, mostly because of overfishing and bleaching.
Problems strike the Caribbean earlier because it is a semi-enclosed basin with high population pressure, Dr. Eakin said.
Neither he nor John Bruno, a professor of marine sciences at the University of North Carolina-Chapel Hill, was a party to the study.
“The rate of collapse has caught me by surprise, and I do a lot of this gloom and doom stuff,” Dr. Bruno said.