It is hard to picture starfish as the thugs of the marine world. But ravenous, thorny starfish have been terrorizing and destroying Australia’s Great Barrier Reef for almost three decades.
A study released in October by the Australian Institute of Marine Science (AIMS) and the University of Wollongong reveals that the reef has lost 50 percent of its coral cover in the last 27 years. The report, published in the Proceedings of the National Academy of Sciences, lists three factors that have led to the reef’s rapid degradation: tropical cyclones, predation by parasitic crown-of-thorns starfish and coral bleaching.
“This is an important study because it uses the best time series of data on corals, collected in a very important coral region, to quantify the rates of change of corals attributable to different factors in nature. That is a difficult task, so the authors have accomplished something very impressive,” said Peter McIntyre, assistant professor at the University of Wisconsin-Madison Center for Limnology.
Coral reefs support one of the most diverse ecosystems in the world by providing irreplaceable sources of food and shelter for all kinds of marine life. Shore communities and commercial fisheries around the world depend on coral reefs to draw in the fish populations they thrive on. Many economies also profit greatly from the coastal tourism that the reefs attract.
A popular tourist spot off the coast off Australia, the Great Barrier Reef has long been proclaimed as a natural wonder of the world, covering 345,000 square kilometers of the Coral Sea. Despite its recognized cultural and economic value, human activities still pose a significant threat to the habitat’s survival. Scientists have recently found that pollution and climate change, the usual culprits of coral degradation, have also been spurring much larger and more dramatic decline of the reef.
Rising ocean temperatures brought about by climate change have hastened the increased death rate of sensitive coral organisms. The coral dies leaving behind a white zombie structure of bleached coral. The study finds that only 10 percent of loss can be attributed to the phenomenon of coral bleaching. The leading offender, causing 48 percent of the damage, was found to be an increased amount of tropical storms, thought to be another symptom of global climate change.
“We can’t stop the storms, and ocean warming is one of the critical impacts of the global climate change,” says AIMS CEO John Gunn in a press release. “However, we can act to reduce the impact of crown-of-thorns [a native parasitic species of starfish].”
Researchers have linked the population explosions of the coral-eating crown-of-thorns starfish (COTS) to an increased level of nutrients in the agricultural and urban runoff that drains into the ocean. The starfish feed on plankton, which thrive in these high-nutrient conditions. Lowering the amount of chemical runoff and improving water quality could lead to a decrease in COTS populations. Another option would be killing COTS populations individually.
The report shows that reducing the amount of cyclones, bleaching and starfish could lead to a maximum coral cover growth of 2.85 percent a year, signaling a slow but possible recovery. But halting man-made global climate change will require worldwide participation and years of action. Scientists warn that if current conditions continue, the Great Barrier Reef will lose half of its current coral cover in five to ten years. They have proven that in the absence of just COTS, coral cover could increase by 0.89 percent each year. Reducing the starfish population could be the much-needed solution to our urgent problem.
“There is a considerable likelihood that when the next generation of Americans reaches adulthood, there will be no corals at all, or only some remnant reefs, left in the world,” said McIntyre.
“Given the inherent beauty and unrivaled marine biodiversity of these ecosystems, this is shameful because most causes of coral declines are direct or indirect consequences of human activities.”
