July 21, 2008 -- Two feet across, with 12 to 20 dark brown arms covered in inch-long spines, the crown-of-thorns starfish sweeps across Australia's Great Barrier Reef, devouring corals and leaving only chalk-white skeletons behind.
But new research suggests that fishing bans help control starfish outbreaks on the world's largest reef system.
Hugh Sweatman, of the Australian Institute of Marine Science in Townsville, Australia, used surveys of crown-of-thorns starfish on the Great Barrier Reef and overlaid them with the locations of no-fish zones.
The first no-fish zones, covering 4.5 percent of the reef, were established in 1989.
"The frequency of outbreaks on reefs that were open to fishing was 3.75 times that on no-take reefs in the mid-shelf region of the Great Barrier Reef where most outbreaks occur," Sweatman said.
Outbreaks of the starfish include hundreds of thousands of the coral-chompers covering miles of reef at a time. Once they polish off the corals on one reef, the starfish produce larvae that float to the next reef, propagating the outbreak.
Exactly how fishing bans reduce these outbreaks is not clear. Evidence that the protected fish control the starfish directly by eating them is scant, Sweatman said.
More likely, he suggests, is that protecting fish causes a trickle-down effect.
Increasing populations of predatory fish reduce the numbers of bottom-dwelling fish such as wrasses, which eat invertebrates on the reef such as shrimp and worms. With fewer wrasses, invertebrate populations can swell -- and these creatures may be eating juvenile crown-of-thorns starfish and keeping outbreaks in check, Sweatman said.
"While for years there has been an element of logical faith that substantial no-take areas can have benefits in biodiversity conservation," Richard Kenchington of the University of Wollongong, Australia, told Discovery News by e-mail. "These are the robust demonstrations, and it is surprising us all that statistically significant evidence of benefits is emerging so soon after the major re-zoning of the Great Barrier Reef Marine Park."
Crown-of-thorns starfish extend through the Indian and Pacific Oceans from the Pacific coast of Panama to the Red Sea, including the "Coral Triangle" of Southeast Asia, so finding ways to reduce outbreaks could have widespread benefits.
"It's another argument for marine protected areas," Sweatman said.
More benefits may be on the horizon in Australia. In 2004, no-take zones were expanded to include 33 percent of the reef.
Related Links:
Jessica Marshall's blog: EnvironMental Case
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