The team found between 300 and 400 crown-of-thorns starfish within a hectare (2.5 acres) of reef around Halmahera, Baird said.
"On [Australia's] Great Barrier Reef, we define an outbreak as 200 animals per hectare," Baird said.
High nutrient levels due to agricultural fertilizer runoff were most likely responsible for the population boom, he added.
"It stimulates blooms of microalgae—plankton—and the larvae of the crown-of-thorns starfish, under those conditions, survive very well," he said.
"In normal years, perhaps one in a million [starfish larvae] might survive. In one of these years, maybe a hundred in a million survive. You get huge recruitment."
Overfishing of the starfish's natural predators, such as triggerfish and the giant triton mollusk, likely worsened the situation.
Survey teams also found evidence of reef blasting—a practice that uses explosives to stun fish or collect coral as construction material.
"A lot of people rely on the reefs for their livelihood and their food. Without healthy reefs, it could result in serious economic hardship," Baird said.
(Related news: "Coral Reefs Vanishing Faster Than Rain Forests" [August 7, 2007].)
For now, the experts noted, certain species on the reef show healthy enough populations that the ecosystem could recover.
"I think the answer lies in good management to prevent the outbreaks in the first place," the Nature Conservancy's Green said.
"We need to be particularly careful about how we manage the land and fisheries in those areas."
A network of marine protected areas, she said, combined with land-use and fisheries reforms, would ensure the survival of the coral triangle.
"Reefs can cope with periodic disturbances if they are healthy. If they've got good fish populations, good water quality, and good coral, they can bounce back within 10 to 15 years."
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