Reducing the amount of coral laid to waste by these starfish will greatly improve overall reef health, according to Sweatman. He estimates that crown-of-thorns starfish are responsible for about 40 percent of the drop in live coral coverage on the Great Barrier Reef. Storms and a phenomenon called bleaching, in which corals expel the algae they house in exchange for food due to elevated water temperatures, together make up less than a third of the coral deaths.
The future looks a bit less dismal for the Great Barrier Reef, given this demonstrated connection between commercial fishing bans and curtailed starfish outbreaks: Just 4.5 percent of the reef was deemed no-take in 1989, but in 2004 this protected area shot up to 33 percent. "This study is yet another argument for instituting marine protection programs," Sweatman says.
Other studies, however, have shown that pristine coral reef systems with a full complement of sea life can actually lead to corals getting sick more often from bacteria and fungus.
"Reefs with more fish tend to have more coral diseases," says U.N.C.'s Bruno. "Overall, it's tough-going for coral these days."