Fish 'janitors' said vital to coral reefs

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ATLANTA, Feb. 13 (UPI) -- Herbivorous marine fish can be picky eaters, U.S. scientists say, which could spell trouble for endangered reef systems that depend on the fish as "cleaners."

Researchers at the Georgia Institute of Technology say studies in the Fiji Islands showed just four species of fish were primarily responsible for removing common and potentially harmful seaweeds from reefs, and each type of seaweed is eaten by a different fish species.

"We did not see much overlap in the types of seaweed that each herbivore ate," biologist Mark Hay said. "Therefore, if any one of these four species was removed, that would potentially allow some macroalgae to proliferate."

Macroalgae -- seaweeds -- pose a major threat to endangered coral reefs, as some emit chemicals that are toxic to corals while others can smother corals, the researchers said.

The seaweed-grazing fish are therefore important in the protection of coral reefs, they said.

"Because different seaweeds use different defense strategies to deter herbivores from eating them, a particular mix of fish -- each adapted to a particular type of seaweed -- is needed to keep seaweeds off the reef," graduate student Douglas Rasher said.

"It's not enough to have herbivorous fish on the reef," agreed Hay. "We need to have the right mix of herbivores."