Field studies have shown for the first time that several common species of seaweeds in both the Pacific (Fiji) and Caribbean (Panama) can kill corals upon contact. They use chemicals to do the deed.

A study documenting the chemical effects of seaweeds on corals was published this week in the early online edition of the journal Proceedings of the National Academy of Sciences (PNAS).

Seaweeds are normally kept in check by herbivorous fish. But in many areas overfishing has reduced the populations of these plant-consumers, allowing seaweeds to overpopulate coral reefs.

“Between 40 and 70 percent of the seaweeds we studied killed corals,” said Mark Hay, a marine ecologist at Georgia Tech.

“We don’t know how significant this is compared to other problems affecting coral, but we know this is a growing problem. For reefs that have been battered by human use or overfishing, the presence of seaweeds may prevent natural recovery from happening at all.”

The coral species chosen for the study–Porites porites in Panama and Porites cylindrica in Fiji–are among the hardiest of corals, suggesting that other species may be even more dramatically affected by the seaweed compounds.

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