Death Spiral Corals send chemical SOS

When a killer seaweed touches a kind of spiky coral, the coral pushes a chemical panic button that brings small resident fish to the rescue.
Unchecked, seaweed algae can overrun a coral reef, as the community dwindles in “a descent into slime,” says marine ecologist Mark Hay of the Georgia Institute of Technology in Atlanta. But within 15 minutes of contact with a toxin-making seaweed, an Acropora nasuta coral releases compounds that prompt goby fish to seek out and trim back the seaweed, Hay and colleague Danielle Dixson report in the Nov. 9 Science.
“We've lost about 80 percent of the living coral in the Caribbean and 50 percent in the western Pacific,” says coral biologist Nancy Knowlton of the Smithsonian Institution in Washington, D.C. “So a better understanding of what keeps corals healthy is essential.”
In reefs, corals and the seaweed algae that form lawns or shrubby thickets compete for light and space. As coral reefs decline from pollution, overfishing, climate change and other insults, biologists have seen swaths of seaweed take over. Lush seaweed intrusions repel or smother larval corals, accelerating what Hay calls the reef “death spiral.”

Source: Science News