Coral Goby Cleans Coral

Preview In some reefs, small fishes such as this broad-barred goby protect corals by eating invading seaweeds.
(Courtesy of Danielle Dixson, Georgia Institute of Technology)

One of the first signs of a sick coral reef is seaweed creeping across the corals, stealing their precious sunny real estate. Healthy corals, however, aren't completely hopeless: in some reefs, small fishes, such as this broad-barred goby (Gobiodon histrio), help eat the seaweeds away. But how do corals contact the fish to ask for cleaning services? By sending out a chemical signal.