Corals Attacked by Toxic Seaweed Signal Fish for Help

A study reported this week in the journal Science shows that threatened corals send signals to fish "bodyguards" that quickly respond to trim back the noxious alga -- which can kill the coral if not promptly removed. Scientists at the Georgia Institute of Technology have found evidence that these "mutualistic" fish respond to chemical signals from the coral like a 911 emergency call -- in a matter of minutes. The inch-long fish -- known as gobies -- spend their entire lives in the crevices of specific corals, receiving protection from their own predators while removing threats to the corals. This symbiotic relationship between the fish and the coral on which they live is the first known example of one species chemically signaling a consumer species to remove competitors. It is similar to the symbiotic relationship between Acacia trees and mutualist ants in which the ants receive food and shelter while protecting the trees from both competitors and consumers. The research, supported the National Science Foundation, the National Institutes of Health and the Teasley Endowment at Georgia Tech, was reported November 8 in the journal Science. The research was done as part of a long-term study of chemical signaling on Fiji Island coral reefs aimed at understanding these threatened ecosystems and discovering chemicals that may be useful as pharmaceuticals. By studying the contents of the fish digestive systems, the researchers learned that one species -- Gobidon histrio -- actually eats the noxious seaweed, while the other fish apparently bites it off without eating it. In the former, consuming the toxic seaweed makes the fish less attractive to predators. The two species of fish also eat mucus from the coral, as well as algae from the coral base and zooplankton from the water column. By defending the corals, the gobies are thus defending the home in which they shelter and feed.