Corals under attack by toxic seaweed do what anyone might do when threatened – they call for help. A study to be 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.
Full citation: Danielle L. Dixson and Mark E. Hay (2012). “Corals chemically signal mutualistic fishes to remove competing seaweeds.” Science 338(6108), 804-807. DOI: 10.1126/science.1225748.
Abstract: Corals in the genus Acropora generate much of the structural complexity upon which coral reefs depend, but they are susceptible to damage from toxic seaweeds. Acropora nasuta minimizes this damage by chemically cuing symbiotic goby fishes (Gobiodon histrio or Paragobiodon echinocephalus) to remove the toxic seaweed Chlorodesmis fastigiata. Within minutes of seaweed contact, or contact from only seaweed chemical extract, the coral releases an odor that recruits gobies to trim the seaweed and dramatically reduce coral damage that would otherwise occur. In turn, chemically defended gobies become more toxic after consumption of this noxious alga. Mutualistic gobies and corals appear to represent a marine parallel to terrestrial ant-plants, in that the host provides shelter and food in return for protection from natural enemies.