Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Coral colonies call for help

Threatened animals summon fish to trim toxic seaweed.

Gobies respond to a chemical cry for help from the coral they live on by eating toxic seaweed. Credit: Danielle Dixson

Coral threatened by toxic seaweeds emit a chemical cry for help that summons fish to eat away the danger.

When Acropora nasuta corals come into contact with the toxic seaweed Chlorodesmis fastigiata, they release a chemical that brings out “inch-long bodyguards” in the form of gobies, fish that live in the crevices and crannies of the coral, says Mark Hay, of the Georgia Institute of Technology in Atlanta. Hay and his colleague Danielle Dixson found that gobies were summoned within minutes of seaweed contact. 

Working in the waters off Fiji, the researchers observed that corals with resident gobies saw a 30% decline in the seaweed's abundance after three days, whereas no change was seen in control corals over the same period. The fishes' stomach contents indicated that one species of goby (Gobiodon histrio) ate the seaweed, whereas a second species (Paragobiodon echinocephalus) merely trimmed it back. G. histrio seemed to gain an added benefit in return, by becoming more toxic to predators after eating the seaweed. Their study is published today in Science1.

To test whether the corals were actively alerting their residents to the threat, Dixson and Hay exposed gobies to water from a selection of locations. Water from around the seaweed itself failed to generate any response in the two goby species. But seawater taken from points where the seaweed was in contact with coral caused the gobies in 20 separate coral colonies to move towards that source. When the experiment was re-run with a related coral species, no response was seen, which Hay likens to knowing that it is your burglar alarm going off, and not your neighbour's.

Have-a-go gobies

Other residents of the corals were not so good at neighbourhood watch. Damselfish exposed to the odour simply abandoned their coral homes within 48 hours. Hay says the damselfish seem to think “The neighbourhood is going to hell, we’re out of here. But the gobies both come out and trim the algae.”

Although the researchers cannot rule out the possibility that the fish are picking up on a chemical the corals might release to anything that stressed them, “the balance of the evidence is it could well be a signal that the coral is sending” to the gobies, says Hay.

Gobies often spend their entire lives on the same coral colony and Hay likens the relationship to that seen between ants and acacia trees, in which the plants provide spaces for the insects to live and in return are ferociously defended by them. Many other land plants are known to release signals when under attack from herbivorous pests that attract predators of the pests.

Finding the links

But teasing out such links is difficult. “The sensory basis for ecological interactions remains enigmatic, especially in marine habitats. Critical linkages are needed to assign individual causes with community-level effects,” says Richard Zimmer, who studies chemical signalling between organisms at the University of California, Los Angeles. “This research by Dixon and Hay bridges the gap.”

Thomas Breithaupt, who researches the sensory ecology of aquatic animals at the University of Hull, UK, says that chemical signals are hugely important in aquatic ecosystems, but that they are relatively unexplored.

“Compared to terrestrial systems, there’s still very little knowledge of chemicals moderating these interactions in aquatic environments,” he says. “Dixson and Hay did a great job of showing how important chemicals are. It’s one of those examples where we really get an interesting insight into a snapshot of ecology of a coral reef.”


  1. Dixson, D. & Hay, M. Science 338, 804-807 (2012).

    ADS  CAS  Article  Google Scholar 

Download references


Related links

Related links

Related links in Nature Research

Spawning coral monitored for effects of climate change 2012-Aug-18

Coral genomes could aid reef conservation 2011-Jul-24

Related external links

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Cressey, D. Coral colonies call for help. Nature (2012).

Download citation

  • Published:

  • DOI:


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing