When there’s invading seaweed in your neighborhood, who you gonna call? Well, a new study by scientists at Georgia Tech shows that when corals are threatened by toxic algae they use chemical signals to call for help from their “bodyguards”, the unassuming goby fish.
The study, carried out on coral reefs in Fiji and published in the November 8 issue of the journal Science, shows that within moments of the coral’s “911 call” the gobies respond to these chemical distress signals and pick off the offending seaweed. What’s in it for the fish? Gobies spend their entire lives with the same patch of coral, using it for protection from predators and even feeding on mucus produced by the coral. It comes as little surprise then that the goby takes any threat to its shelter very seriously.
"The fish are getting protection in a safe place to live and food from the coral," said Mark Hay, a biology professor at Georgia Tech and the study’s co-author. "The coral gets a bodyguard in exchange for a small amount of food. It's kind of like paying taxes in exchange for police protection."
For one species of goby, feeding on the toxic algae has the secondary effect of making the fish itself more toxic to predators.
Coral is under threat worldwide from pollution and ocean acidification from human activity. When corals are stressed, aggressive algae competing for sunlit patches of ocean floor can represent a death blow to coral reefs and the magnificent ecosystems they support. At least one fish, though, isn’t letting the reef go down without a fight.
The crown-of-thorns starfish is named for the brightly-colored spikes that coat its legs. This starfish can grow up to 16 inches across and has between 12 and 19 legs instead of the usual five -- that’s a lot of spikes!
These spikes hold poison that can cause temporary paralysis at the sting site and nausea in humans. Like other starfish, the crown-of-thorns can regrow arms. At the end of each of these arms is an eyespot that can detect light and darkness, although not color or shape.
Crown-of-thorns starfish are avid eaters of coral, and just one starfish can eat 13 square miles of coral each year. In order to eat the coral, the crown-of-thorns starfish pulls its stomach out of its body to cover the coral, then feeds through tiny hairs called cilia. All that remains of the coral is its white skeleton. Despite being voracious eaters, crown-of-thorn starfish can survive food shortages of up to six months by living off reserves.
Since the 1970s, plagues of crown-of-thorn starfish have been occurring more and more frequently, particularly in Australia's Great Barrier Reef. Scientists are still debating whether these are natural or have been caused by overfishing crown-of-thorn predators.
There aren’t many creatures interested in such a prickly snack, but a few mollusks and fish like the giant triton and the titan triggerfish play important roles keeping crown-of-thorn starfish populations under control.
Learn more about the crown-of-thorns starfish and other fascinating animals at Oceana’s marine encyclopedia.