Wrasse and starfish gang up on sea urchins

SEA urchins beware: you are under attack from two sides. Wrasse and starfish are both partial to sea urchin, but struggle to catch it on their own. So they give each other a helping hand to tackle their common prey.

Ornate wrasse, Thalassoma pavo, like to eat the tube feet of sea urchins, but as the urchins keep their feet buried in the sea bed the wrasse can't get to them easily. Marthasterias glacialis, a starfish, also likes sea urchin but isn't always fast enough to catch them.

Nicola Galasso of Tuscia University in Viterbo, Italy, and colleagues have found that the two help each other out. When a sea urchin is attacked by a starfish, it uproots itself and moves away. That exposes its tube foot, so a lurking wrasse can sweep in for a meal. The wrasse's feast disables the sea urchin, allowing the starfish to catch it and finish the job.

The two predators don't seem to be truly cooperating as neither makes a sacrifice for the other. But their actions nevertheless benefit each other. It is further evidence that wrasse are intelligent and can adapt their foraging methods, says Galasso, who presented her research last week at the summer conference of the Association for the Study of Animal Behaviour in St Andrews, UK. She has also found that ornate wrasse have learned to follow scuba divers, as they often break open sea urchins to attract fish.

http://www.newscientist.com/article/mg21128284.300-wrasse-and-starfish-gang-up-on-sea-urchins.html?DCMP=OTC-rss&nsref=online-news