FROM the human point of view Pelagia noctiluca is an enemy. It is a jellyfish, abundant in the Mediterranean Sea, that is the chief cause of stings to swimmers in that popular holidaymakers’ destination. But, as this picture shows, Pelagia noctiluca has enemies of its own. The other creatures in shot are polyps of Astroides calycularis, a type of coral.
Normally, Astroides calycularis feeds on small creatures of the plankton. But researchers led by Tomás Vega Fernández of the Zoological Station in Naples, diving off the coast of Italian islands such as Pantelleria, have show that individual coral-polyps sometimes collaborate to trap and consume jellyfish. They catch hold of various parts of their prey to stop it swimming away, and slowly dismember it. As the team describe in a paper in Ecology, each polyp then consumes part of a tentacle or of the pulsating umbrella the jellyfish uses to swim.
Corals are, essentially, sea anemones with stony cases. Both they and jellyfish belong to the phylum of animals known to zoologists as Cnidaria, the characteristic feature of which is stinging cells called nematocysts. Cnidarians use these to disable their prey. In this example, then, it is a case not so much of “the biter bit” as “the stinger stung”.