Bearded versus thorny: The fireworm Hermodice carunculata preys on the sea urchin Paracentrotus lividus

The bearded fireworm, Hermodice carunculata (Polychaeta: Amphinomidae) has rapidly increased in abundance in Mediterranean infralittoral rocky habitats. We have recently observed the bearded fireworm preying on the sea urchin Paracentrotus lividus, which is a major determinant of algal community structure in this system. To document the full sequence of behaviors in an attack, we observed interactions between H. carunculata and P. lividus under controlled conditions in the lab. Upon a fortuitous contact, a fireworm rapidly initiated an attack on the urchin, everting its pharynx over it and starting to suck and ingest the spines. The attack forced the detachment of the urchin from the substrate and the exposure of its oral side. Then, the fireworm moved toward the urchin mouth, placed its buccal mass over the Aristotle's lantern (the large powerful urchin “jaw”), removed it with a suction generated by the pharyngeal musculature and entered the test. When an increase in P. lividus mortality caused by predation occurs, a top–down control of communities may take place, triggering different habitat formation (algal forest vs. barren). Further research on the effects of the predation of the bearded fireworm on urchin populations is required to assess their potential repercussions for the structure and functioning of Mediterranean rocky reef ecosystem.