Photograph by Walker Magnum of Anegada Horseshoe Reef


         Hermodice carunculata, or fireworm, interacts with many different organisms through many different forms of symbiosis including predation, commensalism, and defense. The fireworm plays a very important role in the tropical ocean ecosystem across the globe (Perez & Gomes 2012; Moreira et al. 2013).
        First, the fireworm is a predator of many different organisms found in the ocean. H. carunculata feeds on many types of algae and sedentary animals such as anemones, gorgonids, scleractinians, and other various types of coral (Perez & Gomes 2012). The fireworm is a corallivore, which prefers to feed off of juvenile and larvae coral (Moreira et al. 2013). The fireworm, a polychaete worm, is known to feed off of a zoanthid species, which belongs to the genus Palythoa; this polychaete then becomes highly concentrated within its organsPhotograph by John Martin Davies of an octocoral with palytoxin from the zoanthid. Marine animals such as the fireworm have a higher tolerance for the palytoxin, which to terrestrial vertebrates is lethal, because most animals in the marine food chain have high toxin concentrations, and they have become immune to it (Gleibs and Mebs 1999). The fireworm consumes polyps from both soft and hard corals (Arias et al. 2013). The feeding process by Hermodice carunculata begins with connecting its everted buccal mass to the prey; this process is very dangerous for the prey because it causes permanent damage to the prey (Perez & Gomes 2012). There is a fine line between grazing on the coral to prevent overgrowth of algae and overconsumption leading to loss of coral recruits, which usually ends up in overeating of the coral by the fireworm (Perez & Gomes 2012; Wolf & Nugues 2012). In fact, a fireworm can consume the branches of a coral for up to 30 minutes (Perez & Gomes 2012), and the most commonly consumed coral by Hermodice carunculata is scleractinian coral (Wolf & Nugues 2012).
Photograph of bleached coral by J. Roff.        Second, H. carunculata plays an important role in its environment through commensalism. The fireworm serves as a winter reservoir for many different types of heterotrophic bacteria, as well as a summer vector (Sussman et al. 2003). One example of a coral-bleaching pathogen that uses Hermodice carunculata as a host is Vibrio shiloi, which is found in the Mediterranean Sea; V. shiloi uses the fireworm because it cannot survive in water less 20°C (Sussman et al. 2003). Studies have shown that areas with fireworms had high concentrations of coral bleaching, but in areas without fireworms, there was no bleaching occurring. However, these bacteria play an important role in the ecosystem because they fixate nitrogen, produce antimicrobials, and they are a food source (Moreira et al. 2013). The fireworm is a host for the various types of bacteria without being effected, so they exhibit a communalistic relationship.

         Third, the fireworm also has a unique type of defense against its own predators. The fireworm has harpoon-like chaetae, which causes skin irritation and a stinging feeling to anything handling it; the cause of this irritation is complanine, a trimethylamine compound (Arias et al. 2013). The fireworm’s defense mechanism can prove dangerous for those who swim near coral reefs because they are risking getting stung.

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