Effects of Predation by the Fireworm Hermodice Carunculata on Milleporid Hydrocorals

Fireworm predation caused permanent damage to the milleporid hydrocorals dominating shallow fringing reefs off St. John, U.S. Virgin Islands. Consumption by Hermodice carunculata opened up 12.9 cm² of new space per 1.0 m² of Millepora complanata per day in spring 1985 and initiated a sequence of algal colonization in the resulting lesions. H. carunculata preyed on four different shapes of M. complanata branch tips in proportion to their abundance, suggesting that fireworms forage randomly within single species prey patches. Lesion size was correlated with worm length and the duration of feeding. A mensurative experiment followed the colonization of fireworm-produced lesions for 1 year. Ninety-seven percent of bare space on the hydrocoral skeleton was colonized by algae 31 days after the creation of lesions. Such rapid colonization was primarily due to settlement of the crustose coralline alga Neogonolithon sp. Millepora regenerated, on average, only 23–25% of space cleared by fireworm predation in 1 year. The vertical growth of M. complanata branch tips consumed by H. carunculata and subsequently colonized by algae was significantly lower than non-consumed branch tips, indicating that predation by fireworms in mean densities of 0.75 individuals per 1.0 m² was sufficient to limit branch growth.