Coral defences: the perilous transition of juvenile crown-of-thorns starfish to corallivory

Abstract

The transition from the post-settlement herbivorous juvenile to the coral-eating stage of crown-of-thorns starfish (COTS) is a fundamental step to seed population outbreaks that decimate tropical coral reefs. How the highly cryptic juveniles fare during this transition is poorly understood. We show that the juveniles are vulnerable to attack by coral during this ontogenetic diet shift to coral prey. We monitored the condition, growth, and survival of juvenile COTS during the first 3.5 mo on a diet of Acropora sp. In initial encounters, juveniles often withdrew their arms to avoid the defensive nematocysts of the corals. Within the first 67 d of being offered coral, 37.8% of the juveniles experienced various levels of sublethal and lethal damage. Damaged arms were reduced to ~65.4% of the length of an intact arm, but most injured juveniles were able to regenerate their arms with an average predicted recovery time of ~4 mo. Although sublethal damage slowed the growth of injured juveniles, their capacity to regenerate is likely to contribute to the success of this highly prolific species. Despite being the prey of COTS, coral can influence the survival of juveniles, and potentially reduce their ecological impact by prolonging their growth to reproductive maturity, delaying their transition into a coral predator, and thereby hindering recruitment into the adult population.