Incidence and severity of injuries among juvenile crown-of-thorns starfish on Australia's Great Barrier Reef

Outbreaks of crown-of-thorns starfish (Acanthaster spp.) represent a major threat to coral reef ecosystems throughout the Indo-Pacific, and there is significant interest in whether no-take marine reserves could moderate the frequency or severity of outbreaks. Herein, we investigate whether the incidence and severity of sublethal injuries among juvenile Pacific crown-of-thorns starfish (Acanthaster cf. solaris, max diameter = 45 mm) differs between areas that are open versus closed to fishing, between microhabitats (i.e. dead coral substratum versus live coral) and with body size. The majority (180 out of 200) of juvenile starfish had conspicuous injuries, presumably caused by predation. The incidence of injuries in juvenile starfish was negatively related to body size, but links between body size and severity of injuries were only evident in individuals collected from dead coral microhabitats. Small (3 mm radius) starfish from dead coral microhabitats had injuries to 68.06% of arms, compared to 12.00% of arms in larger (12 mm radius) starfish from the same microhabitat. Juvenile starfish associated with dead coral habitats had a higher incidence (95 vs. 87% respectively) and severity (i.e. the percentage of injured arms; 21 vs. 6%) of injuries, compared to those associated with live corals. Interestingly, there was no difference in the incidence or severity of injuries between areas that are open versus closed to fishing. Our results show that small juvenile A. cf. solaris are extremely vulnerable to sublethal, if not lethal, predation, and predation risk declines as they grow and change their microhabitat. Predation during and immediately following settlement is, therefore, likely to have a major influence on population dynamics and ontogenetic changes in microhabitat use for A. cf. solaris.