Effects of predators and grazers exclusion on early post-settlement coral mortality

Mortality of newly settled individuals is a key factor in shaping adult population size and distribution of many marine invertebrates. Despite this recognized importance, few studies have addressed early post-settlement mortality rates and causes in reef-building corals. To investigate the effects of exclusion of macro-predators and grazers on mortality of Acropora striata (Verrill) recruits, a caging experiment was completed at Moorea, French Polynesia. More than half of the recruits died within 7 days in the field, and although the exclusion of macro-predators and grazers did not significantly reduce nor enhance mortality, it certainly altered their cause. In the presence of macro-predators and grazers, coral recruits faced significant predation-induced mortality (50.0% of dead recruits presented a heavily damaged or missing skeleton). Conversely, in the absence of macro-predators and grazers, dead recruits were mainly intact (91.7%), and most likely suffered from competition with turf algae and associated sediment trapping. These results underline complex interacting effects of predation, competition with turf algae, and sedimentation on coral early post-settlement mortality.