Influences of Reef Microstructure and Corallivory on Juvenile Scleractinian Coral Survival: A Crevice Theory for Palau’s Eastern Reefs

Abstract

Coral recruitment and juvenile growth are essential processes for coral population maintenance and recovery, especially after disturbances such as climate change impacts, overexploitation and disease outbreaks. A growing body of research has evaluated the influence of reef microstructure on successful coral recruitment and post-settlement survival, suggesting that micro-crevices and cryptic spaces within the reef substratum enhance recruit survivorship. These studies have evaluated recruit morality from competition with macroalgae and from predation by grazing organisms, but few studies have focused specifically on early-life survival from predation by corallivorous piscine species and even fewer studies have evaluated the influence of microstructure on juvenile coral survival from corallivory. Since corals in the juvenile phase (~1-2 cm3 in size or 1-2 years old) still experience high mortality rates, there is a need to better understand the factors that facilitate successful juvenile survival. This study examined whether refugia provided by micro-crevices enhance juvenile coral survival from corallivory. Juvenile corals from two different functional groups, the slow-growing massive Porites lobata and fast-growing branching Pocillopora damicornis, were attached to experimental tiles with micro-crevices and placed on a fore-reef of Palau’s eastern reefs. Coral from both taxa had significantly higher survival rates in micro-crevices than coral in non-crevice locations. These results suggest at the importance of reef microstructure for juvenile coral survival, following early post-settlement recruitment bottlenecks. If reef microstructure is a limiting factor in this regard, it may influence the resilience and the recovery potential of coral communities by facilitating recruitment. This is an important consideration for conservation of coral reef ecosystems, as crevice abundance may be a mechanism for reef bistability.