Spatial refugia mediate juvenile coral survival during coral–predator interactions
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Coral recruitment and juvenile growth are essential processes for coral population maintenance and recovery. A growing body of research has evaluated the influence of reef microstructure on coral settlement and post-settlement survival, showing that physical refugia enhance recruitment. These studies have evaluated coral recruit morality from competition with macroalgae and indirect predation by grazing organisms, but the impact of direct predation by corallivorous piscine species on juvenile corals and how this interacts with reef microstructure is relatively unknown. 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, with average nubbin sizes of 1.4 cm × 0.3 cm and 0.5 cm × 1.0 cm (diameter × height), respectively, were attached to experimental tiles using small (1.44 cm3) and large (8.0 cm3) crevice sizes and were monitored for 29 d on a forereef in Palau. Full crevices (four sided) enhanced coral survival compared to exposed microhabitats in both coral taxa, but crevice size did not alter survival rates. Corallivores targeted recruits within crevices regardless of crevice size; dominant predators included small triggerfish (Balistidae), butterflyfish (Chaetodon), and wrasse (Cheilinus). Overall, Pocillopora suffered much higher rates of mortality than Porites. All Pocillopora were consumed by day 8 of the experiment, but mortality was significantly delayed in full crevices compared to exposed and partial crevice (three sided) microhabitats. In contrast, Por. lobata located in all microhabitats survived the entire experiment up to 29 d, with high survival in full (>90%) and partial crevices (70%), but only 28% survival in exposed microhabitats. These findings show the importance of crevices as spatial refugia from predators for juvenile corals and highlight the importance of structural complexity for juvenile coral growth and survival that enhances reef recovery.
KeywordsCorallivory Crevice Microhabitat Spatial refugia Predation Juvenile
This study was funded by grants to CG from the Department of Ecology and Evolutionary Biology and the Office of the Dean of the College, both at Princeton University, and to CD through an Australian Endeavour Award Postdoctoral Fellowship. We thank Yimnang Golbuu and all the staff of PICRC for their support, along with the Marine Spatial Ecology Lab at The University of Queensland for supporting this collaboration. Mirta Zupan provided valuable field assistance and Professor Stephen Pacala provided valuable guidance. We thank Alice Rogers for reviewing the manuscript prior to submission, and Simon Brandl, Kazuhiko Sakai, and one anonymous reviewer whose efforts greatly improved the manuscript through the review process.
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