Complex interactions with nutrients and sediment alter the effects of predation on a reef-building coral.


Rice, M. M.,Baldwin, D. G.,Fischer, J. N.,Fuchs, C., andBurkepile, D. E.


Marine Ecology


Framework-building corals create the three-dimensional structure of coral reefs and are subject to predation from fishes, echinoderms, and gastropods. Anthropogenic stressors can magnify the effects of such top-down pressure on foundation species. The gastropod Coralliophila violacea (Kiener, 1836) depletes coral energy reserves via predation, potentially increasing coral susceptibility to land-based pollution (i.e., sediment accumulation and nutrient pollution). We hypothesized that sedimentation would worsen coral mortality, while nutrient enrichment would mitigate the harmful effects of sediment and predation on coral mortality by increasing the densities of algal symbionts. To test these hypotheses, we conducted in situ surveys of the fringing reefs in Moorea, French Polynesia to explore the relationships among massive Porites spp. cover, C. violacea densities, and sediment accumulation on coral colonies across low and high nutrient sites. We also conducted a factorial field experiment to test the interactions among these stressors on coral tissue mortality, symbiont densities, and chlorophyll. Massive Porites colonies at higher nutrient sites had C. violacea densities 13 times higher than at low nutrient sites but there was no difference in the amount of live tissue on coral colonies with or without snails among these sites. In our experiment, there were interactions between predation and nutrients as well as nutrients and sediment that impacted coral mortality. Sedimentation and predation by C. violacea increased coral tissue mortality independently by ~20%. Nutrient enrichment reduced this effect in corals under sedimentation or predation pressure by lowering coral tissue mortality by 18% and increasing algal symbiont densities by ~28%. Our results indicate that sediment does not magnify top-down pressure on this coral, and that moderate nutrient enrichment may interact with predation in complex, unexpected ways to alter the responses of corals to top-down pressure.





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Journal Article

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