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 Mo'orea, 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.

中文翻译：

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与养分和沉积物的复杂相互作用改变了捕食对造礁珊瑚的影响

构架珊瑚创造了珊瑚礁的三维结构，并受到鱼类、棘皮动物和腹足动物的捕食。人为压力源可以放大这种自上而下的压力对基础物种的影响。腹足动物Coralliophila violacea(Kiener, 1836) 通过捕食消耗珊瑚能量储备，潜在地增加珊瑚对陆源污染（即沉积物积累和营养物污染）的敏感性。我们假设沉积会加重珊瑚的死亡率，而营养丰富会通过增加藻类共生体的密度来减轻沉积物和捕食对珊瑚死亡率的有害影响。为了验证这些假设，我们对法属波利尼西亚的 Mo'orea 的边缘礁进行了原位调查，以探索大量Porites spp之间的关系。Cover, C. violacea低和高营养点珊瑚群落的密度和沉积物积累。我们还进行了一项因子现场实验，以测试这些压力因素之间对珊瑚组织死亡率、共生体密度和叶绿素的相互作用。高营养位点的大型Porites菌落的C. violacea密度是低营养点的 13 倍，但这些地点之间有或没有蜗牛的珊瑚菌落的活组织数量没有差异。在我们的实验中，捕食和养分以及养分和沉积物之间存在相互作用，影响珊瑚死亡率。C. violacea 的沉积和捕食珊瑚组织死亡率独立增加约 20%。通过将珊瑚组织死亡率降低 18% 并将藻类共生体密度增加约 28%，营养丰富减少了在沉积或捕食压力下珊瑚的这种影响。我们的结果表明，沉积物不会放大这种珊瑚自上而下的压力，适度的营养丰富可能会以复杂的、意想不到的方式与捕食相互作用，从而改变珊瑚对自上而下压力的反应。