Global overfishing of higher‐level predators has caused cascading effects to lower trophic levels in many marine ecosystems. On coral reefs, which support highly diverse food webs, the degree to which top‐down trophic cascades can occur remains equivocal. Using extensive survey data from coral reefs across the relatively unfished northern Great Barrier Reef (nGBR), we quantified the role of reef sharks in structuring coral reef fish assemblages. Using a structural equation modeling (SEM) approach, we explored the interactions between shark abundance and teleost mesopredator and prey functional group density and biomass, while explicitly accounting for the potentially confounding influence of environmental variation across sites. Although a fourfold difference in reef shark density was observed across our survey sites, this had no impact on either the density or biomass of teleost mesopredators or prey, providing evidence for a lack of trophic cascading across nGBR systems. Instead, many functional groups, including sharks, responded positively to environmental drivers. We found reef sharks to be positively associated with habitat complexity. In turn, physical processes such as wave exposure and current velocity were both correlated well with multiple functional groups, reflecting how changes to energetic conditions and food availability, or modification of habitat affect fish distribution. The diversity of species within coral reef food webs and their associations with bottom‐up drivers likely buffers against trophic cascading across GBR functional guilds when reef shark assemblages are depleted, as has been demonstrated in other complex ecosystems.

中文翻译：

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回顾鲨鱼驱动的营养级联在珊瑚礁生态系统中的范例

高级别捕食者的全球过度捕捞已导致许多海洋生态系统的级联效应降低了营养级。在支持高度多样化食物网的珊瑚礁上，自上而下的营养级联发生的程度仍然模棱两可。使用来自相对未捕捞的北部大堡礁（nGBR）上珊瑚礁的大量调查数据，我们量化了礁鲨在构造珊瑚礁鱼群中的作用。使用结构方程模型（SEM）方法，我们探究了鲨鱼数量和硬骨介壳虫与猎物功能组密度和生物量之间的相互作用，同时明确考虑了各地环境变化的潜在混杂影响。尽管在我们的调查地点中发现的礁鲨密度相差四倍，这对硬骨鱼中捕食者或猎物的密度或生物量都没有影响，提供了在整个nGBR系统中缺乏营养级联的证据。取而代之的是，包括鲨鱼在内的许多职能部门对环境驱动因素都做出了积极回应。我们发现礁鲨与栖息地的复杂性呈正相关。反过来，诸如波浪暴露和电流速度之类的物理过程与多个功能组之间的关联也很好，这反映了高能条件和食物供应的变化或生境的改变如何影响鱼类的分布。正如其他复杂的生态系统所证明的那样，当珊瑚礁鲨鱼种群枯竭时，珊瑚礁食物网中物种的多样性及其与自下而上的驱动力的联系可能会缓冲GBR功能行会中的营养级联。