Marine Spatial Ecology Lab, School of Biological Sciences & Australian Research Council Centre of Excellence for Coral Reef Studies, The University of Queensland, Brisbane, Queensland, Australia.
Wildlife Marine, Perth, Western Australia, Australia.
Ecology. 2021 Apr;102(4):e03303. doi: 10.1002/ecy.3303. Epub 2021 Mar 13.
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.
全球范围内高级掠食者的过度捕捞，导致许多海洋生态系统中的底层营养级发生了级联效应。在珊瑚礁中，高度多样化的食物网支持着顶级掠食者的存在，但顶级捕食者的营养级联效应发生的程度仍存在争议。本研究利用大堡礁北部相对未受捕捞影响的珊瑚礁广泛的调查数据，量化了礁鲨在构建珊瑚礁鱼类群落结构中的作用。通过结构方程模型（SEM）方法，我们探讨了鲨鱼丰度与中上层鱼类（包括鲷鱼和石斑鱼）以及猎物功能群密度和生物量之间的相互作用，同时明确考虑了跨站点环境变化的潜在混杂影响。尽管在我们的调查地点观察到礁鲨密度存在四倍的差异，但这对中上层鱼类（包括鲷鱼和石斑鱼）和猎物的密度或生物量没有影响，这表明在 nGBR 系统中不存在营养级联。相反，许多功能群，包括鲨鱼，对环境驱动因素有积极的响应。我们发现礁鲨与栖息地复杂性呈正相关。反过来，物理过程如波浪暴露和流速与多个功能群都有很好的相关性，反映了能量条件和食物供应的变化，或栖息地的改变如何影响鱼类的分布。珊瑚礁食物网中物种的多样性及其与底栖驱动因素的关联，可能在礁鲨群体减少时缓冲了大堡礁功能群的营养级联效应，这在其他复杂生态系统中已经得到了证明。
