Data from: Regime shifts shorten food chains for mesopredators with potential sublethal effects

1. Predator populations are in decline globally. Exploitation, as well as habitat degradation and associated changes in prey availability are key drivers of this process of trophic downgrading. In the short term, longevity and dietary adaptability of large-bodied consumers can mask potential sub-lethal effects of a changing prey base, producing a delayed effect that may be difficult to detect. 2. In coral reef ecosystems, regime shifts from coral- to algae-dominated states caused by coral bleaching significantly alter the assemblage of small-bodied reef fish associated with a reef. The effects of this changing prey community on reef-associated mesopredators remains poorly understood. 3. This study found that the total diversity, abundance and biomass of piscivorous mesopredators was lower on regime-shifted reefs than recovering reefs, 16 years after the 1998 mass coral bleaching event. 4. We used stable isotope analyses to test for habitat-driven changes in the trophic niche occupied by a key piscivorous fishery target species on reefs that had regime-shifted or recovered following climatic disturbance. Using morphometric indices, histology, and lipid analyses, we also investigated whether there were sub-lethal costs for fish on regime-shifted reefs. 5. Stable isotopes demonstrated that fish from regime-shifted reefs fed further down the food chain, compared to recovering reefs. Lower densities of hepatocyte vacuoles in fish from regime-shifted reefs, and reduced lipid concentrations in spawning females from these reefs, indicated a reduction in energy stores, constituting a sub-lethal and potential delayed effect on populations. 6. Reduced energy reserves in mesopredators could lead to energy allocation trade-offs, and decreased growth rates, fecundity, and survivorship, resulting in potential population declines in the longer term.

1. 全球范围内的捕食者种群均呈下降趋势。人类开发、栖息地退化以及由此引发的猎物可获得性变化，是此次营养级降级（trophic downgrading）过程的核心驱动因素。短期内，大型消费者的寿命与饮食适应性可掩盖猎物基础变化所带来的潜在亚致死效应，进而产生难以被察觉的滞后影响。
2. 在珊瑚礁生态系统中，由珊瑚白化引发的从珊瑚主导态向藻类主导态的稳态转换（regime shift），会显著改变依附于珊瑚礁的小型礁栖鱼类群落组成。目前学界对这类猎物群落变化对礁栖中型捕食者（mesopredator）的影响仍知之甚少。
3. 本研究发现，在1998年大规模珊瑚白化事件发生16年后，发生稳态转换的珊瑚礁上，肉食性中型捕食者的总多样性、丰度与生物量均低于恢复中的珊瑚礁。
4. 我们通过稳定同位素分析（stable isotope analysis），检验了在经历气候扰动后发生稳态转换或已恢复的珊瑚礁上，一种重要的渔业目标肉食性物种所占据的营养生态位（trophic niche）是否因栖息地变化而发生改变。同时，我们还利用形态计量学指标、组织学分析与脂质分析，探究了稳态转换珊瑚礁上的鱼类是否存在亚致死代价。
5. 稳定同位素分析结果显示，相较于恢复中的珊瑚礁，稳态转换珊瑚礁上的鱼类所处的营养级更低。稳态转换珊瑚礁上的鱼类肝细胞空泡密度更低，且该礁区产卵雌鱼的脂质浓度也有所降低，这表明其能量储备有所减少，这属于亚致死效应，且可能对种群产生滞后影响。
6. 中型捕食者的能量储备减少可能会引发能量分配权衡，进而导致生长速率、繁殖力与存活率下降，最终在长期内可能造成种群衰退。