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，捕食者种群均呈下降趋势。人类开发活动、栖息地退化以及随之而来的猎物可获得性变化，是引发营养级联衰退（trophic downgrading）这一过程的核心驱动因素。从短期来看，大型消费者的寿命与饮食适应性，能够掩盖猎物基础变化所带来的潜在亚致死效应，进而产生难以被及时察觉的延迟影响。
2. 在珊瑚礁生态系统中，由珊瑚白化引发的珊瑚主导态向藻类主导态的生态状态转换（regime shift），会显著改变与珊瑚礁相关联的小型礁鱼群落组成。目前，此类变化的猎物群落对栖息于珊瑚礁的中型捕食者（mesopredators）所产生的影响仍未得到充分认知。
3. 本研究发现，在1998年大规模珊瑚白化事件发生16年后，发生过生态状态转换的珊瑚礁上，食鱼性中型捕食者的总多样性、种群丰度与生物量均低于正处于恢复阶段的珊瑚礁。
4. 本研究通过稳定同位素分析（stable isotope analyses），针对经历过气候扰动后发生生态状态转换或恢复的珊瑚礁上的关键食鱼性渔业目标物种，检验其栖息环境驱动的营养生态位（trophic niche）变化情况。同时，本研究还利用形态计量学指标、组织学分析与脂质分析，探究了栖息于发生生态状态转换的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，相较于恢复阶段的珊瑚礁，来自发生生态状态转换的珊瑚礁的鱼类，其摄食层级更贴近食物链下游。栖息于此类珊瑚礁的鱼类的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下降，这表明其能量储备出现减少，这一现象构成了对种群的亚致死且具有潜在延迟性的影响。
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，从长期来看可能造成种群数量进一步降低。