Biology Department, Marine Biology, Ghent University, Krijgslaan 281 - S8, 9000, Ghent, Belgium.
Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Coupure Links 653, Building F, 9000, Ghent, Belgium.
Ecol Appl. 2018 Jul;28(5):1342-1353. doi: 10.1002/eap.1737. Epub 2018 May 30.
Human activities increasingly impact the functioning of marine food webs, but anthropogenic stressors are seldom included in ecological study designs. Diet quality, as distinct from just diet quantity, has moreover rarely been highlighted in food web studies in a stress context. We measured the effects of metal and pesticide stress (copper and atrazine) on the contribution of a benthic intertidal diatom community to two processes that are key to the functioning of intertidal systems: biomass (diet quantity) and lipid (diet quality) production. We then examined if stressors affected diatom functioning by selectively targeting the species contributing most to functioning (selective stress effects) or by changing the species' functional contribution (context-dependent effects). Finally, we tested if stress-induced changes in diet quality altered the energy flow to the diatoms' main grazers (harpacticoid copepods). Diatom diet quantity was reduced by metal stress but not by low pesticide levels due to the presence of an atrazine-tolerant, mixotrophic species. Selective effects of the pesticide reduced diatom diet quality by 60% and 75% at low and high pesticide levels respectively, by shifting diatom community structure from dominance by lipid-rich species toward dominance by an atrazine-tolerant, but lipid-poor, species. Context-dependent effects did not affect individual diatom lipid content at low levels of both stressors, but caused diatoms to lose 40% of their lipids at high copper stress. Stress-induced changes in diet quality predicted the energy flow from the diatoms to their copepod consumers, which lost half of their lipids when feeding on diatoms grown under low and high pesticide and high metal stress. Selective pesticide effects were a more important threat for trophic energy transfer than context-dependent effects of both stressors, with shifts in diatom community structure affecting the energy flow to their copepod grazers at stress levels where no changes in diatom lipid content were detected.
人类活动对海洋食物网的功能产生了越来越大的影响，但在生态研究设计中很少考虑人为胁迫因素。此外，在强调胁迫的食物网研究中，很少突出饮食质量（与饮食数量不同）。我们测量了金属和农药胁迫（铜和莠去津）对底栖潮间带硅藻群落对两个关键过程的贡献：生物量（饮食数量）和脂质（饮食质量）的产生。然后，我们检验了胁迫是否通过选择性地针对对功能贡献最大的物种（选择性胁迫效应）或通过改变物种的功能贡献（依赖于背景的效应）来影响硅藻的功能。最后，我们测试了应激诱导的饮食质量变化是否改变了能量流向硅藻的主要捕食者（桡足类桡足类）。金属胁迫降低了硅藻的饮食数量，但低农药水平下的饮食数量没有减少，因为存在一种耐受莠去津的混合营养物种。农药的选择性效应分别使低和高农药水平下的硅藻饮食质量降低了 60%和 75%，这是通过使硅藻群落结构从富含脂质的物种向耐莠去津但脂质贫乏的物种的优势转变而实现的。在低水平的两种胁迫下，背景依赖效应不会影响单个硅藻的脂质含量，但在高铜胁迫下，硅藻失去了 40%的脂质。饮食质量的应激诱导变化预测了从硅藻到其桡足类消费者的能量流动，当桡足类以低水平和高水平的农药和高水平的铜胁迫下生长的硅藻为食时，它们损失了一半的脂质。与两种胁迫的背景依赖效应相比，选择性农药效应对营养能量转移是一个更重要的威胁，硅藻群落结构的变化影响了其桡足类捕食者的能量流动，而在没有检测到硅藻脂质含量变化的胁迫水平下。
