Food quality is known as a major driver of organisms’ performances, but the way it may modulate the response of consumers to environmental stressors now appears as critical issue of trophic ecology. Here we evaluated whether and how food quality mediates the salinity tolerance of the model organism Daphnia magna to assess the resistance of zooplankton populations to salinization, which constitutes a serious threat for freshwater ecosystems worldwide. We showed that diets lacking highly unsaturated fatty acids (HUFA) and sterols reduce the salinity tolerance range of daphnids by more than 30%. Our measurements of individual metabolic rate coupled with the quantification of consumers NaCl body content revealed that this reduction in salinity tolerance arises either from an increased energetic cost of iono-/osmo-regulation when food quality declines or from a lower resistance to NaCl when consumers lack sterols and highly unsaturated fatty acids (HUFA). While improving individual salt tolerance, these two mechanisms may have opposite consequences at ecosystem scale and need to be fully considered when predictions of consumers responses to multifactorial stresses are induced by global change.

食品质量被认为是生物体表现的主要驱动力，但它可能调节消费者对环境压力源的反应的方式现在似乎是营养生态学的关键问题。在这里，我们评估了食品质量是否以及如何调节模式生物Daphnia magna的耐盐性评估浮游动物种群对盐化的抵抗力，盐化对全世界的淡水生态系统构成严重威胁。我们发现，缺乏高度不饱和脂肪酸 (HUFA) 和甾醇的饮食会使水蚤的盐度耐受范围降低 30% 以上。我们对个体代谢率的测量以及消费者 NaCl 身体含量的量化表明，这种耐盐性的降低要么是由于食品质量下降时离子/渗透调节的能量成本增加，要么是由于消费者缺乏对 NaCl 的抵抗力降低。甾醇和高度不饱和脂肪酸（HUFA）。在提高个体耐盐性的同时，