Effects of hypoxia on lake food webs

底层水域的低氧(低氧浓度)是由营养物质和有机物输入增加以及气候变化潜在造成的，现在被认为是对沿海地区和湖泊生态完整性的全球威胁。湖泊中的缺氧会导致整个食物链的生物多样性和生产力的丧失。我们在关于这一生态强迫因素的知识中发现的差距包括需要改进对其程度、持续时间和食物网影响的监测和量化。利用食物链理论的最新发展和基于硫、氮、碳和氧的稳定同位素的生物地球化学方法，我建议解决当前研究计划中的这些空白。我将检验这一假设，即低氧对食物网络结构的影响的一个关键特征是消费者和碎屑之间的联系减弱。硫稳定同位素将在这个项目中发挥中心作用，正如我们在以前的工作中所表明的那样，它可以用来量化鱼类和沉积碎屑之间的营养联系。低氧引起的食物来源数量和季节性的扰动，以及直接暴露在低氧浓度条件下，也可能影响鱼类的生长和繁殖。这些影响，再加上鱼类的硫同位素特征，可能构成这一综合征的有力指标。有限的实验室研究表明，低氧也可能在鱼类的内分泌干扰中发挥重要作用。我将使用沿着低氧梯度的多湖方法，与合作者一起研究食物网中营养位置与溪蟹季节性生长(RNA：DNA比率)和生殖生理(例如卵黄蛋白原、睾酮)变化之间的关系，这是一种经济上重要的敏感鲑鱼物种。因此，这项拟议的研究计划将有助于提高我们预测低氧带来的生态系统简化的能力，低氧本身可能是物种灭绝的前奏。

Hypoxia (low oxygen concentration) in bottom waters, which is caused by increased inputs of nutrients and organic matter, as well as potentially by climate change, is now being recognized as a global threat to the ecological integrity of coastal areas and lakes. Hypoxia in lakes can lead to losses of biodiversity and productivity through the whole food web. Identified gaps in our knowledge concerning this ecological forcing factor include a need to improve its monitoring and quantification of its extent, duration, and food-web impacts. Using recent developments in food web theory and a biogeochemical approach based on stable isotopes of sulphur, nitrogen, carbon, and oxygen, I propose to address those gaps in the present research program. I will be testing the hypothesis that a key feature of the effect of hypoxia on food web structure is the weakening of the linkage between consumers and detritus. Sulphur stable isotopes will play a central role in this project as we have shown in previous work that it can be used to quantify the trophic linkage between fish and sedimentary detritus. Hypoxia-driven perturbations in the quantity and seasonality of food sources, as well as direct exposure to low oxygen concentration conditions, are also likely to affect fish growth and reproduction. These effects, together with the sulphur isotope signature of fish, may constitute powerful indicators of this syndrome. Limited laboratory studies suggest that hypoxia may also play an important role as an endocrine disruptor in fish. Using a multi-lake approach along a gradient of hypoxia, I will examine, with collaborators, the relationship between trophic positioning in the food web and variation in seasonal growth (RNA:DNA ratios) and reproductive physiology (e.g. vitellogenin, testosterone) in brook char, an economically important and sensitive salmonid species. This proposed research program will therefore contribute to improve our ability to predict the simplification of ecosystems brought by hypoxia, a perturbation that itself may be a prelude to extinction of species.