Effects of hypoxia on lake food webs

由于营养物质和有机物输入的增加，以及潜在的气候变化，海底缺氧（低氧浓度）现在被认为是对沿海地区和湖泊生态完整性的全球性威胁。湖泊中的缺氧会导致整个食物网的生物多样性和生产力的丧失。我们对这一生态强迫因素的认识存在空白，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。利用食物网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，我建议解决目前研究计划中的这些空白。我将测试一个假设，即缺氧对食物网结构影响的一个关键特征是削弱了消费者和碎屑之间的联系。硫稳定同位素将在这个项目中发挥核心作用，因为我们在以前的工作中已经表明，它可以用来量化鱼类和沉积碎屑之间的营养联系。缺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，连同鱼类的硫同位素特征，可能构成这种综合症的有力指标。有限的实验室研究表明，缺氧也可能作为鱼类的内分泌干扰物发挥重要作用。使用多湖方法沿着缺氧的梯度，我将检查，与合作者，在布鲁克鲑营养定位在食物网和季节性生长变化（RNA:DNA比率）和生殖生理（如卵黄蛋白原，睾丸激素）之间的关系，鲑鱼是经济上重要的和敏感的物种。因此，这个拟议的研究项目将有助于提高我们预测缺氧带来的生态系统简化的能力，这种扰动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.