Zooplankton play a key role in energy transfer within lake food webs, but we have a poor knowledge concerning their role as phytoplankton grazers in shallow subtropical lakes. In this study, we aimed to determine how zooplankton grazing upon phytoplankton is altered in different scenarios of fish predation and turbidity, and we explored the relevance of grazing compared to other environmental variables, to explain phytoplankton biomass changes. A mesocosm experiment was conducted by including the following treatments: fish, turbidity, fish + turbidity, and a control (without fish or varying turbidity). The experiment lasted 21 days, and samples were taken four times. Zooplankton grazing was only effective for the microphagous group upon Cryptophyceae, while large Chlorophyceae and small pennate Bacillariophyceae biomass were benefited in the presence of copepods and cladocerans, being negatively affected by depletions in nitrogen availability. In the turbidity treatment, a reduction in phytoplankton biomass was obtained, artificially increasing zooplankton grazing on phytoplankton, while fish presence inhibited grazing of adult copepods and cladocerans. The other groups of phytoplankton were only influenced by the environment. This experiment suggests that phytoplankton biomass variations would be more affected by the environment than by zooplankton grazing in shallow lakes from the Paraná River.

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原位中观实验中不同鱼类捕食和混浊情况下浮游动物放牧对浮游植物的驱动评估

浮游动物在湖泊食物网内的能量转移中起着关键作用，但我们对它们作为浅亚热带湖泊中浮游植物食草动物的作用知之甚少。在这项研究中，我们旨在确定在鱼类捕食和浑浊的不同情况下，浮游动物对浮游植物的放牧是如何改变的，并且我们探索了放牧与其他环境变量的相关性，以解释浮游植物生物量的变化。通过包括以下处理进行中宇宙实验：鱼、浊度、鱼+浊度和对照（没有鱼或不同的浊度）。实验历时21天，采样4次。浮游动物放牧仅对隐藻科的微食性群有效，而大型叶绿科和小型羽状芽孢杆菌生物量在桡足类和枝角类动物的存在下受益，但受到氮可用性消耗的负面影响。在浊度处理中，浮游植物生物量减少，人为增加浮游动物对浮游植物的放牧，而鱼类的存在抑制了成年桡足类和枝角类动物的放牧。其他浮游植物群只受环境影响。该实验表明，浮游植物生物量变化受环境的影响比在巴拉那河浅湖中放牧的浮游动物影响更大。人为地增加浮游动物对浮游植物的放牧，而鱼类的存在抑制了成年桡足类和枝角类动物的放牧。其他浮游植物群只受环境影响。该实验表明，浮游植物生物量变化受环境的影响比在巴拉那河浅湖中放牧的浮游动物影响更大。人为地增加浮游动物对浮游植物的放牧，而鱼类的存在抑制了成年桡足类和枝角类动物的放牧。其他浮游植物群只受环境影响。该实验表明，浮游植物生物量变化受环境的影响比在巴拉那河浅湖中放牧的浮游动物影响更大。