Changes in temperature alter the viscosity of fluids, which impacts the force needed to move and the diffusion rates of gases. This is particularly salient for organisms that operate at mid to low Reynolds numbers. In this study, we investigated the independent effects of changes in temperature and viscosity on oxygen consumption rates of two coastal copepods (Acartia tonsa and Parvocalanus crassirostris) and used bioenergetic models to predict how these patterns could influence copepods in the natural environment. We found that only temperature influenced copepod oxygen consumption rates, indicating that copepods were not impacted by reduced oxygen diffusivity or increased energetics of movement resulting from higher seawater viscosity. We developed energy budgets based on novel respiration experiments in conjunction with data from the literature and found that cold temperatures do not result in higher scope for growth, because decreased metabolic costs are offset by reduced feeding capability. Our energy budgets imply that observed copepod temperature ranges in natural waters match theoretical ranges of optimal net carbon assimilation. At cold temperatures, feeding on motile prey yielded higher net carbon assimilation compared to feeding on non-motile prey, implying that motile prey are more favorable and may be actively selected for at cold temperatures. Finally, our models predicted that A. tonsa had a higher maximum net carbon assimilation as a percentage of body mass, indicating that copepods that use a similar sink-and-wait feeding strategy may be better able to exploit ephemeral food sources compared to continuous-swimming copepods such as P. crassirostris.

中文翻译：

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分离温度对桡足类呼吸和能量收支的热效应和粘性效应

温度的变化会改变流体的粘度，从而影响移动所需的力和气体的扩散速率。这对于以中低雷诺数运行的生物体尤为突出。在这项研究中，我们研究了温度和粘度变化对两种沿海桡足类（Acartiatonsa 和 Parvocalanus crassirostris）耗氧率的独立影响，并使用生物能模型来预测这些模式如何影响自然环境中的桡足类。我们发现只有温度会影响桡足类的耗氧率，这表明桡足类不受氧气扩散率降低或海水粘度增加导致的运动能量增加的影响。我们根据新的呼吸实验结合文献数据制定了能量预算，发现低温不会导致更大的生长空间，因为降低的代谢成本被降低的进食能力所抵消。我们的能量预算意味着在天然水中观察到的桡足类温度范围与最佳净碳同化的理论范围相匹配。在低温下，与以非活动猎物为食相比，以活动猎物为食产生更高的净碳同化，这意味着活动猎物更有利，在低温下可能会被主动选择。最后，我们的模型预测 A.tonsa 具有更高的最大净碳同化占体重的百分比，