ABSTRACT: Calanoid copepods dominate mesozooplankton communities in temperate and Nordic seas. The ability of copepods to remain and feed in productive surface waters depends on their ability to overcome downward flows. In this study, we assessed the swimming performance of subarctic Calanus spp. and tested how the copepods can retain their vertical position in a representative range of downward currents (between 0 and 5.4 cm s^-1) simulated in a downwelling flume. Mean vertical and horizontal copepod swimming velocities and accelerations, movement periodicity and trajectory complexity were obtained by tracking individual trajectories in the field of view of 2 cameras. Copepod swimming velocity increased with increasing downward flow and matched downward flows up to 2 cm s^-1. Beyond 2 cm s^-1, animals were still able to significantly reduce their sinking rates, but their motions changed. Trajectories became simpler, swimming velocities changed on shorter time scales and instantaneous acceleration increased. These results are consistent with predictions of balancing depth retention against encounter rates with food and predators. Frequency distributions of vertical swimming speeds were mostly unimodal, with entire experimental populations responding in the same way. Coordination of movements and the ability to resist moderate downwelling flows can result in the accumulation of copepods in large surface swarms as observed in the field.

中文翻译：

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北极亚龟的游泳表现。面对向下的电流

摘要：在温带和北欧海域，类固足类co足类动物占据着中型浮游动物群落。co足类动物残留并进食生产性地表水的能力取决于它们克服向下流动的能力。在这项研究中，我们评估了北极亚龟（Calanus spp）的游泳性能。并测试了pe足类动物如何在下流水槽模拟的向下流的代表性范围（0到5.4 cm s ^-1）内如何保持其垂直位置。通过跟踪2台摄像机视场中的单个轨迹，获得了平均pe足类动物的垂直和水平游泳速度和加速度，运动周期性和轨迹复杂性。pe足类游泳速度随着向下流动的增加而增加，并与向下流动相匹配，直至2 cm s^-1。超过2 cm s ^-1时，动物仍然能够显着降低其下沉速度，但是其运动发生了变化。航迹变得更简单，游泳速度在更短的时间范围内发生了变化，瞬时加速度增加了。这些结果与平衡深度保持与食物和食肉动物的遭遇率之间的预测相一致。垂直游泳速度的频率分布主要是单峰的，整个实验人群的响应方式相同。如在野外观察到的那样，运动的协调性和抵抗中度下降流的能力可能导致po足类动物在大型地表群中的积累。