ABSTRACT: Light is a fundamental environmental cue which influences the migration of many marine organisms. For the salmon louse Lepeophtheirus salmonis, light is believed to drive the diel vertical migration behaviour of their planktonic larvae. Salmon lice are of critical importance to the salmonid industry due to the damage they cause to wild and farmed hosts. Salmon lice larvae have an eyespot and are positively phototactic, yet how light intensity alters their vertical distribution remains unclear. Here, we tested how light intensity (0, 0.5, 10 and 80 µmol m^-2 s^-1), dispersal duration (1, 4 and 12 h) and release point (surface or bottom) influenced the vertical migration of salmon lice nauplii and copepodids under controlled conditions in experimental columns. Overall, higher light intensity increased the proportion of nauplii that aggregated at the surface. Copepodid behaviour differed from that of nauplii, as they swam upwards in both light and fully dark conditions, and surface aggregations increased with dispersal duration. Results from the experiments did not support the existing view that light strongly influences the vertical position of copepodids in the water column. Combined with previous work, our results reveal that salmon lice larval stages display different vertical responses to light, temperature and salinity, which may be explained by the different strategies of nauplii (maximise survival and dispersal) and copepodids (maximise host-finding success). Our results have implications for salmon lice dispersal models, where responses of copepodids and nauplii to light are currently parametrised by the same equations. Implementing stage-specific behaviours towards light may improve the outputs of dispersal models.

中文翻译：

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鲑鱼虱无节幼体和足足对光的响应显示出不同的垂直迁移模式

摘要：光是影响许多海洋生物迁移的基本环境线索。对于鲑鱼虱子Lepeophtheirus鲑鱼，认为光会驱动其浮游幼虫的diel垂直迁移行为。鲑鱼虱对鲑鱼产业至关重要，因为它们对野生和养殖的寄主造成损害。鲑鱼虱幼虫有一个眼点，并且具有正向趋光性，但是光强度如何改变其垂直分布仍不清楚。在这里，我们测试了光强度（0、0.5、10和80 µmol m ^-2 s ^-1），分散时间（1、4和12小时）和释放点（表面或底部）影响了鲑鱼无节幼体和近足在控制条件下在实验柱中的垂直迁移。总体而言，较高的光强度增加了在表面聚集的无节幼体的比例。pe足类的行为与无节幼体的行为不同，因为它们在明亮和完全黑暗的条件下都向上游动，并且表面聚集随着扩散持续时间的增加而增加。实验结果不支持现有观点，即光线强烈影响立足在水柱中的垂直位置。结合先前的工作，我们的结果表明，鲑鱼虱幼虫阶段对光，温度和盐度表现出不同的垂直响应，这可以通过无节幼体（最大存活和扩散）和双足类（最大寄主发现成功）的不同策略来解释。我们的结果对鲑鱼虱子扩散模型有影响，在该模型中，双足纲和无节幼体对光的响应目前由相同的方程式参数化。实施针对光的特定于阶段的行为可能会改善色散模型的输出。