Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882;
Biological Sciences Department, Virginia Institute of Marine Science, Gloucester Point, VA 23062.
Proc Natl Acad Sci U S A. 2021 Aug 10;118(32). doi: 10.1073/pnas.2022977118.
Many zooplankton and fishes vertically migrate on a diel cycle to avoid predation, moving from their daytime residence in darker, deep waters to prey-rich surface waters to feed at dusk and returning to depth before dawn. Vertical migrations also occur in response to other processes that modify local light intensity, such as storms, eclipses, and full moons. We observed rapid, high-frequency migrations, spanning up to 60 m, of a diel vertically migrating acoustic scattering layer with a daytime depth of 300 m in the subpolar Northeastern Pacific Ocean. The depth of the layer was significantly correlated, with an ∼5-min lag, to cloud-driven variability in surface photosynthetically available radiation. A model of isolume-following swimming behavior reproduces the observed layer depth and suggests that the high-frequency migration is a phototactic response to absolute light level. Overall, the cumulative distance traveled per day in response to clouds was at least 36% of the round-trip diel migration distance. This previously undescribed phenomenon has implications for the metabolic requirements of migrating animals while at depth and highlights the powerful evolutionary adaptation for visual predator avoidance.
许多浮游动物和鱼类会在昼夜节律上进行垂直迁徙，以避免被捕食，它们会从白天在较深、较暗水域的栖息地移动到富含猎物的水面觅食，然后在黄昏时分返回深处，黎明前再回到深处。垂直迁徙也会因其他改变局部光强的过程而发生，如风暴、日食和满月。我们观察到在亚北极东北太平洋，一个日夜垂直迁徙的声学散射层会发生快速、高频的迁徙，迁徙范围高达 60 米，该散射层在白天的深度为 300 米。该层的深度与云驱动的海面光合有效辐射变化显著相关，存在约 5 分钟的滞后。一个跟随等光强线游动的模型再现了观察到的层深，并表明高频迁徙是对绝对光强的趋光反应。总的来说，每天为躲避云层而进行的迁徙距离至少是往返昼夜迁徙距离的 36%。这种以前未被描述的现象对在深处迁徙的动物的代谢需求有影响，并强调了视觉躲避捕食者的强大进化适应能力。
