School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, 98195, USA.
School of Oceanography, University of Washington, Seattle, Washington, 98195, USA.
Ecol Appl. 2020 Dec;30(8):e02204. doi: 10.1002/eap.2204. Epub 2020 Aug 28.
In coastal marine ecosystems, the depletion of dissolved oxygen can cause behavioral and distributional shifts of organisms and thereby alter ecological processes. We used the spatiotemporal variation in the onset and intensity of low dissolved oxygen in Hood Canal, Washington, USA, to investigate consequences of seasonally reduced oxygen on fish-zooplankton predator-prey interactions. By simultaneously monitoring densities of zooplankton (primarily the euphausiid; Euphausia pacifica) and zooplanktivorous fish (Pacific herring, Clupea pallasii, and Pacific hake, Mercluccius productus), and the feeding of zooplanktivorous fish, we could separate the effects of dissolved oxygen on fish-zooplankton interactions from other seasonal changes. We expected that fish predators (especially Pacific herring) would be less abundant and have lower feeding rates when oxygen levels declined below biological thresholds, and that this would result in increased zooplankton abundance in areas with lowest dissolved oxygen. However, these expectations were not borne out. Overall, there was mixed evidence for an effect of dissolved oxygen on many of our response variables, and when effects were detected, they were frequently in the opposite direction of our expectations. Specifically, the pelagic fish community became more abundant (as measured by increasing acoustic backscatter), which was particularly pronounced for Pacific herring. Zooplankton had weak evidence for a response to dissolved oxygen, but the direction was negative instead of positive. Although predator feeding composition was unrelated to dissolved oxygen, stomach fullness (an index of feeding intensity) of Pacific herring declined, as per our expectations. These unexpected findings highlight the importance of in situ measurements of multiple aspects of predator-prey linkages in response to environmental stress to enhance our ability to predict ecological consequences of declining oxygen.
在沿海海洋生态系统中，溶解氧的消耗会导致生物的行为和分布发生变化，从而改变生态过程。我们利用美国华盛顿州胡德运河溶解氧季节性减少的时空变化，研究了低氧对鱼类-浮游动物捕食者-猎物相互作用的影响。通过同时监测浮游动物（主要是磷虾；Euphausia pacifica）和浮游动物食性鱼类（太平洋鲱鱼，Clupea pallasii，和太平洋无须鳕，Mercluccius productus）的密度，以及浮游动物食性鱼类的摄食情况，我们可以将溶解氧对鱼类-浮游动物相互作用的影响与其他季节性变化区分开来。我们预计，当氧水平下降到生物阈值以下时，鱼类捕食者（特别是太平洋鲱鱼）的丰度会降低，摄食率也会降低，这将导致低溶解氧区域浮游动物的丰度增加。然而，这些预期并没有得到证实。总的来说，溶解氧对我们许多反应变量的影响存在混合证据，而且当检测到影响时，它们经常与我们的预期方向相反。具体来说，浮游鱼类群落变得更加丰富（如通过增加声学反向散射来衡量），这在太平洋鲱鱼中尤为明显。浮游动物对溶解氧的反应证据较弱，但方向与我们的预期相反。尽管捕食者的摄食组成与溶解氧无关，但太平洋鲱鱼的胃饱满度（摄食强度的指标）却如我们所预期的那样下降了。这些意外的发现强调了在原位测量多个方面的捕食者-猎物联系对环境胁迫的反应的重要性，以提高我们预测氧气减少对生态后果的能力。
