How Does Hypoxia Govern Energy Flows in Pelagic Food Webs?

Low dissolved oxygen (hypoxia) can induce distributional shifts of mobile organisms, and thereby alter their vulnerability to predators. In pelagic food webs, zooplankton might benefit from moderate hypoxia because it may create refuge areas that pelagic fish avoid.  However, if hypoxia becomes more severe, the vertical extent of diel vertical migrations might be compressed, thereby exposing zooplankton to enhanced predation risk.  Here we conducted an extensive, two year sampling of zooplankton and pelagic fish distributions, species composition, and feeding rates across sites the provided a gradient in the intensity, vertical extent, and timing of hypoxia to test a series of nested hypotheses about whether hypoxia can cause energy pathways in food webs to shift.  We find that in Hood Canal, WA, the pelagic food web is remarkable resilient to even very low oxygen levels.  A series of detailed investigations will be important to reveal the mechanisms that confer this resilience.