Coastal marine ecosystems are threatened by widespread and frequent periods when oxygen levels are severely reduced. While marine life may suffer direct mortality as result of low dissolved oxygen, species more commonly undergo physiological or behavioral change to minimize their exposure to harmful conditions. This study evaluated the joint effects of these changes on a marine food web, focusing on the key connection between large zooplankton and their primary prey, herring and hake. This food web linkage is critical to provide food for valued species such as sea mammals, seabirds, and large piscivorous fish such as salmon, cod, and sharks. By tracking changes in what fish were eating, how much they were eating, the density of fish and zooplankton, and their spatial overlap, we were able to identify how eroding oxygen conditions in Hood Canal, WA, affected this critical food web link. We find that spatial overlap is largely maintained, despite the fact that fish and zooplankton have different tolerances for reduced oxygen. The maintenance of spatial overlap is likely due the relatively cold water conditions, which reduced species? oxygen requirements. However, we find that the nature of the food web linkage was substantially affected, as individual herring had reduced feeding rates, possible leading to smaller growth and lower energy stores. However, total energy flow from zooplankton to fish was maintained though shifts in local fish abundance. Future predictions of how coastal marine ecosystems will respond to increasing oxygen depletion, coupled with warming temperatures and lowered pH, will benefit from a new approach that considers effects on key ecological processes rather than on species abundance and distribution. Last Modified: 08/07/2017 Submitted by: Timothy E Essington