Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states

Future projections based on the IPCC high emissions scenario RCP8.5 have previously shown that the Pacific Northwest coastal waters will be subjected to altered ocean states in the upwelled shelf waters, resulting in higher primary productivity and increased regions of hypoxia and acidification in the inner estuarine waters such as the Salish Sea. However, corresponding effects on the lower trophic levels and submerged aquatic vegetation have not yet been quantified. Supported by new synoptic field data, explicit coupled simulation of algae, zooplankton, and eelgrass biomass was accomplished for the first time in the Salish Sea. We re-applied the improved model to evaluate future ecological response and examined potential algal species shift, but with the effects of zooplankton production, metabolism, and predation-prey interactions included. We also evaluated the role of eelgrass with respect to potential for improvements to dissolved oxygen and pH levels and as a mitigation measure against hypoxia and ocean acidification. The results re-confirm the possibility that there could be a substantial area-days increase (≈52-fold) in exposure of benthic and near-bed pelagic species to hypoxic waters in 2095. The projections for ocean acidification similarly indicate ≈ 20 -114% increase in exposure to lower pH corrosive waters with aragonite saturation state ΩA <1. Importantly, projected increase in primary productivity was shown to propagate to higher trophic levels, with ≈ 13% and 25% increases in micro and mesozooplankton biomass levels. However, the preliminary results also point to sensitivity of the eelgrass model to environmental stressor and potential loss eelgrass biomass in the future.