C-CAN OAR April 2

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Risks of ocean acidification in the California Current food web, fisheries, and coastal economies: model projections informed by estimates of species sensitivity.

Abstract: The benefits and ecosystem services that humans derive from the oceans are threatened by numerous global change stressors, including ocean acidification. Here, we describe the effects of ocean acidification on the California Current ecosystem. We used the Atlantis ecosystem model, forced by downscaled global climate models and informed by a meta-analysis of the pH sensitivities of local taxa, to investigate the direct and indirect effects of future pH on biomass and fisheries revenues. The meta-analysis of the pH sensitivities of local taxa is based on a large database of research studies from around the globe and a novel methodology for developing estimates of species sensitivity to OA that are regionally specific. Results indicated that most functional groups in the California current respond negatively to OA conditions. The downscaled global climate model projected a 0.2-unit drop in pH during the summer upwelling season from the year 2013 to the year 2063. This drop in summer pH led to wide-ranging magnitudes of effects across guilds and functional groups in the Atlantis model. The model projects the most dr! amatic direct effects of future pH on epibenthic invertebrates! (crabs, shrimps, benthic grazers, benthic detritivores, bivalves), and strong indirect effects on some demersal fish, sharks, and epibenthic invertebrates (Dungeness crab) because they consume species known to be sensitive to changing pH. Some functional groups were less affected by changing pH in the model than might be expected from experimental studies in the empirical literature due to high population productivity (e.g., copepods, pteropods). Model results suggest strong effects of reduced pH on nearshore state-managed invertebrate fisheries such as the Dungeness crab fishery, but modest effects on the groundfish fishery because individual groundfish species exhibited diverse responses to changing pH.