Projections of climate change impacts on marine ecosystems have revealed long-term declines in global marine animal biomass and unevenly distributed impacts on fisheries. Here we apply an enhanced suite of global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), forced by new-generation Earth system model outputs from Phase 6 of the Coupled Model Intercomparison Project (CMIP6), to provide insights into how projected climate change will affect future ocean ecosystems. Compared with the previous generation CMIP5-forced Fish-MIP ensemble, the new ensemble ecosystem simulations show a greater decline in mean global ocean animal biomass under both strong-mitigation and high-emissions scenarios due to elevated warming, despite greater uncertainty in net primary production in the high-emissions scenario. Regional shifts in the direction of biomass changes highlight the continued and urgent need to reduce uncertainty in the projected responses of marine ecosystems to climate change to help support adaptation planning.

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Flatfish are an economically and ecologically important component of continental shelf ecosystems worldwide. These species are impacted from fishing activities, both as direct targets and through indirect effects on habitat and food supply. We examined 25 years of diet data for juveniles and adults of nine species of flatfish in the Northwest Atlantic on the continental shelf off of the USA and parts of Canada in order to understand how flatfish feeding ecology may have changed after decades of fishing and related impacts on the ocean bottom. Atlantic halibut (Hippoglossus hippoglossus), summer flounder (Paralichthys dentatus) and fourspot flounder (P. oblongus) were generally piscivorous. American plaice (Hippoglossoides platessoides) ate primarily ophiuroids. Yellowtail flounder (Limanda ferruginea), winter flounder (Pseudopleuronectes americanus), windowpane (Scophthalmus aquosus), witch flounder (Glyptocephalus cynoglossus) and gulfstream flounder (Citharichthys arctifrons) ate primarily polychaetes, gammarids and other benthic invertebrates. American plaice, summer flounder and fourspot flounder exhibited significant ontogenetic shifts in diet, consuming fewer polychaetes with increasing size. Summer and fourspot flounder also exhibited significant shifts in diet across the time series. None of the benthivorous flatfish exhibited significant changes in diet composition across the time series. The mean weight of stomach contents declined in all species over the past 20 years. The role of flatfish trophic dynamics is discussed in the context of major changes that have occurred in this continental shelf ecosystem.