| Summary: | International audience Upper trophic level responses to changes in lower trophic level composition and production were compared for the US-GLOBEC study regions in the Southern Ocean (SO), Northern California Current (NCC), coastal Gulf of Alaska (CGoA), and Georges Bank (GB). Similarly structured end-to-end food web models were used to investigate effects on vertebrate predator production of hypothesized future predominance of smaller phytoplankton and zooplankton functional groups in response to climate change. Simulations include: increased small (< 20 μm) vs large (>20 μm) phytoplankton production; increased microzooplankton production at competitive expense to other zooplankton grazers; and reduced euphausiid production with surplus phytoplankton production benefiting copepods and gelatinous zooplankton. Changes in phytoplankton groups had greatest impact on SO top predator production while changes in microzooplankton had greatest effect on GB vertebrate predators. Reduced euphausiid production affected upper trophic level production in SO, NCC and CGoA but not in GB where euphausiids contribute little to vertebrate production. All regions showed large potential impacts from changes in the plankton assemblage size composition.
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