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Climate-mediated oceanographic changes have led to protracted periods of above- or below-average water temperatures over the eastern Bering Sea shelf since the early 2000s. Ecosystem components, from phytoplankton to marine birds, have shown dichotomous responses to these temperature stanzas. Understanding within-stanza responses is fundamental to modelling efforts that project ecosystem responses under future climate scenarios. This study describes fish communities associated with Walleye Pollock during the age-0 period and also examines within-stanza homogeneity of assemblages. Spatial patterns of assemblage structure are compared with pre-defined ecoregions and environmental indices are assessed to determine potential mechanisms that delineate species assemblages. Walleye Pollock, rockfishes, Sand Lance, and Northern Rock Sole contributed to spring assemblages in every year. Assemblages were delineated by across-shelf gradients in 2008 and 2010 while 2009 assemblages showed less spatial structure. In summer, the diversity of fish assemblages increased across years but early-stage juvenile Walleye Pollock represented a small portion of the total abundance in 2009. Environmental gradients were related to fish assemblages, but patterns were along-shelf in 2008 and across-shelf in 2010. In fall, late-stage juvenile Walleye Pollock dominated the catch in 2008, but did not typify any assemblage in 2009. Overall, patterns of assemblage structure were not consistent with pre-defined ecoregions. Assemblage structure in 2009 was unique and indicates that within-stanza variability may complicate modelling projections based on ecosystem-level responses to climate changes. [ABSTRACT FROM AUTHOR]

Ecosystem structure and function in the eastern Bering Sea are impacted by seasonal, interannual, and spatial variation of the zooplankton community. Zooplankton abundance, community composition and individual responses of key taxa, in spring, summer, and fall were evaluated across ecoregions during three years with high sea-ice, 2008-2010 (cold years). Interannual variations were greatest in spring, but less pronounced compared with intra-annual variations. Intra-annual variations were greatest in the south middle domain in spring and the north middle domain in all seasons. Models using environmental variables were able to explain 69-77% of zooplankton community variation within each season. Among individual taxa, Calanus marshallae/glacialis had delayed stage progression in spring 2009 compared with 2008 and 2010 on the south middle shelf, likely due to late ice retreat and cold temperatures that increased development times. In contrast, stage progression was fastest in summer 2008 likely due to warmer temperatures. Our findings indicate that intra-annual variation of zooplankton community composition, life history stage, and abundance within a cold period may affect the amount of high-lipid zooplankton prey (e.g. Neocalanus and Calanus spp. copepods and euphausiids) available seasonally for forage fish (e.g. age-0 walleye pollock) to grow to a sufficient size (to avoid size-dependent predation) and have sufficient lipid stores (to avoid starvation) to survive the first winter at sea. [ABSTRACT FROM AUTHOR]