Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis

Abstract

Hunt, G. L., Coyle, K. O., Eisner, L. B., Farley, E. V., Heintz, R. A., Mueter, F., Napp, J. M., Overland, J. E., Ressler, P. H., Salo, S., and Stabeno, P. J. 2011. Climate impacts on eastern Bering Sea foodwebs: a synthesis of new data and an assessment of the Oscillating Control Hypothesis. – ICES Journal of Marine Science, 68: 1230–1243. Walleye pollock (Theragra chalcogramma) is an important component of the eastern Bering Sea ecosystem and subject to major fisheries. The Oscillating Control Hypothesis (OCH) predicted that recruitment of pollock year classes should be greatest in years with early ice retreat and late blooms in warm water, because more energy would flow into the pelagic (vs. benthic) community. The OCH further predicted that, with pollock population growth, there should be a shift from bottom-up to top-down regulation. New data support the predictions that in those years with early ice retreat, more primary production accrues to the pelagic compartment and that large numbers of age-0 pollock survive to summer. However, in these years, production of large crustacean zooplankton is reduced, depriving age-0 pollock of lipid-rich prey in summer and autumn. Consequently, age-0 pollock energy reserves (depot lipids) are low and predation on them is increased as fish switch to age-0 pollock from zooplankton. The result is weak recruitment of age-1 recruits the following year. A revised OCH indicates bottom-up constraints on pollock recruitment in very warm periods. Prolonged warm periods with decreased ice cover will likely cause diminished pollock recruitment and catches relative to recent values.

Spring bloom dynamics and zooplankton biomass response on the US Northeast Continental Shelf

“…The relationship between bloom timing and recruitment can involve a more nuanced relationship between zooplankton and larval fish. Year-class strength of walleye pollock has also been associated with variation in zooplankton composition related to phytoplankton phenology (Hunt et al, 2011). Spring bloom dynamics have also been observed to influence recruitment success of Argentine anchovy, Pacific herring, and coho and sockeye salmon (Borstad et al, 2011;Chittenden et al, 2010;Marrari et al, 2013;Schweigert et al, 2013).…”

The Barents and Chukchi Seas: Comparison of two Arctic shelf ecosystems

“…During the warm period in the Bering Sea from 2001 to 2005, ice retreat came early and the production of C. marshallae/glacialis was limited . If these copepods, and the euphausiid Thysanoessa raschii are, as is believed, dependent on sea ice or at least a bloom in cold water (Baier and Napp, 2003;Drobysheva, 1994;Ressler et al, 2012), then warming of the northern Bering Sea sufficient to remove seasonal ice cover might result in failure of pollock recruitment, as happened in the southeastern Bering Sea during the warm period of Hunt et al, 2011).…”

Changes in phytoplankton community structure during wind-induced fall bloom on the central Chukchi shelf

“…In the Beaufort Sea, episodic fall blooms have obvious impact on the recruitment of secondary producers (Tremblay et al 2011). Similarly, yearly changes in the timing of the spring bloom have significant impact on the production of higher trophic level organisms through the food web in the Bering Sea (reviewed in Hunt et al 2002Hunt et al , 2011. The impact on secondary producers as a whole remains unknown because the grazing experiments were conducted only for C. glacialis C5, even though they comprise one-third of the total mesozooplankton abundance.…”