The Bering Sea Green Belt: shelf‐edge processes and ecosystem production

Abstract

The concept of a highly productive habitat, or Green Belt, along the edge of the continental shelf in the Bering Sea is based upon compelling but fragmentary and often anecdotal observations of a variety of physical and biological features acquired from many sources over many years. Enhanced production at continental margins is not a novel concept, but in the case of the Bering Sea its importance has been overlooked during studies of the unusually broad continental shelf. The limited data reported from the vicinity of the shelf edge in the Bering Sea indicate that annual primary production can be as high as 175 to 275 g C m˜ year‐, or approximately 60% greater than production in the adjacent outer shelf domain and 270% greater than in the oceanic domain. Estimates of annual secondary production at the eastern shelf edge also average approximately 60% higher than estimates for the outer domain and 260% higher than those for the oceanic domain. Physical processes at the shelf edge, such as intensive tidal mixing and transverse circulation and eddies in the Bering Slope Current, bring nutrients into the euphoric zone and contribute to enhanced primary and secondary production and elevated biomass of phytoplankton and zooplankton. Fishes and squids concentrate in this narrow corridor because of favourable feeding conditions and because of a thermal refuge from cold shelf‐bottom temperatures that can be found at the shelf edge from fall to spring. The abundance of zooplankton, fishes and squids, in turn, attracts large numbers of marine birds and mammals. In aggregate, the observations suggest that sustained primary productivity, intense food web exchange and high transfer efficiency at the shelf edge are important to biomass yield at numerous trophic levels and to ecosystem production of the Bering Sea.

Climate change and control of the southeastern Bering Sea pelagic ecosystem

“…High rates of primary production have been reported throughout the Bering Sea, especially on the northern shelf and along the edge of the eastern shelf (225 g C m À2 yr À1 ; Springer et al, 1996). Over the southeastern Bering Sea shelf, primary production varies among domains, with the greatest production occurring in the outer (145 g C m À2 yr À1 ) and middle domains (135 g C m À2 yr À1 ; Springer et al, 1996).…”

“…The northern shelf is highly productive (225 g C m À2 yr À1 ; Springer et al, 1996). Increasing water temperatures and decreasing ice cover may have facilitated the northward spread of pollock, Pacific cod, rock sole and arrowtooth flounder.…”

“…Over the southeastern Bering Sea shelf, primary production varies among domains, with the greatest production occurring in the outer (145 g C m À2 yr À1 ) and middle domains (135 g C m À2 yr À1 ; Springer et al, 1996). Abundant nutrients and incident radiation support high primary productivity rates during the spring bloom.…”

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

“…This advected zooplankton supplements, and in some cases dominates, the local zooplankton community and its secondary production, and may provide prey before local production has developed sufficiently to support planktivores. Thus, much of the biomass of large, lipid-rich copepods and euphausiids available to seabirds in the Chirikov Basin and Bering Strait is advected in Anadyr Water from the deep waters of the Bering Sea (Springer et al, 1989(Springer et al, , 1996Hunt et al, 2013). In the Chukchi Sea in summer, zooplankton advected in Anadyr and Bering Sea Water support high numbers of postbreeding seabirds (Springer et al, 1996;Piatt and Springer, 2003;Gall et al, 2013;Hunt et al, 2013).…”

“…Thus, much of the biomass of large, lipid-rich copepods and euphausiids available to seabirds in the Chirikov Basin and Bering Strait is advected in Anadyr Water from the deep waters of the Bering Sea (Springer et al, 1989(Springer et al, , 1996Hunt et al, 2013). In the Chukchi Sea in summer, zooplankton advected in Anadyr and Bering Sea Water support high numbers of postbreeding seabirds (Springer et al, 1996;Piatt and Springer, 2003;Gall et al, 2013;Hunt et al, 2013). Advection of zooplankton from the Bering Sea in Anadyr Water is also important in providing foraging opportunities for fin (Balaenoptera physalus), humpback (Megaptera novaeanglia), and bowhead (Balaena mysticetus) whales in the western Chukchi Sea (Dahlheim et al, 1980;HeideJørgensen et al, 2013;Hunt et al, 2013), where they feed on euphausiids in the Siberian Coastal Current front (Moore et al, 1995).…”