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Resource Ecology & Ecosystem Modeling Program

Chukchi Food Web Modeling

figure 1, see caption
Figure 1.  Map of the model area in the eastern Chukchi Sea.  The area is bounded by the U.S.-Russian convention line to the west, Bering Strait to the South, Pt. Barrow to the east, and both the EEZ and 70-m isobath to the north. Near shore the model is bounded by the 20-m isobath.

REEM researcher Andy Whitehouse completed development of a preliminary mass-balance food web model for the continental shelf of the eastern Chukchi Sea (Fig. 1). The model provides a snapshot of community structure averaged over an annual time scale and describes key structural and functional components of the eastern Chukchi Sea food web.

The majority of biomass in this ecosystem was concentrated in benthic invertebrates (Fig. 2) and accordingly most of the mass flow above trophic level 2.0 was through this group. Mass flows to higher trophic levels through pelagic groups like zooplankton were an order of magnitude less.

Arctic cod, Boreogadus saida, were the principal fish prey connecting production between lower and upper trophic levels. Seabirds and marine mammals collectively consumed about 75% of total arctic cod production.

figure 2, see caption
Figure 2.  Food web diagram of the eastern Chukchi Sea.  The boxes are arranged vertically by trophic level and box size is proportional to biomass density.  Red colored boxes are associated with the benthic trophic pathway and blue denotes the pelagic pathway.

To gain a broader perspective on the structure and function of the eastern Chukchi Sea, comparisons were drawn with the nearby subarctic eastern Bering Sea, using a set of system metrics derived from a common modeling framework. The total biomass density (t km2) of the eastern Chukchi Sea was nearly equal the eastern Bering Sea but had less than half the total production (t km2/yr). In practical terms, this fundamental difference between the eastern Chukchi Sea and eastern Bering Sea implies that the Chukchi may not be as resilient to fishing or other mortality agents such as a wide-spread oil spill.

This food web model provides a novel description of the trophic structure and functioning of the eastern Chukchi Sea. In the future it can be used to evaluate trophic changes that might accompany climate change and provides a means of assessing the ecosystem-wide impacts of the removal of fish species by a fishery.

By Andy Whitehouse

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