An Assessment of the Role of Zoogeography in Considerations of Trophic Stability in Marine Ecosystems

Recent analyses have characterized the impacts of fishing exploitation and described shifts in marine community structure on the basis of trends in mean ecosystem trophic level. Both data source and spatial scale have important impacts on the results of such analyses. We develop an integrated assessment of the Bering Sea ecosystem, comparing catch data, survey data and stock assessments to provide a more complete analysis of whether shifts in the trophic levels of catch reflect changes in the ecosystem and at what scale. Trophic stability and diversity indices have been suggested as metrics to evaluate ecosystem stability and resilience. As an alternate approach, we will examine species succession and trends within functional groups. Specifically, we will evaluate the relative impacts of environment and harvest on patterns of species replacement within functional groups. These analyses are intended to evaluate functional guilds to determine whether the components are more variable than in aggregate and to identify the level at which compensation is expressed. We also consider the extent to which species truly are interchangeable from an ecosystem and a market perspective.