Abstract
Abstract The eastern Bering Sea and the Barents Sea share a number of common biophysical characteristics. For example, both are seasonally ice-covered, high-latitude, shelf seas, dependent on advection for heat and for replenishment of nutrients on their shelves, and with ecosystems dominated by a single species of gadoid fish. At the same time, they differ in important respects. In the Barents Sea, advection of Atlantic Water is important for zooplankton vital to the Barents Sea productivity. Advection of zooplankton is not as important for the ecosystems of the southeastern Bering Sea, where high levels of diatom production can support production of small, neritic zooplankton. In the Barents Sea, cod are the dominant gadoid, and juvenile and older fish depend on capelin and other forage fish to repackage the energy available in copepods. In contrast, the dominant fish in the eastern Bering Sea is the walleye pollock, juveniles and adults of which consume zooplankton directly. The southeastern Bering Sea supports considerably larger fish stocks than the Barents. In part, this may reflect the greater depth of much of the Barents Sea compared with the shallow shelf of the southeastern Bering. However, walleye pollock is estimated to occupy a trophic level of 3.3 as compared to 4.3 for Barents Sea cod. This difference alone could have a major impact on the abilities of these seas to support a large biomass of gadoids. In both seas, climate-forced variability in advection and sea-ice cover can potentially have major effects on the productivity of these Subarctic seas. In the Bering Sea, the size and location of pools of cold bottom waters on the shelf may influence the likelihood of predation of juvenile pollock.
Highlights
Primary producers and links to secondary producers north in the Antarctic Circumpolar Current (ACC) system, being north of the Southern ACC Front (SACCF) compared to the western Antarctic Peninsula (wAP), which is south of the SACCF and Southern Boundary of the ACC (SBACC) (Figs. 2 and 4)
The first is that differences in the food webs of the wAP and South Georgia ecosystems relate mainly to evolved adaptations and the resultant lifehistory constraints imposed on different species, rather than being the result of change in overall ecosystem structure and function
The concept of indicators of ecosystem structure that we have suggested can be extended beyond the regions associated with the wAP and South Georgia
Summary
Southern Ocean ecosystems are changing as a result of some of the most rapid regional warming that has been observed anywhere on the planet and further major physical and chemical changes are expected to occur in the coming decades (Costa et al, 2010; Meredith and King, 2005; Montes-Hugo et al, 2009; Schofield et al, 2010; Trivelpiece et al, 2011; Vaughan et al, 2003). Our aim is to develop a comparative analysis of the wAP and South Georgia ecosystems by examining their major structural and functional features and dynamics (i.e. their operation), at regional scales (tens to hundreds of kilometres in extent) to consider the factors generating differences between these ecosystems and their responses to change. An additional aim of this study is, to consider how the methodological basis for comparisons of ecosystems can be developed to examine the importance of different biological and physical processes and interactions over different spatial and temporal scales This comparative study of the wAP and South Georgia ecosystems highlights the spatial and temporal variability of their structure and function, and shows that these ecosystems are more similar than expected from simple views of species occurrence. We develop a generic representation of food web structure for these two areas and suggest that a generic ecosystem model is a viable approach for analysing and modelling South Ocean ecosystems
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