Interannual variability of the South Georgia marine ecosystem: Biological and physical sources of variation in the abundance of krill

Interannual variability is a characteristic feature of the Southern Ocean e cosystem, yet the relative roles of biological and physical processes in ge nerating these fluctuations are unknown. There is now extensive evidence th at there are years when there is a very low abundance of Antarctic krill (E uphausia superba) in the South Georgia area, and that this variation affect s much of the ecosystem, with the most obvious impacts on survival and bree ding success of some of the major predators on krill. The open nature of th e South Georgia ecosystem means this variability has large-scale relevance, but even though there are unique time series of data available, informatio n on some key processes is limited. Fluctuations in year-class success in p arts, or all, of the krill population across the Scotia Sea can generate la rge changes in the available biomass. The ocean transport pathways maintain the large-scale ecosystem structure by moving krill over large distances t o areas where they are available to predator colonies. This large-scale phy sical system shows strong spatial and temporal coherence in the patterns of the interannual and subdecadal variability. This physical variability affe cts both the population dynamics of krill and the transport pathways, empha sizing that both the causes and the consequences of events at South Georgia are part of much larger-scale processes.