Trophic-based analyses of the Scotia Sea ecosystem with an examination of the effects of some data limitations and uncertainties

The Scotia Sea is a sub-region of the Southern Ocean with a unique biological operation, including high rates of primary production, high abundances of Antarctic krill, and a diverse community of land-breeding predators. Trophic interactions link all species in an ecosystem into a network known as the food web. Theoretical analyses of trophic food webs, which are parameterised using diet composition data, offer useful tools to explore food web structure and operation. However, limitations in diet data can cause uncertainty in subsequent food web analyses. Therefore, this thesis had two aims: (i) to provide ecological insight into the Scotia Sea food web using theoretical analyses; and (ii) to identify, explore and ameliorate for the effects of some data limitations on these analyses. Therefore, in Chapter 2, I collated a set of diet composition data for consumers in the Scotia Sea, and highlighted its strengths and limitations. In Chapters 3 and 4, I constructed food web analyses to draw ecological insight into the Scotia Sea food web. I indicated the robustness of these conclusions to some of the assumptions I used to construct them. Finally, in Chapter 5, I constructed a probabilistic model of a penguin encountering prey to investigate changes in trophic interactions caused by the spatial and temporal variability of their prey. I show that natural variabilities, such as the spatial aggregation of prey into swarms, can explain observed foraging outcomes for this predator. Pressures caused by anthropogenically-driven changes to the earth’s climate may alter the community structure in the Scotia Sea. Furthermore, activities by commercial fisheries who operate in the Scotia Sea are increasing, which may impact on the food web. This thesis offers a baseline analysis of the Scotia Sea food web, which will be useful to assess changes to the ecosystem caused by future, external pressures.