Respiration, metabolic enzyme assays, and body composition parameters were measured in the Antarctic krill Euphausia superba during the summer, fall and winter on the Western Antarctic Peninsula (WAP). E. superba of all sizes decrease their metabolism from the summer to the winter. These same parameters were also measured along the WAP during the austral fall 2010. E. superba's enzyme activity indicated that there was a latitudinal gradient to the decline in metabolism along the WAP with the more northerly sites having significantly higher metabolic enzyme activities than the sites to the south. Carbon (δ13C) and nitrogen (δ15N) stable isotopes were measured in E. superba along the WAP to determine if there were any latitudinal trends. δ13C showed a significant trend with latitude with more depleted δ13C values in the southern portion of the WAP. Carbon (δ13C) and nitrogen (δ15N) stable isotopes were also measured in two important prey fishes along the WAP, the silverfish Pleuragramma antarcticum and the myctophid Electrona antarctica. P. antarcticum had a more variable and more enriched δ13C value than E. antarctica indicative of P. antarcticum's more neritic habitat. There were no significant differences between the δ15N values of the two fish, indicating that although they feed in different areas they were feeding at the same trophic level. Carbon (δ13C) and nitrogen (δ15N) stable isotopes were measured in twenty species in the marginal ice zone (MIZ) of the Weddell Sea at the beginning of the austral summer. Samples were taken from under the ice, at the ice edge and in the open ocean. A significant trend in the δ13C values of all species was found with the under-ice δ13C values being more depleted than those in the open ocean. This is most likely due to the reduced atmospheric exchange of CO2, upwelled water with depleted δ13C values, and continuous biological respiration under the ice, all of which contribute to very depleted δ13C values. δ15N values were significantly lower in the open ocean than the other ice conditions due to the increased reliance on primary production. The diapausing copepods Calanoides acutus and Rhincalanus gigas showed similar patterns in their isotopic signatures across the ice zones. Cluster analysis revealed trophic shifts between the different ice zones. The ice edge zone proved to contain the most species and was the best habitat for most species. The trophic shifts observed within species in the differing ice conditions mimicked the seasonal changes they undergo during the course of the productive season every year.