Possible dietary shifts in Antarctic penguin and seal species during the late Holocene inferred from stable isotope analysis

Background/Question/Methods: Several previous studies have identified shifts in the carbon and nitrogen stable isotope values of modern versus ancient krill predator (e.g. penguins, seals, etc.) tissues. These studies have hypothesized these differences reflect dietary shifts from fish to krill in concert with changes in climate and a proposed krill surplus due to historic seal and whale harvesting. Here we examine the stable isotope values of modern and ancient penguin (Pygoscelis sp.) egg membrane and feather, and Antarctic fur seal (Arctocephalus gazella) hair collected at Platter Island, Danger Islands Archipelago, along the northeastern Antarctic Peninsula. Samples were excavated from an active penguin nesting site at 5 cm levels in December 2015. Penguin bones from each level were removed and radiocarbon dated. Eggshell membrane, feathers and seal hair were removed from each level and analyzed for δ¹³C and δ¹⁵N value to test for shifts in stable isotope values similar to those observed in past studies.

Results/Conclusions: The analysis of modern and ancient penguin egg membrane indicates a gradual decrease in δ¹³C over the past 500 years likely due to changes in atmospheric δ¹³C from anthropogenic carbon emissions (i.e. the Suess effect). In contrast, egg membrane δ¹⁵N values exhibited a general increase over the past 500 years, possibly indicating a shift away from a lower trophic level diet focused on krill to a higher trophic level diet focused on fish. This trend differs in direction from those observed in prior studies of Antarctic penguin δ¹⁵N values over time. The results of pending analysis of penguin feathers and seal hair will be presented to provide additional insight on the foraging behaviors of penguins and other Antarctic krill predators during the late Holocene.