Using multiple-stable isotopes (δ13C, δ15N, and δ34S) to assess past and present Adélie penguin foraging grounds in the Ross Sea region, Antarctica

We completed multiple-stable isotope analyses (δ¹³C, δ¹⁵N, and δ³⁴S) of Adélie penguin Pygoscelis adeliae chick-bone collagen to characterize differences in foraging behavior among 15 colony locations across the Ross Sea region. Foraging behavior was represented by δ¹³C, δ¹⁵N, and δ³⁴S values and classified into groups using k-means cluster analyses. Additionally, we report the first stable isotope values for the Adélie penguin colony on Sabrina Island, Balleny Islands. Cluster analyses revealed distinct isotopic signatures for the northernmost and central colonies; however, owing to spatial and temporal variability, isotopic signatures were not strong enough to distinguish the southernmost colonies. Results also indicated that δ¹⁵N values increased with latitude (66-77° S), corresponding to higher krill consumption at colonies that foraged in sensible heat polynyas or the open ocean and increased fish consumption for those foraging in latent heat polynyas to the south. Generally, δ³⁴S values are used to distinguish foraging grounds, specifically inshore/offshore foraging or foraging over the continental slope versus the continental shelf, in marine animals. Although the southern and central colonies currently forage along the continental shelf and the northern colonies forage over the shelf, slope, and/or open ocean, we found no significant difference in δ³⁴S values among colonies. While a positive correlation between δ¹⁵N and δ³⁴S values was evident, δ³⁴S signatures did not exhibit distinct patterns specific to individual colonies or regions. The absence of a clear trend reflecting inshore/offshore foraging underscores the need for additional research to bridge this knowledge gap.