MEPS 695:203-216 (2022)  -  DOI: https://doi.org/10.3354/meps14112

ABSTRACT: The Atlantic sector of the Southern Ocean has been rapidly changing over the last century. Many of those changes are driven by climate anomalies such as the El Niño-Southern Oscillation and the Southern Annular Mode, which affect biological processes that scale up the food web. We used δ¹³C and δ¹⁵N time series of dentine growth layer groups (as a proxy of individual foraging history from multiple years, n = 41 teeth) to assess temporal shifts in foraging habits of subadult/adult male Antarctic fur seals Arctocephalus gazella (AFSs) in 2 areas of high concentration of Antarctic krill Euphausia superba: the South Shetland Islands and the South Orkney Islands. Our analyses, which represent the first long-term isotopic assessment of male AFS sampled in Antarctic waters, revealed a significant decrease of δ¹³C (0.04‰ yr^-1) from 1974 to 2015 and a decrease of δ¹⁵N after the late 1990s. The observed changes are likely driven by shifts in latitudinal and longitudinal distribution of krill and increased incorporation of ¹⁵N-enriched sources (higher trophic level prey and/or feeding in different areas) in the most recent period for reasons that are not yet clear. We were able to trace ecosystem changes through isotopic bio-archives of Antarctic fur seals, highlighting the role of this species as an ecosystem indicator of the trophic cascade effects caused by climate change in the Southern Ocean.

KEY WORDS: Climate change · Southern Ocean · Antarctic krill · Antarctic food webs · Ecological time series