Antarctic fur seals as bioindicators of seasonal and ocean basin scale variation in the Southern Ocean food web

The Southern Ocean exhibits substantial spatiotemporal variation in biogeochemical processes, but our understanding of these variations, especially in remote regions and during winter remains limited. Using biomolecular analysis on blood from wide-ranging female Antarctic fur seals (Arctocephalus gazella) from three key breeding sites (Bird Island, Cape Shirreff and Marion Island), this paper provides the first cross-basin and seasonal comparison of food web baselines (i.e. primary producers), and trophic ecology for this species. This research advances the understanding of trophic ecology in Antarctic fur seals, particularly during the less-studied winter season, when there is potential spatiotemporal overlap with krill fisheries. This study found differences across the three sites studied, with Bird Island and Cape Shirreff seals feeding at lower levels in the food web (i.e. likely krill) compared to the females of Marion Island in summer. We detected seasonal variation in the consumption of krill for females at Bird Island and Cape Shirreff, which shifted their diet in winter, consuming less krill to include prey higher in the food web (i.e., squids and myctophids). This study provides a minimally-invasive method for monitoring changes in the role of the Antarctic fur seal in the Southern Ocean food web and the importance of krill in their diet in the future. The current CEMP review aims to identify environmental variables that can be used to assess the impact of climate changes on the Southern Ocean ecosystem. This paper demonstrates that Antarctic fur seals could serve as an effective bioindicator for monitoring seasonal and long-term changes in primary producers and biogeochemical processes of the Southern Ocean, which could affect the entire food web.