Abstract
Large animals such as sea birds and marine mammals can transport limiting nutrients between different regions of the ocean, thereby stimulating and enhancing productivity. In Antarctica this process is influenced by formation and breakup of sea ice and its influence on the feeding behaviour of predators and their prey. We used analyses of bioactive metals (for example, Fe, Co, Mn), macronutrients (for example, N) and stable isotopes (delta C-13 and delta N-15) in the excreta of Adelie (Pygoscelis adeliae) and emperor penguins (Aptenodytes forsteri) as well as Weddell seals (Leptonychotes weddellii) from multiple sites, among multiple years (2012-2014) to resolve how changes in sea ice dynamics, as indicated by MODIS satellite images, were coincident with prey switching and likely changes in nutrient fluxes between the offshore pelagic and coastal zones. We also sampled excreta of the south polar skua (Stercorarius maccormicki), which preys on penguins and scavenges the remains of both penguins and seals. We found strong coincidence of isotopic evidence for prey switching, between euphausiids (Euphausia superba and E. crystallorophias) and pelagic/cryopelagic fishes (for example, Pleuragramma antarcticum) in penguins, and between pelagic/cryopelagic fishes and Antarctic toothfish (Dissostichus mawsoni) in Weddell seals, with changes in sea ice cover among years. Further, prey switching was strongly linked to changes in the concentrations of nutrients (Fe and N) deposited in coastal environments by both penguins and seals. Our findings have important implications for understanding how the roles of large animals in supporting coastal productivity may shift with environmental conditions in polar ecosystems.