Habitat and trophic ecology of Southern Ocean cephalopods from stable isotope analyses

Although cephalopods play a critical role in marine food webs both as predators and prey, there is a limited knowledge of several basic aspects of their ecology, including their habitat and trophic level, in the Southern Ocean. We examined the ecological role of several Southern Ocean cephalopod species by analyzing delta C-13 and delta N-15 values in lower cephalopod beaks obtained from diet samples of wandering albatross Diomedea exulans from South Georgia (Atlantic Ocean), and from Crozet and Kerguelen Islands (Indian Ocean). Beak delta C-13 values ranged from -25.7 to -17.9 parts per thousand, and were used to assign different cephalopod species to the subtropical, sub-Antarctic or Antarctic Zones. Beak delta N-15 values were more variable among species, ranging from 2.4 to 13.3 parts per thousand, a difference of similar to 11 parts per thousand that represents approx. 3 trophic levels. Differences among islands in isotope ratios in the same cephalopod species (higher delta N-15 and lower delta C-13 values in South Georgia) were attributed to regional oceanographic processes. Antarctic cephalopods occupy niches similar to those found in some pelagic fish, seabirds and marine mammals. As cephalopods are key components in Southern Ocean food webs, these results greatly advance our understanding of the structure, energy and carbon flows in this polar ecosystem.