Isotopic niches of fishes in coastal, neritic and oceanic waters off Adélie land, Antarctica

We used the stable isotope method to investigate the ecological niches of Antarctic fishes, with δ13C and δ15N as proxies of fish habitats and dietary habits, respectively. Muscle isotopic signature was measured for each of 237 delipidated tissue samples from 27 fish species collected offshore Adélie Land, East Antarctica. Overall, δ13C values ranged from −25.3‰ to −18.2‰, thus allowing characterizing of the fish habitats, with inshore/benthic species having more positive δ13C signatures than offshore/pelagic ones. No clear difference in the δ13C values of pelagic fishes was found between species living in neritic and oceanic waters. Overall, the δ15N signatures of neritic pelagic and epibenthic fishes encompassed ∼1.0 trophic level (3.1‰), a higher difference than that (1.4‰) found within the oceanic assemblage. Fishes with the lowest and highest δ15N values are primarily invertebrate- and fish-eaters, respectively. The isotopic niches of fishes illustrate the different mechanisms allowing coexistence, with most fishes segregating at least by one of the two niche axes (δ13C and δ15N). Muscle isotopic values also document interindividual foraging specialization over the long-term in coastal benthic fishes, but not in more offshore pelagic species. Finally, the δ15N signatures of fishes overlap with those of penguins and seals, indicating that seabirds and marine mammals share the upper levels of the Antarctic pelagic ecosystem with some large fish species. In conclusion, the concept of isotopic niche is a powerful tool to investigate various aspects of the ecological niche of Antarctic fishes, thus complementing the use of other conventional and non-conventional approaches.