Mercury in a community of subantarctic seabirds: Chick feather concentrations and influence of foraging habitat and diet

Using top predators as sentinels of the marine environment, Hg contamination was investigated within the large subantarctic seabird community of the Kerguelen Islands, a remote and poorly known area located in the Southern Indian Ocean. Focusing on chicks (21 species), Hg analysis pointed out large inter-specific variations in body feather Hg concentrations, which ranged from 0.08 ± 0.01 to 5.31 ± 1.12 μg∙g-1 dry mass. Seabirds from Kerguelen thus encompass the whole range of chick feather Hg values that were previously collected worldwide. Using stable isotopes, the effects of foraging habitat (reflected by 13C) and trophic positions (reflected by 15N) on Hg concentrations were then investigated. A multivariate analysis showed that the species-related Hg variations were highly and positively linked to feather 15N values, thus highlighting biomagnification processes occurring throughout the subantarctic marine trophic webs. By contrast, Hg contamination overall correlated poorly with seabird foraging habitat. However, when focusing on oceanic species, seabird Hg concentration was related to feather 13C values, with species feeding in colder waters south of Kerguelen Islands being less prone to be contaminated than species feeding in northern warmer waters. In conclusion, the study emphasizes the global effect of anthropogenic Hg emission that is detectable in remote subantarctic islands. Those isolated localities therefore appear as ideal study sites to monitor the temporal trends of global Hg contamination, with the help of some carefully selected seabird specie