Dynamics of mercury contamination within the albatross and petrel community at South Georgia

At the subantarctic islands of South Georgia, albatrosses and petrels occupy a range of trophic niches, from zooplanktivore to top predator. Interspecific variation in mercury (Hg) contamination is therefore expected to be large within this community, as diet is the main exposure pathway. This study compared total Hg (THg) concentrations and stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in feathers of >250 chicks belonging to eight albatross and petrel species at South Georgia during three years (2018-2020). Generally, zooplanktivorous species (Antarctic prion Pachyptila desolata, blue petrel Halobaena caerulea) and the wandering albatross Diomedea exulans (top predator) were least and most contaminated, respectively. However, the order of increasing THg concentrations among giant petrels Macronectes spp. and pelagic generalist species varied annually, likely reflecting shifts in diet or distribution given the diversity of alternative foraging habitats. Accounting for species effects, THg was positively associated with δ¹⁵N in all years, and with δ¹³C in two years, indicating that contamination increased with trophic position and generally, but not always, varied along a foraging habitat or latitudinal gradient. Lastly, pelagic generalists and northern giant petrels M. halli, but neither zooplanktivores nor wandering albatrosses, were more contaminated at Kerguelen than South Georgia, potentially reflecting dietary differences, more complex food chains and a reduced role of Antarctic krill Euphausia superba in the pelagic foodweb of the southern Indian Ocean. Overall, this study highlights the drivers of variation among species, years and regions in THg concentrations, and the need for further work to predict future trends.