Circumpolar assessment of mercury contamination: the Adélie penguin as a bioindicator of Antarctic marine ecosystems

Due to its persistence and potential ecological and health impacts, mercury (Hg) is a global pollutant of major concern that may reach high concentrations even in remote polar oceans. In contrast to the Arctic Ocean, studies documenting Hg contamination in the Southern Ocean are spatially restricted and large-scale monitoring is needed. Here, we present the first circumpolar assessment of Hg contamination in Antarctic marine ecosystems. Specifically, the Adelie penguin (Pygoscelis adeliae) was used as a bioindicator species, to examine regional variation across 24 colonies distributed across the entire Antarctic continent. Mercury was measured on body feathers collected from both adults (n = 485) and chicks (n = 48) between 2005 and 2021. Because penguins' diet represents the dominant source of Hg, feather delta 13C and delta 15N values were measured as proxies of feeding habitat and trophic position. As expected, chicks had lower Hg concentrations (mean +/- SD: 0.22 +/- 0.08 mu g center dot g-1) than adults (0.49 +/- 0.23 mu g center dot g-1), likely because of their shorter bioaccumulation period. In adults, spatial variation in feather Hg concentrations was driven by both trophic ecology and colony location. The highest Hg concentrations were observed in the Ross Sea, possibly because of a higher consumption of fish in the diet compared to other sites (krill-dominated diet). Such large-scale assessments are critical to assess the effectiveness of the Minamata Convention on Mercury. Owing to their circumpolar distribution and their ecological role in Antarctic marine ecosystems, Adelie penguins could be valuable bioindicators for tracking spatial and temporal trends of Hg across Antarctic waters in the future.Adelie penguins are relevant bioindicators of Hg contamination in Antarctic marine ecosystems.Feather Hg concentrations were measured in 24 breeding colonies (adults and chicks).The highest Hg concentrations were found in the Ross Sea.Both trophic ecology and colony location drove feather Hg concentrations.