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

Abstract

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 urgently needed. Here, we present the first circumpolar assessment of Hg contamination across Antarctic marine food webs. More specifically, we studied the Adélie penguin (Pygoscelis adeliae) as a bioindicator species to examine regional variation across 24 colonies distributed across the entire Antarctic continent. Mercury concentrations were 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 carbon- (δ¹³C) and nitrogen- (δ¹⁵N) stable isotopes (proxies of feeding habitat and trophic position) were also analysed. As expected, chicks had lower Hg concentrations (mean ± SD: 0.22 ± 0.08 μg.g‒1) than adults (0.49 ± 0.23 μg.g‒1), likely because of their shorter bioaccumulation period. Overall, feather Hg concentrations were below toxicity thresholds for seabirds (1.62‒10 μg.g‒1). In adults, spatial variation in feather Hg concentrations was driven by both feeding 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, Adélie penguins could be valuable bioindicators for tracking spatial and temporal trends of Hg across the Southern Ocean in the future.