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Mercury concentration in Antarctic krill varies in time and space and with individual size

Rita Franco-Santos , Sam Eggins, Michael Ellwood, Nils Hoem, Peter Nichols, Patti Virtue, William Maher

Abstract

Rationale Mercury (Hg) is passively assimilated from the water by phytoplankton, accumulated by lower trophic levels species, and biomagnified along food chains. Any increases in its bioavailability in Antarctic waters could endanger the survival of vulnerable top predators. With Antarctic food webs reliant on krill, we must understand the temporal, spatial, and biological variability in their Hg concentration to forecast ecosystem-wide impacts of rising Hg levels. Methodology We sampled krill fortnightly from South Georgia, South Orkney Islands, and West Antarctic Peninsula between December 2013 and September 2019 (excluding October and November months). Individuals were weighed, sexed, and analysed for Hg. We assessed the importance of biological (krill size, sex, and life stage) and environmental (location, time, and chlorophyll a) parameters on krill Hg concentrations with generalised linear models, analyses of variance, Gaussian linear models, and vector autoregressive modelling. Results Temporal variation explained most of the differences in krill Hg concentrations, with location and individual size also contributing to the variability. Subsurface chlorophyll a, rather than krill fatty acid content, was likely the driver of observed annual cycles. Discussion Antarctic krill Hg concentrations have remained stable since the 1990s, though our measurements were lower than most. Such historic baseline is indispensable for continued monitoring of Antarctic ecosystems. Krill is considered a key prey species, but our findings and those of biomagnification studies suggest that there may be a gap in our understand of trophic transfer and accumulation of Hg in some top predators. Future biomagnification studies would benefit from conducting mass balance models.

EN24103  Accepted 05 March 2025

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