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

Rita M. Franco-Santos; Sam Eggins; Michael J. Ellwood; Nils Hoem; Peter D. Nichols; Patti Virtue; William A. Maher

doi:10.1071/EN24103

RESEARCH ARTICLE (Open Access)

Contents Vol 22(4)

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

Rita M. Franco-Santos

^A ^B ^# ^* , Sam Eggins ^C ^# ^* , Michael J. Ellwood ^C ^D , Nils Hoem ^E , Peter D. Nichols ^B ^F , Patti Virtue ^B ^F and William A. Maher

^C

+ Author Affiliations

- Author Affiliations

^A CSIRO Environment, Indian Ocean Marine Research Centre, Crawley, WA 6009, Australia.

^B Institute for Marine and Antarctic Studies (IMAS), University of Tasmania, Battery Point, Tas. 7004, Australia.

^C Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia.

^D Australian Centre for Excellence in Antarctic Science, Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia.

^E Aker BioMarine ASA, Lysaker, Norway.

^F CSIRO Environment, Battery Point, Tas. 7004, Australia.

^* Correspondence to: rita.franco-santos@outlook.com, sam.eggins@anu.edu.au

^# These authors contributed equally to this work.

Handling Editor: Graeme Batley

Environmental Chemistry 22, EN24103 https://doi.org/10.1071/EN24103

Submitted: 8 November 2024 Accepted: 5 March 2025 Published: 4 June 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Environmental context

Several predators that eat Antarctic krill may be unintentionally ingesting toxic substances. Studying aspects of krill life to understand the effects of potential increases in Antarctic mercury (Hg) availability revealed that seasons, locations and individual size influence krill Hg concentration. Despite increasing human presence (potential Hg sources) in Antarctica, krill Hg content remains stable, and evidence suggests that Hg accumulates in predators by both short (krill-based) and longer food chains.

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 concentration) 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 concentrations and the affinity of methylmercury to sulfhydryl groups of some proteins, rather than krill fatty acid content, were likely the drivers of observed annual cycles.

Discussion

Antarctic krill Hg concentrations have remained stable since the 1990s, although our measurements were lower than most. Such a 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 understanding of trophic transfer and accumulation of Hg in some top predators. Future biomagnification studies would benefit from conducting mass balance models.

Keywords: chlorophyll-a, euphausiids, fatty acids, food web, maturity stage, mercury, phytoplankton, Southern Ocean.

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