Stable mercury concentrations of tropical tuna in the south western Pacific ocean: An 18-year monitoring study

Type Article
Date 2021-01
Language English
Author(s) Médieu Anais1, Point David2, Receveur Aurore3, Gauthier Olivier1, Allain Valerie3, Pethybridge Heidi4, Menkes Christophe E.5, Gillikin David P.6, Revill Andrew T.4, Somes Christopher J.7, Collin Jeremy1, Lorrain Anne1
Affiliation(s) 1 : Univ Brest, CNRS, IRD, Ifremer, LEMAR, F-29280, Plouzané, France
2 : Observatoire Midi-Pyrénées, GET, UMR CNRS 5563/IRD 234, Université Paul Sabatier Toulouse 3, Toulouse, France
3 : Pacific Community, Oceanic Fisheries Programme, Nouméa, France
4 : CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia
5 : ENTROPIE (UMR 9220), IRD, Univ. de La Réunion, CNRS, Nouméa, New Caledonia
6 : Department of Geology, Union College, 807 Union St., Schenectady, NY, 12308, USA
7 : GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
Source Chemosphere (0045-6535) (Elsevier BV), 2021-01 , Vol. 263 , P. 128024 (14p.)
DOI 10.1016/j.chemosphere.2020.128024
WOS© Times Cited 13
Keyword(s) Methylmercury, Stable isotope data, Yellowfin tuna, Bigeye tuna, Skipjack tuna, New Caledonia-Fiji region
Abstract

Global anthropogenic mercury (Hg) emissions to the atmosphere since industrialization are widely considered to be responsible for a significant increase in surface ocean Hg concentrations. Still unclear is how those inputs are converted into toxic methylmercury (MeHg) then transferred and biomagnified in oceanic food webs. We used a unique long-term and continuous dataset to explore the temporal Hg trend and variability of three tropical tuna species (yellowfin, bigeye, and skipjack) from the southwestern Pacific Ocean between 2001 and 2018 (n = 590). Temporal trends of muscle nitrogen (δ15N) and carbon (δ13C) stable isotope ratios, amino acid (AA) δ15N values and oceanographic variables were also investigated to examine the potential influence of trophic, biogeochemical and physical processes on the temporal variability of tuna Hg concentrations. For the three species, we detected significant inter-annual variability but no significant long-term trend for Hg concentrations. Inter-annual variability was related to the variability in tuna sampled lengths among years and to tuna muscle δ15N and δ13C values. Complementary AA- and model-estimated phytoplankton δ15N values suggested the influence of baseline processes with enhanced tuna Hg concentrations observed when dinitrogen fixers prevail, possibly fuelling baseline Hg methylation and/or MeHg bioavailability at the base of the food web. Our results show that MeHg trends in top predators do not necessary capture the increasing Hg concentrations in surface waters suspected at the global oceanic scale due to the complex and variable processes governing Hg deposition, methylation, bioavailability and biomagnification. This illustrates the need for long-term standardized monitoring programs of marine biota worldwide.

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Médieu Anais, Point David, Receveur Aurore, Gauthier Olivier, Allain Valerie, Pethybridge Heidi, Menkes Christophe E., Gillikin David P., Revill Andrew T., Somes Christopher J., Collin Jeremy, Lorrain Anne (2021). Stable mercury concentrations of tropical tuna in the south western Pacific ocean: An 18-year monitoring study. Chemosphere, 263, 128024 (14p.). Publisher's official version : https://doi.org/10.1016/j.chemosphere.2020.128024 , Open Access version : https://archimer.ifremer.fr/doc/00648/76020/