Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs

Anaïs Médieu (1) , David Point (2) , Takaaki Itai (3) , Hélène Angot (4) , Pearse Buchanan (5) , Valérie Allain (6) , Leanne Fuller (7) , Shane Griffiths (7) , David Gillikin (8) , Jeroen Sonke (2) , Lars-Eric Heimbürger-Boavida (9) , Marie-Maëlle Desgranges (9) , Christophe Menkes (10) , Daniel Madigan (11) , Pablo Brosset (1, 12) , Olivier Gauthier (1) , Alessandro Tagliabue (5) , Laurent Bopp (13) , Anouk Verheyden (8) , Anne Lorrain (1, 14)

1 LEMAR - Laboratoire des Sciences de l'Environnement Marin (LEMAR)
2 GET - Géosciences Environnement Toulouse
3 Department of Earth and Planetary Science [Tokyo]
4 EERL - Extreme Environments Research Laboratory
5 Department of Earth Ocean and Ecological Sciences [Liverpool]
6 Communauté du Pacifique/Pacific Community
7 IATTC - Inter-American Tropical Tuna Commission
8 Union College
9 MIO - Institut méditerranéen d'océanologie
10 ENTROPIE [Réunion] - Ecologie marine tropicale dans les Océans Pacifique et Indien
11 University of Windsor [Ca]
12 DECOD - Dynamique et durabilité des écosystèmes : de la source à l’océan
13 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
14 IRD - Institut de Recherche pour le Développement

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

Mots clés: Methylmercury; skipjack tuna; biogeochemistry; atmospheric inputs; spatial modeling

Domaines: Biodiversité et Ecologie; Sciences de l'environnement; Océan, Atmosphère; Milieux et Changements globaux

Anaïs Médieu, David Point, Takaaki Itai, Hélène Angot, Pearse Buchanan, et al.. Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs. Proceedings of the National Academy of Sciences of the United States of America, 2022, 119 (2), pp.e2113032119. ⟨10.1073/pnas.2113032119⟩. ⟨hal-03535193⟩