Mercury isotopes as tracers of ecology and metabolism in two sympatric shark species

Type Article
Date 2020-10
Language English
Author(s) Le Croizier Gaël1, Lorrain Anne2, Sonke Jeroen E.1, Jaquemet Sébastien3, Schaal Gauthier2, Renedo Marina1, Besnard Lucien2, Cherel Yves4, Point David1
Affiliation(s) 1 : Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), UMR 5563 CNRS/IRD/Université Paul Sabatier, 14 avenue Edouard Belin, 31400, Toulouse, France
2 : Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS/UBO/IRD/IFREMER, BP 70, 29280, Plouzané, France
3 : Laboratoire ENTROPIE, UMR 9220 CNRS/IRD/Université de La Réunion, 15 Avenue René Cassin, BP 92003, 97744, Saint-Denis, La Réunion, France
4 : Centre d’Etudes Biologiques de Chizé (CEBC), UMR 7372 du CNRS-La Rochelle Université, 79360, Villiers-en-Bois, France
Source Environmental Pollution (0269-7491) (Elsevier BV), 2020-10 , Vol. 265 , N. Part B , P. 114931 (11p.)
DOI 10.1016/j.envpol.2020.114931
WOS© Times Cited 26

In coastal ecosystems, top predators are exposed to a wide variety of nutrient and contaminant sources due to the diversity of trophic webs within coastal areas. Mercury contamination could represent an additional threat to shark populations that are declining worldwide. Here we measured total mercury, carbon and nitrogen isotopes as well as mercury isotopes in two co-occurring shark species (the bull shark Carcharhinus leucas and the tiger shark Galeocerdo cuvier) and their prey from a coastal ecosystem of the western Indian Ocean (La Réunion Island), to (i) determine their main trophic Hg source and (ii) better characterize their diet composition and foraging habitat. Hg isotope signatures (Δ199Hg and δ202Hg) of shark prey suggested that bull sharks were exposed to methylmercury (MeHg) produced in the water column while tiger sharks were exposed to mesopelagic MeHg with additional microbial transformation in slope sediments. Δ199Hg values efficiently traced the ecology of the two predators, demonstrating that bull sharks targeted coastal prey in shallow waters while tiger sharks were mainly foraging on mesopelagic species in the slope deeper waters. Unexpectedly, we found a positive shift in δ202Hg (>1‰) between sharks and their prey, leading to high δ202Hg values in the two shark species (e.g. 1.91 ± 0.52‰ in the bull shark). This large shift in δ202Hg indicates that sharks may display strong MeHg demethylation abilities, possibly reflecting evolutionary pathways for mitigating their MeHg contamination.

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Le Croizier Gaël, Lorrain Anne, Sonke Jeroen E., Jaquemet Sébastien, Schaal Gauthier, Renedo Marina, Besnard Lucien, Cherel Yves, Point David (2020). Mercury isotopes as tracers of ecology and metabolism in two sympatric shark species. Environmental Pollution, 265(Part B), 114931 (11p.). Publisher's official version : , Open Access version :