UMR Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), 14 avenue Edouard Belin, 31400 Toulouse, France; Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Av. Joel Montes Camarena S/N, Mazatlán, Sin 82040, Mexico.
UMR Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées (OMP), 14 avenue Edouard Belin, 31400 Toulouse, France.
J Hazard Mater. 2022 Mar 5;425:127956. doi: 10.1016/j.jhazmat.2021.127956. Epub 2021 Dec 1.
Large marine predators exhibit high concentrations of mercury (Hg) as neurotoxic methylmercury, and the potential impacts of global change on Hg contamination in these species remain highly debated. Current contaminant model predictions do not account for intraspecific variability in Hg exposure and may fail to reflect the diversity of future Hg levels among conspecific populations or individuals, especially for top predators displaying a wide range of ecological traits. Here, we used Hg isotopic compositions to show that Hg exposure sources varied significantly between and within three populations of white sharks (Carcharodon carcharias) with contrasting ecology: the north-eastern Pacific, eastern Australasian, and south-western Australasian populations. Through ΔHg signatures in shark tissues, we found that atmospheric Hg deposition pathways to the marine environment differed between coastal and offshore habitats. Discrepancies in δHg and ΔHg signatures among white sharks provided evidence for intraspecific exposure to distinct sources of marine methylmercury, attributed to population and ontogenetic shifts in foraging habitat and prey composition. We finally observed a strong divergence in Hg accumulation rates between populations, leading to three times higher Hg concentrations in large Australasian sharks compared to north-eastern Pacific sharks, and likely due to different trophic strategies adopted by adult sharks across populations. This study illustrates the variety of Hg exposure sources and bioaccumulation patterns that can be found within a single species and suggests that intraspecific variability needs to be considered when assessing future trajectories of Hg levels in marine predators.
大型海洋掠食者体内的汞（Hg）浓度很高，其中以神经毒性的甲基汞形式存在，而全球变化对这些物种中汞污染的潜在影响仍存在很大争议。目前的污染物模型预测并未考虑到 Hg 暴露的种内变异性，可能无法反映未来同种群体或个体 Hg 水平的多样性，尤其是对于表现出广泛生态特征的顶级掠食者而言。在这里，我们使用 Hg 同位素组成表明，具有不同生态特征的三种白鲨（Carcharodon carcharias）种群之间和内部的 Hg 暴露来源存在显著差异：东北太平洋、东澳大利亚和西南澳大利亚种群。通过鲨鱼组织中的 ΔHg 特征，我们发现大气 Hg 向海洋环境的沉积途径在沿海和近海生境之间存在差异。白鲨 δHg 和 ΔHg 特征的差异为种内接触不同来源的海洋甲基汞提供了证据，这归因于觅食生境和猎物组成的种群和个体发育变化。最后，我们观察到不同种群之间 Hg 积累率存在强烈差异，导致大型澳大利亚鲨鱼体内的 Hg 浓度比东北太平洋鲨鱼高三倍，这可能是由于不同种群的成年鲨鱼采用了不同的营养策略。本研究说明了同一物种内可能存在多种 Hg 暴露源和生物累积模式，并表明在评估海洋掠食者未来 Hg 水平轨迹时需要考虑种内变异性。
