Oviparous Catsharks\nAccumulate Mercury in Deep-Sea\nBrine Pool Nurseries

Since the Eocene, oviparous deep-sea sharks and rays\nhave used\ndeep-sea hydrocarbon seeps and hydrothermal vents as nurseries, where\nthey lay eggs en masse. Benthic fluxes in these extreme habitats may\nenrich seawater with toxic metals such as mercury (Hg). We asked whether\nthis phenomenon may lead to Hg accumulation in elasmobranchs. We thus\nanalyzed total Hg (THg) in muscle, liver, and kidney tissues of oviparous <i>Galeus melastomus</i> catsharks and their embryos, which aggregate\nin vast numbers near deep-sea brine pools in the southeastern Mediterranean\nSea. These Hg-rich brines (≤238 ng L<sup>–1</sup>) are\na likely liable geogenic Hg source in this nursery. Shark tissues\ncarried substantial THg [2.7 μg (g of wet weight)<sup>−1</sup>, median], and extreme values were found in kidneys [≤26.7\nμg (g of wet weight)<sup>−1</sup>], likely due to environmental\nuptake. Increased THg in embryos [0.64 ± 0.31 μg (g of\nwet weight)<sup>−1</sup>] implies substantial maternal offloading\n(∼20%). Our results hint at the potential adaptation of elasmobranchs\nto Hg-enriched environments via accumulation and elimination of Hg\nin kidneys.