Oviparous Catsharks Accumulate Mercury in Deep-Sea Brine Pool Nurseries

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