Organotropism of metals and Zn Cu isotope ratios in hydrothermal vent mussels (Bathymodiolus) and sea snails (Ifremeria and Alviniconcha): Implications for bioaccumulation mechanisms

This study investigated metal organotropism and ZnCu isotopic compositions in hydrothermal vent mussels (Bathymodiolus sp.) and sea snails (Ifremeria sp. and Alviniconcha sp.). In mussels, bioaccumulation of Al, V, Cr, Mn, Fe, Co, Ni and Zn occurred mainly in the byssus and digestive gland, whereas Cu, As, Ag, Cd, and Pb were found in the gills, suggesting that bioaccumulation of these metals occurs via the respiratory system. In sea snails, the digestive glands tended to have higher metal concentrations than other organs. Zn showed higher intratissue isotope variability than Cu. For Cu isotopes, the digestive glands of vent mollusks had the highest δ⁶⁵Cu values. However, while Zn concentrations were consistently elevated in the digestive glands, δ⁶⁶Zn values did not exhibit a corresponding trend. In vent mussels, during sequenced transport or metal partitioning processes after accumulation via the gills and digestive glands, Zn and Cu concentrations decreased with isotopic fractionation, indicating that lighter isotopes are preferentially used. Both sea snail species differed from mussels in that they preferentially accumulated lighter Zn isotopes in the digestive glands with higher Zn content. The metal and isotopic signatures accumulated in the internal organs of hydrothermal vent mollusks suggest species-dependent dietary strategies and mechanisms of uptake, accumulation, and detoxification. Our findings related to the organotropism of Zn and Cu isotopes offer new insights into the bioavailability and bioaccumulation processes of hydrothermal vent mollusks.