Multi-element stable isotope geochemistry and arsenic speciation of hydrothermal vent fauna (Alviniconcha sp., Ifremeria nautilei and Eochionelasmus ohtai manusensis), Manus Basin, Papua New Guinea

Deep-sea hydrothermal vent communities, revealing patterns of niche partitioning, live in a limited area characterised by sharp physico-chemical gradients. In this study, we investigated carbon, sulfur, nitrogen stable isotopes as well as arsenic (As) speciations and concentrations for two snails (Alviniconcha sp. and Ifremeria nautilei) and a crustacean, (Eochionelasmus ohtai manusensis), occupying distinct niches in the hydrothermal vent field of the Vienna Woods, Manus Basin, Western Pacific. δ¹³C values of Alviniconcha sp. (foot), I. nautilei (foot and chitin) and E. o. manusensis (soft tissue) are similar, from -28 to -33‰ (V-PDB). The δ¹⁵N values of Alviniconcha sp. (foot and chitin), I. nautilei (foot and chitin) and E. o. manusensis (soft tissue) range from 8.4 to 10.6‰. The δ³⁴S values of Alviniconcha sp. (foot and chitin), I. nautilei (foot) and E. o. manusensis (soft tissue) range from 5.9 to 11.1‰. Using stable isotopes, for the first time, we inferred a Calvin-Benson (RuBisCo) metabolic pathway for Alviniconcha sp. along with the presence of γ-Proteobacteria symbionts for the Vienna Woods communities. For I. nautilei, a feeding pattern is proposed with γ-Proteobacteria symbiosis and a Calvin-Benson-Bassham diet with mixotrophic feeding. E. ohtai manusensis is filtering bacteria with a CBB feeding strategy, with δ¹⁵N values indicating possible higher position in the trophic chain. Arsenic concentrations in the dry tissue of Alviniconcha (foot), I. nautilei (foot) and E. o. manusensis (soft tissue) are high, from 4134 to 8478 μg/g, with inorganic As concentrations of 607, 492 and 104 μg/g, respectively and dimethyl arsenic (DMA) concentrations of 11.12, 0.25 and 11.2 μg/g, respectively. Snails occurring in a vent proximal position have higher As concentration than barnacles, a pattern not observed for S concentrations. Arsenosugars were not put in evidence indicating that the available organic material for the vent organisms are not surface derived.