Hydrogen sulfide, hypoxia, and low salinity tolerance of deep-sea amphipods (Pseudorchomene sp.) collected from the sea floor off Joetsu, Sea of Japan.

Experimental data contributing to the assessment of the environmental impact of deep-sea resource development is very scarce due to limited research opportunities and the difficulty of biological sampling. Experiments using deep-sea organisms are difficult to conduct in deep-sea in situ environments and are more realistically conducted in land-based research facilities. In this study, the environmental tolerance experiments, including hydrogen sulfide (HS), low salinity, and hypoxia, were conducted on a deep-sea amphipod (Pseudorchomene sp.) collected from the seafloor with water temperature <1 °C in a methane hydrate-bearing region off Joetsu, Japan. The 96-h half-lethal concentrations of HS dissolved oxygen saturation and low salinity were 0.58 mg L, 5.9 %, and 19.2 PSU as mean values, respectively. The results of this study suggest that sampling or rearing has no debilitating effects, as Pseudorchomene sp. survived and molted repeatedly for more than one year in rearing experiments conducted in parallel with this study. The methane hydrate-bearing area contains high concentrations of HS and is hypoxic. Therefore, disturbance of the seafloor caused by methane hydrate development has the potential to expose inhabiting organisms to high levels of HS and hypoxia. Generational turnover time of deep-sea organisms is expected to be long; therefore, mitigating lethal effects should be desirable in developing deep-sea resources. This study provides valuable insights for mitigating the lethal impacts associated with deep-sea resource development.