Ecotoxicology of deep-sea environments: Functional and biochemical effects of suspended sediments in the model species Mytilus galloprovincialis under hyperbaric conditions.

The deep-sea is the biggest ecosystem in the world and is characterized by extreme conditions such as high pressure, low temperatures and absence or limited light. Despite the scarce studies due to inaccessibility, these ecosystems are considered highly biodiverse. The deep-sea is subjected to anthropogenic stressors with deep-sea mining being a likely new form of disruption. Understanding how it affects the surrounding environments is paramount to develop guidelines to protect sensitive habitats and allow for responsible exploitation of resources. One of the potential stressors associated with deep-sea mining are the sediment laden plumes that can be generated during the mining process. The present study examined, for the first time, the effects of suspended sediments (0, 1, 2 and 4 g/L) in the model mussel species, Mytilus galloprovincialis, under hyperbaric conditions (1, 4 and 50 Bar). Functional endpoints, i.e. feeding assays, together with biochemical biomarkers of oxidative stress [catalase (CAT), lipid peroxidation (LPO), glutathione-s-transferase (GST) and superoxide dismutase (SOD)] were studied in juvenile mussels. The filtration rate (FR) of M. galloprovincialis decreased with the increment in the sediment concentrations, for all tested pressure conditions (1, 4 and 50 Bar). Significant alterations were also observed for all tested biomarkers, being sediment and pressure-dependent. Interestingly, pressure had an effect in GST activity, that increased in the 4 and 50 Bar experiments in comparison with the results at 1 Bar. Remarkably, filtration rates were significantly affected by pressure. These findings will support the filling of the knowledge gaps related with the hazard assessment of deep-sea mining associated stressors.