Deep-sea mining as an emerging threat to deep sea ecosystems

The deep sea is the biggest ecosystem on Earth, representing around 90% of the marine environment. Despite its remoteness and inaccessibility, the deep sea is under constant threat from anthropogenic activities. Among them is deep-sea mining, that is quickly rising as an appealing alternative to land-based mining. Deep-sea mining refers to the extraction of mineral resources from the seabed, an activity that can potentially, among other consequences, release large plumes of sediments and ore across the water column affecting vast areas of the ocean. The present work aimed at assessing the effects of suspended sediments and ore on several benthic species (Mytilus galloprovincialis, Spisula solida and Adreus fascicularis) under hyperbaric conditions through the assessment of functional, biochemical and molecular endpoints to improve our understanding of how these stressors impact exposed organisms and the marine environment. Sediments and ore were used in different size ranges and concentrations to better represent a realistic scenario of resuspension as a byproduct of mining activities. Experiments lasted for 96h at different pressures (up to 50 Bar) in a hyperbaric chamber. After each exposure experiment, several endpoints were evaluated for each species (i.e. respiratory and filtration rates, oxidative stress biomarkers such as catalase, lipid peroxidation and glutathione s-transferase and transcriptomic profiles). Overall, suspended sediments and ore caused significant harmful effects in all three species, ranging from filtration/respiratory ability decrease to alterations in oxidative stress response and gene expression profiles. These findings highlight the need to establish guidelines and regulatory frameworks before deep-sea mining starts at the commercial level to mitigate potential negative effects, especially for benthic communities in the deep sea.Acknowledgments: This work was developed under the project DEEPRISK [reference PTDC/CTA-AMB/7948/2020].