Deep-sea mining of earth minerals is an emerging activity, as the global demand for metals is growing and the technical limitations of operating in the deep ocean are being resolved. Mining interest exists in both nationally controlled jurisdictions and international waters, where some 31 exploration contract areas have been granted by the International Seabed Authority (ISA). Most of these activities aim to extract mineral deposits (e.g. cobalt, nickel) from three deep-sea habitats: i) polymetallic or manganese nodules on abyssal plains, ii) cobalt-rich ferromanganese crusts on seamounts, and iii) massive sulfide deposits at hydrothermal vents. Deep-sea mining may pose environmental risks to benthic life that would otherwise be virtually undisturbed by human activities. The operation of heavy machinery on the seafloor may lead to sediment disturbance and release toxic concentrations of metals to susceptible benthic communities.
Among deep-sea benthic communities, microorganisms perform numerous ecosystem functions and services to humanity, such as genetic diversity, primary production, nutrient cycling, greenhouse gas removal, among others. The nitrogen cycle in the deep-sea, mediated by microorganisms, accounts for several redox reactions that regulate chemotrophic production, heterotrophic anoxic respiration, dissolved and particulate organic matter conversion, as well as production and reduction of nitrous oxide (N2O), a powerful greenhouse gas. Many of these critical processes are still poorly understood in the deep ocean, especially their resistance to disturbance. Studies in diverse environments have shown that elevated metal concentrations can alter microbial growth, nitrogen cycling activity, and diversity. The specific environmental conditions of the deep-sea, such as low temperatures, high hydrostatic pressure, or low organic matter/inorganic nitrogen ratios, may affect susceptibility to metal exposure. Despite the potential risk for increased mobilization of metals from deep-sea mining activities, the impacts of metals on deep-sea microbial life are currently unknown.
The current knowledge gaps regarding baseline information and thresholds of impact to deep-sea life should be fulfilled soon, before exploitation activities are considered by national and international governing authorities. In this project, an interdisciplinary and international research team will address these knowledge gaps with the overarching goal of evaluating the impacts of metal exposure on deep-sea microbial diversity and nitrogen cycling, key components of ecosystem functioning. A comprehensive methodological approach will be applied, combining a global survey of public metagenomic data with field sampling and controlled experimentation at two different levels of biological organization (complex communities and pure cultures).
This research will contribute to improve our understanding about the multiple roles that deep-sea microbial diversity plays in the ocean, as well as to investigate potential impacts of mining, thus contributing to better inform future decisions regarding deep seabed management. In addition to its global importance, this research may be especially relevant to countries like Portugal, with an extensive deep-sea territory.