Deep-Sea Misconceptions Cause Underestimation of Seabed-Mining Impacts
Authors: Craig R. Smith, Verena Tunnicliffe, Ana Colaço, Jeffrey C. Drazen, Sabine Gollner, Lisa A. Levin, Nelia C. Mestre, Anna Metaxas, Tina N. Molodtsova, Telmo Morato, Andrew K. Sweetman, Travis Washburn, Diva J. Amon
Journal: Trends in Ecology & Evolution (2020)

Scientific misconceptions are likely leading to miscalculations of the environmental impacts of deep-seabed mining. These result from underestimating mining footprints relative to habitats targeted and poor understanding of the sensitivity, biodiversity, and dynamics of deep-sea ecosystems. Addressing these misconceptions and knowledge gaps is needed for effective management of deep-seabed mining. Scientific misconceptions are likely leading to miscalculations of the environmental impacts of deep-seabed mining. These result from underestimating mining footprints relative to habitats targeted and poor understanding of the sensitivity, biodiversity, and dynamics of deep-sea ecosystems. Addressing these misconceptions and knowledge gaps is needed for effective management of deep-seabed mining. The deep sea, that is, ocean depths below 200 m, constitutes more than 90% of the biosphere, harbors the most remote and extreme ecosystems on the planet, and supports biodiversity and ecosystem services of global importance. Deep-sea minerals of commercial interest include: (i) potato-sized polymetallic nodules that precipitate on sharks teeth and other hard particles on some abyssal plains; (ii) polymetallic (massive) sulfides deposited at hydrothermal vents along seafloor spreading centers; and (iii) cobalt-rich (ferromanganese) crusts precipitating on rock surfaces on some seamounts and ridges [1.Hein J.R. et al.Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: comparison with land-based resources.Ore Geol. Rev. 2013; 51: 1-14Crossref Scopus (538) Google Scholar]. The International Seabed Authority (ISA) regulates seabed mining in areas beyond national jurisdiction, with a responsibility to protect the marine environment from serious harm (https://www.isa.org.jm/). The ISA has issued 30 contracts covering ~1.5 million km2 for lower-impact mining exploration, which includes: resource assessment, environmental baseline studies, and test mining. The ISA is currently drafting exploitation regulations for potentially high-impact, full-scale mining, with the regulations to include environmental impact assessment, monitoring, and habitat protection. The ISA's mandate pertains to international waters; however, its exploitation regulations will also be relevant within 'exclusive economic zones.' The United Nations Convention on the Law of the Sea (Part XII, Article 208), specifies that environmental protections for seabed mining within national jurisdictions should be 'no less effective' than those developed by the ISA. Polymetallic nodules, massive sulfides, and cobalt-rich crusts all provide critical habitat for deep-sea biota. Polymetallic nodules in the Clarion Clipperton Zone (CCZ), an area in the equatorial Pacific Ocean with the richest nodule resources, harbor diverse megafauna (e.g., ~100 species within a 30 × 30 km area) [2.Amon D.J. et al.First insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone.Sci. Rep. 2016; 6: 30492Crossref PubMed Scopus (132) Google Scholar] and microbes not found in surrounding waters or sediments [3.Shulse C.N. et al.Polymetallic nodules, sediments, and deep waters in the equatorial North Pacific exhibit highly diverse and distinct bacterial, archaeal, and microeukaryotic communities.MicrobiologyOpen. 2017; 6e00428Crossref Scopus (51) Google Scholar]. The biotic communities of nodules and sediments vary with nodule abundance [2.Amon D.J. et al.First insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone.Sci. Rep. 2016; 6: 30492Crossref PubMed Scopus (132) Google Scholar] as well as along and across the CCZ [4.Wilson G.D.F. Macrofauna abundance, species diversity and turnover at three sites in the Clipperton-Clarion Fracture Zone.Mar. Biodivers. 2017; 47: 323-347Crossref Scopus (40) Google Scholar]. Polymetallic sulfides at active hydrothermal vents provide habitat for novel faunal assemblages that have altered our views of the primary energy sources and origins of life, and exhibit substantial local and regional variation in structure and connectivity [5.Van Dover C.L. et al.Scientific rationale and international obligations for protection of active hydrothermal vent ecosystems from deep-sea mining.Mar. Policy. 2018; 90: 20-28Crossref Scopus (99) Google Scholar]. Polymetallic sulfide mining is expected to target 'extinct' vents due to the extremely corrosive nature of hot venting fluids, but active vents are not yet protected and extinct vents also have characteristic, albeit poorly studied, biotas [6.Van Dover C.L. Inactive sulfide ecosystems in the deep sea: a review.Front. Mar. Sci. 2019; 6: 461Crossref Scopus (36) Google Scholar]. Ferromanganese-encrusted seamounts support productive hotspots of biodiversity that vary within and among seamount chains [7.Rogers A.D. The biology of seamounts: 25 years on.Adv. Mar. Biol. 2018; 79: 137-224Crossref PubMed Scopus (73) Google Scholar]. Where mining removes or buries any of these three mineral habitats, the associated fauna will be damaged or destroyed. To manage deep-seabed mining effectively, regulators, such as the ISA (with 167 member states and the EU) and additional stakeholders (e.g., civil society, industry, scientists, and other concerned parties), should utilize the best scientific predictions of mining impacts. Here, we address several misconceptions in the recent peer-reviewed literature concerning deep-sea ecosystems and the potential impacts of seabed mining. We also highlight knowledge gaps and uncertainties in predicting the spatiotemporal scales of mining disturbance and recovery, underscoring the importance of a precautionary approach, for example, limiting full-scale mining operations until impacts are well characterized. (i)The area disturbed by mining will be very small compared with the scales of deep-sea habitats (e.g., [8.Sharma R. Assessment of distribution characteristics of polymetallic nodules and their implications on deep-sea mining.in: Sharma R. Deep-Sea Mining. Springer, 2017: 229-256Crossref Scopus (5) Google Scholar,9.Koschinsky A. et al.Deep-sea mining: interdisciplinary research on potential environmental, legal, economic, and societal implications.Integr. Environ. Assess. Manag. 2018; 14: 672-691Crossref PubMed Scopus (46) Google Scholar]). Thus, we can afford to lose the 'miniscule proportion' [8.Sharma R. Assessment of distribution characteristics of polymetallic nodules and their implications on deep-sea mining.in: Sharma R. Deep-Sea Mining. Springer, 2017: 229-256Crossref Scopus (5) Google Scholar] of the vast seabed that will be affected by mining. Seafloor mining targets specific deep-sea habitats with characteristic biotas that vary on scales of tens of meters and greater. As a consequence, the scales of impact may not be small when considering the distribution of the targeted habitats. For example, for environmental management purposes, the CCZ has been divided into nine ecological subregions expected to have different seafloor communities [10.Lodge M.W. Verlaan P.A. Deep-sea mining: international regulatory challenges and responses.Elements. 2018; 14: 331-336Crossref Scopus (27) Google Scholar,11.Wedding L.M. et al.From principles to practice: a spatial approach to systematic conservation planning in the deep sea.Proc. Roy. Soc. B. 2013; 280: 20131684Crossref PubMed Scopus (145) Google Scholar] (Figure 1A ), with substantial proportions of three of these subregions targeted for mining because they contain high nodule abundance (Figure 1A). Mining will permanently remove the habitat for the nodule-dependent fauna in these subregions because nodules require 105 –106 years to form [1.Hein J.R. et al.Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: comparison with land-based resources.Ore Geol. Rev. 2013; 51: 1-14Crossref Scopus (538) Google Scholar,10.Lodge M.W. Verlaan P.A. Deep-sea mining: international regulatory challenges and responses.Elements. 2018; 14: 331-336Crossref Scopus (27) Google Scholar]. This lack of recovery, combined with destruction of a high percentage of the nodule habitat within these ecological subregions and the entire CCZ (Box 1), could create real extinction risks for nodule-obligate biota.Box 1Potential Scales of Mining Impacts on Nodule-Rich Habitats in the CCZ.Nodule-rich areas cover ~10–30% of the three ecological subregions with the highest nodule abundances in the central CCZ (Figure 1), yielding ~100 000 to 300 000 km2 of nodule-rich habitat within each of these subregions [11.Wedding L.M. et al.From principles to practice: a spatial approach to systematic conservation planning in the deep sea.Proc. Roy. Soc. B. 2013; 280: 20131684Crossref PubMed Scopus (145) Google Scholar]. For economic viability, a contractor is expected to mine nodule-rich beds at ~400 km2 year-1 [8.Sharma R. Assessment of distribution characteristics of polymetallic nodules and their implications on deep-sea mining.in: Sharma R. Deep-Sea Mining. Springer, 2017: 229-256Crossref Scopus (5) Google Scholar], removing nodules and directly disturbing sediments over ~8000 km2 during a 20-year mining period. Nodule-rich beds typically occur in bands a few kilometers wide separated by intervening nodule-poor (i.e., not mineable) bands 2–10 km wide (Figure I, Figure S1 in the supplemental information online) [2.Amon D.J. et al.First insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone.Sci. Rep. 2016; 6: 30492Crossref PubMed Scopus (132) Google Scholar,13.Thiel H. et al.Polymetallic nodule mining, waste disposal, and species extinction at the abyssal seafloor.Mar. Georesour. Geotechnol. 2005; 23: 209-220Crossref Scopus (12) Google Scholar]. Modeling of sediment plumes predicts sedimentation rates and suspended-particle concentrations 3–4 orders of magnitude above baseline levels at least 10 km from direct mining (e.g., [16.Aleynik D. et al.Impact of remotely generated eddies on plume dispersion at abyssal mining sites in the Pacific.Sci. Rep. 2017; 7: 16959Crossref PubMed Scopus (63) Google Scholar]), with the consequence that surrounding, unmined nodule-poor bands are also expected to be heavily impacted by burial and turbidity. Thus, the disturbance from a single mining operation could easily be 2–4-fold larger than its direct mining footprint (see the supplemental information online), affecting up to ~32 000 km2 over 20 years. Since several subregions contain four to eight exploration contracts (Figure 1A), mining in the 16 contract areas could remove/bury/smother a substantial proportion of the nodule habitat within subregions and across the entire CCZ (>500 000 km2).Figure ISize and Position of Potential Nodule Mining Blocks (Grey Mottling) in a Part of the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER) Exploration Contract Area in the Clarion Clipperton Zone (CCZ).Show full captionApproximately 25% of the total area is considered viable to mine for polymetallic nodules. Data from Thiel et al. [13.Thiel H. et al.Polymetallic nodule mining, waste disposal, and species extinction at the abyssal seafloor.Mar. Georesour. Geotechnol. 2005; 23: 209-220Crossref Scopus (12) Google Scholar].View Large Image Figure ViewerDownload Hi-res image Download (PPT) Nodule-rich areas cover ~10–30% of the three ecological subregions with the highest nodule abundances in the central CCZ (Figure 1), yielding ~100 000 to 300 000 km2 of nodule-rich habitat within each of these subregions [11.Wedding L.M. et al.From principles to practice: a spatial approach to systematic conservation planning in the deep sea.Proc. Roy. Soc. B. 2013; 280: 20131684Crossref PubMed Scopus (145) Google Scholar]. For economic viability, a contractor is expected to mine nodule-rich beds at ~400 km2 year-1 [8.Sharma R. Assessment of distribution characteristics of polymetallic nodules and their implications on deep-sea mining.in: Sharma R. Deep-Sea Mining. Springer, 2017: 229-256Crossref Scopus (5) Google Scholar], removing nodules and directly disturbing sediments over ~8000 km2 during a 20-year mining period. Nodule-rich beds typically occur in bands a few kilometers wide separated by intervening nodule-poor (i.e., not mineable) bands 2–10 km wide (Figure I, Figure S1 in the supplemental information online) [2.Amon D.J. et al.First insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone.Sci. Rep. 2016; 6: 30492Crossref PubMed Scopus (132) Google Scholar,13.Thiel H. et al.Polymetallic nodule mining, waste disposal, and species extinction at the abyssal seafloor.Mar. Georesour. Geotechnol. 2005; 23: 209-220Crossref Scopus (12) Google Scholar]. Modeling of sediment plumes predicts sedimentation rates and suspended-particle concentrations 3–4 orders of magnitude above baseline levels at least 10 km from direct mining (e.g., [16.Aleynik D. et al.Impact of remotely generated eddies on plume dispersion at abyssal mining sites in the Pacific.Sci. Rep. 2017; 7: 16959Crossref PubMed Scopus (63) Google Scholar]), with the consequence that surrounding, unmined nodule-poor bands are also expected to be heavily impacted by burial and turbidity. Thus, the disturbance from a single mining operation could easily be 2–4-fold larger than its direct mining footprint (see the supplemental information online), affecting up to ~32 000 km2 over 20 years. Since several subregions contain four to eight exploration contracts (Figure 1A), mining in the 16 contract areas could remove/bury/smother a substantial proportion of the nodule habitat within subregions and across the entire CCZ (>500 000 km2). By contrast, areas targeted for cobalt-rich crust mining are relatively small (~10–100 km2 [1.Hein J.R. et al.Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: comparison with land-based resources.Ore Geol. Rev. 2013; 51: 1-14Crossref Scopus (538) Google Scholar]), especially compared with nodule-mining footprints; but these crusts occur on seamounts, which often support assemblages of long-lived corals and sponges that create habitat for many other species [7.Rogers A.D. The biology of seamounts: 25 years on.Adv. Mar. Biol. 2018; 79: 137-224Crossref PubMed Scopus (73) Google Scholar]. Seamounts are globally abundant, yet their ecological significance, heterogeneity, the fragility of their fauna, and poor knowledge of their connectivity and biodiversity has resulted in the Food and Agriculture Organization (FAO) considering seamounts to be examples of vulnerable marine ecosystems (VMEs) subject to special protection from fishing activities (e.g., [7.Rogers A.D. The biology of seamounts: 25 years on.Adv. Mar. Biol. 2018; 79: 137-224Crossref PubMed Scopus (73) Google Scholar]). Open-cut mines for polymetallic sulfides would likely have the smallest direct footprint (<10 km2 per mine), although plume and associated ecotoxicological impacts could spread substantially further, for example, 10–100 km in pelagic ecosystems. These deposits form at seafloor hot springs known for specially adapted organisms that rely on inorganic chemicals, rather than sunlight, for their energy. The estimated global area of active hydrothermal vents is <50 km2, making them an extremely rare habitat [5.Van Dover C.L. et al.Scientific rationale and international obligations for protection of active hydrothermal vent ecosystems from deep-sea mining.Mar. Policy. 2018; 90: 20-28Crossref Scopus (99) Google Scholar]. The small scales and remarkable biodiversity of hydrothermal-vent communities has led to their classification as VMEs by the FAO, and several vent fields are classified as ecologically or biologically significant areas (EBSAs) through the Convention on Biological Diversity [5.Van Dover C.L. et al.Scientific rationale and international obligations for protection of active hydrothermal vent ecosystems from deep-sea mining.Mar. Policy. 2018; 90: 20-28Crossref Scopus (99) Google Scholar]. Extinct sulfide deposits are also small in area, and so little is known about their biota [6.Van Dover C.L. Inactive sulfide ecosystems in the deep sea: a review.Front. Mar. Sci. 2019; 6: 461Crossref Scopus (36) Google Scholar] that it is premature to conclude that the loss of habitat and biodiversity from mining extinct deposits would be 'miniscule'.(ii)Polymetallic sulfide communities will recover rapidly from mining (e.g., [9.Koschinsky A. et al.Deep-sea mining: interdisciplinary research on potential environmental, legal, economic, and societal implications.Integr. Environ. Assess. Manag. 2018; 14: 672-691Crossref PubMed Scopus (46) Google Scholar]). Some active-vent communities on the East Pacific Rise, and on the Juan de Fuca Ridge (in the northeast Pacific), recover rapidly from frequent volcanic eruptions. However, vent-community recovery may be much slower where volcanic eruptions occur less frequently. In fact, vent communities on active sulfides in the South Pacific exhibit remarkable stability over a decadal timescale [12.Du Preez C. Fisher C.R. Long-term stability of back-arc basin hydrothermal vents.Front. Mar. Sci. 2018; 5: 54Crossref Scopus (23) Google Scholar], suggesting that recovery from mining disturbance in more stable vent ecosystems could be slower. The massive sulfides of mining interest were formed over thousands of years, so their ecosystem dynamics may be attuned to similarly lengthy timescales. However, the biodiversity and dynamics of entire massive sulfide ecosystems are so poorly understood [6.Van Dover C.L. Inactive sulfide ecosystems in the deep sea: a review.Front. Mar. Sci. 2019; 6: 461Crossref Scopus (36) Google Scholar] that recovery times cannot be reliably estimated.(iii)The deep sea is not a pristine wilderness (e.g., [10.Lodge M.W. Verlaan P.A. Deep-sea mining: international regulatory challenges and responses.Elements. 2018; 14: 331-336Crossref Scopus (27) Google Scholar,13.Thiel H. et al.Polymetallic nodule mining, waste disposal, and species extinction at the abyssal seafloor.Mar. Georesour. Geotechnol. 2005; 23: 209-220Crossref Scopus (12) Google Scholar]). This assertion implies that conservation of deep-sea ecosystems is not warranted since they are already damaged. It is true that human activities influence the entire planet, with fishing, climate change, and pollution penetrating to the deep sea. However, most hydrothermal vents and abyssal areas almost certainly remain among the most intact ecosystems on the planet, largely buffered from anthropogenic damage by their enormous separation from the focus of human activities in the coastal, upper ocean. The development of environmental regulations for seabed mining is hampered by profound gaps in basic knowledge about deep-sea ecosystems and in our ability to predict responses to stressors, although resilience to mining disturbance is generally expected to be low [14.Gollner S. et al.Resilience of benthic deep-sea fauna to mining activities.Mar. Environ. Res. 2017; 129: 76-101Crossref PubMed Scopus (172) Google Scholar]. We do know that some deep-sea animals (e.g., corals on seamounts) can live for centuries but for most we lack basic biological data. Growth rates, life histories, and tolerance to stressors (both acute and chronic) for targeted fauna are needed to fully define the spatial and temporal scales of impacts and potentials for recovery from mining. We have very limited knowledge of the larval connectivity required to maintain communities under both natural and mining-stressed conditions. Furthermore, the combined potential impacts from mining (e.g., habitat removal/burial, sediment plumes) and climate change inflate uncertainties and may exacerbate disturbance from mining. Despite significant funding by governments and industry for deep-sea research, basic documentation of biodiversity and natural variability in areas targeted for deep-seabed mining is incomplete. Recent discoveries underscore the remarkable, unknown species richness and complexity of these communities. While many terrestrial environmental impact assessments work with extensive faunal lists and well-characterized ecosystem functions and services, deep-sea biologists are very early in the process of documenting species occurrences, community structure, biogeography, and ecosystem functions in all the targeted habitats. For example, communities of inactive massive sulfides are mostly undescribed [6.Van Dover C.L. Inactive sulfide ecosystems in the deep sea: a review.Front. Mar. Sci. 2019; 6: 461Crossref Scopus (36) Google Scholar]; the vast majority of seamounts in the ocean have never been sampled [7.Rogers A.D. The biology of seamounts: 25 years on.Adv. Mar. Biol. 2018; 79: 137-224Crossref PubMed Scopus (73) Google Scholar]; the macrofauna and meiofauna of cobalt-rich crust deposits are practically unknown; and most of the >2000 faunal species recently collected in the eastern CCZ are new to science (e.g., [2.Amon D.J. et al.First insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone.Sci. Rep. 2016; 6: 30492Crossref PubMed Scopus (132) Google Scholar]). The behavior of sediment plumes that will be generated directly from seabed mining and from reinjection of mining wastes into the deep sea from surface vessels is also poorly understood. Particle plumes and dissolved chemicals will impact areas larger than the mine site – but how much larger? In the CCZ, with the clearest bottom waters and among the lowest sedimentation rates in the ocean [15.Gardner W. et al.Global comparison of benthic nepheloid layers based on 52 years of nephelometer and transmissometer measurements.Prog. Oceanogr. 2018; 168: 100-111Crossref Scopus (29) Google Scholar], sensitivities to enhanced turbidity and sedimentation are expected to be high, especially when exposure times may last for months to years. Sensitivity thresholds to guide monitoring efforts are very poorly delimited since available data come from shallow-water ecosystems where background levels of sedimentation and turbidity are orders of magnitude higher. Furthermore, we remain unable to predict effects on pelagic ecosystems in response to plumes, noise, and spills because mining technologies are still in development, and the deep pelagic ecosystems are extremely poorly studied. The ISA plans to complete exploitation regulations to enable active seabed mining by 2021. A major obstacle is the uncertainty around the impacts of deep-seabed mining on biodiversity and ecosystem services. Furthermore, seabed-mining impacts are unlikely to be fully understood until full-scale mining has been monitored for years. Thus, the precautionary approach will be a key management tool, for example, allowing only one mining operation to proceed until the environmental impacts of mining this seabed mineral are well documented. Given the unlikelihood of filling all knowledge gaps within the next few years, an important step for deep-sea scientists and regulators is identifying the information most useful to management decisions. Large scientific uncertainties can lead to disagreements about potential impacts, but this should promote healthy debate and focus research and monitoring priorities. The deep sea contains many of the most pristine, poorly studied, and evolutionarily remarkable ecosystems on our planet – in situ scientific knowledge addressing the full scales and intensities of seabed mining should be obtained and properly applied to sustain biodiversity and ecosystem functions in the deep sea if mining is to proceed. All authors contributed to the content and writing. C.R.S., J.C.D., and A.S. were supported by grant number 5596 from the Gordon and Betty Moore Foundation. V.T. was funded by the Canada Research Chairs Foundation. D.A. received funding from the EU's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement number 747946. N.M. was supported by Fundação para a Ciência e Tecnologia, I.P. Portugal (FCT) and Direção-Geral de Política do Mar (DGPM) through the project Mining2/2017/001–MiningImpact 2 (JPI Oceans), and FCT further funded the grants CEECIND005262017 and UID/MAR/00350/2013. T.N.M. was supported by RF State Assignment (0149-2019-0009). T.M. was supported by the FCT (IF/01194/2013) and the H2020 ATLAS projects (678760). A.C. was supported by Program Investigador (IF/00029/2014/CP1230/CT0002) and Mining2/0005/2017 from FCT. L.A.L. was supported by the J.M. Kaplan Fund and the US National Science Foundation (OCE 1634172). S.G. was supported through the JPI Oceans project MiningImpact – 'Environmental Impacts and Risks of Deep-Sea Mining' August 2018 to February 2022 (NWO-ALW grant 856.18.001). The open access fee was paid by the Deep Ocean Stewardship Initiative. Download .docx (.04 MB) Help with docx files Supplementary material