“But there’s strong scientific evidence that the seabed targeted for mining is in fact one of the most biodiverse places on the planet”

Todd Woody, Bloomberg

Environmental groups have focused the public’s attention on the exceptionally high levels of biodiversity on the Pacific Ocean’s abyssal plains as a key reason to resist nodule harvesting.  Yet, this isn’t an honest characterization based on scientific research.  Rather, it is a sensationalistic soundbite employed to elicit an emotional response.  The abyssal plains host modest levels of biodiversity relative to many other ecosystems, based on data and analysis from sampling, and the claim is without merit.  Regardless, biodiversity is an area that deserves serious consideration. 

The stance taken by some environmental NGOs is likely borne out of reaction to the widely held perception that there isn’t anything alive in the extreme conditions present on the abyssal plains (zero light, intensely high pressures, very cold temperatures, few sources of food).  The perception may date back to the early days of marine science.  Edward Forbes, who led ocean expeditions in the mid-1800s, observed that the number of species present declined at increasing depths.  Out of this observation came the Forbes Azoic Hypothesis that theorized life was likely to be impossible below 550 meters depth.  (Paulus, 2021)

While his hypothesis was off-the-mark, Forbes’ ideas weren’t wrong directionally.  For instance, scientists believe that approximately one million species are found in shallow coral reef ecosystems, while the number of metazoan species estimated to inhabit the entire Clarion Clipperton Zone is approximately 8,000. (Rabone, 2023) (Hoegh, 2019) The CCZ is larger than the area occupied by coral reefs, so clearly the deeper waters of the abyssal plains host less biodiversity than shallow waters. (Smithsonian, 2022)

Addressing issues around threats to biodiversity from nodule harvesting requires the evaluation of two principal questions.  First, to what extent is the biodiversity present on the abyssal plains threatened by nodule harvesting activities, and how does that threat compare with threats from terrestrial mining alternatives?  Second, what are the levels of biodiversity on the abyssal plains, and how does that level compare with other environments, especially environments where we currently mine battery minerals? 

Levels of biodiversity may matter less than the proposed activity’s potential to harm the biodiversity that is resident in the ecosystem.  It could be acceptable to operate a project in a highly biodiverse ecosystem if the project imposed very little threat to biodiversity.  On the other hand, it would be difficult to argue in support of a project which had a high potential for harm to biodiversity regardless of where the project was located.   Of course, the idea of operating a project with high potential for harm in an area of exceptional biodiversity would represent the worst outcome possible for society.  So, if we are to properly benchmark nodule harvesting versus terrestrial mining in terms of threat to biodiversity, we need to compare the potential for harm from each of these activities and then assess that potential for harm against the level of biodiversity present in the ecosystem where each operates. 

Terrestrial mining poses great potential for biodiversity loss, both because of its direct and indirect impacts.  Strip mining on land requires the total removal of overburden which destroys or displaces all living species within the mining footprint both above and underground.  This is to say that approximately 100% of biomass and 100% of biodiversity is lost within a strip-mine footprint. 

But the indirect impacts of terrestrial mining may be even more important because they influence a much wider area.  A 2017 study noted that indirect deforestation impacts in tropical rainforests are 12 times larger than impacts within the mining leases alone. (Sonter, 2017)  Mining is said to contribute indirectly to 9% of deforestation of Brazilian rainforests. (Forest Declaration Platform, 2022)

Threats to biodiversity from terrestrial mining extend well beyond deforestation.  For instance, unearthed rock piles from overburden removal can create acid mine drainage when it rains, polluting large portions of an area’s watershed and poisoning people and animals in the process.  Mining contamination through river systems impacts 23 million people directly today, but this number does not account for indirect impacts from food grown on flood plains that is exported from these contaminated areas, nor does it speak to the impacts to biodiversity due to widespread contamination of fresh water sources. (Macklin, 2023)

Air pollution from construction activities and from smelting/processing can threaten all manner of biodiversity with death and disease near mining and processing operations (nodules can be processed in a hydromet workflow that avoids many of these dangers).  The construction of roads and rail lines and the addition of jobs associated with new terrestrial mining locations supports greater human population growth in pristine areas and begets even greater infrastructure and more threats to biodiversity from human encroachment. 

Due to terrestrial mining’s footprint in biological hotspots and its direct and indirect potential for harm, the United Nations’ Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services specifically calls out terrestrial mining for its “significant negative impacts on biodiversity, emissions, water quality, and human health.”  (ISPP, 2019)

Strip mining for battery minerals is the worst of all worlds – it has high potential to harm biodiversity, and it occurs in the most sensitive and biodiverse spots on the planet.

COMRC

By comparison, nodule harvesting requires no overburden removal, thus it does not pose a material threat to biodiversity in the pelagic layer of the ocean where the vast majority of sea life exists (this assumes no mid-water plume).  And because nodule harvesting extracts ore with a grade that is essentially 100% (vs 1-3% for terrestrial mines) it causes far less impact per unit of mineral produced when we begin to examine threats to biodiversity on the seabed. 

Nodule harvesting also imposes far fewer indirect impacts because it doesn’t require any permanent infrastructure to be built on the abyssal plains, nor does it encourage additional human encroachment on the abyssal plains.  The bottom water plumes from harvesting nodules extend the impact area slightly outside the harvesting footprint (possibly as far as 500-1,000 meters according to the most recent work from MIT), and may have a small impact on some species, but plumes from terrestrial mining travel greater distances and contain more toxins and pollutants and therefore represent a greater threat to biodiversity (and to humans). 

Like any extractive activity, nodule harvesting will have an impact on the ecosystem.  Nodule harvesting will mean the loss of animals on nodules that are harvested.  In addition, the loss of the substrate provided by nodules and the animals resident on harvested nodules may impact other animals that depend on each of these for their survival.  Yet, these animals are mobile and because a significant number of nodules will remain after harvesting, and because set-aside areas equaling approximately 30% of the harvested area will be saved, the impacts on mobile organisms will be somewhat mitigated.  Sessile (non-mobile) animals could be damaged or killed by direct contact with harvesters and by bottom water plumes if they are very close to or inside the harvesting track, as their respiratory functions could be compromised depending on the level of sediment accumulation.  This said, these organisms often have defenses that can help shed sediment accumulation and studies have demonstrated little to no impact from plume sedimentation outside the harvesting footprint (see below).

There is less need for speculation with respect to impacts from harvesting nodules than many environmental groups would have us believe.  Marine scientists have been studying the potential for biodiversity impacts from harvesting simulations for the last half century.  At least seven separate, large-scale, benthic impact experiments have been conducted since the 1970’s with a number of subsequent investigations at each of the sites to understand longer-term impacts. (Gausepohl, 2020)  These studies generally produced heavier impacts than seen in actual harvesting activities because the equipment didn’t use buoyancy controls and in many instances areas were subjected to repeat harvesting exposure.  In addition, the equipment often used “plough” like devices that dug deep into the sediment, which is a far more invasive technique than that used by many of the harvesters today. 

The DISCOL Project (DISturbance and reCOLonization experiment) was the most extensively sampled and monitored of these benthic impact programs.  DISCOL intended to mimic the impact of nodule harvesting in a 11km² area of abyssal plain off the coast of South America in the Peru Basin.  The initial experiment was carried out in 1989 and involved a tracked vehicle that repeatedly traversed the ocean floor over the area trailing a specially designed plough-harrow that simulated the impact of a harvesting vehicle. (Discol.de)

The area of interest in DISCOL has been studied at irregular intervals over the thirty-plus years since.  And while each of the studies has shown levels of general impact to biomass and biogeochemical activity as a result of the harvesting simulation, the impacts are relatively small as compared to terrestrial mining, and they have moderated in the 30 years since the first activity took place.  The studies have shown mixed results in terms of impacts on biodiversity. 

The most meaningful impacts were limited to areas that the vehicle tracks had compacted.  The DISCOL monitoring study from 2020 noted that microbial cell numbers were reduced by less than 30% in the 26 year-old tracks from the initial experiment. (Vonnhame, 2020) The damage from the plough-harrow itself was more limited.  “Less similarities to the subsurface communities were found in ridges, while communities in the furrows and the samples outside the track were even more dissimilar to the subsurface and indistinguishable from the reference communities”.(Vonnhame, 2020)   In addition, the microbial biodiversity had not shown significant negative impacts from the experiment: “No significant differences between the diversity indices inverse Simpson, Shannon Wiener, number of operational taxonomic units (OTUs), or Chao1 have been found between the microhabitats or sampling sites”. (Vonnhame, 2020)  Other studies have shown negative impacts to biodiversity soon after the simulated harvesting, as well as potential positive impacts to biodiversity after 25 years of recovery. (Jones, 2017)

More recently, scientists have studied the impact of harvesting nodules in actual nodule harvesting operations using modern equipment undertaken in the CCZ during 2022.  A study by Bryan O’Malley and his team of researchers has noted that biodiversity of foraminifera within the collector tracks decreased by only 20% immediately following harvesting and that biodiversity was not impacted at all in the plume zone.  (O’Malley, 2023) Biomass of foraminifera was reduced by 50% in the tracks and was not impacted at all in the plume zone.  Foraminifera are small, single-celled creatures that are abundant, diverse, mainly sessile, and highly sensitive, so they are seen as excellent bioindicators for ecosystem stressors.

When comparing impacts from nodule harvesting against those from terrestrial mining, a high-level view is instructive.  With respect to nodule harvesting, we examine impacts down to the level of the microbe.  We study soil compaction and perturbance and plume resettle rates for associated impacts.  These same concerns apply to terrestrial mining, but because the other impacts from terrestrial mining are so overwhelming, these smaller impacts are almost always ignored.    

When a Chinese-run nickel mine destroys a tropical rainforest and poisons the surrounding land with acid mine runoff, we don’t study the impact from ground compaction on microbial fauna at the site because the other impacts tower over these concerns.  Few people even pay attention to the plume created from the terrestrial mine and the impact that plume has on the health of workers, nearby residents, or locally grown food.  We cannot study longer term impacts on small animals and microbes that had inhabited that rainforest because the rainforest no longer exists.  Terrestrial strip mining destroys the habitat in the mine’s footprint to the point where we cannot make the same measurements we make to study the impacts of nodule harvesting operations.  Terrestrial strip mining wipes out the rainforest habitat, nodule harvesting disturbs the abyssal plains habitat.    

Terrestrial strip mining destroys the habitat in the mine’s footprint to the point where we cannot make the same measurements we make to study the impacts of nodule harvesting operations.  Terrestrial strip mining wipes out the rainforest habitat, nodule harvesting disturbs the abyssal plains habitat.   

While the activity of nodule harvesting appears to be significantly less threatening to biodiversity and biomass than does terrestrial mining, it is important to contextualize the relative scale of the activity and how that scale translates to a threat.  An activity with significant impact on a small area, as compared to the habitat of the species impacted by the activity, might be seen as acceptable.  A lower impact activity executed at a scale that could overwhelm the species in the area might not be acceptable. 

Unfortunately, we don’t have a lot of information about the ranges of all the species in either tropical rainforests or in abyssal plains to understand at a micro level how terrestrial mining and nodule harvesting might have particularly high impacts on given species.  We know, however, that both environments contain highly specialized animals that may have limited ranges.  As an article on rainforests notes, “Rainforests are diverse, in terms of numbers of species, but any one given species is not necessarily plentiful.  Some rainforest species have populations that number in the millions, whereas others may consist of a handful of individuals. The biology of tropical rainforests is a biology of rare species. The reason for this occurrence is that the majority of rainforest species are scarce over the range of the forest and may be common in only a few small areas where they are particularly well adapted.” (Butler, 2019)

We will never possess complete information on range at a species level in either rainforests or the abyssal plains, as the job of collecting that information is far too large to undertake (especially in rainforests which are home to over 4 million species).  But we can still ascertain the threat to the ecosystems as a whole from the two activities and make threat observations based on that analysis.

The abyssal plains are massive, encompassing as much as half of the earth’s surface.  Nodule fields are expected to cover between 10% to 50%+ of the plains. (Smith, 2020) If we use a 25% figure, this implies nodule fields cover an area approximately 12.5% of the surface of the earth or 63.75 million km².  Tropical rainforests make up around 6% of the earth’s land surface which would mean that they comprise roughly 1.8% of the earth’s total surface or 9.18 million km².

Rainforests are highly threatened today.  Already more than two-thirds of rainforests have been destroyed or significantly degraded by human intervention. (Krogh, 2021) What remains of intact tropical rainforests is being deforested at an alarming rate.  Estimates of annual rainforest destruction range widely with low-end figures hovering around 43,000 km² and high-end estimates at around 300,000 km² .  (Butler, 2020) (Taylor, n.d.) Mining is a large part of the threat to rainforests.  A recent study estimates that around nine percent of tropical rainforest deforestation in the Amazon is due to mining.  (Sonter, 2017) Yet, that figure likely understates mining’s impacts. 

Mining in tropical rainforests is in the process of accelerating due to the increasing demand for battery minerals.  Studies indicate that the demand for many battery minerals could increase fivefold or more over the next twenty years, suggesting we could easily lose over half of our world’s rainforests over that period if we continue to deforest for non-mining purposes as well.  Indonesian nickel production is expected to replace palm-oil plantations as the primary cause of deforestation in that country. (The Economist, 2023) Since tropical rainforests are by far the most sensitive and biodiverse environments in the world, terrestrial mining and other tropical rainforest land use could result in the loss of millions of species and astounding quantities of biomass. 

If the ocean minerals industry were to harvest the entirety of the nodule fields on the abyssal plains, we might not lose a single species based on the data seen thus far.  Yet, we won’t come close to mining all the nodule fields on earth to fuel the energy transition.  If nodules supplied all of the NCM cathode minerals (nickel, cobalt, manganese) needed to electrify the world’s auto fleet, we would need approximately 120 harvesting vessels to meet annual mineral requirements for the next twenty years (assumes 1.567 ktons nickel, 257 ktons cobalt, and 246 ktons manganese annually per IEA estimates). (IEA, 2021)  The 120 vessels would harvest an area equivalent to approximately 319,000 km² over 20 years based on a contractor estimate of 2,660 km² for a single vessel for the period.  The 319,000 km² of disturbed abyssal plain over 20 years would impact only 0.5% of estimated worldwide nodule fields and 0.1% of the abyssal plains.

We note that the surface area impacted by nodule harvesting is larger than that which would be impacted by terrestrial mining because nodules are found on a two-dimensional plane as opposed to a terrestrial mine which digs into the earth (resulting in more harm and emissions).  But the larger size of the harvested ground is more than offset by the relative benefits of harvesting vs. mining. Not only do the indirect impacts from mining extend the area of harm by 10-12x, but the grade and constitution of the ore body extend it further. Mining ore at 2% grade vs. harvesting at 100% means that a mine must unearth ~50x the amount of ore that a harvester must recover to produce the same amount of pay minerals. And since harvesting yields seven or eight valuable minerals and most terrestrial mines produce only a couple, we would need approximately three terrestrial mining operations to produce the minerals we extract from a single harvesting operation. The footprint of a harvesting operation may or may not be as large as those associated with terrestrial mines for equivalent mineral production, but the damage done by harvesting operations to the environment and to humanity are undoubtedly much smaller.

It is clear that the potential to negatively impact biodiversity is far higher in terrestrial mining than in nodule harvesting, but we still need to understand the amount of biodiversity that is subject to that harm in the two very different extraction environments.  Before addressing the level of biodiversity present on the abyssal plains, however, we should note that we only have estimates for the number of species which exist anywhere in the world because indexing and taxonomy work are such time consuming and arduous processes.  In fact, scientists estimate that 86 percent of the world’s 8.7 million estimated species have yet to be identified with most of the undiscovered species said to be resident in rainforest environments.  Within marine environments, the number of undiscovered species is thought to be closer to 91 percent of the 2.2 million estimated marine species. (Mora, 2011)

In recent work on the subject of abyssal plains biodiversity, marine biologists estimated that the CCZ abyssal plains may hold as many as ~8,000 distinct metazoan species, noting that around 92 percent of species have yet to be identified in the region. (Rabone, 2023)  The cited study was specific to the CCZ and did not include abyssal plains outside that region, but it noted that 23% of macrofauna species had type localities outside the CCZ, meaning that they were first discovered elsewhere.   

The estimated levels of biodiversity in the massive area of the CCZ abyssal plains are quite small relative to other ecosystems.  Rainforests, for example, are said to hold approximately half of the world’s 8.7 million estimated species. (Pillay, 2021) (Mora, 2011) Wetlands may hold another quarter of the world’s species. (UNCC, 2018)  The oceans in aggregate are believed to hold approximately 2.2 million species meaning that outside the CCZ approximately 2.192 million species roam the seas and sediment. (Mora, 2011)  Coral reefs also teem with biodiversity with most estimates starting at around 1 million contained species. (US EPA, 2023)

Environmental groups suggest that we don’t know enough about the abyssal plains to harvest nodules.  To support the point, they note that scientists estimate that around 90% of the species on the abyssal plains have yet to be discovered. (Mora, 2011) Yet, the truth is that the 90% undiscovered figure holds for our knowledge of the ocean’s species as a whole.  (Watson, 2011)  All the same, we undertake far more invasive activities than nodule harvesting all over the oceans despite this lack of knowledge (trawling, dredging, construction, oil and gas extraction, waste dumping).  In fact, it is estimated that approximately 86% of the world’s species in total have yet to be identified, meaning that the abyssal plains are about as well characterized in terms of species knowledge as most of the world. (Watson, 2011)

Biology on the abyssal plains has been studied as far back as the mid-19^th century.  Over the last 100 years, scores of independent cruises have sought knowledge of these deep waters for the mineral wealth that they hold, and the cruises have gathered information on the biology as they carried out exploration and sampling activities.  The United Nations’ International Seabed Authority data base (DeepData) contains over 100,000 biological records alone, and there is additional biological sampling data from over 25 research cruises done in the Cook Islands over the years.  A Google Scholar search for studies having to do with the abyssal plains reveals over 50,000 documents. 

While much more data will be gathered during additional exploration and trial harvesting activities, we note two things relevant to our understanding of the abyssal plains ecosystem:  1) our knowledge of this ecosystem exists and grows thanks to the commercial prospectivity of the area, a moratorium on activities would slow or halt that progress; and 2) we understand far more about the biology of the abyssal plains than we did about tropical rainforests when we began industrial mining in those ecosystems in the 1800s. 

It is worth understanding the type of biodiversity exhibited on the abyssal plains.  First, the animals found on the plains are mainly infaunal – they live in the sediment (Sigwart, 2023).  Second, the organisms that are resident are mostly very small.  Over 70% of species believed to inhabit the area are either too small to see with the naked eye or are barely visible (Meiofauna, which are between 150 microns and 300 microns in size, represent 22% of species. (Rabone, 2023) Megafauna, which are between 300 microns and 10 millimeters represent 50% of species).  Around 13% of species in the CCZ are believed to be primarily nodule dwellers. (Rabone, 2023)  

Biodiversity Impact Comparison

Tropical Rainforest Mining vs. Nodule Harvesting on Abyssal Plains

Impact Category	Tropical Rainforest Mining	Abyssal Plains Harvesting
Resident Species Estimate	4,350,000	80,000
Biomass Density	Extremely High	Extremely Low
Level of Damage from Extraction Operations	High (total destruction in mine footprint)	Medium/Low (ground disturbance and compaction, nodule removal)
Indirect Threats to Biodiversity	Many	Few
Ecosystem % of Earth’s Surface	1.8%	12.5%
Proportion of Ecosystem Threatened	50%+	1.25%

Claims that the abyssal plains hold massive biodiversity almost always link to a 2002 paper by Paul Snelgrove and Craig Smith which pushed back against the idea that the deep ocean harbored no life at all. The authors in that paper cited estimates for species richness on the abyssal plains that ranged from 500,000 to 10 million. There are three important caveats to the biodiversity numbers posited in that work. First, the numbers are highly speculative as the authors acknowledge. They noted that the high-end estimates, which environmental groups have latched onto, were “surprising.” The extremely large spread of estimates itself indicates that these numbers are preliminary – basically guesses that are not founded in primary data from the abyssal plains. They also noted that the estimates came from shallow water sampling and the high number used a simple linear extrapolation to come up with an estimate. In other words, it assumed a constant rate of growth in species richness across the entire ocean even though at the time we knew that species counts tended to decline with depth, per a chart provided by the authors.

Second, and perhaps most important, work done since 2002, which depends on actual sampling on the abyssal plains, and species accumulation and rarefaction curves rather than linear extrapolation, has generated species numbers that are far more modest than the high-end estimates referred to by environmentalists. As previously mentioned, the work published in 2023 by Muriel Rabone and her team suggested an upside estimate of around 8,000 species for the CCZ (Rabone, 2023).

Finally, there’s an apples to oranges problem with environmentalists claim. When we cite biodiversity in tropical rainforests, we are normally referring to plants and animals that live predominantly above ground. The environmentalists who claim massive biodiversity on the abyssal plains are referring to macrofaunal organisms (and sometimes microbes) which are subterranean, because these are the majority of the species which inhabit the abyssal plains. Most of these organisms are so small that they are not visible to the human eye. Species estimates for tropical rainforests don’t generally include subterranean species. In fact, scientists believe that there is greater species richness below ground than there is above ground (Anthony, 2023), so it may be the case that we would need to expand the 4.35 million rainforest species significantly to make the comparison a fair one. Regardless, the fact that marine biologists believe approximately 8,000 species live in the muds of the CCZ tells the story adequately.

Terrestrial mining for battery minerals in tropical rainforests and other environmentally sensitive habitats represents the worst outcome for the environment and humanity.  Terrestrial battery mineral mining activities have high potential to harm and are located in the world’s most sensitive environments, areas that are not only exceptional for their biodiversity, but also for their high biomass.  Mining regulations in these areas are often substandard and loosely enforced, and the mining is frequently undertaken by foreign companies from countries that do not emphasize environmental protections.  

By comparison, nodule harvesting has relatively low potential for harm and is carried out in areas where both biomass and biodiversity are very low, in some of the world’s most desolate habitats.   Seabed operators can be more easily tracked than in terrestrial operations because of capital and licensing constraints. 

If we are going to make the energy transition happen, we need energy minerals in abundance. Those who are concerned for the world’s environment and for humanity will conclude that nodule harvesting should be encouraged as part of the solution. We will also need terrestrial minerals as part of the solution and best practices should be employed in both terrestrial and marine environments. If polymetallic nodules can replace some of the supply from the most damaging terrestrial operations, this would be a good outcome for humanity.