Deep trouble

Above: the SHINKAI 6500 submersible at the Edmond hydrothermal vent field on the Central Indian Ridge. Chong CHEN / JAMSTEC.

Next year, the first commercial-scale mining operations in international waters are due to start, helping feed a growing demand for rare-earth metals. Elin Thomas explores what this means for the species that inhabit the extraordinary deep-sea habitats being targeted

May 27^th 2022

For many the deep sea is a distant and dark place that is all too easily disregarded. To quote a famous cartoon published in The New Yorker in 1983: “I don’t know why I don’t care about the bottom of the ocean, but I don’t.” However, some habitats on the deep seafloor now face unprecedented threats that endanger the existence of some of their most charismatic species.

Of the various threats facing the deep sea, surely the most intensely debated is deep-sea mining. Dotted across parts of the deep seafloor are rich mineral deposits, with high concentrations of cobalt, copper, zinc, nickel, silver, gold and rare-earth metals. These metals are commercially valuable, used in batteries, phones and laptops, as well as renewable energy devices and electric vehicles. As societies shift away from fossil fuels towards these more sustainable devices and with terrestrial deposits of such minerals depleting, it has been suggested that mining these resources from the deep may be the only way of supplying such technology. But at what cost?

As well as being rich in metals, these areas are rich in life, supporting important benthic habitats and communities. Hydrothermal vents, for example, are among the most unique and productive habitats on Earth. Discovered only in 1977 on the Galápagos Rift, they host dense aggregations of highly specialised and largely endemic faunal communities sustained by the intense chemical energy of the vents. Picture tall chimney-like structures gushing out superheated jets of mineral-rich ‘black smoke’ and surrounded by extraordinary species, from giant red tubeworms (Riftia pachyptila) and iron-armoured snails (Chrysomallon squamiferum) – which both have specially adapted organs where they host chemosymbiotic bacteria – to hairy squat lobsters (Kiwa sp.) that farm bacteria, and heat-resistant Pompeii worms (Alvinella pompejana).

Around 600 active hydrothermal vent fields have been recorded worldwide, each with unique faunal communities, yet these small oases occupy an area less than the size of Manhattan. Due to the uniqueness of this habitat, the majority of hydrothermal vent species are incapable of colonising other seafloor ecosystems.

Above: Deep-sea fauna on hydrothermal vents, including squat lobsters and vent mussels. Picture courtesy of the NOAA's Submarine Ring of Fire 2006 Exploration and Vents Program.

Toxic targets

The deep-sea mining industry has three main targets: seafloor massive sulphide deposits, which form at hydrothermal vents along tectonically active mid-ocean ridges; polymetallic nodules scattered across areas of the abyssal plain; and cobalt-rich crusts, associated with the summits and flanks of seamounts.

The majority of these resources are located beyond national jurisdiction and as such are regulated by the International Seabed Authority (ISA), while the rest lie within the Exclusive Economic Zones (EEZs) of coastal countries where individual governments hold national jurisdiction. To date, the ISA has granted more than 30 exploratory mining contracts and deep-sea mineral exploration of some form has been undertaken within the EEZs of nine different countries, with full-scale commercial mining just around the corner.

The potential impacts of mining on these insular deep-sea environments have therefore been the focus of intense research over the last decade. Possible impacts include the dispersal of potentially toxic sediment plumes, both along the seafloor and within the water column, shifts in ecosystem structure and functioning, habitat removal and a net loss of biodiversity. Studies clearly demonstrate that mining will have an adverse, perhaps irreversible, impact on deep-sea faunal communities, but the demand for the precious resources in these habitats continues unabated. How many species may disappear from the bottom of the ocean without anyone even knowing about them? After all, contemporary estimates of marine species richness suggest that up to 91% of eukaryotic species in the ocean remain undiscovered.

Above: A polymetallic nodule, the target of most deep-sea mining operations.

The International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species has become the foremost authority on global species extinctions. The Red List applies a series of standardised criteria to classify species within a set of universally recognised extinction risk categories, ranging from Least Concern up to the three threatened categories: Vulnerable, Endangered and Critically Endangered. The Red List has been utilised by scientists for decades and with great success – over 140,000 species have been assessed to date and, in turn, these assessments have informed global conservation planning. It therefore stands that the Red List could also be instrumental in shaping conservation and sustainable development policies in the deep sea. With this in mind we set out to find a way to make the threats that deep-sea mining poses to hydrothermal vent species more visible to the world.

Rating risk

We sought to apply the IUCN Red List to all known vent-endemic molluscs, one of the most dominant faunal groups in these habitats, to provide the first global assessment of extinction risk for an entire taxonomic group in the face of the mining threat. Species were assessed using data on their geographic distribution and the potential for threats to cause significant declines within their ranges, as informed by regional seabed management objectives and regulatory frameworks such as the implementation of mining licences or spatial conservation measures. For example, species located in areas of exploratory mining contracts signed by the ISA were considered to be facing declines in the extent and quality of their habitat, while the presence of marine protected areas (MPAs) within the species’ range that specifically prohibited mining would mitigate such declines.

Of the 184 species assessed, almost two-thirds (62%) were found to be threatened with extinction – that is, listed as either Vulnerable, Endangered or Critically Endangered. A further 24% were listed as Near Threatened, signalling their precarious position with regards to possible extinction. We were then able to use these assessments to study the global patterns of extinction risk across different biogeographic regions. It is perhaps unsurprising that the hydrothermal vent fields found to be under greatest threat were those that lie within mining licence areas. Vent communities in the Indian Ocean, for example, were found to face the greatest extinction risk, with six of the 10 mollusc species assessed there listed as Critically Endangered, their limited ranges coinciding with three exploratory mining contracts issued by the ISA. Moreover, as vent species exhibit such high endemicity and the single greatest threat facing them (mining) is regionally controlled, this Red List of vent-endemic molluscs is likely to be representative of the global distribution of extinction risk for all vent-endemic species.

Above: the “Candelabra” black smoker at 3,300 meters in the Logatchev Hydrothermal Field on the Mid-Atlantic Ridge. Courtesy: MARUM – Centre for Marine Environmental Sciences, University of Bremen.

It is, however, important to remember that these extraordinary hydrothermal vent species are not inherently under threat. Twenty-five species were assessed as Least Concern owing to the safety from mining provided by spatial conservation measures such as MPAs. This highlights that despite their endemicity within a naturally insular environment, without the threat of mining vent species can be left to thrive. Indeed, seabed management consistently had the greatest impact on species’ extinction risk outcomes. It is therefore prudent for us to consider a precautionary conservation approach and stronger protections for hydrothermal vents, including the implementation of a moratorium on deep-sea mining until appropriate data are available to inform any sustainable management of this emerging industry.

At the time of writing, commercial-scale mining is likely to commence in areas beyond national jurisdiction as early as July 2023. It is therefore essential that we ensure the conservation of these incredible deep-sea habitats as a matter of urgency – an initiative that I hope the vent Red List has aided.

Elin Thomas is a PhD student at Queen’s University Belfast, where she studies the conservation of deep-sea benthic invertebrates. She is also affiliated with the IUCN SSC Mollusc Specialist Group through her work on the vent Red List.

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