"Clearly we are in the midst of one of the great extinction spasms of geological history" E.O. Wilson
"We know that seamounts support large pools of undiscovered species, but we cannot yet predict what is on the unstudied ones. The tragedy is that we may never know how many species become extinct before they are even identified" Dr. Frederick Grassle, Rutgers University (1)
Throughout human history the deep ocean has often inspired wonder and fear. It is the home of legendary leviathans of the deep which struck fear in the hearts of ancient mariners and the source of the so-called "primordial ooze", at one time believed to be the origin of life itself.
Recent scientific investigations have confirmed and revealed the truly remarkable extent of the mystery and diversity of life in the deep sea. Among other things, scientists have discovered that there are more species of corals found in the deep ocean than in shallow-water tropical seas. Some of these coral species form reefs many thousands of years old, which support rich and highly endemic ecosystems. Many new and 'relic' species (species previously known only from fossil records) have been discovered on seamounts — the peaks of underwater mountains and mountain chains found throughout the Atlantic, Pacific and Indian Oceans. Most seamounts and other deep-water habitats have not yet been studied but many of the estimated 100,000 or more seamounts worldwide could be unique 'islands' of biodiversity.
Scientists estimate that there may be a million or more species inhabiting the oceans that re as yet undiscovered. Most of these are likely to be found at depths below 200 meters. Research expeditions to the deep sea routinely discover new species or ecosystems, often in unexpected places. For example, two cruises in the past few years south of Australia found 274 new species of corals, starfish, sponges, shrimps, and crabs 1.2 miles (2 kilometers) beneath the surface of the ocean around Antarctica. They also discovered 145 undersea canyons and 80 new seamounts. (2)
But the ability to reach deep into the ocean in search of new forms of life is not restricted to scientific research. As coastal and open ocean species of fish such as cod and tunas are overexploited, large-scale fishing vessels have increasingly turned to developing new fisheries and markets for species such as orange roughy, grenadiers and deep-water prawns found in the deep ocean. The fishing industry has developed the technology to fish the ocean bottom as deep as 2000 meters or more. Similarly, advances in technology and increases in the price of commodities have more recently drawn the mining industry to exploration of the deep seabed, with the possibility of starting exploitation as early as 2016.
The most destructive method of deep-sea fishing is 'bottom trawling' which drags heavy steel plates, cables and nets across the ocean floor destroying cold water corals, sponges, seapens, xenophyophores and many other species that form the basic structure of deep-sea ecosystems. The scale of the threat to the marine biodiversity of the deep-sea as result of bottom trawling as well as other methods of deep-sea fishing is yet unknown, but potentially comparable to the threat to terrestrial biodiversity associated with the loss of tropical rainforests. Many thousands of species may be at risk, most of which are still unknown to science.
Today's trawlers are capable of fishing seamounts, deep-sea canyons and rough seafloor that was once avoided for fear of damaging nets. To capture one or two target commercial species, deep-sea bottom trawl fishing vessels drag huge nets armed with steel plates and heavy rollers across the seabed, pulverizing everything in their path. In order to catch a few 'target' fish species of commercial value, biologically rich and diverse deep-sea ecosystems are plowed through. Often many other species of unwanted fish are caught as 'bycatch' and thrown dead back into the water. In a matter of a few weeks or months, bottom trawl fishing can destroy what took nature many thousands of years to create.
The mouth of the trawl net is held open by two steel plate doors that help to keep the net on the seafloor. One company markets what it calls 'Canyonbusters', trawl doors that weigh up to five tons each and that undoubtedly live up to their name. To allow the net to fish on rugged seafloors, steel balls or rubber bobbins — known as roller gear or rockhoppers — that can measure a meter or more in diameter are attached to a heavy cable that is strung across the bottom of the mouth of the net. In addition, heavy chafing gear is attached to the rear portion of the bottom of the trawl net to further protect the net from being torn as it fills with fish and drags along the bottom of the ocean.
Fragile deep-water ecosystems, coral systems in particular, stand no chance against these ruthlessly effective underwater bulldozers. Deep-sea structures are not merely damaged; they are obliterated in a manner akin to clear-cutting a rainforest. After heavy trawling, coral ecosystems on seamounts are reduced to mostly bare rock and coral rubble.
Once destroyed, slow-growing deep-sea species are either lost forever or unlikely to recover for decades or centuries. Stable, living habitats such as coral and sponge communities in particular tend to be both the most heavily damaged and the slowest to regenerate. To make matters worse, the deep sea's remarkable array of coral, sponge, and other habitat forming species are, in many cases likely to harbour undiscovered and endemic species. The risk of extinguishing whole species never before seen is, therefore, particularly high when bottom trawling strips the surface of seamounts of their coral and sponge habitat.
Considerable damage to deep-water coral communities has been recorded off both coasts of North America, off Europe from Scandinavia to northern Spain, and on seamounts near Australia and New Zealand. In Norwegian waters, for example, the Institute of Marine Research in Bergen, Norway estimates that one-third to one-half of the cold-water coral reefs have been damaged or destroyed by trawling. Photographs document giant trawl scars along the seabed up to 4 kilometers (2.5 miles) long.
On the high seas south of Australia, in an area known as the South Tasman Rise, observers recorded trawlers bringing up an average of 1.6 tons of coral per hour in their nets in 1997 — the first year of the area's orange roughy seamount fishery. Up to several thousand tons of coral were estimated to have been brought up in the nets of the 20 or so deep-sea trawlers working in the area. This figure does not include coral that was damaged but not brought up in the nets. By contrast, the catch of orange roughy — the target species in this fishery — in the first year of the fishery was reported to be less than 4,000 tons.
A study in the Gulf of Alaska observed a trawl path that had pulled up one ton of corals. Thirty-one red tree coral colonies had been in the 700-meter trawl path observed. Seven years after the damage, some of the larger colonies that survived the initial trawl tow were still missing 95—99 percent of their branches. No young corals had replaced the dead ones in the damaged colonies.
Human-occupied vehicles began to take scientists to the deep seabed in the 1930s.(3) Each decade since then has led to increased access to the deep ocean through the use of technologically advanced robotics for exploration and scientific research.
For several decades now research has shown that the deep ocean harbours large deposits of minerals and precious metals such as manganese, cobalt, gold, silver, copper, zinc, and rare earth elements, etc. Yet attempts to mine deep-sea mineral deposits have failed as the reserves proved too expensive to exploit and technologically out of reach - until now.
Today, high commodity prices and the scarcity of some minerals, combined with new advances in robotics, computer mapping and deepwater technology, are reviving interest in deep seabed mining both national and international waters. Manganese nodules, polymetallic sulphides and cobalt-rich ferromanganese crusts are the primary targets, together with the rare earth elements which are key components of many new digital and e-mobility technologies such as computer tablets, smart phones and televisions.
Demand for rare earth elements leapt from 30,000 tonnes in the 1980s to 120,000 tonnes in 2010, higher than the world's current annual (terrestrial) production of 112,000 tonnes, providing a major motivation for making deep-sea mining a viable industry as soon as possible.
Three main types of deep-sea mining are currently in development:
1. Polymetallic Nodules - Manganese nodules are mineral precipitates of manganese and iron oxides. They occur over extensive areas of abyssal plains at depths of 4000-6500m. They grow extremely slowly: several centimetres every million years. Nodules contain nickel, copper, and cobalt, as well as traces of other metals (notably rare earth elements) important to high-tech industries. Ecosystem Impacts: The potential scale of the impacts of this type of mining is huge. In the central eastern Pacific alone, an area of exploratory mining contracts stretching across several thousand kilometres of the deep seabed have been issued.
2. Cobalt-rich Ferromanganese Crusts precipitate onto nearly all rock surfaces in the deep ocean that are free of sediment (mainly seamounts), gradually building layers 1-260mm thick at a rate of 1-5mm per million years. Crusts of economic interest occur at depths of about 800—2500m on seamounts, mainly in the Pacific Ocean. Ecosystem Impacts: Technologically, the mining of cobalt crusts is more complex than manganese nodules, and environmentally probably even more damaging. Cobalt-rich crust mining would involve cutting 5-8cm of the crust on the top of seamounts, and could thus have a significant impact on corals, sponges and other benthic organisms associated with seamounts. The sediment plumes created could also impact these and other suspension feeders 'downstream' from the mining operations.
3. Polymetallic Sulphides - Deep-sea hydrothermal vents, found along mid-ocean ridges and back-arc basins, support some of the rarest and most unique ecological communities known to science. Here organisms derive their energy from sulphide chemicals in extremely hot, mineralized vent fluids. Most species discovered at vents are new to science, and the vents support communities with extremely high biomass relative to other deep-sea habitats. Ecosystem Impacts: Mining of hydrothermal vents would destroy an extensive patch of productive vent habitat, including thousands of vent chimneys, killing virtually all of the attached organisms. The extent of the impacts to vents and other seafloor habitats mined will inevitably be severe at the site scale. Mining is also expected to alter venting frequency and characteristics on surrounding seafloor areas, affecting ecological communities far beyond the mined site. Life forms destroyed may well be endemic, meaning that mining may destroy species before they are even identified.
In 2011, it was reported that high concentrations of rare earth elements can be found in the top few metres of deep-sea clays, as well as in the polymetallic nodules and cobalt crusts. The impacts of deep-sea mud mining may well exceed even those involved with polymetallic nodules, because they will penetrate deeper into the sediment and the operational and discharge plumes may be more severe. Mining operations in muds could also include the application of weak acid during processing, with the residue potentially returning to the seafloor.
All these mining activities will bring large quantities of particle-laden, CO2 and nutrient-rich, cold water to the sea surface. These flows could also potentially be polluted, for example by hydrogen-sulphide. If the waters are released at the surface or in midwater, this may have a number of impacts that alter pelagic and/or benthic ecosystems. Finally, if - as expected - some of the mined material will be processed at sea, this will lead to the deposition of tailings and the potential remobilization of toxic chemicals.
(1) Dr Frederick Grassle of Rutgers University quoted in "Lost worlds of the ocean threatened by trawlers" by Roger Highfield, Science Editor. UK Telegraph 23/8/2003.
(2) National Geographic News 9 Oct 2008.
(4) Van Dover, C.L. (2011). "Tighten regulations on deep-sea mining". Nature, vol.470. 3 February 2011.