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Seafloor ecosystems fare poorly in simulated deep-sea mining

Deep-sea mining has its sights set on polymetallic nodules. Retrieval of these nodules relies on advanced technologies allowing mining ships to cruise the ocean and then vacuum the nodules from off the seafloor. The potential economic profit from these operations is enormous, but so is the cost to the environment. Damage to seafloor and open-water ecosystems are both of concern.  All deep-sea mining technologies under development cause significant disturbance to the seafloor. But studies of seafloor ecosystems indicate that recovery from mining disturbances takes at least 50 years.

The presence of polymetallic nodules in the deep ocean has been known for years. However, it is only now that the technologies for extracting these nodules have matured. Polymetallic nodules range in size from less than an inch up to five or six inches in diameter. However, despite their small size, contained in those nodules are riches in the form of copper, manganese, nickel, and cobalt. These metals are all valuable commodities and under high demand due to their crucial role in manufacturing efficient modern batteries. But mining them should also carry a responsibility to conduct operations in an environmentally responsible manner.  


The DISCOL area in the tropical East Pacific Ocean, 3000 kilometers west of Peru, was the geographical setting for an experiment in 1989. At that time, researchers simulated mining disturbances on the seafloor when they plowed up the ocean bottom sediments 4000 meters below the surface. 

The environment at these depths is quiet and serene. Time moves slowly, and change occurs over decades, not over years. The seafloor is removed from the influence of strong currents, so nothing disturbs the slow pace of life there. Even the build-up of new sediments creeps along with little change from year to year. 

When the experimental site was revisited 26 years later, the original plow tracks were still visible. But this was no real surprise, given the environmental conditions. However, the environmentally significant results from the investigation involved long-term damage to the seafloor ecosystem.

Disruption of the seafloor food chain

The seafloor ecosystem relies on microbial mats in the upper active layer of the sediments. The bacteria that form these mats constitute the lowest level of the seafloor food web. However, a sampling of the bacterial populations revealed that, after 26 years, the plowed areas contained 25 to 50 percent fewer bacteria than found in undisturbed seafloor.

This finding is significant since bacteria are the organisms that convert organic material into edible food for higher trophic levels of the food chain. In the deep oceans, organic matter rains down from above as plankton and other marine creatures that die and sink to the ocean depths. So fewer bacteria on the seafloor means that less of this organic material makes its way into the seafloor ecosystem. 

If mining operations destroy thousands of square kilometers of the seafloor, then they effectively wipe out that ecosystem by eliminating its base-level food supply. Full recovery of seafloor ecosystems takes between 50 and 100 years. How decimation of the seafloor ecosystems affects other parts of the marine environment is unknown. Understanding these knock-on effects should be the first step for mining companies before operations begin.


Seabed mining: Technological marvel or environmental folly? (Source ArcheanWeb) – https://archeanweb.com/2020/01/03/seabed-mining-technological-marvel-or-environmental-folly/  Also:

The economics of environmental pollution (Source: ArcheanWeb) – https://archeanweb.com/2020/01/02/the-economics-of-environmental-pollution/ Also:


Simulated deep-sea mining affects ecosystem functions at the seafloor (Source: Max Planck Institute for Marine Microbiology; Science Daily) – https://www.sciencedaily.com/releases/2020/04/200429144921.htm  Also:

Feature Image: Psychropotes semperiana and manganese nodules  (Modified) –  By Ramirez-Llodra E., Tyler P. A., Baker M. C., Bergstad O. A., Clark M. R., Escobar E., Levin L. A., Menot L., Rowden A. A., Smith C. R. & Van Dover C. L. (2011). “Man and the Last Great Wilderness: Human Impact on the Deep Sea”. PLoS ONE 6(8): e22588 Figure 5a – CC BY 4.0,  https://commons.wikimedia.org/w/index.php?curid=58576941  

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.