Deep-sea mining: encroachment on largely unknown living environments

Deep sea

The deep sea seems empty and barren, but that is deceptive. (Photo: Senckenberg / Nils Brenke)

The rich deposits of raw materials in the deep sea arouse desires. But the living environment at the bottom of the oceans has hardly been explored, as analyzes of environmental DNA from sediment samples in the license area for deep-sea mining confirm: a large part of the genetic material came from species that are still completely unknown to science. In the potential mining area, of all places, the biological diversity was particularly high, as the research team reports.

The deep sea arouses great interest primarily because of its natural metal deposits: Manganese nodules, cobalt crusts and massive sulphides, which contain coveted raw materials, are stored in several kilometers of water. Several countries are therefore already planning to reduce these resources. Studies on technologies and possible consequences are already underway in the licensed areas of the so-called Clarion-Clipperton Zone (CCZ) in the central Pacific. Initial results suggest that a disturbance of the sensitive ecosystems of the deep sea could have consequences for decades.

DNA traces in deep sea sediment

So far, however, knowledge about the possible consequences of deep-sea mining and generally about the environment in the deep sea has been extremely limited. Because the investigation of the areas lying thousands of meters below the surface of the water is time-consuming, expensive and only possible when the sea is calm. “In addition to the necessary and time-consuming analysis of the organisms, we also need other and faster methods with which we can also determine the biological diversity in the deep sea,” explains Angelika Brandt from the Senckenberg Research Institute and Nature Museum in Frankfurt. Together with an international team of researchers led by Franck Lejzerowicz from the University of California in San Diego, she tried to use a special method to investigate the deep-sea environment more closely.

“In our new study, we used environmental DNA from sediments in the Clarion-Clipperton Zone and other deep-sea regions around the world to examine the bottom-living deep-sea fauna,” explains Brandt. This so-called eDNA is not obtained directly from organisms, but from environmental samples such as water or sediments. By comparing it with DNA databases, scientists can determine which organisms have left their genetic traces in these samples. For their study, the team analyzed Overall, Lejzerowicz and his colleagues analyzed eDNA from 310 deep-sea sediment samples. Most of it came from the Clarion-Clipperton Zone, but samples were also tested from the rest of the Pacific, Atlantic and Arctic Oceans.

Most of the organisms are still unknown

“The results underline that the biodiversity of the deep sea is still almost unknown,” says Pedro Martínez Arbizu from Senckenberg am Meer. The researchers were unable to assign a large part of the DNA from their samples to any of the previously described species. More than 60 percent of the benthic foraminifera, a group of shell-bearing unicellular organisms, and almost a third of the organisms that carry cell nuclei are still completely unknown to research. Among the multicellular animals in the sediment, representatives of roundworms (nematodes) dominated – and the team was only able to assign around half of them to a known species. Crustaceans and flatworms were also common, as Lejzerowicz and his colleagues report.

“The most striking result, however, was the uniqueness of the Clarion-Clipperton zone,” report the scientists. “It is characterized by a large number of taxonomic units that only occur there.” The phylogenetic diversity in this area is also higher than in most of the other deep-sea regions sampled. This suggests that there are significant geographic differences between different deep-sea areas. According to Lejzerowicz and his team, this underscores how incomplete knowledge about the life of the deep sea has been up to now. As long as it is not better researched, there is a risk that deep-sea mining will destroy countless species and communities that are not even known.

Source: Senckenberg Research Institute and Nature Museums, Article: Frontiers in Marime Science, doi: 10.3389 / fmars.2021.671033

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