Giant worms, snails… Life teems under the earth’s crust, below the bottom of the oceans… This unexpected scientific discovery on the East-Pacific ridge opens up new research perspectives, and confirms the need for precautions with regard to seabed mining.
There is a real ecosystem under the ocean floor. This is what an international team of researchers discovered after exploring the East Pacific Ridge, off the coast of Central America. They had the idea of scraping the local underwater earth’s crust, of volcanic origin, using a remote-controlled robot from the Schmidt Ocean Institute. What was their surprise to find snails, tube worms (which live in a tube that they construct) giants of almost 46cm, molluscs, chemosynthetic bacteria…
Pierre Chevaldonné, researcher at IMBE, the CNRS Mediterranean Institute of Marine and Continental Biodiversity, reminds La 1ère.fr that these ecosystems, thousands of meters under the sea, are still poorly known. Even if we have studied them for a long time:
When you take a camera across the seabed, you don’t have to stop at what you see. Because beyond what we see, under the seabed, there may be cavities, underground systems, invisible to the naked eye, which shelter this rather particular fauna. We already knew that we could find micro-organisms (microbes, etc.) under the ocean floor, but here, the discovery is macro-organisms!!…
Pierre Chevaldonné researcher at IMBE, the CNRS Mediterranean Institute of Marine and Continental Biodiversity
For Jyotika Virmani, director of the Schmidt Ocean Institute, we have there “a new proof that life exists in incredible places’.
The Schmidt Ocean Institute’s remotely operated vehicle (ROV) SuBastian recovered from the Galapagos Marine Reserve by the research vessel Falkor on October 26, 2023. • ©(illustrative photo) (MISHA VALLEJO PRUT / SCHMIDT OCEAN INSTITUTE)
How can animals evolve in cavities (around 10 cm high) at a depth of 2500 m, under pressure 250 times greater than at the surface, and in the dark?
In fact, they live almost under hydrothermal vents, also called hydrothermal mounts, or hydrothermal vents, or smokers.
Since the 1970s, we have known of the existence of worms, mussels, and other living beings near these prominences which result from the movements of tectonic plates.
These movements cause magma to rise. As a result, seawater infiltrated into volcanic cracks and crevices heats up near this magma. It is then spat out in the form of geysers of gaseous fluids loaded with chemical compounds, notably hydrogen sulphide.
Black smokers, sorts of underwater geysers located on seismic ridges. These waters contain dissolved mineral substances and black particles of iron sulfide giving them this characteristic appearance. • ©CHEMINEE JEAN LOUIS / CNRS IMAGES
As they exit into the cold ocean at less than 2°C, the dissolved minerals will aggregate (precipitate), forming these kinds of chimneys which continue to emit the hot fluid. This immediately mixes with seawater, promoting life locally.
it will create an environment with a slightly intermediate temperature (Editor’s note: 25°C at the location of the research mentioned here) which will be extremely enriched in hydrogen sulphide, which will greatly appeal to certain bacteria which will develop there. And these bacteria themselves will greatly please a certain number of organisms, which will notably host them in their bodies in the form of a symbiosis (Editor’s note: for example, inside worms, bacteria would use minerals to produce sugars and other molecules). These animals themselves, they will be eaten by other animals. And so a sort of food chain is created in these places which is almost disconnected from what we know on the surface, us, living in areas lit by the sun. So food chain systems which are almost independent of light, the sun and photosynthesis.
Pierre Chevaldonné researcher at IMBE, the CNRS Mediterranean Institute of Marine and Continental Biodiversity
These hydrothermal sources are also at the origin of terrestrial life according to scientists.
The international team was studying the path of tube-dwelling larvae that quickly establish themselves on new hydrothermal vent fields after an eruption. Monika Bright, professor of marine biology at the University of Vienna, member of the group, considers, like her colleagues, that “theThe larvae (…) can be carried with cold water from deep into the crust, where this water mixes with the fluid in the chimneys, before being expelled to the surface and settling there.
It is clear, in any case, that the fauna of the seabed and that of its subsoil are connected.
Tube-dwelling polychaete annelids, “Ditrupa arietina”, whose population evolution is observed in the Gulf of Lion, during sediment sampling. • ©LECOMTE JEAN / CNRS IMAGES
It was by turning over rocks to collect samples that oceanologists discovered that there were cavities underneath populated by animals. These cavities, like those where water infiltrates towards the magma, are in fact of volcanic origin, linked to flows of very viscous lava, explains Pierre Chevaldonné:
“These lava flows will harden on the surface (Editor’s note: only). And when the magma will gradually withdraw, when the lava will withdraw from these flows, what will remain, what will remain due to cooling, of the surface layer, is a kind of tunnel. And so a whole bunch of cavities will be created at these eruption sites. »
After the discovery on the East-Pacific ridge, we can wonder. Could we discover similar fauna in the marine subsoil off the French overseas territories? This is not impossible but it is unlikely. Even though there are volcanic areas in these regions. Apart from a few special cases, this type of situation seems to only concern oceanic ridges.
The researchers who authored the study do not hesitate to assert that “the study of the underwater biosphere for animal life has only just begun” (cSome scientists even claim that millions of underwater species are still unknown, whereas, for example, understanding their adaptation to extreme conditions could advance science, particularly medicine). The discovery of animal habitats in the subsoil of the crust, the extent of which is unknown, would therefore increase the urgency of protecting the seabed against possible human impacts, such as those from deep-sea mining. .
©CNRS
It is true that the seabed contains manganese, cobalt, and nickel (used in the manufacture of batteries), particularly in the form of pebbles, polymetallic nodules, in the South Pacific. Pierre Chevaldonné sounds the alarm in the face of very controversial exploitation projects:
What that would represent (Editor’s note: as a risk) is to come and scrape the bottom of the sea with a sort of vacuum bulldozer. And then all that would come to the surface, would be sorted on the surface, because obviously we don’t need the underwater mud, we just need the nodules. And a huge plume of silt would then be released into the middle of the ocean. These are all kinds of things that are extremely harmful to wildlife! These are gigantic disruptions! And which would be practiced on equally gigantic surfaces!
However, these deep ecosystems would need a lot of time to reach maturity. They would recover very badly from the disturbances that could be made to them. Their protection could therefore become a major issue in the years to come. Recent and future scientific discoveries could make it possible to better measure this.
