It is the least explored region of the planet, although it occupies more than 60% of the earth’s crust.
The abyssal zone, also popularly known as the abyssal kingdom, is a layer of the deep ocean where much of the seabed is found.
It is a world where conditions are extreme and which, however, harbors a great wealth of life.
Scientists from eight countries carried out the largest analysis to date of DNA from water and sediments in the deep ocean.
The study, which has just been published in the journal Science Advances, revealed that much of the species living in the abyssal realm are totally new to science.
Three Spanish experts, authors of the study, explained to BBC Mundo what the abyssal zone is, what the main findings of the new research are and why it is urgent to protect this almost unknown world.
What is and where does the abyssal kingdom begin?
“It is the zone of the oceans that starts at 4,000 meters deep”, pointed out Covadonga Orejas Saco del Valle, a researcher at the Gijón Oceanographic Center, belonging to the Spanish Institute of Oceanography (CSIC).
“It is said that it is the last frontier because of the little we know about it. In fact, the surfaces of the Moon and Mars are fully mapped, but only 20% of the ocean floor has been mapped to date”, added the Spanish expert.
The abyssal zone reaches up to 6,000 meters, and from there begins what is called hadal area.
Much of the ocean floor is at depths of about 4,000 to 5,500 meters.
“There are still other parts in the trenches where you can reach depths of up to 10,000, 15,000 meters, but that is simply 5 or 6% of the planet,” explained Pedro Martínez Arbizu, a marine biologist and researcher at the Senckenberg Museum of Natural History. in Germany.
What is that extreme world like and who lives there?
In the abyssal zone the pressure is very great. “(There are) 500 to 600 atmospheres of pressure500 to 600 times more than the atmospheric pressure that we have on the surface”, pointed out Martínez Arbizu.
On the other hand, as explained by Orejas Saco del Valle, “temperatures are very low (between 2 and 3 degrees) and the light does not come”.
“Fauna is varied, belonging to various taxonomic groups, from tiny organisms to different species of fish, and this study shows that it is even more diverse than previously thought,” added the researcher.
Since no light reaches these depths, photosynthesis is not possible.
In the abyssal zone the organisms “they feed only on what falls from the ocean surface in what we call marine snow”, pointed out Martínez Arbizu.
“They are remains of the algae and remains of the carcasses of the small inhabitants of the zooplankton that fall little by little and reach those depths.”
However, only 5% of what is produced on the surface is what reaches down there, added the scientist. The rest is consumed on the surface or in transit through the water column.
Ramon Massana, a researcher at the Institut de Ciències del Mar (CSIC) in Barcelona and a specialist in microbial ecology, explained that the organisms that live in abyssal sediments include a wide variety of animals (nematodes, crustaceans, annelids) and also microbial eukaryotes and prokaryotes. “They are species fully adapted to these extreme conditions”.
Eukaryotes are those organisms, such as plants and animals, including humans, composed of eukaryotic cells, which have a differentiated nucleus protected by a membrane.
Prokaryotes, on the other hand, are microorganisms such as bacteria, whose cells —prokaryotes— do not have a defined nucleus and in which the genetic material is dispersed in the cytoplasm).
Why is so little known about the nether realm?
The study was the result of a major international effort in which samples obtained by 15 international expeditions.
“It is an ecosystem that is difficult to access, that is why we know so little about it. And it is very expensive to carry out these investigations. Hence the importance of pooling efforts and resources and establishing international collaborations such as the one shown in this research,” said Orejas Saco del Valle.
Martínez Arbizu explained, for example, that to take a sample with a dredger at a depth of 5,000 meters, a vessel must have a cable of more than 10 km and there are few vessels that have that capacity.
What did the study reveal?
The scientists analyzed 1,700 samples of water and sediments from the abyssal zone, and two billion DNA sequences.
The results of this massive sequencing were in turn compared with those of samples from different levels in the water column in all the world’s oceans.
“The main finding has been to characterize the great diversity that inhabits the abyssal and hadal bottoms, and how much we still have to discover in them,” said Orejas Saco del Valle.
“The study shows that the diversity of the bottoms, which had been thought to be less than that of the water column, is very high, in fact up to three times higher. All this shows us a new image of life in the oceanic sedimentary bottoms”, added the researcher.
“It’s surprising,” said Martínez Arbizu, “because in reality almost all animal groups have a family that is represented on the abyssal platform.”
“They can be starfish, crustaceans like small shrimp, corals, sponges, but they are different forms from what we know from the surface.”
About two-thirds of this diversity cannot be assigned to any known group.
“These species are new, no one has investigated them yet, there are no references in international databases. Many times we do not know to which animal group they belong”, added Martínez Arbizu.
Orejas Saco del Valle pointed out that the ancient DNA deposited in the sediments will also contribute to reconstructing the past characteristics of the ocean.
Why is the study said to present a unified view of DNA in the ocean?
The study represents the first unified view of the eukaryotic biodiversity of the oceans on a global scale, based on analysis of DNA from the ocean surface to deep ocean sediments.
The results will therefore make it possible to address marine ecology issues on a global scale for the first time.
“Before this study, the results of circumnavigation campaigns, such as the Malaspina and TaraOceans expeditions, which had characterized the diversity of microbial eukaryotic plankton at the global ocean level, had been published, but there was a very partial and fragmented knowledge of the diversity in deep sediments”, Ramon Massana explained.
“In this study, the data collected in 15 international expeditions in deep sediments are put together, which also allows us to give a global vision of benthic diversity.” (benthosor seafloor in Greek, is a reference to organisms that live on the ocean floor, as opposed to those that live in the water column like plankton).
Massana added that thanks to the new research, “for the first time these two components, plankton and benthos, can be compared on a global scale.”
What role does the abyssal kingdom play in the “biological bomb”?
A key aspect of the study is that the scientists managed to differentiate the DNA of the planktonic organisms whose remains fell to the bottom of the ocean, from the DNA of the indigenous organisms that live in the abyssal zone.
This distinction allows us to better understand what is known as the “biological pump”: the process that transfers atmospheric carbon dioxide to the deep oceanthus regulating the global climate and lessening the impact of climate change.
“The benthic ecosystems of the seabed are the basis of two important ecosystem services of global importance,” explained Massana.
On the one hand, they participate in the recycling of inorganic nutrientshe pointed. “The organic matter that reaches these regions is remineralized, and in the long run, the inorganic nutrients will return to the surface layers to allow photosynthesis”.
“On the other hand, some of the settled carbon is stored in the sediments on geological time scales,” he continued.
“This constitutes the biological carbon pump: photosynthesis captures atmospheric CO2, a small part sediments and gets sequestered in deep sediments.”
“This process is currently contributing to partially mitigate the effects of the contribution of CO2 to the atmosphere due to the use of fossil fuels”.
Is it a threatened ecosystem?
Orejas Saco del Valle underlines the relevance of the information from the study in order to design appropriate management and protection strategies for deep ocean ecosystems, “which are unique and functionally very important.”
The abyssal kingdom “is like a treasure”, Martínez Arbizu defines it. And he points out that enzymes or other potentially necessary products may be found in their bodies.
“Is the same thing that happens with the Amazonian forest: if we destroy all that diversity, the ability to achieve some solution for the problems that we will have in the future goes with it”.
There is currently a growing interest in extracting minerals from the ocean floor.
“For all we know the effects are going to be quite negative”, pointed out Martínez Arbizu.
“The areas that can be impacted by mining, for example manganese nodules, are quite large.”
“Due to the low temperature, all the vital processes of the fauna that lives there are very slow. If you damage an ecosystem in deep waters for it to recover, it will take many years, we are thinking that maybe 50, 100, 200 years or even more”.
Source: Eluniverso
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