Paris (AFP)- Shrouded in darkness and mystery, deep ocean creatures exist in a world of improbable abundance, surviving on little food and under pressure that would crush human lungs.
This extremely hostile environment, which will be in the spotlight at a major United Nations ocean summit in Lisbon this week, has caused its inhabitants to develop a prodigious array of extraterrestrial characteristics and idiosyncratic survival techniques.
A vast assortment of animals populate the sunless depths, from the colossal squid, which coiled its tentacles around the imaginations of sailors and storytellers, to beings with immense veiled eyes, or whose bodies are as transparent as glass.
And the angler fish, with its devilish stares lit by a built-in headlamp, showing that deep black is alive with lights.
– “Incredible” creatures –
Until the middle of the 19th century, scientists believed that life was impossible beyond a few hundred meters.
“They imagined that there was nothing, because of the absence of light, the pressure, the cold and the lack of food”, explains to AFP Nadine Le Bris, professor at Sorbonne University.
Between 200 and 1,000 meters (650 to 3,300 feet), the light fades until it disappears completely, and with it the plants; at 2,000 meters, the pressure is 200 times greater than that of the atmosphere.
From abyssal plains to cavernous pits plunging deeper than Everest is high, aquatic existence continues in spectacular diversity.
“When people think of the deep sea, they often think of the seabed,” said Karen Osborn of the Smithsonian’s Natural History Museum.
“But all that water in between is full of amazing animals. There’s a ton of life.”
These open water dwellers face a formidable challenge: they have nowhere to hide.
“There’s no seaweed to hide in, no caves or mud to dig in,” Osborn said.
“There are predators coming from below, from above, from everywhere.”
– Masters of Disguise –
One tactic is to become invisible.
Some creatures are red, which makes them difficult to distinguish in an environment where red light no longer filters through.
Others make themselves transparent.
Take the transparent worm, which ranges in size from a few millimeters to around a meter in length and glistens in the water, flapping its frilly limbs.
“They look like a fern frond,” Osborn said.
“They are beautiful animals and they emit yellow bioluminescent light from the tips of their arms. What could be better than that.”
Bioluminescence is especially common in fish, squid and types of jellyfish, according to the US National Oceanic and Atmospheric Administration, which states that about 80% of animals living between 200 and 1,000 meters produce their own light.
This chemical process could be useful for defense, reproduction, or finding food — but no one knows for sure why so many creatures developed it, NOAA says.
With no plants around and animals scattered across the vastness doing their best to disappear, the creatures of the ocean depths often struggle to find a living meal.
“If you happen to be lucky and touch a piece of your food, bingo! But you might not see another one for three weeks,” Osborn said.
Another option is to feast on the dead.
Organic particles from surface waters – disintegrated bodies of animals and plants, mixing with feces – drift into what is called “sea snow”.
These corpse confetti are part of a process that sequesters carbon dioxide in the depths of the ocean.
It is also a lifeline for many deep-sea animals, including the blood-red vampire squid which, contrary to its reputation, peacefully sucks up sea snow.
When giants like dead whales sink to the bottom of the sea, they are quickly reduced to bones by scavengers.
With most oceans still unexplored, it is often said that we know more about the surface of Mars than the seabed of our own planet.
But unlike outer space, scientists continue to find life even in the most hostile conditions.
Like hot hydrothermal vents at cracks between oceanic plates that spit chemicals like hydrogen sulfide.
Microorganisms use it to create organic matter via “chemosynthesis”, like plants use the sun for photosynthesis, which in turn fuels “exuberant” ecosystems, said Pierre-Marie Sarradin, head of the department. deep ecosystems at the French research agency Ifremer.
These hydrothermal vents were completely unknown until the 1970s.
Scientists have so far identified some 250,000 marine species, but there could still be at least a million yet to be discovered.
Could there be an elusive sea monster lurking in the depths? Despite being over 10 meters long, the colossal squid has been seen very rarely.
“I don’t think we’re going to find a megalodon,” Osborn said, referring to the shark’s giant ancestor.
Humans may not have explored the deep seas much, but they have left their mark, via global warming, overfishing and pollution.
Oceans are acidifying as they absorb more and more CO2, there is a growing prevalence of oxygen-free “dead zones”, while microplastics have been found in crustaceans nearly 11 kilometers deep in the Mariana Trench .
Food reaches the bottom in smaller amounts.
Nadine Le Bris said that species that “already live at the limits in terms of oxygen or temperature”, are already “disturbed”.
© 2022 AFP