Life in the abyss, a spectacular and fragile struggle for survival
Cloaked in darkness and mystery, the creatures of the deep oceans live in a world of improbable abundance, surviving on scarce food and under pressure that would crush human lungs.
This extremely hostile environment, which will be in the spotlight this week at a major United Nations ocean summit in Lisbon, has led its inhabitants to develop a wondrous array of alien features and idiosyncratic survival techniques.
An enormous assortment of animals inhabit the sunless depths, from the colossal squid, which wrapped its tentacles around the imaginations of sailors and storytellers, to creatures with enormous cloudy eyes, or whose bodies are as transparent as glass.
And the fisherman, with his devilish appearance illuminated by a built-in headlight, shows that the deep dark is alive with lights.
Until the mid-19th century, scientists believed that life outside a few hundred meters was impossible.
“They thought there was nothing, because of the absence of light, the pressure, the cold and the lack of food,” Nadine Le Bris, a professor at Sorbonne University, told AFP.
Between 200 and 1,000 meters (650 to 3,300 feet), the light fades until it disappears completely, planting with it; at 2,000 meters, the pressure is 200 times that of the atmosphere.
From the abyssal plains to the cavernous gullies that plunge deeper than Everest is high, aquatic life continues in spectacular diversity.
“When people think of the deep sea, they often think of the seafloor,” says Karen Osborn of the Smithsonian’s Natural History Museum.
“But all that water in between is full of incredible animals. There’s a lot of life.”
These inhabitants of the open water face a huge challenge: they have nowhere to hide.
“There’s no seaweed to hide in, no caves or mud to dig in,” Osborn said.
“Predators are coming at them from below, from above, from everywhere.”
masters of disguise
One tactic is to become invisible.
Some creatures are red, making them difficult to distinguish in an environment where red light no longer filters through.
Others make themselves transparent.
Take the transparent gossamer worm, which ranges in size from a few millimeters to about a meter in length and moves through the water by fluttering its shaggy limbs.
“They look like a frond,” Osborn said.
“They are beautiful animals and they shoot yellow bioluminescent light from the tips of their arms. What could be more beautiful than that.”
Bioluminescence is especially common in fish, squid and jellyfish species, according to the U.S. National Oceanic and Atmospheric Administration, which says about 80 percent of animals living between 200 and 1,000 feet produce their own light.
This chemical process may be useful for defense, reproduction or finding food, but no one knows for sure why so many creatures evolved it, NOAA says.
Because there are no plants nearby and animals scattered across the expanse do their very best to disappear, creatures in the depths of the ocean often have a hard time finding a living meal.
“If you’re lucky and hit 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 the surface water – disintegrated bodies of animals and plants, mixed with feces – float down in what is known as “marine snow”.
This cadaver-like confetti is part of a process that traps carbon dioxide in the depths of the ocean.
It’s also a lifeline for many deep-sea creatures, including the blood-red vampire squid that, contrary to its reputation, peacefully soaks up marine snow.
When giants sink to the sea floor like dead whales, they are quickly reduced to bone by scavengers.
Because most of the oceans are still unexplored, it is often said that we know more about the surface of Mars than we do about the seafloor on our own planet.
But unlike space, scientists continue to find life even under the most hostile conditions.
Like the searing hydrothermal vents in the cracks between oceanic plates that spew chemical compounds like hydrogen sulfide.
Microorganisms use this to create organic matter via “chemosynthesis,” much like plants use the sun for photosynthesis, which in turn feeds “exuberant” ecosystems, said Pierre-Marie Sarradin, head of the Deep Ecosystems division at the French research firm Ifremer. .
These hydrothermal vents were totally unknown until the 1970s.
Scientists have identified some 250,000 marine species so far, although at least a million remain to be discovered.
Could there be an elusive sea monster lurking in the depths? Despite a length of more than 10 meters, the colossal squid is only very rarely seen.
“I don’t think we’ll find a megalodon,” Osborn said, referring to the shark’s giant ancestor.
Humans may not have explored much of the deep seas, but they have left their mark on global warming, overfishing and pollution.
Oceans are acidifying because they contain more and more CO . record2there is a growing prevalence of “dead zones” without oxygen, while microplastics have been found in crustaceans at a depth of almost 11 kilometers in the Mariana Trench.
Food reaches the bottom in smaller quantities.
Nadine Le Bris said species that are “already living at the limits in terms of oxygen or temperature” are already “disturbed”.
Video: Bioluminescence: Living light in the deep sea
© 2022 AFP
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