Shrouded in darkness and mystery, the creatures of the deep ocean exist in a world of unlikely bounty, surviving on scarce food and under pressures that would crush human lungs.
This highly 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 an amazing array of extraterrestrial traits and idiosyncratic survival techniques.
A wide variety of animals populate the sunless depths, from the colossal octopus that coils its tentacles around the fantasies of sailors and storytellers, to beings with huge dim eyes or whose bodies are as transparent as glass.
And the monkfish, with its devilish appearance illuminated by a built-in headlamp, shows that the deep darkness is full of lights.
– “Incredible” Creatures –
Until the mid-19th century, scientists believed that life beyond a few hundred meters was impossible.
“They imagined there was nothing because of the lack 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 ft) the light fades until it disappears completely, taking plants with it; At 2,000 meters, the pressure is 200 times that of the atmosphere.
From the abyssal plains to the cavernous rifts deeper than Everest’s height, aquatic existence continues in spectacular diversity.
“When people think of the deep sea, they often think of the ocean floor,” said Karen Osborn of the Smithsonian’s Natural History Museum.
“But all the water in between is full of incredible animals. There is a lot of life.”
These open-water dwellers face a formidable challenge: they have nowhere to hide.
“There’s no algae to hide in, no caves or mud to dig in,” Osborn said.
“Predators come at them from below, from above, from everywhere.”
– Master of Disguise –
One tactic is to turn invisible.
Some creatures are red, making them difficult to distinguish in an environment where red light can no longer penetrate.
Others make themselves transparent.
Take, for example, the transparent, gossamer-thin worm, which ranges in size from a few millimeters to about a meter and swings through the water with fluttering ruffled limbs.
“You look like a fern frond,” Osborn said.
“They are beautiful animals, and they shoot yellow bioluminescent light from the tips of their arms. What could be better than that.”
Bioluminescence is particularly common in fish, squid and jellyfish species, according to the US National Oceanic and Atmospheric Administration, which says about 80 percent of animals that live between 200 and 1,000 meters produce their own light.
This chemical process could be helpful for defense, reproduction, or foraging — but no one knows exactly why so many creatures evolved it, says NOAA.
– “Sea Snow” –
With no plants around and animals scattered in the expanse, doing everything they can to disappear, creatures in the ocean depths often have trouble finding a living meal.
“If you’re lucky and hit a spot on your food, bingo! But you don’t see another one for maybe three weeks,” Osborn said.
Another option is to feast on the dead.
Organic particles from the surface waters—decayed animal and plant bodies that mix with feces—float down in what is known as “sea snow”.
This carcass confetti is part of a process that sequesters carbon dioxide in the ocean depths.
It’s also a lifeline for many deep-sea creatures, including the blood-red vampire squid, which contrary to its reputation, peacefully sucks up sea snow.
When giants sink to the ocean floor like dead whales, scavengers quickly break them down to bones.
– Last Frontier –
Since 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 sea floor on our own planet.
But unlike outer space, scientists continue to find life in even the most adverse conditions.
Like the scorching hydrothermal vents at the cracks between oceanic plates that spew out chemical compounds like hydrogen sulfide.
Microorganisms use this to create organic matter through “chemosynthesis,” just as plants use the sun for photosynthesis, which in turn feeds “exuberant” ecosystems, said Pierre-Marie Sarradin, head of the Deep Ecosystems department at French research agency Ifremer .
These hydrothermal vents were completely unknown until the 1970s.
Scientists have identified about 250,000 marine species so far, although there are at least a million yet to be discovered.
Could an elusive sea monster lurk in the depths? Despite being over 10 meters long, the colossal octopus has only very rarely been sighted.
“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 much of the deep sea, but they have made their mark through global warming, overfishing, and pollution.
Oceans are acidifying as they absorb more and more CO2, there are more and more “dead zones” without oxygen, and microplastics have been found in crustaceans at a depth of almost 11 kilometers in the Mariana Trench.
Food comes down in smaller amounts.
Nadine Le Bris said species that “already live at the oxygen or temperature limit” are already “disturbed”.
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