The abyssal bottoms , flatter than any of the immense plains that we find in America or Australia, extend from the ridges to the steep slopes that give rise to the continents. These bottoms are the largest habitat on the planet, a place, cold, dark and deep . In them the temperature is around freezing and the pressure is crushing . The conditions are so inhospitable that the living things that live there grow and reproduce slowly. The necessities for life, air to breathe and food to eat, are imported. Currents originating from the surface carry oxygen to the depths while the remains of plants and animals that sink to the bottom are consumed many times along their inevitable path to the depths. Anything that ends up reaching the bottom has lost virtually all of its nutritional value. That’s why deep-sea fish are designed to eat anything that’s edible.
It is not surprising that the inhabitants of the deep ocean are scarce : at 4,000 m from the surface the abundance of life has been reduced by 99%. But it is in those depths where living beings are found that seem to have come from another planet. And not just because of her looks. For example, near hydrothermal vents live some eyeless shrimp that seem to have a patch on their back: it is the vestige of an eye capable of detecting the subtle and almost imperceptible bursts of light that appear in the gas bubbles that arise from the interior. of the earth, or of the flashes of the fracture of mineral crystals. And there, in those murky depths, are photosynthetic organisms , too. But they do not use the light of a Sun that never arrives, but those same flashes. There is a sulphurous bacterium that lives bordering on its own survival and that divides very slowly, once every two or three years. Baptized with the nondescript name of GSB1 , it is the only known organism that carries out photosynthesis without the help of the Sun. Could life on other planets far from its star be similar to that of this bacterium?
At the center of the Atlantic Ocean is a hydrothermal vent field known as the Lost City, where every bit of limestone is home to 10 to 100 million microbes, proving that life can survive in impossible environments. They breathe methane, which opens a new window to the past, looking for clues about the first life on Earth. A little further from these sources we find the Lamellibrachia luymesi , a tube worm that lives 250 years.
And if we go to the Indian Ocean, on the Carlsberg ridge there is a volcano that, along 70 km and rising 1,400 m from the seabed, releases 4,540 km3 of water into the sea with each explosion, more than 100 times the water contained in the largest dam in the world (Three Gorges, China), and much more than the hydrothermal vents in the area release in a year. This ridge is the northern part of a broader one, the Central Indian, border between the African plate and the Indo-Australian plate. In it we find the Kairei fumarole field where a peculiar snail has been discovered. Unlike any mollusk today, it is more like the armored animals that first appeared 500 million years ago. His feet are covered in magnetic black scales that overlap like roof tiles. Their usefulness is not at all clear, perhaps they serve to repel the poison darts of predators. But whatever its use, a hydrothermal vent is a ripe environment for a snail in iron armor.
Close to Ascension Island , an island in the middle of the Atlantic and south of the equator inhabited only by the British and North American military and telecommunications operators (one of the five monitoring stations of the GPS system in the world is located there), we find the Turtle Pits fumarole field, right where the African and South American plates separate; there is the temperature record for a submarine hydrothermal source, 407 ºC. We might think that in environments like these it is impossible for life to prosper, but it is not. In the autoclave, the device used to sterilize surgical material and that reaches 250 ºC, the archaea Geogemma barossii, collected from a fumarole in the Pacific Northwest called Finn, not only survives in that device but in one day is capable of doubling your number.
Other beings, on the contrary, support the lowest known temperatures. In the Atlantic Ocean, 2,000 km from the Cape of Good Hope, lies Bouvet, a tiny ice-covered island that abruptly ends in sheer cliffs with black volcanic sand beaches. Disembarking is not easy and the best way to do it is from a helicopter. In 1928 the Norwegian ship Norvegia landed on the island in order to turn it into a refuge and store of provisions for shipwrecked sailors. Among the crew members was the ship’s biologist, Ditlef Rustad, a zoology student, who captured a curious fish : large eyes, a jaw full of teeth, long spines on the pectoral and tail and the most surprising thing, that when looking at it it gave the impression of being transparent. Examining it more carefully, he discovered that the appearance of this ” white crocodile fish ” was due to the fact that its blood had no color at all.
Champsocephalus gunnari , like many other fish that live in the cold Antarctic waters, does not have red blood cells . To reduce the increase in blood viscosity due to extremely low water temperatures, fish living near the piolos must reduce the density of red blood cells in the blood. In this way, if we have a hematocrit of 45%, they have lowered it from 15 to 18%. Well, this fish has taken the reduction to the extreme, so that its blood only carries 1% of cells, and all of them are white blood cells. Ice water literally runs through his veins. In addition , its heart, pale in color, is larger than that of the rest of the fish of its size. It also generates antifreeze proteins produced by the mutation of a gene that in the past encoded a digestive enzyme, thus preventing it from becoming an ice statue.
This is our seabed: a strange world, almost extraterrestrial.