The unknown life in the depths of the ocean

The ocean remains the great unknown. Not even 20% of the seabed has been explored. We know the Moon better and, every day more,
Mars, than what is under the layer of water that covers 70% of our planet. The reason this is so is that the ocean is difficult to explore and there has been little technology to do so until very recently.

The life it harbors is another mystery. Biologists calculate that they contain 80% of the life on our planet, with thousands, perhaps millions of species yet to be discovered, described and known. Especially in its depths. In fact, it was not until 1864 that Norwegian researchers such as Georg Ossian Sars obtained samples of life more than 3,100 meters deep. Until then, the general idea was that in the depths of the ocean there was no life, since there was no light for photosynthesis.

From that moment on, the discoveries that have been showing us forms of life that seem strange to us, adapted to the enormous pressure, darkness and cold of the deep sea, multiplied.

The deepest layers of the ocean

For study, the ocean is divided into three main zones. The first is the
sunlight layer, which reaches a depth of 200 meters. It is approximately 5% of the average depth of the oceans and fishing activity is carried out there as well as being where algae and other forms of plant life produce around 50% of all the oxygen on the planet. Between 200 and 1,000 meters is the
twilight zone, where enough light reaches for photosynthesis to take place and where about 25% of the carbon dioxide produced by human activity is absorbed. And it is here that the first amazing bioluminescent creatures were seen.

Until 1864 the general idea was that in the depths of the ocean there was no life, since there was no light for photosynthesis

Below a thousand meters, the deep ocean is further subdivided into the
midnight zone (up to 4,000 meters), the abyss, which reaches up to 6,000 meters and is on average the ocean floor, and the trenches, areas of great depth, the largest of which is the Mariana Islands trench, which reaches 11,034 meters. And even there, more than 200 microorganisms and small crustaceans have been identified that live and reproduce in its icy waters, with high acidity and enormous pressure, without ever seeing the light of their existence. And as for fish, they have been identified in several trenches living at depths of more than 8,000 meters, which means that species cannot be ruled out even lower.

After all, a total of 12 people have walked the surface of the Moon while only three have reached the deepest depths of the sea: Jacques Piccard and Don Walsh in 1960, and film director James Cameron in 2012.

Who lives?

In the competition for the strangest beings on the planet, at least from our point of view, the bacteria that produce energy from chemical reactions that they carry out with the mineral substances that expel the hydrothermal vents from the bottom of the ocean together have a very prominent place. with water at temperatures of up to 400 degrees Celsius, hot enough to melt lead. These hydrothermal sources were not discovered until 1977 and, with them, the bacteria that use them as substitutes for photosynthesis and that live in symbiosis with various species of clams, mussels, shrimp and worms, providing them with nutrients.

By studying tube worms called Riftia pachyptila around a hydrothermal vent, the researchers found that the hemoglobin in their blood was able to bind oxygen and hydrogen sulfide from the vents, which bacteria living in their tissues use. to create its organic matter, which is the subsequent food of the worm. Photosynthesis is replaced by various forms of chemosynthesis.

It was this discovery that abandoned the idea that sunlight was essential for life and, in the process, reminded us that the adaptability of life is always greater than even science fiction writers imagine.

The secrets that a simple grain of sand reveals to us

The most colorful inhabitants of the abyssal depths are, without a doubt, the beings capable of emitting light using different procedures. Among the best known are the lofiform fish of the depths; relatives of the anglerfish that use a lure evolved from the first spine of its dorsal fin and in which, in symbiosis with the fish, live bacteria that have a gene, called 'lux', that allows them to synthesize proteins that emit light that It lures prey into the fish's sharp-toothed mouths.

Bioluminescence is not only a feeding strategy... different animals use it to surprise, attract attention or seek a mate or, in the highest layers of the dark zone of the ocean, to camouflage themselves by imitating the little light that comes from the surface.

Much of the food that the beings of the depths have comes from the death of others in more superficial layers. A dead whale is a feast for literally hundreds of species of crustaceans, mollusks, fish, and other creatures that take advantage of its organic matter. The smallest pieces of organic matter that reach the bottom are known as 'sea snow'.

Many fish and the tiny beings that make up zooplankton travel from the deepest areas to the surface every day to feed, usually at night, only to return to the shelter of their dark domains during the day. Giant squid, whose habitat is the deep, carry out these vertical migrations, causing otherwise unfounded alarms.

The so-called sea angels stand out, whose transparent bodies and the protuberances with which they swim, which resemble small wings, are visually attractive. These are slugs that in their evolution have left behind not only the shell of the snails, but also their old space on the sea floor, to travel the waters in search of prey.

Keep investigating

Much of what remains to be discovered is at risk like all life on the planet. Climate change, acidification and deoxygenation of the oceans, affect the seabed, but this, according to researchers such as those of the National Oceanographic Partnership Program in the US, can teach us a lot about how to mitigate and prevent the consequences of our actions.

We can also find large arthropods related to the cochineal and very similar to it, but up to 40 cm long, called giant isopods. Other giants are the siphonophores, relatives of jellyfish that can measure up to 40 meters long with the appearance of a rope deposited on the seabed and that use bioluminescence to capture the fish that feed them.

And so much remains to be discovered...

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