To eat, hide from predators, cool off and control the route – scientists believe that for these reasons sea creatures sink deep into the seabed.
How to live miles under water?
To live at such depths, creatures have developed different anatomical and physiological characteristics. For example, they are covered in thick, insulating fat, their blood vessels function as heat exchange systems, and they have lungs that store oxygen and hypersensitive eyes.
Why do these creatures dive so deep?
To most biologists, the answer is obvious: food. However, this was very difficult to prove. After decades of research, there is ample evidence that many large predators dive so deep into the seabed in search of prey.
But food may not be the only factor. The behavior of deep-sea animals and the way they dive are different. Some dive many times an hour, others many times less.
Fish, turtles, sharks and, in general, most sea creatures, descend to a depth of 200 to 1,000 m. This area is called the mid-ocean, another name is the twilight zone.
Biologists have studied these dives and observed that they occur in different ways. For example, in one case, the animals sank quickly and also emerged quickly, and in the other, on the contrary, they swam slowly and for a long time. Scientists conclude that if creatures dive in different ways, then their goals are different.
There are many suggestions as to why one should dive slowly. One theory is that deep, dark water makes it easier to hide from predators or cool off. Biologists make various hypotheses, but none of them are dominant.
How to hide from a predator in the background?
The yellowfin tuna, Thunnus albacares, spends most of its time at 200 meters above the ocean. In 2020, biologist Tim Lam of the University of Massachusetts at Boston reported that six of the 17 tons he identified with special devices appeared to have encountered a predator.
Four tons dived abruptly to the bottom – three of them at a depth of about 1,000 meters, and then lost their marks. Another suddenly descended from a depth of 134 m to 1,592 m.
Elephant seals also seem to dive to great depths to dodge their enemies. During the study, biologist Selen Fregosi of Oregon State University attached labels to young elephant seals that produced unexpectedly different sounds, such as clicks and whistles from elephant seal enemies, killer whales, and killer whales. From these sounds, elephant seals began to dive sharply into the depths.
Last year, researchers reported that elephant seals not only hide in the dark, but also rest there. Most likely, these creatures will die if they live in the bright upper layers of the ocean, where sharks and killer whales are often found. The researchers found that they prefer to rest at a depth of several hundred meters. And the more mature and strong a person becomes, the deeper he sinks.
Which creatures live in the deepest depths?
Almost all vertebrate species in the oceans can swim in the deep. This is done by large vertebrate fish such as tuna and swordfish. Dive on sharks and rays, as well as air-breathing animals – penguins, sea turtles, toothed whales and seals. All this can reach amazing depths with just one breath of air.
Most of them dive so deep that they reach the twilight zone, where the light almost disappears. Some even sink into the darkness of the midnight zone – this is the deep sea zone, which starts from a depth of 1,000 to 4,000 m.
The current record for the deepest swim is the Cuvier whale, which reached 2,992 meters off the coast of Southern California in 2014. The fish catch record belongs to the whale shark, which in 2010 sank 1,928 meters in the Col. .
In the 19th century, naturalists believed that few people lived at depths of more than 500 meters, but in the 1940s, Navy sonar pilots discovered a zone in which their device recorded many mesoplagous organisms. This nutrient-rich mattress moved up and down: at night, the organisms emerged to feed and returned to deep water during the day.
In the twilight zone of the ocean, there were unexpectedly many different living creatures: muscular squid, lantern fish and hairy teeth. In 1980, fisheries scientists estimated global biomass of Mediterranean fish at one billion metric tons. In 2014, a study based on acoustic research showed that the rate should be 7 to 10 times higher.
Why else do marine animals dive so deep?
Another common theory is about navigation. Almost all large marine predators migrate at some point in their lives, and these are huge distances.
It is known that some of them, including sharks and turtles, can receive signals from the Earth’s magnetic field and also perceive magnetic power and anomalies.
If the animal senses this signal, then it can dive deeper to enhance perception. For example, leatherback turtles dive to extreme depths during large migrations. This is supposed to control the route.
There is only one example of a species that dives to cool off. Atlantic bluefin tuna spend several months each year in the icy waters of the temperate zone and have developed an extremely effective way to keep their bodies warm.
The latest theory is that at great depths, sea creatures communicate more comfortably. In an area ranging from hundreds to several thousand meters, the sound spreads further. When blue whales and humpback whales are in this area, they can hear each other from about 1,700 kilometers away. But scientists still do not know if they swim to such depths for this purpose.
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