deep sea


May 17, 2022

The deep sea is the part of the oceans deeper than approximately 500 to 1000 meters. No sunlight penetrates there, so no plants that depend on photosynthesis can grow. The pelagic zone between 1000 and 4000 meters depth is the bathyal zone and the pelagic zone from 4000 meters depth to the seabed is the abyssal zone. The hadale zone is below 6000 meters. Compared to research into the universe, little is known about the deep sea. For a long time, scientists believed that no life was possible in the deep seas. Today, scientific research has proven the opposite: the sea depths are the largest habitat on Earth. In this total darkness lives a unique deep-sea fauna, animals that are found nowhere else. Some deep-sea fish feed on dead animals and plants that sink to the bottom (sea snow). Other fish have huge jaws and long set back teeth to grab and swallow anything that swims by. These fish have a large, extensible stomach and can eat prey larger than themselves. At the bottom of the deep sea, deep-sea benthos such as anemones, worms, sea cucumbers, brittle stars, crabs, shrimps and other crustaceans live in the mud in search of food. Most of the fish that live here are bioluminescent, making their own light through a chemical reaction in photophores. The light can be bright, like a signal from the fish looking for a mate, or muted, like camouflage in twilight. Some of the fish species that live here include deep-sea eels, anglerfish, catch-toothed fish, mother-of-pearl fish, viper-toothed fish, lanternfish, sea lily, sea cucumber, deep-sea squid and several species of sea anemone.

Water pressure

Lay people sometimes assume that deep-sea fauna must be adapted to withstand the enormous water pressure, but that is not the case: inside their bodies there is the same pressure, so they cancel each other out. The situation is not significantly different from that of animals living near the sea's surface. Even life forms on the Earth's surface already experience the pressure of 10,000 kilograms of air per square meter and this too is compensated because the same pressure prevails inside plants and animals as outside. The situation is different with submarines: the air pressure inside is much lower than the outside pressure. These must be heavily armored and have a round shape as much as possible to withstand the pressure well.

Ascending and Descending

Life forms only encounter problems with water pressure when they rise or fall quickly: the inner pressure then becomes out of balance with the outer pressure. If the descent is too fast, the body will be compressed, if the rise is too fast, the body will swell up like a balloon. This manifests itself first and foremost in the gases in the body, which are easily compressible. The caisson disease is an expression of this. The sperm whale, which quickly dives to depths of up to three thousand meters during the hunt, does have adaptations to absorb the pressure difference. For example, the rib cage is flexible to allow the lungs to collapse, so that less nitrogen enters the lungs. In humans, nitrogen bubbles in the blood are a major cause of caisson disease.

External link

Census of Marine Life