The creatures of the abyssal plains are not only those in the ecosystems found in the “oases” without sunlight represented by the hydrothermal sources and the hydrocarbon seeps. In the ocean depths, a strange fauna, perfectly adapted to its surroundings, evolves in complete tranquillity. At the present time, scientists estimate the number of these species at several thousand, even several tens of thousands.
Even though they live in darkness, all these animals depend indirectly on the sun’s energy. Indeed, at the base of their food chain, one finds residues of plants or animal corpses which have fallen to those depths by gravity. Therefore, these inhabitants of the abyssal plains owe their survival to organic matter resulting from photosynthesis on the surface.
Portrait gallery
A presentation of several examples of the strange creatures of the abyssal plains, during an extended dive to the ocean floor.
At a depth of 500 meters, the light is so feeble that human eyes cannot detect it. Certain living creatures, adapted to these conditions, have developed enormous eyes in the course of evolution that are capable of capturing the tiniest light source. Others, jellyfish for example, are capable of producing light, a phenomenon known as bioluminescence.
From a depth of 1000 meters the sun’s light is totally absent. The temperature falls below 4°C and the pressure is 100 times greater than at the surface (100 kg/cm²). Among the creatures that one finds at these depths, the lantern fish constitutes, without any doubt, one of the most abundant species. It measures 10 to 15 cm in length and agitates a luminous lure about its head. The light is produced by bacteria living inside that organ. This veritable tiny lantern enables the fish to attract prey towards its wide open mouth. It is also very useful for attracting sexual partners.
To feed themselves, certain animals adopt a strategy which allows them to economise on their energy. They wait absolutely immobile while their prey come to them. It is the case of the sea devil. This predator, 60 cm in width, is bristling with 100 sensitive antennae by means of which it can detect the least movement. Another example: the saccopharynx. Its form is very surprising. It possesses an extremely sensitive tail, 1 meter in length, and its head accounts for a quarter of its body. The saccopharynx waits without moving, its jaws wide open and swallows everything which comes into its range. Its special physiognomy enables it to gulp down prey as big as itself.
At a depth of 4000 meters, on the oceanic floor, the pressure can reach 400 times that at the surface (400kg/cm²). Food is scarce. Only 3% of the organic matter produced at the surface arrives in the ocean deeps. Numerous species manage to feed themselves on it by sucking in the sediments to extract the comestible particles. Sea cucumbers are examples of those animals which patrol the ocean floor in search of food.
Even fish can be found at these depths, for example the tripod fish. Its fins end in very long rays. Two of them, situated at the back of the animal’s head, are extremely sensitive and allow it to pinpoint its prey.
The marine depths cover 70% of the Earth’s surface. Less than 5% of the oceans have been explored as at today. In other words, at a time when we are looking for the presence of water on Mars, more than half of our planet remains to be explored. It its absolutely certain that the world of the abyssal plains reserves many more surprises for scientists …
Did you know?
- When a sperm whale dives to a depth of 1000 meters, it finds itself in surroundings subjected to a pressure 100 times greater than that it finds at the surface. Its lungs are reduced to 1% of their surface volume.
- The mythic architeuthis, the giant squid, leaves scientists frustrated. This 18 meter-long invertebrate has never yet been observed alive. Until now, researchers have had to be content to study dead specimens thrown up on the beaches or fished from depths that can reach 1000 meters.
- Fish from these enormous depths are impossible to study in a laboratory. Indeed, once raised to the surface, the temperature change is generally fatal to them.
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