11/13/2023 0 Comments Nocturnal definition oceanography![]() As the fish ascends, the pressure in the swimbladder must adjust to prevent it from bursting. The swimbladder is inflated when the fish wants to move up, and, due to the high pressures in the mesopelegic zone, this requires significant energy. Fish undertake these migrations with the assistance of a swimbladder. These vertical migrations often occur over large vertical distances. They ascend at night into the shallow epipelagic zone, often following similar migrations of zooplankton, and return to the mesopelagic depths for safety when there is daylight. Most mesopelagic organisms, including mesopelagic fish, squid and siphonophores, make daily vertical migrations. During the day, they return to the dark, cold, oxygen deficient waters of the mesopelagic where they are relatively safe from predators. Most mesopelagic fishes are small filter feeders which ascend at night to feed in the nutrient rich waters of the epipelagic zone. The name is derived from the fact that the first people to see these measurements erroneously reported that they had discovered sunken islands. The phantom bottom is caused by the sonar misinterpreting as the ocean floor a layer of small seagoing creatures that congregate between 1,000 and 1,500 feet (300 and 460 m) below the surface. Description Lanternfish account for as much as 65 percent of all deep sea fish biomass and are largely responsible for the deep scattering layer of the world's oceans Sonar reflects off the millions of lanternfish swim bladders, giving the appearance of a false bottom. ![]() Lanternfish account for much of the biomass responsible for the deep scattering layer of the world's oceans. The layer is deeper when the moon is out, and can become shallower when clouds pass over the moon. These organisms migrate up into shallower water at dusk to feed on plankton. It turned out to be due to millions of marine organisms, most particularly small mesopelagic fish, with swim bladders that reflected the sonar. Initially, this mysterious phenomenon was called the ECR layer using the initials of its three discoverers. Sonar operators, using the newly developed sonar technology during World War II, were puzzled by what appeared to be a false sea floor 300–500 metres (980–1,640 ft) deep at day, and less deep at night. It can be seen to rise and fall each day in keeping with diel vertical migration. For this reason it is sometimes called the false bottom or phantom bottom. It was discovered through the use of sonar, as ships found a layer that scattered the sound and was thus sometimes mistaken for the seabed. The deep scattering layer, sometimes referred to as the sound scattering layer, is a layer in the ocean consisting of a variety of marine animals. The swim bladders of large numbers of mesopelagic fishes cause sonar waves to be reflected in a recognisable layer The swim bladder (marked here as S and S') of Alburnoides bipunctatus. The backscattered signal (green) above the bottom is likely the deep scattering layer.
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