Deep scattering layer

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Static image of a sonar scan. The backscattered signal (green) above the bottom is likely the deep scattering layer. Static image of sonar data scan.jpg
Static image of a sonar scan. The backscattered signal (green) above the bottom is likely the deep scattering layer.
The swim bladder (marked here as S and S') of Alburnoides bipunctatus. The swim bladders of large numbers of mesopelagic fishes cause sonar waves to be reflected in a recognisable layer PSM V20 D769 Longitudonal section of a bleak.jpg
The swim bladder (marked here as S and S') of Alburnoides bipunctatus. The swim bladders of large numbers of mesopelagic fishes cause sonar waves to be reflected in a recognisable layer

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. 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. For this reason it is sometimes called the false bottom or phantom bottom. It can be seen to rise and fall each day in keeping with diel vertical migration.

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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. Initially, this mysterious phenomenon was called the ECR layer using the initials of its three discoverers. [2] It turned out to be due to millions of marine organisms, most particularly small mesopelagic fish, with swim bladders that reflected the sonar. These organisms migrate up into shallower water at dusk to feed on plankton. The layer is deeper when the moon is out, and can become shallower when clouds pass over the moon. [3] Lanternfish account for much of the biomass 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. [4]

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 California headlightfish.png
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

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. [5] [6] The name is derived from the fact that the first people to see these measurements erroneously reported that they had discovered sunken islands. [6] Most mesopelagic fishes are small filter feeders which ascend at night to feed in the nutrient rich waters of the epipelagic zone. During the day, they return to the dark, cold, oxygen deficient waters of the mesopelagic where they are relatively safe from predators. [6]

Most mesopelagic organisms, including mesopelagic fish, squid and siphonophores, make daily vertical migrations. 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. [7] [8] [9] These vertical migrations often occur over large vertical distances. Fish undertake these migrations with the assistance of a swimbladder. 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. As the fish ascends, the pressure in the swimbladder must adjust to prevent it from bursting. When the fish wants to return to the depths, the swimbladder is deflated. [10] Some mesopelagic fishes make daily migrations through the thermocline, where the temperature changes between 10 and 20 °C, thus displaying considerable tolerances for temperature change.

In 1998, sampling via deep trawling indicated lanternfish account for as much as 65% of all deep sea fish biomass. [11] Lanternfish are among the most widely distributed, populous, and diverse of all vertebrates, playing an important ecological role as prey for larger organisms. The previous estimated global biomass of lanternfish was 550–660 million tonnes, about six times the annual tonnage captured worldwide by fisheries. However, this was revised upwards as these fish have a special gland for detecting movement from up to 30 metres away (e.g. fishing nets and fish sampling nets). In 2007 global sonar detectors indicated a more accurate figure for the global biomass was between 5,000 and 10,000 million tonnes: a truly massive weight of living mass. [4] [12]

Time lapse video of a 3-D mapping of water column sonar data by the NOAA research ship Okeanos Explorer in the North Atlantic Ocean [1]

See also

Related Research Articles

<span class="mw-page-title-main">Deep-sea fish</span> Fauna found in deep-sea areas

Deep-sea fish are fish that live in the darkness below the sunlit surface waters, that is below the epipelagic or photic zone of the sea. The lanternfish is, by far, the most common deep-sea fish. Other deep-sea fishes include the flashlight fish, cookiecutter shark, bristlemouths, anglerfish, viperfish, and some species of eelpout.

The aphotic zone is the portion of a lake or ocean where there is little or no sunlight. It is formally defined as the depths beyond which less than 1 percent of sunlight penetrates. Above the aphotic zone is the photic zone, which consists of the euphotic zone and the disphotic zone. The euphotic zone is the layer of water in which there is enough light for net photosynthesis to occur. The disphotic zone, also known as the twilight zone, is the layer of water with enough light for predators to see but not enough for the rate of photosynthesis to be greater than the rate of respiration.

<span class="mw-page-title-main">Swim bladder</span> Gas-filled organ that contributes to the ability of a fish to control its buoyancy

The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish to control their buoyancy, and thus to stay at their current water depth without having to expend energy in swimming. Also, the dorsal position of the swim bladder means that the expansion of the bladder moves the center of mass downwards, allowing it to act as a stabilizing agent in some species. Additionally, the swim bladder functions as a resonating chamber, to produce or receive sound.

The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word pelagic is derived from Ancient Greek πέλαγος (pélagos) 'open sea'. The pelagic zone can be thought of as an imaginary cylinder or water column between the surface of the sea and the bottom. Conditions in the water column change with depth: pressure increases; temperature and light decrease; salinity, oxygen, micronutrients all change. Somewhat analogous to stratification in the Earth's atmosphere, but depending on how deep the water is, the water column can be divided vertically into up to five different layers.

The mesopelagiczone, also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins at the depth where only 1% of incident light reaches and ends where there is no light; the depths of this zone are between approximately 200 to 1,000 meters below the ocean surface.

The bathypelagic zone or bathyal zone is the part of the open ocean that extends from a depth of 1,000 to 4,000 m below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypelagic is also known as the midnight zone because of the lack of sunlight; this feature does not allow for photosynthesis-driven primary production, preventing growth of phytoplankton or aquatic plants. Although larger by volume than the photic zone, human knowledge of the bathypelagic zone remains limited by ability to explore the deep ocean.

<span class="mw-page-title-main">Benthic zone</span> Ecological region at the lowest level of a body of water

The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "the depths." Organisms living in this zone are called benthos and include microorganisms as well as larger invertebrates, such as crustaceans and polychaetes. Organisms here generally live in close relationship with the substrate and many are permanently attached to the bottom. The benthic boundary layer, which includes the bottom layer of water and the uppermost layer of sediment directly influenced by the overlying water, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, and bay mud.

<span class="mw-page-title-main">Lanternfish</span> Family of fishes

Lanternfish are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. Lanternfishes are aptly named after their conspicuous use of bioluminescence. Their sister family, the Neoscopelidae, are much fewer in number but superficially very similar; at least one neoscopelid shares the common name "lanternfish": the large-scaled lantern fish, Neoscopelus macrolepidotus.

<span class="mw-page-title-main">Pelagic fish</span> Fish in the pelagic zone of ocean waters

Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs.

<span class="mw-page-title-main">Demersal fish</span> Fish that live and feed on or near the bottom of seas or lakes

Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes. They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks. In coastal waters they are found on or near the continental shelf, and in deep waters they are found on or near the continental slope or along the continental rise. They are not generally found in the deepest waters, such as abyssal depths or on the abyssal plain, but they can be found around seamounts and islands. The word demersal comes from the Latin demergere, which means to sink.

<span class="mw-page-title-main">Viperfish</span> Genus of fishes

A viperfish is any species of marine fish in the genus Chauliodus. Viperfishes are mostly found in the mesopelagic zone and are characterized by long, needle-like teeth and hinged lower jaws. A typical viperfish grows to lengths of 30 cm (12 in). Viperfishes undergo diel vertical migration and are found all around the world in tropical and temperate oceans. Viperfishes are capable of bioluminescence and possess photophores along the ventral side of their body, likely used to camouflage them by blending in with the less than 1% of light that reaches to below 200 meters depth.

<span class="mw-page-title-main">Mueller's pearlside</span> Species of fish

Maurolicus muelleri, commonly referred to as Mueller's pearlside,Mueller's bristle-mouth fish, or the silvery lightfish, is a marine hatchetfish in the genus Maurolicus, found in deep tropical, subtropical and temperate waters of the Pacific Ocean and the Atlantic Ocean, from the surface to depths of 1,500 metres (4,900 ft). It can grow to a maximum total length of 8 centimetres (3.1 in).

<i>Electrona</i> (fish) Genus of fishes

Electrona is a genus of lanternfishes in the family Myctophidae.

<span class="mw-page-title-main">Warming's lantern fish</span> Species of fish

Warming's lantern fish, Ceratoscopelus warmingii, is a lanternfish of the family Myctophidae, found circumglobally in both hemispheres, at depths of between 700 and 1,500 m during the day and between 20 and 200 m at night. Its length is about 8 cm (3.15 in).

<span class="mw-page-title-main">Diel vertical migration</span> A pattern of daily vertical movement characteristic of many aquatic species

Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" comes from Latin: diēs, lit. 'day', and refers to a 24-hour period. The migration occurs when organisms move up to the uppermost layer of the water at night and return to the bottom of the daylight zone of the oceans or to the dense, bottom layer of lakes during the day. DVM is important to the functioning of deep-sea food webs and the biologically-driven sequestration of carbon.

<span class="mw-page-title-main">Deep-sea community</span> Groups of organisms living deep below the sea surface, sharing a habitat

A deep-sea community is any community of organisms associated by a shared habitat in the deep sea. Deep sea communities remain largely unexplored, due to the technological and logistical challenges and expense involved in visiting this remote biome. Because of the unique challenges, it was long believed that little life existed in this hostile environment. Since the 19th century however, research has demonstrated that significant biodiversity exists in the deep sea.

<span class="mw-page-title-main">Oceanic zone</span> Part of the ocean beyond the continental shelf

The oceanic zone is typically defined as the area of the ocean lying beyond the continental shelf, but operationally is often referred to as beginning where the water depths drop to below 200 metres (660 ft), seaward from the coast into the open ocean with its pelagic zone.

<i>Cyclothone</i> Genus of fishes

Cyclothone is a genus containing 13 extant species of bioluminescent fish, commonly known as 'bristlemouths' or 'bristlefishes' due to their shared characteristic of sharp, bristle-like teeth. These fishes typically grow to around 1-3 inches, though some can be larger. They are most commonly found in the mesopelagic zone of the ocean, mostly at depths of over 300 meters, and many species have bioluminescence.

<i>Galiteuthis glacialis</i> Species of squid

Galiteuthis glacialis is a species of glass squid from the Antarctic Convergence. It is in the cranchiidae family and subfamily taoniinae. They are endemic to the Antarctic and are found in the Southern Ocean, around the Weddell Sea and the South Shetland Islands. Galiteuthis glacialis are one of the most plentiful and widely dispersed species of Antarctic squid. These squids are found in the mesopelagic and bathypelagic layers of the open ocean and demonstrate vertical migration. They can reach a maximum mantle length of 500 mm (0.5m).

A micronekton is a group of organisms of 2 to 20 cm in size which are able to swim independently of ocean currents. The word 'nekton' is derived from the Greek νήκτον, translit. nekton, meaning "to swim", and was coined by Ernst Haeckel in 1890.

References

  1. 1 2 Water Column Sonar Data National Geophysical Data Center, NOAA.
  2. ↑ Carson, Rachel (2011) [1951]. The Sea Around Us . Open Road Media. ISBN   978-1-4532-1476-3. The discovery was made by three scientists, C. F. Eyring, R. J. Christensen, and R. W. Raitt, aboard the USS Jasper in 1942...
  3. ↑ Ryan P "Deep-sea creatures: The mesopelagic zone" Te Ara - the Encyclopedia of New Zealand. Updated 21 September 2007.
  4. 1 2 R. Cornejo, R. Koppelmann & T. Sutton. "Deep-sea fish diversity and ecology in the benthic boundary layer". Archived from the original on 27 September 2007.
  5. ↑ Rachel Carson (29 March 2011). The Sea Around Us. Open Road Media. pp. 33–36. ISBN   978-1-4532-1476-3 . Retrieved 20 June 2013.
  6. 1 2 3 Rachel Carson (1999). Lost Woods: The Discovered Writing of Rachel Carson. Beacon Press. p. 81. ISBN   978-0-8070-8547-9 . Retrieved 20 June 2013.
  7. ↑ Moyle and Cech, 2004, p. 585
  8. ↑ Bone & Moore 2008, p. 38.
  9. ↑ Barham EG (May 1963). "Siphonophores and the Deep Scattering Layer". Science. 140 (3568): 826–828. Bibcode:1963Sci...140..826B. doi:10.1126/science.140.3568.826. PMID   17746436. S2CID   43485719.
  10. ↑ Douglas EL, Friedl WA and Pickwell GV (1976) "Fishes in oxygen-minimum zones: blood oxygenation characteristics" Science, 191 (4230) 957–959.
  11. ↑ Hulley, P. Alexander (1998). Paxton, J.R.; Eschmeyer, W.N. (eds.). Encyclopedia of Fishes. San Diego: Academic Press. pp. 127–128. ISBN   978-0-12-547665-2.
  12. ↑ Rowan at Facts in Motion. "How this tiny fish is cooling the planet". YouTube .

Further references

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