Minimum depth of occurrence

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The minimum depth of occurrence (MDO) is the shallowest depth in the ocean at which a species is observed. Because some aberrant individuals often can be found far outside their typical depth range, the MDO is sometimes defined as the depth below which 90% of individuals are observed or captured. [1] In practice, observations of pelagic organisms are limited to trawling at a known depth, scuba diving observations, or use of underwater vehicles such as ROVs or AUVs. A species' MDO can change throughout ontogeny if the species is an ontogenetic vertical migrator; that is, it changes its habitat depth as it matures (typically descending deeper with increased maturity). Additionally, some species undergo diel vertical migration in which they migrate vertically each day. In these taxa, the MDO is defined based on their shallowest depth during their diel migration.

Ocean A body of water that composes much of a planets hydrosphere

An ocean is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. The word "ocean" is often used interchangeably with "sea" in American English. Strictly speaking, a sea is a body of water partly or fully enclosed by land, though "the sea" refers also to the oceans.

In biology, a species ( ) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.

Trawling

Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl.

Relation to metabolic rate

For pelagic visually oriented organisms such as cephalopods, fishes, and crustaceans, metabolic rate decreases with increasing minimum depth of occurrence (MDO). [1] [2] In other words, the shallower an organism ever has to go, the higher its metabolic rate must be. This is because inhabiting shallow waters requires locomotory ability to evade visually-hunting predators and function well as a visual predator on one's own prey. The visual-interactions hypothesis is the idea that many pelagic animals in the ocean have decreasing activity levels and metabolic rates with increasing minimum-depth of occurrence (MDO) due to decreasing light levels. According to this hypothesis, [3] high metabolic rates are not an asset but a high cost to an organism, unless that high metabolic rate is necessary for survival. In well-lit euphotic waters, a high metabolic rate is advantageous because it helps an organism both avoid visually hunting predators and perform well as a visual predator itself. At depths below the euphotic zone, however, the efficiency of visual predation is substantially lessened, and thus high metabolic rates are no longer strongly selected.

Organism Any individual living physical entity

In biology, an organism is any individual entity that exhibits the properties of life. It is a synonym for "life form".

Predation A biological interaction where a predator kills and eats a prey organism

Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism. It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as a seed predator is both a predator and a herbivore.

Light electromagnetic radiation in or near visible spectrum

Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared and the ultraviolet. This wavelength means a frequency range of roughly 430–750 terahertz (THz).

In addition to light levels, other factors (notably food limitation, oxygen, temperature, and pressure) are sometimes ascribed to be the driver of low metabolic rates in the deep sea. It has been well demonstrated, however, that the decrease in metabolic rate with depth is indeed due to visual predation rather than other factors. [3] Firstly, the decline in metabolic rate is only observed in visually hunting predators such as most fishes, cephalopods, and crustaceans. Gelatinous zooplankton such as chaetognaths and jellies, for example, are semi-transparent and are not visual hunters themselves and thus their metabolic rate is light-independent. Seibel et al. (2007) assessed the merits of these factors on impacting the relationship between metabolic rate and MDO and found decreasing light to be the dominating factor. [4] Their evidence was as follows:

Oxygen Chemical element with atomic number 8

Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.

Temperature physical property of matter that quantitatively expresses the common notions of hot and cold

Temperature is a physical quantity expressing hot and cold. It is measured with a thermometer calibrated in one or more temperature scales. The most commonly used scales are the Celsius scale, Fahrenheit scale, and Kelvin scale. The kelvin is the unit of temperature in the International System of Units (SI), in which temperature is one of the seven fundamental base quantities. The Kelvin scale is widely used in science and technology.

Pressure Force distributed continuously over an area

Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.

Antarctica Polar continent in the Earths southern hemisphere

Antarctica is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. At 14,200,000 square kilometres, it is the fifth-largest continent. For comparison, Antarctica is nearly twice the size of Australia. About 98% of Antarctica is covered by ice that averages 1.9 km in thickness, which extends to all but the northernmost reaches of the Antarctic Peninsula.

The relationship between MDO and metabolic rate is similar for both aerobic and anaerobic potential. [5] While hiding is a good primary defense, if this fails, the organisms still need to be able to quickly escape from a predator. Thus, anaerobic potential must stay high in the high predatory-risk epipelagic, but can drop off in the less risky darker depths.

Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.

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Andaman Sea Marginal sea of the eastern Indian Ocean

The Andaman Sea is a marginal sea of the eastern Indian Ocean separated from the Bay of Bengal by the Andaman Islands of India and Myanmar and the Nicobar Islands of India and touching Myanmar, Thailand, and the Malay Peninsula. Its southernmost end is defined by Breueh Island, an island just north of Sumatra.

Benthos community of organisms which live on, in, or near the seabed

Benthos is the community of organisms that live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.

Deep sea fish

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.

Vampire squid species of mollusc

The vampire squid is a small cephalopod found throughout temperate and tropical oceans in extreme deep sea conditions. Unique retractile sensory filaments justify the vampire squid's placement in its own order, Vampyromorphida, as it shares similarities with both octopuses and squid. As a phylogenetic relict, it is the only known surviving member of its order. The first specimens were collected on the Valdivia Expedition and they were originally described as an octopus in 1903 by German teuthologist Carl Chun, but later assigned to a new order together with several extinct taxa.

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), meaning 'open sea'. The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes from the surface of the sea almost to the bottom. Conditions differ deeper in the water column such that as pressure increases with depth, the temperature drops and less light penetrates. Depending on the depth, the water column, rather like the Earth's atmosphere, may be divided into different layers.

Mesopelagic zone

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 1000 meters below the ocean surface. It hosts a diverse biological community that includes bristlemouths, blobfish, bioluminescent jellyfish, giant squid, and a myriad of other unique organisms adapted to live in a low-light environment. It has long captivated the imagination of scientists, artists and writers; deep sea creatures are prominent in popular culture, particularly as horror movie villains.

Gonatidae family of molluscs

The Gonatidae, also known as armhook squid, are a family of moderately sized squid. The family contains about 19 species in three genera, widely distributed and plentiful in cold boreal waters of the Pacific Ocean. At least one species is known from Antarctic waters, and two from the North Atlantic. The genus Eogonatus was created for the species known as Eogonatus tinro because it did not have hooks on the tentacular club and it has 5 rows of teeth on the radula. Molecular studies in allozymes and mitochondrial DNA have indicated that this species nests within the genus Gonatus, although other authorities treat it as a synonym of Gonatopsis okutanii.

Oxygen minimum zone The zone in which oxygen saturation in seawater in the ocean is at its lowest

The Oxygen minimum zone (OMZ), sometimes referred to as the shadow zone, is the zone in which oxygen saturation in seawater in the ocean is at its lowest. This zone occurs at depths of about 200 to 1,500 m (660–4,920 ft), depending on local circumstances. OMZs are found worldwide, typically along the western coast of continents, in areas where an interplay of physical and biological processes concurrently lower the oxygen concentration and restrict the water from mixing with surrounding waters, creating a “pool” of water where oxygen concentrations fall from the normal range of 4–6 mg/l to below 2 mg/l.

Meroplankton organisms that are planktonic for only a part of their life cycles

Meroplankton is a wide variety of planktonic organisms, which spend a portion of their lives in the benthic region of the ocean. These organisms do not remain as plankton permanently, rather, they are planktonic components in transition, which eventually become larger organisms. After a period of time in the plankton, meroplankton either graduate to the nekton or adopt a benthic lifestyle on the seafloor. Meroplankton consists of larval stages of organisms such as sea urchins, starfish, and crustaceans. Success of meroplankton populations depends on many factors, such as adult fecundity, fertilization success, growth and larval stage duration, behaviour, dispersal, and settlement. Mortality depends on many factors, such as predation, competition, disease, parasites, and physiological stresses. Survival and mortality of meroplankton has a direct effect on adult population numbers of many species. Many of the common, well-known animals found on the Great Barrier Reef spend time as free-swimming meroplankton, bearing little or no resemblance to the adult they will become. The differences between the appearance of larval and adult stages led to much confusion in the past when larval forms were often believed to be completely different species from the adults. Larvae spend varying amounts of time in the plankton, from minutes to over a year. However, just how long these tiny animals can be considered truly planktonic is under some debate.

The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – is the part of the pelagic zone 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 average temperature hovers at about 4 °C (39 °F). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated. Sunlight does not reach this zone, meaning primary production, if any, is almost nonexistent. There are no known plants because of the lack of sunlight necessary for photosynthesis. It is known as the midnight zone because of this feature.

Pelagic fish Fish living in the pelagic zone of ocean or lake waters – being neither close to the bottom nor near the shore

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, which do live on or near the bottom, and reef fish, which are associated with coral reefs.

A lake ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions.

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 migration occurs when organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone of lakes during the day. The word diel comes from the Latin dies day, and means a 24-hour period. In terms of biomass, it is the greatest migration in the world. It is not restricted to any one taxa as examples are known from crustaceans (copepods), molluscs (squid), and ray-finned fishes (trout). Various stimuli are responsible for this phenomenon, the most prominent being response to changes in light intensity, though evidence suggests that biological clocks are an underlying stimulus as well. The phenomenon may arise for a number of reasons, though it is most typically to access food and avoid predators. While this mass migration is generally nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, the timing can be altered in response to the different cues and stimuli that trigger it. Some unusual events impact vertical migration: DVM is absent during the midnight sun in Arctic regions and vertical migration can occur suddenly during a solar eclipse.

Marine larval ecology is the study of the factors influencing dispersing larvae, which many marine invertebrates and fishes have. Marine animals with a larva typically release many larvae into the water column, where the larvae develop before metamorphosing into adults.

This is a glossary of terms used in fisheries, fisheries management and fisheries science.

Deep sea community 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.

Underwater camouflage

Underwater camouflage is the set of methods of achieving crypsis—avoidance of observation—that allows otherwise visible aquatic organisms to remain unnoticed by other organisms such as predators or prey.

Counter-illumination method of camouflage

Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength.

Octopine dehydrogenase family

In molecular biology, the octopine dehydrogenase family of enzymes act on the CH-NH substrate bond using NAD(+) or NADP(+) as an acceptor. The family includes octopine dehydrogenase EC 1.5.1.11, nopaline dehydrogenase EC 1.5.1.19, lysopine dehydrogenase EC 1.5.1.16 and opine dehydrogenase EC 1.5.1.-. NADPH is the preferred cofactor, but NADH is also used. Octopine dehydrogenase is involved in the reductive condensation of arginine and pyruvic acid to D-octopine.

European flying squid species of squid

The European flying squid is a species of squid from the continental slope and oceanic waters of the eastern Atlantic Ocean and the Mediterranean Sea. It is the type species of the genus Todarodes, the type genus of the subfamily Todarodinae of the pelagic squid family Ommastrephidae. It is a species which is targeted by some fisheries, although it is more often a bycatch.

References

  1. 1 2 Childress, James J. 1975. The respiratory rates of midwater crustaceans as a function of depth of occurrence and relation to the oxygen minimum layer off Southern California. Comparative Biochemistry and Physiology Part A: Physiology. 50(4):787-799
  2. ↑ Seibel, Brad A., Thuesen, Erik V., Childress, James J., Gorodezky, Laura A. 1997. Decline in Pelagic Cephalopod Metabolism with Habitat Depth Reflects Differences in Locomotory Efficiency. Biological Bulletin. 192:262-278
  3. 1 2 Childress, James J. 1995. Are there physiological and biochemical adaptations of metabolism in deep-sea animals? Trends in Ecology & Evolution 10:30-36
  4. ↑ Seibel, Brad A., Drazen, Jeffrey C. 2007. The rate of metabolism in marine animals: environmental constraints, ecological demands and energetic opportunities. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 362(1487):2061-2078.
  5. ↑ Seibel, Brad A., Thuesen, Erik V., Childress, James J. 2000. Light-Limitation on Predator-Prey Interactions: Consequences for Metabolism and Locomotion of Deep-Sea Cephalopods. Biological Bulletin. 198:284-298
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