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61-416: Marine hatchetfishes or deep-sea hatchetfishes are small deep-sea mesopelagic ray-finned fish of the stomiiform subfamily Sternoptychinae . They should not be confused with the freshwater hatchetfishes , which are not particularly closely related Teleostei in the characiform family Gasteropelecidae. The scientific name means " Sternoptyx -subfamily", from Sternoptyx (the type genus ) +

122-405: A retroreflector behind the retina . Flashlight fish have this plus photophores , which combination they use to detect eyeshine in other fish (see tapetum lucidum ). Organisms in the deep sea are almost entirely reliant upon sinking living and dead organic matter which falls at approximately 100 meters per day. In addition, only about 1 to 3% of the production from the surface reaches

183-417: A few hundred meters below the surface, but their entire depth range spans from 50 to 1,500 meters deep. The body is deep and laterally extremely compressed, somewhat resembling a hatchet (with the thorax being the "blade" and the caudal peduncle being the "handle"). The genus Polyipnus is rounded, the other two – in particular Sternoptyx – decidedly angular if seen from the side. Their pelvis

244-451: A form of camouflage . The two main methods by which this is achieved are reduction in the area of their shadow by lateral compression of the body, and counter illumination via bioluminescence . This is achieved by production of light from ventral photophores , which tend to produce such light intensity to render the underside of the fish of similar appearance to the background light. For more sensitive vision in low light , some fish have

305-528: A large component of sources for algae loss from surface water. Most organic components of marine snow are consumed by microbes , zooplankton and other filter-feeding animals within the first 1,000 metres of their journey. In this way marine snow may be considered the foundation of deep-sea mesopelagic and benthic ecosystems : As sunlight cannot reach them, deep-sea organisms rely heavily on marine snow as an energy source. The small percentage of material not consumed in shallower waters becomes incorporated into

366-407: A much higher total mass than either phytoplankton or bacteria but is not readily available due to size characteristics of the particles in relation to potential consumers. The colloidal fraction must aggregate in order to be more bioavailable . Aggregates that sink more quickly to the bottom of the ocean have a greater chance of exporting carbon to the deep sea floor. The longer the residence time in

427-543: A number of organisms surviving by feeding on marine snow . Marine snow is organic material that has fallen from upper waters into the deep sea. In 1960, the bathyscaphe Trieste descended to the bottom of the Mariana Trench near Guam , at 10,911 m (35,797 ft; 6.780 mi), the deepest known spot in any ocean. If Mount Everest (8,848 m or 29,029 ft or 5.498 mi) were submerged there, its peak would be more than 2 km (1.2 mi) beneath

488-605: A projected indicator of climate change , may result in a decrease in the production of marine snow due to the enhanced stratification of the water column. Increasing stratification decreases the availability of phytoplankton nutrients such as nitrate , phosphate and silicic acid , and could lead to a decrease in primary production and, thus, marine snow. The microbial communities associated with marine snow are also interesting to microbiologists . Recent research indicates transported bacteria may exchange genes with previously thought to be isolated populations of bacteria inhabiting

549-407: A rapid sedimentation rate that results in low particulate organic carbon inputs. It is yet to be resolved what effect microbes have on the global carbon cycle. Studies show that microbes in the deep ocean are not dormant, but are metabolically active and must be participating in nutrient cycling by not only heterotrophs but by autotrophs as well. There is a mismatch from the microbial carbon demand in

610-442: Is a protein that is essential for different cellular functions. The α-actin serves as a main component for muscle fiber, and it is highly conserved across numerous different species. Some Deep-sea fish developed pressure tolerance through the change in mechanism of their α-actin. In some species that live in depths greater than 5000m, C.armatus and C.yaquinae have specific substitutions on the active sites of α-Actin, which serves as

671-661: Is also common among deep water squid to combine the gelatinous tissue with a flotation chamber filled with a coelomic fluid made up of the metabolic waste product ammonium chloride , which is lighter than the surrounding water. The midwater fish have special adaptations to cope with these conditions—they are small, usually being under 25 centimetres (10 in); they have slow metabolisms and unspecialized diets, preferring to sit and wait for food rather than waste energy searching for it. They have elongated bodies with weak, watery muscles and skeletal structures. They often have extendable, hinged jaws with recurved teeth. Because of

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732-480: Is defined as the sedimentation out of the surface layer (at approximately 100 m depth) and sequestration flux is the sedimentation out of the mesopelagic zone (at approximately 1000 m depth). A portion of the particulate organic carbon is respired back to CO 2 in the oceanic water column at depth, mostly by heterotrophic microbes and zooplankton, thus maintaining a vertical gradient in concentration of dissolved inorganic carbon (DIC). This deep-ocean DIC returns to

793-518: Is known about the Moon than the deepest parts of the ocean. This is a common misconception based on a 1953 statement by George E.R. Deacon published in the Journal of Navigation , and largely refers to the scarce amount of seafloor bathymetry available at the time. The similar idea that more people have stood on the moon than have been to the deepest part of the ocean is likewise problematic and dangerous. Still,

854-477: Is large enough to undergo sinking. It also has the components necessary to fit the "aggregate spinning wheel hypothesis". Evidence for this has been found by Alldredge and Cohen (1987) who found evidence of both respiration and photosynthesis within aggregates, suggesting the presence of both autotrophic and heterotrophic organisms. During zooplankton's vertical migration, the abundances of aggregates increased while size distributions decreased. Aggregates were found in

915-455: Is limited. Pressure increases at approximately one atmosphere for every 10 meters meaning that some areas of the deep sea can reach pressures of above 1,000 atmospheres. This not only makes great depths very difficult to reach without mechanical aids, but also provides a significant difficulty when attempting to study any organisms that may live in these areas as their cell chemistry will be adapted to such vast pressures. Marine snow In

976-435: Is mining. One study found that at one mining site fish populations had decreased at six months and at three years, and that after twenty six years populations had returned to the same levels as prior to the disturbance. There are a number of species that do not primarily rely upon dissolved organic matter for their food. These species and communities are found at hydrothermal vents at sea-floor spreading zones. One example

1037-416: Is more energetically favorable. Given the abundance of denitrifying and sulfate-reducing bacteria, it is thought that these metabolisms are able to thrive within marine snow aggregates. In a model developed by Bianchi et al., it shows the various redox potentials within an aggregate. Because of the relatively long residence time of the ocean's thermohaline circulation , carbon transported as marine snow into

1098-571: Is not recycled ( remineralised ) before it sinks into the aphotic zone . Because of the role of export production in the ocean's biological pump , it is typically measured in units of carbon (e.g. mg C m d ). The term was coined by explorer William Beebe as observed from his bathysphere . As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents . Marine snow can be an important food source for organisms living in

1159-435: Is rotated to a vertical position. The mouth is located at the tip of the snout and directed almost straight downwards. Their scales are silvery, delicate and easily abraded. In some species, such as the highlight hatchetfish ( Sternoptyx pseudobscura ), large sections of the body at the base of the anal fin and/or caudal fin are transparent. They have perpendicular spines and blade-like pterygiophores in front of

1220-460: Is the symbiotic relationship between the tube worm Riftia and chemosynthetic bacteria. It is this chemosynthesis that supports the complex communities that can be found around hydrothermal vents. These complex communities are one of the few ecosystems on the planet that do not rely upon sunlight for their supply of energy. Deep sea fish have different adaptations in their proteins, anatomical structures, and metabolic systems to survive in

1281-419: The dorsal fin . The anal fin has 11–19 rays and in some species is divided in two parts; almost all have an adipose fin . Their large, sometimes tube-shaped eyes can collect the faintest of light and focus well on objects both close and far. They are directed somewhat upwards, most conspicuously in the genus Argyropelecus . This allows them to discern the silhouettes of prey moving overhead against

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1342-431: The euphotic zone using solar energy and produce particulate organic carbon . The particulate organic carbon formed in the euphotic zone is processed by marine microorganisms (microbes), zooplankton and their consumers into organic aggregates (marine snow), which is then exported to the mesopelagic (200–1000 m depth) and bathypelagic zones by sinking and vertical migration by zooplankton and fish. Export flux

1403-431: The photic zone . The sinking organic material is composed of algal particulates, detritus, and other forms of biological waste, which is collectively referred to as marine snow . Because pressure in the ocean increases by about 1 atmosphere for every 10 meters of depth, the amount of pressure experienced by many marine organisms is extreme. Until recent years, the scientific community lacked detailed information about

1464-443: The "black smoker" chimneys may be as high as 400 °C (it is kept from boiling by the high hydrostatic pressure) while within a few meters it may be back down to 2 to 4 °C. Regions below the epipelagic are divided into further zones, beginning with the bathyal zone (also considered the continental slope ) which spans from 200 to 3000 meters below sea level and is essentially transitional, containing elements from both

1525-478: The Deep sea, where the inhabitants have to withstand great amount of hydrostatic pressure. While other factors like food availability and predator avoidance are important, the deep-sea organisms must have the ability to maintain well-regulated metabolic system in the face of high pressures. In order to adjust for the extreme environment, these organisms have developed unique characteristics. Proteins are affected greatly by

1586-908: The abdomen in zooplankton indicating their grazing will fragment larger aggregates. Aggregates may also form from colloids trapped on the surface of rising bubbles . For example, Kepkay et al. found that bubble coagulation leads to an increase in bacterial respiration since more food is available to them. Particles and small organisms floating through the water column can become trapped within aggregates. Marine snow aggregates are porous, however, and some particles are able to pass through them. Planktonic prokaryotes are further defined into two categories, free-living or particle associated. The two are separated by filtration. Particle-associated bacteria are often difficult to study because marine snow aggregates are often ranging in sizes from 0.2 to 200 μm, often rendering sampling efforts difficult. These aggregates are hotspots for microbial activity. Marine bacteria are

1647-485: The ability of TMAO being able to protect proteins from high hydrostatic pressure destabilizing proteins, the osmolyte adjustment serves are an important adaptation for deep sea fish to withstand high hydrostatic pressure. Deep-sea organisms possess molecular adaptations to survive and thrive in the deep oceans. Mariana hadal snailfish developed modification in the Osteocalcin ( burlap ) gene, where premature termination of

1708-426: The aggregates slowly sink to the bottom of the ocean, the many microorganisms residing on them are constantly respiring and contribute greatly to the microbial loop . Aggregates begin as the colloidal fraction, which typically contains particles sized between one nanometer and several micrometers . The colloidal fraction of the ocean contains a large amount of organic matter unavailable to grazers. This fraction has

1769-645: The aphotic zone, particularly for organisms that live very deep in the water column. Marine snow is made up of a variety of mostly organic matter, including dead or dying animals and phytoplankton , protists , fecal matter, sand, and other inorganic dust. Most trapped particles are more vulnerable to grazers than they would be as free-floating individuals. Aggregates can form through abiotic processes (i.e. extrapolymeric substances). These are natural polymers exuded as waste products mostly by phytoplankton and bacteria . Mucus secreted by zooplankton (mostly salps , appendicularians , and pteropods ) also contribute to

1830-424: The atmosphere on millennial timescales through thermohaline circulation . Between 1% and 40% of the primary production is exported out of the euphotic zone, which attenuates exponentially towards the base of the mesopelagic zone and only about 1% of the surface production reaches the sea floor. The largest component of biomass are marine protists (eukaryotic microorganisms). Marine snow aggregates collected from

1891-410: The bathypelagic zone were found to consist largely of fungi and labyrinthulomycetes . Smaller aggregates do not harbor as many eukaryotic organisms which is similar to what is found in the deep ocean. The bathypelagic aggregates mostly resembled those found in the surface ocean. It implies higher rates of remineralization in the bathypelagic zone. Numerically, the largest component of marine snow are

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1952-414: The bottom, but the rate is much slower. The cold water stems from sinking heavy surface water in the polar regions . At any given depth, the temperature is practically unvarying over long periods of time, without seasonal changes and with very little interannual variability. No other habitat on earth has such a constant temperature. In hydrothermal vents the temperature of the water as it emerges from

2013-474: The c.12 cm (4.7 in)-long giant hatchetfish ( Argyropelecus gigas ). They are small deep-sea fishes which have evolved a peculiar body shape and like their relatives have bioluminescent photophores . The latter allow them to use counter-illumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below. They typically occur at

2074-399: The constituents of marine snow aggregates. These aggregates grow over time and may reach several centimeters in diameter, traveling for weeks before reaching the ocean floor. Marine snow often forms during algal blooms . As phytoplankton accumulate, they aggregate or get captured in other aggregates, both of which accelerate the sinking rate. Aggregation and sinking is actually thought to be

2135-446: The deep ocean and the carbon export from the surface ocean. Dissolved inorganic carbon fixation is on similar orders of magnitude as heterotrophic microbes in the surface ocean. Model-based data reveal that dissolved inorganic carbon fixation ranges from 1 mmol C m d to 2.5 mmol C m d . Large aggregates can become anoxic which gives rise to anaerobic metabolisms. Typically anaerobic metabolisms are confined to areas where it

2196-401: The deep ocean by the biological pump can remain out of contact with the atmosphere for more than 1000 years. That is, when the marine snow is finally decomposed to inorganic nutrients and dissolved carbon dioxide , these are effectively isolated from the surface ocean for relatively long time scales related to ocean circulation . Consequently, enhancing the quantity of marine snow that reaches

2257-407: The deep ocean in regions with high dust deposition is strongly controlled by dust input to the surface ocean while suspended dust particles in deeper water layers do not significantly interact with sinking aggregates. Once particles have aggregated to several micrometers in diameter, they begin to accumulate bacteria, since there is sufficient site space for feeding and reproduction. At this size, it

2318-445: The deep ocean is the basis of several geoengineering schemes to enhance carbon sequestration by the ocean. Ocean nourishment and iron fertilisation seek to boost the production of organic material in the surface ocean, with a concomitant rise in marine snow reaching the deep ocean. These efforts have not yet produced a sustainable fertilization that effectively transports carbon out of the system. Increases in ocean temperatures,

2379-438: The deep ocean, marine snow (also known as " ocean dandruff ") is a continuous shower of mostly organic detritus falling from the upper layers of the water column . It is a significant means of exporting energy from the light -rich photic zone to the aphotic zone below, which is referred to as the biological pump . Export production is the amount of organic matter produced in the ocean by primary production that

2440-469: The deep sea, at about 35 parts per thousand. There are some minor differences in salinity, but none that are ecologically significant, except in largely landlocked seas like the Mediterranean and Red Seas . The two areas of greatest temperature gradient in the oceans are the transition zone between the surface waters and the deep waters, the thermocline, and the transition between the deep-sea floor and

2501-442: The deep-sea remains one of the least explored regions on planet Earth. Pressures even in the mesopelagic become too great for traditional exploration methods, demanding alternative approaches for deep-sea research. Baited camera stations, small crewed submersibles, and ROVs ( remotely operated vehicles ) are three methods utilized to explore the ocean's depths. Because of the difficulty and cost of exploring this zone, current knowledge

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2562-405: The effects of pressure on most deep sea organisms because the specimens encountered arrived at the surface dead or dying and weren't observable at the pressures at which they lived. With the advent of traps that incorporate a special pressure-maintaining chamber, undamaged larger metazoan animals have been retrieved from the deep sea in good condition. Salinity is remarkably constant throughout

2623-494: The elevated hydrostatic pressure, as they undergo changes in water organization during hydration and dehydration reactions of the binding events. This is due to the fact that most enzyme-ligand interactions form through charged or polar non-charge interactions. Because hydrostatic pressure affects both protein folding and assembly and enzymatic activity, the deep sea species must undergo physiological and structural adaptations to preserve protein functionality against pressure. Actin

2684-417: The exception of the upper parts of the mesopelagic . Since photosynthesis is not possible, plants and phytoplankton cannot live in this zone, and as these are the primary producers of almost all of earth's ecosystems, life in this area of the ocean must depend on energy sources from elsewhere. Except for the areas close to the hydrothermal vents, this energy comes from organic material drifting down from

2745-517: The gene was found. Osteocalcin gene regulates bone development and tissue mineralization, and the frameshift mutation seems to have resulted in the open skull and cartilage-based bone formation. Due to high hydrostatic pressure in the deep sea, closed skulls that organisms living on the surface develop cannot withstand the enforcing stress. Similarly, common bone developments seen in surface vertebrates cannot maintain their structural integrity under constant high pressure. It has been suggested that more

2806-489: The hot water flows at the hydrothermal vents. Thermoclines vary in thickness from a few hundred meters to nearly a thousand meters. Below the thermocline, the water mass of the deep ocean is cold and far more homogeneous . Thermoclines are strongest in the tropics, where the temperature of the epipelagic zone is usually above 20 °C. From the base of the epipelagic, the temperature drops over several hundred meters to 5 or 6 °C at 1,000 meters. It continues to decrease to

2867-410: The lowest levels in 58 years. Ocean acidification is particularly harmful to deep sea corals because they are made of aragonite, an easily soluble carbonate, and because they are particularly slow growing and will take years to recover. Deep sea trawling is also harming the biodiversity by destroying deep sea habitats which can take years to form. Another human activity that has altered deep sea biology

2928-500: The main component of muscle fiber. These specific substitutions, Q137K and V54A from C.armatus or I67P from C.yaquinae are predicted to have importance in pressure tolerance. Substitution in the active sites of actin result in significant changes in the salt bridge patterns of the protein, which allows for better stabilization in ATP binding and sub unit arrangement, confirmed by the free energy analysis and molecular dynamics simulation. It

2989-411: The most abundant organisms in aggregates followed by cyanobacteria and then nanoflagellates . Aggregates can be enriched about one thousand times more than the surrounding seawater. Seasonal variability can also have an effect on microbial communities of marine snow aggregates with concentrations being the highest during the summer. As illustrated in the diagram, phytoplankton fix carbon dioxide in

3050-601: The muddy "ooze" blanketing the ocean floor, where it is further decomposed through biological activity. Marine snow aggregates exhibit characteristics that fit Goldman's "aggregate spinning wheel hypothesis". This hypothesis states that phytoplankton, microorganisms and bacteria live attached to aggregate surfaces and are involved in rapid nutrient recycling. Phytoplankton have been shown to be able to take up nutrients from small local concentrations of organic material (e.g. fecal matter from an individual zooplankton cell, regenerated nutrients from organic decomposition by bacteria). As

3111-610: The prokaryotes that colonize the aggregates. Bacteria are largely responsible for the remineralisation and fragmentation of aggregates. Remineralization occurs typically below 200 m depth. Microbial communities that form on the aggregates vary from the communities in the water column. The concentration of attached microbes are typically orders of magnitude larger than free-living microbes. Isolated bacterial cultures have up to 20 times more enzymatic activity within 2 hours of aggregate attachment. The dark ocean harbors around 65% of all pelagic Bacteria and Archaea.(Whitman et al., 1998) It

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3172-669: The sea bed mostly in the form of marine snow. Larger food falls, such as whale carcasses , also occur and studies have shown that these may happen more often than currently believed. There are many scavengers that feed primarily or entirely upon large food falls and the distance between whale carcasses is estimated to only be 8 kilometers. In addition, there are a number of filter feeders that feed upon organic particles using tentacles, such as Freyella elegans . Marine bacteriophages play an important role in cycling nutrients in deep sea sediments. They are extremely abundant (between 5×10 and 1×10 phages per square meter) in sediments around

3233-581: The shelf above and the abyss below. Below this zone, the deep sea consists of the abyssal zone which occurs between the ocean depths of 3000 and 6000 meters and the hadal zone (6000 – 11,000 meters). Food consists of falling organic matter known as ' marine snow ' and carcasses derived from the productive zone above, and is scarce both in terms of spatial and temporal distribution. Instead of relying on gas for their buoyancy, many deep-sea species have jelly-like flesh consisting mostly of glycosaminoglycans , which provides them with very low density. It

3294-401: The slightly brighter upper waters. There are three genera in this subfamily , with some 40 species altogether: Four fossil genera are also known: Deep-sea Organisms living within the deep sea have a variety of adaptations to survive in these conditions. Organisms can survive in the deep sea through a number of feeding methods including scavenging, predation and filtration, with

3355-465: The sparse distribution and lack of light, finding a partner with which to breed is difficult, and many organisms are hermaphroditic . Because light is so scarce, fish often have larger than normal, tubular eyes with only rod cells . Their upward field of vision allows them to seek out the silhouette of possible prey. Prey fish however also have adaptations to cope with predation . These adaptations are mainly concerned with reduction of silhouettes,

3416-564: The standard animal family suffix "-inae". It ultimately derives from Ancient Greek stérnon (στέρνον, "breast") + ptýx (πτύξ, "a fold/crease") + Latin forma ("external form"), the Greek part in reference to the thorax shape of marine hatchetfishes. Found in tropical , subtropical and temperate waters of the Atlantic , Pacific and Indian Oceans , marine hatchetfishes range in size from Polyipnus danae at 2.8 cm (1.1 in) to

3477-570: The surface. After the Trieste was retired, the Japanese remote-operated vehicle (ROV) Kaikō was the only vessel capable of reaching this depth until it was lost at sea in 2003. In May and June 2009, the hybrid-ROV Nereus returned to the Challenger Deep for a series of three dives to depths exceeding 10,900 m (35,800 ft; 6.8 mi). Natural light does not penetrate the deep ocean, with

3538-528: The water column the greater the chance of being grazed upon. Aggregates formed in high dust areas are able to increase their densities faster and in more superficial layers compared to aggregates formed without dust particles present and these aggregates with increased lithogenic material have also been correlated with particulate organic carbon fluxes, however when they become heavily ballasted with lithogenic material they cannot scavenge any additional minerals during their descent, which suggests that carbon export to

3599-471: The world. Despite being so isolated deep sea organisms have still been harmed by human interaction with the oceans. The London Convention aims to protect the marine environment from dumping of wastes such as sewage sludge and radioactive waste . A study found that at one region there had been a decrease in deep sea coral from 2007 to 2011, with the decrease being attributed to global warming and ocean acidification , and biodiversity estimated as being at

3660-408: Was found that deep sea fish have more salt bridges in their actins compared to fish inhabiting the upper zones of the sea. In relations to protein substitution, specific osmolytes were found to be abundant in deep sea fish under high hydrostatic pressure. For certain chondrichthyans , it was found that Trimethylamine N-oxide (TMAO) increased with depth, replacing other osmolytes and urea. Due to

3721-445: Was previously thought that due to fragmentation, bacterial communities would shift as they travel down the water column. As seen in experiments, it now appears that the communities that form during aggregation remain associated with the aggregate and any community changes are due to grazing or fragmentation rather than new bacterial colony formation. The deep ocean harbors more than 98% of the dissolved inorganic carbon pool, along with

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