1.
Pelagic zone
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Any water in a sea or lake that is neither close to the bottom nor near the shore can be said to be in the pelagic zone. The word pelagic is derived from Greek πέλαγος, 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 such that as pressure increases with depth. Depending on the depth, the column, rather like the Earths atmosphere. The pelagic zone occupies 1,330 million km3 with a depth of 3.68 km. Pelagic life decreases with increasing depth and it is affected by light intensity, pressure, temperature, salinity, the supply of dissolved oxygen and nutrients, and the submarine topography, which is called bathymetry. In deep water, the zone is sometimes called the open-ocean zone. In other contexts, coastal water not near the bottom is still said to be in the pelagic zone, the pelagic zone can be contrasted with the benthic and demersal zones at the bottom of the sea. The benthic zone is the region at the very bottom of the sea. It includes the sediment surface and some subsurface layers, Marine organisms living in this zone, such as clams and crabs, are called benthos. The demersal zone is just above the benthic zone and it can be significantly affected by the seabed and the life that lives there. Demersal fish are known as bottom feeders and groundfish. Depending on how deep the sea is, the zone can extend over up to five horizontal layers in the ocean. From the top down, these are, From the surface down to around 200 m This is the zone at the surface of the sea where enough light is available for photosynthesis. Nearly all primary production in the ocean occurs here, consequently, plants and animals are largely concentrated in this zone. Examples of organisms living in this zone are plankton, floating seaweed, jellyfish, tuna, many sharks, from 200 m down to around 1,000 m The name for this zone stems from Greek μέσον, meaning middle. Although some light penetrates this second layer it is insufficient for photosynthesis, at about 500 m the water also becomes depleted of oxygen. Organisms survive this environment by having more efficient gills or by minimizing movement, examples of animals that live here are swordfish, squid, Anarhichadidae or wolffish and some species of cuttlefish
2.
Mesopelagic zone
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The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all, although some light penetrates the mesopelagic zone, it is insufficient for photosynthesis. The general types of forms found are daytime visiting herbivores, detritivores feeding on dead organisms and fecal pellets. Examples of animals in the zone are, bristlemouth, swordfish, squid, wolf eels, cuttlefish. The bristlemouth is the Earths most abundant vertebrate, numbering in the hundreds of trillions to quadrillions, the small amount of sunlight is sufficient for animals, such as the chain catshark, to be fluorescent. As of 2015 its small commercial fishery targeted meal, oil, the quantity of mesopelagic life is large enough to play a significant role in global carbon cycling. As the fish participate in the chain, they acquire carbon rendered from carbon dioxide absorbed by surface waters. Upon death, they transport that carbon into the abyss, as of 2015 the revised estimates of mesopelagic life had yet to be incorporated into climate models
3.
Bathyal zone
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The bathyal zone or bathypelagic – from Greek βαθύς, deep – is the part of the pelagic zone that extends from a depth of 1000 to 4000 meters below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below, the average temperature hovers at about 4 °C. Although larger by volume than the euphotic zone, the 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 zone because of this feature. Because of the lack of light, some species do not have eyes, however those possessing eyes in this include the viperfish. Many forms of live in the bathyal zone, such as squid, large whales. In the bathyal, some of the worlds largest whales feed, sponges, brachiopods, sea stars, and echinoids are also common in the bathyal zone. Animals in the zone are not threatened by predators that can see them. This zone is difficult for fish to live in, since it is hard to find nutrients. They have become very efficient, and many have slow metabolic rates to conserve energy. The fish are characterized by weak muscles, soft skin and slimy bodies, the adaptations of some of the fish that live there include small eyes and transparent skin. Except where the ocean is deep, the bathyal zone extends to the benthic zone on the ocean bed of that part of the continental slope that lies between 1000 and 4000 meters deep. The bathyal zone contains sharks, squid, octopuses, and many different species of fish, bathyal zones on the Mediterranean continental slope, An attempt. Research on marine benthos, 9th Iberian Symposium on Studies of Marine Benthos
4.
Abyssal zone
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The abyssal zone or abyssopelagic is a layer of the pelagic zone of the ocean. Abyss derives from the Greek word ἄβυσσος, meaning bottomless, at depths of 4,000 to 6,000 metres, this zone remains in perpetual darkness and never receives daylight. These regions are characterised by continuous cold and lack of nutrients. The abyssal zone has temperatures around 2 °C to 3 °C through the large majority of its mass. It is the part of the midnight zone which starts in the bathypelagic waters above. The area below the zone is the sparsely inhabited hadal zone. The zone above is the bathyal zone, the deep trenches or fissures that plunge down thousands of metres below the ocean floor are almost unexplored. Previously, only the bathyscaphe Trieste, the remote control submarine Kaiko, however, as of March 25,2012 one vehicle, the Deepsea Challenger was able to penetrate to a depth of 10,898.4 metres. Abyssal plain Deep sea Mariana Trench
5.
Hadal zone
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The hadal zone, also known as the hadopelagic zone and composed of trench zones, is the delineation for the deepest trenches in the ocean. The hadal zone is found from a depth to the bottom of the ocean of around 6,000 to 11,000 metres and exists in long, in total there are 33 trenches and 13 troughs around the world—46 individual hadal habitats in total. All the trenches together occupy an area less than one-quarter of one percent of the entire seafloor, the hadal zone has low population and low diversity of marine life. It is believed that most life at this depth is sustained by marine snow or the chemical reactions around thermal vents, the low nutrient level, extreme pressure and lack of sunlight create hostile living conditions in which few species are able to exist. As no sunlight reaches this layer of the ocean, deep sea creatures have reduced eyesight, the most common organisms include jellyfish, viperfish, tube worms and sea cucumbers. The hadal zone can reach far below 6,000 meters deep, at such depths the pressure in the hadal zone exceeds 1,100 standard atmospheres. In 1960, Jacques Piccard and Don Walsh reached the bottom of the Mariana Trench, the deepest known trench on Earth, james Cameron also reached the bottom in 2012 using the Deepsea Challenger. Abyssal plain Deep sea Alan Jamieson, The hadal zone - life in the deepest oceans, forscher filmen lebende Fische in Rekordtiefe from Spiegel 10/09/2008 about an expedition filming fish at a depth of more than 7,000 m
6.
Demersal zone
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The demersal zone is the part of the sea or ocean consisting of the part of the water column near to the seabed and the benthos. The demersal zone is just above the zone and forms a layer of the larger profundal zone. The distinction between species of fish and pelagic species is not always clear cut. Two types of fish inhabit the zone, those that are heavier than water and rest on the seabed. In many species of fish, neutral buoyancy is maintained by a swim bladder which can be expanded or contracted as the circumstances require. A disadvantage of this method is that adjustments need to be made constantly as the pressure varies when the fish swims higher and lower in the water column. An alternative buoyancy aid is the use of lipids, these are less dense water and squalene. In the velvet belly lanternshark, a species, 17% of the bodyweight is liver. Benthic rays and skates have smaller livers with lower concentrations of lipids, they are denser than water. Some fish have no buoyancy aids but use their pectoral fins which are so angled as to lift as they swim. The disadvantage of this is that, if they stop swimming, the fish sink, demersal fish have various feeding strategies, many feed on zooplankton or organisms or algae on the seabed, some of these feed on epifauna, while others specialise on infauna. Others are scavengers, eating the remains of plants or animals while still others are predators. Zooplankton are animals that drift with the current, but many have limited means of locomotion and have some control over the depths at which they drift. They use gas-filled sacs or accumulations of substances with low densities to provide buoyancy, where the adult, benthic organism is limited to life in a certain range of depths, their larvae need to optimise their chances of settling on a suitable substrate. Cuttlefish are able to adjust their buoyancy using their cuttlebones, lightweight rigid structures with cavities filled with gas and this enables them to swim at varying depths. Another invertebrate that feeds on the seabed and has swimming abilities is the nautilus, which stores gas in its chambers and adjusts its buoyancy by use of osmosis, pumping water in and out
7.
Benthic zone
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The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos, e. g. the benthic community, including crustaceans. The organisms generally live in relationship with the substrate bottom. Examples of contact soil layers include sand bottoms, rocky outcrops, coral, the benthic region of the ocean begins at the shore line and extends downward along the surface of the continental shelf out to sea. The continental shelf is a gently sloping benthic region that extends away from the land mass, at the continental shelf edge, usually about 200 meters deep, the gradient greatly increases and is known as the continental slope. The continental slope drops down to the sea floor. The deep-sea floor is called the plain and is usually about 4,000 meters deep. The ocean floor is not all flat but has submarine ridges, for comparison, the pelagic zone is the descriptive term for the ecological region above the benthos, including the water-column up to the surface. For information on animals that live in the areas of the oceans see aphotic zone. Generally, these life forms that tolerate cool temperatures and low oxygen levels. Benthos are the organisms live in the benthic zone, and are different from those elsewhere in the water column. Many are adapted to live on the substrate, in their habitats they can be considered as dominant creatures, but they are often a source of prey for Carcharhinidae such as the lemon shark. Many organisms adapted to deep-water pressure cannot survive in the parts of the water column. The pressure difference can be very significant, because light does not penetrate very deep into ocean-water, the energy source for the benthic ecosystem is often organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains the benthic food chain, most organisms in the zone are scavengers or detritivores. Some microorganisms use chemosynthesis to produce biomass, Benthic organisms can be divided into two categories based on whether they make their home on the ocean floor or an inch or two into the ocean floor. Those living on the surface of the floor are known as epifauna. Those who live burrowed into the floor are known as infauna
8.
Stratification (water)
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These layers are normally arranged according to density, with the least dense water masses sitting above the more dense layers. Water stratification also creates barriers to nutrient mixing between layers and this can affect the primary production in an area by limiting photosynthetic processes. When nutrients from the benthos cannot travel up into the photic zone, lower primary production also leads to lower net productivity in waters. Stratification may be upset by turbulence and this creates mixed layers of water. Forms of turbulence may include surface friction, upwelling and downwelling. Marshall et al. suggest that baroclinic eddies may be an important factor in maintaining stratification, canfield ocean Cline Lake stratification Meromictic
