Benthos is the community of organisms that live on, in, or near the seabed, also known as the benthic zone.[1] 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.

Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column. The pressure difference can be very significant (approximately one atmosphere for each 10 metres of water depth).[2][3]

Because light is absorbed before it can reach deep ocean-water, the energy source for deep benthic ecosystems 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 benthic zone are scavengers or detritivores.

The term benthos, coined by Haeckel in 1891,[4] comes from the Greek noun βένθος "depth of the sea".[1][5] Benthos is also used in freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams.[6] There is also a redundant synonym, benthon.[7]

Tidepools Small
Seaweed and two chitons in a tide pool.

Food sources

Scheme eutrophication-en
Effect of eutrophication on marine benthic life

The main food sources for the benthos are algae and organic runoff from land. The depth of water, temperature and salinity, and type of local substrate all affect what benthos is present. In coastal waters and other places where light reaches the bottom, benthic photosynthesizing diatoms can proliferate. Filter feeders, such as sponges and bivalves, dominate hard, sandy bottoms. Deposit feeders, such as polychaetes, populate softer bottoms. Fish, such as dragonets, as well as sea stars, snails, cephalopods, and crustaceans are important predators and scavengers.

Benthic organisms, such as sea stars, oysters, clams, sea cucumbers, brittle stars and sea anemones, play an important role as a food source for fish, such as the California sheephead, and humans.

By size


Macrobenthos comprises the larger, more visible, benthic organisms that are greater than 1 mm in size. Some examples are polychaete worms, bivalves, echinoderms, sea anemones, corals, sponges, sea squirts, turbellarians and larger crustaceans such as crabs, lobsters and cumaceans.

They are easily visible to the naked eye with the lower range of body size at 0.5 mm but usually larger than 3 mm. In the coastal water ecosystem, they include several species of organisms from different taxa including Porifera, Annelids, Coelenterates, Mollusks, Crustaceans, Arthropods etc.[2]

Floridian seagrass bed
Seagrass growing off the coast
A sea squirt being used as a substrate for a nudibranch's spiral egg
Benthic GLERL 1
Microphotograph of typical macrobenthic animals, (from top to bottom) including amphipods, a polychaete worm, a snail, and a chironomous midge larvae


Meiobenthos comprises tiny benthic organisms that are less than 1 mm but greater than 0.1 mm in size. Some examples are nematodes, foraminiferans, water bears, gastrotriches and smaller crustaceans such as copepods and ostracodes.


Microbenthos comprises microscopic benthic organisms that are less than 0.1 mm in size. Some examples are bacteria, diatoms, ciliates, amoeba, flagellates.
Diatoms through the microscope
Marine diatoms

By type

"A variety of marine worms": plate from Das Meer by M. J. Schleiden (1804–1881).


Zoobenthos comprises the animals belonging to the benthos.


Phytobenthos comprises the plants belonging to the benthos, mainly benthic diatoms and macroalgae (seaweed).

By location


Endobenthos lives buried, or burrowing in the sediment, often in the oxygenated top layer, e.g., a sea pen or a sand dollar.


Epibenthos lives on top of the sediments, e.g., like a sea cucumber or a sea snail crawling about.


Hyperbenthos lives just above the sediment, e.g., a rock cod.

See also

Contrast the terms plankton (the organisms that float or drift within the water), nekton (the organisms that swim (powerfully) in the water), and neuston (the organisms that float on the water).


  1. ^ a b Benthos from the Census of Antarctic Marine Life website
  2. ^ a b Walag, Angelo Mark; Mae Oljae P. Canencia (2016). "Physico-chemical parameters and macrobenthic invertebrates of the intertidal zone of Gusa, Cagayan de Oro City, Philippines" (PDF). Advances in Environmental Sciences. 8 (1): 71–82. Retrieved October 27, 2015.
  3. ^
  4. ^ Haeckel, E. 1891. Plankton-Studien. Jenaische Zeitschrift für Naturwissenschaft 25 / (Neue Folge) 18: 232-336. BHL.
  5. ^ βένθος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
  6. ^ North American Benthological Society website
  7. ^ Nehring, S. & Albrecht, U. (1997). Benthos und das redundante Benthon: Neologismen in der deutschsprachigen Limnologie. Lauterbornia 31: 17-30, [1].


External links

Bathyal zone

The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is the part of the pelagic zone that extends from a depth of 1,000 to 4,000 m (3,300 to 13,100 ft) 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 (also twilight or dark) zone because of this feature.

Benthic zone

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. Organisms living in this zone are called benthos and include microorganisms (e.g., bacteria and fungi) 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.

Bottom feeder

A bottom feeder is an aquatic animal that feeds on or near the bottom of a body of water. The body of water could be the ocean, a lake, a river, or an aquarium. Bottom feeder is a term used particularly with aquariums. Biologists often use the terms benthos — particularly for invertebrates such as shellfish, crabs, crayfish, sea anemones, starfish, snails, bristleworms and sea cucumbers — and benthivore or benthivorous, for fish and invertebrates that feed on material from the bottom. However the term benthos includes all aquatic life that lives on or near the bottom, which means it also includes non-animals, such as plants and algae.

Biologists also use specific terms that refer to bottom feeding fish, such as demersal fish, groundfish, benthic fish and benthopelagic fish. Examples of bottom feeding fish species groups are flatfish (halibut, flounder, plaice, sole), eels, cod, haddock, bass, grouper, carp, bream (snapper) and some species of catfish and shark.

Demersal zone

The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of the larger profundal zone.

Being just above the ocean floor, the demersal zone is variable in depth and can be part of the photic zone where light can penetrate and photosynthetic organisms grow, or the aphotic zone, which begins between depths of roughly 200 and 1,000 m (700 and 3,300 ft) and extends to the ocean depths, where no light penetrates.


Dictyotales is a large order in the brown algae (class Phaeophyceae). Members of this order generally prefer warmer waters than other brown algae. One genus in this order is calcareous, Padina, the only calcareous member of this phylum.Dictyota dominates 70% of the benthos biomass in the Florida Keys reef tract. The successful spread of this alga is due in part to its ability to asexually reproduce from fragments created by "biotic and abiotic disturbances".

External fertilization

External fertilization is a male organism's sperm fertilizing a female organism's egg outside of the female's body.Internal fertilization, on the other hand, is the occurrence of internal insemination as the mode of combining sperm and egg. External fertilization occurs in water or a moist area because it gives the sperm external mobility to get to the egg. While in the water, the sperm and ova can shed simultaneously to fertilize the egg. The release of eggs and sperm into the water is known as spawning. When females spawn, they release a batch of eggs into a spot of their choice or just into the water, as in bottom dwelling or sessile species and all of the males start to release sperm that are in close proximity. Within vertebrates, it is the amphibians and fish that use external fertilization. When it comes to invertebrates, most are benthic, sessile, or benthic sessile combined animals such as coral, sea anemones, and tube dwelling polychaetes. The benthic zone is the lowest level of the ocean where organisms called benthos reside. An organism that is sessile does not have the ability to move or be mobile. Benthic marine plants such as algae also go through external fertilization to reproduce. Overall, environmental factors and the timing have a heavy influence over the success of external fertilization.In external fertilization some of the eggs laid by the animals gets wasted due to huge rainfall, floods etc.

Mini Rover ROV

The Mini Rover ROV was the world's first small, low cost remotely operated underwater vehicle (ROV) when it was introduced in early 1983. After a demonstration to industry professionals, in the Spring of 1984, it made a significant entry to the remotely operated vehicle market. It is a self-propelled, tethered, free swimming vehicle that was designed and built by Chris Nicholson of Deep Sea Systems International, Inc. (DSSI). The Mini Rover ROV entered the ROV market at a price of $26,850 when the next lowest cost ROV was $100,000. Nicholson built the first Mini Rover ROV in his garage in Falmouth, MA. It was 26 inches long and weighed 55 pounds. It could be carried on airplanes as luggage.The Mini Rover ROV has been involved in many undersea expeditions including the 1989 3D filming of the SS Edmund Fitzgerald and the 1989 and 1990 Pearl Harbor Project with the National Park Service and National Geographic to survey the USS Arizona Memorial.In the 1989 James Cameron film, The Abyss, the Mini Rover MKII ROV is credited as "Little Geek".The size and portability of the Mini Rover ROV made it easily deployable for emergency situations anywhere in the world. On November 2, 1999, a Mini Rover ROV was on board the USNS Mohawk (T-ATF-170) at the scene of the October 31, 1999, EgyptAir Flight 990 crash site to be used to identify target locations.Benthos, Inc. (Teledyne Benthos) acquired exclusive designs, trademarks, marketing and manufacturing rights for the Mini Rover ROV from DSSI in 1987. Benthos had been manufacturing and servicing the Mini Rover ROV for DSSI since 1984.


Nekton or necton refers to the aggregate of actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms that were carried along by the current, the plankton. As a guideline, nektonic organisms have a high Reynolds number (greater than 1000) and planktonic organisms a low one (less than 10). However, some organisms can begin life as plankton and transition to nekton later on in life, sometimes making distinction difficult when attempting to classify certain plankton-to-nekton species as one or the other. For this reason, some biologists choose not to use this term.

New Harbour (Antarctica)

New Harbour is a bay about 10 miles (16 km) wide between Cape Bernacchi and Butter Point along the coast of Victoria Land, due west of Ross Island. It was discovered by the British National Antarctic Expedition (1901–04) and so named because this new harbor was found while the Discovery was seeking the farthest possible southern anchorage along the coast of Victoria Land. The Ferrar Glacier flows into the bay, which overlooked by Mount Barnes, which sits at the eastern end of the Kukri Hills range.Explorers Cove indents the harbor at its northwest head. Explorers Cove was named in 1976 by the Advisory Committee on Antarctic Names (US-ACAN) in recognition of the large number of explorers that have worked in the vicinity of this cove. Quinn Gully, an ice-free gully at the lower end of Taylor Valley, descends to the seashore here. On the north side of the entrance is McClintock Point, named by US-ACAN in 1997 for James B. McClintock, Associate Professor of Biology at the University of Alabama at Birmingham, who studied the benthos of McMurdo Sound west of Ross Island and along the coast from Granite Harbour to Cape Chocolate, including extensive work in New Harbour in proximity to this point.


Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typically around 1 mm (0.039 in) in size, but varying from 0.2 to 30 mm (0.008 to 1.181 in) in the case of Gigantocypris. Their bodies are flattened from side to side and protected by a bivalve-like, chitinous or calcareous valve or "shell". The hinge of the two valves is in the upper (dorsal) region of the body. Ostracods are grouped together based on gross morphology. While early work indicated the group may not be monophyletic; and early molecular phylogeny was ambiguous on this front, recent combined analyses of molecular and morphological data found support for monophyly in analyses with broadest taxon sampling Ecologically, marine ostracods can be part of the zooplankton or (most commonly) are part of the benthos, living on or inside the upper layer of the sea floor. Many ostracods, especially the Podocopida, are also found in fresh water, and terrestrial species of Mesocypris are known from humid forest soils of South Africa, Australia and New Zealand. They have a wide range of diets, and the group includes carnivores, herbivores, scavengers and filter feeders.

As of 2008, around 2000 species and 200 genera of nonmarine ostracods are found. However, a large portion of diversity is still undescribed, indicated by undocumented diversity hotspots of temporary habitats in Africa and Australia. Of the known specific and generic diversity of nonmarine ostracods, half (1000 species, 100 genera) belongs to one family (of 13 families), Cyprididae. Many Cyprididae occur in temporary water bodies and have drought-resistant eggs, mixed/parthenogenetic reproduction, and the ability to swim. These biological attributes preadapt them to form successful radiations in these habitats.

Pelagic zone

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.

The pelagic zone occupies 1,330 million km3 (320 million mi3) with a mean depth of 3.68 km (2.29 mi) and maximum depth of 11 km (6.8 mi). Fish that live in the pelagic zone are called pelagic fish. Pelagic life decreases with increasing depth. 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 pelagic zone is sometimes called the open-ocean zone and can be contrasted with water that is near the coast or on the continental shelf. 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 ecological 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. It can be significantly affected by the seabed and the life that lives there. Fish that live in the demersal zone are called demersal fish, and can be divided into benthic fish, which are denser than water so they can rest on the bottom, and benthopelagic fish, which swim in the water column just above the bottom. Demersal fish are also known as bottom feeders and groundfish.


Pleuston are the organisms that live in the thin surface layer existing at the air-water interface of a body of water as their habitat. Examples include some cyanobacteria, some gastropods, the ferns Azolla and Salvinia and the seed plants Lemna, Wolffia, Pistia, Eichhornia crassipes and Hydrocharis. Some fungi and fungi-like protists may be ad.


Psammon (from Greek "psammos", "sand") is a group of organisms inhabiting coastal sand moist — biota buried in sediments. Psammon is a part of water fauna, along with periphyton, plankton, nekton, and benthos. Psammon is also sometimes considered a part of benthos due to its near-bottom distribution. Psammon term is commonly used to refer to freshwater reservoirs such as lakes.


The Rotaliida are an order of Foraminifera, characterized by multilocular tests (shells) composed of bilammelar perforate hyaline lamellar calcite that may be optically radial or granular.

In form, rotaliid tests are typically enrolled, but may be reduced to biserial or uniserial, or may be encrusting with proliferated chambers. Chambers may be simple or subdivided by secondary partitions; the surface is smooth, papillate, costate, striate, or cancellate; the aperture is simple or with an internal toothplate, entosolenian tube, or hemicylindrical structure; it may have an internal canal or stolen systems.

Rotaliids are primarily oceanic benthos, although some are common in shallower estuarine waters. They also include many important fossils, such as the nummulitids.

Sea of Azov

The Sea of Azov (Russian: Азо́вское мо́ре, Azóvskoje móre; Ukrainian: Азо́вське мо́ре, Azóvśke móre; Crimean Tatar: Azaq deñizi, Азакъ денъизи, ازاق دﻩﯕىزى) is a sea in Eastern Europe. To the south it is linked by the narrow (about 4 km or 2.5 mi) Strait of Kerch to the Black Sea, and it is sometimes regarded as a northern extension of the Black Sea. The sea is bounded in the northwest by Ukraine, in the southeast by Russia. The Don and Kuban are the major rivers that flow into it. The Sea of Azov is the shallowest sea in the world, with the depth varying between 0.9 and 14 metres (2 ft 11 in and 45 ft 11 in). There is a constant outflow of water from the Sea of Azov to the Black Sea.

The sea is largely affected by the inflow of numerous rivers, which bring sand, silt, and shells, which in turn form numerous bays, limans, and narrow spits. Because of these deposits, the sea bottom is relatively smooth and flat with the depth gradually increasing toward the middle. Also, due to the river inflow, water in the sea has low salinity and a high amount of biomass (such as green algae) that affects the water colour. Abundant plankton results in unusually high fish productivity. The sea shores and spits are low; they are rich in vegetation and bird colonies.


The seabed (also known as the seafloor, sea floor, or ocean floor) is the bottom of the ocean.

Sevan trout

The Sevan trout (Salmo ischchan) is an endemic fish species of Lake Sevan in Armenia, known as ishkhan (իշխան, pronounced [iʃˈχɑn]) in Armenian. It is a salmonid fish related to the brown trout.

The fish is endangered, because various competitors were introduced into the lake during the Soviet period, including common whitefish (Coregonus lavaretus) from Lake Ladoga, goldfish (Carassius auratus) and narrow-clawed crayfish (Astacus leptodactylus); and because of lake level change. On the other hand, the Sevan trout itself has been successfully introduced to Issyk Kul lake in Kyrgyzstan.A resolution by Armenia's Council of Ministers in 1976 stopped the commercial fishing of Sevan trout and organized Sevan National Park. The fish are nowadays also reared in hatcheries.The Sevan trout has four (or two) distinct strains differing in their breeding time and place, and growth rate:

winter bakhtak (Salmo ischchan ischchan)

summer bakhtak (Salmo ischchan aestivalis)

gegharkuni (Salmo ischchan gegarkuni)

bojak (Salmo ischchan danilewskii).The winter bakhtak is the largest form and can grow to considerable size, up to 90 cm and 15 kg. It breeds within the lake. The summer bakhtak is smaller (<50 cm), and breeds naturally both in rivers and within lake near river mouths. Gegharkuni is a migratory form that naturally breeds exclusively in rivers; it also feeds on plankton in addition to benthos. Bojak in turn is a dwarfed form that breeds within the lake in the winter, and does not exceed 33 cm and 0.25 kg.Water level regulation has been destructive for sevan trout reproduction. Currently, the summer bakhtak and gegharkuni are mainly propagated by hatcheries. The winter bakhtak and bojak may be extinct within the lake.From a study of historical samples, the four strains or forms are not diagnosable by their mitochondrial DNA sequences. As a whole, the Sevan trout is phylogenetically very close to the Caspian trout, within the brown trout complex.

Stratification (water)

Water stratification is when water masses with different properties - salinity (halocline), oxygenation (chemocline), density (pycnocline), temperature (thermocline) - form layers that act as barriers to water mixing which could lead to anoxia or euxinia. 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. 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, phytoplankton may be limited by nutrient availability. Lower primary production also leads to lower net productivity in waters.

Wadden Sea Conservation Station

The Wadden Sea Conservation Station (German: Schutzstation Wattenmeer) is a non-profit, NGO in North Germany. The organisation was founded in 1962 and, since then, has been one of the official NGO partners of the Wadden Sea National Parks. Today the conservation group employs about 30 young people, both volunteers and paid workers, at its headquarters in Husum and the station at Hallig, Hooge.

The main work of the organisation is running continuous monitoring programmes, such as bird-monitoring, monitoring of the tidal-influenced benthos and coastal-monitoring. Also the station carries out a wide programme of guided tours, information evenings and other PR activities.

At Westerhever and at Hallig Hooge the stations run two training establishments. Since 2009 there has been a German Foundation "Stiftung Schutzstation Wattenmeer" which supports the everyday work of the organisation.

Aquatic ecosystems
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