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)[1][2] as well as larger invertebrates, such as crustaceans and polychaetes[3]. 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.


The benthic region of the ocean begins at the shore line (intertidal or littoral zone) and extends downward along the surface of the continental shelf out to sea.[4] 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 deep sea floor. The deep-sea floor is called the abyssal plain and is usually about 4,000 meters deep. The ocean floor is not all flat but has submarine ridges and deep ocean trenches known as the hadal zone.

For comparison, the pelagic zone is the descriptive term for the ecological region above the benthos, including the water-column up to the surface. Depending on the water-body, the benthic zone may include areas that are only a few inches below water, such as a stream or shallow pond; at the other end of the spectrum, benthos of the deep ocean includes the bottom levels of the oceanic abyssal zone.

For information on animals that live in the deeper areas of the oceans see aphotic zone. Generally, these include life forms that tolerate cool temperatures and low oxygen levels, but this depends on the depth of the water.


Benthos are the organisms that live in the benthic zone, and are different from those elsewhere in the water column.[4] Many have adapted to live on the substrate (bottom). 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.[5] 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 meters of water depth).

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 benthic 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 a few centimeters into the ocean floor. Those living on the surface of the ocean floor are known as epifauna.[6] Those who live burrowed into the ocean floor are known as infauna.[7] Extremophiles, including piezophiles, which thrive in high pressures, may also live there.

Nutrient flux

Sources of food for benthic communities can derive from the water column above these habitats in the form of aggregations of detritus, inorganic matter, and living organisms.[4] These aggregations are commonly referred to as marine snow, and are important for the deposition of organic matter, and bacterial communities.[8] The amount of material sinking to the ocean floor can average 307,000 aggregates per m2 per day.[9] This amount will vary on the depth of the benthos, and the degree of benthic-pelagic coupling. The benthos in a shallow region will have more available food than the benthos in the deep sea. Because of their reliance on it, microbes may become spatially dependent on detritus in the benthic zone. The microbes found in the benthic zone, specifically dinoflagellates and foraminifera, colonize quite rapidly on detritus matter while forming a symbiotic relationship with each other.[10][11]


Modern seafloor mapping technologies have revealed linkages between seafloor geomorphology and benthic habitats, in which suites of benthic communities are associated with specific geomorphic settings.[12] Examples include cold-water coral communities associated with seamounts and submarine canyons, kelp forests associated with inner shelf rocky reefs and rockfish associated with rocky escarpments on continental slopes.[13] In oceanic environments, benthic habitats can also be zoned by depth. From the shallowest to the deepest are: the epipelagic (less than 200 meters), the mesopelagic (200–1,000 meters), the bathyal (1,000–4,000 meters), the abyssal (4,000–6,000 meters) and the deepest, the hadal (below 6,000 meters).

The lower zones are in deep, pressurized areas of the ocean. Human impacts have occurred at all ocean depths, but are most significant on shallow continental shelf and slope habitats.[14] Many benthic organisms have retained their historic evolutionary characteristics. Some organisms are significantly larger than their relatives living in shallower zones, largely because of higher oxygen concentration in deep water.[15]

It is not easy to map or observe these organisms and their habitats, and most modern observations are made using remotely operated underwater vehicles (ROVs), and rarely submarines.

Ecological research

Benthic macroinvertebrates have many important ecological functions, such as regulating the flow of materials and energy in river ecosystems through their food web linkages. Because of this correlation between flow of energy and nutrients, benthic macroinvertebrates have the ability to influence food resources on fish and other organisms in aquatic ecosystems. For example, the addition of a moderate amount of nutrients to a river over the course of several years resulted in increases in invertebrate richness, abundance, and biomass. These in turn resulted in increased food resources for native species of fish with insignificant alteration of the macroinvertebrate community structure and trophic pathways.[16] The presence of macroinvertebrates such as Amphipoda also affect the dominance of certain types of algae in Benthic ecosystems as well.[17] In addition, because benthic zones are influenced by the flow of dead organic material, there have been studies conducted on the relationship between stream and river water flows and the resulting effects on the benthic zone. Low flow events show a restriction in nutrient transport from benthic substrates to food webs, and caused a decrease in benthic macroinvertebrate biomass, which lead to the disappearance of food sources into the substrate.[18]

Because the benthic system regulates energy in aquatic ecosystems, studies have been made of the mechanisms of the benthic zone in order to better understand the ecosystem. Benthic diatoms have been used by the European Union's Water Framework Directive (WFD) to establish ecological quality ratios that determined the ecological status of lakes in the UK.[19] Beginning research is being made on benthic assemblages to see if they can be used as indicators of healthy aquatic ecosystems. Benthic assemblages in urbanized coastal regions are not functionally equivalent to benthic assemblages in untouched regions.[20]

Ecologists are attempting to understand the relationship between heterogeneity and maintaining biodiversity in aquatic ecosystems. Benthic algae has been used as an inherently good subject for studying short term changes and community responses to heterogeneous conditions in streams. Understanding the potential mechanisms involving benthic periphyton and the effects on heterogeneity within a stream may provide a better understanding of the structure and function of stream ecosystems.[21] Benthic gross primary production (GPP) may be important in maintaining biodiversity hotspots in littoral zones in large lake ecosystems. However, the relative contributions of benthic habitats within specific ecosystems are poorly explored and more research is needed.[22]

See also


  1. ^ Wetzel, Robert G. (2001). Limnology: Lake and River Ecosystems, 3rd edn. Academic Press, San Diego. pp. 635–637.
  2. ^ Fenchel, T.; King, G.; Blackburn, T. H. (2012). Bacterial Biogeochemistry: The Ecophysiology of Mineral Cycling, 3rd edn. Academic Press, London. pp. 121–122.
  3. ^ "What Are Benthos?". 2006-01-23. Retrieved 2013-11-24.
  4. ^ a b c Angelo Mark P. Walag; Mae Oljae P. Canencia (2016). "Physico-chemical Parameters and Macrobenthic Invertebrates of the Intertidal Zone of Gusa, Cagayan de Oro City, Philippines". Advances in Environmental Sciences - International Journal of the Bioflux Society. 8 (1): 71–82. Retrieved 2015-12-08.(registration required)
  5. ^ Bright, Michael (2000). The private life of sharks: the truth behind the myth. Mechanicsburg, Pennsylvania: Stackpole Books. ISBN 0-8117-2875-7.
  6. ^ "Epifaunal - Definition and More from the Free Merriam-Webster Dictionary". 2012-08-31. Retrieved 2013-11-24.
  7. ^ "Infauna - Definition and More from the Free Merriam-Webster Dictionary". 2012-08-31. Retrieved 2013-11-24.
  8. ^ Alldredge, Alice; Silver, Mary W. (1988). "Characteristics, dynamics and significance of marine snow". Progress in Oceanography. 20: 41–82. doi:10.1016/0079-6611(88)90053-5.
  9. ^ Shanks, Alan; Trent, Jonathan D. (1980). "Marine snow: sinking rates and potential role in vertical flux". Deep-Sea Research. 27A (2): 137–143. doi:10.1016/0198-0149(80)90092-8.
  10. ^ "Foraminifera". Retrieved 7 December 2014.
  11. ^ "foraminifera". Retrieved 7 December 2014.
  12. ^ Harris, P. T.; Baker, E. K. 2012. "GeoHab Atlas of seafloor geomorphic features and benthic habitats – synthesis and lessons learned", in: Harris, P. T.; Baker, E. K. (eds.), Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of seafloor geomorphic features and benthic habitats. Elsevier, Amsterdam, pp. 871-890.
  13. ^ Harris, P. T.; Baker, E. K.; 2012. Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of seafloor geomorphic features and benthic habitats. Elsevier, Amsterdam, p. 947.
  14. ^ Harris, P. T., 2012. "Anthropogenic threats to benthic habitats", in: Harris, P. T.; Baker, E. K. (eds.), Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of seafloor geomorphic features and benthic habitats. Elsevier, Amsterdam, pp. 39-60.
  15. ^ Royal Belgian Institute of Natural Sciences, news item March 2005 Archived September 28, 2011, at the Wayback Machine
  16. ^ Minshall, Wayne; Shafii, Bahman; Price, William J.; Holderman, Charlie; Anders, Paul J.; Lester, Gary; Barrett, Pat. "Effects of nutrient replacement on benthic macroinvertebrates in an ultraoligotrophic reach of the Kootenai River, 2003–2010". Freshwater Science. doi:10.1086/677900. JSTOR 10.1086/677900.
  17. ^ Duffy, J. Emmett; Hay, Mark E. (2000-05-01). "Strong impacts of grazing amphipods on the organization of a benthic community". Ecological Monographs. 70 (2): 237–263. CiteSeerX doi:10.1890/0012-9615(2000)070[0237:SIOGAO]2.0.CO;2. ISSN 0012-9615.
  18. ^ Rolls, Robert; Leigh, Catherine; Sheldon, Fran (2012). "Mechanistic effects of low-flow hydrology on riverine ecosystems: ecological principles and consequences of alteration". Freshwater Science. 31 (4): 1163–1186. doi:10.1899/12-002.1. JSTOR 10.1899/12-002.1.
  19. ^ Bennion, Helen; Kelly, Martyn G.; Juggins, Steve; Yallop, Marian L.; Burgess, Amy; Jamieson, Jane; Krokowski, Jan (2014). "Assessment of Ecological Status in UK lakes using benthic diatoms" (PDF). Freshwater Science. 33 (2): 639–654. doi:10.1086/675447. JSTOR 10.1086/675447.
  20. ^ Lowe, Michael; Peterson, Mark S. (2014). "Effects of Coastal Urbanization on Salt-Marsh Faunal Assemblages in the Northern Gulf of Mexico". Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science. 6: 89–107. doi:10.1080/19425120.2014.893467.
  21. ^ Wellnitz, Todd; Rader, Russell B. (2003). "Mechanisms influencing community composition and succession in mountain stream periphyton: interactions between scouring history, grazing, and irradiance". Journal of the North American Benthological Society. 22 (4): 528–541. doi:10.2307/1468350. JSTOR 1468350.
  22. ^ Althouse, Bryan; Higgins, Scott; Vander Zanden, Jake M. (2014). "Benthic and Planktonic primary production along a nutrient gradient in Green Bay, Lake Michigan, USA". Freshwater Science. 33 (2): 487–498. doi:10.1086/676314. JSTOR 10.1086/676314.

External links

Aracana aurita

Aracana aurita, striped cowfish, Shaw's cowfish, striped boxfish, or Shaw's boxfish is a species of boxfish native to the Eastern Indian Ocean. The species was first described by George Shaw in 1798.

It is carnivorous and exposes prey in the benthic zone by blowing a jet of water onto sediment.

Benthic lander

Benthic landers are observational platforms that sit on the seabed or benthic zone to record physical, chemical or biological activity. The landers are autonomous and have deployment durations from a few days (for biological studies) to several years (for physical oceanography studies).

Benthic landers come in a variety of shapes and sizes depending upon the instrumentation they carry, and are typically capable of working at any ocean depth.


Benthos is the community of organisms that live on, in, or near the seabed, river, lake, or stream bottom, also known as the benthic zone. This community lives in or near marine or freshwater 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 upperparts of the water column. The pressure difference can be very significant (approximately one atmosphere for each 10 metres of water depth).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, comes from the Greek noun βένθος "depth of the sea". Benthos is used in freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams. There is also a redundant synonym, benthon.

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.


Ectodini is a tribe of cichlids that are endemic to Lake Tanganyika in East Africa. They live in the benthic zone. Most of the genera in this tribe are monotypic. These fishes show diverse morphology and behaviour and the tribe includes taxa which live in sandy, muddy and rocky habitats.


Holoplankton are organisms that are planktic (they live in the water column and cannot swim against a current) for their entire life cycle. Examples of holoplankton include some diatoms, radiolarians, some dinoflagellates, foraminifera, amphipods, krill, copepods, and salps, as well as some gastropod mollusk species. Holoplankton dwell in the pelagic zone as opposed to the benthic zone. Holoplankton include both phytoplankton and zooplankton and vary in size. The most common plankton are protists.

Lake ecosystem

A lake ecosystem includes biotic (living) plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions.Lake ecosystems are a prime example of lentic ecosystems. Lentic refers to stationary or relatively still water, from the Latin lentus, which means sluggish. Lentic waters range from ponds to lakes to wetlands, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with lotic ecosystems, which involve flowing terrestrial waters such as rivers and streams. Together, these two fields form the more general study area of freshwater or aquatic ecology.

Lentic systems are diverse, ranging from a small, temporary rainwater pool a few inches deep to Lake Baikal, which has a maximum depth of 1642 m. The general distinction between pools/ponds and lakes is vague, but Brown states that ponds and pools have their entire bottom surfaces exposed to light, while lakes do not. In addition, some lakes become seasonally stratified (discussed in more detail below.) Ponds and pools have two regions: the pelagic open water zone, and the benthic zone, which comprises the bottom and shore regions. Since lakes have deep bottom regions not exposed to light, these systems have an additional zone, the profundal. These three areas can have very different abiotic conditions and, hence, host species that are specifically adapted to live there.

Littoral zone

The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal environments, the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. The littoral zone always includes this intertidal zone, and the terms are often used interchangeably. However, the meaning of littoral zone can extend well beyond the intertidal zone.

The term has no single definition. What is regarded as the full extent of the littoral zone, and the way the littoral zone is divided into subregions, varies in different contexts. (Lakes and rivers have their own definitions.) The use of the term also varies from one part of the world to another, and between different disciplines. For example, military commanders speak of the littoral in ways that are quite different from marine biologists.

The adjacency of water gives a number of distinctive characteristics to littoral regions. The erosive power of water results in particular types of landforms, such as sand dunes, and estuaries. The natural movement of the littoral along the coast is called the littoral drift. Biologically, the ready availability of water enables a greater variety of plant and animal life, and particularly the formation of extensive wetlands. In addition, the additional local humidity due to evaporation usually creates a microclimate supporting unique types of organisms.

The word littoral may be used both as a noun and as an adjective. It derives from the Latin noun litus, litoris, meaning "shore". (The doubled tt is a late-medieval innovation, and the word is sometimes seen in the more classical-looking spelling litoral.)

Marine botany

Marine botany is the study of aquatic plants and algae that live in seawater of the open ocean and the littoral zone, along shorelines of the intertidal zone, and in brackish water of estuaries.

It is a branch of marine biology and botany.

Neritic zone

The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately 200 meters (660 ft) in depth.

From the point of view of marine biology it forms a relatively stable and well-illuminated environment for marine life, from plankton up to large fish and corals, while physical oceanography sees it as where the oceanic system interacts with the coast.

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.

Polymixia nobilis

Polymixia nobilis, the stout beardfish, is a species of beardfish. This species can grow up to 30 centimetres (12 in) TL. P. nobilis lives on both sides of the Atlantic Ocean on gravel and sandy bottoms. Scientists do not know how they behave or reproduce. The species's dorsal fin has five spines and 34-27 soft rays. The habitat of the fish is in the benthic zone.

Sarawak pygmy swellshark

The Sarawak pygmy swellshark (Cephaloscyllium sarawakensis) is a species of catshark, belonging to the family Scyliorhinidae. It is found in the benthic zone near the edge of the Pacific continental shelf, at depths of 118–165 m.

Sebastes rastrelliger

Sebastes rastrelliger is a species of fish in the rockfish family found in tide pools and on rocky bottoms in the Eastern Pacific. It is commonly known as a grass rockfish, grass rockcod, grass bass, or a grassy. It lives in the benthic zone and feeds on crustaceans and small fish. This fish is an ambush predator and waits—hiding in kelp, rocks and holes—until prey passes by. Its coloration can vary from a mottled sandy brown, to a reddish brown to a dark green, depending on where it is holding to structure and feeding.

Shorthead redhorse

The shorthead redhorse (Moxostoma macrolepidotum) is a wide-ranging species in North America. The shorthead redhorse is native to central and eastern North America. However, its range has expanded to include areas like the Hudson estuary and Grayson County, Texas. It inhabits small to large rivers and lakes, and lives in the benthic zone. Shorthead redhorse feed on benthic invertebrates and can consume plant material from the benthic environment that it inhabits. When it spawns, shorthead redhorse move into more shallow streams and spawn over gravel or rocky shoals. They will also spawn in springs with swift moving water. The shorthead redhorse is important to humans because it is a game fish. It is also important to anglers because of its role in the ecosystem; it is prey for larger game fish such as northern pike and muskellunge.

Slender-spined porcupine fish

The slender-spined porcupine fish or globefish (Diodon nichthemerus) is a porcupinefish of the family Diodontidae, found in the waters of southern Australia, as far north as Port Jackson to Geraldton, Western Australia. It is most common in Port Phillip Bay and the coastal waters of Tasmania in shallow coastal waters and under manmade jettys.

It is one of the smallest members of the porcupinefish family. It is similar in appearance to the three-bar porcupinefish (Dicotylichthys punctulatus), only smaller (growing to a maximum length of 28 cm) and with slight differences in its markings. It feeds on benthic zone invertebrates. It has slender yellow spines used in predator defence and has the ability to blow its body so its sharp spines protrude when alarmed.

Survey vessel

A survey vessel is any type of ship or boat that is used for mapping. It is a type of research vessel.


Thermales is an order of bacteria belonging to the Deinococcus–Thermus phylum. They are particularly resistant to heat, and live in the benthic zone of the Gulf of Mexico.

Yellowbanded perch

The yellowbanded perch (Acanthistius cinctus) is a species of fish in the family Serranidae, the groupers and sea basses. It is native to the southern Pacific Ocean, where it occurs along the coasts of eastern Australia and New Zealand. It is also known as the yellowbanded wirrah and girdled rock cod.This species reaches up to 50 centimeters in length. It is yellowish in color with thick vertical dark bands.This fish lives in the benthic zone along coastlines. It can be found on reefs, including the Great Barrier and Middleton Reefs.

Ocean zones
Sea level

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.