The benthic zone is the ecological region of the lowest level of a body of water such as an ocean or a lake , including the sediment surface and some sub-surface layers. Living organisms in this area are called benthos , eg the benthic invertebrate community, including crustaceans and polychaetes .  The whole world is permanently attached to the bottom. The superficial layer of the soil, the benthic boundary layer, is an integral part of the benthic zone, as it greatly influences the biological activity that takes place there. Examples of touch soil layers include sand bottoms, rocky outcrops, coral , and bay mud .
The benthic region of the ocean begins on the shore line ( intertidal or eulittoral zone) and extends downward along the surface of the continental shelf to sea.  [ not in citation Given ] The continental shelf is gently sloping to benthic That area extends away from the land mass. At the continental shelf, usually about 200 meters deep, the gradient greatly increases and is known to 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 deepocean trenches known as the hadal zone .
For comparison, the pelagic area 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 such a stream or shallow pond; at the other end of the spectrum, the benthos of the deep ocean includes the bottom levels of the abyssal oceanic zone .
For information on animals in the deeper areas of the oceans see aphotic area . 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 .  [ not in citation given ] 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 .  Many organisms adapted to deep-water pressure can not 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 it does not matter much in the water, the energy source for the ecosystem is often higher than the depths. This dead and decaying matter sustains the benthic food chain ; most organisms in the area are scavengers or detritivores . Some microorganisms use chemosynthesis to produce biomass .
Benthic organisms may be divided into two categories based on their presence in the ocean floor. Those living on the surface of the ocean floor are known as epifauna .  Those who live in the ocean floor are known as infauna .  Extremophiles, including piezophiles , which thrive in high pressures, may also live there.
These habitats in the form of aggregations of detritus , inorganic matter, and living organisms.  [ not in citation Given ] These aggregations are Commonly Referred to as marine snow , and are significant for the deposition of organic matter, and bacterial communities.  The amount of material can be 307,000 aggregates per m 2 per day. 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 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.  
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.  Examples include cold-water coral communities associated with seamounts and submarine canyons, rocky cliffs and rocky escarpments on continental slopes.  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), theAbyssal (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.  Many benthic organisms have had their historic evolutionary characteristics. Some organisms are significantly larger than their relative living in shallower areas, largely because of higher oxygen concentration in deep water. 
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 .
Benthic macroinvertebrates have many important ecological functions, such as regulating the flow of materials and energy in their ecosystems through their food web linkages. Because of this correlation between the 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 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.  The presence of macroinvertebrates such as Amphipoda also affects the dominance of certain types of algae in Benthic ecosystems as well.  In addition, because they are influenced by the flow of organic matter , there has been a study conducted on the relationship between water and river flows and the resulting effects on the benthic zone. Low flow events show a restriction in nutrient transport from benthic substratesto food webs, and causes a decrease in benthic macroinvertebrate biomass, which leads to the disappearance of food sources on the substrate. 
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 determine the ecological status of lakes in the UK.  Beginning research is being done 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. 
Ecologists are attempting to understand the relationship between heterogeneity and biodiversity in aquatic ecosystems. Benthic algae has been used as a heterogeneous condition in the past. Understanding the potential mechanisms involving benthic periphyton and the effects on heterogeneity within the framework of the structure of the ecosystem.  Benthic gross primary production (GPP) may be important in maintaining biodiversity hotspots in coastal areas in large lake ecosystems. However, the relative contributions of benthic habitats within specific ecosystems are poorly explored and more research is needed. 
- Armor (hydrology)
- Benthic fish
- Benthopelagic fish
- Bottom trawling
- Deep sea
- Intertidal zone
- Lake stratification
- Coastal area
- Neritic area
- Photic area
- Profundal area
- Sediment Profile Imagery
- Stream bed
- Tide pool
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