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Benthos (), also known as benthon, is the community of that live on, in, or near the bottom of a seabed, river, lake, or stream, also known as the benthic zone. Benthos from the Census of Antarctic Marine Life website This community lives in or near marine or freshwater sedimentary environments, from along the intertidal zone, out to the continental shelf, and then down to the abyssal zone.
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 every 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 detritus sustains the benthic food chain; most organisms in the benthic zone are scavengers or detritivores.
The term benthos, coined by Haeckel in 1891,Haeckel, E. 1891. Plankton-Studien. Jenaische Zeitschrift für Naturwissenschaft 25 / (Neue Folge) 18: 232–336. BHL. 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.Nehring, S. & Albrecht, U. (1997). Benthos und das redundant Benton: Neologismen in der deutschsprachigen Limnologie. Lauterbornia 31: 17-30, [3].
Marine microbenthos are microorganisms that live in the benthic zone of the ocean – that live near or on the seafloor, or within or on surface seafloor sediments. Microbenthos are found everywhere on or about the seafloor of continental shelves, as well as in deeper waters, with greater diversity in or on seafloor sediments. In benthic diatoms dominate as photosynthetic organisms. In changing strongly control opportunities for microbenthos.
Both foraminifera and diatoms have planktonic and benthic forms, that is, they can drift in the water column or live on sediment at the bottom of the ocean. Regardless of form, their shells sink to the seafloor after they die. These shells are widely used as climate proxy. The chemical composition of the shells are a consequence of the chemical composition of the ocean at the time the shells were formed. Past water temperatures can be also be inferred from the ratios of stable in the shells, since lighter isotopes evaporate more readily in warmer water leaving the heavier isotopes in the shells. Information about past climates can be inferred further from the abundance of forams and diatoms, since they tend to be more abundant in warm water.Bruckner, Monica (2020) How Can We Infer Past Climates?" SERC, Carleton College. Modified 23 July 2020. Retrieved 10 September 2020. sudden extinction event which killed the dinosaurs 66 million years ago also rendered extinct three-quarters of all other animal and plant species. However, deep-sea benthic forams flourished in the aftermath. In 2020 it was reported that researchers have examined the chemical composition of thousands of samples of these benthic forams and used their findings to build the most detailed climate record of Earth ever. Earth barreling toward 'Hothouse' state not seen in 50 million years, epic new climate record shows LiveScience, 10 September 2020.
Some have extremely long lives. In 2013 researchers reported evidence of endoliths in the ocean floor, perhaps millions of years old, with a generation time of 10,000 years.Bob Yirka 29 Aug 2013 These are slowly metabolizing and not in a dormant state. Some Actinomycetota found in Siberia are estimated to be half a million years old. Sussman: Oldest Plants, The Guardian, 2 May 2010
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 photosynthesis diatoms can proliferate. , such as and , dominate hard, sandy bottoms. Deposit feeders, such as , populate softer bottoms. Fish, such as dragonets, as well as , , , and are important predators and scavengers.
Benthic organisms, such as , , , Holothuroidea, and , play an important role as a food source for fish, such as the California sheephead, and .
Benthos can be used as of water pollution through ecological population assessments or through analyzing . In ecological population assessments, a relative value of water pollution can be detected. Observing the number and diversity of macro-invertebrates in a waterbody can indicate the pollution level. In highly contaminated waters, a reduced number of organisms and only pollution-tolerant species will be found. In biomarker assessments, quantitative data can be collected on the amount of and direct effect of specific pollutants in a waterbody. The Biochemistry response of macro-invertebrates' internal tissues can be studied extensively in the laboratory. The concentration of a chemical can cause many changes, including changing feeding behaviors, inflammation, and genetic damage, effects that can be detected outside of the stream environment. Biomarker analysis is important for mitigating the negative impacts of water pollution because it can detect water pollution before it has a noticeable ecological effect on benthos populations.
Organic matter produced in the sunlit layer of the ocean and delivered to the sediments is either consumed by organisms or buried. The organic matter consumed by organisms is used to synthesize biomass (i.e. growth) converted to carbon dioxide through respiration, or returned to the sediment as faeces. This cycle can occur many times before either all organic matter is used up or eventually buried. This process is known as the biological pump. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
In the long-term or at steady-state, i.e., the biomass of benthic organisms does not change, the benthic community can be considered a black box diverting organic matter into either metabolites or the geosphere (burial). The macrobenthos also indirectly impacts carbon cycling on the seafloor through bioturbation.
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