View source for Detritus

{{other uses}}
{{short description|Dead particulate organic material}}
[[File:Horse Manure and Hay Detritus.jpg|thumb|[[Horse]] [[feces]] and [[straw]] are forms of detritus, and are used as [[manure]].]]

In [[biology]], '''detritus''' ({{IPAc-en|d|ə|ˈ|t|r|aɪ|t|ə|s}} or {{IPAc-en|ˈ|d|ɛ|t|r|ɪ|t|ə|s}}) is [[organic matter]] made up of the [[decomposition|decomposing]] remains of [[organism]]s and plants, and also of [[feces]]. Detritus usually hosts communities of [[microorganism]]s that colonize and [[decomposition|decompose]] ([[Remineralisation|remineralise]]) it. Such microorganisms may be [[decomposer]]s, [[detritivore]]s, or [[coprophage]]s. 

In terrestrial [[ecosystem]]s detritus is present as [[plant litter]] and other organic matter that is intermixed with [[soil]], known as [[soil organic matter]]. The detritus of [[aquatic ecosystem]]s is organic substances suspended in the [[water]] and accumulated in depositions on the floor of the [[body of water]]; when this floor is a [[seabed]], such a deposition is called [[marine snow]].

== Theory ==
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[[File:Sequoiadendron giganteum 08130.JPG|left|thumb|''[[Sequoiadendron giganteum]]'' (giant sequoia) cones and foliage, sugar pine and white fir foliage, and other plant litter constitute the [[Plant litter|duff]] layer that covers the ground of [[Mariposa Grove]] in [[Yosemite National Park]], [[United States]].]]

The remains of decaying plants or animals, or their tissue parts, and [[feces]] gradually lose their form due to physical processes and the action of [[decomposers]], including grazers, [[bacteria]], and [[fungi]].<ref>{{Cite web |title=Decomposition and decay |url=https://treesforlife.org.uk/into-the-forest/habitats-and-ecology/ecology/decomposition-and-decay/ |access-date=2024-05-30 |website=Trees for Life |language=en-GB}}</ref> [[Decomposition]], the process by which [[organic matter]] is decomposed, occurs in several phases. Micro- and macro-organisms that feed on it rapidly consume and absorb materials such as [[protein]]s, [[lipid]]s, and [[sugars]] that are low in [[molecular weight]], while other compounds such as [[complex carbohydrate]]s are decomposed more slowly.{{cn|date=October 2024}} The decomposing microorganisms degrade the organic materials so as to gain the resources they require for their survival and reproduction.<ref>{{Cite journal |last1=Anderson |first1=N. H. |last2=Sedell |first2=James R. |date=1979 |title=Detritius Processing by Macroinvertebrates in Stream Ecosystems |url=https://andrewsforest.oregonstate.edu/sites/default/files/lter/pubs/pdf/pub1674.pdf |journal=[[Oregon State University]] |volume=24 |pages=351–377 |via=[[Annual Reviews Inc.]]}}</ref> Accordingly, simultaneous to microorganisms' decomposition of the materials of dead plants and animals is their [[Assimilation (biology)|assimilation]] of decomposed compounds to construct more of their [[biomass (ecology)|biomass]] (i.e., to grow their own bodies).<ref>{{Cite journal |last1=Moore |first1=John C. |last2=Berlow |first2=Eric L. |last3=Coleman |first3=David C. |last4=De Ruiter |first4=Peter C. |date=2004 |title=Detritus, trophic dynamics and biodiversity |url=https://doi.org/10.1111/j.1461-0248.2004.00606.x |journal=[[Ecology Letters]] |volume=7 |issue=7 |pages=584–600 |doi=10.1111/j.1461-0248.2004.00606.x |bibcode=2004EcolL...7..584M |via=[[Wiley Online Library]]|url-access=subscription }}</ref> When microorganisms die, fine organic particles are produced. If small animals (that normally feed on microorganisms) eat these particles, the particles collect inside the [[intestine]]s of the consumers, and change shape into large pellets of [[Feces|dung]]. As a result of this process, most of the materials of dead organisms disappear and are not visible and recognizable in any form, but are present in the form of a combination of fine organic particles and the organisms that used them as [[nutrient]]s. This combination is detritus.

In [[ecosystem]]s on land, detritus is deposited on the surface of the ground, taking forms such as the humic soil beneath a layer of fallen leaves. In aquatic ecosystems, most detritus is suspended in water, and gradually settles. In particular, many different types of material are collected together by currents, and much material settles in slowly flowing areas.

A large amount of detritus is used as a source of nutrition for [[animal]]s. In particular, many [[Bottom feeder|bottom feeding]] animals ([[benthos]]) living in [[mud flat]]s feed in this way. In particular, since excreta are materials which other animals do not need, whatever energy value they might have, they are often unbalanced as a source of nutrients, and are not suitable as a source of nutrition on their own. However, there are many [[microorganisms]] which multiply in natural environments. These microorganisms do not simply absorb nutrients from these particles, but also shape their own bodies so that they can take the resources they lack from the area around them, and this allows them to make use of excreta as a source of nutrients. In practical terms, the most important constituents of detritus are [[complex carbohydrate]]s, which are persistent (difficult to break down), and the microorganisms which multiply using these absorb carbon from the detritus, and materials such as nitrogen and phosphorus from the water in their environment to synthesise the components of their own cells.

A characteristic type of [[food chain]] called the detritus cycle takes place involving detritus feeders ([[detritivores]]), detritus and the microorganisms that multiply on it. For example, mud flats are inhabited by many [[univalve|univalves]] which are detritus feeders. When these detritus feeders take in detritus with microorganisms multiplying on it, they mainly break down and absorb the microorganisms, which are rich in proteins, and excrete the detritus, which is mostly complex carbohydrates, having hardly broken it down at all. At first, this dung is a poor source of nutrition, and so univalves pay no attention to it, but after several days, microorganisms begin to multiply on it again, its nutritional balance improves, and so they eat it again. Through this process of eating the detritus many times over and harvesting the microorganisms from it, the detritus thins out, becomes fractured and becomes easier for the microorganisms to use, and so the complex carbohydrates are also steadily broken down and disappear over time.

What is left behind by the detritivores is then further broken down and recycled by [[decomposer]]s, such as [[bacterium|bacteria]] and [[fungus|fungi]].

This detritus cycle plays a large part in the so-called purification process, whereby organic materials carried in by rivers is broken down and disappears, and an extremely important part in the breeding and growth of [[marine resources]]. In ecosystems on land, far more essential material is broken down as dead material passing through the detritus chain than is broken down by being eaten by animals in a living state. In both land and aquatic ecosystems, the role played by detritus is too large to ignore.

== Aquatic ecosystems ==
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In contrast to land ecosystems, dead materials and excreta in aquatic ecosystems are typically transported by water flow; finer particles tend to be transported farther or suspended longer. In freshwater bodies organic material from plants can form a [[silt]] known as ''mulm'' or [[humus]] on the bottom. This material, some called ''undissolved organic carbon'' breaks down into [[dissolved organic carbon]] and can bond to heavy metal ions via [[chelation]]. It can also break down into [[colored dissolved organic matter]] such as [[tannin]], a specific form of [[tannic acid]]. 
In saltwater bodies, organic material breaks down and forms a [[marine snow]]. This example of detritus commonly consists of organic materials such as dead [[phytoplankton]] and [[zooplankton]], the outer walls of diatoms and coccolithophores, dead skin and scales of fish, and fecal pellets. This material will slowly sink to the seafloor, where it makes up the majority of sediment in some areas. Once settled, the material will not only contribute to sediments but will help to feed different species of [[detritivore]], organisms which feed on detritus, such as annelid worms and sea cucumbers, to name a few. The exact composition of this detritus varies based on location and time of year, as it is very closely tied to [[primary production]].

==Terrestrial ecosystems==
Detritus occurs in a variety of terrestrial habitats including forest, chaparral and grassland. In forests, the detritus is typically dominated by leaf, twig, and bacteria litter as measured by biomass dominance. This [[plant litter]] provides important cover for seedling protection as well as cover for a variety of arthropods, reptiles<ref>C.M. Hogan, 2008</ref> and amphibians. Some insect larvae feed on the detritus.<ref>D.A. Grimaldi, 2005</ref> Fungi and bacteria continue the decomposition process<ref>B.C. Patten, 1975</ref> after grazers have consumed larger elements of the organic materials, and animal trampling has assisted in mechanically breaking down organic matter. At the later stages of decomposition, [[mesophilic]] [[micro-organism]]s decompose residual detritus, generating heat from exothermic processes; such heat generation is associated with the well known phenomenon of the elevated temperature of [[composting]].

=== Consumers ===
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There is an extremely large number of [[detritus feeder]]s in water. After all, a large quantity of material is carried in by water currents. Even if an organism stays in a fixed position, as long as it has a system for filtering water, it will be able to obtain enough food to get by. Many [[Sessility (motility)|immobile]] organisms survive in this way, using developed [[gill]]s or [[tentacle]]s to filter the water to take in food, a process known as [[filter feeding]].

Another more widely used method of feeding, which also incorporates filter feeding, is a system where an organism secretes mucus to catch the detritus in lumps, and then carries these to its mouth using an area of [[cilius|cilia]]. 

Many organisms, including sea slugs and serpent's starfish, scoop up the detritus which has settled on the water bed. Bivalves which live inside the water bed do not simply suck in water through their tubes, but also extend them to fish for detritus on the surface of the bed.

=== Producers ===
In contrast, from the point of view of organisms using photosynthesis such as [[plants]] and [[plankton]], detritus reduces the transparency of the water and gets in the way of this process. Given that these organisms also require a supply of [[nutrient salts]], in other words [[fertilizer]], for photosynthesis, their relationship with detritus is a complex one.

In land ecosystems, the waste products of plants and animals collect mainly on the ground (or on the surfaces of trees), and as decomposition proceeds, plants are supplied with fertilizer in the form of inorganic salts. In water ecosystems, relatively little waste collects on the water bed, and so the progress of decomposition in water takes a more important role. Investigating the level of inorganic salts in sea ecosystems shows that unless there is an especially large supply, the quantity increases from winter to spring—but is normally extremely low in summer. As such, the quantity of seaweed present reaches a peak in early summer and then decreases. The thinking is that organisms like plants grow quickly in warm periods and thus the quantity of inorganic salts is not enough to keep up with the demand. In other words, during winter, plant-like organisms are inactive and collect fertilizer, but if the temperature rises to some extent they will use this up in a very short period.

It is not entirely true that their productivity falls during the warmest periods. Organisms such as [[dinoflagellate]] have mobility, the ability to take in solid food, and the ability to photosynthesise. This type of micro-organism can take in substances such as detritus to grow, without waiting for it to be broken down into fertilizer.

== Aquariums ==
{{unreferenced section|date=November 2012}}

In recent years, the word detritus has also come to be used with [[aquarium]]s (the word "aquarium" is a general term for any installation for keeping aquatic animals).

When animals such as fish are kept in an aquarium, they produce substances such as excreta, mucus, and dead skin cast off during [[moulting]]. These substances naturally generate detritus, which is continually broken down by microorganisms.

Modern sealife aquariums often use the [[Berlin Method]], which employs a piece of equipment called a [[protein skimmer]], which produces air bubbles which the detritus adheres to and forces it outside the tank before it decomposes and also a highly porous type of natural rock called [[live rock]] where many [[benthos]] and bacteria live (hermatype which has been dead for some time is often used), which causes the detritus-feeding benthos and micro-organisms to undergo a detritus cycle. The Monaco system, where an anaerobic layer is created in the tank, to [[denitrification|denitrify]] the organic compounds in the tank, and also the other nitrogen compounds, so that the decomposition process continues until the stage where water, carbon dioxide, and nitrogen are produced, has also been implemented.

Initially, as the name suggests, filtration systems in water tanks often worked using a physical filter to remove foreign substances in the water. Following this, the standard method for maintaining the water quality was to convert [[ammonium]] or [[nitrate]]s in excreta, which has a high degree of [[neurotoxicity]], but the combination of [[Detritivore|detritus feeders]], detritus and micro-organisms has now brought aquarium technology to a still higher level.

== See also ==
* [[Biofact (biology)]]
* [[Coarse woody debris]]
* [[Organic material]]
* [[Soil food web]]

==Citations==
{{Reflist}}

==Sources==
{{more footnotes|date=November 2012}}
{{refbegin}}
* Bernard C. Patten (1975) ''Systems Analysis and Simulation in Ecology'', Academic Press, 607 pages  {{ISBN|0-12-547203-X}}
* C. Michael Hogan (2008) "Western fence lizard (''Sceloporus occidentalis'')", Globaltwitcher, ed. Nicklas Stromberg [https://web.archive.org/web/20120213134001/http://www.globaltwitcher.com/artspec_info.asp?thingid=55037]
* David Author Grimaldi and Michael S. Author (2005) ''Engelevolution of the insects'', Cambridge University Press  {{ISBN|0-521-82149-5}}
* Some of this article was translated from the [[:ja:デトリタス|equivalent article in the Japanese-language Wikipedia]], as it was on September 1, 2006.
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{{Wiktionary}}

{{Modelling ecosystems}}

[[Category:Aquatic ecology]]
[[Category:Ecology terminology]]