In water and piles up on seabed floors which is referred to as marine snow.
- Theory 1
- Aquatic ecosystems 2
Terrestrial ecosystems 3
- Consumers 3.1
- Producers 3.2
- Aquariums 4
- See also 5
- Citations 6
- Sources 7
Dead plants or animals, material derived from animal tissues (such as skin cast off during moulting et cetera) gradually lose their form, due to both physical processes and the action of nutrients. This combination is detritus.
In ecosystems 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.
Much detritus is used as a source of nutrition for complex carbohydrates, which are persistent (difficult to break down), and the micro-organisms 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 moon shells. When these detritus feeders take in detritus with micro-organisms multiplying on it, they mainly break down and absorb the micro-organisms, 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, micro-organisms 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 micro-organisms from it, the detritus thins out, becomes fractured and becomes easier for the micro-organisms to use, and so the complex carbohydrates are also steadily broken down and disappear over time.
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.
In contrast to land ecosystems, dead materials and excreta in aquatic ecosystems do not settle immediately, and the finer the particles involved are, the longer they tend to take.
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 composting.
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 cilia. This is called mucus feeding.
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.
In contrast, from the point of view of organisms using photosynthesis such as 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 fertiliser 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 fertiliser, 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 fertiliser.
In recent years, the word detritus has also come to be used in relation to aquariums (the word "aquarium" is a general term for any installation for keeping aquatic animals).
When animals such as fish are kept in an aquarium, substances such as excreta, mucus and dead skin cast off during moulting are produced by the animals and, naturally, generate detritus, and are continually broken down by micro-organisms.
Modern sealife aquariums often use the Monaco system, where an anaerobic layer is created in the tank, to 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, the filtration systems in water tanks often worked as the name suggests, 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 nitrates in excreta, which have a high degree of neurotoxicity, but the combination of detritus feeders, detritus and micro-organisms has now brought aquarium technology to a still higher level.
- C.M. Hogan, 2008
- D.A. Grimaldi, 2005
- B.C. Patten, 1975
- 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 
- 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 equivalent article in the Japanese-language WorldHeritage, as it was on September 1, 2006.