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Detritus

    In biology '''detritus''' is microscopic biotic material|organic waste material It originates from decomposing dead organisms pieces of material from organisms or their excreta and is normally caused by communities of micro-organisms forming on the surface or inside of the material The term is sometimes used to refer to organic fragments intermixed with soil on the land but in many cases describes material found in water Together with plankton detritus is an important constituent of seston (materials in suspension) and is also found in large quantities in deposit

    General theory

    Dead plants or animals material derived from body tissues such as skin cast off during moulting and matter derived from organisms in the form of excreta all gradually lose their form due to physico-chemical processes and being broken down by agents such as micro-organisms In general science textbooks this process is described as an inorganic process but in fact these changes do not take place all at once Materials like proteins sugars with low molecular weight and lipids are rapidly taken in and absorbed by micro-organisms or organisms that feed on dead matter and thus diappear butmaterials such as complex carbohydrates are only broken down slowly In addition the purpose of the various micro-organisms involved is not to break down these materials but to use them to gain the resources they require for ther own survival and proliferation and they are merely breaking them down as part of that process Accordingly at the same time that the materials of plants and animals are being broken down the materials (biomass) making up the bodies of the micro-organisms are built up by a process of assimilation When micro-organisms die fine organic particles are produced and if these are eaten by small animals which feed on micro-organisms they will collect inside their intestines and change shape into large pellets of dung As a result of this process most of the materials from dead bodies of organisms disappears from view and is not obviously present in any recognisable form but is in fact present in the form of a combination of fine organic particles and the organisms using them as 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 water-based 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 animals In particular many bottom-dwelling animals (bentos) living in mud flats feed in this way In particular since excreta are materials which other animals do not needwhatever 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 micro-organisms which multiply in natural environments These micro-organisms 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 good use of excreta as a source of nutrients In practical terms the most important constituents of detritus are 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 food chain called the detritus cycle takes place involving detritus feeders (detritivores) detritus and the micro-organisms that breed on it. For example mud flats are inhabited by many univalves which are detritus feeders such as moon shells When theses detritus feeders take in detritus with micro-organisms breeding 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 breed 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
    (What is left behind by the detritivores is then further broken down and recycled by decomposers such as bacteria and 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

    Detritus is particulary important in aquatic ecosystems 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

    Consumers

    There are an extremely large number of detritus feeders in water After all such a lot 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 rooted organisms survive in this way using developed gills or tentacles 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 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 simple 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 their photosynthesis However given that they also require a supply of nutrient salts in other words fertiliser 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 However in water not so much waste collects on the water bed and so the progress of decomposition in water takes a more important role However investigating the level of inorganic salts in sea ecosystems shows that unless there is an especially large supply the level increases from winter to spring but is normally extremely low in summer In line with this the quantity of seaweed present reaches a peak in early summer and then decreases This is thought to be because organisms like plants grow quickly in warm periods and the level 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 use this up in a very short period
    However it is not the case 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 photosynthetise This type of microorganism can take in substances such as detritus to grow without waiting for it to be broken down into fertiliser

    Aquariums

    See also