Closed ecological system

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Closed ecological systems (CES) are ecosystems that do not rely on matter exchange with any part outside the system.

Although the Earth itself fits this definition, the term is most often used to describe much smaller manmade ecosystems. Such systems are scientifically interesting and can potentially serve as a life support system during space flights, in space stations or space habitats, or in submarines.

In a closed ecological system, any waste products produced by one species must be used by at least one other species. If the purpose is to maintain a higher life form, such as a mouse or a human, waste products such as carbon dioxide, faeces and urine must eventually be converted into oxygen, food, and water.

A closed ecological system must contain at least one autotrophic organism. While both chemotrophic and phototrophic organisms are plausible, almost all closed ecological systems to date are based on a phototroph such as green algae.

Major (large-scale) closed ecological systems include Biosphere 2, MELISSA, and the BIOS-1, BIOS-2, and BIOS-3 projects.

An ecosphere is a glass enclosed, self-contained and self-sustaining closed ecosystem sold primarily as a gift or experiment. It can include tiny shrimp, algae, gravel, decorative shells, and gorgonia.