سابح

السابح Nekton، هو ما يسبح من الأحياء في الماء، مثل الأسماك وغيرها من الحيوانات السابحة.

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 التاريخ

Nekton (organisms that swim against water currents) can be contrasted with plankton (organisms that drift with water currents), neuston (organisms that live at the ocean surface) and benthos (organisms that live at the ocean floor)

The term was first proposed and used by the German biologist Ernst Haeckel in 1891 in his article Plankton-Studien where he contrasted it with plankton, the aggregate of passively floating, drifting, or somewhat motile organisms present in a body of water, primarily tiny algae and bacteria, small eggs and larvae of marine organisms, and protozoa and other minute consumers. Today it is sometimes considered an obsolete term because it often does not allow for the meaningful quantifiable distinction between these two groups. Some biologists no longer use it.

 تعريف

As a guideline, nekton are larger and tend to swim largely at biologically high Reynolds numbers (>10³ and up beyond 10⁹), where inertial flows are the rule, and eddies (vortices) are easily shed. Plankton, on the other hand, are small and, if they swim at all, do so at biologically low Reynolds numbers (0.001 to 10), where the viscous behavior of water dominates, and reversible flows are the rule. Organisms such as jellyfish and others are considered plankton when they are very small and swim at low Reynolds numbers, and considered nekton as they grow large enough to swim at high Reynolds numbers. Many animals considered classic examples of nekton (e.g., Mola mola, squid, marlin) start out life as tiny members of the plankton and then, it was argued, gradually transition to nekton as they grow.

 سوابح المحيطات

Oceanic nekton comprises animals largely from three clades:

• Vertebrates form the largest contribution; these animals are supported by either bones or cartilage.
• Mollusks are animals such as squids and scallops.
• Crustaceans are animals such as lobsters and crabs.

There are organisms whose initial life stage is identified as being planktonic but when they grow and increase in body size they become nektonic. A typical example is the medusa of the jellyfish.

 انظر أيضاً

• Neuston (organisms, including microscopic, living at the surface of the water)
• Plankton (organisms, including microscopic, floating and drifting within water)
• Benthos (organisms, including microscopic, living at the bottom of a body of water)
• Pelagic fish (fish living in the pelagic zone of ocean or lake waters – living neither close to the bottom nor near the shore)

 انظر أيضا

• عوالق (the organisms that float or drift within the water)
• neuston (the organisms that float on the water)
• benthos (the organisms at the bottom of a body of water)

 وصلات خارجية

• Stefan Nehring and Ute Albrecht (1997): "Hell und das redundante Benthon: Neologismen in der deutschsprachigen Limnologie". In: Lauterbornia H. 31: 17-30, Dinkelscherben, December 1997 E-Text (PDF-Datei)