Nekton

Nekton or necton refers to the aggregate of actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms that were carried along by the current, the plankton. As a guideline, nektonic organisms have a high Reynolds number (greater than 1000) and planktonic organisms a low one (less than 10). However, some organisms can begin life as plankton and transition to nekton later on in life, sometimes making distinction difficult when attempting to classify certain plankton-to-nekton species as one or the other. For this reason, some biologists choose not to use this term.

History

The term was first proposed and used by the German biologist Ernst Haeckel in 1890 in his book 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.^[1]

Definition

As a guideline, nekton were 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 were considered plankton when they are very small and swim at low Reynolds numbers, and considered nekton as they grew 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 transitioned to nekton as they grew.

Oceanic nekton

Oceanic nekton comprised animals largely from three clades

Vertebrates formed 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 part of their lives were identified as being planktonic but when they grew and increased in body size they become nektonic. A typical example was the medusa of the jellyfish.

References

↑ Aleyev, Yu. G. (1977). Nekton. doi:10.1007/978-94-010-1324-6.

External links

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)

The dictionary definition of nekton at Wiktionary

Aquatic ecosystems – general and freshwater components

General	Acoustic ecology Adaptation Agent-based models Algal bloom Anoxic waters Aquatic animals (Insects Mammals) Aquatic plants Aquatic science Benthos Biodiversity research Bioluminescence Biomass Biomonitoring Cascade effect Colored dissolved organic matter Camouflage and mimicry Dead zone Ecohydrology Ecosystems Eutrophication Fisheries science Food chain Food web GIS and aquatic science Hydrobiology Hypoxia Isotope analysis Microbial ecology Microbial food web Microbial loop Nekton Neuston Particle Pelagic zone Photic zone Phytoplankton Plankton Pleuston Predation Productivity Ramsar Convention Respiration Schooling Sediment trap Siltation Spawning Substrate Thermal pollution Toxicology Trophic level Water column Zooplankton More...

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Aquatic ecosystems – marine components

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Groups of organisms in aquatic ecosystems

Benthos Macrobenthos Meiobenthos Herpon Nekton Neuston Pechton / Pecton / Pekton Plankton Pleuston Plocon Seston Tripton

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