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Marine Plankton

The diatom Coscinodiscus wailesii. The two ‘valves’ of the cell can be seen in the top left image. Image taken by M. Hoppenrath, provided courtesy of Plankton*Net (image # 12641) [1].

Plankton consists of a diverse range of living organisms that spend at least a part of their life cycle suspended in water. The term plankton is actually a Greek word, meaning that which is made to wander or drift. This term is further divided into the phytoplankton and zooplankton, meaning plant- (Gk. phyto) and animal- (Gk. zoön) drifters respectively.

Planktonic organisms may have a limited ability to control their fine-scale distribution in the water column, but are otherwise at the mercy of oceanic currents and water movements. Holoplantkon refers to those organisms that spend their entire life in the plankton, as opposed to the meroplantkon, which are only planktonic for a part of their lives. Organisms that are capable of resisting the powers of currents, such as fish and squid, are referred to as neckton.

Planktonic organisms are typically classified into broad size categories according to the ‘Sieburth-scale’ , originally proposed in 1978. Viruses and jelly fish sit at opposite ends of this scale, which runs from fractions of a millimetre to metres.
  1. Plankton Net; Data Provider at the Alfred Wegener Insitute for Polar and Marine Research: http://planktonnet.awi.de/