What is Plankton?
{{For|the character|Sheldon J. Plankton}} [[File:Phytopla.jpg|thumb|right|200px|Phytoplankton include tiny one-celled [[eukaryotes]] which do [[photosynthesis]]]] [[File:Noctiluca scintillans varias.jpg|thumb|right|200px|''[[Noctiluca scintillans]]'' is a [[dinoflagellate]] which eats up other tiny plankton]] [[File:Meganyctiphanes norvegica2.jpg|thumb|right|200px|Northern [[krill]], the favourite food of the [[baleen whale]]s]] '''Plankton''' are drifting [[organism]]s that live in the surface layers of the [[ocean]]. They live in the top layer of the ocean, called the [[Pelagic zone|epipelagic zone]]. They are not strong enough to swim against ocean currents. The term is in contrast to '''nekton''', who can control their movements.<ref>Thurman H.V. 1997. ''Introductory oceanography''. Prentice Hall, N.J. {{ISBN|0-13-262072-3}}.</ref> There are three groups: * Phytoplankton: which live at the surface of the ocean and [[photosynthesis]]e (use light to make sugars and other [[molecule]]s). ** Eukaryote [[algae]]: [[diatom]]s, [[coccolithophore]]s, some [[dinoflagellate]]s. ** Bacteria: [[cyanobacteria]]. * Zooplankton: small [[protozoa]]ns or [[metazoa]]ns: [[Ctenophore]]s; [[jellyfish]]; [[rotifer]]s; [[foraminifera]]; tiny [[crustacea]] and other [[animal]]s. Some [[egg (biology)|eggs]] and [[larva]]e of larger animals such as fish, crustaceans, and [[annelid]]s. Apart from the eggs, they all feed on other plankton. * Some groups fall into both categories. [[Dinoflagellate]]s can be either photosynthetic producers or [[heterotroph]] consumers; many species are ''mixotrophic'' depending upon their circumstances. It is also hard to fit [[virus]]es into this scheme; yet they are present in great numbers. Plankton are important in the ocean's [[food chain]]. They are the main source of food for almost all [[fish]] larvae as they switch from their yolk sacs to catching [[Predation|prey]]. [[Basking shark]]s and [[blue whale]]s feed on them directly; other large fish feed on them indirectly, by eating fish of sma