Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters. They provide a crucial source of food to many large aquatic organisms, such as fish and whales.

These organisms include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification.


An antarctic copepod (Calanoida ) is regarded as a type of plankton (about 1-2 mm long). image: wikipedia

Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish.

Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim actively in the water, which are called nekton.


Siphonophora – the "conveyor belt" of the upgrowing larvae and the ovarium can be seen. image: wikipedia

Plankton often include a wide range of animals that vary from microscopic to relatively large (over tens of centimetres). Many are crustaceans or jellyfish.


Diatoms are a major group of algae, and are among the most common types of phytoplankton. image: wikipedia

Origin of the name plankton

The name plankton is derived from the Greek adjective πλαγκτός - planktos, meaning errant, and by extension "wanderer" or drifter. It was coined by Victor Hensen. Plankton typically flow with ocean currents.

Distribution of plankton

Blue: low levels, Dark Green: high levels. image: KVDP /wikipedia

Source adapted from: Wikipedia contributors. (2019, March 4). Plankton. In Wikipedia, The Free Encyclopedia. Retrieved 09:08, April 1, 2019, from