Plankton are a diverse collection of organisms found in water or air that are unable to propel themselves against a current or wind. They are carried by tides and currents and cannot swim well enough to move against these forces. Plankton are usually microscopic, often less than one inch in length, but they also include larger species like some crustaceans and jellyfish. The word "plankton" comes from the Greek for "drifter" or "wanderer". The individual organisms constituting plankton are called plankters. Scientists classify plankton in several ways, including by size, type, and how long they spend drifting. But the most basic categories divide plankton into two groups: phytoplankton (plants) and zooplankton (animals) .
Phytoplankton are microscopic plants that live in the ocean and can convert light energy to chemical energy through photosynthesis. They are the base of the aquatic food web, as they fix carbon through photosynthesis, and in turn are grazed upon by animal members of the plankton (zooplankton) . Zooplankton are animal members of the plankton that feed on phytoplankton and other zooplankton. They are then eaten by larger animals such as fish (nekton) .
Plankton are incredibly important to the ocean ecosystem, and very sensitive to changes in their environment, including in the temperature, salinity, pH level, and nutrient concentration of the water. They are the foundation of freshwater and seawater food pyramids. Without plankton, there would be few living organisms on earth, and certainly no Great Barrier Reef.
