plankton

noun

plank·​ton ˈplaŋ(k)-tən 

-ˌtän

plural plankton also planktons

: the passively floating or weakly swimming usually minute organisms (such as dinoflagellates, diatoms, copepods, radiolarians, and larval crustaceans and fish) of a body of water

Note: An individual organism found in plankton is technically referred to as a plankter.

… photosynthesizing plankton will grow at their intrinsic rates until nutrients become limiting, light is reduced by shading, and grazing organisms become abundant enough to check the increase …

—W. H. Berger

Almost all marine invertebrates, such as corals, clams, and starfish, reproduce by releasing microscopic larvae that drift in the plankton for a period ranging from minutes to months.

—Randy Olson et al.

Dense schools of menhaden … pour through these waters, toothless mouths … slurping up plankton and detritus …

—H. Bruce Franklin

The prolific zebra mussels have extremely efficient filtering systems, removing enormous quantities of plankton from the water …

—Nelson Bryant

see also phytoplankton, zooplankton

planktonic

plaŋ(k)-ˈtä-nik 

adjective

Other planktonic forms are grazers—tiny animals that filter algae and other organic matter out of the water and consume it.

—Wyoming Wildlife

Examples of plankton in a Sentence

fish that feed mainly on plankton

Recent Examples on the Web

Tiny, microscopic plankton grow, feeding larger plankton that are eaten by many species, including fish and manta rays. — Lauren Sommer, NPR, 13 Oct. 2026

Ethnographic accounts from native elders describe how during unique warm-water events in late summer, people voyaged out at night into the fjords, aided by natural bioluminescent plankton. — Torben Rick, The Conversation, 12 Oct. 2026

For thousands and sometimes millions of years, marine plankton all over the world built their spiral shells in one direction. — Quanta Magazine, 11 Sep. 2026

The bay contains bioluminescent plankton that creates a blue-green glow in the water when disturbed. — Andrea Margolis, FOXNews.com, 1 Sep. 2026

Word History

Etymology

German, from Greek, neuter of planktos drifting, from plazesthai to wander, drift, middle voice of plazein to drive astray; akin to Latin plangere to strike — more at plaint

First Known Use

1889, in the meaning defined above

Rhymes for plankton

• yankton

Kids Definition

plankton

noun

plank·​ton ˈplaŋ(k)-tən 

-ˌtän

: the floating or weakly swimming animal and plant life of a body of water

planktonic

plaŋ(k)-ˈtän-ik 

adjective