(Science: marine biology) small (often microscopic) plants and animals floating, drifting or weakly swimming in bodies of fresh or salt water. The aggregate of small plant and animal organisms that float or drift in great numbers in fresh or salt water.Small organisms that inhabit aquatic communities that mostly lie suspended in the water. Definition
Of, relating to, resembling, or pertaining to plankton
Plankton pertain to the small organisms that drift, float, or weakly swimming in aquatic habitats. Some of them may be capable of diel vertical migration but they, in general, flow with their surrounding currents. The term is used in contrast to nekton that include those organisms capable of swimming against the current.
Most of them are microscopic, such as algae, bacteria, protozoa, archaea, etc. Few of them are macroscopic, such as certain species of jellyfishes. A single organism is referred to as a plankter. Many of them serve essentially as food to many large aquatic organisms. The term plankton is coined by Victor Hensen. It is derived from the Greek word planktos, meaning drifter or wanderer.
Plankton may be classified based on their life cycle: (1) holoplankton and (2) meroplankton. They may also be classified into trophic level groups: (1) phytoplankton, (2) zooplankton, (3) bacterioplankton, and (4) mycoplankton. Another way to divide them into groups is based on their size: (1) femtoplankton (< 0.2 µm), (2) picoplankton (0.2-2 µm), (3) nanoplankton (2-20 µm), (4) microplankton (20-200 µm), (5) mesoplankton (0.2-20 mm), (6) macroplankton (2-20 cm), and (7) megaplankton (> 20 cm).