From the Greek φυτóν - plant and πλανκτον - wandering, wandering.

Phytoplankton - microscopic plant organisms that float passively in the thickness of marine and freshwater. They make up about 90% of the entire plant kingdom. Represented by protozoans, diatoms, greens, blue-greens and many other groups of algae. Occurs in the photic zone of waters, inhabiting the water column. Phytoplankton is the primary producer of organic matter in a body of water and serves as food for zooplankton and zoobenthos. The rapid reproduction of phytoplankton causes "water blooms".