Planktonic
Drifting passively in the water column, unable to swim against currents. Specifically describes larval stages or microbes that depend entirely on water movement and zooplankton for survival.
Planktonic describes organisms, particularly microbial or larval stages, that drift passively in the water column rather than swimming actively. Derived from the Greek 'planktos' (to wander), it denotes a lifestyle entirely dependent on water currents for movement and zooplankton for sustenance, distinct from nektonic species.
What this means in real life
Jellyfish and tiny algae are planktonic—they bob along with ocean currents rather than swimming to a destination or anchoring to rocks like seaweed does.
What it isn’t
Not synonymous with 'microscopic.' Many planktonic organisms are visible to the naked eye (jellyfish, some crustaceans), while many microscopic bacteria are not planktonic—some are attached to surfaces or live in soil.
Commonly misused online
Often used metaphorically to mean 'aimless' or 'drifting through life,' conflating the biological term with a lifestyle judgment. The word itself is neutral—it simply describes how an organism moves in water.