Terminology
The name plankton is derived from the Greek adjective πλαγκτός - planktos, meaning "errant", and by extension "wanderer" or "drifter". Plankton typically flow with ocean currents. While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day (a behavior called diel vertical migration), their horizontal position is primarily determined by the surrounding currents. This is in contrast to nekton organisms that can swim against the ambient flow and control their position (e.g. squid, fish, and marine mammals).
Within the plankton, holoplankton spend their entire life cycle as plankton (e.g. most algae, copepods, salps, and some jellyfish). By contrast, meroplankton are only planktic for part of their lives (usually the larval stage), and then graduate to either a nektic or benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.
Plankton abundance and distribution are strongly dependent on factors such as ambient nutrient concentrations, the physical state of the water column, and the abundance of other plankton.
The study of plankton is termed planktology and a planktonic individual is referred to as a plankter.
The adjective planktonic is widely used in both the scientific and popular literature, and is a generally accepted term. However, from the standpoint of formal grammar the less commonly used planktic is more strictly the correct adjective. When deriving English words from their Greek or Latin roots the gender specific ending (in this case "-on," which indicates the word is neuter) is normally dropped, using only the root of the word in the derivation.
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