The word “plankton” comes from the Greek word meaning “drifter” or “wanderer.” Plankton are organisms that drift with ocean currents and tides because they cannot swim strongly enough to move against them. Some plankton remain in this drifting state for their entire lives, while others are only considered plankton during their early life stages. As they grow, some species develop the ability to swim and are no longer classified as plankton.

• Plankton are usually microscopic in size, often measuring less than an inch. However, not all plankton are tiny. Some larger organisms, like certain jellyfish and crustaceans, are also classified as plankton because they rely on currents to move.
• Scientists classify plankton in different ways, such as by their size, type, or how long they spend drifting. But the most basic and common classification divides them into two main groups: phytoplankton and zooplankton. Phytoplankton are plant-like organisms that perform photosynthesis, helping produce oxygen and forming the base of the aquatic food chain. Zooplankton, on the other hand, are animal-like organisms that often feed on phytoplankton or other small organisms in the water.
• Plankton play a vital role in aquatic ecosystems by supporting life at every level of the food chain, from tiny fish larvae to massive whales.