Plankton are organisms that drift in the pelagic zone of the world oceans and seas, as well as large bodies of fresh water. Plankton are commonly thought of as microscopic in size. However, from a scientific classification perspective, the size of planktic organisms varies enormously. It may surprise some people to learn that the species covers a wide range of organisms, including jellyfish. The singular form is plankter.
They are a critical source of food for many larger organisms, including many cetacean and fish. Ironically the whale shark, largest mammal in the world, feeds solely on plankton, one of the tiniest organisms in the world. The scientific study of plankton is planktology. Plankton are usually categorized by ecological niche rather than on a taxonomic or phylogenetic basis.
Their name derives from the Greek planktos, an adjective not a noun. Its meaning is wanderer, errant or drifter. Planktic is the adjective not, as is commonly supposed, planktonic.
Most of these organisms cannot move independently of the water in which they are immersed. For the most part, they usually cannot control their drift direction. Their drift is set by the prevailing current. The forms of the organism capable of independent movement can only swim vertically, not horizontally against the current. The vertical movement can be quite large, amounting to hundreds of meters in a day.
Most forms of the organism spend their whole life as a plankter. This type of organism are referred to as holoplankton. By contrast, another type of the organism spend only part of their life in planktic form before transforming to another type of organism. This type are referred to as meroplankton. These creatures transform to a creatures that inhabit either the benthic or nektic zone. Examples of meroplankton creatures include the eggs of crustaceans, marine worms, starfish, sea urchins and most fish.
The abundance and distribution of plankton is determined by several factors including water temperature, nutrient concentrations, the physical composition of the water column, the abundance of other plankton and the speed and direction of water current.
Find more regarding plankton species in our complete guide to everything an individual will need to know regarding marine phytoplankton and plaktology plus marine sciences .