Plankton are organisms that are classified as not having control over their movements in the water. They are carried by the water currents. However, having no control over their horizontal movements doesn't mean they cannot move vertically. Some species migrate vertically in the water column. In some zooplankton, this means that they sink during daylight hours (when their visual predators have a better chance at seeing them) and rise during the darkness to feed (diel vertical migration).

There are two basic categories of plankton:

There is great diversity within these categories. Marine bacteria and viruses are technically plankton, but are separated from the broad group by most scientists. Any organism that spends only part of its life as plankton, such as larval fish, usually do for dispersal reasons. Some plankton can be harmful to humans, like those that cause red tide or paralytic shellfish poisoning.

As plankton are at the bottom of the food web, more and more study is being done on their ecosystems. If their stocks are harmed, life as we know it in the oceans is in extreme danger.

Plank"ton (pla&nsm;k"ton), n. [NL., fr. Gr. plagto`n, neut. of plagto`s wandering, pla`zesqai to wander.] (Biol.)

All the animals and plants, taken collectively, which live at or near the surface of salt or fresh waters. -- Plank*ton"ic (#), a.


© Webster 1913

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