Plankton: Meaning (information, definition, explanation, facts)

Plankton is the aggregate community of weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. The name comes from the Greek term, math_unknown_error—meaning "wanderer" or "drifter". While some forms of plankton can move several hundreds of meters vertically in a single day (a behavior called diel vertical migration), their horizontal position is mostly determined by water movement (currents) in the body of water they inhabit. Larger organisms, such as squid, fish, and marine mammals that can control their horizontal movement and swim against the average flow of the water environment, are called nekton. The study of plankton is termed planktology.

Plankton concentration and distribution are sensitive to chemical and physical changes in the water.

Size groups

The smaller organisms in the plankton are often described in terms of their size:

• Nanoplankton are plankton organisms that are 2 to 63 μm diameter.
• Picoplankton are even smaller bacterio-plankton (marine bacteria) and some phytoplankton, between 0.2 and 2 μm in diameter. Note that the size of a water molecule is roughly 0.2 μm, so to plankton of this size water would seem very viscous.
• Femoplankton are the smallest yet identified, between 0.02 to 0.2 μm and consist of viro-plankton (or marine viruses)

The existance and importance of the organisims in these small size ranges were only discovered during the 1980s, and they are thought to make up the largest proportion of all plankton by number.

The larger plankton can also be grouped by size into:

• Mesoplankton 0.2 to 20 mm
• Macroplankton 2 to 20 cm
• Megaplankton 20 to 200 cm; only a few of the nekton fall into (the lower end of) this range.

Plankton are divided into broad functional groups:

• Phytoplankton (from Greek phyton or "plant") – algae that live near the water surface where there is sufficient light to support photosynthesis;
• Zooplankton (from Greek zoo or "animal") – small protozoa, crustaceans, copepods, krill, etc. that feed on phytoplankton or on other zooplankton; also included in the zooplankton are eggs and larvae of larger aquatic animals (notably fishes, crustaceans, and annelids).

A hyperiid amphipod
(Hyperia macrocephala)

A copepod (Calanoida sp.) ca. 1-2mm long