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, πλαγκτoν—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.
Femtoplankton, smaller than 0.2 μm, consisting of marine viruses
However, some of these terms may be used with very different boundaries, especially on the larger end of the scale. The existence and importance of nano- and even smaller plankton was only discovered during the 1980s, but they are thought to make up the largest the proportion of all plankton in number and diversity.
Zooplankton (from Greekzoon or animal), small protozoa, crustaceans, and various other animals that feed on other plankton. Some of the eggs and larvae of larger animals, such as fish, crustaceans, and annelids, are included here.
Zooplankton are useful indicators of future fisheries health because they are a food source for organisms at higher trophic levels, such as finfish.
Zooplankton are planktonicanimals that range in size from microscopic rotifers to macroscopic jellyfish.
Zooplankton, like phytoplankton, make excellent indicators of environmental conditions within the Bay, because they are sensitive to changes in water quality.
An accurate model of the feeding ecology of zooplankton is critical to understanding the marine nutrient cycle, but explanations for the extensive diel vertical migration of zooplankton have failed to completely account for the observed behavior (1, 2, 3, 4, 5).
Zooplankton typically descend hundreds of meters at dawn and rise toward the surface at dusk.
Zooplankton may also find an advantageous decline in viscosity of water at depth, if conditions are encountered where the viscosity increase induced by lowered temperature is outweighed by the viscosity decrease associated with increasing pressure.
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