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of plankton organisms]] Plankton are any drifting organism that inhabits the Water Column of Ocean s, Sea s, and bodies of Fresh Water . It is a description of life-style rather than a genetic classification. They are widely considered to be some of the most important organisms on Earth, due to the food supply they provide to most aquatic life. DEFINITIONS s - a key Phytoplankton group]] Within the plankton, itself, Holoplankton are those organisms that spend their entire Life Cycle as part of the plankton (e.g. most Algae , Copepod s, Salp s, and Jellyfish ). By contrast, ''' Meroplankton ''' are those organisms that are only planktonic for part of their lives (usually the larval stage), and then graduate to either the nekton or a Benthic (sea floor) existence. Examples of meroplankton include the larvae of Sea Urchin s, Starfish , Crustacean s, marine Worm s, and most Fish . Plankton abundance and distribution are strongly dependent on factors such as ambient Nutrients concentrations, the physical state of the water column, and the abundance of other plankton. The study of plankton is termed Planktology . Individual plankton are referred to as plankters. FUNCTIONAL GROUPS (''Hyperia macrocephala'')]] Plankton are primarily divided into broad functional (or Trophic Level ) groups:
This scheme divides the plankton community into broad producer, '''consumer''' and '''recycler''' groups. In reality, the trophic level of some plankton is not straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species are Mixotrophic depending upon their circumstances. SIZE GROUPS – the "conveyor belt" of the upgrowing larvae and the ovarium can be seen]] 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 1980 s, but they are thought to make up the largest proportion of all plankton in number and diversity. DISTRIBUTION ]] Plankton are found throughout the oceans, seas and lakes of Earth. However, the local abundance of plankton varies horizontally, vertically and seasonally. The primary source of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy (but see Chemosynthesis ), and this confines primary production to surface waters, and to geographical regions and seasons when light is abundant. A secondary source of variability is that of nutrient availability. Although large areas of the Tropical and Sub-tropical oceans have abundant light, they experience relatively low primary production because of the poor availability of nutrients such as Nitrate , Phosphate and Silicate . This is a product of large-scale Ocean Circulation and Stratification of the water column. In such regions, primary production, still usually occurs at greater depth, although at a reduced level (because of reduced light). While plankton are found in the greatest abundance in surface waters, they occur throughout the water column. At depths where no primary production occurs, zooplankton and bacterioplankton instead make use of organic material sinking from the more productive surface waters above. This flux of sinking material can be especially high following the termination of Spring Bloom s. BIOGEOCHEMICAL SIGNIFICANCE (''Calanoida'' sp.) ca. 1-2 Mm long]] Aside from representing the bottom few levels of a Food Chain that leads up to Commercially important Fisheries , plankton Ecosystem s play a role in the Biogeochemical Cycle s of many important Chemical Element s. Of particular contemporary significance is their role in the ocean's Carbon Cycle . As stated, phytoplankton fix Carbon in sunlit surface waters via photosynthesis. Through (primarily) zooplankton grazing, this carbon enters the planktonic foodweb, where it is either Respired to provide Metabolic energy, or accumulates as Biomass or Detritus . As living or dead organic material is typically more Dense than Seawater it tends to sink, and in open ocean ecosystems away from the Coast s this leads to the transport of carbon from surface waters to the deep. This process is known as the Biological Pump , and is one of the reasons that the oceans constitute the largest (active) pool of carbon on Earth . IMPORTANCE TO FISH Zooplankton are initially the sole prey item for almost all Fish Larvae as they use up their yolk sacs and switch to external feeding for nutrition. Fish species rely on the density and distribution of zooplankton to coincide with first-feeding larvae for good survival of larvae, which can otherwise starve. Natural factors (i.e. variations in oceanic currents) and man-made factors (i.e. dams on rivers) can strongly affect zooplankton density and distribution, which can in turn strongly affect the larval survival, and therefore breeding success and stock strength, of fish species. POPULAR CULTURE phytoplankter]]
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