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see marine biologymarine biology,
study of ocean plants and animals and their ecological relationships. Marine organisms may be classified (according to their mode of life) as nektonic, planktonic, or benthic. Nektonic animals are those that swim and migrate freely, e.g.
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Animals that inhabit the water column of oceans and lakes and lack the means to counteract transport currents. Zooplankton inhabit all layers of these water bodies to the greatest depths sampled, and constitute a major link between primary production and higher trophic levels in aquatic ecosystems. Many zooplankton are capable of strong swimming movements and may migrate vertically from tens to hundreds of meters; others have limited mobility and depend more on water turbulence to stay afloat. All zooplankton, however, lack the ability to maintain their position against the movement of large water masses.

Zooplankton can be divided into various operational categories. One means of classification is based on developmental stages and divides animals into meroplankton and holoplankton. Meroplanktonic forms spend only part of their life cycles as plankton and include larvae of benthic worms, mollusks, crustaceans, echinoderms, coral, and even insects, as well as the eggs and larvae of many fishes. Holoplankton spend essentially their whole existence in the water column. Examples are chaetognaths, pteropods, larvaceans, siphonophores, and many copepods. Nearly every major taxonomic group of animals has either meroplanktonic or holoplanktonic members.

Size is another basis of grouping all plankton. A commonly accepted size classification scheme includes the groupings: picoplankton (<2 micrometers), nanoplankton (2– 20 μm), microplankton (20–200 μm), mesoplankton (0.2–20 mm), macroplankton (20–200 mm), and megaplankton (>200 mm).

The classic description of the trophic dynamics of plankton is a food chain consisting of algae grazed by crustacean zooplankton which are in turn ingested by fishes. This model may hold true to a degree in some environments such as upwelling areas, but it masks the complexity of most natural food webs. Zooplankton have an essential role in linking trophic levels, but several intermediate zooplankton consumers can exist between the primary producers (phytoplankton) and fish. Thus, food webs with multiple links to different organisms indicate the versatility of food choice and energy transfer and are a more realistic description of the planktonic trophic interactions.

Size is of major importance in planktonic food webs. Most zooplankton tend to feed on organisms that have a body size smaller than their own. However, factors other than size also modify feeding interactions. Some phytoplankton are noxious and are avoided by zooplankton, and others are ingested but not digested. Furthermore, zooplankton frequently assume different feeding habits as they grow from larval to adult form. They may ingest bacteria or phytoplankton at one stage of their life cycle and become raptorial feeders later. Other zooplankton are primarily herbivorous but also ingest heterotrophic protists and can opportunistically become carnivorous. Consequently, omnivory, which is considered rare in terrestrial systems, is a relatively common trophic strategy in the plankton. In all food webs, some individuals die without being consumed and are utilized by scavengers and ultimately by decomposers (bacteria and fungi). See Ecology, Ecosystem, Marine ecology, Phytoplankton


Microscopic animals which move passively in aquatic ecosystems.
References in periodicals archive ?
Scientific Collecting Permit for zooplankton and bivalves
On the basis of work carried out by the MSFD HELCOM zooplankton working group, a core indicator of food web structure based on mesozooplankton, i.
Spring water was added if needed, but the zooplankton suspension usually replaced the volume of water lost to evaporation.
They were mean water temperature ([degrees]C), mixed-layer depth (m), an index of geostrophic flow, the log of volume displaced by zooplankton captured in nets (mL/1000 [m.
While the Scripps scientists said the cause of the decline in zooplankton remains uncertain, they suspect the gradual warming of ocean surface waters over the last four decades may be to blame.
This year the scientists-oceanographers, marine biologists, and others-are narrowing their focus to the larvae's main source of nutrition, the zooplankton in the cold waters of the strait, according to James D.
An international team of researchers from the INFERNO project (2006-9), many of whom were from the Norwegian Institute of Marine Research, set out to address the hypothesis that the planktivorous fish populations feeding in the Norwegian Sea have interactions that negatively affect individual growth, mediated through depletion of their common zooplankton resource.
Indeed, in the field and laboratory, freshwater zooplankton was found to trigger Bd infection in two amphibian species by directly consuming Bd zoospores.
Analysis of zooplankton communities of 16 European lakes from latitudes between 60[degrees]N and 44[degrees]N revealed the presence of 20-25 species, with 2-5 rotifers and 1-3 copepods being dominant; both cold-water species and perennial, eurythermal species contributed to the zooplankton community (Dokulil and Herzig, 2009).
The computer modeled jellyfish - unlike the real gelatinous zooplankton filmed in lab settings - allows researchers to control movements of the creature however fast they wish, and in any desired direction.
Zooplankton of the Atlantic and Gulf coasts; a guide to their identification and ecology, 2d ed.
During 13 monthly expeditions, Jaspers and colleagues collected zooplankton samples from four different regions of the central Baltic Sea.