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Jai Ganesh

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Plankton

Plankton

Gist

Plankton are marine and freshwater organisms that, because they are nonmotile or too small or weak to swim against the current, exist in a drifting state. The term plankton is a collective name for all such organisms—including certain algae, bacteria, protozoans, crustaceans, mollusks, and coelenterates, as well as representatives from almost every other phylum of animals. Plankton is distinguished from nekton, which is composed of strong-swimming animals, and from benthos, which includes sessile, creeping, and burrowing organisms on the seafloor. Large floating seaweeds (for example, Sargassum, which constitutes the Sargasso Sea) and various related multicellular algae are not considered plankton but pleuston. Pleuston are forms of life that live at the interface of air and water. Organisms resting or swimming on the surface film of the water are called neuston (e.g., the alga Ochromonas).

Plankton is the productive base of both marine and freshwater ecosystems, providing food for larger animals and indirectly for humans, whose fisheries depend upon plankton. As a human resource, plankton has only begun to be developed and exploited, in view of its high biological productivity and wide extent. It has been demonstrated on several occasions that large-scale cultures of algae are technically feasible. The unicellular green alga Chlorella has been used particularly in this connection. Through ample culture conditions, production is directed toward protein content greater than 50 percent. Although this protein has a suitable balance of essential amino acids, its low degree of digestibility prevents practical use. Phytoplankton may become increasingly important in space travel as a source for food and for gas exchange. The carbon dioxide released during respiration of spacecraft personnel would be transformed into organic substances by the algae, while the oxygen liberated during this process would support human respiration.

Summary

The word “plankton” comes from the Greek for “drifter” or “wanderer.” An organism is considered plankton if it is carried by tides and currents, and cannot swim well enough to move against these forces. Some plankton drift this way for their entire life cycle.

Others are only classified as plankton when they are young, but they eventually grow large enough to swim against the currents. Plankton are usually microscopic, often less than one inch in length, but they also include larger species like some crustaceans and jellyfish.

Scientists classify plankton in several ways, including by size, type, and how long they spend drifting. But the most basic categories divide plankton into two groups: phytoplankton (plants) and zooplankton (animals).

Phytoplankton are microscopic plants, but they play a huge role in the marine food web. Like plants on land, phytoplankton perform photosynthesis to convert the sun’s rays into energy to support them, and they take in carbon dioxide and produce oxygen. Because they need the sun’s energy, phytoplankton are found near the water’s surface.

Zooplankton include microscopic animals (krill, sea snails, pelagic worms, etc.), the young of larger invertebrates and fish, and weak swimmers like jellyfish. Most zooplankton eat phytoplankton, and most are, in turn, eaten by larger animals (or by each other). Krill may be the most well-known type of zooplankton; they are a major component of the diet of humpback, right, and blue whales. During the daylight hours, zooplankton generally drift in deeper waters to avoid predators. But at night, these microscopic creatures venture up to the surface to feed on phytoplankton. This process is considered the largest migration on Earth; so many animals make this journey that it can be observed from space.

Plankton are incredibly important to the ocean ecosystem, and very sensitive to changes in their environment, including in the temperature, salinity, pH level, and nutrient concentration of the water. When there are too many of certain nutrients in the water, for instance, harmful algal blooms like red tides are the result. Because many zooplankton species eat phytoplankton, shifts in timing or abundance of phytoplankton can quickly affect zooplankton populations, which then affects species along the food chain. Researchers are studying how climate change affects plankton, from the timing of population changes to the hardening of copepod shells, and how those effects ripple through ecosystems.

Details

The microscopic plants and animals of the plankton family are the foundation of freshwater and seawater food pyramids.

Though they are microscopic in size, organisms called plankton play a big role in marine ecosystems. They provide the base for the entire marine food web. The word plankton comes from the Greek word planktos, which means “drifter.” Their name fits, because plankton do not swim on their own or stay in one place like coral. They drift about in the water, allowing tides, currents, and other factors determine where they go.

There are two main types of plankton: phytoplankton, which are plants, and zooplankton, which are animals. Zooplankton and other small marine creatures eat phytoplankton and then become food for fish, crustaceans, and other larger species.

Phytoplankton make their energy through photosynthesis, the process of using chlorophyll and sunlight to create energy. Like other plants, phytoplankton take in carbon dioxide and release oxygen. Phytoplankton account for about half of the photosynthesis on the planet, making them one of the world’s most important producers of oxygen. Phytoplankton rely on nutrients found in their surroundings, such as phosphate, nitrate, and calcium, to thrive.

In addition to phytoplankton and zooplankton, two even smaller kinds of plankton can be found floating in the sea. Bacterioplankton are bacteria and virioplankton are viruses.

Plankton can be found in saltwater and freshwater. One way to tell if a body of water has a large plankton population is to look at its clarity. Very clear water usually has less plankton than water that is more green or brown in color.

While plankton populations are needed for thriving marine ecosystems, too many plankton in one area can create a serious environmental problem. When a plankton population suddenly swells, it is called a “bloom.” When this happens with certain types of phytoplankton that release dangerous toxins, the region may experience a red tide or other serious algal bloom. These temporary conditions can cause high fish mortality and other damage to the marine ecosystem. Contaminated fish that are caught and served to people may also cause illness and even death.

Because the aquatic food chain depends so heavily on plankton, the survival of these tiny plants and animals is essential for healthy marine ecosystems. Climate change and rising sea temperatures pose serious risks to plankton populations.

National Geographic Explorer Gabrielle Corradino is a U.S. Department of the Interior Climate Science fellow whose research interests include the role of plankton in the marine food web. The more that scientists like Corradino understand how to protect these critical marine species, the more likely it is that their research will help creatures further up the food chain survive threats such as climate change.

Additional Information

Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial source of food to many small and large aquatic organisms, such as bivalves, fish, and baleen whales.

Marine plankton include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit the saltwater of oceans and the brackish waters of estuaries. Freshwater plankton are similar to marine plankton, but are found in lakes and rivers. Mostly plankton just drift where currents take them, though some, like jellyfish, swim slowly but not fast enough to generally gain control from the influence of currents.

Although plankton are usually thought of as inhabiting water, there are also airborne versions that live part of their lives drifting in the atmosphere. These aeroplankton include plant spores, pollen and wind-scattered seeds. They may also include microorganisms swept into the air from terrestrial dust storms and oceanic plankton swept into the air by sea spray.

Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish. This is because plankton are defined by their ecological niche and level of motility rather than by any phylogenetic or taxonomic classification. The "plankton" category differentiates these organisms from those that float on the water's surface, called neuston, those that can swim against a current, called nekton, and those that live on the deep sea floor, called benthos.

Terminology

Plankton (organisms that drift with water currents) can be contrasted with nekton (organisms that swim against water currents), neuston (organisms that live at the ocean surface) and benthos (organisms that live at the ocean floor).
The name plankton was coined by German marine biologist Victor Hensen in 1887 from shortening the word halyplankton from Greek "sea" and to "drift" or "wander".  While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day (a behavior called diel vertical migration), their horizontal position is primarily determined by the surrounding water movement, and plankton typically flow with ocean currents. This is in contrast to nekton organisms, such as fish, squid and marine mammals, which can swim against the ambient flow and control their position in the environment.

Within the plankton, holoplankton spend their entire life cycle as plankton (e.g. most algae, copepods, salps, and some jellyfish). By contrast, meroplankton are only planktic for part of their lives (usually the larval stage), and then graduate to either a nektic (swimming) or benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.

The amount and distribution of plankton depends on available nutrients, the state of water and a large amount of other plankton.

The study of plankton is termed planktology and a planktonic individual is referred to as a plankter. The adjective planktonic is widely used in both the scientific and popular literature, and is a generally accepted term. However, from the standpoint of prescriptive grammar, the less-commonly used planktic is more strictly the correct adjective. When deriving English words from their Greek or Latin roots, the gender-specific ending (in this case, "-on" which indicates the word is neuter) is normally dropped, using only the root of the word in the derivation.

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