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Red Tide

Red tide

Red tides are a marine phenomenon in which water is stained a red, brown, or yellowish color because of the temporary abundance of a particular species of pigmented dinoflagellates (these events are known as "blooms"). Also called phytoplankton, or planktonic algae, these single-celled organisms of the class Dinophyceae move using a tail-like structure called a flagellum. They also photosynthesize, and it is their photosynthetic pigments that can tint the water during blooms. Dinoflagellates are common and widespread. Under appropriate environmental conditions, various species can grow very rapidly, causing red tides. Red tides occur in all marine regions with a temperate or warmer climate.

The environmental conditions that cause red tides to develop are not yet understood. However, they are likely related to some combination of nutrient availability, nutrient ratios, and water temperature. Red tides are ancient phenomena. Scientists suspect that human activities that affect nutrient concentrations in seawater may be having an important influence on the increasingly more frequent occurrences of red tides in some areas. In particular, the levels of nitrogen, phosphorous, and other nutrients in coastal waters are increasing due to runoff from fertilizers and animal waste. Complex global changes in climate also may be affecting red tides. Water used as ballast in ocean-going ships may be introducing dinoflagellates to new waters.

Sometimes the dinoflagellates involved with red tides synthesize toxic chemicals. Genera that are commonly associated with poisonous red tides are Alexandrium, Dinophysis, and Ptychodiscus. The algal poisons can accumulate in marine organisms that feed by filtering large volumes of water, for example, shellfish such as clams, oysters, and mussels. If these shellfish are collected while they are significantly contaminated by red-tide toxins, they can poison the human beings who eat them. Marine toxins can also affect local ecosystems by poisoning animals. Some toxins, such as that from Ptychodiscus brevis, the organism that causes Florida red tides, are airborne and can cause throat and nose irritations.

Red tides can cause ecological damage when the algal bloom collapses. Under some conditions, so much oxygen is consumed to support the decomposition of dead algal biomass that anoxic (lack of oxygen) conditions develop. This can cause severe stress or mortality in a wide range of organisms that are intolerant of low-oxygen conditions. Some red-tide algae can also clog or irritate the gills of fish and can cause stress or mortality by this physical effect.

Saxitoxin is a natural but potent neurotoxin that is synthesized by certain species of marine dinoflagellates. Saxitoxin causes paralytic shellfish poisoning, a toxic syndrome that affects humans who consume contaminated shell-fish. Other biochemicals synthesized by dinoflagellates are responsible for diarrhetic shellfish poisoning, another toxic syndrome. Some red tide dinoflagellates produce reactive forms of oxygensuperoxide, hydrogen peroxide, and hydroxyl radicalwhich may be responsible for toxic effects. A few other types of marine algae also produce toxic chemicals. Diatoms in the genus Nitzchia synthesize domoic acid, a chemical responsible for amnesic shellfish poisoning in humans.

Marine animals can also be poisoned by toxic chemicals synthesized during blooms. For example, in 1991, a bloom in Monterey Bay, California, of the diatom Nitzchia occidentalis resulted in the accumulation of domoic acid in filter-feeding zooplankton . These small animals were eaten by small fish, which also accumulated the toxic chemical and then poisoned fish-eating cormorants and pelicans that died in large numbers. In addition, some humans who ate shellfish contaminated by domoic acid were made ill.

In another case, a 1988 bloom of the planktonic alga Chrysochromulina polylepis in the Baltic Sea caused extensive mortalities of various species of seaweeds, invertebrates, and fish. A bloom in 1991 of a closely related species of alga in Norwegian waters killed large numbers of salmon that were kept in aquaculture cages. In 1996, a red tide killed 149 endangered manatees in the coastal waters of Florida.

Even large whales can be poisoned by algal toxins. In 1985, 14 humpback whales died in Cape Cod Bay, Massachusetts, during a five-week period. This unusual mortality was caused by the whales eating mackerel that were contaminated by saxitoxin synthesized during a dinoflagellate bloom. In one observed death, a whale was seen to be behaving in an apparently normal fashion, but only 90 minutes later, it had died. The symptoms of the whale deaths were typical of the mammalian neurotoxicity that is associated with saxitoxin, and fish collected in the area had large concentrations of this poisonous chemical in their bodies.

See also Photosynthetic microorganisms; Plankton and planktonic bacteria

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Red Tide

Red tide

Red tide is a condition in which a huge area of seawater turns to a reddish-brown hue. This rusty-red discoloration is caused by an exploding population of tiny single-celled microorganisms called dinoflagellates, which are usually found in ocean water , but occasionally in lakes and rivers as well. Red tides have occurred naturally since oceans were formed, but today they are becoming more common because of human influence. During summer months, the warm Sun and an abundance of food in the water create optimal conditions for the breeding of dinoflagellates, which are a type of phytoplankton. This multiplication, or bloom, happens rapidly, and the seawater becomes extremely dense with dinoflagellates; sometimes their numbers can reach many millions per cup of seawater. Even though most red tides are harmless, many of them are toxic and extremely dangerous to fish, shellfish, birds, and even humans. Certain species of dinoflagellates are capable of producing highly-toxic substances.

When these toxic red tides appear in warm coastal places like Texas and Florida, people are warned not to swim, fish, or eat locally-caught fish. Clams, oysters, mussels, and other shellfish are especially dangerous because they feed on the dinoflagellates and retain the toxins. If ingested by humans, contaminated shellfish can cause nausea and diarrhea or worse. In severe cases, the poisons attack human muscle fibers and can cause partial paralysis or even death. In addition to being warned not to eat or catch fish, people are generally advised to stay away from coastal areas during red tide. Decaying bodies of dead fish and birds can create foul smells in the air. Moreover, when people inhale the air around wind-blown red tide, their lungs can become irritated.

Today, red tides are increasingly common in the Gulf of Mexico . Many rivers, including the Mississippi, empty into the Gulf, depositing sewage, industrial waste, and chemicals into the ocean. These pollutants contain phosphorous and nitrogen which then serve as food for the dinoflagellate algae. As the algae organisms consume the nitrogen and phosphorous, they spread their color across the water, cutting off sunlight and oxygen to other marine life. The severity of red tide is unpredictable because of such factors as the weather , water composition, marine life, and pollution levels. Red tides can last for a few hours or up to several months. The size can range from less than a few square yards to more than 1,000 miles (1613 km).

See also Environmental pollution; Oceans and seas; Water pollution

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red tide

red tide A sudden often toxic proliferation of marine phytoplankton, notably dinomastigotes, that colours the sea red, brown, or yellowish due to the high concentration of the organisms' photosynthetic accessory pigments. Some dinomastigotes, such as Gonyaulax, produce potent toxins, which may kill fish and invertebrates outright or accumulate in the food chain, posing a hazard to humans eating shellfish and other seafood. These phytoplankton blooms may be related to nutrient-rich inputs from the land, or upwelling oceanic waters, and are initiated by the activation of cystlike forms lying on the seabed.

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red tide

red tide A phenomenon in which blooms of certain dinoflagellates colour the water of seas or estuaries red or reddish. The dinoflagellates, particularly species of Gonyaulax, are concentrated, along with their toxins, by filter-feeding shellfish, and when the shellfish are subsequently eaten by humans, poisoning results. Fish and shellfish may also die by poisoning.

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"red tide." A Dictionary of Plant Sciences. . Encyclopedia.com. 20 Jul. 2017 <http://www.encyclopedia.com>.

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red tide

red tide A phenomenon in which blooms of certain dinoflagellates colour the water of seas or estuaries red or reddish. The dinoflagellates, particularly species of Gonyaulax, are concentrated, along with their toxins, by filter-feeding shellfish, and when the shellfish are subsequently eaten by humans poisoning results. Fish and shellfish may also die by poisoning.

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"red tide." A Dictionary of Ecology. . Encyclopedia.com. 20 Jul. 2017 <http://www.encyclopedia.com>.

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"red tide." A Dictionary of Ecology. . Retrieved July 20, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/red-tide

red tide

red tide Sudden, unexplained increase in numbers of toxic organisms (dinoflagellates) in the sea which cause fish and shellfish feeding on them to become toxic.

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red tide

red tide: see Dinoflagellata.

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