<P> Red tides in the Gulf of Mexico are a result of high concentrations of Karenia brevis, a microscopic marine algae that occurs naturally but normally in lower concentrations . In high concentrations, its toxin paralyzes the central nervous system of fish so they cannot breathe . Dead fish have been observed to wash up on gulf beaches of Mexico and Texas . In addition to killing fish and contaminating shellfish, the toxins released by Karenia brevis blooms can kill marine animals including dolphins and manatees . Red tide is very harmful to the environment and ocean inhabitants, because toxins produced by it can affect the central nervous systems of fish, birds, mammals, and other animals . Dense concentrations appear as discolored water, often reddish in color . It is a natural phenomenon, but the exact cause or combination of factors that result in a red tide outbreak are unknown . Red tide causes economic harm and for this reason red tide outbreaks are carefully monitored . For example, the Florida Fish and Wildlife Conservation Commission provides an up - to - date status report on the red tide in Florida . Texas also provides a current status report . </P> <P> Red tides also occur regularly in the Coral Sea, Torres Strait, and along the south coast of Papua New Guinea . The intensities observed are much lower than those found on the Chilean coast, and often go unnoticed . Only two deaths, occurring in April 1972, have ever been confirmed . The closely related ciguatera fatal poisoning is, however, found across large areas of the Western Pacific . While there is no one particular cause of red tides, there are many different factors that contribute to its presence . These factors can include things such a water and coastal pollution which originates from sources such as human sewage and agricultural runoff . There are other factors that have been associated with the increase in red tides, such as weather and tidal patterns, although the correlation isn't always quite clear . </P> <P> Red tide is also potentially harmful to human health . Humans can become seriously ill from eating oysters and other shellfish contaminated with red tide toxins . "In general, bivalves will contain much larger amounts of toxin compared to univalves . Symptoms are very similar to the those found in the closely related ciguatera poisoning ." Shellfish consume the organisms responsible for red tide and concentrate saxitoxin (produced from these organisms) in their tissues . Saxitoxin blocks sodium channels and ingestion can cause paralysis within 30 minutes . Karenia brevis blooms can potentially cause eye and respiratory irritation (coughing, sneezing, tear production, and itching) to beachgoers, boaters and coastal residents . People with severe or persistent respiratory conditions (such as chronic lung disease or asthma) may experience stronger adverse reactions . The National Oceanic and Atmospheric Administration's National Ocean Service provides a public conditions report identifying possible respiratory irritation impacts in areas affected by red tides . </P> <P> There is debate over the cause of red tides . Red tides occur naturally off coasts all over the world . Not all red tides have toxins or are harmful . </P>

What is the cause of red tide poisoning
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