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Protists: A Microbial Grab Bag |
Chapter: 5
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The Red Tide A gentle breeze, a sunny seashore, the soft lapping of the water . . . what vacationer could ask for more? Unfortunately, the same scenario appeals to dinoflagellates as well. When the ocean is warm and nutrients are plentiful, dinoflagellates experience a burst of reproductive activity and fill the water with their immense numbers. So many are present that the water appears to turn a rusty red. These so-called red tides occur periodically on the Atlantic and Pacific coasts, and virtually anywhere that conditions are favorable.
Red tides are hazardous to health because dinoflagellates produce a toxin that is poisonous to humans and animals. The toxin concentrates in molluscs such as mussels, clams, and scallops. When ingested by humans, the toxin may cause neuromuscular disturbances such as tingling and numbing of the lips, tongue, and fingertips, followed by uncertain balance, lack of muscular coordination, slurred speech, and difficulty in swallowing. There is no known antidote to the toxin.
During the 1900s, hundreds of cases of red-tide intoxication were recorded in California, with numerous deaths. For this reason, the California state Health Department imposes an annual 6-month quarantine on the harvesting of mussels, by any except commercial operations. The taking of clams and scallops is not restricted unless toxic mussels are discovered nearby, because these shellfish do not accumulate toxin as rapidly as mussels. Other states also restrict shellfish harvesting when red tides set in.
Red tides are also dangerous to those who swim in the water because toxins can be ingested directly from the water. Moreover, the depletion of oxygen in the water contributes to the death of plants and animals, and causes the water to develop an obvious stench from decaying organic matter. Beachgoers often wish they had opted for a vacation in the mountains.
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