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