When the Tides Bloom
by Randi Lynn Mrvos
Fact or fiction? The sea can change color and even turn red. Fact! Strange but true, this phenomenon is called a red tide.
Red tides are produced by several kinds of microscopic plants. These kinds of plants are known as microalgae or phytoplankton. Phytoplankton are found at the base of the marine food chain. They are so small that one million of them can fit into a teaspoon of sea water! Phytoplankton live near the surface of water, close to the sunlight. They drift on the waves. Their name comes from Greek words meaning "floating plants." The first phytoplankton lived 3 billion years ago.
Phytoplankton can be grouped into many groups. One of these groups is called dinoflagellates. Some dinoflagellates store bright-red pigments. These pigments can discolor the water, especially when dinoflagellates occur in large numbers. When they bloom, the dinoflagellates produce a rosy color. The color may linger for a few days or for many weeks.
Dinoflagellates multiply in water that is warm and low in salinity. They also grow rapidly in the presence of rich nutrients. The nutrients can come from man-made sources like fertilizers. They can also come from natural sources like upwelling. Upwelling occurs when cold nutrient-rich waters rise to the surface. Scientists now think that these nutrients may be intensifying and prolonging red tides.
Of the more than 60 various kinds of phytoplankton that cause red tides, 4 or 5 are toxic. Scientists use the term HAB (harmful algae bloom) to describe toxic red tides. An HAB can kill pelicans, dolphins, and even whales! When humans eat shellfish contaminated by an HAB, they may become ill. Numbness, diarrhea, memory loss, and even death may result from eating contaminated shellfish.
Shellfish such as clams, oysters, mussels, and scallops are filter-feeders. Filter-feeders eat by straining suspended food particles from water. These shellfish eat dinoflagellates. Following a red tide, the meat of the shellfish can become toxic within a few days. It can harbor the toxin for up to two years after the bloom. Generally, it is thought that the filter-feeding shellfish are not affected by the toxin. But sometimes after a bloom, even the shellfish can die because of a lack of oxygen in the water. When dinoflagellates decompose, bacteria multiply and deplete the oxygen in the water.
Crabs, lobster, and shrimp are safe to eat even if they are caught in red tide waters. These marine animals are not filter-feeders. Filter-feeders however, are dangerous to eat before or after a visible red tide. It takes weeks of flushing with clean water to rid the shellfish of toxin and to make them safe to eat. Cooking doesn't destroy red tide toxin.
Only a few kinds of phytoplankton are harmful. Most are beneficial. They produce more than half of the Earth's oxygen. They also remove the greenhouse gas carbon dioxide, which is harmful to animals. Furthermore, phytoplankton are food for fish, birds, invertebrates, and mammals.
Red tides are found in many parts of the world. They often appear after an extended period of warm sunny days that follow an extended period of heavy rain. Red tides can occur anytime from spring to fall. Usually, they appear during the late summer. At this time, winds and heavy rains are frequent and nutrient levels are high. As long as conditions are favorable, dinoflagellates will continue to bloom. They will color the sea as they have for billions of years.
The author wishes to thank Dr. Gavin W. Maneveldt for his expertise.
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About the Author: Randi Lynn Mrvos is a columnist for The Creativity Connection, an editor for the educational website www.Viatouch.com,
and a former consultant for Pearson Digital Learning. Randi's publishing credits include KidVisions Magazine, Scholastic Books, Gryphon House, Learning through History Magazine, Fun for Kids, Highlights for Children, and Nature Friend. Randi has also been published by Byline, Mothering, and The Christian Scientist Monitor.
About the Art: Red tide photo courtesy of Wikipedia.
Note:
The term "red tides" is misleading. They are not associated with tides. And their blooms are not always red. Depending on the kind of phytoplankton, the ocean may appear green, brown, orange, purple, or even yellow.
For more information, check out:
"Antarctic icebergs are 'hot spots' for life". Courier Journal,
Bendick, Jeanne. Exploring an Ocean Tide Pool. NY: Henry Holt, 1992.
Cerullo, Mary. Sea Soup. ME: Tilbury House, 1999.
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Hedlund, Steven. "Don't let sales ebb when red tide hits: educate consumers about the causes and effects of this natural event." Seafood Business 24, no.5 (May 2005): 30.
Raloff, Janet. "Rain of foreign dust fuels red
tides." Science News 160, no. 13 (
Kelley, Ken. "Pollution may be a cause of worldwide toxic algae blooms." National Fisherman 72, no. 9 (Jan. 1992):28-30.
Stevens, Betsy. Sea Soup Teacher's Guide. ME: Tilbury House, 1999.
Internet:
www.botany.uwc.ac.za/Envfacts/redtides/
http://www.gso.uri.edu/criticalscales/about/kinds/phyto/phytotxt.html
http://www.heraldtribune.com/apps/pbcs.dll/article?AID=/20050904/COLUMNIST13/509040727
www.mi.mun.ca/mi-net/fishdeve/redtide.htm
http://www.nmnh.si.edu/highlight/sem/highlight/dinos/dinoflagellates.htm
www.seagrant.gso.uri.edu/factsheets/redtide.html
http://www.whoi.edu/redtide/whathabs/whathabs.html