Red Menace

Algae blooms threaten coastal waters with potent toxins.

Edward F. Gibbons, Jr.

July/August 2009


Four years ago, one of the worst outbreaks of red tide swept across Florida’s Gulf Coast. Huge grouper floated dead and sea turtles, too weakened to dive, also died. The bodies of manatees and dolphins littered beaches; dead sponges and coral, the seabed. The waters had a reddish-brown tint. People near the shore complained that their eyes and throats felt irritated. Those with asthma or other respiratory problems struggled to breathe.

This scenario plays out along coastlines around the world, though not always as severe as the 2005 outbreak that lasted an entire year and covered 26,000 square miles of water. At the heart of red tides is a species of phytoplankton, Karinia brevis, which produces toxins that can harm people and wildlife.

K. brevis produces blooms in the Gulf of Mexico (the most frequent site) and on the east coast from Florida to North Carolina. But red tide is not exclusive to southern coastal communities. Also in 2005, a red tide crept across New England waters, forcing the closure of large areas to shellfishing at the height of tourism season, amounting to a $15 million economic loss to Massachusetts, according to the Natural Resources Defense Council. Shellfishing was not safe in some areas for a year afterward, the NRDC says.

Deadly Tide Origins

Though their precise origin is unknown, red tide blooms begin in low-nutrient waters approximately 11 to 46 miles offshore and can be transported to coastal waters by currents and winds, according to a hypothesis cited by Gabriel A. Vargo, PhD in the journal Harmful Algae (July/August 09).


Agricultural run-offs and the decay of dead fish are among the nutrient sources that may lead to red tide. “K. brevis can utilize nitrogen and phosphorus compounds, and these nutrients can play a role in the maintenance of Florida red tide blooms,” says Cynthia Heil, PhD, senior research scientist with the Fish and Wildlife Research Institute (FWRI) of the Florida Fish and Wildlife Conservation Commission. Optimal temperature and salinity ranges for K. brevis blooms are 71.6-82.4°F and 25-45 grams of salt per 1,000 grams of water, respectively, she adds.

Choked off from oxygen, fish and vertebrates apparently die as a result of respiratory failure. Shellfish, however, have adapted a tolerance for the toxins produced by K. brevis, known as brevetoxins, and typically survive Florida red tide blooms, says Jan Landsberg, PhD, research scientist with the FWRI. But, Landsberg adds, “Shellfish accumulate concentrations of the brevetoxins in their tissue, thus providing a mechanism to transport these toxins within the food chain, and posing a risk to public health from Neurotoxic Shellfish Poisoning (NSP).”

Heil notes that people can be affected by K. brevis blooms either by eating contaminated shellfish or by inhaling microscopic particles that escape into the air; these particles can trigger asthma episodes, coughing and throat irritation. While there have not been any reported human deaths due to NSP or through particle inhalation, the Centers for Disease Control notes that symptoms from NSP begin one to three hours after eating the contaminated shellfish and include numbness, tingling in the mouth, arms and legs, a lack of coordination, and an upset stomach. Recovery typically takes two to three days.

One theory is that major storms precede red tides. Four hurricanes crossed Florida in August and September 2004, dumping as much as 27 inches of rain in central Florida according to NASA. That increased groundwater levels and rates of surface runoff, two conditions believed to lead to a red tide bloom.

Currently, research is focusing on the use of biological, chemical and physical control of red tide blooms. One promising solution is the use of natural clays to sink or entrap agal cells.
Though hurricanes may be beyond our control, manageable factors such as pollution and overdevelopment have made the ecosystem more fragile, some environmentalists believe. Limiting those factors could make it easier for marine and other life in areas affected by red tide to recover.

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