By staff February 1, 2006

It's a scenario that plays itself out at least once a year in Southwest Florida: You take your family out for a boat ride on a pleasant day, but within minutes the excursion turns into an all-too familiar maritime horror story. Eyes began to water, chests feel congested and shoals of dead fish float ominously along the water's surface. Too often, a sunny morning on the beach ends in the doctor's office as our local menace-red tide-continues to hang out offshore, causing tourists and residents to suffer from itchy, watery eyes, congestion, coughing and even difficulty breathing.

"We see it whenever there is a bloom out," says Dr. Hugh Windom, an allergist and associate clinical professor at the University of South Florida. "People with underlying lung or nose sensitivities are more prone to problems such as itchy, burning nose, itchy, watery, burning eyes, and cough and congestion in the chest."

Dr. Barbara Kirkpatrick, a senior scientist at Mote Marine Lab in Sarasota, has been studying the effects of red tide on humans for six years with a team of researchers from several agencies, including the Centers for Disease Control, Florida Department of Health and the University of Miami. A former respiratory therapist, Kirkpatrick became interested in the topic when she heard accounts of people visiting hospitals with irritating reactions from red tide. Kirkpatrick says that her gut instinct is that red tide is getting worse; indeed, she feels that harmful algal blooms are getting worse worldwide. However, it's difficult to prove that the incidence of red tide has increased.

"With better monitoring, the more we look for it, the more we find it," she says. "With satellite pictures, if there is a bloom 30 miles offshore, we can aim our boat toward it and get a sample. And as we populate the coastline, there are more people getting affected; that's a no-brainer."

Florida red tide occurs when there is a bloom, a larger-than-usual concentration of a species of algae, Karenia brevis. Paradoxically, the bloom does not always turn the water red; it can appear green, brown, purple or even unchanged.

K. brevis has always naturally existed in the Gulf of Mexico off Florida's coast. When the algae get into warm water rich in nutrients, they multiply, or bloom. When this happens, they release a toxic vapor into the surrounding water and air, causing fish and marine-mammal deaths (147 manatees died during the 1996 bloom), contaminating shellfish beds, irritating mucosal membranes and allergies in humans, and causing congestion, swelling and secretions.

Scientists have pointed to runoff from a massive part of the agricultural United States being carried down the Mississippi and into the Gulf, creating a nutrition-rich environment for the phytoplankton to bloom in ever-larger numbers. But there's presently no way of predicting when a bloom will hit an area.

Red tide has been documented as far back as 1840. Even further back, the logs of Spanish explorers noted massive fish-kills centuries ago. Red tide was first linked to irritation in humans in 1948; but research has been sporadic, and not much has concentrated on the effects of the aerosol on humans. That's what interests Kirkpatrick, who is studying two human populations to try to figure out exactly what red tide does to us.

One group consists of Sarasota County lifeguards, who are occupationally exposed to red tide. Kirkpatrick and her fellow researchers examined the lifeguards before and after their day at work, and found that irritation was limited to the upper airway-eyes and nose-with no change in breathing patterns. However, in the second population she studied-asthmatics׫she found upper respiratory irritations as well as lower chest congestion, wheezing and changes in airflow parameters.

"People are more prone if they have asthma or emphysema," says Dr. Joel Moll, medical director of the emergency department at the Cleveland Clinic of Florida. "Some asthmatics have triggers that are environmental."

Moll says that news reports of blooms usually coincide with increased numbers of people coming into the emergency room with complaints of coughing and wheezing. The good news, says Moll, is that the only solution is an easy one: Avoid the beach when a red tide alert is put out. There is no "cure" for the response people have to red tide, other than treating the symptoms. A common misconception is that red tide is an allergen; Windom points out that it is actually only an irritant-just like cigarette smoke, perfume, strong fragrances and gas.

"It's a difference in mechanism," says Windom. "Both [allergens and irritants] make you feel weird. You can treat the end results, such as with cough medicine, but you can't use allergy shots because you cannot turn off sensitivity to irritants. There's no specific treatment. You just have to get out of the environment."

There are helping measures, however. Kirkpatrick's research shows that for asthmatics, normal asthma medication decreases the effects of the toxin. The inhaler that is prescribed as an emergency inhaler also reversed the effects of the toxin in animal studies, she says.

"If you're an asthmatic and there's red tide in town, now is not the time to cheat on your medicine," says Kirkpatrick, who's concerned about those who don't have good health insurance and are forced to stretch one month's medication into two or more months to save money.

Other common-sense measures are to watch for the "red tide tickle," that persistent cough that irritates many people during a bloom. If you hear many people on the beach coughing, says Kirkpatrick, go home; there's probably a bloom offshore. Tourists and residents should pay attention to media reports, and if there's a report of a bloom, avoid going to the beach, especially if there's an onshore wind.

Everyone except, of course, Kirkpatrick and her researchers, who head directly into a bloom. While a more than 50-year body of red tide research exists, it is not continuous, and there has been less than five years of research into the aerosols that affect humans, so there's a lot of work for Kirkpatrick to do.

"We have a lot of anecdotal information, but we don't have science, and science sets policy," says Kirkpatrick. "Until you have science, you can't set the public health message."


Fish and Wildlife Research Institute Fish-Kill Hotline: (800) 636-0511

Call to report fish-kills, diseased fish or fish with other abnormalities, not to request dead-fish cleanup.

FWC Wildlife Alert Hotline: (888) 404-3922

FWRI Manatee Contact: (727) 893-2904

FWRI Sea Turtle Stranding Contact: (904) 573-3930

FWRI Puffer Fish Kill Contact: (727) 896-8626


Marine and Freshwater Toxins Hotline: (888) 232-8635

Florida Department of Health, Aquatic Toxins Program: (850) 245-4299

Manatee County Red Tide Alert Line: (941) 745-3779

Collier County Red Tide Hotline: (239) 732-2591

SOURCE:, Web site of the Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute.


What is red tide? In Florida, red tide is what occurs when there is an unusually high concentration, or bloom, of an alga called Karenia brevis. This sometimes discolors the water, turning it red, green, brown or purple. The alga releases a toxin that affects fish, marine animals and even humans.

How does red tide affect humans? The toxin released by K. brevis is an irritant for some people, causing itchy, watery eyes, coughing, sneezing and, in some cases, trouble breathing. Symptoms are usually temporary, and all you have to do if you feel them is leave the area. If you have asthma, emphysema or other such respiratory problems, avoid the beach when there is a red tide alert.

Can I swim during a red tide? Unless you are easily irritated by plant products, it should be safe to swim. If you experience irritated skin and burning eyes, get out of the water and wash yourself thoroughly. Do not swim among dead fish; they may be associated with harmful bacteria.

Can I eat shellfish during a red tide? No, do not eat shellfish during red tide; in fact, during red tides, it is forbidden to harvest bivalve mollusks. Avoid mollusks such as clams, coquinas and oysters. It is, however, safe to eat edible parts of other animals commonly called shellfish, such as crabs, shrimp and lobsters, because the toxin does not work its way into the edible tissues of these animals. Scallops are fine to eat as long as you eat only the muscle. Cooking does not destroy the red tide toxin.

SOURCE:, Web site for the Fish and Wildlife Research Institute.

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