Red Tide Scourges Florida’s Southwest Coast

September 7, 2018 — Down in Southwest Florida residents have been seeing red this summer – as in red tide. This disturbing scourge is the worst it has been in more than a decade. It has killed huge amounts of marine life as well as cost millions in lost tourism dollars in communities like Marco Island. One charter boat captain there says his business is down 80%; to stay busy he has been volunteering to assist researchers out on the water.

In a 120 mile stretch of coast work crews have been spending their mornings cleaning up fish kills on the beach. The organism in red tide releases a deadly toxin that kills marine life like fish and shellfish, along with dolphins, sea turtles, pelicans, and loggerhead turtles. Local animal clinics are experiencing abnormal numbers of injured creatures being brought into their facilities for treatment. Tourists are staying away from the bad smells and air irritants.

Currently the red tide exists in a long stretch from Pinellas County (Tarpon Springs above St. Petersburg) south to Naples and into Collier County. Its appearance is not uniform, but varies in intensity from area to area. Observations of greater than 1,000,000 K. brevis cells per liter ( very “high” concentrations) occurred in samples collected in or offshore of Hillsborough, Charlotte, Lee and Collier counties, but not in Pinellas, Manatee or Sarasota counties.
See map below:

To answer some of the most common questions about it, we are reprinting some information from the Florida Fish and Wildlife Commission below. For even more information go the FL Fish & Wildlife Commission FAQ page.

What is a red tide?
A red tide, or harmful algal bloom, is a higher-than-normal concentration of a microscopic alga (plantlike organism). In Florida and the Gulf of Mexico, the species that causes most red tides is Karenia brevis, often abbreviated as K. brevis. To distinguish K. brevis blooms from red tides caused by other species of algae, researchers in Florida call the former the “Florida red tide.”

Are red tides red?
At high enough concentrations, Florida red tide can discolor water a red or brown hue. Blooms caused by other algal species can appear red, brown, green or even purple. The water can also remain its normal color during a bloom.

Is red tide a new phenomenon?
No, red tides were documented in the southern Gulf of Mexico as far back as the 1700s and along Florida’s Gulf coast in the 1840s. Fish kills near Tampa Bay were even mentioned in the records of Spanish explorers.

How long do Florida red tides last?
Red tides can last as little as a few weeks or longer than a year. They can even subside and then reoccur. The duration of a bloom in nearshore Florida waters depends on physical and biological conditions that influence its growth and persistence, including sunlight, nutrients and salinity, as well as the speed and direction of wind and water currents. Tropical Storm Gordon that passed through recently seems to have helped reduce the problem.

Has coastal (nutrient) pollution caused the Florida red tide?
Florida red tides develop 10-40 miles offshore, away from man-made nutrient sources. In contrast to the many red tide species that are fueled by nutrient pollution associated with urban or agricultural runoff, there is no direct link between nutrient pollution and the frequency or initiation of red tides caused by K. brevis. Red tides occurred in Florida long before human settlement, and severe red tides were observed in the mid-1900s before the state’s coastlines were heavily developed. However, once red tides are transported inshore, they are capable of using man-made nutrients for their growth. The redirection of fresh water flow from Lake Okeechobee has probably not been helpful.

Why are red tides harmful?
Many red tides produce toxic chemicals that can affect both marine organisms and humans. The Florida red tide organism produces brevetoxins that can affect the central nervous system of fish and other vertebrates, causing these animals to die. Wave action can break open K. brevis cells and release these toxins into the air, leading to respiratory irritation. For people with severe or chronic respiratory conditions, such as emphysema or asthma, red tide can cause serious illness. The red tide toxins can also accumulate in molluscan filter-feeders such as oysters and clams, which can lead to Neurotoxic Shellfish Poisoning in people who consume contaminated shellfish.

Comments? Has the red tide made you nervous about retiring to Southwest Florida? Or if you live there already, has it affected your way of life? Please share your thoughts in the Comments section below.

For further reading:
FL Fish and Wildlife info on Red Tide