How Does Red Tide Threaten Florida’s Coastline?

Peak red tide season is approaching, and these toxic blooms can negatively impact marine life, beach safety, and human health. 

A Deadly Bloom

Murky, reddish-brown sludge replaced the once beautiful, crystal-clear waters near John’s Pass in Madeira Beach. A putrid odor clung to the air. Between the stench and the heat, it was hard to breathe. The mud-like water was thick with dead marine life.  

“Every fish under the sun was dead,” said Torin Clarke, a captain at One More Charters. From his boat, Clarke saw fish of all colors and sizes, from small pinfish to massive Goliath Grouper, floating lifelessly near the Skyway Bridge. 

People in green hazmat-looking suits collected fish with trident-like poles, hauling thousands of them into bags. Boats brought in even more huge nets full of them. Every boat ramp in the area had dumpsters set up to accommodate the waste. The scene, a particularly severe red tide bloom around 2016,  was devastating. 

As an intercoastal fisherman, Clarke is typically less than nine miles off shore. Nutrient runoff from fertilizers pollutes these intercoastal waterways easily, as humans have easy access to them, intensifying the effects of red tide.  

“I've seen red tie to a point where I thought that we were not going to be able to keep fish for five years,” said Clarke, who’s been fishing in the St. Pete area his whole life. As a charter captain, red tide directly affects his business. When a bloom hits, fish become toxic and inedible.

Every year, harmful algal blooms (HAB) caused by the bacteria Karenia brevis, better known as red tide, plague Gulf Coast waters, killing marine life and damaging fishing and tourism industries around Tampa Bay. Driven by warming waters and nutrient pollution, red tide blooms have been intensifying. 

New Science Targets Red Tide

As these blooms continue to threaten coastal communities, scientists and conservationists are leaning on new research to help reduce its effects.

Researchers at the University of Florida (USF) have just published the first study in an academic journal, mSphere, that successfully identifies the viruses associated with red tide in Florida. By utilizing DNA sequencing tools, these scientists can piece together the genetic material of viruses and figure out which ones are present in red tide blooms.

Compared to current approaches used to mitigate blooms, like chemical treatments and clay flocculation, viruses can infect specific groups or species of phytoplankton without harming other marine life, explained Dr. Jean Lim, the study’s lead author and researcher at USF’s College of Marine Science. 

This technology has the potential to give scientists the ability to reduce widespread negative impacts on the marine ecosystem, said Lim, which in turn would prevent economic and tourism losses across the coast. 

“That's the ambitious goal for the future,” Lim said.

The Toll on Local Waters

Red tide occurs when microscopic algae multiply and reach higher than average concentrations, which discolors the water. These algae blooms are dangerous because they produce toxins that can kill marine life and trigger serious respiratory issues in humans.  

A 2022 study published by the National Oceanic and Atmospheric Administration (NOAA) analyzing over 60 years of data found that red tide blooms now impact Southwest Florida nine out of every ten years, with some blooms causing greater respiratory irritation and lasting longer than in the past. 

A Florida Politics article states the summer of 2021 was one of the worst blooms on record. Tampa Bay experienced its most severe red tide event in 50 years, its effects exacerbated by the 200 million gallons of nutrient-rich wastewater released into the bay in the Piney Point phosphate plant spill. 

Florida has experienced consistent annual red tide blooms since 1998, with the 2018 bloom being the most extensive on record. The bloom caused massive marine life die-offs and significant economic losses, according to Florida Sea Grant. 

Red tide blooms can heavily affect Florida’s economy, as per the Florida Fish and Wildlife Conservation Commission (FWC). Tourism-reliant communities lose millions of dollars when dead fish wash up on the shore or beachgoers face respiratory irritation. The shellfish-harvesting businesses, fisheries and charter companies also lose income. 

“A study of three red tide blooms that occurred in the 1970s and 1980s estimated losses from each to be between $15 million and $25 million,” the FWC stated. 

Tracking and Treating the Bloom 

In the short term, Dr. Lim’s research will be used to improve monitoring for red tide blooms, which are currently monitored through a combination of satellite imaging, water sampling, and advanced molecular tools, according to FWC. 

“Forecasting, or predicting Karenia brevis blooms is really important, and in Florida, we have certain thresholds for Karenia brevis concentrations. If they are above a certain level, that's when we would advise shellfish or fisheries to close down to prevent the toxins from going into fish and affecting consumers,” said Lim. 

By accurately predicting blooms, scientists can put out warnings in advance to fishermen, beachgoers, and fisheries to minimize the impact of red tide for human health and safety.

While red tide is a naturally occurring event, nutrient pollution intensifies its effects. By reducing pollution, we could better manage and predict red tide, according to Dr. Lim. The effects of global warming on red tide are not clear, although some studies have suggested that increasing ocean temperatures could cause harmful algal blooms in general to be worse, she said. 

If there are red tide warnings in your area, stay out of the water and away from the beach. The toxins will irritate your throat and noise and cause itchy eyes, sometimes leading to further health complications. Do not eat any fish or shellfish you catch during a red tide event.

Red Tide: The Bottom Line

There are a lot of misconceptions about red tide, especially about the role viruses may play in controlling it.

“Not all viruses are bad,” said Mackenzie Kerr, outreach coordinator at USF's College of Marine Science. “These viruses aren’t going to hurt you. Karenia brevis, the cell that causes red tide — the reason it's harmful is because it releases a toxin.”

As scientists continue to study how these viruses interact with and affect algal blooms, it is the hope that their findings will shape a future in which Florida’s coastline and waterways are better protected, both environmentally and economically.

While red tide may never be fully eradicated, new research like Lim’s offers a way to begin better managing its impact.