This year, as in many past, millions have flocked to Florida’s Gulf Coast for spring break vacations. These travelers bring in vital revenue for the Sunshine State, with one county alone, Pinellas County, raking in $13 million in tax revenue in March last year. But a biological phenomenon known as red tide is putting spring break revenue and the health of locals and revelers alike at risk.
Nearly every fall, the crystal clear waters of the Gulf Coast turn red due to high quantities of Karenia brevis, a type of harmful algal bloom. Last month, right when spring break travel was set to heat up, harmful levels of the algae were found across Pinellas County, home to the city of Clearwater, leading to the cancellation of festivals and sweeping beach clean-ups. The bloom, which began in October, is now found across the southwest coast of the state.
Karenia brevis is present in Florida waters year-round, but it usually exists at such low levels that it has no effect on marine life or people, said Michael Crosby, the president and CEO of Mote Marine Laboratory and Aquarium, an independent research institution in Sarasota. However, when the algae — which produces a neurotoxin, called brevetoxin — washes up and grows on the coastline at higher levels, it causes major environmental, economic, and health damage.
Red tide can start causing respiratory irritation at just over 1,000 cells per liter of water, and at 5,000 cells per liter disrupts the shellfish industry. As of April 6, there are reports of red tide at much higher levels than this along the Gulf Coast, with one location reporting over 1,000,000 cells per liter of water, and six locations reporting between 100,000 and 1,000,000 cells per liter of water.
A single red tide bloom can kill tens of thousands of fish — leading to expensive clean-up efforts — and poisons shellfish like clams, making them dangerous to consume by humans and animals. In humans, swimming in water or walking along beaches where there is red tide can cause skin irritation and burning eyes. Such blooms are found across the world — including the coasts of China, Chile, and the US — but Karenia brevis is almost exclusively found in the Gulf of Mexico. Nevertheless, these other types of red tide are just as toxic to marine life, and therefore finding a way to prevent or treat its growth is vital.
If Florida, one of the places hit hardest by red tide, can find a way to mitigate its red tide blooms, then millions of dollars and thousands of animals’ lives can be saved. But that starts with understanding how the blooms naturally form and how human activities intensify the deadly algae.
Copper waters signal danger
Dust from the Sahara Desert initiates Florida’s red tide blooms. Yes, really.
As Crosby explains it, iron-rich Saharan dust blows over to the Gulf of Mexico. Around 30 to 40 miles offshore, blue-green algae make use of that iron to produce nutrients, which in turn promote the growth of Karenia brevis.
After the algae form, a perfect storm of environmental conditions — strong winds, and warm, nutrient-rich, high salinity waters — must occur to bring it from the deeper waters of the Gulf to Florida’s southwest shoreline. In high enough quantities, the algae turn the water a rusty red or orange color, hence the colloquial name red tide.
In 2022, Hurricane Ian created these prime conditions and ushered in a red tide bloom that has lasted until now. Since October, red tide has killed 104 sea turtles in Florida, including 63 vulnerable loggerhead turtles. And in 2021, 84 manatees died as a result of a different red tide event — particularly concerning given there are only an estimated 6,000 to 7,000 Florida manatees left in the wild.
Red tide can also affect land animals, such as household pets. Ocean waves can aerosolize the neurotoxin from the algae and send it into the air up to a mile inland. People who walk along beaches where red tide is present may experience burning eyes, coughing, sneezing, and if they suffer from conditions like asthma, severe respiratory irritation. During a 2005 red tide outbreak, emergency room visits to hospitals in Sarasota County for gastrointestinal and respiratory illnesses increased significantly.
The southwest coast of Florida is especially susceptible to Karenia brevis blooms because of the area’s warm and naturally nutrient-rich water. But now it’s known that nutrients produced from pollution seem to be making the phenomenon much worse.
“It had long been suspected that nutrient runoff from developed areas can make these blooms worse once they reach the coast, like adding fuel to a fire,” said Miles Medina, a research scientist at the University of Florida’s Center for Coastal Solutions and the co-author of a 2022 study that linked human activity to red tide’s severity.
“Increasing nutrient pollution [is] among the causes leading to algae being out-of-balance to the degree we are seeing,” said Maya K. van Rossum, an environmentalist, and founder of Green Amendments for the Generations, a national nonprofit organization. “Instead of normal nutrient regimes, and thus normal rates of beneficial algae and harmful algae, we are in a ‘dystrophic’ state where the regular and beneficial algae aren’t able to compete and keep up with their normal growth.”
Still, some scientists believe this connection between human activity and the intensity and duration of red tide blooms needs to be studied further. Crosby noted that red tide is “self-perpetuating,” and therefore gains much of its needed nitrogen from the fish it kills, and not other nutrient sources that may exist in the water, such as pollution.
“Karenia brevis would be occurring without any input from humans,” said Crosby. “However, there is no question that any nutrients that are human-produced and run off into the coastal environment contribute to the overall pool of available nutrients.”
How to save the manatees, the turtles, the fish, the dolphins, and the people
While human pollution is not causing red tide on its own, it is magnifying it.
This means one way to save the lives of manatees, turtles, fish, and more is to limit pollution in Florida waterways (after all, it’s a way to decrease the severity of red tide, while also preventing other forms of harmful algal blooms).
Florida policymakers could prevent environmental and economic disasters by limiting pollution. They could do so through tactics such as getting residents to switch from septic systems to the larger sewer system, upgrading wastewater system infrastructure, promoting best practices in the agricultural industry, and building “green infrastructure” to support the Florida wetlands, said Medina.
Environmentalists have remained critical of Florida’s inadequate oversight of its waterways and poor management of its stormwater and sewer systems. That insufficient governance became clear in 2019 when sewage systems across the state of Florida failed. In Sarasota , storms led to the spillage of over 900,000 gallons of raw, untreated sewage and human waste. And in Jacksonville and Daytona Beach, system failures released tens of thousands of gallons of waste. The waste can enter a city’s storm drainage system, where it then flows untreated into natural waterways (lakes, ponds, rivers, and oceans).
Although today the standard sewage system material is PVC plastic, the majority of homes built in Florida before 1975 used cast iron pipes. Florida experienced a population boom in the mid-1950s, meaning many homes equipped with these older iron pipes are at risk of leaks and cracks, and releasing “black water” (sewage-infested water containing bacteria and fungi).
Florida also experiences more hurricanes than any other state. The intense wind, rain, and flooding in these storms stir up nutrients and, as was the case with Hurricane Ian in September 2022, can flush them into the Gulf. Storms can also cause wastewater tanks to overflow.
In response, van Rossum is helping Floridians concerned about the condition of the state’s waterways pursue the Florida Green Amendment. This amendment adds the “right to clean water” to the state’s constitution and makes it a “duty of state government to protect the state’s natural water systems,” said van Rossum. The state constitutions of Pennsylvania, Hawaii, Massachusetts, and Montana include the protection of clean air and water.
Especially at the local level, city leaders implemented some policies to address these issues in the last few years. For example, city council members in Venice, Florida — a Gulf Coast town with a population of just over 26,000 people — passed a resolution in 2018 calling on residents to stop using fertilizer on their lawns, and have been improving the city’s outfall points (where waste leaves the sewer system, usually into a basin or the ocean) so that solids are filtered out prior to entering the Gulf. The city is also offering free septic system inspections and is continuously evaluating water quality prior to discharging it into the ocean.
Similarly, the City of Naples has taken several steps to protect water quality within its jurisdiction, including banning fertilizer use between June 1 and September 30. “As we enter [the] rainy season each summer in Southwest Florida, the risk of nutrient runoff is high,” wrote Naples’ Natural Resources Division in a statement. “Fertilizers are one of the largest contributors to nutrient runoff along the coast.”
At the state level, Gov. Ron DeSantis established the Center for Red Tide Research at the Fish and Wildlife Research Institute in 2019 and signed legislation that allocated $3 million annually to an initiative researching red tide and red tide mitigation and elimination.
Since 2019, Mote Laboratory, in collaboration with the Fish and Wildlife Research Institute, has been leading one such initiative; a six-year project to find a way to kill red tide and neutralize its toxin, while not harming other marine life. “We’ve known for quite some time how to kill red tide,” said Crosby. “You get a crop duster, you load it up with a bunch of copper sulfate, you spray it all over the top of that red tide bloom in the ocean or in the bay, and it kills the red tide. Unfortunately, it also kills everything else.”
In the first four years of the project, the team discovered over a dozen compounds capable of nullifying red tide’s toxin without harming non-target species, said Crosby. The priority for the next two years of the project will be figuring out how to deploy it, he added. Depending on the location of the tide — a canal system with boats and people, a larger bay with a greater surface area, or even deeper in the Gulf where the tide grows — the combination of compounds and how to deploy them will vary, said Crosby.
Still, simply limiting the pollution that turbocharges the algae’s growth remains one of the state’s best strategies for mitigating the effects of red tide. “The real question is, where exactly do we need to target effective interventions to achieve water quality improvements for the public?” said Medina.
Red tide doesn’t just put a damper on spring breakers’ vacations, but also has drastic consequences for Florida businesses and the state’s economy, which relies on tourism. And crucially, the lives of thousands of fish, turtles, manatees, and dolphins could be saved in the next decade.