In photos from the scene, hundreds of dead fish fill the frame, their bodies discolored and pale against the mottled waters. This is Florida red tide, a naturally occurring, harmful algal bloom that comes to the southwest part of the state nearly every year but every so often becomes incredibly severe. It kills fish, creates a bad smell in the air, and causes respiratory irritation in humans.
Now 2021 will go down as another year in which red tide ravaged parts of Florida’s Gulf Coast. Almost 1,700 tons of red tide debris, consisting of dead fish, sand, and seaweed, have been removed from Pinellas County beaches and waterways, according to local officials. At least four counties in southwest Florida have reported high concentrations — the uppermost designation — of red tide, based on information from the Florida Fish and Wildlife Conservation Commission.
It’s easy to become desensitized to the nightmarish images of fish corpses lining Florida shores. After all, it’s just one in a long line of extreme climate events that seem only to be getting worse. In just the past several weeks, flash floods in western Europe left more than 200 people dead, while the Bootleg fire continues to crackle in southern Oregon, burning more than 400,000 acres of land in the process.
But for tourists who come to Florida, the sight of red tide is often a shock. They wonder at its presence, how long it will last, and whether climate change has made it more frequent. These are questions that even scientists can’t fully answer.
What is red tide?
Scientists explain that Florida red tide differs from the algae blooms found in other states, such as Maine and Alaska. “Usually, these blooms are not very predictable, but in Florida, come fall, there’s a red tide,” Cynthia Heil, director of the Red Tide Institute at Sarasota’s Mote Marine Laboratory, tells Teen Vogue.
Generally, scientists expect harmful algae blooms — these occur when algae “grow out of control” — to begin around the end of August or early September and last for about three to four months. According to Heil, more than 75% of blooms end by April. That makes the current bloom, which is persisting in mid-to-late July, rare. “It’s highly unusual that we get a bloom that’s lasting through the summer,” she says.
The species of algae that creates red tide in this area, Karenia brevis, can survive in a variety of conditions across temperature, salt concentrations, and diverse sets of nutrient sources, says Kate Hubbard, a research scientist with the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute.
Florida red tide can also occur in Florida’s Panhandle, while Texas can get blooms that spread from the coast of Mexico. Mississippi, Alabama, and Louisiana can be affected by blooms that spread from northwest Florida.
For those who live in southwest Florida, some kind of red tide is to be expected almost every year, as predictably as summer thunderstorms and hurricane season. But this summer, it’s the staggering amount of dead fish that has surprised tourists and locals alike.
Red tide can affect fish in a variety of ways, but it’s the brevetoxins that the algae species creates that infect the animal’s central nervous system. Hubbard has seen red tide-affected fish on the brink of death but not yet dead; they roll over in the water, flailing and gasping for air.
How does climate change and pollution affect red tide?
As to whether climate change has impacted Florida red tide, scientists don’t have a definitive answer. It’s a question they’re currently studying. “Florida is very susceptible to climate change because we’re subtropical," Heil says. "So, theoretically, these blooms should be susceptible to climate change.”
The first blooms that were described in Florida date back to the 1840s, according to Hubbard. Monitoring since the 1950s shows that severe red tide events are often interspersed with more mild blooms. Climate change didn’t cause red tide, but there is a chance — as with so many other naturally occurring phenomena — that it’s had an impact.
Other forms of human-made pollution may have also had an impact. In the spring, a leak in the former Piney Point phosphate plant in Florida caused more than 200 million gallons of wastewater to be released into Tampa Bay. Heil says it’s “potentially contributing” to the bloom.
Hubbard says she can’t really say whether blooms have gotten worse over time. On average, really severe events happen every 10 years or so, she notes, and though they sometimes occur back-to-back, her team hasn’t seen “a lot of evidence to suggest that they’re getting a lot more severe.”
What researchers want to do now is anticipate. Hubbard wants to understand why some years yield no major bloom and others lead to multiple severe blooms in a row. What are the factors that lead to these conditions?
That study will happen through routine sampling of offshore water when a bloom is present and when it is not. After scientists have a full understanding of the drivers of red tide, modeling might be able to more accurately reflect the duration and severity of a coming event. “There’s a lot of promise there in terms of being able to address these questions moving forward," Hubbard says. “But it’s really hard to say with any amount of certainty that they’re getting worse.”
What can we do to mitigate red tide?
In the scientific world, mitigation can be a tricky topic. Think of Newton’s third law: For every action, there is an equal and opposite reaction. If red tide is somehow mitigated through human intervention that’s not well thought-out, what might then happen?
In the 1950s, state and federal agencies decided, as Heil puts it, to “dump tons of copper sulfate” in a bloom off of St. Petersburg in an effort to kill the red tide cells. It didn’t go well. “While it did kill the cells, when the cells break up, you release the toxin,” Heil explains. “The tides brought the cells back a week or two later.”
This is a cautionary tale of mitigation, but scientists are testing other strategies that could have a more beneficial impact. In fact, the act of removing dead fish is really something of an attempt to control a bloom: The bodies of the fish that red tide kills release nitrogen, which helps the algae thrive. Researchers at Mote Marine Laboratory looked at 12 different nutrient sources for blooms and found that decaying fish were the number one source of nitrogen and phosphorus for the red tide organism.
Hubbard envisions a day when scientists might be able to identify and mitigate a bloom at the early stage. “If you can treat it at a very small stage and mitigate those drivers at the beginning point, before it turns into something extremely severe,” she says, “I think that’s a goal that we all share.”
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