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A year ago, toxic red tide took over Florida’s Gulf Coast. What would it take to stop it next time?

Killing red tide cells en masse can unleash their potent toxin. That means researchers need to get creative.

ByAllison EckNOVA NextNOVA Next
Aerial image of red tide bloom.jpg

A bloom of the naturally occurring Florida red tide algae, Karenia brevis, is visible off the coast of Sarasota, Florida in August 2018. Image Credit: Vince Lovko/Mote Marine Laboratory

Later this summer, the Gulf Coast of Florida could play host to a deadly phenomenon: red tide.

Rapid growths, or blooms, of microscopic algae occur in waters all over the world, but red tide refers to the explosive growth of one species, Karenia brevis, which calls the Gulf of Mexico home. Such blooms typically occur in late summer and fall when, after spawning about 10 to 40 miles offshore, populations of K. brevis spike and invade the shoreline—wreaking havoc on marine life, tourism, and human health.

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The last bloom was especially bad. It began in October 2017, and by the time it dissipated some 16 months later, around February 2019, it had killed nearly 150 dolphins and hundreds of tons of fish. In the first 11 months alone, more than 400 sea turtles washed ashore and at least 100 manatees died. At its peak, the red tide event afflicted an area larger than the state of Connecticut.

But at Sarasota’s Mote Marine Laboratory on a sunny May afternoon this year, you’d have no idea that swaths of the deadly K. brevis phytoplankton had been just a stone’s throw away. Sandwiched between tiki bars and beach resorts, the colorful facility is the site of ongoing research into why such blooms happen and what can be done to stop them. And that’s no easy task.

“When one considers the complexity of red tide in Florida, it is several times more complex than a hurricane,” says Gary Kirkpatrick, an expert in phytoplankton ecology at Mote. “And the actual initiation of the red tide growth is pretty much a mystery. We don’t know what the trigger mechanism is.”


Evidence of a large-scale fish kill on Lido Beach following a bloom of Florida red tide off Sarasota, Florida. Image Credit: Conor Goulding/Mote Marine Laboratory

The 2018 event wasn’t the worst toxic algal bloom recorded in the region (one bloom about 15 years ago lasted 17 months), but ecologist and K. brevis specialist Cynthia Heil says it was a wake-up call to the West Florida community.

“We have so many new residents that for a lot of people in Florida, this was actually the worst bloom they’ve experienced,” Heil says. “And it’s a huge health problem.”

Heil is the director of Mote’s Red Tide Institute, the result of a $1 million philanthropic investment that aims to concentrate research efforts on predicting and mitigating harmful algal blooms like K. brevis. This tiny species, which can appear red when clumped by the millions, is ever-present in the Gulf of Mexico and typically harmless. But when populations soar and overrun the shoreline, they release a powerful suite of toxins called brevetoxins. These can cause a host of health problems in humans: Ingesting shellfish contaminated with the compound can lead to neurotoxic shellfish poisoning, marked by nausea, vomiting, and a variety of neurological symptoms. And crashing waves tear apart K. brevis cells, releasing the brevetoxins into the air, which can cause respiratory illness.

It’s clear the stakes for curbing K. brevis blooms are high: It only takes 10,000 cells per liter of water to damage animal and human health. At the peak of the most recent bloom, experts measured 1 million cells of K. brevis per liter throughout much of the affected region, which spanned 1,000 miles from Pensacola on Florida’s Panhandle to the state’s southern tip and up the eastern coast to Port Canaveral.

A perfect storm

The blue-green algal blooms that occur in freshwater systems like Florida’s Lake Okeechobee have a single, direct cause: agricultural nutrient runoff. But a red tide bloom is deeply intertwined with the life cycles of other microscopic creatures.

There are two major types of phytoplankton (plant plankton): dinoflagellates (microscopic tadpole-like creatures) and diatoms. K. brevis is a type of dinoflagellate that is often in competition with diatoms, which are geometric, jewel-like single-celled algae.


Karenia brevis cell, also known as the Florida red tide algae. Image Credit: FWC Fish and Wildlife Research Institute, flickr

There are 12 species of Karenia in the Gulf of Mexico, but K. brevis is by far the most abundant—and infamous. Only K. brevis rivals diatoms in a Gulf-wide census, particularly when it blooms.

But experts say K. brevis’ dominance during blooms is a mathematical mystery. Whereas diatoms can reproduce four times per day, K. brevis multiplies 12 times slower. That means that in three days, K. brevis will have reproduced just once—while one diatom will have turned into about 8,000. In addition, analyses have shown that many diatom species are resistant to the chemical warfare that K. brevis inflicts on surrounding organisms. So why does K. brevis still win out in the end?

Scientists aren’t asking just because they’re curious. The answer could help them understand how K. brevis relates to its environment, and ultimately improve early detection of blooms. One clue might lie in the physics of the West Florida Shelf, the area from the beach to about 150 miles offshore. Past this point, the Gulf floor drops precipitously, giving way to a deep, dark expanse of water rich in oxygen and nutrients. Scientists surmise that K. brevis spends a lot of time growing and multiplying in the shallower waters of the outer shelf. Then, thanks to the effects of summer winds blowing in from the north, a nitrogen-containing compound called nitrate gets pushed up onto the shelf in a process called upwelling. Too much upwelling causes diatoms to flourish. But just the right amount of upwelling seems to give K. brevis the upper hand, staving off diatoms’ dramatic growth. A similar effect driven by winds from the south provides circulation needed to concentrate K. brevis and move it closer to shore.

Once the algal bloom is close to the shore, a combination of drainage from phosphate mines and land runoff from sources like cattle ranches, septic systems, sugar plantations, and even theme parks “fertilizes” it, fueling further growth. Finally, nutrients released from marine life killed by the bloom prolong its growth, paving the way for a total takeover of the coast.

In piecing together this chain of events, scientists have found yet another player. A “helper” type of saltwater cyanobacteria called Trichodesmium sometimes shows up before red tide does. It’s a nitrogen fixer, which means it can spur K. brevis’ growth by turning atmospheric nitrogen into digestible food. “Often we see it as a precursor to red tide,” Hall says.

In May, residents of Manatee and Sarasota counties spotted yet another nitrogen fixer, called Lyngbya, which can cause skin dermatitis and respiratory problems, floating around some docks.

“No matter what type of bloom we’re looking at, it’s important to try to understand it,” says Mote scientist Emily Hall. “It’s going to affect the local people. It’s going to affect the economy.”

How to vanquish a toxin

Dealing with a red tide bloom requires patience, ingenuity, and a smidge of humility. A relic of primordial times, K. brevis is one of the most complex non-protein entities known to exist on Earth. Its genome is 33 times larger than the human genome; many traditional genome-sequencing methods don’t even work on dinoflagellates because they’re far too elaborate.

“Imagine the complexity that’s possible for that organism,” Kirkpatrick says.

Add in everything else in the Gulf system—zooplankton, small fish, variable water chemistry, and so on—and a scientist studying red tide here is faced with the colossal task of understanding how to minimize toxic blooms without disrupting the ecosystem.

It may seem like the most straightforward approach to curbing red tide would be to simply kill Karenia brevis cells. After all, scientists can destroy them in the lab with a quick blast of bleach. But the moment these cells die is precisely when they release their potent toxins. Destroying K. brevis cells won’t work unless scientists find a way to vanquish the toxins at the same time. From ozonation technologies to autonomous underwater vehicles equipped with a red tide detector nicknamed the BreveBuster, experts are experimenting with new tools that could help minimize the toxin’s ill effects without re-engineering the entire Gulf. “You don’t want to alter the system,” Heil says.

Meanwhile, at the Red Tide Institute, Heil and her colleagues are testing different compounds in the lab to see if they can do the trick. A recent contender is barley extract, a freshwater algaecide. If it works on a K. brevis-spiked natural water sample, the researchers will test it on a larger scale in a walled-off portion of the canal.

Richard Pierce, who leads Mote’s ecotoxicology division, is working on a different solution. He and his team designed an ozone contacting system that restores red tide-impacted areas by annihilating decomposing organic matter that feeds K. brevis—including harmful algae—while simultaneously oxygenating the water.


Richard Pierce and his team study the effect of Florida red tide on bivalves at the Mote Marine Laboratory. Image Credit: Haley Preininger/Mote Marine Laboratory

Ozone is a particularly powerful molecule because it has three oxygen atoms (water has just two), which makes it highly unstable. When ozone comes into contact with K. brevis, that third, weakly bonded oxygen atom breaks free and kills off the unsuspecting dinoflagellates by damaging their membranes, infecting critical proteins, and catalyzing cell death. What’s left over are pure oxygen molecules.

Ozone isn’t something you can just blast into the Gulf, though. “The problem is it’s a machine you have to pump water into, and then you have to pump it back,” Heil says. “It’s an effective treatment, but there are logistical issues.” So far, Pierce’s team has been able to do a proof-of-concept test in a canal on Boca Grande’s Damfino Street. While the experiment was successful, it’s likely not scalable: To deal with hundreds of miles of coastline, they’d need a much bigger ozone machine. Maybe even two.

Dumping a compound straight into the water would be a much greater ordeal. “If one were to think about trying to apply something to the water on one of those large blooms, it would rely on technology that is not commercially available yet for locating the edges of the bloom,” Kirkpatrick says. Moreover, practically speaking, the entire operation for mending a 10-square-mile patch of water would cost something on the order of $10 million (Kirkpatrick says that under less-than-ideal conditions, it could cost more like $50 to 100 million.)

“It would be environmentally risky and probably logistically impossible," he says.

Changing tides

As climate change causes waters to warm and ocean currents to change course, understanding red tide may become even more urgent—especially since some research suggests that exposure to K. brevis might be linked to neurodegenerative diseases like Alzheimer’s or Parkinson’s later in life.

Researchers are looking into many aspects of red tide blooms, from their connection to hurricane severity to the possibility that warming waters will cause them to thrive in full force beyond the typical summer and fall season.

“We have to keep thinking outside the box,” Hall says. “This isn’t a pond. It’s very hard to do something and expect that it’s going to be a cure.”

Some scientists are turning to biophysical models of the Gulf and its creatures’ movements. Teams at North Carolina State University and the University of South Florida are working on simulations of how K. brevis’ swimming behavior interacts with the motion of the water. Though the word “plankton” is derived from a Greek word meaning “wanderer,” Florida red tide is anything but aimless: It appears to perform a calculated dance, swimming to the surface during the day and plunging into the depths at night. The simulations combine this up-and-down motion with a model of Gulf currents to predict—in a very basic way—how red tide moves toward or away from the shore.


Mote Marine Laboratory’s Strandings Investigations Program recovers a young bottlenose dolphin off of Manasota Key, Florida, in August 2018. Image Credit: Conor Goulding/Mote Marine Laboratory

Heil says the work of understanding the dynamics of the Gulf, in particular, continues to be important, and that as long as Mote and other research organizations like the Florida Fish and Wildlife Conservation Commission can maintain funding, we might stand a chance of limiting toxic red tide.

“There’s not going to be a silver bullet for red tide mitigation,” she says. “There are too many issues associated with it, but we’re looking for a toolbox [that] could be effective in different situations.”

Above all, Heil also stresses a “do no harm” mentality. It’s not as though we can embark on the aquatic equivalent of crop dusting the red tide, which Florida attempted with copper sulfate in the 1950s. The copper sulfate killed the cells but released the toxins. “That was a lesson learned,” she says.

But after decades of additional research, the urgency of these environmental toxins hasn’t abated.

“We have to do something to alleviate it on a local level,” Heil says. “There are a whole lot of people sitting in the canals breathing [the toxins] in.”

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