A red tide devastated Florida marine life for 16 months. Why?

Researchers wonder how much climate change is fueling killer algae around the world.

The Florida Problem: A Special Report. Struggling crops. Salty aquifers. Invading wildlife. Piles of dead fish. The Sunshine State feels the squeeze of environmental change on its beaches, farms, wetlands, and cities. But what afflicts the peninsula predicts the perils that will strike north and west of Apalachicola, and so it demands our attention. If Florida is in trouble, then so are we all.

One morning in August 2018, a man named Ralph Breeden telephoned the Florida Fish and Wildlife Conservation Commission to report that a dead manatee was bobbing in the bay behind his house in a quiet Sarasota suburb. Soon, two biologists, Gretchen Lovewell and Rebeccah Hazelkorn, were on their way to recover the corpse in a pickup truck fitted with a portable crane. Lovewell and Hazelkorn are the equivalent of marine EMTs and coroners, performing rescues and necropsies, operations that often require them to handle turtles that weigh more than 200 pounds and dolphins over 6 feet long. They work out of the Mote Marine Laboratory in Sarasota, which the wildlife commission had contacted to collect the carcass. They’re tough women, each sporting marine tattoos (Lovewell has a dolphin, manatee, turtle, and whale on her left ankle; Hazelkorn, an octopus creeping around her right thigh).

When they arrived at the home, three of Breeden’s grandchildren and their mother, Siri Falconer, were waiting on the lawn, and the kids eagerly pointed out the animal. The manatee, almost 8 feet long, was floating on its back, and had blown up so large that its skin split down the belly, gray intestines spilling out. Lovewell and Hazel­korn fastened a chain around the animal’s body and hoisted it onto the bed of the truck, blood and feces splashing over their equipment. Falconer, Breeden’s wife, and the children watched the grisly operation in disgusted fascination. Lovewell and Hazelkorn were less impressed; this was the 209th dead manatee of the year.

The summer of 2018 was apocalyptic. Across the Northern Hemisphere, railroad lines warped and pavement cracked. Nuclear plants cut power output when their water sources became too hot. Reindeer sought relief inside Norwegian roadway tunnels as temperatures above the Arctic Circle approached 90 degrees Fahrenheit. Historic, unrelenting rain in Japan caused deadly floods. Record-breaking wildfires burned in California and also in Sweden.

In Florida, the apocalypse reeked of dead marine life. All along the Gulf coast, fish, sea turtles, and dolphins washed up lifeless on the sand. Cleanup crews on Sanibel Island, usually a popular tourist beach, filled garbage bags with more than 400 tons of carcasses. The killer was a red tide: a huge bloom of Karenia brevis, a marine algae that releases a potent class of neurotoxin called brevetoxins that, in large enough concentrations, can debilitate or kill manatees and other animals. Karenia brevis wasn’t even the only bloom to hit Florida that year; an explosion of freshwater blue-green algae in the canals coming out of Lake Okeechobee forced the governor to declare a state of emergency.

Red tides are common in Florida, and have been documented as far back as the 17th century. They normally start in early fall and disperse with cooler winter winds. But in 2018, as winter turned into spring, the bloom persisted.

Around the world, coastal communities are grappling with algae blooms showing up at abnormal times and places, and with greater frequency than in the past. The events close beaches and fisheries, suffocate aquaculture, and cost millions in economic losses.

“Is there a combatant, an antidote?” Falconer asked Hazelkorn and Lovewell. The red tide had kept the family out of the water and away from the beach all summer.

“That’s the million-dollar question,” Hazelkorn replied as she and Lovewell prepared to depart with the disfigured manatee safely ensconced in the truck.

In Florida, 73 percent of businesses in the area affected by the red tide reported economic losses of more than $500,000 each. Residents, business owners, and government officials were all turning to scientists for answers: What caused the bloom? How can we get rid of it?

The problem is, nobody knows how to stop toxic ­algae—​or even fully understands when and why they happen. The phenomenon has been widely monitored and studied for only 30 years. Now, scientists in Florida are on the front lines of a race to decipher and learn how to deal with them. Globally, researchers are throwing everything they can at the problem: citizen science, drones, satellites, robots, genetic analysis, and experimental techniques that might defeat it.

Some scientists suspect climate change has a role. Researchers have shown that unusually warm waters off the U.S. West Coast caused an unprecedented bloom of toxic Pseudo-nitzschia in 2015, and that with rising ocean temperatures, the range of Gambierdiscus, an algae that makes dangerous ciguatoxins, is expanding from the tropics toward more-temperate waters.

Investigators don’t know enough about Karenia ­brevis to say whether the same is true in Florida. One thing is certain: Devastating red tides like the one that hit the state will happen again. In the meantime, scientists are struggling to understand and grapple with a problem as complex as anything nature can unleash—all while the natural world itself is changing rapidly.

Hazelkorn and Lovewell brought manatee No. 209 to a state lab in St. Petersburg. There, a technician would measure the corpse and take tissue samples for toxicology, to determine if red tide was the killer. Researchers believe the mammals are usually poisoned by ingesting filter feeders such as anemones and sponges, which live on the sea grass manatees graze. The tiny creatures quickly accumulate brevetoxins from Karenia, which can cause seizures or paralyze the sea cows’ respiratory systems and result in their drowning.

The wildlife commission’s efforts to monitor and study Karenia are headed by ecologist Kate Hubbard, lanky and subdued and sporting her own aquatic ink (a freshwater algae and a jellyfish). Even at the height of the bloom, as she and her researchers are inundated with specimens to process, she navigates the hubbub in a quiet, unhurried manner. The monitoring is a multi­pronged effort: They test water from the coast and offshore, conduct aerial surveys, and coordinate with scientists from the ­National Oceanic and Atmospheric Administration, who use satellite imagery to try to forecast the bloom’s movements. Citizen volunteers also pitch in, sending water samples from areas the commission can’t cover. Crews sometimes work around the clock—even through an official hurricane closure—to examine every specimen. They identify whether Karenia brevis was present, and in what concentrations, in order to keep a status map on their website up-to-date.

Karenia brevis is a dinoflagellate, a type of ­single-​­celled phytoplankton equipped with a pair of tail-like flagella, which it uses to swim. But that doesn’t make the organism speedy—it can propel itself at only about 3 feet per hour. By observing the tiny creatures in controlled water columns in the lab, and installing new instruments equipped with microscopes to observe Karenia in real time in the ocean, Hubbard and her colleagues are trying to find out more about how they live. “I don’t mean to sound happy about them, because it’s a really serious situation that impacts a lot of people,” Hubbard says in a cluttered, windowless lab, “but they’re fascinating.” She wants to know how the algae migrates between deep and shallow water, how light impacts its behavior, and how it uses nutrients (chemicals such as nitrogen and phosphorous) to fuel its growth.

The latter is of particular interest because it’s at the center of public outrage over the bloom. Many environmentalists believe that pollution from land-based sources is responsible for the duration and intensity of red tides. The local Sierra Club, and some area scientists, are convinced that nutrient runoff from agriculture and housing developments caused this situation, and blame lax environmental regulations under then-Governor Rick Scott. On August 12, 2018, thousands of people showed up at beaches up and down the coastline for a protest called Hands Along the Water. The group’s Facebook page said its goal was to “show that we do not, and will not, stand for our beautiful beaches, wildlife, homes and livelihoods to continuously be destroyed and impacted by the water released from Lake O.”

Workers collect fish killed by a huge bloom of Karenia brevis
Workers collect fish killed by a huge bloom of Karenia brevis. Joe Cavaretta / South Florida Sun Sentinel / TNS via Getty images

Lake Okeechobee, the state’s largest freshwater body at 730 square miles, feeds into canals and rivers that flow into the Gulf of Mexico and the Atlantic. It is bordered by dense residential neighborhoods and many ranches and sugar-cane farms, whose contaminated drainage ends up in the water. That pollution proved to be a major factor in causing the blue-green algae bloom that struck inland Florida when the red tide surged last summer. But the role of runoff in fueling Karenia brevis is fuzzy. ­Karenia infestations begin far offshore in the Gulf, and they can derive sustenance from a variety of sources, ­including their own dead cells. Most scientists agree that nutrient pollution probably exacerbates the ­problem, but the total contribution is unclear—and will most likely remain that way for years until researchers painstakingly document the details.

When it is not congregating in high concentrations, Karenia brevis plays an important role in the environment. Like any other phytoplankton, it photosynthesizes, taking up carbon dioxide and producing oxygen. Besides the brevetoxins, it produces other molecules that disable its algal competitors, and it also acts as a predator, grazing on bacteria. Removing it entirely could disrupt the microscopic ecosystem that it inhabits.

“We can’t eliminate red tide, because it is a natural part of the phytoplankton community in the Gulf of Mexico,” says Richard Pierce, a chemical oceanographer who is Mote’s associate vice president for research. “In the past it has been taboo even to consider trying to knock it back, and change the system. But with the severe economic effects, and public health, and the destruction of so many sea turtles, dolphins, manatees, and fish, the environment is changing.”

Now Pierce’s mission is to try to find ways to mitigate the effects of Karenia when it gets out of hand. In mid-August last year, Pierce and a team of engineers and scientists headed out to a saltwater canal in Boca Grande to test a new tool: an ozone water-purification system inspired by the setup Mote uses to clean seawater for tanks at the aquarium. The idea was to flow water through a chamber containing the toxic gas ozone, killing the Karenia in the process. The “ozonator” was a hulking apparatus of PVC pipes and gas tubing that sprawled out of a trailer and extended into the channel.

The canal dead-ended in a residential area, and ­Karenia had been growing there for weeks. Breezes had carried brevetoxins into the air, which stung like a very fine mist of pepper spray. It wore on the locals whose homes bordered the water. The neighborhood was so frustrated, residents had pooled their money—more than $100,000 —to help fund the study. The ozone system had a limited capacity, but the hope was that in such a small, partly enclosed area, it could make a big difference.

The final results aren’t published yet, but preliminary data suggests they were lackluster. The treated water was effectively cleansed of algae and toxins and re­oxygenated, but the ozonator was too small to have much effect on the canal as a whole. Pierce sees the test as a proof of concept; it seemed like the result would be better with a bigger, more powerful apparatus.

Pierce’s team is also taking part in a mitigation trial led by Don Anderson, a world-renowned harmful-algae researcher based at the Woods Hole Oceanographic Institution in Massachusetts. Anderson is an advocate of clay flocculation, a process in which specially treated clay is sprayed onto water containing a toxic bloom. The particles attract the algae and drag it to the bottom.

Anderson’s team has enlisted purified clay that is similar to the material used for porcelain dishes, enhanced with polyaluminum chloride to give it an opposite surface charge from the algal cells. They’d brought it in from China, where studies have shown it to be extremely efficient; Anderson says the ecological effects are minimal, especially when compared with the damage done by the bloom itself.

A few months after the ozone test, Anderson, Pierce, and scientists from five different research institutions headed to a marina in Sarasota, near Mote, to begin the first test. Unfortunately, a couple of days before the trial was to begin, the algae dispersed and dropped to normal levels. Since their primary goal was to test the equipment and get the team working together, they proceeded anyway, attaching the clay solution to what looked like a large garden hose and spraying the slurry out into the water.

Anderson and scientists from Mote had attempted the process once before, in 2004, during another big ­Karenia infestation. But the project ended quickly amid local controversy: The clay they’d used came from Mosaic, a mining company with a long history of bad environmental practices in Florida, and contained mined phosphate, which had low levels of radioactivity. In addition to bad press generated by the association with Mosaic, there was concern the phosphatic clay might also introduce new problems to the environment.

The whole debacle was a “naive mistake,” Anderson says. He maintains the new stuff is safer, and is adamant that the blooms are so destructive to the natural habitat that it’s important to take action. “These events are true ecological, economic, and public-health disasters,” he says. “There’s no reason those same sorts of planes that are dropping flame retardant or spraying for mosquitos can’t spray this clay in a slurry over big areas.”

In late February 2019, after 16 months, the bloom finally faded to normal levels, but Karenia still lurks offshore. Hubbard’s lab confirmed that it had killed manatee No. 209. Calls about dead marine life tapered off to normal levels. Lovewell and Hazelkorn worked through their backlog of dead sea turtles in need of necropsies and were back to their routine of rescue and recovery of stranded marine life. Pierce is investigating the potential of chemical additives to help bloom mitigation efforts. Hubbard moved forward with a new field study to monitor the life cycles of algae in the natural environment.

There are basic details about the Karenia life cycle that remain unknown. Scientists hypothesize that it has a cyst phase, a seedlike stage when the algae is dormant before it blooms. But no one has observed it, so no one knows for sure. Finding out whether this stage exists, and what it looks like, would be important information. With some other harmful species, scientists are able to monitor for cysts in the sediment and predict when a bloom is likely. But it could take years for Hubbard’s team to reach a definitive conclusion.

Biology isn’t the only factor controlling the blooms, or the only one that’s poorly understood. Weather and physical ocean dynamics often ultimately determine whether a red tide will last or disperse: the thickness of the layers of warm and cold or salty and less-salty water, the amount of rainfall and when during the bloom cycle it happens, and the strength and direction of the winds. Meanwhile, many of these conditions are diverging from the historical precedent. Ocean temperatures are rising; currents, wind, and rainfall are changing. Hurricanes are becoming more frequent and intense. This complicates researchers’ ability to make sense of and forecast the next Karenia bloom, and could fundamentally shift its dynamics.

Many of Florida’s environmentalists want to focus on reducing pollution, and they see anything less as enabling polluters. “Improving water quality is a good measure to take,” Hubbard agrees.

Zooming out from Florida, the complexity of the toxic algae problem is even more dizzying. Karenia brevis is just one of dozens of harmful species that have been identified around the world. All respond to their environment in different ways. Some like warmer water, others colder. Some grow faster as the amount of CO2 in water increases. In recent years, algal blooms have appeared to be getting more frequent in many coastal areas. In addition to the historic West Coast Pseudo-nitzschia infestation in 2015, Maine had to close shellfish grounds in 2016 for the first time due to domoic acid from Pseudo-nitzschia—the catch could have poisoned anyone who ate it. While scientists don’t know yet whether the changing climate has had an impact on the frequency and duration of Karenia blooms, they agree it’s likely to influence things in the future.

“Are we going to be able to stop those types of events?” Hubbard wonders. “I honestly don’t know.”

As the natural world becomes less hospitable, the public will increasingly turn to scientists for explanations and solutions. But the progress of research is slow, and usually proceeds with a healthy helping of uncertainty. Meanwhile, we’ve ignored one certainty that scientists have repeated for years: We are fundamentally altering the environment. Now as we watch that change unfold, we will have to accept that our actions have upended a system whose complexity we had yet to grasp.

Reporting supported by the UC ­Berkeley–​​11th Hour Food and Farming Journalism Fellowship.

This article was originally published in the Summer 2019 Make It Last issue of Popular Science.