People and fish alike along Florida’s west coast are feeling the effects of an ongoing red tide. The toxic algae bloom is making both humans and sea life sick as it persists along nearly 150 miles of the Sunshine State’s coastline.
At least 13 tons of dead fish have washed up along Fort Myers Beach over the past few days, according to a local news report from News-Press. And that’s just on one 7-mile-long beach. Potentially harmful concentrations of the offending algae have been detected in the waters along about 145 miles of Florida’s Gulf Coast, Matthew Garrett, a biologist at the state’s Fish and Wildlife Research Institute, told Earther in a phone call. Offshore, the algal bloom extends between 5 and 10 miles out to sea, depending on location, he added.
The red tide has been confirmed in patches from Palm Harbor to the north, all the way south to Marco Island and even appears to include waters just north of the Florida Keys, according to data from the state’s Fish and Wildlife Commission. Accordingly, local officials have reported fish kills suspected to be related to the red tide in (and offshore of) seven different counties. People have been experiencing respiratory irritation in those same areas.
What do red tides do?
Red tides occur in many different parts of the world as a result of lots of different types of algae. The alga causing this particular event in Florida, Karenia brevis. The single-celled organism is known to trigger lung and airway symptoms in some people, like coughing, sneezing, itchy throat, and watering eyes when it blows onshore en masse and ends up in the air, according to Florida’s Health Department and its Fish and Wildlife Conservation Commission.
K. brevis exists in Florida’s Gulf waters all of the time, but during blooms the algae’s density skyrockets, explained Garrett. The single-celled, dinoflagellate organism produces a set of neurotoxins called brevetoxins, and it’s these compounds that harm both human and marine health. Exposure to enough of these toxins can make fish, seabirds, sea turtles, and even marine mammals ill. In high enough concentrations, the toxins are deadly for sea life.
So far, during this red tide that began to show up in routine monitoring tests in late October, Florida Fish and Wildlife has received numerous reports of sick and dead seabirds and manatees, on top of the fish, according to Garrett. He urged readers in Florida who come across dead or dying fish or other marine life to report those observations to either the state’s Fish Kill Hotline or the state’s wildlife alert hotline.
For humans, direct contact with the water during a red tide can cause further health problems like rashes and burning skin and eyes. Eating some locally caught seafood during a red tide can lead to neurotoxic shellfish poisoning. Though, commercial fisheries carefully monitor water quality, and food served in restaurants or bought in stores remains generally safe.
Why is it called a red tide?
Red tides are named for the rusty red hue that some toxic algae blooms can dye the ocean, but in the case of K. brevis, it’s a misnomer, said Garrett. The befouled water around Flordia’s west coast is more of a greenish gold than red—though the change is certainly visible in the waves that wash ashore.
Why do red tides happen?
Such events are common for Florida’s west coast, most typically occurring in the fall. However, Garrett noted the timing of this bloom isn’t particularly unusual. “It just depends on the ocean dynamics,” he explained. The biologist, who studies and monitors harmful algae in Florida, called red tides “near-annual events” in the region—caused by a complicated confluence of factors, from ocean geography to marine currents to human impacts.
In 2021 and 2018, much rarer, early summer red tides drew lots of concern and attention. 2021's summer red tide killed hundreds of tons of marine life between Tampa and Sarasota. In 2018, then-Governor Rick Scott declared a state of emergency over the particularly severe algal disaster. In both cases, those red tides lasted for more than a year, while the current one in southwest Florida has only been going on for about five months, said Garrett.
Red tides have been documented on Florida’s Gulf coast as far back as the 1840's and result from both natural and human causes. Off the state’s southwest coast, a geologic shelf that creates a relatively stagnant area of more shallow water is thought to contribute to the region’s frequent algal blooms, explained Garrett. Then, there’s the influence of current and temperature (warm but not too warm is best for the algae).
Research suggests that human-caused pollution also increases the frequency and severity of red tides, since excess nutrients in the water can promote algal growth. In the current, ongoing case, some officials and reports have theorized that devastating category 4 Hurricane Ian may have contributed by triggering an influx of waste and nutrients from runoff or by perturbing the marine balance and causing a shift in currents. However, Garrett noted it’s currently impossible to say for sure what if any impact Ian and other recent storms have had at the moment, because there’s no tracking of runoff once it’s out to sea.
Climate change, too, seems to also be contributing to worsening algal blooms, in both marine and freshwater environments, according to recent research. In Florida, the combination of shifting rainfall and weather regimes, warmer water temperatures, salinity shifts, and climate-associated upwelling and current changes could make the emergence of future red tide disasters impossible to avoid.