Red tide, a naturally occurring algae that produces toxins when it occurs in large concentrations, could grow even bigger and sicken Florida residents inland due to Hurricane Michael. The side effect of the strongest storm to hit Florida since 1851 could lead to mass fish kills and harm fishing livelihoods, including shellfish harvesting.
A massive algae bloom that stretches 145 miles along the southeast Florida coast and 10 miles into the Gulf of Mexico could be fed as heavy rains drive nutrients into the water from agricultural fertilizers, farm animal waste lagoons and storage tanks, and septic systems.
“The heavy rain will dilute farm and agriculture areas of all the nutrients, nitrates, phosphates and rain them into the beaches and coastal areas that serve to fertilize the red tide,” David Hastings, a professor of Marine Science and Chemistry at Eckerd College told a CBS News station in Tampa, Florida.
But depending on wind direction and rainfall, the hurricane could also help disperse the bloom, driving it further into the gulf, and killing it off through lower temperatures. Aileen Marty, an infectious disease expert and professor at Florida International University, told Accuweather, “More likely than not, the hurricane is going to reduce the problem in the west coast, where it’s worse, for now.”
The Florida red tide results from Karenia brevis, an alga that’s generally harmless in small quantities—but in the right conditions it can reproduce into the billions, and release significant amounts of a toxic byproduct into the water and air. Red tide can cause humans to suffer respiratory ailments from airborne toxins. They can also get sicken or even die from eating affected marine life.
Red tides predate large-scale farm and agricultural operations, and other species of algae cause similar blooms and toxins elsewhere. However, global warming has produced more frequent and larger toxic blooms, and that’s expected to continue to increase in pace.
Fish kills have also become frequent, as the algae consume oxygen in the water and their toxins poison fish. Birds, manatees, sea turtles, and other animals and species can also be poisoned directly by red tide, or by eating affected animals. A Florida news station reported that beaches facing the Gulf of Mexico in Pinellas County, which includes St. Petersburg, were recently covered with dead fish.
The State of Florida’s red tide information site says that nutrient off-flows don’t cause red tides, but the Conservancy of Southwest Florida points to 2014 research that found certain nutrients feed them, or feed other algae blooms that red tides in turn feed from.