Red tide blooms are building along much of Florida’s southwestern coast extending from Sanibel to Port Charlotte, resulting in fish kills and other harmful aquatic ecosystem impacts. South Florida has been experiencing an increasing number of Harmful Algae Blooms (HABs) over the last few years, like the 2021 bloom in St. Petersburg which killed 477 tons of marine life. Now, South Florida faces another potentially devastating red tide outbreak in the midst of trying to recover from one of the worst hurricanes in the last century.
These blooms are the result of a high concentration of the microscopic algae Karenia brevis. While K. brevis occurs naturally, excess nutrients fuel red tide blooms as the algae rapidly reproduce. The dinoflagellate, K. brevis, belongs to a group of algae that produce potent neurotoxins. In high concentrations, it can be deadly to fish, mammals, and other sea life that succumb to its toxins.
Excess Nutrients Cause Red Tide
The harmful red tide blooms occurring in South Florida over the last 10 years are a result of excess nutrients washing into the gulf. The issue begins at Lake Okeechobee. The lake feeds the complex system of wetlands to the south, known as the Everglades. Excess water from Lake Okeechobee filters through Florida’s wetlands and aquatic vegetation until it reaches the coast. Land development and a vast network of agriculture around the lake have resulted in habitat fragmentation and controlled water discharges.
Additionally, the agricultural industry borrows water from Lake Okeechobee to water crops. The water is then contaminated with extra nutrients from fertilizers and returned back to the lake through a series of canals. When the Army Corps of Engineers decides to discharge water from Lake O, the majority of it travels west along the Caloosahatchee River until it reaches the Gulf Coast. The then nutrient-rich water travels offshore where it causes naturally-occurring K. brevis to form red tide blooms. As the winds blow inshore, these harmful blooms push up along the coast, gaining strength from nutrient-rich shallow water areas which result in massive fish kills.
Late Season Hurricanes Spur Additional Red Tide Blooms
In recent years, the majority of the blooms occurred during late spring and early summer, coinciding with the rainy season. The influx of water creates added runoff that drains into the Gulf of Mexico resulting in red tide. Now, Florida is experiencing red tide blooms in the fall as a result of a late push of Hurricanes. For a fishery already struggling to recover from spring and summer blooms, more fish kills could be devastating to the ecosystem and the livelihoods of the captains who guide there.
In the wake of Hurricane Ian and Hurricane Nicole, a red tide bloom is growing rapidly from Port Charlotte down to Sanibel. High winds during Hurricane Ian triggered an upwelling event that pushed existing red tide to the surface. Additional storm surge and excessive runoff poured extra nutrients into the Gulf from coastal rivers and estuaries.
With the recent passing of Hurricane Nicole, onshore winds pushed the blooms closer to shore and wave action caused K. brevis to lyse (the breaking of the cell wall that releases neurotoxins). The resulting red tide blooms have already begun to kill marine life. Fish kills have already been reported offshore and inshore from local captains and beachgoers. Many game fish like tarpon, snook, cobia, and countless bait fish have started washing up dead.
Potential for More Damage
“Although the current situation has not been influenced by Lake Okeechobee releases, Hurricane Nicole brought more water over the system. The concern is that water managers might look to release these nutrient-rich heavy discharges to the coast which may intensify the bloom further,” says Dr. Tracy Fanara, a hydrologist and environmental engineer, in a recent Captains for Clean Water Instagram post.
Lake Okeechobee has risen from 12.5 feet in September to 16 feet after the storms according to the Army Corps of Engineers water height gauges. If released, the abundance of nutrient-rich water would fuel the red tide for months to come.
Captains for Clean Water is a coalition of local captains and conservationists who are actively trying to minimize harmful algae blooms and restore Florida’s fisheries. They focus on policy change, water cleanup, and habitat restoration to restore natural flow from Lake Okeechobee and reduce red tide events.
Conservation Organizations Urge Minimal Water Releases
In a recent letter written by Captains for Clean Water and the Sanibel-Captiva Conservation Foundation, the two organizations urge the Army Corps to keep discharges to a minimum. “Our concern is that nutrient-rich releases from Lake Okeechobee will exacerbate the present red tide bloom, like pouring fuel on a fire,” stated the letter. “We saw this scenario after Hurricane Irma in 2017 that led to a year-long red tide outbreak that devastated our area.”
Large releases from the lake through the Caloosahatchee River would be catastrophic to existing blooms. The extra nutrients would prolong and grow the blooms across much of Southwest Florida. After crushing red tide blooms in 2018 and 2021, another extended bloom is a worse case scenario for Florida’s fisheries.