Persistent offshore winds have decreased red tide’s stain on Florida’s southwest coast and scientists hope a swipe from Tropical Storm Gordon could further weaken the unusually tenacious scourge.
NOAA researchers said there is no historical evidence of a tropical cyclone erasing a red tide in the Gulf of Mexico, but Gordon’s spin could push it farther away from popular beaches, alleviating the scratchy throats and watery eyes that are symptoms of a Karenia brevis bloom.
Beyond winds moving the harmful algae around, experts were wary about speculating too much on Gordon’s eventual impact on the bloom that started in November and never left.
Tracy Fanara, a staff scientist with Mote Marine Laboratory and Aquarium in Sarasota, said gusty winds skimming the top three feet of water may burst fragile algae cells, killing them. At the same time, if Gordon dug too deep, nutrient-heavy sediment from the bottom of the Gulf of Mexico could get stirred up, helping feed surviving cells.
“There are so many factors that come into play,” Fanara said. “We know the ingredients, but are still trying to figure out the recipe that creates and dissipates the blooms.”
Gordon became a tropical storm Monday morning, zipping through the upper Keys and into the Gulf of Mexico off Marco Island. It was expected to make landfall Tuesday night as a strong tropical storm or low-end Category 1 hurricane near Gulfport, Miss.
Hurricane warnings stretched from Alabama to Louisiana on Tuesday, with tropical storm and storm surge warnings pushing east into Florida’s Panhandle. Moderate chances of flash flooding reached as far north as Arkansas.
While Gordon is no Hurricane Katrina, scientists are pointing to the devastating 2005 storm for some evidence of how red tide and dead zones in the Gulf of Mexico may react to a tropical system.
A red tide bloom that began in 2004 lasted for 18 months, including through Katrina’s Aug. 29 landfall near Buras, La.
But Katrina did disrupt a dead zone in the Gulf of Mexico similar to one that is currently off the coast of Collier County, said Richard Stumpf, a scientist with the National Centers for Coastal Ocean Science.
Dead zones happen when water becomes stratified with warmer water trapping cooler water underneath it. When things die they fall to the bottom and decompose, stealing oxygen from the water. Without mixing of the warm top layer with the cool bottom, a dead zone of lower oxygen is created.
“One positive side with Gordon is given where it came through, its winds were enough to stir everything up and that would be a good thing,” Stumpf said. “It’s been warm enough and calm enough in the Gulf for it to get stratified.”
Stumpf said it’s unusual for the Gulf of Mexico to have dead zones, but that dying Karenia brevis cells, and the tons of fish they have killed could be contributing to it this summer.
“While we see fish floating up to the surface, they don’t stay up there forever,” Stumpf said.
Red tide, which produces a toxin that attacks the nervous system, grows far offshore in the Gulf of Mexico and can pile up near the coast in the fall as wind patterns change. It’s usually gone by March.
This year, a bloom that started in November has endured through the summer months, littering west coast beaches and canals with all manner of dead sea life, manatees and turtles.
Fanara said a shift to an easterly wind in late August has lowered Karenia brevis cell counts along the coastline.
A Gulf of Mexico harmful algal bloom report released by NOAA on Tuesday showed no areas where high levels of respiratory irritation were expected, but dead fish are still being seen in Pinellas, Manatee, Sarasota, Lee and Collier counties.
“We are getting a little bit of a break and it’s making a lot of people very happy right now,” said Betty Staugler, a Florida Sea Grant agent in Charlotte County. “Fingers crossed, maybe there will be more good news.”
Keith Williams, public works director for the City of Sanibel in Lee County, said there were fewer dead fish washing up in the week before Monday’s tropical storm.
But he’s not celebrating.
“I think there’s just less out there to die,” he said.