Southeast
via NOAA National Centers for Coastal Ocean Science

FL - Red tide is blooming in Southwest Florida after Hurricane Ian. Will it reach Tampa Bay?

Blooms were detected in 18 water samples across four counties last week.

In October 2017, about one month after Hurricane Irma wreaked havoc on Florida, researchers detected the initial whispers of red tide.

It first appeared, as harmful algal blooms normally do, in trace amounts. A little bit here, a little bit there.

But by the second month after Irma’s landfall, right around November, red tide had peaked in the Charlotte Harbor area, where it spread, it smelled and it stuck around. Federal ocean scientists referred to the event as “unusually persistent” — it ultimately flowed north to the Panhandle and over to the Atlantic Coast.

With Hurricane Irma then, and Ian now, scientists are trying to piece together what impact storms have on red tide. They know the storms don’t cause red tide (the organism typically originates offshore, and then is pushed east toward land). But hurricanes may contribute to red tide’s intensity and location based on which way the current or wind moves water and, crucially, what’s in that water.

“The real question is going to be: With all the runoff stirring up all the sediments, how will Hurricane Ian influence red tide development — will it make it worse? Will it make it last longer?” asked Michael Parsons, director of the Water School at Florida Gulf Coast University. “That’s the big question.”

It’s an important question for Tampa Bay, where red tide is becoming too close for comfort. Bloom concentrations were detected in 18 water samples across Southwest Florida last week: four in Sarasota County, nine offshore of Charlotte County and five offshore of Lee County, according to the latest Florida Fish and Wildlife Conservation Commission data.

At least one report of somebody having trouble breathing, likely because of red tide, was documented last week in Sarasota County, according to the commission.

The latest red tide forecasts from the University of South Florida show very low concentrations of the red tide-causing karenia brevis drifting north from the Sarasota area over the next few days. But whether red tide will make it to Tampa Bay remains unclear, according to Kate Hubbard, director of the Florida Fish and Wildlife Conservation Commission’s Center for Red Tide Research.

“Each year is different, and the uncertainty with hurricane impacts make it extremely difficult to predict more than a few days out,” Hubbard wrote in an email. “At the present time, it’s hard to say whether the cells we are seeing now will remain localized.”

It’s also hard to say what impact the billions of gallons of runoff left in Ian’s wake will have on red tide formation, according to Hubbard. Karenia brevis can feed on a diversity of nutrients and use them as fuel. But too much freshwater can also deter red tide because its organism survives best in saltier marine environments. In short, Ian’s runoff doesn’t cause red tide, but can intensify it if algae cells are already present.

On Sept. 30, two days after Ian’s landfall, satellite imagery captured murky runoff accumulating in the middle-lower Tampa Bay area after rainfall flooded from the bay’s tributaries, according to visuals provided by Chuanmin Hu, a professor of optical oceanography at the University of South Florida. The root beer-like color originates from discharges from waterways like the Little Manatee and Alafia rivers, and other runoff, Hu said.

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