In October 2017, about a month after Hurricane Irma wreaked havoc in Florida, scientists noticed the initial whispers of red tide.
It first appeared in trace amounts, as harmful algal blooms usually do. A little here, a little there.
But by the second month after Irma’s landfall, right around November, the red tide peaked in the Charlotte Harbor area, where it spread, smelled, and stayed. Federal ocean scientists described the event as “unusually persistent” — eventually flowing north toward the Panhandle and across the Atlantic coast.
With Hurricane Irma then and Ian now, scientists are trying to piece together what, if any, effects the storms have had on red tide. They know that storms don’t cause red tide (the organism usually originates from the coast and is then pushed eastward inland). But hurricanes can contribute to the intensity and location of red tide based on how the current or wind moves the water and, most importantly, what’s in that water.
“The real question will be: How will Hurricane Ian affect the development of red tide when all the runoff stirs up all the sediments — will it make it worse? Will it last longer?” asked Michael Parsons, director of the Water School at Florida Gulf Coast University. “That’s a big question.
It’s an important question for Tampa Bay, where the red tide is getting too close for comfort. Concentrations of blooms were detected in 18 water samples in Southwest Florida last week: four in Sarasota County, nine in coastal Charlotte County and five in coastal Lee County, according to the latest data from the Florida Fish and Wildlife Conservation Commission.
According to the Commission, at least one report of someone having trouble breathing was documented in Sarasota County last week, possibly due to the high tide.
The latest red tide forecasts from the University of South Florida show very low concentrations of red tide causing karenia brevis drift north from the Sarasota area over the next few days. But it’s unclear whether red tide will reach Tampa Bay, according to Kate Hubbard, director of the Florida Fish and Wildlife Conservation Commission’s Red Tide Research Center.
“Every year is different, and the uncertainty of hurricane impacts makes it extremely difficult to predict more than a few days,” Hubbard wrote in an email. “At the moment, it’s hard to say whether the cells we’re seeing now will remain localized.”
It’s also hard to say what impact the billions of gallons of runoff from Ian’s wake will have on red tide formation, according to Hubbard. Karenia brevis they can feed on a variety of nutrients and use them as fuel. But too much fresh water can also discourage red tide, as its organism survives best in saltier marine environments. In short, Ian’s outflow does not cause red tide, but it can amplify it if algal cells are already present.
On Sept. 30, two days after Ian’s landfall, satellite images captured murky runoff accumulating in the middle and lower Tampa Bay area after rain flooded 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 comes from runoff from waterways like the Little Manatee and Alafia rivers and other runoff, Hu said.
The lack of saltier water from this outflow could also determine whether Tampa Bay sees any significant rise in red tide. According to Parsons, algal blooms will not grow when the water is about one-third fresh water.
“If there’s still a lot of runoff going into Tampa Bay, the water may be too fresh.” That’s another thing to think about,” Parsons said. One of the few continuous monitoring stations that monitors salinity levels in the bay was knocked out by the storm and went offline last week.
At least for now, Florida manatees have been spared the return of red tide in Southwest Florida, according to Fish and Wildlife Research Institute spokeswoman Carly Jones. That’s good news for the species, which experienced a record extinction in 2021, leaving 1,100 animals dead due to the loss of seagrass caused by pollution, particularly on Florida’s east coast.
Another variable is also at play with the red tide: ocean currents. A red tide usually flares up when there is a steady ocean current from the southeast. A storm can add to this coastal current or it can reduce it. After Hurricane Ian, “the deep circulation is favorable for coastal traffic since Ian’s passage,” Jones said.
In other words: Currents help push red tide closer to shore.
Conditions are most favorable for red tide from September to January, which happens to coincide with some peak hurricane season. In any given year, scientists can detect red tide cells before or after a storm. Because of this, it’s hard to say whether this winter is shaping up to be a harsh one for the red tide, according to Yonggang Liu, director of the Ocean Circulation Lab at the University of South Florida.
The bad red tide that flared up in early 2017 wasn’t caused by Irma, but Liu said it still may have had an effect. There was a nearly two-month lag between Irma and the arrival of the red tide that year, which may have been caused by repeated cold fronts.
Red tide blooms, Liu noted, were predicted earlier this year. The first phase of red tide, the lack of deeper, cooler ocean water rising to the surface in late spring, was an indicator of what was to come. If northerly currents continue in the coming weeks, the red tide cells that are currently to the south could be carried into the Tampa Bay area. But Liu said he doesn’t think that will happen.
“Hurricane Ian’s heavy rainfall and drainage may contribute nutrients to the coastal ocean ecosystem, but they are not a game changer,” he said.
So what is Liu’s prediction for Tampa Bay’s red tide in the coming months?
“Keep our fingers crossed.”