Florida’s Gulf Coast is approaching the end of an above-average hurricane season and record marine heat, but it’s been a lackluster fall for what’s become a common beachgoers’ experience: red tide.

Last year, Tampa Bay-area red tide outbreaks started in November and lasted through the winter. The toxic algae kept many people off local beaches and resulted in a series of fish kills.

But this fall’s absence of Karenia brevis, the algae that causes red tide, has puzzled researchers.

An El Niño weather pattern, like the ongoing one, usually brings more rainfall to the Southeast. The National Oceanic and Atmospheric Administration is predicting a 70% chance of above-average rainfall there this winter.

In Florida, that can mean more rainwater mixes with nutrients and becomes polluted before it dumps into waterways such as Tampa Bay, the Caloosahatchee River and Sarasota Bay, among others along the Gulf of Mexico.

A growing body of scientific research suggests that red tide-causing organisms feed off that rain runoff pollution, potentially making blooms more intense.

Even if this year’s El Niño does become rainier in the coming months, it doesn’t mean an El Niño would cause a red tide, explained Bob Weisberg, the former director of the University of South Florida’s Ocean Circulation Lab.

“El Niño’s effect is relatively minor in regards to red tide. The origin of the red tide tends to be from offshore and moves towards the beach. If it starts killing fish, it can actually make its own nutrients and it doesn’t need the runoff from rain to grow,” Weisberg told the Tampa Bay Times.

But runoff from extra rainfall can make the problem worse, Weisberg added.

“As winter progresses, and if we get more rainfall, yeah, it might add to an existing appearance of red tide,” Weisberg said. “But it’s not going to cause it.”

Weisberg pointed to 2016, an El Niño year that brought plenty of moisture to the Tampa Bay area. That year, the region’s stormwater infrastructure was stretched to the limit and millions of gallons of sewage dumped into area waters.

Red tide flared up that year, defying forecasters and researchers who expected a mild year. This year, the opposite has held true: Weisberg expected an intense red tide in October but it didn’t pan out. And overall, it’s been a quiet fall compared to last year.

One theory for why? Hurricane Idalia.

“Idalia went right over the continental shelf where we believe red tide forms,” Weisberg said.

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When red tide cells rupture, or break, they release toxins into the air. That’s what you feel in your throat when a red tide is blooming at the beach.

But turbulent water, like the angry seas caused by Idalia, can help rupture those red tide cells earlier. That could mean less red tide makes it to shore, according to Weisberg.

“Idalia really stirred up the water this year,” he said.

That turbulent water is expected to last through the winter, as El Niño’s westerly winds increase storm chances.

But this windy weather is far weaker than the strength of hurricane winds, and El Niño’s effects won’t reach the scale whipped up by Idalia, said Ben Kirtman, an Earth sciences professor at the University of Miami’s Rosenstiel School of Marine, Atmospheric and Earth Science.

“I would expect our winter season to be more windy, so I would expect more turbulence in the ocean,” Kirtman said. “Is it enough to really break up the risk of red tides? I don’t know.”

Climate models show the current El Niño has entered its peak, which is expected to run through January. But the weather pattern likely won’t be fully gone until June.

This year’s El Niño is partly to blame for the summer marine heatwave, Kirtman said. And while surface temperatures are cooling, they are still higher than normal.

In the Gulf of Mexico and along Florida’s east coast, water temperatures are still 1 to 2 degrees Fahrenheit above average for this time of year, Kirtman said.

This lasting heat could help fuel red tide if an algal bloom does break out.

A 2019 study published by Florida State University researchers found that warmer waters resulted in increased growth rates for Karenia brevis. Another study showed the algae may release more toxins in warmer climates.

On paper, heat combined with runoff provided by increased rainfall created ripe conditions for red tide to proliferate. Still, researchers aren’t sure how a red tide event and a strong El Niño would interact this winter.

Kate Hubbard, who leads the harmful algal bloom program at the Florida Fish and Wildlife Conservation Commission’s research institute, said there is an ecological window where red tide benefits most from nutrients provided by runoff.

An algae bloom would have to happen “in the right place at the right time” for El Niño to have an effect on a red tide outbreak, she said.

With no coastal blooms yet this fall and six months left in the current El Niño cycle, Hubbard said it’s anyone’s guess what might happen.

“It makes it even more difficult to assess since we are still waiting to see how intense either will be,” she said.

Red Tide coverage

Tampa Bay has Red Tide questions. Here are some answers.

Is it safe to eat seafood? Here’s how Red Tide affects what you eat.

Can I go fishing? The state is limiting saltwater fishing.

Piney Point: The environmental disaster may be fueling Red Tide.

Red tide resources

• The Florida Fish and Wildlife Conservation Commission has a website that tracks where Red Tide is detected.

• Florida Poison Control Centers have a toll-free 24/7 hotline to report illnesses, including from exposure to Red Tide: 1-800-222-1222

• To report dead fish for clean-up in Tampa Bay, call the Florida Fish and Wildlife Conservation Commission at 1-800-636-0511 or file a fish kill report online.

• In St. Petersburg, call the Mayor’s Action Center at 727-893-7111 or use St. Petersburg’s seeclickfix website.

• Visit St. Pete/Clearwater, the county’s tourism wing, runs an online beach dashboard at www.beachesupdate.com.

How to stay safe near the water

• Do not swim around dead fish.

• Those with chronic respiratory problems should be careful and stay away from places with a Red Tide bloom. Leave if you think Red Tide is affecting you.

• Do not harvest or eat mollusks or distressed and dead fish from the area. Fillets of healthy fish should be rised with clean water, and the guts thrown out.

• Pet owners should keep their animals away from the water and from dead fish.

• Residents living near the beach should close their windows and run air conditioners with proper filters.

• Beachgoers can protect themselves by wearing masks.

Source: Florida Department of Health in Pinellas County