Here’s how climate change could make future red tide worse

Red tide blooms have been plaguing Florida for hundreds of years at least, and scientists say they’re going nowhere.

But could they get worse?

It is certainly possible in a warming world. The first problem is that scientists don’t know enough to predict what will happen.

“There is a lot of speculation about the impact of climate change on red tides,” said Cynthia Heil, director of the Red Tide Institute at Mote Marine Laboratory & Aquarium.

RELATED: New NOAA tool predicts red tide impacts for beachgoers along Florida’s west coast

Researchers are “at the very beginning” of studying how changing conditions might affect blooms, Heil said. After years of inconsistent funding, even more immediate questions remain unanswered, like what exactly ends a bloom and why Red Tide’s severity varies so much from year to year.

Meanwhile, the region around Tampa Bay saw its second devastating bloom since the start of 2018.

“It’s always: Well, it’s complicated,” said Don Anderson, senior scientist at the Woods Hole Oceanographic Institution. “And that’s certainly the story here.”

Zachary T. Samson


Tampa Bay Weather

Sarah Klass, principal investigator at the Mote Marine Laboratory & Aquarium’s Red Tide Institute, collects water samples during a research cruise July 21.

Out of tens of thousands of algae, Anderson said, it’s hard to determine how a species will respond to climate change. The red tide that typically devastates the Gulf Coast near Tampa Bay is made up of a microscopic organism called Karenia brevis.

More intense rainfall is one obvious way climate change could affect the red tide. The flowers feed on nutrients, especially nitrogen, which are dumped into waterways in excess through runoff from fertilizer-coated yards and leaky septic tanks or sewers. More rain coming during heavy storms could make the runoff problem worse and provide Red Tide with more nutrients.

“What would have been a natural phenomenon is subject to exacerbation if effective management fails,” said Douglas Rader, chief ocean scientist at the Environmental Defense Fund, an advocacy group.

RELATED: Gulf of Mexico ‘dead zone’ larger than average for 2021

Some forecasts suggest Florida will see more severe droughts followed by intense downpours during the rainy season, said Lisa Krimsky, water resources officer with Florida Sea Grant.

“Both could potentially influence Karenia brevis for the negative for us,” she said.

Lower river droughts levels, which means less fresh water is flowing into bodies like Tampa Bay. The estuary becomes saltier and this higher salinity can be conducive to red tide. It is believed that a dry winter and spring are one reason a flower traveled so high in the bay this year.

Warming ocean temperatures are another way conditions could change. But Karenia brevis has shown to thrive in a range of temperatures, the researchers said, and slight fluctuations may not have a big effect. Major changes could even make the water so warm that it becomes less hospitable to algae.

Studies have been inconclusive as to whether rising carbon dioxide, a major contributor to global warming, will directly affect Red Tide, said Krimsky of Florida Sea Grant. Carbon dioxide is emitted into the atmosphere when people burn fossil fuels.

RELATED: How to Spot and Help Seabirds Affected by Red Tide

Red tides typically appear off Florida’s west coast in the fall, said Rick Stumpf, an oceanographer with the National Oceanic and Atmospheric Administration. He called it “little concern” that 2021 brought a summer bloom just three years after the last such red tide hit the region.

It is, however, far too early to tell if persistent outbreaks will become common, Stumpf said, or if it has a link to climate change.

“I hope it’s just a fluke,” Stumpf said. “We will look into that. We will try to investigate to see if we can sort out the models.

Researchers take water samples

Zachary T. Samson


Tampa Bay Weather

Sarah Klass, principal investigator at the Mote Marine Laboratory & Aquarium’s Red Tide Institute, and Mote staff biologist Cody Cole take water samples during a research cruise July 21.

These red tide theories will take years to be verified, and they envision just one of the multiple harmful algal blooms troubling Florida. While red tide is a blight on the central Gulf Coast, blue-green algae is a problem elsewhere, particularly Lake Okeechobee and the St. Lucie, St. Johns, and Caloosahatchee rivers.

Cyanobacteria in such blooms thrive in warm conditions, said Anderson, of Woods Hole.

“There will be winners and losers, and for now the only clear winners will be freshwater cyanobacteria,” he said.

Although the science around Red Tides is less established, Anderson said, Florida is in a better position than anywhere else to help researchers find answers. The state has a substantial record of water quality data from past blooms, spanning several decades.

“At some point there will be information that can be extracted from this,” he said.

This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative created to cover the impacts of climate change in the state.

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