Will Hurricane Michael make Florida’s red tide better or worse?

When Hurricane Michael headed toward the Florida Panhandle, it churned up waters containing a toxic soup of algae called a red tide. For months, the red tide has been killing off sea creatures and wafting toxins towards land — and nobody really knows whether the storm will finally end the bloom, or fuel it even further.

Now the big question is what will happen to the red tide in the wake of the hurricane, as Quartz first reported. The storm could churn the water enough to break up the algae bloom and disperse the cells, says Tracy Fanara, an environmental engineer at the Mote Marine Laboratory in Sarasota, Florida. That’s what she suspects will happen in the Florida Panhandle, where Hurricane Michael made landfall. But the hurricane could also move the algae to new areas that weren’t previously affected, says Ed Phlips, a professor who studies algal physiology and ecology at the University of Florida. Still, he says, “It’s very difficult to predict whether that’s going to lead to a red tide.” That uncertainty means a natural science experiment is now taking place.

Florida’s red tides occur when a kind of algae called Karenia brevis, which starts out in the sediments on the ocean floor miles off the coast, gets too populous, Vox reports. Scientists don’t know exactly what starts a red tide. But every so often, the algae start multiplying. And if these algae get close enough to shore, they can feed on nutrient-rich runoff from surface waters to form a massive flotilla that produces deadly neurotoxins. When those neurotoxins kill other creatures, that decay can suck up the ocean’s oxygen and also release nutrients, fueling even more algal growth.

It’s a toxic combination that leads to spiraling, widespread die-offs. “Dead fish, dolphins, manatee, shark, pygmy whale — the wildlife fatality count has been just heartbreaking,” says Fanara. Even people on land are affected: the neurotoxins from the red tide can blow inland on the wind to irritate people’s eyes and lungs, triggering potentially deadly asthma attacks. The first time Fanara got a whiff of the stuff, she says, “I started coughing out of nowhere, there was no real warning.”

This particular red tide has been clinging to roughly 145 miles of Florida coastline on and off for about a year, says Richard Pierce, an ecotoxicologist at the Mote Marine Laboratory in Sarasota, Florida. In the past few weeks, winds blowing offshore helped push the algal bloom away from the coast, although there are some bays and estuaries where the algae could be hiding, Pierce says. “Based on what we’ve seen in Sarasota County this week, the red tide is pretty well gone,” he says.

But it still could come back with shifting winds blowing onshore, he says. And the hurricane may also have indirect effects on the bloom — through rainfall. For instance, the rain Michael dumps on Florida could mean more runoff, and that runoff may pick up things that can feed the blooms. It’s a speculative connection, but it’s one that previous research has suggested. “We have seen a correlation between hurricane events preceding really long blooms,” Fanara says. And Hurricane Irma, for example, struck Florida last fall, and the latest bloom has persisted almost ever since.

So scientists will be keeping watch and monitoring the red tide as the storm passes through the area. Fanara has been training citizen scientists to monitor the algae using a cell phone microscope: they take a video of a drop of seawater, and an algorithm calculates the algae concentration.

 Video courtesy of Tracy Fanara
Cellphone microscope footage of K. brevis

No one really knows how the hurricane will affect how much of the toxin finds its way to people’s lungs — it’s possible that cells breaking in the turbulence could deliver more of the toxin, sickening people. But it’s also possible that all that wind disperses the toxins quickly. Pierce’s team has been measuring the algae and toxins in the water, as well as in the air. The air sampling involves using what Pierce calls “a glorified vacuum cleaner that pulls a lot of air through a filter.” That allows them to monitor whether the red tide is returning, and whether those toxins are making it into the air, potentially making people ill.

The big question is what causes these red tides to start, and stop — and for that, the scientists agree, they need more data. “You don’t know if the cells are happy or not. It’s hard to ask them because they are very close-mouthed about it,” Phlips says. As it stands, he says, “I would be hard pressed to predict one way or another if there will be a red tide event because of this.”