Photograph by Logan Cyrus, AFP, Getty Images
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Hurricane Isaias approaches Myrtle Beach, South Carolina, on August 3, 2020. The storm's floodwaters spread more than a hundred invasive species, according to the U.S. Geological Survey.

Photograph by Logan Cyrus, AFP, Getty Images

Intensifying hurricanes are helping invasive species spread across the U.S.

More than a hundred species—including Asian swamp eels and zebra mussels—hitched a ride on Hurricane Isaias' floodwaters, scientists say.

With record-breaking intensity, the 2020 Atlantic hurricane season has surged past the average 12 named storms per year. When Hurricane Zeta made landfall in Mexico on October 26, it became the 27th named storm of the season and 11th named hurricane.

While hurricanes are notorious for producing tornados and causing widespread destruction, they have another devastating, yet lesser-known effect: Spreading invasive species to new habitats. (Here’s how hurricanes form—and why they’re so destructive.)

When Hurricane Isaias slammed into the Caribbean and eastern U.S. this summer, rising water levels allowed at least 114 non-native aquatic species to ride from one watershed to the next, according to the United States Geological Survey’s Nonindigenous Aquatic Species team.

Since 2017, the scientists have combined flood data and invasive species sightings to map how these animals disperse following Atlantic Ocean hurricanes, as well as study what makes some species more likely to benefit from the storms than others.

Take the apple snail, a family of large freshwater mollusks popular among aquarium owners. Native to South America, the six-inch species first came to America via the aquarium trade, and it has since become a destructive pest in rice fields and other aquatic croplands. Apple snails “actually take air into their shell and float along the water,” says Wesley Daniel, a fishery biologist with the USGS Wetland and Aquatic Research Center in Florida, whose tropical climate has made it a hot spot for invasives. “We’ve seen them spread in numerous hurricanes on the Gulf Coast and in Florida like this.”

Since apple snails were already established in many coastal freshwater ecosystems throughout the southeastern U.S., it’s likely that the recent active hurricane season has pushed them farther inland. Not only have hurricanes and tropical storms formed far earlier this year than usual, 10 have made landfall on the mainland U.S., smashing a record set in 1916.

Before 2017, few scientists had investigated the role of hurricanes in the spread of invasive species, which as a whole cost the U.S. economy at least $120 billion a year. But as hurricanes are projected to become both more frequent and intense due to climate change, the potential for non-natives to further degrade ecosystems is a huge concern, says Daniel: “There are consequences for the ecosystems where these animals spread.”

Storm superspreaders

Because most non-native species first arrive via the aquarium and pet trades, “there’s always the possibility, with a major flooding event, that you’re going to release things in captivity that we never anticipated,” says Daniel.

For instance, some scientists have speculated that 1992’s Hurricane Andrew damaged a Burmese python breeding facility in South Florida, releasing dozens of the 10-foot-long reptiles into the wild. Whether the story is true or not, the USGS noted that the invasive species proliferated in the area after that natural disaster. Since then, the snakes have taken over the Everglades, eating everything from rabbits to alligators.

Hurricane Andrew also caused the release of captive red lionfish—a striking animal native to the Indo-Pacific—into the oceans around Florida. Now that it’s established there, the voracious predator has decimated native fish populations and altered the composition of reefs.

Invasive Species 101 Invasive species cost the global economy over a trillion dollars each year. Find out how these non-native organisms are introduced into an ecosystem, how they impact local communities, and which measures can be taken to help prevent the introduction of invasive species.

Also in the 1990s, Asian swamp eels likely escaped from aquariums, fish farms, or live food markets into South Florida, eventually taking up residence in the Everglades. This slippery carnivore, endemic to India, China, and the Malay Archipelago, is displacing other species and disrupting the freshwater food chain. Now hurricanes are helping them slither inland and northward, where researchers have spotted them encroaching on the Carolinas, Daniel says.

Daniel calls these “classic examples of first introductions from hurricanes.” They have also been some of the most destructive, he adds.

Invasion of the water bodies

Such accidental introductions can have far-reaching effects, says Nicholas Phelps, director of the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota.

“They’ll restructure food webs once they get in there,” Phelps says, “or they’ll create new types of habitat when they start growing really dense and outcompete native species.”

A prime example is the zebra mussel, a tiny mollusk originally from the Caspian Sea. Believed to have entered the U.S. via ballast water from ships in the 1980s, it has since infested U.S. lakes and waterways, causing hundreds of millions of dollars in damage every year. The zebra mussels not only edge out native mussels, they attach en masse to any human-made structure, disrupting municipal systems for drinking water and irrigation. (Read about a freshwater mussel apocalypse underway in the U.S.)

Zebra mussels have traveled down the Mississippi and are now creeping into the mid-Atlantic region as well; they’ve been reported in Maryland, Virginia, and North Carolina.

Sightings in these areas after recent hurricanes, including Isaias, suggest that the storms are abetting the species’ expansions, says Daniel. It takes only a few individuals to start a whole new population, he adds.

The problem was already here

However, hurricanes aren’t the most important invasion pathway. We are, says Steve A. Johnson, an associate professor of wildlife ecology and conservation at the University of Florida in Gainesville.

“People already brought them here,” he says. “Animals escape, and people release them into the wild because they get tired of them. This makes the pet trade a major source of how invasive species of animals get established.” (Read why wild animals make terrible pets.)

It's valuable to understand how hurricanes figure in the spread of invasive species. But ultimately, Johnson says, the most effective way to combat that spread may be responsible pet ownership—for example, not buying a pet that’s an established invasive in the U.S.

“If you’re going to get an exotic pet, you need to do your homework,” he says. “If you get tired of it, you cannot just go dump it in the woods or a state park or somewhere. You need to find a home for it.”

Editor's note: This story was originally published October 22, 2020. It was updated October 27 with information about Hurricane Zeta.