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Aquatic hitchhikers might have taken a ride on Hurricane Dorian’s floodwaters

 Invasive animals and plants migrate after hurricanes, too

Media preview of the frogs! exhibit at the Minnesota Zoo, -- A Cuban tree frog rested his chin on his front legs as the exhibit was put together in the terrariums around him.
Researchers are keeping an eye out for the Cuban treefrog to see if it spread to new areas thanks to Hurricane Dorian

Hurricane Dorian has passed, but people and ecosystems are still dealing with its fallout. In the wake of a major storm, it’s not just people who migrate. Plants and animals can hitch a ride on floodwaters, leading to the spread of invasive species. To track — and potentially stem — these sudden migrations in the wake of disasters, researchers build maps to predict how floods and storms might spread aggressive crayfish, propeller-tangling plants, and even frogs that secrete eye-irritating “slime” into new territories.

Since 2017, the United States Geological Survey (USGS) has monitored the spread of species after every major storm in the US. It developed “storm tracker” maps after Hurricane Harvey inundated the Houston area and allowed freshwater animals and plants to travel along the Gulf Coast to new habitats. USGS gathers data on what species are present along the path of a storm in order to identify potential areas where they could spread to places where they shouldn’t be. They particularly focus on movement between watersheds — areas of land where all rivers, rain, or streams drain toward a single body, such as an ocean or lake. Those initial maps help scientists on the ground after the storm document what movement took place and figure out how to manage the damage.

The Verge spoke with Matthew Neilson, fishery biologist with the United States Geological Survey, about his work and what’s going down in the aftermath of Hurricane Dorian.

How can hurricanes like Dorian lead to the spread of non-native species?

There are two potential ways that a hurricane could move things around. The first would be storm surge. As the Hurricane’s coming, it’s pushing ocean water onto shore. For any species that is a little salt tolerant, storm surge could make connections across all of those coastal watersheds and give them ways of moving around. The second would be through rainfall-associated flooding. We get lots of water getting dumped on the land, which raises the height of the water on those interior watersheds. Where it floods, water can spill from one watershed to the other.

As things become more widespread, the impact is harder to manage and the costs associated with the management of a particular species will also go up. By trying to model the risk of spread of a species, we can try to hopefully catch new introductions, new spread into new watersheds early on.

a red swamp crayfish against a background of stone and leaf litter
One of the species that researchers are on the lookout for in the wake of Hurricane Dorian is the red swamp crayfish.

What are we seeing in the wake of Hurricane Dorian?

It’s a little too soon for that, just because the storm is so recent. There hasn’t been a lot of time to go out and survey yet.

One of the taxa on our list here for Dorian is one called the red swamp crayfish. And that one has mainly been observed in North Carolina and South Carolina, and this is a fairly aggressive crayfish. It can outcompete a lot of the native crayfishes. So there’s some potential for it to spread locally in South Carolina, North Carolina.

Aquatic plants are actually a good case study to look at for hurricane flooding, because a lot of the introduced aquatic plants are ones that float. So they are very easily moved with flood waters. Water hyacinth is one that can grow very densely on lakes and rivers. So that can impact things like boating and fishing.

Are more frequent and intense storms, as a result of climate change, a concern?

Any potential increase in storm frequency or severity could increase the potential for species spread through the flooding. If there is a higher incidence of flooding, there’s just more opportunity. Generally, whenever any sort of vector has a higher frequency, you tend to see a higher rate of introduction.

Why should we care about the spread of non-native species?

The biological resources of the nation are important. Native species and people rely on biodiversity a lot. In some areas, there are fisheries that generate millions to billions of dollars for the local economy. And those particular resources can be impacted by the introduction and establishment of non-native species.

An Asian carp leaps into the air against a backdrop of buildings in Peoria, Illinois
The state of Indiana warns that a “fish-human collision” with jumping Asian carp could be “quite serious.”

There’s [also] potential for human health risks. The Cuban tree frog is a good example. That has secretions on its skin, which is irritating to mucus membranes of humans. If you were to touch one and rub your eye it would be irritating. Think about things like Asian Carp; we’re seeing videos of boats driving down the Mississippi River and these giant schools of fish jumping. They react to the frequency of propellers as boats are going down and it causes them to have a startle response; they jump out of water. These are 30-plus pound fish that can jump four to eight feet out of the water. If you were to get hit by one as your boat’s driving 20 miles an hour, that could cause some serious injury.

There’s also potentially economic impacts to things like infrastructure. [Consider] the introduction of Dreissena mussels, zebra and quagga mussels, into the Great Lakes. These are relatively small mussels originally from the Black and Caspian seas region, but they grow in super high density and they’ll grow on hard surfaces. This can impact things like power plant water intakes. A power plant will have to pull in water from bodies like Lake Erie to help cool the power plant. Dreissena muscles can grow all along the inside of those pipes, and can basically constrict that pipe almost to the point where it won’t even work anymore. So the power plant can’t pull in and intake clean water.