WILLIAM BRANGHAM: Invasive species are, quite simply, invaders, usually brought by humans into a new ecosystem where they often push out existing native species.

This week, a new report backed by the U.N. documented that these invaders not only harm those ecosystems globally, but they're also costly.

The price tag for the global economy $423 billion each year.

And a number of researchers believe that estimate may be just the tip of the iceberg.

Earlier today, I spoke to one of the study's authors, Laura Meyerson of the University of Rhode Island.

I asked her about the ways that invasive species affect us some obvious, some not so obvious.

LAURA MEYERSON, University of Rhode Island: A lot of the costs associated with invasive alien species have to do with losses.

So, for example, a species can come in and cause great damage to agriculture or to forestry, and that is income foregone.

There are other damage that happen, for example, to infrastructure.

There are many, many species, for example, the zebra mussel, that do great damage to our infrastructure, such as water intake pipes.

And then there are other costs that are a little less tangible.

For example, cost associated with illness, people, you know, missing work due to an introduced pathogen.

By its nature, the problem of invasive alien species is a global problem because it's one of people moving organisms from one region to another.

A good example is the American mink in Europe, which is a voracious predator.

It's escaped from fur farms there and is causing great damage .

In the United States, we've had many species brought in, such as the invasive lionfish.

We know that is causing real trouble in fisheries down in the Caribbean and around Florida, and it's also damaging our coral reefs.

So the lionfish predates or eats fish that graze on the algae that grow on coral reefs.

And without those grazers, the coral reefs become smothered in the algae, and they begin to decline and degrade.

WILLIAM BRANGHAM: We're talking principally here about species that hitch a ride in some way on humans, and we are the ones that move them around, is that right?

LAURA MEYERSON: That's part of the story.

There are many hitchhikers and stowaways, but there are also many intentional introductions.

So some species have been introduced because of their perceived benefits.

A good example in the southeast of the United States is the introduction of kudzu.

And kudzu is known as the vine that ate the south.

And a lot of people that live down there surely know this species.

It was introduced for erosion control back in the 1930s by the Civilian Conservation Corps, and it does its job.

But it also escaped, and it now grows everywhere, grows on top of trees.

It will swallow even cars and houses.

Sometimes you'll get an exotic pet, and it will be carrying a pathogen or a beautiful plant that you bought at your local nursery.

And in the soil of that plant is some kind of worm or a nematode or perhaps even a fungus that will escape and cause harm.

WILLIAM BRANGHAM: This all seems to point to one of the key, I guess, prevention strategies, which is to try to do a better job of monitoring those stowaways, so to speak.

What else can we do to try to stem this issue?

LAURA MEYERSON: Well, I think we need greater cooperation.

You know, this is a problem of moving species from one country to another.

So, you know, we need more cooperation where we're screening before things are transported.

So pre border control.

Another really important aspect of this is to engage with the public.

Citizen science has proved incredibly important in managing and preventing species invasions.

So people are out there all the time.

They've got cell phones.

They can use apps like Inaturalist or Leafsnap to begin to identify those invasive species.

So education is critical.

People getting involved to manage invasions, but also being careful about what they buy or what they bring in, what they maybe bring home from a trip.

If they found something pretty, you know, alive plant, don't bring it back, because there could be an invasive species associated with it.

WILLIAM BRANGHAM: Are there examples of communities that have done a good job of identifying an invasive species and then doing everything they can to push it back or get rid of it?

LAURA MEYERSON: There really are a lot of really fantastic local examples.

For example, here in Rhode Island, we work really hard to control many of our invasive species.

There is a new introduction of a waterborne plant called Hydrilla, and it's just been found, and we're already taking action to control it.

So there are many instances and examples of where people have been able to control invasions and slow the impacts.

WILLIAM BRANGHAM: As I mentioned that there are some researchers who believe that this estimate, as jaw dropping as that number is, that it could be an underestimate.

Do you share that concern that we could still just be only getting a slight glimpse at how severe this problem is?

LAURA MEYERSON: I do.

I do.

We know that there are many other impacts out there that we haven't been able to account for.

So, for example, how do we put a value on the extra time that people have to spend weeding to remove invasive species?

That's impacting small farmers.

It's impacting the production on their farms so that time is being taken away from them.

You know, or another example might be, what is the cost of a species extinction?

Can we put a price tag on that when a species is gone from the planet, it's gone forever.

And those kinds of costs are not included in that just jaw dropping estimate.

WILLIAM BRANGHAM: Laura Meyerson of the University of Rhode Island, thank you so much for being here.

LAURA MEYERSON: Thank you so much for having me.