Most living things on Earth have evolved over millions of years in their native habitats, where creatures interact with a complex community of other living things and with their physical environment. They are adapted to the place, and in balance with it. But if you take a creature out of its native habitat and plunk it down somewhere else, there's no telling what effect its presence will have on the neighborhood. The results can be devastating. One misplaced animal is wreaking havoc on its new home.
At the Blackwater National Wildlife Refuge in the eastern state of Maryland, thousands of small, furry animals are clawing and chomping their way through marshland near the Chesapeake Bay, devastating the delicate ecosystem. The nutria invasion is in full swing.
"Nutria really are a poster child for the invasive species work our agency is doing," said Steve Kendrot, a wildlife biologist who supervises the Nutria Control Project in Dorchester County, Maryland. "It is a classic example of what can go wrong when you carelessly or unthinkingly introduce an animal to what is a very sensitive habitat."
He explains that nutria are members of the rodent family that resemble rats but are larger - about 50 centimeters long, weighing around 8 or 9 kilograms. They have long, rat-like tails and huge orange teeth. They were brought here from Argentina.
"Nutria were brought to the Eastern Shore of Maryland in the late 1930s, early 1940s in order to try and establish a fur market," Mr. Kendrot said. "These were nutria farms, essentially, where they raised nutria in captivity and then harvested them for their pelts to supply the world market for fur. Unfortunately, that market never really took off like they thought it would. As a result, the people who invested heavily in nutria farms either released the animals or as the conditions of the farms got dilapidated, they escaped. The animals basically introduced themselves to this ecosystem and found it much to their liking."
These semi-aquatic mammals have since destroyed thousands of hectares of marsh here with their destructive eating habits, heavily overgrazing the native marsh grasses and, as a result, causing severe erosion.
"The nutria feed primarily on the roots and tubers of the marsh plants that hold the marsh surface together," Mr. Kendrot said. "With out the plants, you'd have no marsh. The soil underneath, it's almost an organic soup and without the fibers of these plant roots holding that top surface layer together, it just washes away with the tide, with the wind and rain."
Out on the marsh, biologist Steve Kendrot shows the signs of the nutria's impact.
Kendrot: You can see this area of open water. It's maybe the size of half a football field in the middle of the marsh. A lot of the grass that you see there, that lush green with the sort of brown tops is American three-square and that's a nutria eatout. Where we're floating now used to be primarily marsh."
Saner: So it was all grasses?
Kendrot: At one point, yeah, and it actually sloughs off in big chunks. As those clumps get further and further separated, they finally just break free and float out to the Bay like little icebergs.
These fast-disappearing marsh grasses are essential for birds, fish - all kinds of wildlife that depend on this habitat for food, hiding places from predators, and for reproducing. Mr. Kendrot says marshland is what helps keep the whole Chesapeake Bay watershed healthy.
"These marshlands are really the transition between the Chesapeake Bay and our uplands on either shore of the Bay. And many species of fish and invertebrates are dependent on this ecosystem for some stage of their life cycle," he said. "A lot of fish spawn up in these marshes, so it's critical as nursery areas. Crabs come up into these marshes and molt and spawn, so they're really critical for the whole Bay's ecological economy, as well as its financial economy."
Biologists estimate that as many as 50,000 nutria live in this wildlife refuge, and that they have killed off 3,000 hectares of marsh. Mr. Kendrot says these animals reproduce very easily and quickly.
"Unfortunately, there's no such thing as a few nutria for very long. They do reproduce extremely quickly," he said. "They're breeding year round three to four litters per year, an average of four to five young per litter. So they can produce an extraordinary amount of young. They reach sexual maturity at six months of age. At that point, the young that they'd given birth to in the spring are ready to breed by the fall."
A major problem is that there are no natural predators in Maryland to keep this exploding population in check. In their native South American habitats, the nutria are a favorite meal of an alligator-like reptile called the caiman. There are no such reptiles on Maryland's eastern shore. Troy Lawson, a wildlife biologist from the neighboring state of Virginia, says nutria are starting to appear in his state. He's visiting the refuge area to better understand their habits.
"What I expected to learn is how to trap them and control them," he said. "I had no idea they were capable of this kind of damage and destruction."
One form of nutria control that's being tested is a type of floating trap set in the marsh like a raft.
"This is a floating platform that we're using to attract nutria. Nutria are good swimmers, but they like to rest as well," he said. "And they'll often climb up on anything. We can outfit that raft with traps and actually catch the animal once they're used to it."
Nutria are nocturnal. Their night-time swimming habits make them difficult to track.
Trapping every nutria in the refuge and neighboring areas is the goal of researchers here. At the same time, Steve Kendrot says they are working on ways to restore what marshland has been lost by pumping sediments from out in the open water into these backwater areas, and replanting the decimated marsh grasses. Steve Kendrot and Troy Lawson say the extermination of the nutria is a high price to pay to save the marsh. But, that is a price invasive species often have to pay.
Kendrot: It's a sad situation. I wouldn't wish this on nutria. We all have empathy for the species because it didn't ask to be brought here. It was brought here by our own foolishness, and now we have to fix a serious problem that we created. And it's an unfortunate thing that nutria have to pay the price for that. But if you look out at the marsh there, the ecological arguments for what we're doing are pretty compelling.
Lawson: It's almost inconceivable for me to look at an expanse of water and think it was once grass - it is now meter deep water, and maybe through the efforts that are going on now, a hundred years from now there'll be grass again.
The battle to save marshlands from the ravages of this South American rodent is being fought intensely in Maryland and Louisiana, a southern state where they have also done considerable damage. There, a bounty of $4 is offered for every nutria tail that trappers bring in.
But, biologists say these battles are just part of a larger and expanding war - the nutria is proliferating now in 14 other American states from Virginia to Texas.