An unwelcome species of seaweed is spreading in Maine, where divers found it in recent months off Appledore Island and Cape Elizabeth. A biologist in Connecticut first spotted the invasive, red Asian seaweed washed up on a beach in Rhode Island in 2009. Since then, it's migrated into Massachusetts waters and up the coast to New Hampshire and Maine. Scientists worry its spread will doom native species of seaweed and plug up the traps of more and more lobstermen. Jay Field reports.

Craig Schneider teaches biology at Trinity College in Hartford, Connecticut. Seaweed is Schneider's thing. He's made his living "as a person who studies seaweeds and knows pretty much what you're going to find any time of the season."

Which made his trip to Rhode Island in the summer of 2009 so weird. Schneider was walking along a beach and saw some seaweed he'd never seen before. It was red. "You can't tell, looking at it, what it is. So I actually brought it back to the lab."

Schneider put the red seaweed under a microscope. "And I immediately knew that this genus did not exist in New England. So took two seconds to know that we had an alien species."

The seaweed came to the U.S. from Japan, via Europe, most likely in the ballast tanks of large cargo ships. Three years later, it's easy to see why Schneider moved so quickly to label it as an invasive species. The red Asian seaweed has since moved northward up the coast and into Maine, where divers found it in recent months off Appledore Island and Cape Elizabeth. 

And native species, it turns out, don't like it one bit when an uninvited guest begins squatting in the inter-tidal zone.

"The native species in the ecosystem each play important roles in making that system function efficiently," says Matthew Bracken, a fellow seaweed researcher who teaches marine and environmental science at Northeastern University. "As those species are lost, for example due to displacement by this invader, those roles are no longer being served."

As the red Asian seaweed spreads, organisms that depend on the native seaweed no longer have food. In Europe, whole inter-tidal ecosystems have been altered - though Craig Schneider from Trinty College says he knows of no native species that's been completely wiped out.

The invasive seaweed grows on top of oyster beds and native seaweed. Matthew Bracken says there's also some evidence that its also crowding out eelgrass, which acts as a nursery for lobster and various species of groundfish. In Massachusetts, Bracken says, there are now stretches of coastline where the Asian invader is now the most abundent species of seaweed.

"We're doing experiments right now to figure out if that's actually a causal relationship - in other words, whether the invader is causing these species to go locally extinct," Bracken says. "The other possibility is that areas that have a higher native diversity are more resistant to the invasion."

The Asian seaweed is also creating a huge headache for two other groups of people. In Massachusetts, beachfront homeowners have grown tired of smelly mounds of the stuff washing ashore on their property. The seaweed also has a unique ability to clog up the traps of lobstermen. At a time when many lobstermen have struggled to get a good price for their catch, that's a problem they'd rather not have to deal with.