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.”

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