SALEM — Niels Hobbs, a researcher from the University of Rhode Island, was on his knees at Hawthorne Cove Marina Tuesday when he found two crabs not much bigger than a quarter.
One was an Asian shore crab, the other a European shore crab. Neither belong in Salem's waters, he explained.
"When they arrived, they pushed out a lot of native crabs," Hobbs said, as the European shore crab tried to make a run for it up his right arm, an escape shut down by a fast-cupping hand. "They had a substantial impact on prey species, like different kinds of snails."
Hobbs, along with about a dozen researchers from all over the region, were at the marina Tuesday afternoon, reaching under piers and grabbing for signs of life. They were wrapping up the second day of their three-day survey of invasive species along the New England coast.
At each stop, "we have an hour to go and find as many organisms as we can. And in the evening, we go to a lab and process all the species," said Adrienne Pappal, a coastal habitat and water quality manager with the state's Office of Coastal Zone Management.
Through the work, researchers determine what lives in local waters and how that changes over time. It's the sixth such survey they've done in Salem since 2000.
"In Salem, it's really interesting," Pappal said, "because in 2010 we found a shrimp for the first time in North America, from Europe. We've since tracked that shrimp all the way south to Connecticut and all the way north to Maine."
It's important work, because it charts how species are doing over time, not to mention where they live. That information could be used to protect either those or other species if they're in danger, according to Pappal.
Researchers can also see parallels between what's thriving in an area and how that might be affected by the local environment. For example, Williams College professor James Carlton recalled seeing European sea anemones in Salem as recently as 2010. But come 2013, they were gone.
"They were established for ... what, eight years?" Carlton said. "They were linked to the power plant property, to warm water."
With the shutdown of the coal-fired Salem Harbor Station, the warm water disappeared, and so did local sightings of the species, Carlton said.
The group spent Monday in New Bedford, Sandwich and at the Massachusetts Maritime Academy. They hit Rowes Wharf in Boston before arriving in Salem on Tuesday. On Wednesday, they were scheduled to visit a site in Maine.
"This is a short, rapid assessment," he said, "just three surgical-strike days."
The surveys also help chart the activity between species in the waters, which evokes its own interesting debate on whether a species is invasive or not, Carlton explained.
"'Invasive' is subjective," he said. "In science, invasive is ... is it harmful? Bothersome? A nuisance?" Carlton said. " We have no quantitative boundaries."
To Pappal, space in the marine world "is at a premium, and if you have someone moving in, taking up that space, that might be taking space away from another native species," Pappal said. "Or, they could be preying on another species or transferring disease in the marine environment."
What happens with the research they gather, and whether it leads to any new policy protecting the ecosystem, depends on the audience. Carlton calls the targets for their presentations "the three Ps: public, press and politics." Some topics understandably work better in specific demographics, he explained.
Others? Not so much.
"We have an awful lot of non-native species that are having impacts in the structure of the environment in their communities. It isn't something I've ever sold to anyone in Washington, D.C. over the years," Carlton said. "But that aside, these rapid assessment surveys constantly maintain the baseline."