Two non-native species newly found throughout Long Island Sound pose a threat to the estuary's ecosystem and its shellfishing industry, but these discoveries are just part of a much bigger problem that's likely to worsen.

"About once every 24 months we find a new invasive in Long Island Sound," James Carlton, director of the Williams College-Mystic program at Mystic Seaport, said Wednesday. He's been studying the invasives in the Sound since the 1970s and noted that non-natives like Japanese shore crab and European periwinkle have become some of the most common creatures there. Carlton was responsible for one of the most recent new non-native findings when he collected samples of Asian shrimp last year in the Mystic River just offshore from the Seaport.

He had heard it had been found in the Bronx River, "so I decided to look right here at our doorstep."

As waters of the Sound warm with climate change, Carlton said, more non-native species are moving in, and others that have been here in limited numbers for decades, brought in with ship ballast water or in bait supplies, are suddenly exploding.

"There's no question the warming of Long Island Sound is going to be conducive to a longer growing season," he said. "We're seeing the southern species moving north. It's Caribbean creep."

On Wednesday on a dock at the New Haven waterfront, two University of New Haven marine biology professors announced their findings about two invasive species, the Asian shrimp and a type of tunicate, or sea squirt.

The more troubling of the two is the sea squirt, Styela clava. It has been located in marinas as far west as Bridgeport, said professor Carmela Cuomo, head of the university's marine biology program. The greenish-brown invertebrate, which grows in chains of plum-sized pods in large colonies, had previously been found only in the eastern Sound.

Cuomo's work was done in collaboration with professor Robert Whitlatch of the University of Connecticut's Avery Point campus in Groton. Whitlatch has been studying various species of tunicates for years, and has identified colonies of Styela clava in waters off Groton, Niantic, Waterford and elsewhere in the eastern Sound.

"This is truly a potential threat, if they do what they have done in other parts of the world," Cuomo said.

Native to marine waters off Korea, Styela clava have colonized parts of the English and Canadian coasts, she said, causing problems for shellfishing and fishing gear.

"They foul oyster colonies, ships, lines, hulls and docks," she said. "They can foul lobster cages, crab cages."

The fast-reproducing sea squirt grow in dense colonies that can be removed only with labor-intensive efforts, she said, and then must be disposed of on land to prevent regrowing.

Finding the sea squirt in the western Sound, Cuomo said, is particularly concerning because that is where most of the state's $30 million shellfishing industry is located.

David Carey, director of the Bureau of Aquaculture at the state Department of Agriculture, said his office has talked with federal officials about developing programs or obtaining grants for projects to control invasives.

"Anytime you find a new invasive in an area, it's always alarming," he said. "Any invasive needs to be monitored closely."

At the Noank Aquaculture Cooperative, president James Markow said he periodically has to clean his gear and oyster beds of the invasive sea squirts.

"But it's been manageable," he said.

A bigger problem for him has been an invasive seaweed, codia. Nicknamed "the oyster thief," codia "encapsulates the oyster," then forms a kind of paddle that allows currents to drag the shellfish off the beds. To remove it from the areas he's leased for his beds, "we drag a dredge across it," Markow said.

"I can fill the boat up in an hour with the stuff," he said. "It's a constant battle."

The potential problems posed by the arrival of the Asian shrimp in Long Island Sound are less clear, said John Kelly, assistant professor of marine biology at the University of New Haven.

"It's rapidly spreading, and it's well established," Kelly said.

There are several questions that require further research, Kelly said. Are native fish that eat native shrimp also eating Asian shrimp? Are the newcomers out-competing the natives for habitat? Are they carrying viruses or bacteria that can cause illnesses in native species?

Carlton said that once an invasive is established, there's little anyone can do to totally remove it from an ecosystem - especially one with as many entry points as Long Island Sound. Keeping it out of a limited area such as a shellfish bed may be possible, however.

"That's why we often focus on control and prevention, working with the bait and seafood trade and ballast water," he said.

Cuomo said she's looking for the public's help to keep the sea squirt problem from getting worse. Fishermen, boaters and others who find it on their boats and lines should photograph it, remove it and discard it on land, then report it. Invasives can be reported to: hitchhikers@mit.edu.

"We're trying to nip it in the bud," Cuomo said.

j.benson@theday.com