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There's a new sea squirt in town

They look like squishy, rubbery potatoes.

They have no heads, eyes or mouths, just siphons for sucking in sea water.

And yet sea squirts, which evolved hundreds of millions of years ago, are remarkably similar to humans, with a primitive spine, called a notochord. They are the only pre-vertebrate that has a nervous system on the back part of the body, like humans, and not on the belly side.

They also have an immune system, a thyroid gland and, like humans, will reject foreign matter introduced to their bodies.

These similarities have scientists puzzling over their genetic makeup to better understand, for instance, human immunology.

But it is the more pernicious side of sea squirts that is being studied by Robert Whitlatch, professor of marine science at the University of Connecticut at Avery Point in Groton.

Whitlatch, an expert on invasive marine species, is concerned about the impact sea squirts — not native to the United States but increasingly common in Connecticut waters — could have on native species here.

In particular, there is growing concern about the damage they may do to commercial shellfish beds, since the squirts may either ingest the larvae of shellfish, or worse, grow over the shellfish and suffocate them.

“I would hate to put them on the top of a list of potential problems, but they are certainly something we are concerned about replacing native flora and fauna and have the potential to interfere with commercial species,” he said.

Whitlatch said he has had reports of problems from fishermen in Fishers Island Sound and he also has been invited to Canada, where sea squirts there are overgrowing blue mussels.

The sea squirts — named for their tendency to squirt water when they are squeezed — are especially worrisome because they are so resilient, have no natural predators and are adept at muscling out native species.

“They are very good competitors, and when they are competing with natives, they seem to do much better,” Whitlatch said.

He said the sea squirts are getting a lot of scientific attention lately, but much about them remains unstudied. Work on marine invasive species is, in general, less advanced than the scientific knowledge of invasive species on land, which are much more visible.

“It is really only in the last decade or so that we have focused on this problem and how widespread it is,” he said.

Like most other marine invasive species, sea squirts likely arrived here long ago from Europe, South America or Asia, probably on the hulls of ships, Whitlatch said. They attach themselves to surfaces — such as rocks, pilings or boats, like barnacles — and usually remain in one place their entire life, generally several years. They glean nutrition from the sea water they ingest and then squirt back out.

Whitlatch said he hopes to learn more about what makes some areas more likely for invasion. Study so far indicates that invaders like the squirts have more success in areas where there are fewer native species, suggesting they might prey on environmental weaknesses.

“What is it about them that makes them so successful, and which habitats are the most vulnerable?” he said. “With respect to the latter question, there is a very strong relationship between the chance of an environment being invaded and the number of native species there.

“Those habitats where there are a lot of native species are less susceptible. Those that are species poor are more vulnerable.

“Although we have been studying them for a number of years, we don't know enough about them at this stage. Do they grow differently than natives? What is it that has allowed them to have such an impact on native fauna? They don't have natural predators. We also feel some may be chemically defendant, that is they are noxious to predators.”

More attention needs to be paid to the idea of controlling invasive marine species, but it is a daunting task, Whitlatch said.

“Unfortunately, once they are here there is not a lot you can do about them without drastic measures. Clearly, what we are trying to do is identify which species we should be most concerned about,” he said. “We see new species coming in all the time, and by the time you see them, they are in abundance and difficult to control.”

In Australia, all of a native species in a particular bay were lost in an effort to wipe out an invasive species of crab.

“Obviously, you can't do drastic things without affecting everything,” he said. “But (right now) that's about all you can do.”
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