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Scientists Investigate Mystery Of Invasive Sea Squirt Species

Aboard the RV Connecticut -- From the sea floor of Long Island Sound about a mile south of Stonington Point, video cameras attached to an undersea robot trained their lenses Tuesday on freakish, pustular creatures spreading their rubbery, whitish-orange membranes over rocks, gravel and decaying lobster traps.

Back on board the research vessel Connecticut, scientists gathered around television monitors to study the images being transmitted from the watery world 90 feet below. Were they peering at an invasive blob bent on destruction, a benign enigma of marine biology, or the basis of a strange, emerging sea habitat?

“There's a lot of hypothesis about this species,” said Robert Whitlatch, marine sciences professor at the University of Connecticut's Avery Point campus and one of the leaders of Tuesday's research cruise. “Clearly they're changing the habitat. We're in a steep learning curve about this beast.”

The species' origin is uncertain, and it doesn't even have a formal name yet. For now, as they await results of genetic testing from samples being collected around the world, scientists like Whitlatch just refer to it by the Latinate didemnum sp., the sp. standing for species.

Descriptive nicknames like “pancake batter,” “alien vomit” and “soggy scrambled eggs” have been used by laymen, but marine biologists prefer “carpet tunicate,” to connote both its appearance and zoological classification. It is one of the types of animals known as didemnum, or sea squirts, characterized by their gelatinous anatomy and habit of attaching themselves to marine structures, shellfish and rocks. Several of the sea squirts found in Long Island Sound are invasive species from other parts of the world, but none is attracting the attention of didemnum sp.

“Right now, there is no effective control for this species,” said Whitlatch, who's been studying invasive sea squirts for about 15 years, and first saw this one in 2002. Unlike many of the other sea squirts, he said, this one favors colder, deeper waters.

“There are more researchers working on this, because of the potential impacts on shellfish growers,” Whitlatch said.

It has been plaguing Pacific marine environments from New Zealand to China, Japan, Chile, British Columbia and northern California, Whitlatch said. In the Atlantic, it's covering large areas of the Georges Bank, an important area for commercial fishermen and scallopers, and is growing off the New England coast near Buzzards Bay, Cape Cod Bay and Narragansett Bay. In Long Island Sound it's been found off Latimer Point in Stonington, in Niantic Bay and as far west as Clinton. The main concern about these creatures, Whitlatch explained, is that they grow very fast — about 15 square inches in three weeks — and form impenetrable mats over rocks and other surfaces that would otherwise provide habitat for kelp, shellfish and finfish. Commercial shellfish crops are ruined once didemnum sp. finds them, because it smothers the muscles, clams or scallops as it grows in blankets over them.

“It just covers everything,” said Whitlatch.

With the pH of stomach acid, didemnum sp has no known predators, except perhaps the tiny mollusk called the Greedy Dove Snail. They are filter feeders, sucking in tiny organisms that pass by the hundreds of openings on the mats it forms.

“But we don't know enough about its biology,” Whitlatch said.

For this trip, Whitlatch and his team of graduate and post-graduate students teamed up with scientists from the National Undersea Research Center for the North Atlantic and Great Lakes. The UConn group provided the biological impetus for the cruise — to learn about didemnum sp. — and the NURC crew provided the technology to gather the information with one of its ROVs, — remotely operated robot vehicles equipped with lights and cameras and controlled on board the Connecticut by ROV pilot Craig Bussel's aplomb with joysticks and switches. NURC is part of the National Oceanic and Atmospheric Administration and has its offices and garage for its ROVs at Avery Point.

“This is a shakedown cruise for us,” said NURC Director Ivar Babb, explaining that his crew is readying its ROVs for three weeks of research next month off the southeast U.S. coast.

The researchers studied two sites in eastern Long Island Sound, painstakingly poring over the video monitors for hours as the ROV cameras encountered not only didemnum sp. but also the sea's more comely life forms — clusters of sponges forming natural sculptures, graceful sea robins, red starfish and anemones, brightly-tipped hydroids, mating squid pairs and lobsters poking furtively from rock crevices. The first site was a mostly sandy-bottomed area where little didemnum sp. was found, and the second a spot where Jeff Mercer, a graduate student, has taken samples and photographs during 12 scuba dives over the past three years.

Finding didemnum sp. there was a near certainty, since Mercer has repeatedly found it growing there in abundance. But the kinds of information that can be gathered through diving is limited, he explained, because he can only cover so much ground per dive. With the ROV transmissions, which are plotted to specific geographic coordinates, he and other researchers can begin to figure out how large an area didemnum sp. is impacting.

“It would be nice to get an idea of how wide an area this is covering,” Mercer said. “But we're not going to get rid of it. It's already here.”

The cruise has two additional goals, Whitlatch explained. One is to compare the size of various patches of didemnum sp. at this time of year, when its growth cycle is beginning, to the size on a planned return trip in September, when the animal begins to shrink for the winter months.

The third goal, he said, is to better understand the types of habitats that are most conducive to the growth of didemnum sp., so that habitat managers and shellfish farmers can be warned ahead of time. Whitlatch is also planning to work on a project to find ways to prevent its spread in shellfish beds, perhaps by advising aquaculturists to air out or spray vinegar on their traps between uses to kill any organisms.

“We're looking at potential ways of controlling this in localized areas,” Whitlatch said.

The images collected during the cruise were captured on video tapes, which will be reviewed by Whitlatch and his team back at Avery Point. Data and observations from the tapes will then be sent to the Woods Hole Oceanographic Institute in Massachusetts, which is gathering information on didemnum sp. for researchers to share.

“Because of its worldwide outbreak,” Whitlatch said, “there is a lot of interest in this.”
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