A marine invasive species appears to be spreading in Cobscook Bay. The tunicate Didemnum, or sea squirt, was first identified in the area by researchers near the former toll bridge between Eastport and Perry, but now it is being found in a number of areas of Cobscook Bay, in substantial quantities. In some areas of the world it threatens to interfere with fishing as the species takes over the bottom.

     Eastport fisherman Scott Emery says he found it on some old lobster traps near the weather buoy in Cobscook Bay, and Joe Storey Jr. of Perry, who has a few traps near the Estes Head cargo pier, discovered quite a bit around the pilings, which he says has been there four or five years. "It seems quite widespread."

      Larry Harris, a professor of marine biology at the University of New Hampshire, estimates that the amount on the pier pilings "could probably fill a dump truck." Along with having found it all over the bottom in Half Moon Cove this year, he notes that he saw it on the float next to the pier at Phoenix Salmon in Broad Cove. "I was surprised how much there was this year, and the size of the colony."

      "It is a very impressive creature," says Harris of the pale sea squirt that looks like spilled pancake batter and hangs down in tendrils. "It's kind of scary stuff, the way it grows."
When it was first found in New Zealand, nearly 26 tons of the tunicate were removed from the bottom of a cargo barge. A recent survey on Georges Bank found that approximately 88 square miles of bottom is covered. In New England, it's been found from Connecticut to Eastport. In Maine, it's been seen in Casco Bay and Penobscot Bay, with it being very common around Damariscotta.

      The sea squirt was first reported in Cobscook Bay by the late Eastport fisherman Bruce McInnis in Half Moon Cove. It was seen again by Harris last year in that area, just before a Rapid Assessment of Marine Invasive Species that was held in Cobscook Bay in August.
It is believed to originate in Japan and was first documented on the east coast of the U.S. in the 1970s in the Damariscotta River. Government labs had been introducing Japanese oysters into Maine estuaries for aquaculture, and the University of Maine's Darling Marine Center on the Damariscotta became involved with aquaculture beginning in the 1970s. The Passamaquoddy Tribe tried to establish an oyster farm in Half Moon Cove in the late '70s with oysters from the Darling Center.

      Concerning how the tunicate spreads, Harris believes that it is reproducing in Cobscook Bay, with the larvae drifting around, but when draggers rip it off the bottom and pieces get thrown back, fragments can colonize on the rocky bottom. It can also grow on the bottom of recreational vessels or be carried to other areas on aquaculture nets or buoys. "It probably won't be able to travel very far on its own by reproducing. It probably has to hitchhike on something else."

      Harris believes the sea squirt probably will not be a problem for salmon farms, but it can smother scallops. There may also be less food for lobsters in areas where it is found. "Nothing has been found yet that eats it. Not even urchins feed on it," he notes. "Where it's growing, nothing else is growing."

      Harris expects it will not be as much of a problem in the Cobscook Bay area as it is in other areas, partly because the water is colder, so it can't grow as fast. It regresses during the winter, and it does not appear to grow in soft sediment such as mud. "It may not have an opportunity to be more than a pest rather than a serious threat to anything."

     At present not enough research has been done on the species, with scientists and other researchers just documenting its spread. "Even on Georges we don't know if it's had an effect on other species yet," says Harris. "No one's figured out yet how to prevent its spread."

      Harris suggests that it would be a good idea to monitor other hard-bottom areas and other piers and to have fishermen aware of what the tunicate looks like. "If they find it some place else it may be possible to moderate its impact in areas," says Harris, noting that divers could strip it from localized pilings. However, he suspects those efforts would involve a great deal of work and only succeed in setting back a bit the tunicate's spreading over the bottom.