The observed spread of pancake batter tunicate -- also known as sea vomit -- in multiple locations around Passamaquoddy Bay is prompting marine scientists in the region to sound the alarm. Capable of smothering sea beds and fouling fishing gear, the sea squirt is the most significant in a list of threats posed by invasive marine species that have arrived in the area through warming temperatures and irresponsible aquaculture and shipping practices in the past.
      Pancake batter tunicate, known to scientists as Didemnum vexillum, was first found in the region in 2005 by fisherman Bruce McInnis. Characterized by its appearance, which resembles dripping pancake batter, the tunicate was soon spotted around the island. One colony of note was found by the Estes Head pilings; it appeared to be four to five years in age, according to an assessment at the time by Larry Harris, professor of biological sciences at the University of New Hampshire.
      During his most recent dives in 2019, Harris found that the pancake batter tunicate, along with other tunicates, had become "extensive on both of those pier pilings" at Estes Head and at the salmon pier, along with spreading to a mussel recruitment study site by the WaCo Diner and being visible on the floats in the harbor.
      The pancake batter tunicate is on the watch list for marine scientists because of the potential trouble it represents to local aquaculture. In Canada, the more than $60 million mussel industry in Prince Edward Island (PEI) has been engaged in a heated battle with four tunicates since the arrival of the clubbed tunicate in 1998. While the overall impact of the tunicates is difficult to tabulate, the cost of packing the mussels has gone up by 20% as a direct result of their arrival.
      In Maine, the scallop industry is most vulnerable. "Sea vomit suffocates animals that it becomes established on, prevents establishment of young animals and reduces scallop survival," says Tom Trott, professor of biology at Suffolk University. "It also impacts aquaculture by fouling nets and farmed mussels on suspended ropes."
      Believed to have originated in Japan, the tunicate is now thought to have been brought to the area as part of a shipment of Japanese oysters that were introduced to Maine estuaries by government labs ? which were then, in turn, provided to oyster farming operations, including one started by the Passamaquoddy Tribe in Half Moon Cove in the 1970s.
      In the half century since then, pancake batter tunicate has enjoyed a steady spread. Proliferating across the seafloor, it gets picked up and broken up by scallop draggers, with the broken pieces then becoming whole organisms. Whenever it settles on nets or on farmed scallops or mussels, it gets blasted off by high-pressure hoses, similarly serving to increase its abundance "since each fragment easily becomes reestablished and starts growing," Trott says. That's one reason that mussel farmers in PEI have stopped using high-pressure hoses to clean their nets, he adds.
      It isn't yet known how much the tunicate has spread throughout Passamaquoddy Bay, but based on the species' ability to proliferate in favorable conditions, concern is merited. Georges Bank, where the species was first observed in 2000, had a recorded 88 square miles of coverage in 2006, increasing to 140 square miles by 2018.

Study seeks to determine breadth of spread
      Scientists at the Huntsman Marine Science Centre in St. Andrews have been monitoring the pancake batter tunicate since it was first spotted in Eastport, located just a few miles away. Despite the close proximity and shared waters, the tunicate was seemingly reluctant to cross the invisible border between the two countries, with its first official detection logged just six years ago in 2018 in St. Andrews. Its discovery prompted annual monitoring off Deer Island and Campobello beginning in 2020, during which time the surveying team initially noted "a few small patches" of the tunicate, according to Dr. Claire Goodwin, research scientist at Huntsman.
      In 2021, "there were a few more" patches of note, Goodwin says, but it wasn't especially significant or noteworthy. That changed suddenly last year when the team came across "really large patches" they hadn't seen before. "These areas have multiple patches on the seabed," Goodwin summarizes.
      A simultaneous deep-water survey painted an even more ominous picture, finding "very extensive coverage" in deep-water areas near the islands, Goodwin says.
      In response to the new findings, Goodwin and her team -- in collaboration with Trott -- are looking to start a multi-year research project soon that will help determine how extensive sea vomit has become in the region.
      Trott notes that Canadian monitoring of such species and their possible impacts is "much more robust" than in the U.S. "There has not been a survey for introduced or invasive species in Cobscook Bay since 2005, and that study never produced a report. Maine does a poor job at funding any of this kind of work, and finances that do come forward do not come from the state."
      "In the meanwhile, Canada has extensive and strong tracking programs, some sampling four times a year, annually, using shore and diver surveys and e DNA," Trott continues. "Until introduced species are regarded as a threat to food security like they are in Canada, our best way forward for Cobscook Bay and Passamaquoddy Bay will be to rely on those efforts."
      Citizen scientists in Canada are invited to report sightings of marine invaders on INaturalist by visiting the site and searching for "Fundy Shore Sealife Seekers" or clicking www.inaturalist.org/observations?project_id=182234 to find the project and the species being tracked. Register on the site to submit observations.

Other species pose threats
      While the pancake batter tunicate is the "most concerning" invasive species that scientists are contending with in Passamaquoddy Bay, according to Goodwin, it's far from the only threat. Seaweeds, invertebrates, sponges, green crabs and the Asian shore crab are all among the species of concern.
      The red alga, Dasysiphonia japonica, was found on Grand Manan last summer, according to Trott, "so it is likely in Passamaquoddy Bay." In the southern part of the state, it is a "big nuisance, coming ashore like sargassum in the Caribbean and producing a foul smell," Trott says. There are no local predators, and it carpets the bottom once it becomes established. "I hope that doesn't happen in Passamaquoddy Bay."
      An amphipod native to Japan, Caprella mutica, is now present in Passamaquoddy Bay, Trott reports. They are relatively large amphipods, growing up to two inches in length, and can be very abundant. They displace, outcompete and feed on native species, while having no predators in turn.
      Some marine invasive species are well established in the area, with the green crab being the most historically devastating to local ecosystems. Arriving in the 1800s in the ballast of European ships, the crabs feast on soft-shell clams and mussels while tearing apart marsh banks, contributing to erosion and slowing eel grass growth.
      The green crab may be facing competition soon from the Asian shore crab, a species that is gaining a foothold in the Gulf of Maine. "Their abundance, where they have become established, can be extremely high, up to 100 per square meter, and their impacts extensive -- as extensive, and possibly more, than green crabs," Trott says.
      The first Asian shore crab found in the area was recorded in October 2021 by Robin Hadlock Seeley, former research associate with Cornell University, while conducting an annual crab survey at Gleason Point in Perry. She recently returned to the spot where she found the Asian shore crab but did not find any other specimens. "My prediction is that Asian crabs will continue to be found as single specimens from time to time in our area but will not establish stable populations until the ocean temperature warms further," Seeley says.
      Noting that the Gulf of Maine is warming three times faster than the global oceans as a whole, "We can expect established populations of Asian crabs in our area at some point in the future," Seeley adds.
      "With all the boat traffic and warming, things will continue to change, including the spread of invasives," agrees Harris, who notes multiple additional invasive tunicates, seaweeds and nudibranchs that have been spotted in the area. "Unfortunately, that is the way things are going. It is particularly difficult to deal with invaders in the marine environment once they are established, and it is only then that they are discovered."
      "In summary, even if direct effects are yet to be examined, all of these introduced species occupy space otherwise used by native species. Therefore, they reduce habitat availability for feeding, reproduction and maintaining populations," Trott says. "This is not just hand waving -- these effects are known."