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Invasive Species — Didemnum Tunicate (Didemnum vexillum)

Scroll down to the Control section to learn more about the work ADF&G did with the Smithsonian Environmental Research Center to investigate the efficacy of biocides to control Didemnum vexillum.

Early Detection

In June 2010, The Alaska Department of Fish and Game (ADF&G) sponsored a Marine Invasive Species BioBlitz in Sitka. Marine invasive species experts from the Smithsonian Environmental Research Center (SERC) and the Romberg Tiburon Center at San Francisco State University (RTC-SFSU) joined ADF&G biologists and a consortium of state, federal, tribal and local biologists, students and volunteers for a two-day investigation of nonnative marine species. On the first day of the event biologists who organized the event along with University of Alaska professors and students visited an aquatic farm. Later that evening members of the Sitka public attended an educational presentation at the Sitka Sound Science Center (SSSC) to learn the objectives of a bioblitz, characteristics of invasive species and keys to identifying the species of interest. Samples of nonnative organisms were on hand for viewing in a lab, where microscopes were set up, and questions could be asked of experts. Day two of the event involved surveying for invasive marine species in local harbors. In total participants were looking for six nonnative species, including D. vexillum, at ten various sites.

During the field trip to the aquatic farm, a lantern net- a cylindrical net used in oyster production- was observed approximately 50 percent covered by an orange-ish beige, lobed organism. The net was pulled from the water so samples could be taken in order to identify what was overtaking it. RTC-SFSU professor C. Sarah Cohen oversaw the DNA analysis, and concluded the organism was D. vexillum.

For more information, please read the News Release (PDF 21 kB) or visit the Alaska Fish and Wildlife Newsletter article about the Sitka Marine Invasive Species Bioblitz and detection of Didemnum vexillum in Alaska.

Rapid Response

In August, immediately after receiving confirmation of the DNA analysis, reconnaissance surveys were completed to get a better understanding the extent of the D. vexillum infestation in Whiting Harbor, Sitka. ADF&G, Sitka Tribe of Alaska and UAS biologists surveyed the aquatic farm from above the water to learn about the distribution on the aquatic farm infrastructure. D. vexillum was observed growing on some of the floatation structures as well as on lantern nets near the net pulled during the bioblitz. When the biologists pulled that same net during their August survey, the fibers of the net were less visible while the lobes of tunicate had grown in length considerably. Meanwhile, ADF&G, SSSC and local divers surveyed the seafloor beneath the aquatic farm. Mats of the tunicate were observed on the seafloor and growing on debris that was scattered around on the seabed. It was evident that a more detailed survey would be necessary.

Findings from the reconnaissance survey were reported to organizers of the bioblitz. This group agreed a rapid response team should be established to determine future needs and actions. Federal, state, tribal, and local stakeholders and marine invasive species experts were contacted to invite their participation. Teleconferences occurred bi-weekly with all stakeholders welcome to participate. Outreach to the local community became the primary interest. A stakeholder meeting was held in Sitka and shortly after a community meeting was held to inform members of the public about the species, the potential threats to marine ecosystems and to ask the public to report sightings of organisms suspected to be the invasive tunicate. When funding was secured, a contractor in Sitka was hired to help educate the public and southeast aquatic farmers about marine invasive species, investigate reports of the tunicate, and prepare a draft response plan for D. vexillum in Whiting Harbor.

In January 2011, ADF&G divers completed a thorough survey of Whiting Harbor to assess the distribution of the tunicate. It is noteworthy that the tunicate had died back notably compared to the distribution in August, due to decrease in water temperatures. Divers swam transects from shore toward the center of the harbor to the depth of sixty feet. The tunicate was observed growing on a variety of substrata from large boulders, to cobbles to gravel. Populations of the D. vex were seen to be concentrated at the head of the embayment and beneath the aquatic farm. Understanding the distribution was one key element to planning for future planning.


Although ADF&G does not have the authority to close Whiting Harbor to commercial or recreational vessels, motorized or non-motorized boats or other users, the department has requested the public avoid the area unless there is an emergency in order to reduce the potential of translocating the tunicate to new areas.

During summer 2013, ADF&G deployed buoys in Whiting Harbor to alert boaters, commercial fishermen, and watercraft operators about the presence of an invasive species in Whiting Harbor and requesting they AVOID THE AREA.

Working with stakeholders, ADF&G will remove remaining superstructures floating in Whiting Harbor to reduce the potential for them to become unmoored and exit the area.


Between May and August, 2015, ADF&G and Smithsonian Environmental Center, Marine Lab deployed domes on the seafloor at 30 test sites where they investigated the effects of salt, chlorine and cement dust to control the invasive colonial tunicate, Didemnum vexillum. Check out the Alaska Fish and Wildlife Newsletter for more details, and view the video to see Division Commercial Fisheries Dive Safety Officer, Jeff Meucci talking to school children about the project.