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Invasive Species — Didemnum Tunicate (Didemnum vexillum)
Response

Scroll down to the Control section to learn more about the work ADF&G's partnership with the Smithsonian Environmental Research Center Marine Lab (SERC) and the Bureau of Land Management (BLM) 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.

Containment

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.

Control

For thousands of years unwanted plants have been pulled, burned, and treated with all manner of agents to remove them from tracts of land. More recently, invasive species are removed from terrestrial and freshwater systems as a manner of natural resource management. Here in Alaska, the Department of Fish & Game (ADF&G) has aggressively implemented measures to reduce northern pike populations in Southcentral waters where they are not native, and rats have successfully been eradicated from an Aleutian island. While there are plenty of instances of successful terrestrial and freshwater invasive species control projects, examples of marine invasive species eradication projects are few. Consequently, ADF&G and the Smithsonian Environmental Research Center (SERC) had to take lessons from known projects and employ novel methods to explore techniques to remove invasive colonial tunicates from the seafloor.

ADF&G partnered with the Smithsonian and Bureau of Land Management (BLM) in 2014-2015 to investigate the feasibility of controlling D. vexillum, an invasive tunicate established on the seafloor in Whiting Harbor near Sitka. During the 2015 field season, we visited Whiting Harbor on four occasions. Twice we performed field trials using lime (cement dust), chlorine granules, and salt which were introduced into custom, water tight domes situated over colonies of D. vexillum established on the seabed. After each field trial we returned to measure the effects of the treatments on the tunicate colonies. Divers took photographs of treatment plots before biocides were introduced, immediately after the treatments were completed and again three weeks later as a means to evaluate changes in tunicate colonies overtime.

The biocides were effective at reducing D. vexillum in varying degrees. Both salt and chlorine eliminated tunicate colonies on flat, even substrate. Yet, on rocky sloped areas, the chlorine was significantly more effective. Because of its proven efficacy on two different seabed substrates, ADF&G, SERC and BLM are presently working on a North Pacific Research Board-funded project to scale-up the D. vexillum infested area to be treated with chlorine.

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.