Invasion
Invasion Description
1st Records: Groton/CT/Long Island Sound (2000, Osman and Whitlach 2007); Tripps Marina, Westport/MA/Buzzards Bay (2000, MIT Sea Grant 2003); Massachusetts Marine Academy, Bourne/MA/Buzzards Bay (2000, MIT Sea Grant 2003)
Geographic Extent
Chatham/MA/Chatham Harbor (39.9 min N lat, 69 deg 57.4, 8/7/2003, USGS Woods Hole Science Center 2003-2007 ); Osterville/MA/Cotuit Bay (2005, USGS Woods Hole Science Center 2003-2007); Woods Hole/MA/Eel Pond (Vineyard Sound) (41 deg 31.2 min N lat, 70 deg 40.0 W lon, 1-1-2000, USGS Woods Hole Science Center 2003-2007); Oak Bluffs, Martha's Vineyard/MA/Vineyard Sound (41 deg 27.6 min N lat, 70 deg 33.6 min W (1/22/04, USGS Woods Hole Science Center 2003-2007); Vineyard Haven/MA/Vineyard Sound (2004, MIT Sea Grant 2003-2007; USGS Woods Hole Science Center 2003-2007); Tisbury, Marthas Vineyard/MA/Lake Tashmoo (2008, Carman and Grunden 2010, on eelgrass, Zostera marina); 13 of 24 aquaculture sites, Martha's Vineyard/MA/in 19 surveyed embayments (2008, Carman et al. 2010); Marthas Vineyard/MA/Stonewall Pond (2012-2013, Colarusso et al. 2016); West Falmouth/MA/West Falmouth Harbor (2004, USGS Woods Hole Science Center 2003-2007); Tripps Marina, Westport/MA/Buzzards Bay (2000, MIT Sea Grant 2003; 2010, Massachusetts Office of Coastal Zone Management 2013); Massachusetts Marine Academy, Bourne/MA/Buzzards Bay (2000, MIT Sea Grant 2003; 2010, Massachusetts Office of Coastal Zone Management 2013); South Pier, Prudence Island/RI/Narragansett Bay (2005, Auker and Oviatt 2005); Fort Wetherill, Jamestown/RI/East Passage, Narragansett Bay (2005, Auker and Oviatt 2005); Jamestown Boatyard, Jamestown/RI/Narragansett Bay (Ruiz et al., unpublished data); Fort Adams State Park/Newport/RI/Narragansett Bay (2010, Massachusetts Office of Coastal Zone Management 2013); New England Boatworks, Jamestown/RI/Narragansett Bay (Ruiz et al., unpublished data); Coasters Harbor Island, Newport/RI/East Passage, Narragansett Bay (2003, MIT Sea Grant 2003-2007) ; URI Dock, Graduate School of Oceanography (2002, USGS Woods Hole Science Center 2003-2007; Auker and Oviatt 2008), 41 deg 29.3 min N lat, 71 deg 25.5 min W lo), Beavertail Point, Jamestown/RI/Narragansett Bay (2005, USGS Woods Hole Science Center 2007); Block Island/RI/Great Salt Pond (2007, 41o10'62" 71o34'58", Carman et al. 2009); Matunuck, Point Judith Maina/RI/Point Judith Pond (2009, MIT Sea Grant 2011; Massachusetts Office of Coastal Zone Management 2013); Avery Point, Groton/CT/Long Island Sound (2000, Osman and Whitlatch 2007); South end of Old Ponquogue Bridge, east of new Ponquogue Bridge, Long Island/NY/Shinnecock Bay (12/3/2004) (USGS Woods Hole Science Center 2003-2007; Bullard et al. 2007); Georges Bank; November, 2003; in a 6 sq mi area centered on 41 deg 58 min N lat, 67 deg 31 min W lon; water depth 48 m, (157 ft). Source: P. Valentine, J. Collie, R. Reid. (USGS Woods Hole Science Center 2003-2007; Avery Point, Groton/CT/Long Island Sound (2000, Osman and Whitlach 2007)
Vectors
| Level | Vector |
|---|---|
| Probable | Hull Fouling |
Regional Impacts
| Ecological Impact | Competition | |
| Didemnum vexillum overgrows benthic fauna, including scallops, mussels, and other sessile species, on the Georges Bank (Valentine et al. 2007). On bare experimental plates in Fishers Island Sound, Connecticut, Didemnum was most competitive at sites with cooler temperatures, where it outgrew other tunicates, such as Botrylloides violaceus, Botryllus schlosseri, and Ascidiella aspera. However, Didemnum was less dominant on plates in which colonies of other species were already established (Osman and Whitlatch 2007). Invasion success of D. vexiullum in experimental fouling communities was dependent on the presence of large amounts of unoccupied space (Janiak et al. 2013). In experiments at Eel Pond, Woods Hole, Didemnum began to recruit later than other species, in October, and rapidly expanded its coverage on plates in October-December (Agius 2007). In Narragansett Bay, Didemnum dominated plates in the fall, and overgrew recruits of the Blue Mussel (Mytilus edulis) (Auker and Oviatt 2008). In field experiments with a diversity of competitors and predators, Didemnum vexillum was less successful than when predators were excluded. However, the ability of colonies to form tendrils for dispersal, to fuse, to form extensive colonies on pebble and cobble surfaces, and to resist grazing, due to calcareous spicules in the tunic, enable D. vexillum to form extensive colonies in open areas (Stefaniak 2017). On Georges Bank, the abundance of Didemnum vexillum had a negative asssociation with that of both juvenile and Sea Scallops (Placopecten magellanicus. Didemnnum vexillum was more abundant i areas open to trawling than in areas closed to fishing, indicating that it may be favored by disturbance (Kaplan et al. 2017) | ||
| Ecological Impact | Habitat Change | |
| Didemnum vexillum overgrows gravel and benthic fauna, including scallops, mussels, and other sessile species. The surface of D. vexillum appears to repel settlement of secondary fouling organisms, suggesting that large areas of D. vexillum may reduce the amount of seabed suitable for settlement of larvae of other benthic species, including sea scallops. The mats of Didemnum sp. may also reduce the amount of suitable shelter available for juvenile fish and other organisms (Valentine et al. 2007). On Georges Bank, the abundance of Didemnum vexillum had a negative asssociation with that of both juvenile and Sea Scallops (Placopecten magellanicus. Didemnum vexillum may inhibit the settling of Sea Scallops, because of the acidity of its tunic (Kaplan et al. 2017). | ||
| Ecological Impact | Food/Prey | |
| Dense mats of Didemnum vexillum colonies possibly form a barrier between fish and their benthic prey such as worms and bivalves, on the Georges Bank (Valentine et al. 2007). Some predation occurred on Didemnum, by the snail Astyris lunata and probably by fish on uncaged plates, but this tunicate appears less limited by predation than other tunicates, whose recruits are less likely to survive in open, deeper waters than Didemnum (Osman and Whitlatch 2007). Many benthic invertebrates on Georges Bank were positively associated with D. vexillum, and many of these invertebrates were important components of 5 important species of fishes (Winter Skate (Leucoraja ocellata), Little Skate (Leucoraja erinacea), Haddock (Melanogrammus aeglefinus), Winter Flounder (Pseudopleuronectes americanus), and Longhorn Sculpin (Myoxocephalus octodecemspinosus) (Smith et al. 2014). | ||
| Economic Impact | Fisheries | |
| Economic impacts on 'wild' fisheries, such as bottom fishes, scallops and lobsters are expected due to habitat change and replacement of food resources. Didemnum vexillum was found fouling aquaculture gear at 11 sites, and cultured Bay Scallops (Argopecten irradians) at three sites, of 26 aquaculture sites surveyed on Marthas Vineyard (Carman et al. 2010). This tunicate was also reported at aquaculture sites in Rhode Island (Carman et al. 2010). On Georges Bank, a major concern was possible negative impacts on the commercially important Sea Scallop (Placopecten magellanicus). Experiments indicate that can negatively affect larval settlement (Morris et al. 2009) and escape responses of the scallops (Dijkstra et al. 2011; Kaplan et al. 2017). However, the commerically important fishes Haddock Melanogrammus aeglefinus and Winter Flounder (Pseudopleuronectes americanus) fed heavily on benthic invertebrates positively associated with D. vexillum (Smith et al. 2014). | ||