- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Habitat List
- Biology and Ecology
- Water Tolerances
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Economic Impact
- Risk and Impact Factors
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Didemnum vexillum Kott, 2002
Local Common Names
- Netherlands: druipzakpijp
Summary of InvasivenessTop of page
D. vexillum, a compound ascidian (tunicate or sea squirt), belongs to the family Didemnidae (Kott, 2002; Lambert, 2009; Stefaniak et al., 2009). Since its identification in 1988 (Kott, 2002), sightings of this species have dramatically increased across the globe. The specific vectors for introduction are largely unknown (see Coutts and Forrest, 2007), though international shipping, local boat traffic and transport of aquaculture species are likely sources (Carlton, 1989; Dijkstra et al., 2007a). Didemnids possess chemical defences (Pisut and Pawlik, 2002) and an acidic tunic (Bullard et al., 2007a), and tolerate a wide range of temperatures (Bullard et al., 2007a; Dijkstra et al., 2007a; Valentine et al., 2007b, 2009), salinities (Dijkstra et al., 2007a; Bullard and Whitlatch, 2009) and nutrients (Carman et al., 2007). Like all ascidians, they produce lecithotrophic larvae that spend less than 24 hours in the water column before settling on suitable substrate and metamorphosing into adult colonies that allow them to build up local populations. In addition, didemnids can disperse through larvae or through fragmentation (Bullard et al., 2007b). They have few known predators (Lambert, 2009) and undergo fast rates of growth (Valentine et al., 2007b). All of these characteristics allow D. vexillum to successfully occupy new habitats and become a dominant spatial competitor.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Chordata
- Subphylum: Tunicata
- Class: Ascidiacea
- Order: Enterogona
- Suborder: Aplousobranchia
- Family: Didemnidae
- Genus: Didemnum
- Species: Didemnum vexillum
Notes on Taxonomy and NomenclatureTop of page
Didemnum vexillum is a compound ascidian (tunicate or sea squirt) and belongs to the family Didemnidae (Kott, 2002).
DistributionTop of page
D. vexillum is likely to originate from Japan (Lambert, 2009) and is now found in the northeast Pacific (British Columbia to Southern California (Cohen et al., 2001; Lambert, 2009), northeast of the USA (Bullard et al., 2007a; Dijkstra et al., 2007a), New Zealand (Coutts, 2002; Coutts and Forrest, 2007), the Netherlands (Lambert, 2009), northwestern France (Lambert, 2009), Ireland (Minchin and Sides, 2006; Minchin, 2007), England (Arenas et al., 2006) and North Wales (USGS, 2009).
D. vexillumn is found around the world in temperate waters (A Gittenberger, Gimaris, The Netherlands, personal communication, 2009).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Atlantic, Northeast||Widespread||Arenas et al., 2006; Minchin and Sides, 2006; Minchin, 2007; Lambert, 2009||The Netherlands, England, Ireland, France|
|Atlantic, Northwest||Widespread||Invasive||Dijkstra et al., 2007a; Valentine et al., 2007b; Osman and Whitlatch, 2007||New York (NY) to Eastport (ME), Georges Bank, introduced to the Gulf of Maine in the 1970s|
|Indian Ocean, Eastern||Present||Coutts, 2002; Coutts and Forrest, 2007||North Island|
|Pacific, Northeast||Widespread||Invasive||Cohen et al., 2001; Lambert, 2009||Found in coast off Alaska, British Columbia to Ensenada, Baja California.|
|Netherlands||Present||1974||Invasive||Gittenberger, 2007||Threat to native ecosystems, especially in the province of Zeeland, as Didemnum sp.|
Habitat ListTop of page
|Inland saline areas||Present, no further details||Natural|
|Coastal areas||Secondary/tolerated habitat||Natural|
|Intertidal zone||Present, no further details||Natural|
|Benthic zone||Present, no further details||Natural|
|Inshore marine||Present, no further details||Natural|
Biology and EcologyTop of page
Both global and local population genetics studies are being carried out by a number of institutes in the USA and New Zealand (A Gittengerber, Gimaris, The Netherlands, personal communication, 2009). For further details see Stefaniak et al. (2009).
Like all colonial ascidians, D. vexillum has two types of reproduction: asexual and sexual. Asexual reproduction occurs through budding which produces colonies of genetically identical zooids. It is made up of individual genetically identical zooids that are not connected by an internal vascular system. Zooids appear randomly embedded in a transparent, spiculated tunic (see Kott (2002) and Lambert (2009) for a full description).
Physiology and Phenology
Colonies exhibit a wide range of morphological variation and within their tunic have calcium carbonate spicules (Bullard et al., 2007a). They range in colour from pinkish, tan or pale orange and can form undulating encrusting mats or rope-like tendrils on vertical surfaces (Bullard et al., 2007a). In its reported range, this species has an extremely rapid growth, quickly covering large areas (100 km2). In coastal zones, D. vexillum has seasonal cycles, undergoing regression during the coldest winter months (Dijkstra et al., 2007a). It grows on both horizontal and vertical surfaces on a wide variety of substrata including intertidal, subtidal rocky surfaces and man-made substrates (Bullard et al., 2007a; Dijkstra et al., 2007a; Valentine et al., 2007b). Colour and growth form are likely related to environmental parameters and substrate orientation. For example, on vertical surfaces D. vexillum tends to form rope-like tendrils whereas colonies on horizontal surfaces or in areas of high current velocities tend to be mat-like (Bullard et al., 2007a; Valentine et al., 2007b). Rope-like tendrils can break off, float away and are capable of reattachment and growth (Bullard et al., 2007a; Coutts and Forrest, 2007; Valentine et al., 2007b). These fragments may increase local recruitment as they may contain brooded larvae that are capable of being released (Lambert, 2009). Although some introduced species remain restricted to artificial substrates in harbours, D.vexillum colonizes and overgrows healthy natural subtidal surfaces (Dijkstra et al., 2007a; Osman and Whitlatch, 2007; Valentine et al., 2007a, 2007b).
Once established in an area, D. vexillum overgrows shellfish (e.g. mussels, scallops) and other sessile invertebrate species (Valentine et al., 2007b) and inhibits settlement of invertebrate species (Dijkstra et al., 2007b; Morris et al., 2009). Very few species settle on the tunic of living colonies as it can be acidic (Dijkstra et al., 2007b). Its rapid growth and acidic tunic reduces the availability of space for settlement and their short larval dispersal allows them to build up local populations. It is a pest to mussel farmers and must be removed either manually or by innovative engineering (Coutts and Forrest, 2007).
D. vexillum is currently observed in areas that experience temperature ranges between 0-28°C (Bullard et al., 2007a; Valentine et al., 2007a). However, Gittenberger (2007) reports that the optimal growing temperature for Didemnum sp. appears to be 14-18°C with virtually all colonies dying when water temperatures are lower than 4°C. D. vexillum is common in marine waters (33 psu), though it can be observed in estuaries (Dijkstra et al., 2007a). In areas with fluctuating salinity regimes, its growth is significantly reduced (Bullard and Whitlach, 2009; J Dijkstra, University of New Hampshire, USA, personal communication, 2009). In addition, its colour can be dependent on temperature and salinity (Lambert, 2009). During periods of heavy rainfall or in estuaries, the colour of D. vexillum can change from white to tan and looks very similar to a sponge. Change in colour from white to tan results from a reduction in size of spicules and in some cases colonies lose their spicules (Lambert, 2009).
Water TolerancesTop of page
|Parameter||Minimum Value||Maximum Value||Typical Value||Status||Life Stage||Notes|
|Salinity (part per thousand)||Optimum||~20-45 tolerated|
|Water temperature (ºC temperature)||14||18||Optimum||2-28 tolerated, only surviving at extremes of temperature for a short amount of time|
Notes on Natural EnemiesTop of page
Means of Movement and DispersalTop of page
Pathway CausesTop of page
Pathway VectorsTop of page
Economic ImpactTop of page
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Is a habitat generalist
- Pioneering in disturbed areas
- Tolerant of shade
- Fast growing
- Has high reproductive potential
- Reproduces asexually
- Ecosystem change/ habitat alteration
- Modification of natural benthic communities
- Monoculture formation
- Negatively impacts aquaculture/fisheries
- Threat to/ loss of native species
- Competition - monopolizing resources
- Competition - smothering
- Interaction with other invasive species
- Rapid growth
- Highly likely to be transported internationally accidentally
- Difficult to identify/detect as a commodity contaminant
- Difficult to identify/detect in the field
- Difficult/costly to control
Prevention and ControlTop of page
Management of D. vexillum has been restricted to attempts in New England (J Dijkstra and L Harris, University of New Hampshire, USA, personal communication, 2009) and New Zealand (Coutts and Forrest, 2007). During their study, Coutts and Forrest (2007) examined a variety of eradication techniques and determined that regional eradication is unlikely, but eradication at small-scales may be possible. Denny (2008) tested several chemical techniques and determined a 2% bleach solution worked best. Establishing monitoring programs is likely the most effective management strategy.
ReferencesTop of page
Arenas F; Bishop J; Carlton J; Dyrynda P; Farnham W; Gonzales D; Jacobs M; Lambert C; Lambert G; Nielsen S; Pederson J; Porter J; Ward S; Wood C, 2006. Alien species and other notable records from arapid assessment survey of marinas on the south coast of England. Journal of the Marine Biological Association UK, 86:1329-1337.
Bullard SG; Lambert G; Carman MR; Byrnes J; Whitlatch RB; Ruiz GM; Miller RJ; Harris LG; Valentine PC; Collie JS; Pederson J; McNaught DC; Cohen AN; Asch RG; Dijkstra J; Heinonen K, 2007. The Invasive colonial ascidian Didemnum sp.: current distribution, basic biology, and potential threat to marine communities of the northeast and west coasts of the United States. J. Exp. Mar. Biol. Ecol, 342:99-108.
Bullard SG; Sedlack B; Reinhardt JF; Litty C; Gareau K; Whitlatch RB, 2007. Fragmentation of colonial ascidians: differences in reattachment capability among species. Journal of Experimental Marine Biology and Ecology, 342(1):166-168. http://www.sciencedirect.com/science/journal/00220981
Bullard SG; Whitlatch RB, 2009. In situ growth of the colonial ascidian Didemnum vexillum under different environmental conditions. Aquatic Invasions, 4(1):275-278. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Bullard_Whitlatch.pdf
Carman MR; Bullard SG; Donnelly JP, 2007. Water quality, nitrogen pollution, and ascidian diversity in coastal waters of southern Massachusetts, USA. Journal of Experimental Marine Biology and Ecology, 342(1):175-178. http://www.sciencedirect.com/science/journal/00220981
Cohen A; Berry H; Mills C; Milne D; Britton-Simmons K; Wonham M; Secord D; Barkas J; Bingham B; Bookheim B; Byers J; Chapman J; Cordell J; Dumbauld B; Fukuyama A; Harris L; Kohn A; Li K; Mumford T; Radashevsky V; Sewell A; Welch K, 2001. Washington state exotics expedition 2000: a rapid survey of exotic species in the shallow waters of Elliott Bay, Totten and Eld Inlets, and Willapa Bay. Olympia, : Washington State Department of Natural Resources.
Coutts ADM; Forrest BM, 2007. Development and application of tools for incursion response: lessons learned from the management of the fouling pest Didemnum vexillum. Journal of Experimental Marine Biology and Ecology, 342(1):154-162. http://www.sciencedirect.com/science/journal/00220981
Denny CM, 2008. Development of a method to reduce the spread of the ascidian Didemnum vexillum with aquaculture transfers. ICES Journal of Marine Science, 65(5):805-810. http://icesjms.oxfordjournals.org/cgi/content/abstract/65/5/805
Dijkstra J; Harris LG; Westerman E, 2007. Distribution and long-term temporal patterns of four invasive colonial ascidians in the Gulf of Maine. Journal of Experimental Marine Biology and Ecology, 342(1):61-68. http://www.sciencedirect.com/science/journal/00220981
Dijkstra J; Sherman H; Harris LG, 2007. The role of colonial ascidians in altering biodiversity in marine fouling communities. Journal of Experimental Marine Biology and Ecology, 342(1):169-171. http://www.sciencedirect.com/science/journal/00220981
Gittenberger A, 2007. Recent population expansions of non-native ascidians in The Netherlands. Journal of Experimental Marine Biology and Ecology [Proceedings of the 1st International Invasive Sea Squirt Conference, Woods Hole, Massachusetts, USA, April 21-22, 2005.], 342(1):122-126. http://www.sciencedirect.com/science/journal/00220981
Minchin D, 2007. Rapid coastal survey for targeted alien species associated with floating pontoons in Ireland. Aquatic Invasions, 2(1):63-70. http://www.aquaticinvasions.ru/2007/AI_2007_2_1_Minchin.pdf
Minchin D; Sides E, 2006. Appearance of a cryptogenic tunicate, a Didemnum sp. fouling marina pontoons and leisure craft in Ireland. Aquatic Invasions, 1(3):143-147. http://www.aquaticinvasions.ru/2006/AI_2006_1_3_Minchin_Sides.pdf
Morris JA Jr; Carman MR; Hoagland KE; Green-Beach ERM; Karney RC, 2009. Impact of the invasive colonial tunicate Didemnum vexillum on the recruitment of the bay scallop (Argopecten irradians irradians) and implications for recruitment of the sea scallop (Placopecten magellanicus) on Georges Bank. Aquatic Invasions, 4(1):207-211. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Morris_etal.pdf
Osman RW; Whitlatch RB, 2007. Variation in the ability of Didemnum sp. to invade established communities. Journal of Experimental Marine Biology and Ecology, 342(1):40-53. http://www.sciencedirect.com/science/journal/00220981
Pederson J; Bullock R; Carlton JT; Dijkstra J; Dobroski N; Dyrynda P; Fisher R; Harris L; Hobbs N; Lambert G; Lazo-Wasem E; Mathieson AC; Miglietta MP; Smith J; Smith IIIJ; Tyrrell M, 2005. Marine invaders of the Northeast: Rapid assessment survey of non-native and native marine species of floating dock communities, August 2003. Massachusetts Institute of Technology Sea Grant College Program Publication No. 05-3.
Ruiz GM; Fofonoff PW; Carlton JT; Wonham MJ; Hines AH, 2000. Invasion of coastal marine communities in North America: apparent patterns, processes and biases. Annual Review of Ecology and Systematics, 31:481-531.
Stefaniak L; Lambert G; Gittenberger A; Zhang H; Lin SJ; Whitlatch RB, 2009. Genetic conspecificity of the worldwide populations of Didemnum vexillum Kott, 2002. Aquatic Invasions, 4(1):29-44. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Stefaniak_etal.pdf
Valentine PC; Carman MR; Blackwood DS; Heffron EJ, 2007. Ecological observations on the colonial ascidian Didemnum sp. in a New England tide pool habitat. Journal of Experimental Marine Biology and Ecology, 342(1):109-121. http://www.sciencedirect.com/science/journal/00220981
Valentine PC; Carman MR; Dijkstra J; Blackwood DS, 2009. Larval recruitment of the invasive colonial ascidian Didemnum vexillum, seasonal water temperatures in New England coastal and offshore waters, and implications for spread of the species. Aquatic Invasions, 4(1):153-168. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Valentine_etal.pdf
Valentine PC; Collie JS; Reid RN; Asch RG; Guida VG; Blackwood DS, 2007. The occurrence of the colonial ascidian Didemnum sp. on Georges Bank gravel habitat: Ecological observations and potential effects on groundfish and scallop fisheries. J. Exp. Mar. Biol. Ecol, 342:179-181.
ContributorsTop of page
30/03/09 Original text by:
Jenn Dijkstra, University of New Hampshire, USA
Distribution MapsTop of page
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