No data for Australia

General Information

Kott, 2002

Please use the following citation for this material
NIMPIS 2010, Didemnum vexillum general information, National Introduced Marine Pest Information System, viewed 03 September 2010 <http://www.marinepests.gov.au/nimpis>.

Habitat

Didemnum vexillum occur in a wide range of habitats. In calm areas they tend to be found as a thin rope-like form, and in areas with rough conditions (e.g. strong currents) they are found as a thick encrusting mat (Bullard et al. 2007).

Habitat classification

For the purposes of NIMPIS, habitats have been divided into four categories: Hard, soft, water and organism. The habitat types assigned to these categories reflect the variety of substrata available for organisms to colonise. Habitat types listed for this species are those that have been recorded in the literature.

Hard

This category contains both natural and artificial habitats that are solid, fixed or permanent substrata. Species can reside on (e.g. attached externally) or within (e.g. boring into) the habitat type.

• Concrete
  
• Wood
  

Soft

This category contains habitats that are not fixed or permanent, and are able to be affected by water movement. Species can reside on (e.g. living on the sediment-water interface) or within (e.g. burrowing into) the habitat type.

• Boulder
  
• Cobble
  
• Gravel
  

Tidal Range

• Mid-tide
  
• Low-tide
  
• High-tide
  
• Sub-tidal
  

Habitat survival parameters

	Minimum	Maximum
Adult temperature	1.0 °C Field observations report a minum temperature of 1 °C with colony degradation occuring below 4 °C. (Lambert 2005; Valentine et al. 2007).	31.0 °C Laboratory-based studies of temperature tolerance predict a maximum tolerance of 31 °C but field observations report 24 °C (Lambert 2005; Valentine et al. 2007). Colony growth rates decline when temperatures exceed 21 °C for seven consecutive days (Daley and Scavia 2008).
Adult salinity	10.0 ppt	33.0 ppt
Dissolved oxygen	N/a	N/a

Reproduction and growth

Didemnum vexillum are hermaphroditic and ovoviviparous. New colonies can be produced through asexual budding and fragmentation which gives many colonies a rope or mound-like structure. Sperm are released into the sea through the atrial siphon and then travel into the oral siphon of another zooid where an egg is fertilised. The larvae brood in the tunic below the zooid and once developed are released from the colony. Eggs can mature within the colony in several weeks and a typical zooid will produce one to 20 eggs (Daniel and Therriault 2007).

Minimum reproductive temperature	14.0 °C Valentine et al. (2009).
Maximum reproductive temperature	20.0 °C Valentine et al. (2009)
Cues	N/a
Strategy	Budding occurs when fragments of Didemnum vexillum become separated and re-attach to suitable substrate. These buds can then give rise to an entirely new fertile colony (Bullard et al. 2007b). Larval ascidians are brooded in the tunic and released as swimming non-feeding tadpoles (Bullard et al. 2007b).
Season	N/a

Life cycle

Age to maturity 365 days
Colonial ascidians typically live for one to three years; generally development during the first year is followed by breeding and death in subsequent years (Berrill, 1950; O'Clair and O'Clair 1998).

Please use the following citation for this material
NIMPIS 2010, Didemnum vexillum reproduction and habitat, National Introduced Marine Pest Information System, viewed 03 September 2010 <http://www.marinepests.gov.au/nimpis>.

Feeding Preferences

Trophic status: suspension feeder

Food

Competitors

Stage: adult

Didemnum vexillum competes with the blue mussel Mytilus edulis for space and food. It also can use the mussel as a substrate which restricts the mussels valve movements (Auker and Oviatt 2007). The invasive colonial tunicates Botrylloides violaceous and Botryllus schlosseri had reduced growth rates in the presence of Didemnum vexillum (Auker and Oviatt 2007). The tunic of Didemnum vexillum generally has a surface pH of between two and three or lower. This defense adds to its ability to compete for substrate and resources (Bullard et al. 2007a).

Predators

Please use the following citation for this material
NIMPIS 2010, Didemnum vexillum feeding and predators, National Introduced Marine Pest Information System, viewed 03 September 2010 <http://www.marinepests.gov.au/nimpis>.

Impacts

Didemnum vexillum has the ability to overgrow benthic organisms, spread by fragmentation and survive well in human-dominated habitats. With high reproductive and population growth rates, a tolerance to a wide range of environmental conditions and an apparent scarcity of predators (Bryon and Scavia 2008), these ecological traits make for a very tenacious invasive species.

Vectors

Descriptions of the vector types that are relevant to this species are displayed below.

Fisheries and Aquaculture

This class encompasses vectors associated with fisheries and aquaculture activities and trade. An example of a vector from this class is Fisheries intentional, which would incorporate, for example, the introduction of the Pacific oyster Crassostrea gigas for aquaculture purposes. Other vectors included in this class are: Discarded bait, Fisheries accidental (not mollusc), mollusc accidental, mollusc intentional, packing material and scientific escape.

Fisheries - accidental (not mollusc)	The accidental translocation of species through aquaculture and fisheries activities. This vector includes the accidental release of live fish, crustaceans and molluscs (other than oysters) imported for human consumption, This vector also includes the accidental translocation of species attached to aquaculture gear (floats, cages, etc).
Fisheries - intentional (not mollusc)	The deliberate translocation of fish, crustaceans or molluscs (not oysters) to establish or support a new fishery. For example many aquaculture operations use species that are not native, which involves introducing species from elsewhere in the world.
Oyster accidental	The introduction of organisms associated with molluscs and their deliberate translocation. Species of molluscs are highly valued aquaculture species and have been translocated across the globe for farming. Many species live cryptically on mollusc shells and have subsequently been introduced along with molluscs into new localities. This was more common historically when shells were not cleaned of other species.
Discarded bait	The release of unused, unsuccessful or excess bait species (and associated organisms) from commercial fishing operations, sport and recreational fishing activities. It is possible that two species of prawn that are introduced into San Francisco Bay, were originally imported for sale as bait or human food. The dumping of organisms from vessels or release from shore may have led to the establishment in the wild.

Please use the following citation for this material
NIMPIS 2010, Didemnum vexillum impacts and vectors, National Introduced Marine Pest Information System, viewed 03 September 2010 <http://www.marinepests.gov.au/nimpis>.

Additional Information

General Notes

adult

A Didemnum vexillum colony contains many small zooids, 1 to 2 mm in length, embedded in a gelatinous matrix (tunic or test) along with calcerous spicules. Thin encrusting sheets are normally formed by younger colonies, while more mature colonies tend to be in the form of lobe-encrusted mounds or rope-like structures. This is because of the fragmentation method of reproduction which involves budding (Daniel and Therriault 2007). The form the matrix takes is also dependent on environmental conditions; sheet-like forms tend to favoured in areas with rough seas (e.g. strong currents) and mound/rope-like forms favour calmer conditions (Bullard et al. 2007a). Individuals change colour as they mature, which is thought to depend on the mineral elements available in the surrounding environment. Therefore, colour varies between colonies, but not necessarily species in the genus (Daniel and Therriault 2007).

larvae

Key characteristics of Didemnum larvae are the presence of: a tubular notochord composed of 40 discoidal cells, dorsal central nervous system, locomotory tail, a head, three rows of incompletely developed stigmata, and three adhesive papillae (Daniel and Therriault 2007).

Identification Notes

Similar Species

adult	Didemnum incanum is a native to New Zealand and can be distinguished from Didemnum vexillum because it is cream in colour (not yellowish) and it has veins that are cream-coloured, smooth, raised and leaf-like, and lacks pores (Didemnum vexillum has pores) (USGS National Geologic Studies of Benthic Habitats, 2010).

Please use the following citation for this material
NIMPIS 2010, Didemnum vexillum additional information, National Introduced Marine Pest Information System, viewed 03 September 2010 <http://www.marinepests.gov.au/nimpis>.

References

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