Botrylloides violaceus (violet tunicate)

Pictures

Picture	Title	Caption	Copyright
Title Colour morphs Caption Botrylloides violaceus colonies occur in many colours and can overgrow large areas. Netherlands coast. Copyright Adriaan Gittenberger/GiMaRIS	Colour morphs	Botrylloides violaceus colonies occur in many colours and can overgrow large areas. Netherlands coast.	Adriaan Gittenberger/GiMaRIS
Title Invasive habit Caption The reddish Botrylloides violaceus colonies overgrow and potentially suffocate the mussels. Massachusetts coast, USA. Copyright Adriaan Gittenberger/GiMaRIS	Invasive habit	The reddish Botrylloides violaceus colonies overgrow and potentially suffocate the mussels. Massachusetts coast, USA.	Adriaan Gittenberger/GiMaRIS
Title Invasive habit Caption The purple and reddish Botrylloides violaceus colonies overgrow and potentially suffocate the mussels. Massachusetts coast, USA. Copyright Adriaan Gittenberger/GiMaRIS	Invasive habit	The purple and reddish Botrylloides violaceus colonies overgrow and potentially suffocate the mussels. Massachusetts coast, USA.	Adriaan Gittenberger/GiMaRIS
Title Colonising habit Caption The reddish colonies have only just settled and consist of one to several individuals. The white Botrylloides colony is a few weeks older. Massachusetts coast, USA. Copyright Adriaan Gittenberger/GiMaRIS	Colonising habit	The reddish colonies have only just settled and consist of one to several individuals. The white Botrylloides colony is a few weeks older. Massachusetts coast, USA.	Adriaan Gittenberger/GiMaRIS
Title Colonising habit and a natural enemy Caption The small red patches are the recently settled Botrylloides violaceus colonies. They are Massachusetts coast, USA. Copyright Adriaan Gittenberger/GiMaRIS	Colonising habit and a natural enemy	The small red patches are the recently settled Botrylloides violaceus colonies. They are Massachusetts coast, USA.	Adriaan Gittenberger/GiMaRIS
Title Colonising habit and a natural enemy Caption The small red patches are the recently settled Botrylloides violaceus colonies. They are threatened by grazers like sea-urchins. Massachusetts coast, USA. Copyright Adriaan Gittenberger/GiMaRIS	Colonising habit and a natural enemy	The small red patches are the recently settled Botrylloides violaceus colonies. They are threatened by grazers like sea-urchins. Massachusetts coast, USA.	Adriaan Gittenberger/GiMaRIS

Identity

Preferred Scientific Name

• Botrylloides violaceus Oka, 1927

Preferred Common Name

• violet tunicate

International Common Names

• English: orange sheath tunicate

Local Common Names

• Netherlands: slingerzakpijp

Summary of Invasiveness

B. violaceus is a compound ascidian (tunicate or sea squirt) and belongs to the subfamily Botryllinae. It is made up of individual genetically identical zooids and ampullae that are connected by an internal vascular system. Like all colonial ascidians, it has two types of reproduction: asexual reproduction, a process known as blastogenesis, and sexual reproduction.

It is native to the west Pacific, and is now found in the Northeast Pacific (Alaska, British Columbia to Ensenada, Baja California; Lambert and Sanamyan, 2001; Cohen et al., 2005), Sydney Harbour, Australia, the Venetian Lagoon, the Netherlands, and the coast of Japan. It can tolerate a wide range of environmental factors including temperature, salinity and nutrients (Carman et al., 2007; Dijkstra et al., 2008).  B. violaceus overgrows shellfish (e.g. mussels) and other sessile invertebrate species. It is a pest to mussel farmers and must be removed either manually or by innovative engineering.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Chordata
•             Subphylum: Tunicata
•                 Class: Ascidiacea
•                     Suborder: Stolidobranchia
•                         Family: Styelidae
•                             Genus: Botrylloides
•                                 Species: Botrylloides violaceus

Description

B. violaceus is a compound ascidian (tunicate or sea squirt) and belongs to the subfamily Botryllinae. It is made up of individual genetically identical zooids (measuring ~2 mm in diameter) and ampullae that are connected by an internal vascular system. Zooids are arranged in loose circles or rows and are embedded in a transparent tunic.

Distribution

Distribution Table

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.

Introductions

Habitat

Habitat List

Biology and Ecology

Genetics

For information on the genetics of this species see Lejeusne et al. (2011).

Reproductive Biology

Like all colonial ascidians, B. violaceus has two types of reproduction: asexual reproduction, a process known as blastogenesis, and sexual reproduction. Asexual reproduction occurs through budding which produces colonies of genetically identical zooids. Studies have shown that small substrates limit asexual reproduction and induce sexual reproduction. B. violaceus is a hermaphrodite that undergoes sexual reproduction between 10 and 12°C. Sexual reproduction begins when the gonads of both sexes develop on either side of the zooid with the ovary situated behind the testis. The egg is ovulated in a brood pouch that forms as an outgrowth of the body wall. Within the brood pouch, the egg is fertilized and develops until the larva escapes. The brooding period depends on several factors including temperature, salinity and number of asexual reproductive cycles (Sabbadin, 1955; Millar, 1971). More on growth and reproductive cycles can be found in Yamaguchi (1975). Brown et al. (2009) report further on whole body regeneration in this species.

Larvae, when release, are relatively large (0.01-0.02 mm) and are brightly coloured. They are lecithotrophic and spend less than 24 hours in the water column before settling on suitable substrate and metamorphosing into adult colonies. During metamorphosis, the larvae sticks to the substrate and begins to form a circle of ampullae. All Botrylliodes of the same generation appear, grow, and die synchronously. Both the zooids bearing embryos and the sterile zooids of the oldest generation begin to disintegrate and are eventually reabsorbed into the common vascular system.

Environmental Requirements

B. violaceus can tolerate a wide range of environmental factors including temperature, salinity and nutrients (Carman et al., 2007; Dijkstra et al., 2008). 

Associations

B. violaceus overgrows shellfish (e.g., mussels) and other sessile invertebrate species.

Water Tolerances

Notes on Natural Enemies

Means of Movement and Dispersal

At least three potential mechanisms account for the introduction of colonial ascidians to the Gulf of Maine: 1) hull fouling, 2) ballast water, and 3) aquaculture. Because colonial ascidians produce lecithotrophic larvae that have an abbreviated planktonic stage (Lambert, 1968; Olson, 1985; Svane and Young, 1989), the likelihood of larvae surviving in ballast water is very low (Carlton and Geller, 1993). Thus, the most likely vectors for transport are hull fouling, aquaculture or rafting. Rafting on broken leaves and other debris to which they are attached can transport colonies both long and short distances. Some studies show evidence that rafting events occur frequently, and thus may have a substantial effect on population dynamics. Dijkstra et al. (2007) found bivalve aquaculture to the likely mechanism of long-distance (trans-oceanic) spread for this species. Other vectors include sea chests (Coutts and Forrest, 2007). Once transported to a site, further introduction to sites in the region (kms apart) can be from hull fouling of recreational or commercial vessels.

Pathway Causes

Pathway Vectors

Impact

Risk and Impact Factors

Impact mechanisms

• Competition - monopolizing resources
• Competition - smothering
• Filtration
• Fouling
• Interaction with other invasive species
• Rapid growth

Impact outcomes

• Ecosystem change/ habitat alteration
• Modification of natural benthic communities
• Modification of successional patterns
• Monoculture formation
• Negatively impacts aquaculture/fisheries

Invasiveness

• Abundant in its native range
• Fast growing
• Has high reproductive potential
• Highly adaptable to different environments
• Is a habitat generalist
• Pioneering in disturbed areas
• Proved invasive outside its native range
• Reproduces asexually
• Tolerant of shade

Likelihood of entry/control

• Difficult to identify/detect as a commodity contaminant
• Difficult to identify/detect in the field
• Difficult/costly to control
• Highly likely to be transported internationally accidentally

References

Bock DG, Zhan A, Lejeusne C, MacIsaac HJ, Cristescu ME, 2011. Looking at both sides of the invasion: patterns of colonization in the violet tunicate Botrylloides violaceus. Molecular Ecology, 20(3):503-516. http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-294X

Brown FD, Keeling EL, ADLe , Swalla BJ, 2009. Whole body regeneration in a colonial ascidian, Botrylloides violaceus. Journal of Experimental Zoology, 312B(8):885-900.

Callahan AG, Deibel D, McKenzie CH, Hall JR, Rise ML, 2010. Survey of harbours in Newfoundland for indigenous and non-indigenous ascidians and an analysis of their cytochrome c oxidase I gene sequences. Aquatic Invasions [Proceedings of the 16th International Conference on Aquatic Invasive Species, Montreal, Canada, 19-23 April 2009.], 5(1):31-39. http://www.aquaticinvasions.ru/2010/AI_2010_5_1_Callahan_etal.pdf

Carlton J, Geller J, 1993. Ecological roulette: The global transport of nonindigenous marine organisms. Science, 261:78-82.

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

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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

DAISIE, 2011. European Invasive Alien Species Gateway. http://www.europe-aliens.org/

Davidson IC, Zabin CJ, Chang AL, Brown CW, Sytsma MD, Ruiz GM, 2010. Recreational boats as potential vectors of marine organisms at an invasion hotspot. Aquatic Biology, 11(2):179-191. http://www.int-res.com/abstracts/ab/v11/n2/p179-191/

Dijkstra J, Dutton A, Westerman E, Harris L, 2008. Heart rates reflect osmotic stress in two introduced colonial ascidians: Botryllus schlosseri and Botrylloides violaceus. Marine Biology, 154:805-811.

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

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Contributors

23/10/08 Original text by:

Jenn Dijkstra, University of New Hampshire, USA

Distribution Maps

• = Present, no further details
• = Evidence of pathogen
• = Widespread
• = Last reported
• = Localised
• = Presence unconfirmed
• = Confined and subject to quarantine
• = See regional map for distribution within the country
• = Occasional or few reports

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