Short description of Ciona robusta, Vase tunicate

Ciona robusta is a conspicuous solitary seasquirt with a semi-opaque, whitish, gelatinous body, up to 15cm long but commonly around 8cm, and capable of significant contraction. C. robusta individuals do not exhibit the yellow (or occasionally orange)  siphon rims typically seen in C. intestinalis, a key field identification characteristic, or the orange tinge to the body of C. intestinalis. Small lumps, or tubercles, are often seen on the siphons of C. robusta, but are always lacking in C. intestinalis.

Impact summary: Ciona robusta, Vase tunicate

Ciona (C. intestinalis and/or C. robusta) is a well-known fouling organism worldwide, and can be particularly detrimental to aquaculture industries due to the cost of equipment cleaning and maintenance. As a filter feeder it also competes for food with farmed species such as mussels and oysters. Fouling costs also affect marina operators and boat owners.

Habitat summary: Ciona robusta, Vase tunicate

(refers to C. intestinalis and C. robusta)
A fouling organism found commonly on anthropogenic substrates, notable in marinas and harbours, and on boat hulls and ship wrecks but also on rocky seabeds and occasionally macroalgae. Prefers low-wave–action environments.

Overview table

Environment	Marine
Species status	Non-Native
Native range	Northwestern Pacific
Functional type	Filter-feeder
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	Plymouth
Date of first record	2003

Origin

Northwest Pacific Ocean (Japan).

First Record

The existence of the 2 distinct types within the nominal species Ciona intestinalis was only realized in 2005 when samples from Plymouth (of the type now retaining the name C. intestinalis) and from the Pacific (C. robusta) were compared at a molecular level. The first currently documented occurrence of C. robusta in the wild in GB was in Plymouth in October 2003, identified retrospectively from photographs of specimens from a marina (JDDB).

Pathway and Method

It is thought that the presence of this species in the NE Atlantic is attributable to anthropogenic introduction, possibly of the adult phase attached to the outside of ships  or in ballast tanks, or with commercial movements of shellfish.

Species Status

This species is established at a handful of marina sites in SW England (and NW France), where it undergoes marked seasonal fluctuations on shallow substrates (presumably re-colonized from deeper substrates). Distribution in NW Europe is perhaps incompletely documented due to past failure to distinguish C. intestinalis and C. robusta. Genetic markers and recent literature detailing field identification are likely to lead to a rapid re-classification of Ciona populations into C. intestinalis and C. robusta. Since it is believed that C. robusta is native to the NW Pacific, it is presumably an introduced species where it occurs on the west coast of North America and the Atlantic coast of South Africa, and in the Mediterranean Sea, Australia and New Zealand.

Dispersal Mechanisms

(refers to C. intestinalis and C. robusta)
With only 2 or 3 days in the water column to develop from eggs to embryos to larvae before attachment and metamorphosis, dispersal in the natural environment is limited. However settlement on boatship hulls, intake into ballast tanks or hitch-hiking with commercial movements of shellfish can carry the species significantly longer distances.

Reproduction

(refers to C. robusta and C. intestinalis)
    Ciona does not brood its young and cannot self-fertilize. Adults release eggs and sperm separately into the water column where eggs can remain for 1 to 2 days before fertilisation. Around 24hrs after fertilisation embryos hatch into free-swimming larvae. These can remain in the water column for 2 to 10 days, although settlement generally occurs within a few minutes or hours of hatching. As soon as they have settled metamorphosis begins into sessile juveniles.
Reproduction by C. robusta in Plymouth marinas occurs generally from August to November.

Known Predators/Herbivores

(refers to C. intestinalis and C. robusta)
On naturally occurring benthic substrates, invertebrate and fish predators have been seen to graze-out populations of Ciona, whereas artificial structures such as pontoons and pilings limit access for these organisms, and Ciona populations appear to grow when released from significant predation.

Resistant Stages

No resistant or resting stage in life cycle.

Habitat Occupied in GB

(refers to C. intestinalis and C. robusta) Prefers areas of low wave action in the immediate subtidal zone. Commonly seen on anthropogenic structures including ship wrecks but also on rocks and boulders and occasionally on macroalgae.

This species is found in its native range of the Northwest Pacific Ocean (Japan). It has also been definitely identified on both the French and English coasts (Falmouth, Plymouth and Torquay) of the western English Channel, Mediterranean Spain, the Atlantic coast of South Africa, Australia and New Zealand, Chile and the west coast of North America (Zhan et al. 2010; Nydam & Harrison 2010).

Environmental Impact

C. robusta co-occurs in England and NW France with the native Ciona intestinalis and possibly competes with it; additionally, limited natural hybridisation between C. intestinalis and C. robusta has been suggested in this region. A study conducted in San Francisco Bay, and thus presumably involving C. robusta, showed that dense growth of Ciona depressed species richness on settlement panels of various sizes and altered the composition of the assemblage of other species (Blum et al., 2007).

Health and Social Impact

None known.

Economic Impact

(refers to C. intestinalis and C. robusta)
Aquaculture enterprises, specifically mussel, oyster and scallop farms, have reported higher mortality, lower overall size and decreased condition of stock in the presence of Ciona. The added cost of equipment cleaning and maintenance also impacts these industries.
As a fouling organism, Ciona undoubtedly contributes to the cost marina operators incur cleaning pontoons, ropes and buoys.

Identification

Brunetti, R., Gissi, C., Pennati, R., Caicci, F., Gasparini, F., Manni, L., 2015. Morphological evidence that the molecularly determined Ciona intestinalis type A and type B are different species: Ciona robusta and Ciona intestinalis. Journal of Zoological Systematics and Evolutionary Research 53: 186-193.

Sato A, Satoh N, Bishop JDD (2012). Field identification of 'types' A and B of the
ascidian Ciona intestinalis in a region of sympatry. Marine Biology 159(7): 1611-1619.

Nydam ML, Harrison RG (2010a). Polymorphism and divergence within the ascidian genus Ciona. Molecular Phylogenetics and Evolution 56(2): 718-726.

Nydam ML, Harrison RG (2010b). Introgression despite substantial divergence in a broadcast spawning marine invertebrate. Evolution 65: 429-442.

Caputi L, Andreakis N, Mastrototaro F, Cirino P, Vassillo M, Sordino P (2007). Cryptic speciation in a model invertebrate chordate. Proceedings of the National Academy of Sciences of the United States of America 104(22): 9364-9369.

Suzuki MM, Nishikawa T, Bird A (2005). Genomic approaches reveal unexpected genetic divergence within Ciona intestinalis. Journal of Molecular Evolution 61(5): 627-635.

Zhan A, Macisaac H, Cristescu ME (2010). Invasion genetics of the Ciona intestinalis species complex: from regional endemism to global homogeneity. Mol Ecol 19: 4678-4694.

Biology, ecology, spread, vectors

Dumont CP, Gaymer CF, Thiel M (2011). Predation contributes to invasion resistance of benthic communities against the non-indigenous tunicate Ciona intestinalis. Biological Invasions 13(9): 2023-2034.

Management and impact

Daigel RM, Herbinger CM (2008). Ecological interactions between the vase tunicate (Ciona intestinalis) and the farmed blue mussel (Mytilus edulis) in Nova Scotia, Canada. Aquatic Invasions 4(1): 177-187.

Blum JC, Chang AL, Liljesthrom M, Schenk ME, Steinberg MK & Ruiz GM (2007). The non-native solitary ascidian Ciona intestinalis (L.) depresses species richness. J Exp Mar Biol Ecol 342: 5-14.

Carver CE, Chisholm A, Mallet AL (2003). Strategies to mitigate the impact of Ciona intestinalis (L.) biofouling on shellfish production. J. Shellfish Res. 22, 621–631.

McKindsey CW, Lecuona M, Huot M & Weise AM (2009) Biodeposit production and benthic loading by farmed mussels and associated tunicate epifauna in Prince Edward Island. Aquaculture 295, 44-51.

General

Angus Jackson 2008. Ciona intestinalis. A sea squirt. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 15012013]. Available from: http:www.marlin.ac.ukspecieshabitats.php?speciesID=2991