sea vase ascidian

Description/How to recognize a……..

The body of C. robusta is long reaching a maximum length of 100 mm and attached to the substratum by the posterior end or more frequently by the left side near the posterior end of the body. The test of Ciona species varies in consistency and thickness with that of C. robusta being cartilaginous and so robust that such individuals in a preserved state in formalin can be held upright by fingers. The rigidity of the test is quite continuous from hard to soft. Both siphons are situated at the anterior end of the body nearly equal in length in individuals with the hard test. The test may attain to 1-2 mm in thickness in the anterior part of the body and 5 mm at the posterior attachment portion in individuals with the hard test. The surface of the robust test may be covered partly by colonies of some compound ascidians or some mytilid bivalves and thus the test becomes quite opaque. The mantle is very delicate such that the internal structure of the body can be seen through it. Its mantle is scarcely pigmented.It is faintly greenish, but lacks any orange pigmentation, except ocelli (eye) on the siphonal margin, 8 on the branchial and 6 on the atrial siphon side (Hoshino and Takasi, 1967; Michibata, 1984). 

Getting around

All Ciona species are marine and live attached to rocks or any submerged hard surfaces such as ropes, chains and boat hulls (Holland, 2002).


No communication has been documented for Ciona robusta.


Ciona robusta is generally assumed to be native to the NW Pacific, where it was described. It has been reported as an introduced species in the northern and southern hemisphere: in the Atlantic, Mediterranean Sea, Oceania, and North and South Pacific oceans (Bouchemousse et al., 2016a). Also, C. robusta is expanding its range in northern-central Chile (Jofré Madariaga et al., 2014).  The species is distributed along temperate and warm-temperate coasts. The larger range of C. robusta is attributed to its tolerance to a larger temperature range compared to C. intestinalis (Bouchemousse et al., 2016a; Peters, 2013). In South Africa, C. robusta  is found in Mossel Bay, Hout Bay, Table Bay (Peters, 2013).


The species is well established in artificial habitats including marinas and harbours; they are important members of fouling communities (infrastructure and other organisms) and is recognized as introduced/invasive species in parts of the world (Bouchemousse et al., 2016a). Ciona robusta has also been reported inhabiting natural substrates (Almanza et al., 2012; Turon et al., 2016).


Ciona robusta is a filter-feeder that feeds on phytoplankton (Schiewer, 2008).


Sex: Ciona robusta reproduces by means of regeneration; it has a short life span and shows reduced abilities to accurately replace missing tissues with age (Jeffery, 2015). The estimated life span of C. robusta is 12-18 months. Their reproductive capability is size-dependent as they reach maturity within 2 months of settlement in winter and 1month in higher summer temperatures. C. robusta can spawn continuously over a 3 months period. Also, it can tolerate a wide range of environmental conditions and has the potential to rapidly establish substantial populations on floating structures (Carver CE, Chisholm A, 2003).

Family life:

Ciona robusta is a solitary ascidian (Michibata, 1984).


Ciona robusta


Friends and Foes

C. robusta is regarded as the most invasive species of the genus Ciona. It is reported to cause damage and economic losses to cultures of scallop Argopected purpuratus (Lamarck, 1819) (Turon et al., 2016).  

 Smart Strategies

Ciona robusta, in comparison with Ciona intestinalis is reported to have a competitive advantage due to its faster growth rate during the warmer season and as such may have a better adaptive potential (Bouchemousse et al., 2016b). C. robusta  directs more effort toward growing much stiffer and voluminous tunic which helps in lowering predation but has potential to hinder rapid expansion of the juvenile body (Tarallo et al., 2016).

People & I

*Any observations of this species can be uploaded on to iSpot in order to feed into the current project to map the distribution of marine alien species in South Africa.

Conservation status and what the future holds

 F. enigmaticus is a non-indigenous species, listed as an invasive in The National Environmental Management: Biodiversity Act (NEMBA), Act No. 10 of 2004 under category 3; which refers to species that require permits before entering the Republic from outside of the country according to the NEMBA.


References and further reading


Almanza, V., Buschmann, A.H., Hernández-González, M.C., Henríquez, L. a., 2012. Can giant kelp(Macrocystis pyrifera) forests enhance invertebrate recruitment in southern Chile? Marine Biology Research 8, 855–864. doi:10.1080/17451000.2012.692159

Bouchemousse, S., Bishop, J.D.D., Viard, F., 2016a. Contrasting global genetic patterns in two biologically similar, widespread and invasive Ciona species (Tunicata, Ascidiacea). Scientific Reports 6, 1–15. doi:10.1038/srep24875

Bouchemousse, S., Lévêque, L., Dubois, G., Viard, F., 2016b. Co-occurrence and reproductive synchrony do not ensure hybridization between an alien tunicate and its interfertile native congener. Evolutionary Ecology 30, 69–87. doi:10.1007/s10682-015-9788-1

Carver CE, Chisholm A, M. AL, 2003. Strategies to mitigate the impact of Ciona intestinalis (L.) biofouling on shellfish production. Journal of Shellfish Research 9, 257–312.

Holland, P.W.H., 2002. Quick guide Ciona. Current Biology 12, R609.

Hoshino, Z., Takasi, T., 1967. An unusually Robust Ciona From the Northeastern. Seto Marine Biological Laboratory 4, 275–290.

Jeffery, W.R., 2015. The tunicate Ciona : a model system for understanding the relationship between regeneration and aging. Invertebrate Reproduction & Development 59, 17–22. doi:10.1080/07924259.2014.925515

Jofré Madariaga, D., Rivadeneira, M.M., Tala, F., Thiel, M., 2014. Environmental tolerance of the two invasive species Ciona intestinalis and Codium fragile: their invasion potential along a temperate coast. Biological Invasions 2507–2527. doi:10.1007/s10530-014-0680-7

Michibata, H., 1984. Comparative study on amounts of trace elements in the solitary ascidians, Ciona intestinalis and Ciona robusta. Comp. Biochem. Physiol. 78, 285–288.

Peters, K., 2013. Marine alien species in Western Cape harbours, South Africa: A tool for strategically focusing monitoring efforts. Masters Thesis 1–63.

Schiewer, U., 2008. Ecology of Baltic Coastal Waters, Ecological Studies. Springer Berlin Heidelberg.

Tarallo, A., Yagi, M., Oikawa, S., Agnisola, C., D’Onofrio, G., 2016. Comparative morpho-physiological analysis between Ciona robusta and Ciona savignyi. Journal of Experimental Marine Biology and Ecology 485, 83–87. doi:10.1016/j.jembe.2016.09.001

Turon, X., Cañete, J.I., Sellanes, J., Rocha, R.M., López-legentil, S., 2016. Too cold for invasions? Contrasting patterns of native and introduced ascidians in subantarctic and temperate Chile. Management of Biological Invasions 7, 77–86.






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    13 February 2019
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