Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Styela plicata
(pleated sea squirt)



Styela plicata (pleated sea squirt)


  • Last modified
  • 22 November 2019
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Styela plicata
  • Preferred Common Name
  • pleated sea squirt
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Chordata
  •       Subphylum: Tunicata
  •         Class: Ascidiacea
  • Summary of Invasiveness
  • S. plicata is a widely distributed, temperate to subtropical tunicate. As a pest species, S. plicata can outcompete native encrusters and exclude them from hard substrates. It is a known fouler of sea vesse...

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Preferred Scientific Name

  • Styela plicata Lesuer, 1823

Preferred Common Name

  • pleated sea squirt

Other Scientific Names

  • Ascidea plicata
  • Ascidia plicata Lesueur, 1823
  • Styela barnhart Ritter & Forsyth, 1917
  • Styela gyrosa Heller, 1877
  • Styela pinguis Herdman, 1899
  • Tethyum plicatum Hartmeyer, 1909

International Common Names

  • English: leathery tunicate; rough tunicate; sea squirt; solitary ascidian

Summary of Invasiveness

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S. plicata is a widely distributed, temperate to subtropical tunicate. As a pest species, S. plicata can outcompete native encrusters and exclude them from hard substrates. It is a known fouler of sea vessels and other hard substrates, travelling the oceans in this fashion.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

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Styela plicata, the pleated sea squirt, is an ascidian (the term ascidian can be used interchangeably with the term 'sea squirt'). In other words, it belongs to the Class Ascidiacea, Subphylum Tunicata, (hence, it is also a tunicate).


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S. plicata is an ovular, greyish to tannish-white benthic tunicate. This solitary sessile ascidian is cloaked in an unstalked tunic that is large, tough, warty and ridged (Fuller, 2007; Howey, 1998). Perry & Larson (2004) report that the lumpy surface of the tunic gives it the appearance of a cobblestone pavement. Internal structures are protected by this tunic, which is composed largely of cellulose and contains a circulatory system of "blood" transport vesicles. Dividing the tunic is a membrane which allows fluid to flow up one side and down the other. S. plicata has an incurrent siphon that intakes water into the pharyngeal basket where food particles are filtered out; the waste is then excreted through the excurrent siphon (Howey, 1998). The two short siphons have red or purple stripes on the inside of the siphons and four lobes (Fuller, 2007). When physically disturbed, S. plicata expels water, which is where the term sea squirt derives from. S. plicata is a eurythermal tunicate; it is able to tolerate changes in seawater between 10°-30°C. It can tolerate salinities between 22%-34% (Thiyagarajan & Qian, 2003). NIMPIS (2002) reports that S. plicata can tolerate brackish waters and some level of pollution. Adults can reach sizes between 40-70mm, even up to 90mm in some cases (NIMPIS, 2002). S. plicata is a protandric hermaphrodite, meaning it is male earlier in life and turns female later in life. S. plicata has "testes” - small and attached along most of the length of each ovary, with two gonads on the left side of the body and five on the right (Lambert et al., 2005).


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Native range: East coast of the USA, Northern Gulf of Mexico, and the Caribbean (Fuller, 2007). Based on genetic analysis, de Barros et al. (2009) suggest that the northwestern Pacific region is where S. plicata originates.
Known introduced range: Australia, West coast of USA, Mediterranean Sea, Brazil, Uruguay, Argentina, Japan, Hong Kong, Indian Ocean (Hayes et al., 2005; Lambert & Lambert, 1998; Lambert et al., 2005; NBNG, 2004; NIMPIS, 2002; NEMESIS, 2006; STRI, undated; PSIS, undated).

Distribution Table

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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.

Last updated: 10 Feb 2022
Continent/Country/Region Distribution Last Reported Origin First Reported Invasive Reference Notes


South AfricaPresentOriginal citation: World Register of Marine Species (WoRMS) (2012)
TanzaniaPresentOriginal citation: World Register of Marine Species (WoRMS) (2012)


ChinaPresentPresent based on regional distribution.
Hong KongPresent


GreecePresentOriginal citation: World Register of Marine Species (WoRMS) (2012)
PortugalPresentPresent based on regional distribution.
-AzoresPresentOriginal citation: World Register of Marine Species (WoRMS) (2012)
United KingdomPresentOriginal citation: World Register of Marine Species (WoRMS) (2012)

North America

United StatesPresent2002
-North CarolinaPresentNative
-Rhode IslandPresent
-South CarolinaPresent


-New South WalesPresentIntroduced
-Western AustraliaPresentIntroducedInvasive
New ZealandPresent

Sea Areas

Atlantic - Western CentralPresentNative
Indian Ocean - WesternPresentIntroduced
Mediterranean and Black SeaPresentIntroduced

South America



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The different life cycle stages of S. plicata have different habitat requirements for survival. The larval and juvenile stages of S. plicata live on marinas and docks, oyster reefs, rocks and coarse woody debris, wheareas the adults prefer marinas, docks and hard rocky substrates (NEMESIS, 2006). S. plicata can also live in coral reef habitats (STIR, undated). S. plicata is found from the low intertidal zone to depths of 30m (NIMPIS, 2002). It can also tolerate brackish and polluted waters.

Habitat List

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LittoralCoastal areas Present, no further details
BrackishEstuaries Present, no further details
Marine Present, no further details

Biology and Ecology

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S. plicata is a suspension filter feeder that preys primarily on phytoplankton, zooplankton and organic materials. Snails, crustaceans, sea stars and fish have been known to prey on S. plicata (NIMPIS, 2002). For example, the sea snail Linatella caudata is known to prey upon S. plicata (Morton, 1989).

S. plicata is a protandric hermaphrodite. Initially, S. plicata is a male then later it changes to a female. Fertilization is external; eggs and sperm are released into the water column in the late afternoon and the larvae - 1.3mm in total length - hatch the next morning and settle that day (NIMPIS, 2002; Yamaguchi, 1975).  S. plicata undergoes reproductive cycles yearly in conjunction with annual temperature changes. According to West & Lambert (1975), S. plicata must experience a period of darkness; approximately 8.5 hours long, prior to the release of gametes. Spawning can occur between 11°-28° C (West & Lambert, 1975), with 20°C being optimal (Yamaguchi, 1975). Water filtration is not optimal during the release of gametes (Fiala-Medlioni, 1978). S. plicata is sexually mature at 40 mm (de Barros et al., 2009).

Lifecycle stages
The eggs of S. plicata are surrounded by a complex ovular envelope (Mansueto et al. 2003) that supplies the larvae with its nutritional requirements (Pisut & Pawlik, 2002). Once hatched, the larvae attempt to find a suitable substrate. S. plicata can have an extended swimming period of over 2 days prior to settlement without a cost to metamorphosis (Thiyagarajan & Qian, 2003). Larval settlement is most successful in the spring and fall (Fisher, 1977). A functional sea squirt can formed after as little as 4 days of attachment and larval metamorphosis, although this depends on temperature (de Barros et al., 2009). S. plicata has a life span of less than one year that is characterised by rapid growth; it usualy lives for five to nine months (de Barros et al., 2009; Lambert & Lambert, 1998). Yamaguchi (1975) reported that S. plicata reached sexual maturity in 2 months during the summer and 5 months during the winter. S. plicata has an extended breeding season, reproducing all year except during winter (NIMPIS, 2002). Cold winters kill S. plicata, limiting its northern distribution to Cape Hatteras, North Carolina. One way this is thought to happen is by dislodgement from substrates during cold (growth inhibiting) periods (Fisher, 1976). Populations of S. plicata fluctuate; they may be abundant one year and absent the next (Lambert & Lambert, 1998).

Interactions with other species
As a defence mechanism, S. plicata concentrates deterrant chemicals in its gonads so that they may be passed on to larvae, thus protecting them from predation (Pisut & Pawlik, 2002). Alcohol from the body of S. plicata exhibits anti-Hepatitis B properties (STRI, undated). The presence of secondary metabolites on the body wall of S. plicata causes it to be unpalatable to predators, particularly fish (de Barros et al. 2009).

S. plicata harbours the amphipod Leucothoe spinicarpa and an ascidicolous copepod (Thiel, 1998).

Means of Movement and Dispersal

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Introduction pathways to new locations
Live food trade:Hayes et al. (2005) report that S. plicata was introduced to Australia accidently with the translocation of fish or shellfish.
Ship ballast water:S. plicata can be introduced to new locations in ship ballast water (Fuller 2007).
Ship/boat hull fouling:S. plicata can be introduced to new locations by hull/ship fouling (Fuller 2007).

Local dispersal methods
Other (local):S. plicata can be spread by fouling of recreational boats (Wyatt et al. 2005).


    Pathway Causes

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    CauseNotesLong DistanceLocalReferences
    Live food or feed trade Yes Yes

    Pathway Vectors

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    VectorNotesLong DistanceLocalReferences
    Ship ballast water and sediment Yes Yes
    Ship hull fouling Yes Yes

    Impact Summary

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    Fisheries / aquaculture Negative
    Native fauna Negative


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    S. plicata competes with other organisms, excluding them from the space it occupies. Its larvae are capable of invading occupied space and growing to a large size in a relatively short period of time. It can attach to other organisms and S. plicata then sloughs off because of its large size, often taking other marine organisms with it.The presence of this tunicate also inhibits the recruitment or growth of other larval species (Sutherland, 1978). S. plicata has replaced native solitary tunicates Pyura haustor and Ascidia ceratodes (Fuller, 2007). Rius et al. (2009) investigated the effect of S. plicata on a native tunicate species, Microcosmus squamiger, in Australia. S. plicata inhibited the settlement of native larvae and, the presence of S. plicata was associated with a tenfold increase in the post-settlement mortality of M. squagimer, as well as an initial reduction of growth in the native, possibly due to competition for food. In addition to its potential to impact upon native species, S. plicata is a fouler of ships, boats, docks, power plants and shellfish ponds, attaching to hard substrates and remaining there until removed (NEMESIS, 2006). Because it can foul shellfish cultures, it can have negative impacts on shellfish aquaculture; for example, by competing with the shellfish for food and predating their larvae (de Barros et al., 2009). S. plicata is usually covered with non-ascidian epibionts, which can travel on the tunicate – in this way non-indigenous species can be transferred between aquatic ecosystems (Lambert & Lambert, 1998). Wyatt et al. (2005) claims that S. plicata acts as a vector for the invasive Bugula neritina in Australia.

    Risk and Impact Factors

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    • Fast growing
    Impact outcomes
    • Threat to/ loss of native species
    Impact mechanisms
    • Competition (unspecified)
    • Fouling
    • Interaction with other invasive species


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    S. plicata is a host to several different kinds of organisms, including brittle stars, mussels, chitons, sponges, polychaete worms, diatoms, eggs, etc., that live on its tunic (Howey, 1998).
    S. plicata also has potential to be used for bioremediation (Draughon et al., 2010; Cestone et al., 2008).

    Similarities to Other Species/Conditions

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    Styela plicata is often confused with Styela clava. The tunic of S. plicata is tough but not leathery. Its gut loop is deeply curved, "without a distinct stalk, but attached directly by the side or base." S. clava is leathery and its gut loop is simple and vertical, and stalked in the larger individuals (NIMPIS, 2002).

    Prevention and Control

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    Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

    Chemical: Tributylin (TBT) has been used in anti-fouling paints, wood preservation, slime control in paper mills and other industrial processes. It affects S. plicata by blocking the sperm-egg interaction, thus preventing fertilization (Mansueto et al, 2003). However, TBT is banned by the International Maritime Organization (IMO, 2002). The Pesticide Action Network (PAN, 2006) reports that Butyltrichlorostannane, Cyhexatin, Dibutyltin dichloride, Fenton hydroxide, Tributylin chloride, Triphenyltin acetate and Triphenyltin chloride cause mortality in S. plicata cells acquired post-fertilisation (PAN, 2006). Copper sulphate was proposed as a broadcast spray control method, but scientists deemed it too expensive and non-specific, lethal to non-target species. It is also absorbed by the soil and ineffective at high pH levels.

    Physical: Plastic wraps have been applied to timber pylons in intertidal to subtidal zones, which prevent oxygenated water from touching S. plicata, thus suffocating it (NIMPIS, 2002).


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    Centre for Environment, Fisheries & Aquaculture Science (CEFAS)., 2008. Decision support tools-Identifying potentially invasive non-native marine and freshwater species: fish, invertebrates, amphibians.

    CONABIO. 2008. Sistema de información sobre especies invasoras en México. Especies invasoras - Otros invertebrados. Comisión Nacional para el Conocimiento y Uso de la Biodiversidad. Fecha de acceso.

    Fiala-Medlioni, A. 1978. Filter-Feeding Ethology of Benthic Invertebrates (Ascidians). III. Recording of Water Current in s i t u - Rate and Rhythm of Pumping. Marine Biology 45, 185-190

    Fisher, T. 1976. Oxygen Uptake of the Solitary Tunicate Styela plicata. Biol Bull 151: 297-305.

    Fisher, T. 1977. Metabolic Maintenance Costs of the Suspension Feeder Styela plicata. Marine Biology 41, 361-369

    Fuller, Pam., 2007. Styela plicata. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.

    Hayes, K., Sliwa, C., Migus, S., McEnnulty, F., Dunstan, P. 2005. National priority pests: Part II Ranking of Australian marine pests. An independent report undertaken for the Department of Environment and Heritage by CSIRO Marine Research.

    Howey, R. 1998. Tunicates with Salad on the Side. Micscape Magazine.

    Invasions Lab Online Databases (ILOD). 2006. Styela plicata. Marine Invasions Research Lab. Smithsonian Environmental Research Center.

    Lambert, C. & G. Lambert. 1998. Non-indigenous ascidians in southern California harbors and marinas. Marine Biology 130: 675±688

    Lambert, G., Faulkes, Z., Scofield, Z., and C. Lambert. 2005. Ascidians of South Padre Island, Texas, with a key to species. Texas J. SCI. 57(3): 251-262.

    Mansueto, C., Villa, L., D’Agati, P. Marcian`, V., Pellerito, C., Fiore, T., Scopelliti, M., Nagy, L., and L. Pellerito. 2003. Effects of tributyltin (IV) chloride on fertilization of Styela plicata (Ascidiacea: Tunicata): II. Scanning and transmission electron microscopy studies. Appl. Organometal. Chem. 17: 553–560

    Morton, B. 1989. Prey Capture, Preference and Consumption by Linatella caudata (Gastropoda: Tonnoidea: Ranellidae) in Hong Kong. J. Moll. Stud. 56, 477-486.

    National Exotic Marine and Estuarine Species Information System (NEMESIS). 2006. Styela plicata. Smithsonian Environmental Research Center.

    National Introduced Marine Pest Information System (NIMPIS), 2002. Styela plicata species summary. National Introduced Marine Pest Information System (Eds: Hewitt C.L., Martin R.B., Sliwa C., McEnnulty, F.R., Murphy, N.E., Jones T. & Cooper, S.).

    Orme, S. and S. Kegley, 2006. PAN Pesticide Database, Pesticide Action Network, North America (San Francisco, CA. 2006).

    Perry & Larson. 2004. Styela plicata. Guide to Shelf Invertebrates, Gulf of Mexico.

    Pisut, P. & J. Pawlik. 2002. Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids? Journal of Experimental Marine Biology and Ecology 270 (2002) 203– 214.

    Port Survey for Introduced Species [PSIS]. Undated. Sydney Harbour. Australian Museum Business Services.

    Smithsonian Tropical Research Institute (STIR). Undated. Styela plicata. Bocas Del Toro Species Database.

    Sutherland, P. 1978. Functional roles of Schizoporella and Styela in the fouling community at Beaufort, North Carolina. Ecology, 59(2). pp. 257-264.

    Thiel, M. 1998. Host-use and population demographics of the ascidian-dwelling amphipod Leucothoe spinicarpa: indication for extended parental care and advanced social behaviour. Journal of Natural History, 33, 193± 206

    Thiyagarajan, V. & P. Qian. 2003. Effect of temperature, salinity and delayed attachment on development of the solitary ascidian Styela plicata (Lesueur). Journal of Experimental Marine Biology and Ecology 290; 133– 146.

    Varnham, K. 2006. Non-native species in UK Overseas Territories: a review. JNCC Report 372. Peterborough: United Kingdom.

    West, A. & C. Lambert. 1975. Control of Spawning in the Tunicate Styela plicata by Variations in a Natural Light Regime. J. Exp. Zool., 195: 263-270.

    Wyatt, A., Hewitt, C., Walker, Di., & T. Ward. 2005. Marine introductions in the Shark Bay World Heritage Property, Western Australia: a preliminary assessment. Diversity and Distributions, (Diversity Distrib.)11, 33–44

    Yamaguchi, M. 1975. Growth and Reproductive Cycles of the Marine Fouling Ascidians Ciona intestinalis, Styela plicata, Botrylloides violaceus, and Leptoclinum mitsukurii at Aburatsubo-Moroiso Inlet (Central Japan). Ymrine Biology 29, 253-259.


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    Barros RCde; Rocha RMda; Pie MR, 2009. Human-mediated global dispersion of Styela plicata (Tunicata, Ascidiacea). Aquatic Invasions [Proceedings of the 2nd International Invasive Sea Squirt Conference, Prince Edward Island, Canada, 2-4 October 2007.], 4(1):45-57.

    Cestone A; Natale Mdi; Rosa Sde, 2008. Toxicity and biodegradation of the LAS surfactant 1-(p-sulfophenyl)nonane in presence of the ascidian Styela plicata. Chemosphere, 71(8):1440-1445.

    Draughon LD; Scarpa J; Hartmann JX, 2010. Are filtration rates for the rough tunicate Styela plicata independent of weight or size? Journal of Environmental Science and Health. Part A, Toxic/Hazardous Substances & Environmental Engineering, 45(2):168-176.

    International Maritime Organization, 2002. Focus on IMO - Anti-fouling systems.

    ISSG, 2011. Global Invasive Species Database (GISD). Invasive Species Specialist Group of the IUCN Species Survival Commission.

    Rius M; Turon X; Marshall DJ, 2009. Non-lethal effects of an invasive species in the marine environment: the importance of early life-history stages. Oecologia, 159(4):873-882.

    Smithsonian Institute, 2012. Smithsonian Marine Station at Fort Pierce. Styela plicata.

    World Register of Marine Species (WoRMS), 2012. Styela plicata.

    Distribution References

    CABI, Undated. Compendium record. Wallingford, UK: CABI

    CABI, Undated a. CABI Compendium: Status inferred from regional distribution. Wallingford, UK: CABI

    CABI, Undated b. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI

    Invasive Species Specialist Group (ISSG), 2011. Global Invasive Species Database (GISD). In: Global Invasive Species Database (GISD), Auckland, New Zealand: University of Auckland.

    Seebens H, Blackburn T M, Dyer E E, Genovesi P, Hulme P E, Jeschke J M, Pagad S, Pyšek P, Winter M, Arianoutsou M, Bacher S, Blasius B, Brundu G, Capinha C, Celesti-Grapow L, Dawson W, Dullinger S, Fuentes N, Jäger H, Kartesz J, Kenis M, Kreft H, Kühn I, Lenzner B, Liebhold A, Mosena A (et al), 2017. No saturation in the accumulation of alien species worldwide. Nature Communications. 8 (2), 14435.

    Links to Websites

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    GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway source for updated system data added to species habitat list.
    Global register of Introduced and Invasive species (GRIIS) source for updated system data added to species habitat list.


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      Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)

      Last Modified: Tuesday, May 08, 2007

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