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   Ciona intestinalis (tunicate)
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    Taxonomic name: Ciona intestinalis (Linnaeus, 1767)
    Synonyms: Ascidia viridiscens (Brugiere, 1792), Ciona canina (Mueller, 1776), Ciona diaphanea (Quoy & Gaimard, 1834), Ciona ocellata (Agassiz, 1850) , Ciona pulchella (Alder, 1863) , Ciona robusta (Hoshino & Tokioka, 1967), Ciona sociabilis (Gunnerus, 1765) , Ciona tenella (Stimpson, 1852), Phallusia intestinalis (Linnaeus, 1767), Tethyum sociabile (Gunnerus, 1765)
    Common names: ascidie jaune (French), cione (French), doorschijnende zakpijp (Dutch), gelbe seescheide (German), sea vase (English), vase tunicate (English), yellow sea squirt (English)
    Organism type: tunicate
    The sea vase, Ciona intestinalis, is a tunicate that has such widespread distribution that its natural range continues to be a source of constant debate. A major pest on shellfish aquaculture production, C. intestinalis is a highly competitive species. There is evidence of C. intestinalis displacing native species, reducing biodiversity, and altering community properties in some invaded habitats. Control of C. intestinalis is difficult due to its rapid recolonisation, difficulty of containment and proximity to valuable aquaculture production that limits the control options able to be used.
    Description
    Like all Ciona spp. Ciona intestinalis has a sessile adult stage which lives attached to submerged hard substrates (Holland, 2002). C. intestinalis usually adheres vertically to these substrates, with its siphons pointing downward (Marins et al, 2009). The body of C. intestinalis is cylindrical, reaching to 100 - 150 mm in length, with its two siphons at the anterior end (Marins et al, 2009). All Ciona spp. are encased in a soft leathery tunic, which in the case of C. intestinalis, it is thin, soft, gelatinous, translucent, and clear to greenish coloured, making the internal organs visible (McDonald, 2004; Jackson, 2008; in Marins et al, 2009).

    The inhalant anterior opening into the gut is larger and terminal with eight lobes while the atrial siphon is smaller and shorter with six lobes (McDonald, 2004). Larvae are free swimming and tadpole-like in appearance, with a dorsal nerve cord, a rudimentary brain and a notochord (Holland, 2002). After dispersal, larvae attach to a surface with their head after which the tail is reabsorbed and metamorphosis into a sessile filter-feeding adult occurs (Holland, 2002).

    Once settled, C. intestinalis provide a poor substrate for other settlers, producing strong anti-microbial compounds that may restrict epibiosis and therefore limit recruitment of other species (Finslay & Smith, 1995; in Blum et al, 2007). The maximum reported lifespan of individuals is 2 years, but a more typical lifespan is 1 year (Jackson, 2000; in Blum et al, 2007).

    Occurs in:
    marine habitats
    Habitat description
    Ciona intestinalis lives attached to submerged rocks or other hard surfaces, such as ropes, chains and boat hulls (Holland, 2002). C. intestinalis has a cosmopolitan distribution, tolerates organic pollution and a wide range of enviornmental conditions. It is abundant in ports and marinas all over the world (Meliane, 2003; in Marins et al, 2009; Therriault & Herborg, 2008a).
    General impacts
    The most severe impacts of Ciona intestinalis worldwide have been on aquaculture production, causing substantial economic losses to the shellfish industry in particular (Robinson et al, 2005). Higher C. intestinalis densities are generally linked to lower mussel size and condition, with heavy fouling resulting in up to 50 % mussel mortality (Daigle & Herbinger, 2009). This is due mainly to inhibited growth and yield through food and space competition (Daigle & Herbinger, 2009; Rocha et al 2009) as well as increasing weight of gear, leading to difficulties in handling and processing (Locke et al., 2009b).

    Additionally, as a highly competitive species within subtidal, epibenthic communities, C. intestinalis has also displaced native species, lowered biodiversity, and altered community properties in some invaded habitats (Blum et al 2007; Therriault & Herborg, 2008b).

    Uses
    Species of sea squirt, including Ciona spp., were popular models for embryological research in the early part of the twentieth century. Ciona spp. were instrumental in the discovery of cytoplasmic determinants, and were one of the first animals to have a cell lineage mapped (Holland, 2002). More recently, numerous developmentally expressed genes have been cloned from Ciona spp., hundreds of gene expression patterns are published, and there are powerful methods for introducing gene constructs into Ciona spp. embryos using electroporation (Holland, 2002).
    Notes
    The origin of Ciona intestinalis populations in Canada is a source of debate. Locke (2009) describes populations in sourthern Nova Scotia as cryptogenic while populations in Atlantic Canadian waters are non-indigenous. In contrast, Therriault & Herborg (2008a) describe populations in Atlantic Canadian waters as cryptogenic and populations in Pacific Canadian waters as non-indigenous.
    Geographical range
    The native range of Ciona intestinalis is unresolved and the focus of continuing debate (Therriault & Herborg, 2008a). C. intestinalis has been identified on both sides of the North Atlantic, in North America and Europe and has been noted to have spread to the west coast of North America, South America, Australia, New Zealand, Asia and Africa (Therriault & Herborg, 2008b).
    Introduction pathways to new locations
    Aquaculture: Ciona intestinalis is spread primarily as a hull fouling species on commercial vessels or associated with aquaculture transfers (Cohen et al, 2000; in Therriault & Herborg, 2008b).
    Ship/boat hull fouling: Ciona intestinalis is spread primarily as a hull fouling species on commercial vessels or associated with aquaculture transfers (Cohen et al, 2000; in Therriault & Herborg, 2008b), with fouling on slow moving ships (eg. barges) being considered the most important vector by experts (Therriault & Herborg, 2008b).


    Local dispersal methods
    Natural dispersal (local): The larval stage of Ciona intestinalis is free-swimming and capable of limited dispersal (Holland, 2002). Additionally, C. Intestiinalis is a broadcast spawner (Silva & Smith, 2008), freely releasing gametes into the water which can be then be dispersed short distances via natural means.
    On animals: Although no evidence for Ciona intestinalis has been found, other tunicate species such as Botrylloides violaceus and Botryllus schlosseri were found on rock crabs and a lobster in Northumberland Strait near Prince Edward Island, raising the possibility of epibiosis as a dispersal vector both on a regional scale, through the movements of crustaceans, and on a global scale via the export of crustacean species (Bernier et al, 2009).
    On animals: Although no evidence for Ciona intestinalis has been found, other tunicate species such as Botrylloides violaceus and Botryllus schlosseri were found on rock crabs and a lobster in Northumberland Strait near Prince Edward Island, raising the possibility of epibiosis as a dispersal vector both on a regional scale, through the movements of crustaceans, and on a global scale via the export of crustacean species (Bernier et al, 2009).
    Management information
    Please follow this link for detailed information on the management of Ciona intestinalis. A brief summary can by found below.

    Preventative measures: A risk assessment carried out by Hayes et al (2005) in Australia determined that C. intestinalis was one of top ten species in both its likelihood to be spread to uninfected bioregions by shipping and its damage potential. Preventative requirements on Prince Edward Island, Canada failed to stop the spread of C. intestinalis (Locke et al., 2009b). The only regulated vector in Canada is ballast water coming in from commercial shipping (Locke et al., 2009a)

    Monitoring: Tunicate collectors were created and used to detect the presence and distribution of exotic tunicate species in the Bay of Fundy, including Ciona intestinalis (LeGresley et al, 2008).

    Physical control: Aquaculture farmers surveyed by Clancey & Hinton (2003) revealed that physical removal methods such as hand scrubbing, scraping or high pressure spraying were the most common treatments used to remove tunicates that had become established on gear, however C. intestinalis quickly re-established populations within short periods.

    Chemical control: A number of chemical treatments to control C. intestinalis have been trialed (Carver et al, 2003). While some like acetic acid and calcium hydroxide have shown promising results, chemicals have the potential to alter estuarine pH are and have been shown to be biocidal to a variety of non-target organisms such as species of bacteria, shrimp and fish (Locke et al, (2009b).

    Biological control: Potential biological control agents include the rock crab, Cancer irroratus and green crab, Carcinus maenas. The use of crab predators for the control of C. intestinalis in aquaculture is limited for a number of reasons (Carver et al, 2003). Grazing species such as Littorina littorea and the shrimp Rhynchocinetes typus have also been trialled, with the shrimp in particular showing promising results (Dumont et al., 2009).

    Cultural control: These refer to aquaculture management practices and generally include avoiding times of high C. intestinalis recruitment, changing or rotating the gear used or air drying depending on the species being farmed and the gear being used. More information on C. intestinalis recruitment patterns and population development is necessary to develop more effective management procedures (Ramsay, et al, 2009).

    Nutrition
    Ciona intestinalis is a filter feeding organism, feeding on particles in the water column (Daigle & Herbinger, 2009). Clearance rates increase in an approximately linear relationship with increasing temperature with rates ranging from 4.6 ml per min per individual at 4 °C to about 29 ml per min per individual at 19 °C (Daigle & Herbinger, 2009).
    Reproduction
    As with all Ascidians, Ciona intestinalis is hermaphroditic and potentially capable of self-fertilisation (Silva & Smith, 2008). It is also a solitary (opposed to colonial) Ascidian which undergoes broadcast spawning (Silva & Smith, 2008). Each mature individual can potentially spawn once per day over the spawning period, releasing appproximately 500 eggs per day (Carver et al, 2003). Eggs are negatively buoyant and released in mucus strings that tangle and attach to nearby adults, contributing to the dense aggregations of adults (MarLIN, 2004; in McDonald, 2004).
    Lifecycle stages
    Larvae are free swimming and tadpole-like in appearance, with a dorsal nerve cord, a rudimentary brain and a notochord (Holland, 2002). After dispersal over a period of 1 - 5 days (Dybern, 1965; in Howes et al, 2007), larvae attach to a surface with their head after which the tail is reabsorbed and metamorphosis into a sessile filter-feeding adult occurs (Holland, 2002).
    Reviewed by: Under expert review
    Compiled by: IUCN SSC Invasive Species Specialist Group (ISSG) with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
    Last Modified: Monday, 7 May 2007


ISSG Landcare Research NBII IUCN University of Auckland