BIOTIC Species Information for Ciona intestinalis
Researched byAngus Jackson Data supplied byMarLIN
Refereed byDr John Bishop
Scientific nameCiona intestinalis Common nameA sea squirt
MCS CodeZD71 Recent SynonymsNone

PhylumChordata SubphylumTunicata
Superclass ClassAscidiacea
Subclass OrderEnterogona
Suborder FamilyPhlebobranchiata
GenusCiona Speciesintestinalis

Additional InformationAlso sometimes known as a sea vase.
Taxonomy References Svane & Havenhand, 1993, Naranjo et al., 1996, Millar, 1970, Fox, 1994(a),
General Biology
Growth formCylindrical
Feeding methodActive suspension feeder
Mobility/MovementPermanent attachment
Environmental positionEpifaunal
Typical food typesSeston HabitAttached
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityFragile SizeMedium(11-20 cm)
HeightUp to 15 cm Growth Rate10-20 mm/month
Adult dispersal potentialNone DependencyIndependent
General Biology Additional InformationAlthough not strictly gregarious, Ciona intestinalis occurs mainly in dense aggregations such that it dominates the substratum. These aggregations are believed to be caused by hydrodynamic conditions rather than some preferential selection mechanism by the larvae (Havenhand & Svane, 1991) but see Adult distribution. In Swedish shallow waters there are two distinct growth phases: in summer/autumn after settling and in spring/early summer before spawning. Growth rates have also been recorded as up to 0.7 percent of body length per day. Growth rate is dependent on temperature and body size. The species is permanently hermaphroditic so the sexes are not separate. Filter feeders including ascidians are known to be able to accumulate trace elements such as heavy metals. A detailed account of the anatomy of Ciona sp. is provided by Millar (1953).
Biology References Robbins, 1985, Svane & Havenhand, 1993, Schmidt, 1983, Naranjo et al., 1996, Petersen et al., 1995, Millar, 1970, Fox, 1994(a), Millar, 1953,
Distribution and Habitat
Distribution in Britain & IrelandWidely distributed round British and Irish coasts.
Global distributionWidely distributed throughout temperate regions of the world.
Biogeographic rangeNot researched Depth rangeLower shore to at least 500 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationGrowths of the hydroid %Tubularia larynx% may greatly enhance the settlement and may be a causative factor for ascidian blooms (Schmidt, 1983). Ciona intestinalis is believed to have originated as a North Atlantic species but has spread widely through shipping to all temperate regions.

Substratum preferencesOther species (see additional information)
Artificial (e.g. metal/wood/concrete)
Large to very large boulders
Small boulders
Physiographic preferencesOpen coast
Offshore seabed
Strait / sound
Ria / Voe
Enclosed coast / Embayment
Biological zoneUpper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral
Wave exposureModerately Exposed
Very Sheltered
Extremely Sheltered
Ultra Sheltered
Tidal stream strength/Water flowModerately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)
SalinityFull (30-40 psu)
Reduced (18-30 psu)
Variable (18-40 psu)
Habitat Preferences Additional Information
Distribution References Svane & Havenhand, 1993, Schmidt, 1983, Havenhand & Svane, 1991, Naranjo et al., 1996, Millar, 1970, Fox, 1994(a), Branch et al., 1994,
Reproduction/Life History
Reproductive typePermanent hermaphrodite
Developmental mechanismLecithotrophic
Reproductive SeasonAll year Reproductive LocationWater column
Reproductive frequencyAnnual protracted Regeneration potential No
Life span1-2 years Age at reproductive maturity<1 year
Generation time<1 year Fecundity2000-3000 eggs per spawn
Egg/propagule size160 µm diameter Fertilization typeExternal
Larval/Juvenile dispersal potential100-1000m Larval settlement period
Duration of larval stage2-10 days   
Reproduction Preferences Additional InformationReproductive frequency: The Plymouth Marine Fauna (Marine Biological Association, 1957) recorded Ciona intestinalis reproduction throughout the year. In more northerly populations (Sweden), gamete release peaks in May / June. In Sweden, a variety of reproductive frequencies occur. In shallower waters (0-8m) and reduced salinity (20 psu) the species tends to be semelparous whereas in deeper (15-30m), more stable waters with full salinity (30-32 psu) the species reaches larger sizes, lives longer and is more iteroparous. Adults may reach 2-3 years of age although more typically live for just one year.
Spawning: Reproductive capability is size rather than age dependent. In the laboratory, settlement and spawning can be controlled by manipulation of light levels (Whittington, 1967; Woollacott, 74). Light intensity may have some role in the field but spawning and settlement may occur at any time. Whittington (1967) noted that Ciona intestinalis spawned within 4min (±2.6) of exposure to light. Therefore, light exposure may synchronize spawning in some instances, and Ciona intestinalis has been reported to spawn around dawn (Whittingham, 1967).
The species is not self fertile and fertilization is external. Sperm remain viable for up to 16 hours after release in the absence of egg substances. However, in the presence of egg substances the sperms viability is reduced to 1.5 hours (Bolton & Havenhand, 1996).
After release, the eggs remain viable for fertilisation for up to 30 hours. The eggs are negatively buoyant and sink in still water. They are adhesive and stick to the substratum. The eggs are about 160 microns in diameter, yolky and red or green in colour. Long tapering outer follicle cells radiate from the surface of the eggs. Eggs may be released individually or in mucus strings. The mucus strings tangle with and readily adhere to nearby adults.
Dispersal: The embryonic period of development occurs over around 24 hours but is temperature dependent. The newly hatched 'tadpole' larvae may escape from the mucus strings to disperse in the plankton (40-60% of larvae) or may be retained until settlement. Retention in the mucus string may explain the dense aggregations of adults found. In the laboratory, settlement of the swimming larva may take up to six days but in the field this is usually much less (minutes or hours). Some dispersal is possible at the egg stage but most occurs during the short swimming larval stage and is, therefore, limited.
Reproduction References Svane & Havenhand, 1993, Naranjo et al., 1996, MBA, 1957, Millar, 1953, Whittingham, 1967, Bolton & Havenhand, 1996, Yamaguchi, 1975,
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