Ciona intestinalis (Common sea squirt)


Type of fouling organism: Sea Squirt

Ascidians or sea squirts are sessile filter feeding animals commonly found in the subtidal. This group of fouling organisms can be colonial or unitary and are often of indefinite shape and the surrounding tunic can give an appearance that resembles sponges, bryozoans or cnidarians. All are hermaphroditic but usually unitary species release eggs into the sea and colonial species incubate embryos internally. The larval duration can vary greatly affecting dispersal potential.

Ciona intestinalis is a solitary sea squirt with a soft, retractile and a pale translucent greenish/yellow body. The internal organs are often visible through the soft test. The 2 siphons are close together at one end of the body and are lobed frequently with yellow margins and orange/red spots. They are host for various parasite copepods.

Environment and Habitat

- Subtidal (from the lower shore down to 500 m).
- Epifaunal.
- Filter-feeder.
- Growth is dependent on temperature and size.
- Prefers low wave exposure and some water flow.
- High intolerance of substratum loss, abrasion and displacement.
- Intermediate tolerance of smothering, desiccation, change in temperature and wave exposure.
- Low intolerance of changes in wave exposure and suspended sediment.
- Tolerant of changes in turbidity.


- Reproductive type: hermaphrodite & Oviparous.
- Reproductive frequency: Annual protracted.
- Development: Lecithotrophic.
- Age at maturity: insufficient information.
- Fecundity: 1 - 10,000 eggs.
- Larval duration: 2 - 10 days.
- Dispersal potential: 100 m - 1 km.
- Life span: 1 - 2 years.


- Solitary or gregarious.
- Sessile, non-migratory.
- Commonly occur in dense unfused aggregations.
- Growth of the hydroid Tubularia larynx may greatly increase settlement and may be a causative factor in ascidian blooms.


- Mussel rope culture, oyster and suspended pectinid culture.
- Fishnets, cages, pontoons, shellfish trays, tanks, pipes.

Effects and Impacts

- Problematic for stock species as can compete for space and resources, reducing meat yield.
- Increases the weight of equipment particularly lines making them so heavy that mussels can slip off before they can be harvested.
- Increases labour and production costs as a result of cleaning and removal of biofouling.

Control/ Strategies and Management

- Onshore Net washing
- Coatings (Copper sulphate, fouling release coatings e.g. silicon)
- Mechanical cleaning of infrastructure (Disk cleaners)
- Air drying nets
- Manual cleaning (scrubbing and/or brushing)
- Low power washing
- High power washing
- Jet washing
- Air drying
- Lowering trays below photic zone during major spatfalls
- Biological Control (Sea urchins and periwinkles)
- Coatings (Copper sulphate, fouling release coatings e.g. silicon)
- Manual Cleaning
- Mechanical Cleaning
- Hot water 55oC for 5 seconds (Stock mortalities of ca 5% with this method)
- Dipping (Freshwater or chemical solution)
- Lowering lines below photic zone during major spatfalls
- Biological control (Sea urchins and periwinkles)
- Coatings (Copper sulphate, spiky coatings, fouling release coatings e.g. silicon)

Principles of Management

C Combat Settlement
P Protect Equipment and Stock
R Remove Biofouling


- Thought to be a North Atlantic species but now distributed worldwide as a result of shipping.


Jackson, A., 2005. 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 05/02/2007]. Available from: species/Cionaintestinalis.htm

Ciona intestinalis Picton, B.E. & Morrow, C.C., 2005. [In] Encyclopedia of Marine Life of Britain and Ireland

Janet Moore (2001) An Introduction to the Invertebrates. Cambridge University Press

Hayward P, Nelson-Smith T & Shields C (1996) Seashore of Britain and Northern Europe. HarperCollins Pubs.

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