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information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Star ascidian (Botryllus schlosseri)

NBN Interactive08-05-2008

Map accurate at time of writing. Visit NBN or OBIS to view current distribution

Researched byDr Keith Hiscock Refereed byThis information is not refereed.
Authority(Pallas, 1766)
Other common names- Synonyms-

Summary

Description

Flat or fleshy colonies with zooids 2-4 mm across arranged in conspicuous star shaped systems, each with a central cloacal opening. Colonies vary greatly in colour including green, violet, brown and yellow.

Recorded distribution in Britain and Ireland

Found all around Britain and Ireland

Global distribution

Present from the Faeroe Islands and west and south Norway to the Mediterranean including the Adriatic and Black Seas. Also present in the western Atlantic from Maine to New Jersey and in Florida.

Habitat

Grows on a variety of stable substrata including algae and artificial substrata. Thrives in sheltered areas including docks. Although mainly found on the lower shore and in shallow depths, Berrill (1950) notes that it has been found at depths of several hundred metres.

Depth range

Intertidal to ca. 200m

Identifying features

  • Gelatinous often colourful colonies.
  • The zooids arranged as 'stars' 2-4 mm across.

Additional information

No text entered

Listed by

- none -

Further information sources

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Biology review

Taxonomy

PhylumChordataSea squirts, fish, reptiles, birds and mammals
ClassAscidiaceaSea squirts
OrderStolidobranchia
FamilyStyelidae
GenusBotryllus
Authority(Pallas, 1766)
Recent Synonyms

Biology

Typical abundance
Male size range1-20cmMale size at maturity
Female size rangeMedium(11-20 cm)Female size at maturity
Growth formCushionGrowth rateData deficient
Body flexibilityMobility
Characteristic feeding methodActive suspension feeder, Non-feeding
Diet/food source
Typically feeds onSuspended particulates.
Sociability Environmental positionEpifaunal
DependencyIndependent.
SupportsNone
Is the species harmful?No information

Biology information

Colonies that encrust algae may completely cover their substratum and appear pendant-like. Provides a source of food for cowries (Trivia spp.).

Habitat preferences

Physiographic preferencesOpen coast, Offshore seabed, Strait / sound, Sea loch / Sea lough, Ria / Voe, Estuary, Enclosed coast / Embayment
Biological zone preferencesLower eulittoral, Lower infralittoral, Sublittoral fringe, Upper circalittoral, Upper infralittoral
Substratum / habitat preferencesBedrock, Cobbles, Large to very large boulders, Small boulders
Tidal strength preferencesModerately Strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Very Strong > 6 knots (>3 m/sec.), Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferencesExposed, Moderately exposed, Sheltered, Very exposed, Very sheltered
Salinity preferencesFull (30-40 psu), Variable (18-40 psu)
Depth rangeIntertidal to ca. 200m
Other preferencesNo text entered
Migration PatternNon-migratory / resident

Habital Information

Populations in the western Atlantic may have arrived on shipping and it is likely that, as a fast-growing fouling organism, Botryllus schlosseri may spread readily to other parts of the world.

Life history

Adult characteristics

Reproductive type Permanent (synchronous) hermaphrodite Reproductive frequency No information
Fecundity (number of eggs) 2-10 Generation time <1 year
Age at maturity c. 50 days Season Insufficient information
Life span <1 year

Larval characteristics

Larval/propagule type - Larval/juvenile development Lecithotrophic
Duration of larval stage < 1 day Larval dispersal potential 1 km -10 km
Larval settlement period

Life history information

Up to eight eggs are produced per zooid. After fertilization and development to a tadpole stage, the tadpole is released and is free swimming for up to 36 hours (Berrill 1950; Berrill, 1975).

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
High High Moderate High
Botryllus schlosseri is a sessile species dependant on the continued presence of the substratum to which it is attached. Removal of the substratum would remove the species. However, providing that suitable substratum remains after disturbance, settlement and growth from larvae is high.
High High Moderate Low
Botryllus schlosseri occurs in areas where high levels of smothering due to siltation may occur but is generally found where silt is unlikely to settle (down-facing or suspended surfaces) suggesting that it is intolerant of smothering. Smothering may prevent feeding and respiratory flows through the colony and the species may not survive burial. However, providing that suitable substratum is available after the smothering event is over, settlement and growth from larvae is high.
High High Moderate Moderate
Botryllus schlosseri occurs in areas where high levels of siltation and smothering may occur but is generally found where silt is unlikely to settle (down-facing or suspended surfaces) suggesting that it is intolerant of siltation. Silt may clog feeding and respiratory flows through the colony. However, providing that suitable substratum is available, settlement and growth from larvae is high.
No information
Intermediate High Low Moderate
Botryllus schlosseri occurs only in shaded areas on the lower shore in the intertidal where the atmosphere remains damp. Exposure to air and sunshine (for instance if boulders with colonies are overturned) would be likely to destroy colonies. However, providing that suitable substratum is available after a desiccation event, settlement and growth from larvae is high.
Intermediate High Low Moderate
Botryllus schlosseri occurs only in shaded areas on the lower shore in the intertidal where the atmosphere remains damp. Increased exposure to air would be likely to destroy colonies. However, providing that suitable substratum is available after a emergence event, settlement and growth from larvae is high.
No information
Intermediate High Low Low
Water flow rate is important for maintaining colonies free of silt where they occur in sheltered areas. If water flow rate is decreased in such areas, and siltation occurs, colonies are likely to be adversely affected. However, once a high water flow rate is regained, settlement and growth from larvae is high.
No information
Low Very high Very Low Moderate
Botryllus schlosserioccurs from sub-arctic to warm temperate conditions and most likely tolerates a wide range of temperatures. Recolonization of suitable substrata would be rapid following once temperatures return to normal.
No information
Low Immediate Not sensitive Low
Botryllus schlosserioccurs in areas where high levels of turbidity occur although, as a passive suspension feeder, it may be susceptible to clogging (see siltation above). Increased turbidity may decrease phytoplankton productivity which may indirectly decrease food availability. Recolonization of suitable substrata would be rapid once turbidity returned to normal.
No information
Intermediate Moderate Moderate Low
Increase in wave exposure or storm events would remove predominantly the plants on which Botryllus schlosseri grows and therefore incidentally Botryllus schlosseri. Speed of recovery would depend on regrowth rates of the plant substrata.
No information
Tolerant Not relevant Not sensitive High
Botryllus schlosseri has no organs for detecting noise.
Tolerant Not relevant Not sensitive Moderate
Botryllus schlosseri has no organs for visual perception.
Intermediate High Low Low
Abrasion from sand is likely to be tolerated and Botryllus schlosseri occurs attached to algae on surf beaches. However, abrasion caused by mobile hard substrata, and anchor or dredge, is likely to remove colonies. Recolonization of suitable substrata would be rapid following cessation of abrasion.
High Moderate Moderate Low
Botryllus schlosseri is permanently attached to the substratum and displacement is likely to have the same effect as substratum loss. Speed of recolonization would depend on the presence of suitable substrata.

Chemical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information Not relevant No information Not relevant
Recolonization following cessation of exposure to a damaging non-persistent chemical is likely to be rapid.
Heavy metal contamination
No information Not relevant No information Not relevant
Recolonization following cessation of exposure to a damaging non-persistent chemical is likely to be rapid.
Hydrocarbon contamination
No information Not relevant No information Not relevant
Recolonization following cessation of exposure to a damaging non-persistent hydrocarbon is likely to be rapid.
Radionuclide contamination
No information Not relevant No information Not relevant
No recorded adverse effects of radionuclides on Botryllus schlosseri or similar species have been found.
Changes in nutrient levels
Low High Low Very low
No recorded adverse effects of nutrients on Botryllus schlosseri or similar species were found.
Intermediate High Low Moderate
Botryllus schlosseri lives in enclosed waters including docks and in estuaries where salinity is variable. However, its absence from low salinity conditions in upper estuaries and lagoons suggests that colonies will be intolerant of low salinities. Recolonization following cessation of exposure to low salinity is likely to be rapid.
No information
Intermediate High Low Very low
Botryllus schlosseri lives in habitats where periods of calm conditions may result in short term reduced oxygen levels. However, no studies relevant to de-oxygenation effects have been found.

Biological pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information High No information Very low
No information was found concerning pathogens or parasites in Botryllus schlosseri.
Tolerant* Not relevant Not sensitive* Low
Some non-native species (Sargassum muticum) provide additional substrata for colonization.
Not relevant Not relevant Not relevant High
This species is not targeted for extraction.
High Moderate Moderate Low
Extraction of algae on which Botryllus schlosseri grows will remove the Botryllus schlosseri. Colonization of new algal substrata will be high once algae have grown.

Additional information

No text entered

Importance review

Policy/legislation

- no data -

Status

National (GB) importance-Global red list (IUCN) category-

Non-native

Native-
Origin- Date ArrivedNot relevant

Importance information

-none-

Bibliography

  1. Berrill, N.J., 1950. The Tunicata with an account of the British species. London: Ray Society.

  2. Berril, N.J., 1975. Chordata: Tunicata. In Reproduction of marine Invertebrates, vol. II, (ed. A.C. Geise & J.S. Pearse), pp. 241-282. New York: Academic Press.
  3. Chadwick-Furman, N.E., & Weissman, I.L., 1995. Life histories and senescence of Botryllus schlosseri (Chordata: Ascidiacea) in Monterey Bay. Biological Bulletin, Marine Biological Laboratory, Woods Hole, 189, 36-41.
  4. Howson, C.M. & Picton, B.E. (ed.), 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]
  5. Rumohr, H. & Kujawski, T., 2000. The impact of trawl fishery on the epifauna of the southern North Sea. ICES Journal of Marine Science, 57, 1389-1394.

Citation

This review can be cited as:

Hiscock, K. 2008. Botryllus schlosseri Star ascidian. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/species/detail/1340

Last Updated: 08/05/2008