A colonial sea squirt (Morchellium argus)

Colonies of Morchellium argus.

Photographer: Paul Newland Copyright: Paul Newland

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help

Researched by	Dr Keith Hiscock	Refereed by	This information is not refereed
Researched by Dr Keith Hiscock	Refereed by This information is not refereed
Authority	(Milne Edwards, 1841)
Authority (Milne Edwards, 1841)
Other common names	-	Synonyms	-
Other common names -	Synonyms -

Summary

Description

Clumps of pink or red lobes each about 4 cm long and consisting of many zooids. Distinguished from other polyclinids especially by the sand coating on the column.

Recorded distribution in Britain and Ireland

Recorded from all around the coasts of Britain and Ireland except parts of the eastern coast of England and parts of the eastern and southern coasts of Ireland. Few records from Shetland.

Global distribution

Known from Britain and Ireland and parts of the French Atlantic coast.

Habitat

Present on the shore mainly on vertical surfaces, under overhangs and in caves. In the sublittoral, often conspicuous amongst foliose algae in the lower infralittoral especially in wave sheltered areas.

Depth range

+1 to -10 m chart datum

Identifying features

Colonies of pink or red lobes joined at the base.
Each lobe is about 4 cm long with a stalk diameter of about 1 cm.
Each lobe has a long firm sand-coated stalk and a wider rounded head.
The zooid has eight lobes on the oral siphon and a small pointed atrial languet with four red spots on the base of the oral siphon.

Additional information

No text entered

Listed by

- none -

Biology review

Taxonomy

Level	Scientific name	Common name
Phylum	Chordata	Sea squirts, fish, reptiles, birds and mammals
Sea squirts, fish, reptiles, birds and mammals
Class	Ascidiacea	Sea squirts
Sea squirts
Order	Aplousobranchia

Family	Polyclinidae
Genus	Morchellium
Authority	(Milne Edwards, 1841)
Recent Synonyms

Biology

Parameter	Data
Typical abundance	Moderate density
Male size range	4cm
Male size at maturity
Female size range	Small-medium(3-10cm)
Female size at maturity
Growth form	Cushion
Growth rate
Body flexibility
Mobility
Characteristic feeding method	Active suspension feeder, Non-feeding
Diet/food source
Typically feeds on	Suspended organic matter.
Sociability
Environmental position	Epifaunal
Dependency	Independent.
Supports	None
Is the species harmful?	Yes Moderate levels of toxicity were found against invertebrate larvae by Teo & Ryland (1995).

Biology information

-none-

Habitat preferences

Parameter	Data
Physiographic preferences	Open coast, Offshore seabed, Strait or Sound, Sea loch or Sea lough, Ria or Voe, Estuary, Enclosed coast or Embayment
Biological zone preferences	Lower eulittoral, Lower infralittoral, Sublittoral fringe, Upper infralittoral
Substratum / habitat preferences	Bedrock, Large to very large boulders, Small boulders
Tidal strength preferences	Moderately strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Very weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferences	Exposed, Extremely sheltered, Moderately exposed, Sheltered, Ultra sheltered, Very sheltered
Salinity preferences	Full (30-40 psu), Variable (18-40 psu)
Depth range	+1 to -10 m chart datum
Other preferences
Migration Pattern	Non-migratory or resident

Habitat Information

No text entered

Life history

Adult characteristics

Parameter	Data
Reproductive type	Permanent (synchronous) hermaphrodite
Reproductive frequency
Fecundity (number of eggs)	100-1,000
Generation time	<1 year
Age at maturity
Season	June - October
Life span	1-2 years

Larval characteristics

Parameter	Data
Larval/propagule type	-
Larval/juvenile development	Lecithotrophic
Duration of larval stage	< 1 day
Larval dispersal potential	100 -1000 m
Larval settlement period	Insufficient information

Life history information

Eggs are about 0.34 mm diameter. Larvae are held in the atrial cavity and have a trunk about 0.8 mm long. The free-swimming period of the larva is about 2-3 hours. Berrill (1950) suggests that brooding colonies are present in September and October but records in the Plymouth Marine Fauna suggest breeding June to September.

Sensitivity reviewHow is sensitivity assessed?

The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.

Physical pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Substratum loss [Show more] Substratum loss Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details Evidence Colonies are sessile and will therefore be lost along with their substratum. Larvae disperse in the water column so that, providing coonies survive nearby, recovery will occur following the late summer larval dispersal phase.	High	High	Moderate	High
Smothering [Show more] Smothering Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details. Evidence Colonies rely on being able to pump water for respiration and feeding and cannot extend to any great extent to above layer of smothering sediment. Whilst they may survive for a little time in conditions where they are unable to draw water though the siphons, it is expected that they would be killed by smothering that lasts more than a few days. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	High	High	Moderate	Moderate
Increase in suspended sediment [Show more] Increase in suspended sediment Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details Evidence Colonies produce mucous which is shed to remove deposited silt. Colonies live in areas where high suspended sediment levels commonly occur and it is therefore expected that intolerance is low. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Low	High	Low	Moderate
Decrease in suspended sediment [Show more] Decrease in suspended sediment Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details Evidence			No information
Desiccation [Show more] Desiccation A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details. Evidence Colonies are likely to dry and be damaged by exposure to air and especially sunshine in non-damp situations on the shore. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	High	High	Moderate	Moderate
Increase in emergence regime [Show more] Increase in emergence regime Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details Evidence Colonies live in the intertidal only in locations where damp conditions prevail (under overhangs and under boulders). In such a situation, there will be some tolerance to increased emersion times but it is likely that colonies will not survive during periods of hot drying weather. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Intermediate	High	Low	Low
Decrease in emergence regime [Show more] Decrease in emergence regime Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details Evidence			No information
Increase in water flow rate [Show more] Increase in water flow rate A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details Evidence Morchellium argus lives in a wide range of flow regimes. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Low	High	Low	Low
Decrease in water flow rate [Show more] Decrease in water flow rate A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details Evidence			No information
Increase in temperature [Show more] Increase in temperature A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges. For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details Evidence Morchellium is in the middle of its geographical range in Britain and Ireland suggesting that it will survive slightly higher and lower temperatures.	Low	Very high	Very Low	Moderate
Decrease in temperature [Show more] Decrease in temperature A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges. For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details Evidence Morchellium is in the middle of its geographical range in Britain and Ireland suggesting that it will survive slightly higher and lower temperatures. Crisp (1964) did not record any specific effects on Morchellium following the severe cold winter of 1962/63 but noted that compound ascidians were slower to recover from winter de-differentiation, or may have been killed in North Wales.	Intermediate	High	Low	Moderate
Increase in turbidity [Show more] Increase in turbidity A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details Evidence Morchellium lives in areas such as the entrances to estuaries where highly turbid conditions occur from time-to-time especially as a result of river run-off. Morchellium does not rely on light penetration and so, although populations seem to be restricted to shallow depths, is unlikely to be affected by changes in light levels.	Low	High	Low	Low
Decrease in turbidity [Show more] Decrease in turbidity A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details Evidence			No information
Increase in wave exposure [Show more] Increase in wave exposure A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details Evidence Morchellium lives in a wide range of flow regimes although vigorous wave action may detach colonies. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Low	High	Low	Low
Decrease in wave exposure [Show more] Decrease in wave exposure A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details Evidence			No information
Noise [Show more] Noise Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details Evidence Tunicates are not known to have organs sensitive to noise.	Tolerant	Not relevant	Not sensitive	High
Visual presence [Show more] Visual presence Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details Evidence Tunicates are not known to respond to visual presence.	Tolerant	Not relevant	Not sensitive	High
Abrasion & physical disturbance [Show more] Abrasion & physical disturbance Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details. Evidence Colonies are very flexible and soft providing a buffer against external abrasion from such factors as a fishing pot landing on a colony. Morchellium lives in a wide range of flow regimes although high currents or vigorous wave action may detach colonies. However, individuals and colonies may be scraped off the rock by an anchor or passing dredge. Intolerance is therefore assessed as intermediate. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Intermediate	High	Low	Moderate
Displacement [Show more] Displacement Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details Evidence The colonies are attached permanently to the substratum and will not re-attach so that displacement, even if to a suitable habitat, would most likely result in mortality. Morchellium lives in a wide range of flow regimes although high currents or vigorous wave action may detach colonies. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	High	High	Moderate	Moderate

Chemical pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Synthetic compound contamination [Show more] Synthetic compound contamination Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example: evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity; evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity; evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity. The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details. Evidence	No information	Not relevant	No information	Not relevant
Heavy metal contamination [Show more] Heavy metal contamination Evidence	No information	Not relevant	No information	Not relevant
Hydrocarbon contamination [Show more] Hydrocarbon contamination Evidence	No information	Not relevant	No information	Not relevant
Radionuclide contamination [Show more] Radionuclide contamination Evidence	No information	Not relevant	No information	Not relevant
Changes in nutrient levels [Show more] Changes in nutrient levels Evidence Morchellium occurs where nutrient levels are likely to reach high levels (at the entrance to estuaries). The species is dependant on food sources that are not likely to be affected by local nutrient concentrations.	Tolerant	Not relevant	Not sensitive	Moderate
Increase in salinity [Show more] Increase in salinity A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details. Evidence Colonies occur in full and variable salinity conditions suggesting significant tolerance to at least lowered salinity. Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Intermediate	High	Low	Low
Decrease in salinity [Show more] Decrease in salinity A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details. Evidence			No information
Changes in oxygenation [Show more] Changes in oxygenation Benchmark. Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details. Evidence	No information	Not relevant	No information	Not relevant

Biological pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Introduction of microbial pathogens/parasites [Show more] Introduction of microbial pathogens/parasites Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details. Evidence	No information	Not relevant	No information	Not relevant
Introduction of non-native species [Show more] Introduction of non-native species Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details. Evidence	No information	Not relevant	No information	Not relevant
Extraction of this species [Show more] Extraction of this species Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details. Evidence Larvae disperse in the water column so that, providing colonies survive nearby, recovery will occur following the late summer larval dispersal phase.	Intermediate	High	Low	Moderate
Extraction of other species [Show more] Extraction of other species Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details. Evidence where extraction of other species from under boulder habitats results in the stones being left downside up, there will be significant damage to Morchellium colinies. However, most other forms of extraction of species that co-occur with Morchellium (especially deployment of pots or creels to catch shellfish) are unlikely to cause damage to Morchellium.	Intermediate	High	Low

Additional information

Importance review

Policy/legislation

- no data -

Status

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

Non-native

Parameter	Data
Native	-
Origin	-
Date Arrived	-

Importance information

-none-

Bibliography

Berrill, N.J., 1950. The Tunicata with an account of the British species. London: Ray Society.
Crisp, D.J. (ed.), 1964. The effects of the severe winter of 1962-63 on marine life in Britain. Journal of Animal Ecology, 33, 165-210.
Crisp, D.J., Southward, A.J. & Southward, E.C., 1981. On the distribution of the intertidal barnacles Chthamalus stellatus, Chthamalus montagui and Euraphia depressa. Journal of the Marine Biological Association of the United Kingdom, 61, 359-380.
Howson, C.M. & Picton, B.E., 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.]
JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid
MBA (Marine Biological Association), 1957. Plymouth Marine Fauna. Plymouth: Marine Biological Association of the United Kingdom.
Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.
Teo, S.L.-M. & Ryland, J.S., 1995. Potential antifouling mechanisms using toxic chemicals in some British ascidians. Journal of Experimental Marine Biology and Ecology, 188, 49-62.

Datasets

Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.
Dorset Environmental Records Centre, 2018. Ross Coral Mapping Project - NBN South West Pilot Project Case Studies. Occurrence dataset:https://doi.org/10.15468/mnlzxc accessed via GBIF.org on 2018-09-25.
Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01
Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: https://www.kentwildlifetrust.org.uk/ accessed via NBNAtlas.org on 2018-10-01.
Manx Biological Recording Partnership, 2022. Isle of Man historical wildlife records 1990 to 1994. Occurrence dataset:https://doi.org/10.15468/aru16v accessed via GBIF.org on 2024-09-27.
National Trust, 2017. National Trust Species Records. Occurrence dataset: https://doi.org/10.15468/opc6g1 accessed via GBIF.org on 2018-10-01.
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
Norfolk Biodiversity Information Service, 2017. NBIS Records to December 2016. Occurrence dataset: https://doi.org/10.15468/jca5lo accessed via GBIF.org on 2018-10-01.
OBIS (Ocean Biodiversity Information System), 2025. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2025-05-21
South East Wales Biodiversity Records Centre, 2023. SEWBReC Marine and other Aquatic Invertebrates (South East Wales). Occurrence dataset:https://doi.org/10.15468/zxy1n6 accessed via GBIF.org on 2024-09-27.

Citation

This review can be cited as:

Hiscock, K. 2006. Morchellium argus A colonial sea squirt. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21-05-2025]. Available from: https://www.marlin.ac.uk/species/detail/1373

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Last Updated: 09/11/2006

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