Sabellaria spinulosa, didemnids and other small ascidians on tide-swept moderately wave-exposed circalittoral rock

26-04-2006
Researched byAngus Jackson & Dr Keith Hiscock Refereed byThis information is not refereed.
EUNIS CodeA4.2212 EUNIS NameSabellaria spinulosa, didemnid and small ascidians on tide-swept moderately wave-exposed circalittoral rock

Summary

UK and Ireland classification

EUNIS 2008A4.2212Sabellaria spinulosa, didemnid and small ascidians on tide-swept moderately wave-exposed circalittoral rock
EUNIS 2006A4.2212Sabellaria spinulosa, didemnid and small ascidians on tide-swept moderately wave-exposed circalittoral rock
JNCC 2004CR.MCR.CSab.Sspi.AsSabellaria spinulosa, didemnids and other small ascidians on tide-swept moderately wave-exposed circalittoral rock
1997 BiotopeCR.MCR.As.MolPol.SabDense ascidians, bryozoans and hydroids on a crust of Sabellaria spinulosa on tide-swept circalittoral rock

Description

Bedrock in moderately exposed, slightly tide-swept conditions with high turbidity with an almost entire crust of Sabellaria spinulosa tubes; few other species present. Ciona celata, Alcyonium digitatum and Hypoglossum hypoglossoides present in NE England, very extensive Mytilus edulis in South Wales (Gower). The fauna attached to the Sabellaria crust in many cases seem to reflect the biotopes on nearby rock. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

The MERMAID database (JNCC, 1999) shows two records of MCR.Sspi from northeast England and Hiscock (1979) records a community that probably corresponds to this biotope from the Gower peninsula, Wales. The biotope most likely also occurs in the Solway Firth (K. Hiscock, own observations). The most recent (2003) version of the biotopes classification records the biotope (as CR.MCR.CSAB.Sspi) as recorded from the Lleyn Peninsula, Lundy Island (including the wreck of the MV Robert) and the north-east and south coast of England.

Depth range

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Additional information

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Listed By

Further information sources

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JNCC

Habitat review

Ecology

Ecological and functional relationships

Sabellaria spinulosa crusts on the substratum may be sufficiently dense to prevent the settlement or attachment of other species to the substratum (although the crust may itself act as a substratum). On the horizontal surface of the wreck of the MV Robert off Lundy, Sabellaria spinulosa was an initial colonizer dominating the surface and possibly blocking contaminants from anti-fouling paints. The crust of Sabellaria spinulosa was colonized by a rich community including especially erect bryozoans and hydroids and colonial tunicates (Hiscock, 1981, Hiscock & Rostron, unpublished). The community on the MV Robert is now (revised 2003 classification) recognised as included in MCR.Sspi, now CR.MCR.CSAB.Sspi: Sabellaria spinulosa encrusted circalittoral rock. Ophiothrix fragilis, selected as an important functional species in the biotope, may occur in dense aggregations (George & Warwick, 1985) but more typically in lower densities (Connor et al., 1997(a)). Dense aggregations of brittle stars may also occupy space that could otherwise be taken up by other species. Both Sabellaria spinulosa and Ophiothrix fragilis are suspension feeders. In dense brittle star beds, food availability may be monopolised by Ophiothrix fragilis restricting the growth of other species (George & Warwick, 1985). Urticina felina is a passive carnivore, waiting to trap animals that stumble into its tentacles. Other characteristic species from the biotope are scavengers (Pagurus bernhardus) and detrital grazers (Gibbula cineraria).

Seasonal and longer term change

Most of the characterizing species in the biotope have a longevity of several years (Davoult et al., 1990; Gage , 1990; Wilson, 1971; Chia & Spaulding, 1972). High recruitment of Sabellaria spinulosa may result in 'reinforcement' of the crust of tubes on the substratum. Winter storms can break up these crusts, particularly if on more mobile substrata. Areas where Sabellaria spinulosa had been lost due to winter storms appeared to recolonize up to a maximum thickness of 2.4 cm during the following summer (R. Holt, pers. comm. in Jones 1998). Potential high recruitment of Ophiothrix fragilis following mild winters (Smaal, 1994) may cause increases in numbers of brittle stars present in aggregations on the ross worm crusts. Ophiothrix fragilis also appears, in some areas, to have a multi-annual (about 4 years) cycle (Davoult et al., 1993). The community described from the wreck of the MV Robert that is recognised as MCR.Spi was described five years after the sinking of the vessel.

Habitat structure and complexity

Habitat complexity will vary depending on the species composition of the biotope. Dense crusts of Sabellaria spinulosa can provide greater structural complexity to bare bedrock habitats and may consolidate areas with more mobile substrata such as cobbles, or muddy gravels. The crusts can provide a textured substratum, and shelter between tubes etc. Species that burrow into soft substrata may also occur in thick crusts. For a list of associated species in a thoroughly sampled example of a Sabellaria spinulosa crust, see George & Warwick, 1985). However, crusts are often quite bare of other epibiota. The presence of dense aggregations of Ophiothrix fragilis also contributes to increases in structural complexity and considerable numbers of species may utilise these beds (Warner, 1971). Extensive Mytilus edulis has been noted from the biotope in south Wales and these will also increase structural diversity.

Productivity

George and Warwick, (1985) note that in a hard-bottom reef community with Sabellaria spinulosa, production is overwhelmingly dominated by the suspension feeding Ophiothrix fragilis. Much of this production may be through regeneration of broken arms (Sköld, 1998) Since the biotope is circalittoral, few algae are present and consequently, primary production is low. Sabellaria spinulosa larvae may settle in swarms and result in very high recruitment (Wilson, 1929). Rapid growth in suitable conditions may result in high productivity.

Recruitment processes

Sabellaria spinulosa, Ophiothrix fragilis and most of the other associated sessile species have planktonic larvae and the potential for dispersal over considerable distances (Wilson, 1929; Davoult et al., 1990). Recruitment of Sabellaria spinulosa is probably enhanced by the presence of adults or even just sand grain tubes of the same species (Wilson, 1929). In areas with considerable water movement, populations of Ophiothrix fragilis probably do not autorecruit due to the long duration (26 days) of the larval stage (Davoult et al., 1990). Ophiothrix fragilis larvae may settle on dense aggregations of adults (Warner, 1971). Some characteristic species may not recruit so readily, for instance the larva of Urticina felina inhabits the water column, but is not considered to be truly pelagic and probably has limited dispersal abilities (Solé-Cava et al., 1994). Areas where Sabellaria spinulosa had been lost due to winter storms appeared to recolonize up to a maximum thickness of 2.4 cm during the following summer (R. Holt, pers. comm. in Jones 1998). Sabellaria spinulosa adults are permanently attached to the substratum so no immigration of adults is possible. Recruitment processes of other species will vary according to the species composition of the biotope which may reflect in some measure the species present in nearby rocky biotopes.

Time for community to reach maturity

Sabellaria spinulosa recruits readily although environmental conditions can affect success. In ideal conditions, (extrapolated from the similar species Sabellaria alveolata), growth can be rapid and sexual maturity reached within the first year. Other species in the biotope may not be so quick in reaching maturity. For instance, Urticina felina is noted as being a slow growing, large anemone living for several years (Chia & Spaulding, 1972). The smallest recorded fertile anemone was at least 1.5 years old (Wedi & Dunn, 1983). There is considerable debate over the growth rate and longevity of Ophiothrix fragilis. Gage, (1990) worked on growth bands in the skeletal ossicles of the brittle star. Growth rates were estimated to be slow and life span to be at least 10 years, with sexual maturity probably achieved at about 10 mm disk diameter (several years old). Davoult et al., (1990) estimate longevity to be as short as 9 months with development to maturity taking from 6-10 months depending on time of recruitment. The overall time for the community to reach maturity will also depend to some extent on other species in the biotope (sometimes occurring in high densities) e.g. Mytilus edulis (Hiscock, 1979). Other species in this biotope may reflect, in some measure , the species found in nearby rocky biotopes. The community described from the wreck of the MV Robert that is recognised as MCR.Spi was described five years after the sinking of the vessel.

Additional information

Sabellaria spinulosa appears to occur in high densities and form crusts especially in turbid and polluted waters. It occurs extensively in the Severn Estuary and Bristol Channel (with Sabellaria alveolata) (George & Warwick, 1985) and on tide-swept mobile substrata such as the English Channel (K. Hiscock pers. comm.). It was an initial colonizing species on a wreck off Lundy and was abundant in an area severely polluted by an acidified halogenated effluent (Hoare & Hiscock, 1974).

Preferences & Distribution

Recorded distribution in Britain and IrelandThe MERMAID database (JNCC, 1999) shows two records of MCR.Sspi from northeast England and Hiscock (1979) records a community that probably corresponds to this biotope from the Gower peninsula, Wales. The biotope most likely also occurs in the Solway Firth (K. Hiscock, own observations). The most recent (2003) version of the biotopes classification records the biotope (as CR.MCR.CSAB.Sspi) as recorded from the Lleyn Peninsula, Lundy Island (including the wreck of the MV Robert) and the north-east and south coast of England.

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients Data deficient
Salinity
Physiographic
Biological Zone
Substratum
Tidal
Wave
Other preferences High levels of suspended sediment.

Additional Information

  • Density of Sabellaria spinulosa is high. At the Bristol Channel location studied by George & Warwick (1986), densities in excess of 4,000/m² for loosely aggregated Sabellaria spinulosa were recorded whilst the area sampled by Hiscock & Rostron (unpublished) on a level hard substratum had a single layer crust with 9,561 individual Sabellaria spinulosa in 1.4m².
  • High levels of suspended sediment are required in order for Sabellaria spinulosa to construct its tubes.

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

    -

    Additional information

    Although there are two records of the MCR.Sspi biotope in the MNCR survey database, species richness information is available for only one with 42 species being noted. In the study undertaken by George & Warwick (1985) of aggregations most likely on cobbles and pebbles, 24 different species were recorded but only 'countable' species were included.

    Sensitivity reviewHow is sensitivity assessed?

    Explanation

    In this biotope, Sabellaria spinulosa forms an almost complete crust on rocky substrata. This crust may increase structural diversity through creation of crevices, nooks and crannies. The worm tubes themselves provide an alternative substratum for settlement or attachment of other species and burrowing species may live in thick crusts. There are few characteristic species in this biotope and fauna found on Sabellaria spinulosa probably reflects those species present in near-by rocky biotopes. Ophiothrix fragilis, although not always present in this biotope, may occur in high densities but is more typical in lower densities located round the lobes of Alcyonium digitatum etc (Sköld, 1998). The suspension feeding habits of Ophiothrix fragilis can have an important role in coastal environments, removing substantial amounts of suspended sediment (Davoult & Gounin, 1995) and also in nutrient exchange at the water-sediment interface (Lefebvre & Davoult, 1997). Aggregations of Ophiothrix fragilis also modify the complexity of the habitat providing structure and shelter. In some high water flow, coarse sediment communities Urticina felina, along with Ophiothrix fragilis and Alcyonium digitatum (also present in the biotope in NE England) can make up a large percentage of the biomass (Mign & Davoult, 1995; Mign & Davoult, 1997). Although less important in this biotope, Urticina felina is still an important characterizing species as a passive carnivore and with a potential role in nutrient exchange.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name
    Important functionalOphiothrix fragilisCommon brittlestar
    Key structuralSabellaria spinulosaRoss worm
    Important functionalUrticina felinaDahlia anemone

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
    High High Moderate Major decline High
    The key structural species (Sabellaria spinulosa), important functional and characterizing species (such as Ophiothrix fragilis and Urticina felina) and other species (Alcyonium digitatum) in the biotope are all benthic, some of them permanently attached. Substratum loss would cause destruction of the biotope. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions. Other species that may occur in the biotope (e.g. Urticina felina) might take longer to return due to poor dispersal (Solé-Cava et al., 1994) and slow growth (Chia & Spaulding, 1972).
    Intermediate High Low Major decline High
    The key structural species in the biotope (Sabellaria spinulosa), although a suspension feeder and permanently attached to the substratum has only low intolerance to smothering. The similar Sabellaria alveolata can tolerate several weeks of smothering by sand (Wilson, 1971). Feeding and breeding will be curtailed. Of the other species in the biotope, few are sufficiently mobile or powerful enough diggers to be able to escape from smothering sediment. Other species in the biotope such as Ophiothrix fragilis and Alcyonium digitatum are likely to be killed by smothering. Therefore an overall intolerance of intermediate has been recorded. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions.
    Low Very high Very Low Minor decline Moderate
    The biotope occurs in silty turbid conditions so must tolerate or require some degree of suspended sediment. Sabellaria spinulosa, the key structural species in the biotope requires suspended sediment in order to construct the tubes in which it lives. Increases in suspended sediment may benefit this species (Hughes, 1998). (NB Sabellaria spinulosa requires quite coarse grains for tube construction). Urticina felina (a passive carnivore) and Ophiothrix fragilis, species selected as representative of the biotope as well as other species such as Alcyonium digitatum (both suspension feeders) are likely to suffer 'clogging' or interference with feeding mechanisms following large increases in siltation and in extreme cases even suffocation (Aronson, 1992). However, as suspension feeders, these species have a requirement for some suspended particles. It may take some while for the species affected by changes in suspended particle availability to regain condition or for growth rates to return to normal.
    Low High Moderate Decline Moderate
    The biotope occurs in silty turbid conditions so must tolerate or require some degree of suspended sediment. Sabellaria spinulosa, the key structural species in the biotope requires suspended sediment in order to construct the tubes in which it lives. Decreases in the amount of suspended sediment may limit growth rates of the worm and reduce the carrying capacity of this biotope for this species. (NB Sabellaria spinulosa requires quite coarse grains for tube construction). However, as suspension feeders, these species have a requirement for some suspended particles. It may take some while for the species affected by changes in suspended particle availability to regain condition or for growth rates to return to normal.
    Low Very high Very Low Minor decline Low
    Although the biotope itself is circalittoral, the key structural species (Sabellaria spinulosa) is occasionally found in the intertidal (as individuals rather than dense crusts). Other species often in the biotope, Ophiothrix fragilis and Urticina felina, can also be found intertidally, typically on the lower shore. These 3 species, as well as other species that may be in the biotope (e.g. Pagurus bernhardus, Gibbula cineraria, Mytilus edulis) may be tolerant of some degree of desiccation. However, other species such as Alcyonium digitatum are entirely subtidal and would be highly intolerant of desiccation. Exposure of the biotope to an hour of air and sunshine may cause the loss of a few species but the biotope as a whole would probably remain physically and functionally intact. As a circalittoral biotope, it is unlikely to be exposed to desiccating influences. It could potentially take several years for those species affected by desiccation to recolonize and return to their former status. During this time the biotope will probably continue to exist albeit with slightly fewer species.
    Intermediate High Low Decline Low
    Emergence is relevant in the case of this biotope as, because of the silty conditions in which it is found, circalittoral habitats may occur in the intertidal. Several of the other species in the biotope are found intertidally (e.g. Urticina felina, Ophiothrix fragilis, Mytilus edulis) and can tolerate some level of emergence. However, the key structural species in this biotope (Sabellaria spinulosa) (although occasionally found intertidally as individuals rather than dense crusts) is typically subtidal. It can probably tolerate a small level of emergence but may die if regularly exposed to the air for an hour. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions. Other species that may occur in the biotope (e.g. Urticina felina) might take longer to return due to poor dispersal (Solé-Cava et al., 1994) and slow growth (Chia & Spaulding, 1972).
    Tolerant* Not sensitive Rise High
    Emergence is relevant in the case of this biotope as, because of the turbid conditions in which it is found, circalittoral habitats may occur in the intertidal. The biotope is circalittoral and is likely to benefit from decrease in emergence.
    Tolerant Not relevant Not sensitive No change Moderate
    Sabellaria spinulosa is dependent on water movement for a supply of suspended particles which it uses to construct its tube. Increased water flow rate may enhance the supply of suspended particles and therefore favour the most structurally important species in this biotope. Other species that may be found in the biotope such as Urticina felina are found in a variety of water flow regimes and are unlikely to be greatly affected by changes in this factor. However, Ophiothrix fragilis may be swept away by increased flow rates (Hiscock, 1983). Overall, the biotope would be expected to persist with some changes in the composition of ancillary species.
    Intermediate High Low Minor decline Low
    Sabellaria spinulosa is dependent on water movement for a supply of suspended particles which it uses to construct its tube. Reductions in water flow rate may reduce the amount of suspended sand grains available. This may limit growth of the worms or reduce the density of worms that can be supported in a particular area. Other species that may be found in the biotope such as Urticina felina are found in a variety of water flow regimes and are unlikely to be greatly affected by changes in this factor. However, species in the community benefit from water flow which brings them suspended food and removes silt. It seems likely that some loss of species may occur. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily (see additional information). Recruitment may be aided by the presence of adults and/or empty tubes which form a preferred substratum (Wilson, 1929). Recovery is therefore likely to be rapid.
    Low Very high Very Low Minor decline Moderate
    Sabellaria spinulosa is distributed south of Britain and Ireland and it would therefore be expected to be unaffected by moderate warming. The geographical distributions of the selected important or characterizing species extend both north and south of the British Isles into warmer and colder waters. However, Ophiothrix fragilis has intermediate intolerance to thermal shocks (short acute changes in temperature). Stress can cause a reduction in the loading of symbiotic subcutaneous bacteria and this can be followed by death (Newton & McKenzie, 1995). However, mild winters have been noted to result in highly successful recruitments of Ophiothrix fragilis (Smaal, 1994). It should take only a short time for Sabellaria spinulosa growth rates to return to normal following periods of time below 5 °C. It may take longer for species such as Urticina felina to regain condition and full reproductive function.
    Tolerant Not relevant No change Moderate
    Growth of the key structural species in this biotope (Sabellaria spinulosa) is inhibited below 5 °C (Wilson, 1971) although the species is distributed north of the British Isles into the Arctic. Crisp (1964) did not record any mortality of Sabellaria spinulosa during the cold 1962/63 winter. The geographical distributions of the selected important or characterizing species extend both north and south of the British Isles into warmer and colder waters. No adverse effect of decreased temperature is expected.
    Low Very high Very Low Minor decline Low
    The biotope occurs in silty turbid conditions so the component species must be able to tolerate or require some degree of light attenuation in comparison with clear water. Few of the species are likely to be highly intolerant of changes in turbidity. Some species (Sabellaria spinulosa and Ophiothrix fragilis) feed primarily on phytoplankton. Phytoplankton require light for photosynthesis. Decreases in light availability may limit phytoplankton abundance and reduce food available for suspension feeders. It may take a while for 'normal' levels of phytoplankton to return and for the suspension feeders to regain condition.
    Low High Low Minor decline Low
    Decrease in turbidity may be sufficient to reduce availability of suspended particles, hindering growth, repair and feeding of the key structural species in the biotope Sabellaria spinulosa. Effects are likely to be sublethal in the short-term but may reduce viability of populations and result in decline if the turbidity decrease is chronic. Decrease in turbidity may also reduce supply of suspended food to ancillary species. Light levels will also increase and the biotope may become dominated by algae. For a short-term decrease in turbidity, effects are likely to be minor but for more chronic decrease some species might be lost. Recovery is likely to be rapid (see additional information).
    Intermediate High Low Decline Low
    The key structural species (Sabellaria spinulosa), in addition to several other species that may be found in the biotope (Ophiothrix fragilis, Urticina felina, Mytilus edulis), inhabit a wide range of wave exposures (from sheltered to very exposed). Increases in wave exposure of the biotope are unlikely to have a great effect where it occurs on bedrock or other stable hard substrata. However, where it occurs on consolidated cobbles and pebbles may disturb the substratum and destroy beds. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily so that recovery is likely to be rapid (see additional information). Recruitment may be aided by the presence of adults and/or empty tubes which form a preferred substratum (Wilson, 1929).
    Intermediate High Low Minor decline Low
    Wave action may have an important role in suspending the sediment that is required by Sabellaria spinulosa to build its tubes. Decreases in wave exposure may reduce the amount of available sand grains suspended in the water column, potentially limiting growth of the worm tubes and restricting abundance. Decrease in wave exposure may also allow siltation to occur adversely affecting some species in the biotope. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily so that recovery is likely to be rapid (see additional information). Recruitment may be aided by the presence of adults and/or empty tubes which form a preferred substratum (Wilson, 1929).
    Tolerant Not relevant Not relevant No change Low
    Sabellaria spinulosa, the key structural species in the biotope is considered not sensitive to noise disturbance. It is possible that predator avoidance behaviour in Ophiothrix fragilis may be triggered by noise vibrations although this has not been recorded.
    Tolerant Not relevant Not relevant No change High
    The key structural species (Sabellaria spinulosa) and other selected important or characterizing species (Urticina felina, Ophiothrix fragilis, Alcyonium digitatum, Mytilus edulis) that may be found in the biotope are not sensitive to visual disturbance.
    Intermediate High Low Decline Low
    Physical disturbance may cause damage to or loss of some of the Sabellaria spinulosa crust and organisms that live on or in it. However, the key structural species (Sabellaria spinulosa) is likely to be resilient to some physical abrasion. The ability of the structurally similar Sabellaria alveolata to repair tubes is well developed (Cunningham et al., 1984; Vorberg, 2000). Other selected important or characterizing species (Urticina felina, Ophiothrix fragilis, Mytilus edulis), sponges and tunicates may be more susceptible and the species richness of the biotope reduced so that the biotope is identified as having intermediate intolerance to abrasion and physical disturbance. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions (see additional information). Recruitment may be aided by the presence of adults and/or empty tubes which form a preferred substratum (Wilson, 1929).
    High High Moderate Decline High
    Although displacement may not affect some of the species that may live in the biotope (e.g. Urticina felina, Ophiothrix fragilis), the key structural species (Sabellaria spinulosa) is permanently attached to the substratum. Displacement would result in death of this species and loss of the main structure of the biotope. The biotope may also contain other permanently attached species (e.g. Alcyonium digitatum) which are likely to be highly intolerant of displacement. Mobile species in the biotope are unlikely to be affected. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions (see additional information). Other permanently attached species may take longer to recover but these are unlikely to have a great effect on the biotope.

    Chemical Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    Intermediate High Low Decline Moderate
    Sabellaria spinulosa, the key structural species in this biotope has been recorded as thriving in an area affected by an acidified halogenated effluent (Hoare & Hiscock, 1974). The biotope may therefore replace other biotopes in pollution stressed situations or be an initial colonizing biotope. However, echinoderms such as Ophiothrix fragilis and Ophiopholis aculeata, which may be found in this biotope, are generally considered to be very sensitive to marine pollution (Newton & McKenzie, 1995) and any examples of the biotope present in locations affected by synthetic chemicals may be impoverished. On the other hand, Sabellaria spinulosa colonized the wreck of the MV Robert at Lundy possibly blocking the effect of antifouling chemicals and allowing a rich community to develop. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions (see additional information). Other species may take longer to recover but these are unlikely to have a large role in the biotope.
    Heavy metal contamination
    No information No information No information Insufficient
    information
    Not relevant
    Insufficient
    information is available to make an assessment. One of the species characteristic of this biotope, Ophiothrix fragilis, is noted as being an efficient bioaccumulator of heavy metals (Hutchins et al., 1996).
    Hydrocarbon contamination
    No information No information No information Insufficient
    information
    Not relevant
    It is not known how the key structural species in this biotope (Sabellaria spinulosa) reacts to hydrocarbon contamination although it is recorded as thriving in some rather extremely polluted conditions (Hoare & Hiscock, 1974). Echinoderms such as Ophiothrix fragilis and Ophiopholis aculeata which may be found in this biotope are generally considered to be very sensitive to marine pollution. Some laboratory experiments have shown Ophiothrix fragilis to be intolerant of hydrocarbon pollution (Newton & McKenzie, 1995).
    Radionuclide contamination
    No information No information No information Insufficient
    information
    Not relevant
    Insufficient
    information is available to make an assessment. Ophiothrix fragilis is noted as being an efficient bioaccumulator of radionuclides (Hutchins et al., 1996).
    Changes in nutrient levels
    Low Very high Very Low Minor decline Moderate
    It is not known whether changes in nutrient concentration will have any direct effect on the key or important species in this biotope. However, several species within the biotope are suspension feeders, trapping mainly phytoplankton. Reductions in nutrient concentration may reduce the abundance of phytoplankton and consequently the amount of food available. Nutrient limitation has been noted to cause stress and potentially mortality in Ophiothrix fragilis (Newton & McKenzie, 1995). When food supplies return to normal it may take some while for suspension feeders to regain body condition.
    No information Not relevant No information Insufficient
    information
    Not relevant
    Intermediate High Low Decline Moderate
    Sabellaria spinulosa is found primarily in fully marine (saline) conditions. However, dense populations do occur in the Solway Firth and Bristol Channel, both areas at the entrance to estuaries. There are occasional records from the intertidal where some reduced salinity must be experienced from precipitation run-off. Reductions in salinity in the circalittoral are likely to have detrimental effects for this key structural species. Urticina felina, a characterizing species in this biotope is likely to be highly intolerant of reductions in salinity. Ophiothrix fragilis is recorded from salinities as low as 10 psu (Wolff, (1968) so it is unlikely that this species would be affected. Sabellaria spinulosa has a long lived larva with good dispersive ability and can recruit readily although this can be affected by environmental conditions (see additional information). Other species may take longer to recover but these are unlikely to have a great effect on the biotope.
    No information No information No information Insufficient
    information
    Not relevant
    Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l. Insufficient
    information is available regarding the key structural species (Sabellaria spinulosa) tolerance to decreases in oxygenation. Although another species in the biotope, Ophiothrix fragilis, is known to have a low respiration rate (Migné & Davoult, 1997(b)), particularly during colder winter temperatures, extreme hypoxia is known to cause mass mortality (Stachowitsch, 1984).

    Biological Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    No information No information No information Insufficient
    information
    Not relevant
    Insufficient
    information
    No information No information No information Insufficient
    information
    Not relevant
    Insufficient
    information
    Low Very high Very Low No change Moderate
    Extraction of Sabellaria spinulosa, the key structural species in this biotope is highly unlikely and the species is the subject of a UK Biodiversity Action Plan. If there is a continued increase in the marine aquarium trade for cold water species then Urticina felina, a component species of this biotope, could be a potential target species for extraction. Urticina felina is a slow growing anemone with poor dispersive abilities. It may take several years for recovery to occur but removal and recovery of this species may not have an important role in the viability and functioning of the biotope. Therefore a low intolerance with very high recovery has been suggested.
    Low Very high Very Low Minor decline Low

    Additional information

    Recoverability
    Sabellaria spinulosa is the most important species in this biotope. There are few frequent characterizing species although more studies of the biotope MCR.Csab.Sspi although it is replaced by CR.MCR.CSAB.Sspi in the 2003 version of the biotopes classification which has more species listed as characterizing. The species present in this biotope probably reflect the species composition of nearby biotopes. Because characterization of this biotope relies predominantly on the presence of a crust of Sabellaria spinulosa, intolerance or recoverability of species other than Sabellaria spinulosa may not have a great bearing on that of the biotope as a whole. Sabellaria spinulosa is most frequently found in disturbed and polluted conditions and is a ‘r-strategist’ (a life strategy which allows a species to deal with the vicissitudes of climate and food supply by responding to suitable conditions with a high rate of reproduction. R-strategists are continually colonizing habitats of a temporary nature (from Baretta-Bekker et al., 1992)). Areas where Sabellaria spinulosa had been lost due to winter storms appeared to recolonize up to a maximum thickness of 2.4 cm during the following summer (R. Holt, pers. comm. in Jones 1998). The rich community described from the MV Robert (Hiscock, 1981) identified as this biotope was surveyed five years after the vessel sank suggesting rapid development of the biotope. Recoverability is therefore expected to be high for the biotope.

    Importance review

    Policy/Legislation

    Habitats of Principal ImportanceSabellaria spinulosa reefs [England]
    Habitats of Conservation ImportanceSabellaria spinulosa reefs
    Habitats Directive Annex 1Reefs
    OSPAR Annex VSabellaria spinulosa reefs
    UK Biodiversity Action Plan Priority

    Exploitation

    The biotope itself is unlikely to be exploited. Reefs of Sabellaria spinulosa that may be trawled for shrimps are found on sediments and are not this biotope. Species in the biotope are unlikely to be exploited.

    Additional information

    The UK BAP for Sabellaria spinulosa reefs is most likely to be a different biotope: CMX.SpiMx (Sabellaria spinulosa and Polydora sp. on stable circalittoral mixed sediment). There has been considerable concern about decline in Sabellaria spinulosa reefs and shrimp fisheries have been implicated in the decline. However, Vorberg (2000) could find no damage caused after experiments with shrimp trawls in the Wadden Sea and suggests that declines might be more associated with changing patterns of currents perhaps associated with construction, dredging and dumping.

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    Citation

    This review can be cited as:

    Jackson, A. & Hiscock, K. 2006. Sabellaria spinulosa, didemnids and other small ascidians on tide-swept moderately wave-exposed circalittoral rock. 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/habitat/detail/348

    Last Updated: 26/04/2006