Suberites spp. and other sponges with solitary ascidians on very sheltered circalittoral rock

10-05-2002
Researched byGeorgina Budd Refereed byThis information is not refereed.
EUNIS Code EUNIS Name

Summary

UK and Ireland classification

EUNIS 2008
EUNIS 2006
JNCC 2004
1997 Biotope

Description

Silty very sheltered circalittoral rock, (often vertical surfaces) subject to only weak tidal streams with a rich mixture of sponges (Polymastia boletiformis, Suberites carnosus, occasionally Suberites ficus, Iophon hyndmanni, Dysidea fragilis, Raspailia ramosa and Stelligera rigida) and a variety of large solitary ascidians (Ascidia virginea, Ascidiella aspersa, Ascidia mentula and, more rarely, Phallusia mammillata and Styela clava). (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

Recorded in Scotland in Loch Feochan and around Jura and Uist, along the south coast in Southampton docks, the rias of Devon and Cornwall and in Milford Haven and the Abereiddy Quarry Wales. In Ireland the biotope was found in Mulroy Bay and Bantry Bay.

Depth range

-

Additional information

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JNCC

Habitat review

Ecology

Ecological and functional relationships

  • The biotopes represented by SCR.SubSoAs are sponge and ascidian dominated. Sponges are noted as being inhabited by a wide diversity of invertebrates. Sponges can provide hard substrata for attachment, refugia and shelter, an enhanced food supply in feeding currents and a potential food source themselves (Klitgaard, 1995; Koukouras et al., 1996).
  • The hydroid, Nemertesia antennina, also acts as a host for other species. As many as 150 species were found in association with it and examination of single stems revealed clear distributional patterns that correlated with the requirements of each epizoic species, and the range of abiotic conditions from the top to the base of the host (Hughes, 1975).
  • Sessile organisms are often limited by the space available for attachment and thus competition for such space is intense. Competitive success can result from physical or chemical aggression, 'bull-dozing', smothering and possibly by localized food depletion. Whilst some sessile organisms form flat sheets over the surface, others retain a small point of attachment and grow upwards and form a canopy above the substratum. Such variation in growth forms may be one form of 'niche partitioning' on homogenous rock surfaces (Sebens, 1985).
  • The various mobile echinoderms that may be present in the biotope (e.g. Marthasterias glacialis, Henricia oculata) play a role in modifying epilithic populations through predation. Although Henricia oculata can suspension feed by extending its arms in the water to trap suspended particles in mucus, it also feeds on sponges and hydroids by stomach eversion (Fish & Fish, 1996). The anemone, Metridium senile, is heavily preyed upon by the nudibranch Aeolidia papillosa and in most years Aeolidia papillosa is the only important source of mortality to Metridium senile in the absence of rocks or boulders that could move and damage it during storms (Sebens, 1985).
  • Predatory echinoderms and nudibranchs hunt by chemosensation and touch, tracking their prey along a sensory gradient. Thus it is advantageous for the prey species to posses some means of chemical or tactile camouflage. Wicksten (1983) suggested that encrusting animals such as sponges produce chemical products that mask their metabolic by-products or accumulate secondary metabolites which render themselves distasteful or poisonous. Sessile organisms may also use such biologically active compounds as a form of antifouling to prevent the larvae of other species from settling and growing on their surfaces, and also in interactions with established neighbours (Wood, 1987).
  • In the SCR.AmenCio.Met biotope, also represented by this review, the interactions among Metridium senile, Alcyonium digitatum and Aplidium spp. can be quite complex, and these three species can each dominate patches of vertical wall indefinitely (Sebens, 1985). Purcell (1977) documented cases of damage inflicted on Alcyonium digitatum by neighbouring Metridium senile, presumably caused by nematocysts in specialized "catch-tentacles" which are used agonistically against other anemones. Large Metridium senile (8 cm tall when contracted) can certainly resist encroachment of Aplidium spp., whilst small Alcyonium digitatum and Metridium senile are frequently overgrown by Aplidium spp. (Sebens, 1986).
  • Also in the SCR.AmenCio.Met biotope, a symbiotic relationship may exist between the plumose anemone Metridium senile and Modiolus modiolus. Laboratory experiments have shown that the presence of the anemone significantly reduced predation of Modiolus modiolus by starfish (Kaplan, 1984). The anemone was thought to benefit from the feeding activities of its host, which circulated food in its direction.
  • The small bivalve Modiolarca tumida is sometimes found living as a commensal in the test of the ascidian Acidia mentula (Fish & Fish, 1996).

Seasonal and longer term change

It is likely that some temporal changes in the coverage and shelter provided by the species in the biotope will occur. For instance, there is much seasonal variability in abundance of individual hydroids, e.g. Nemertesia antennina, and experiments have shown that hydroid colony growth is highest over a defined temperature range (Gili & Hughes, 1995).

Habitat structure and complexity

The diversity of species within the biotope can be striking even where the physical heterogeneity of the substratum is not. Whilst the rock surface may be smooth and free of discernibly different micro-habitats, some microhabitats are likely to be provided by cracks and crevices in the rock. However, many of the species characteristic of this community add considerable physical complexity to the biotope. Species such as sponges and hydroids can provide substrata for attachment, refugia and shelter for a number of animals (Klitgaard, 1995; Koukouras et al., 1996) The biotope occurs in very sheltered conditions and any upward facing surfaces are likely to accumulate silt which may attract small species such as amphipods, worms and meiofauna.

Productivity

No photosynthetic species are listed as characterizing species in SCR.SubSoAs, a circalittoral biotope. Consequently, primary production is not regarded as a major component of productivity. The biotope SCR.AmenCio.Met may have a small algal component of coralline crusts. Nevertheless, the biotopes represented by this review are often species rich and may contain quite high animal densities and biomass. Specific information about the productivity of characterizing species or about the biotopes in general was not found.

Recruitment processes

  • Sponges may proliferate both asexually and sexually. A sponge can regenerate from a broken fragment, produce buds either internally or externally or release clusters of cells known as gemmules which develop into a new sponge. Most sponges are hermaphroditic but cross-fertilization normally occurs. The process may be oviparous, where there is a mass spawning of gametes through the osculum which enter a neighbouring individual in the inhalant current. Fertilized eggs are discharged into the sea where they develop into ciliated larvae, known as planulae. However, in the majority, development is viviparous, whereby the larva develops within the sponge and is then released. Larval life varies from a few hours to a few weeks and metamorphosis follows settlement. Adults may live several years (Fish & Fish, 1996).
  • Ascidians are also generally hermaphroditic with self-fertilization, but some rely on cross-fertilization. In solitary forms gametes are released in to the open water for fertilization and larval development to occur, whilst compound forms tend to retain the zygote in the atrium until the 'tadpole' larva is fully developed. The larvae are lecithotrophic and have a free-swimming life varying from a few minutes to a few days. Asexual reproduction by budding is also common and reproduction by fission occurs in some colonial species (Fish & Fish, 1996).
  • Two sets of hypotheses explaining patterns of larval settlement have become established. The first proposes that active habitat selection determines the distribution of newly settled larvae. The second suggests that distribution and abundance are determined by passive deposition of competent larvae (i.e. purely hydrodynamic processes) (Havenhand & Svane, 1991) (see Meadows & Campbell,1972; Scheltema, 1974; Butman, 1987). Although these two hypotheses have been regarded by some authors to be conflicting, they are not necessarily mutually exclusive (Butman, 1987). For example, the presence of conspecific adults can be an important factor in determining habitat selection. Long-term data from populations of the ascidian Ascidia mentula occurring on subtidal vertical rock indicated that recruitment of Ascidia mentula larvae was positively correlated with adult population density, and then by subsequent active larval choice at smaller scales. Factors influencing larval settlement were light, substratum inclination and texture (Havenhand & Svane, 1989). However, the swimming power of an ascidian tadpole larva is relatively low (Chia, Buckland-Nicks & Young, 1984), and on a larger scale hydrodynamic variables will most probably determine distribution (Olson, 1985; Young, 1986).
  • Time for community to reach maturity

    No information concerning the development of this specific community was found. However, many of the species present in SCR.SubSoAs and the other biotopes also represented by this review, are present in the biotopes described by Sebens (1985) which were considered to be dynamic and fast growing. Many sponges recruit annually, growth can be quite rapid, with a life span of one to several years. Other species present can be relatively long-lived. For example, the ascidian Ascidia mentula has been reported to live seven years in some populations, whilst Ascidiella aspersamay live between one to one and a half years around the British Isles compared with two to three years in Norwegian waters, and Ciona intestinalis may live up to one and a half years (Fish & Fish, 1996).

    Additional information

    No text entered.

Preferences & Distribution

Recorded distribution in Britain and IrelandRecorded in Scotland in Loch Feochan and around Jura and Uist, along the south coast in Southampton docks, the rias of Devon and Cornwall and in Milford Haven and the Abereiddy Quarry Wales. In Ireland the biotope was found in Mulroy Bay and Bantry Bay.

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients Field unresearched
Salinity
Physiographic
Biological Zone
Substratum
Tidal
Wave
Other preferences

Additional Information

No text entered.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

  • Phallusia mammillata

Additional information

Full MarLINsensitivity reviews for Suberites carnosus and Nemertesia antennina have not been completed, therefore these species are absent from the tables detailing species used to indicate biotope sensitivity and recoverability of the biotope. However, whenever information concerning their sensitivity was available it has been used.

Sensitivity reviewHow is sensitivity assessed?

Explanation

The biotope is dominated by a rich mixture of sponges and a variety of large solitary ascidians. Suberites carnosus is found with high frequency in the biotope and provides a key structural component. Suberites carnosus also acts as a functionally similar representative for other species of sponge. Ciona intestinalis and Clavelina lepadiformis represent the ascidians and Nemertesia antennina the hydroids.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingCiona intestinalisA sea squirt
Important characterizingClavelina lepadiformisLight bulb sea squirt
Important characterizingNemertesia antenninaSea beard
Key structuralSuberites carnosusA sponge

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Moderate Moderate Major decline Moderate
The majority of the species within the biotope are permanently attached to the substratum or are slow moving therefore substratum removal would result in loss of faunal populations so the intolerant of the biotope has been assessed to be high. Following the loss of adult populations recovery would be dependent upon re-colonization by larvae. Recoverability has been assessed to be moderate (see additional information below).
High Moderate Moderate Major decline Low
Although the biotope and those biotopes it represents, occur in fairly silty environments, sudden smothering by 5 cm of sediment is likely to result in the death of many species. Feeding structures of the sea-squirts and pores of the sponges would probably become clogged and suffocate the organisms (Bakus, 1968). Some of the mobile predators such as Marthasterias glacialis may be able to uncover themselves. However, many species are likely to die so intolerance has been assessed to be high. Furthermore in the sheltered conditions in which this biotope is found smothering material is not likely to be removed very rapidly. Following the loss of adult populations recovery would be dependent upon re-colonization by larvae, but recoverability has been assessed to be moderate (see additional information below).
Low Immediate Not sensitive No change Low
Many of the species are suspension feeders and an increase in suspended sediment may cause interference and blockages, for example in sponge canals and pores. Whilst some species may have an adaptive mechanism to 'slough' off relatively small amounts of such material, an energetic cost would be involved and thus intolerance has been assessed to be low, as the viability of species may be reduced. At the benchmark level the factor operates for a period of one month, so recovery should be very rapid on return to prior conditions. Recoverability has therefore been assessed to be immediate.
Low Very high Not relevant No change Moderate
Many of the species are suspension feeders and a decrease in suspended sediment may reduce interference and blockages, for example of sponge canals and pores. However, the species in the biotope are reliant on suspended organic material as a food resource, consequently a reduction would have an effect upon the species viability. However for the duration of one month effects are unlikely to be significant and intolerance has been assessed to be low. Recovery has been assessed to be immediate as optimal feeding would commence on return to prior conditions.
Not relevant Not relevant Not relevant Not relevant Not relevant
The biotope is entirely subtidal and will not be subject to desiccation.
Not relevant Not relevant Not relevant Not relevant Not relevant
The biotope is entirely subtidal and will not be subject to emergence.
Not sensitive* Not relevant
The biotope is entirely subtidal and will not be subject to emergence.
High Moderate Moderate Decline Moderate
The biotope consists mainly of species firmly attached to the substratum and which would be unlikely to be displaced by an increase in the strength of tidal streams at the benchmark level. However, many of the species in this biotope are active suspension feeders An increase in tidal flow rate to moderately strong or strong (0.5 -3 m / sec) may cause loss of posture and interfere with feeding mechanisms, particularly in the more delicate species like Ciona intestinalis and Hiscock (1983) illustrated how the inhalant siphons of Ascidia mentula closed when exposed to a flow of 0.3 m /s. Feeding activity would be reduced subsequently affecting species viability. In increased tidal flow and over a period of one year the biotope would probably begin to change to another, with species tolerant of limited wave action and higher tidal flow, the biotope would not be recognized and intolerance has therefore been assessed to be high. Recovery has been assessed to be moderate on return to prior conditions (see additional information below).

In the SCR.AmenCio.Met biotope the plumose anemone, Metridium senile may benefit from increased water flow rate. Hiscock (1983) described the reaction of Metridium senile to increasing flow rate (to 90 cm/s) in a flume. The anemones were stimulated to expand tentacles as flow increased and only withdrew them at flow rates in excess of 70 cm/s. They were not swept away. Whilst large Metridium senile thrive in tidal narrows where surface velocity may be in the region of 3-5 knots, they do not appear to occur in very strong tidal flows (exceeding 5 knots) such as in the Gulf of Corryvreckan or Strangford Lough Narrows. Increase in water flow rate is therefore likely to favour settlement and growth of Metridium senile especially because of increased food supply. However, above 5 knots, adverse effects including inability to feed and possible displacement may occur.
Not sensitive* Not relevant
The characterizing species of the biotopes are active suspension feeders and whilst they create their own inhalant current to draw food to them, they are still in part, reliant on some water flow, even if very weak, to deliver food. Water flow rates at locations where the biotopes are found are typically weak or very weak. A further reduction may consequently have an effect on the community as a result of reduced food supply. Over the duration of one year loss of condition and reduced viability might be expected, intolerance has therefore been assessed to be low. Recoverability has been assessed to be very high on return to prior conditions as optimum feeding commences.
Tolerant Not relevant Not relevant Not relevant Very low
Many of the species found within the biotopes represented by this review have distributions that extend to the south of the British Isles, suggesting that the communities would be tolerant of a long-term chronic increase in temperature of 2°C. There are shorter term cyclical temperature fluctuations operating in the north Atlantic (Maximov et al., 1972), such as those associated with the now named North Atlantic Oscillation (NAO), with a period of 7-8 years. A variety of benthic populations have been demonstrated to co-fluctuate in abundance accordingly (Gray & Christie, 1983), and such cyclic fluctuations are recorded from typical rocky circalittoral species such as Ciona intestinalis (Lundläv, 1985) and Ascidia mentula (Lundälv & Christie, 1986). For instance, northerly populations of Ciona intestinalis did not begin to reproduce until temperatures rose above 8°C. No evidence has been found of adverse effects of short-term temperature increases, therefore an assessment of not sensitive has been made but with very low confidence.
Low Very high Moderate No change Moderate
During the severe winter of 1962-63, although no significant mortality was noted, Crisp et al. (1964) found that many compound ascidians were retarded in renewal of the colony after 'winter budding'. In the Mediterranean, growth of Ciona intestinalis is optimal at between 15-20°C and most of the adult population dies below 10°C. During cold spells the population is maintained through survival of young individuals which are more cold tolerant. Furthermore, the species occur extensively in shallow water habitats of Swedish and Norwegian fjords where water temperatures fall to low levels (K. Hiscock, pers. comm.). Intolerance has therefore been assessed to be low. Recovery from surviving tissue is likely to be rapid and re-colonization will occur from annual recruitment from the plankton. Recoverability has therefore been assessed to be very high.
Low Immediate Not sensitive Minor decline Low
It is unlikely that the light attenuating effects of an increase in turbidity would be of direct significance to the biotopes, as the biotope is an animal dominated community, dependent on secondary production rather than light dependent photosynthesis. However, as active suspension feeders, sponges and ascidians would feed upon phytoplankton as well as suspended detritus and increased turbidity may consequently impact upon a food resource. Intolerance has been assessed to be low as viability of the community would probably be reduced for the duration of one year. Recovery has been assessed to be immediate on return to prior conditions as optimal feeding would resume.
Tolerant Not sensitive* Not relevant Low
The biotope is an animal dominated community, dependent on secondary production rather than light dependent photosynthesis. Following a decrease in turbidity and increased water clarity, competition with encrusting red algae for the substratum may increase in the SCR.AmenCio.Met biotope. However, a slight change in the species composition in the biotope will not radically alter the nature of the community and an assessment of not sensitive has been made.
High Moderate Moderate Decline Moderate
Increased wave action would clear silt from vertical surfaces of the substratum, making rock available for settlement of species more characteristic of wave exposed conditions, for instance erect Bryozoa and barnacles. It seems most likely that individual sponges would contract during strong wave action but survive for short periods. Suberites carnosus can contract to about ¼ of its fully expanded size when disturbed. However, the stalk of fig-shaped massive Suberites carnosus breaks when bent through 20 degrees (when in contracted condition) which is likely if subjected to wave oscillation for an extended period (Ackers & Moss, 1985). Furthermore, if sponges remain contracted for a prolonged period owing to a disturbance, feeding opportunities will be minimised and reduced viability would result. Suberites carnosus is a key structural and characterizing species in the SCR.SubSoAs biotope, following its loss the biotope would not be recognized and intolerance has been assessed to be high. Recoverability has been assessed to be moderate (see additional information below).
Not sensitive* Not relevant
The biotopes occur in locations which are already very or extremely wave sheltered. Whilst water movement is required to bring food to suspension feeding species in the biotope, tidal streams are probably more important than wave oscillation in doing so. Consequently, an assessment of a further decrease in wave exposure was not considered relevant.
Tolerant Not relevant Not relevant Not relevant Not relevant
Species in the biotope are likely to have poor ability for detection of noise vibrations and as such are unlikely to be intolerant of noise
Tolerant Not relevant Not relevant Not relevant Not relevant
Species characteristic of the biotope are sessile invertebrates and are no capable of visual perception. Other species that frequent the biotope e.g. crabs and fish may be temporally disturbed but there would be no effect on the biotope.
High Moderate Moderate Major decline Moderate
Physical impact is likely to cause damage and mortality to exposed individuals but, because sponges such as Suberites carnosus may be able to regenerate from fragments it seems likely that damaged individuals may re-grow. Mobile fishing gear is likely to scrape individuals off the substratum and damage others. In the SCR.AmenCio.Met biotope Metridium senile is soft, flexible and can reform its attachment to the substratum, the species also habitually reproduces by basal laceration so will regrow. Many species of ascidian are soft and delicate so would probably be damaged and recovery would be reliant on recolonization by larvae. For example, Ciona intestinalis is a large ascidian, with a soft, retractile body. Physical disturbance by a passing scallop dredge is likely to cause physical damage and death. The light bulb tunicate is permanently attached to the substratum and is unable to move out of the way from abrasive objects. The body of the species is soft and delicate, so abrasion is likely to cause physical damage and possibly death. Overall, physical disturbance by mobile fishing gear is likely to remove a proportion of all groups within the community and attract scavengers to the community in the short term. Therefore, an intolerance of intermediate has been recorded. Large scale physical disturbance would be similar to substrate removal (see above).

The recolonization of epifauna on vertical rock walls was investigated by Sebens (1985, 1986). He reported that rapid colonizers such as encrusting corallines, encrusting bryozoans, amphipods, and tubeworms recolonized within 1-4 months. Ascidians such as Dendrodoa carnea, Molgula manhattensis and Aplidium spp. achieved significant cover in less than a year, and, together with Halichondria panicea, reached pre-clearance levels of cover after 2 years. A few individuals of Alcyonium digitatum and Metridium senile colonized within 4 years (Sebens, 1986). Large sponges and anemones would probably take longer to reach pre-clearance levels. Therefore, a recoverability of moderate has been recorded.

High Moderate Moderate Major decline Moderate
The many sponge and ascidian species within the biotope are sessile organisms attached to the substratum that cannot re-attach once removed, thus intolerance has been assessed to be high. Recoverability has been assessed to be moderate (see additional information below).
However, Wahl (1984) observed that Metridium senile detached from the substratum during the first week of deoxygenation in the Inner Flensburg Fjord and may drift away eventually to resettle. Metridium senile from the SCR.AmenCio.Met biotope therefore seems able to survive displacement from the substratum and intolerance may be lower, but, presumably the anemone may be damaged during the displacement in which case some repair may be needed.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Low High Low Not relevant Very low
The plumose anemone, Metridium senile is a major component of the SCR.AmenCio.Met biotope represented by this review. Mercier et al. (1998) exposed Metridium senile to tri-butyl tin contamination in surrounding water and in contaminated food. The species produced mucus 48 hours after exposure to contaminated seawater. TBT was metabolised but the species accumulated levels of butyl tins leading the authors to suggest that Metridium senile seemed vulnerable to TBT contamination. However, Mercier et al., (1998) did not indicate any mortality and, since Metridium senile is a major component of jetty pile communities immediately adjacent to large vessels coated with TBT antifouling paints, intolerance has been assessed to be low specifically to TBT. No other information has been found on effects of contaminants on other species of the biotopes, so confidence is very low.
Heavy metal contamination
No information Not relevant No information Not relevant Not relevant
Several species of ascidian are known to accumulate high concentrations of trace metals. However, no information was found with reference to effects on specific species of the biotope and insufficient information has been recorded. However, Cole et al. (1999) stated that arsenic, mercury, lead, zinc and copper are very toxic to invertebrates in general, and that cadmium is considered toxic to them.
Hydrocarbon contamination
No information Not relevant No information Not relevant Not relevant
Insufficient
information.
Radionuclide contamination
No information Not relevant No information Not relevant Not relevant
Insufficient
information.
Changes in nutrient levels
Tolerant* Not relevant Not sensitive* No change Very low
There is some evidence that increased levels of organic nutrients is of benefit to populations of Ciona intestinalis (Naranjo et al., 1996). Dissolved organic matter can also form a nutritional component for other species such as sponges and an assessment of not sensitive* has been made, as improved growth and fecundity may result form moderate nutrient enrichment.
Not relevant Not relevant Not relevant Not relevant Not relevant
The biotope occurs in fully saline waters (Connor et al., 1997a) so an increase in salinity has been assessed not to be relevant.
Low Very high Moderate No change Moderate
Components of the biotope community are tolerant of variable salinities. For instance Ascidia mentula survives down to 20 psu, Ascidiella aspersa is tolerant of salinities down to 18 psu and is often common in estuaries, whilst Ciona intestinalis is tolerant of salinities as low as 11 psu (Fish & Fish, 1996). Shallow examples of the biotope may be subject to some reduction in salinity and, in view of the tolerance of at least some component species an intolerance assessment of low has been made. Recoverability has been assessed to be very high on return to prior conditions following a short term decline in salinity as species would remain in situ. Over a period of one year some component species may decline in abundance and recovery may therefore take longer (see additional information below).
Intermediate Moderate Moderate Decline Very low
The biotope may be found in locations with restricted water renewal (tidal streams: weak or very weak) where oxygen concentrations may drop. Cole et al. (1999) suggested possible adverse effects on marine species below 4 mg O2/l and probable adverse effects below 2 mg O2/l. As a consequence of deoxygenation characteristic species of the biotope would probably be affected in terms of mortality, diminished condition, feeding or reproductive capability. The biotope may become degraded so intolerance has been reported to be intermediate. For instance, Hiscock & Hoare (1975) studied the sublittoral ecology of Abereiddy Quarry, Wales. During the summer the quarry developed a marked thermocline at 12-14m below which the water was 4°C colder, had lower light transmittance and was deoxygenated with a high level of hydrogen sulphide. Stratification of the water body occurred between spring and autumn resulting in a sharp decline in the amount of dissolved oxygen present for respiration. The oxycline was suggested to be responsible for the drastic reduction in species diversity below depths of 10-12 m. During July 1973, water at 10 m was only 55% saturated with oxygen, and the maximum depth to which various species extended was suggested to indicate their tolerance to low oxygen concentrations. On the stone wall Suberites carnosus was found occasionally down to 10 m depth but was more frequent at 8 m depth. Recoverability of characteristic species of the biotope has been assessed to be moderate (see additional information below).

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information Not relevant No information Not relevant Not relevant
Insufficient
information.
Low Very high Very Low Minor decline High
The ascidian,Styela clava, which occurs in the biotope, but is rare, is a non-native species originating from the Pacific. It was introduced into European waters, from the Mediterranean to SW Britain by shipping and was first recorded in Plymouth in 1953 (Carlisle, 1954). It is a hardy species capable of tolerating salinity changes and temperature fluctuations and has spread rapidly (Eno, 1997; Houghton & Millar, 1960). As Styela clava is a hardy species it is unlikely that it will disappear once established, however, Styela clava has not been observed to dominate areas but rather occurs amongst other species in the biotope, usually growing taller than surrounding biota. However, competition for food between individuals and with other species can occur and therefore intolerance has been assessed to be low as the viability of other species within the biotope may suffer. Recoverability has been assessed to be very high as species would not be lost from the biotope (see additional information below).
Not relevant Not relevant Not relevant Not relevant Not relevant
It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.
Not relevant Not relevant Not relevant Not relevant Not relevant

Additional information

Recoverability:
Immediate colonization following a catastrophic disturbance would depend on the availability of planktonic larvae at the time and any subsequent succession to the re-establishment of the biotope. Work undertaken by Sebens (1986) suggests that many of the species characteristic of the biotope would be likely to re-colonize rapidly. For instance, the sponge Halichondria panicea and the colonial ascidian Aplidium reached pre-removal cover in just under two years following experimental removal whilst Metridium senile took four years to become re-established in the same experiment. However, for some characterizing species, such as species of Suberites or branching sponges, little is known of colonization or growth rates. Whilst the biotope may be re-established within five years, the presence of all characteristic species fully grown may take longer and recoverability has been assessed to be moderate.

Importance review

Policy/Legislation

- no data -

Exploitation

No text entered.

Additional information

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Bibliography

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  2. Butman, C.A., 1987. Larval settlement of soft-sediment invertebrates: the spatial scales of pattern explained by active habitat selection and the emerging role of hydrodynamical processes. Oceanography and Marine Biology: an Annual Review, 25, 113-165.

  3. Carlisle, D.B., 1954. Styela mammiculata, a new species of ascidian from the Plymouth area. Journal of the Marine Biological Association of the United Kingdom, 33, 329-334.
  4. Chia, F., Buckland-Nicks, J. & Young, C.M., 1984. Locomotion of marine invertebrate larvae: a review. Canadian Journal of Zoology, 62, 1205-1222.

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  10. Eno, N.C., Clark, R.A. & Sanderson, W.G. (ed.) 1997. Non-native marine species in British waters: a review and directory. Peterborough: Joint Nature Conservation Committee.
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Citation

This review can be cited as:

Budd, G.C. 2002. Suberites spp. and other sponges with solitary ascidians on very sheltered 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/94

Last Updated: 10/05/2002