Molgula manhattensis and Polycarpa spp. with erect sponges on tide-swept moderately exposed circalittoral rock

31-05-2002
Researched byDr Keith Hiscock Refereed byThis information is not refereed.
EUNIS Code EUNIS Name

Summary

UK and Ireland classification

EUNIS 2008
EUNIS 2006
JNCC 2004
1997 Biotope

Description

This biotope occurs in the shallower reaches of the circalittoral (upper and lower) at depths of around 8 to 13 m with the main ascidian cover of Molgula manhattensis with some Polycarpa pomaria and a wide variety of other ascidians mixed in. Sponge species associated with this biotope include Tethya, Cliona, Stelligera rigida, Stelligera stuposa, Raspailia ramosa, Esperiopsis, Hemimycale and Dysidea. There are also several records with Axinella dissimilis and Axinella infundibuliformis. Nemertesia antennina occurs at most sites, also with Alcyonium digitatum and Actinothoe. Flustra is common in all these ascidian biotopes, but Chartella is only found in this one. Red algae associated with the upper circalittoral occur sporadically - more an artefact of the way in which the habitat records have been split. This biotope has some parallels with the erect sponge biotopes (e.g. MCR.ErSPbolSH), although it appears to be far siltier at most sites. (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 south-west England and west Wales and off the coast of Kent in south-east England.

Depth range

-

Additional information

The main characteristic of this biotope is the dominance of rock by ascidians. However, the associated species are ones that are found in a wide range of biotopes.

Listed By

Further information sources

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JNCC

Habitat review

Ecology

Ecological and functional relationships

Conspicuous members of the community include active and passive suspension feeders that compete intensely for space. The conspicuous members of the community provide substratum for attached bryozoans and hydroids and microhabitats for amphipods, worms and small crustaceans that are most likely scavengers. Apart from competition for space, there is little interaction between members of the community.

Seasonal and longer term change

The most likely seasonal change in this community will be the occurrence of annual algae and the growth of new fronds in perennial algae where the community occurs at shallow depths. Some members of the community, such as the often dominant ascidians Molgula manhattensis and most likely Polycarpa spp and Distomus variolosus, settle and grow rapidly and may also be lost in, for instance, storm events thus freeing space for settlement by other species. Many of the more sparsely distributed species such as the branching sponges are believed to be long-lived and slow growing. For instance, Hiscock (1994) records growth rates of less than 1 mm a year in the branching sponge Axinella dissimilis that can grow to 20 cm tall.

Habitat structure and complexity

Productivity

The organisms found in this biotope are secondary producers and no information has been found on levels of productivity.

Recruitment processes

Recruitment is predominantly from planktonic propagules.

Time for community to reach maturity

The dominant species in the community (the ascidians) are likely to colonize and grow very quickly (establishment within one year) if propagules are present at the time that bare rock is available. Some of the associated species (for instance, Nemertesia spp., Alcyonium digitatum, Pomatoceros triqueter, other ascidians) will colonize and grow within a few years. However, some of the species associated with the community most likely reproduce and settle infrequently and are slow growing (especially cushion and branching sponges). Little evidence is available for the longevity and growth of these sponges although Hiscock (1994) observes that Axinella dissimilis has a growth rate of less than 1 mm a year.

Additional information

No additional information.

Preferences & Distribution

Recorded distribution in Britain and IrelandRecorded in south-west England and west Wales and off the coast of Kent in south-east England.

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients No information found
Salinity
Physiographic
Biological Zone
Substratum
Tidal
Wave
Other preferences

Additional Information

The biotope is present on reef habitats and usually found on upward facing rock in the circalittoral. Whilst the biotope appears to be predominantly found in south-west Britain, that may be a result of the preference of the biotopes for harbours. There is nothing in the biology of component species to suggest that they are restricted to warmer waters in Britain and Ireland.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

Additional information

The Marine Nature Conservation Review (JNCC, 1999) recorded a total of 512 taxa from examples of this biotope including some species groups that would have been identified to species elsewhere.

Sensitivity reviewHow is sensitivity assessed?

Explanation

Molgula manhattensis and similar ascidians including Polycarpa spp. are dominant in the biotope and, without them, the biotope would not be recognised. The range of other animal species present in the biotope is large but the most abundant species appear to be fast growing species that most likely settle readily when space becomes available (for instance after storms have destroyed existing but old populations) and would recover rapidly following an impact. Examples of those species have been included to represent sensitivity. However, many of the species listed as characteristic of the biotope, especially the branching and cushion sponges, are slow growing and recruit infrequently. There is very little literature on those species that are believed to be long-lived and slow growing but, wherever information is known, it has been used in assessments.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingAlcyonium digitatumDead man's fingers
Key structuralMolgula manhattensisSea grapes
Important characterizingNemertesia ramosaA hydroid
Important characterizingUrticina felinaDahlia anemone

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Moderate Moderate Major decline High
Removal of the substratum will result in loss of the community. Therefore, an intolerance of high has been recorded.
Recoverability will depend on recruitment from adjacent or nearby populations and may take many years (see additional information below).
Intermediate High Low Minor decline Moderate
The biotope occurs in habitats that are silted and so are likely to be subject to cover by silt from time-to-time. The dominant ascidians should be capable of expanding their siphons to an extent and possibly clearing a passage through silt. Nevertheless, some mortality may occur in the dominant species and in some associated species. Large epifauna such as Alcyonium digitatum, Nemertesia antennina, large branching or cushion sponges and anemones (e.g. Urticina felina) are unlikely to be adversely affected by smothering with 5cm of sediment. The species that are believed to be long-lived and slow growing (branching sponges especially) are likely to protrude above the sediment or have efficient mucus cleaning systems. Recoverability will depend on recruitment from survivors, from adjacent or nearby population and may take many years to be complete (see additional information below).
Recoverability relates to the species that form a layer over the rock and which are likely to recolonize rapidly and grow quickly. Smothering by impermeable material will have a greater effect.
Low Very high Very Low No change Low
The biotope occurs in locations (for instance at the entrances to harbours and estuaries) where suspended sediment levels are often high. Increased suspended sediment concentrations may clog suspension feeding apparatus. However, production of mucus in hydroids, sponges and other species is likely to clear deposited silt whilst Molgula manhattensis seems well able to cope with increased level of suspended sediment being ingested (Naranjo et al., 1996). Some loss of condition may occur and an overall biotope intolerance of low has been recorded.

Recovery of epifaunal species is likely to be rapid once the prior conditions return.
Tolerant Moderate Not sensitive* Major decline Moderate
A decrease in suspended sediment levels may lead to reduction in food supply as some will be associated with silt. However, the energy expenditure in clearing silt (production of mucus, unclogging of feeding nets) will be advantageous to organisms in the biotope. Overall, there will be favourable and adverse effects of decrease in turbidity and not sensitive is indicated.
Not relevant Not relevant Not relevant Not relevant Low
Molgula manhattensis was assessed as intermediate intolerance to desiccation (see review). Subtidal epifaunal bryozoans, hydroids, ascidians and sponges are likely to be highly intolerant of desiccation. However, this biotope is subtidal and circalittoral and is unlikely to be exposed to the air. The shallower water extent of this biotope may be exposed for short periods during on extreme low water tides. However, overall this factor is not relevant.
Not relevant Not relevant Not relevant Not relevant Low
Subtidal epifaunal bryozoans, hydroids, ascidians and sponges are likely to be highly intolerant of desiccation resulting from increased emergence. However, this biotope is subtidal and circalittoral and is unlikely to be exposed to the air. The shallower water extent of this biotope may be exposed for short periods during on extreme low water tides. However, overall this factor is not relevant.
Not sensitive* Not relevant
The biotope is subtidal and, since it does not occur on the shore, not relevant is appropriate.
High Moderate Moderate Decline Low
The biotope occurs in strong or moderately strong tidal currents and many of the sponges and hydroids present in the biotope are found in stronger currents. Ascidians, which are the most important characterizing species, may be adversely affected by increase in water flow. High water flow rates may be detrimental to feeding ability and posture. Hiscock (1983) found that, for the solitary ascidian Ascidia mentula, siphons closed when the current velocity rose above about 15 cm/sec. It seems likely therefore that some reduction in feeding would occur with increased water flow rate although that would result in slower growth and loss of condition but not mortality. Tidal currents alone are not believed to result in detachment of the main species present in this biotope. However, if tidal flow increased from Moderate or Strong to Very Strong (>6 knots) for one year, there is a possibility that encrusting sponges such as Halichondria panicea and Esperiopsis fucorum would smother the ascidians and the biotope would perhaps become ECR.BalHpan (Balanus crenatus, Halichondria panicea and Alcyonidium diaphanum on extremely tide-swept sheltered circalittoral rock). The biotope MCR.MolPol would therefore be lost and intolerance would be high. ECR.BalHpan has a lower species diversity. On return to previous conditions, the species requiring strong currents would take some time to regress and settlement of lost characterizing species is likely to be within a few years so that a recoverability of moderate is likely
Tolerant* Not sensitive Rise Moderate
In the absence of wave action, water flow is likely to be very important in preventing siltation and stagnation and in bringing food. The species in this biotope require a reasonable water flow rate in order to ensure sufficient food availability and oxygen supply. However, one of the characterizing ascidians at least, Molgula manhattensis, is frequently found in areas with minimal water exchange and renewal such as harbours, marinas and docks. Sagasti et al. (2000) demonstrated that Molgula manhattensis can withstand episodes of hypoxia and so, even if stagnation occurs for short periods, mortality is unlikely to occur. Many of the sessile species in the biotope (mainly sponges and ascidians) are active suspension feeders and do not rely on external currents to bring them food. Some of the species in the biotopes, especially hydroids, may suffer from shortage of food and lose condition. However, overall, the biotope is expected to persist albeit with the loss of some species. On resumption of normal energy expenditure and feeding, condition should be restored rapidly.
Tolerant Not relevant Not relevant No change Low
Species that characterize the biotope are widely distributed in the north Atlantic. However, the biotope appears to be restricted to Wales and south-west England and to Kent. If temperature rather than geographical location is important, then increased temperature would be expected to result in an expansion of the distribution of the biotope northwards. However, since the key characterizing species including dominant species have a wide geographical distribution in Britain and Ireland, it seems that some features of habitat and physical environmental conditions are important in determining distribution. Intolerance is, therefore, indicated as not sensitive but with a low confidence.
Tolerant Not sensitive* No change Low
Species that characterize the biotope are widely distributed in the north Atlantic. However, the biotope appears to be restricted to Wales and south-west England and to Kent. If temperature rather than geographical location is important, then decreased temperature would be expected to result in an reduction of the distribution of the biotope northwards. However, since the key characterizing species including dominant species have a wide geographical distribution in Britain and Ireland, it seems that some features of habitat and physical environmental conditions are important in determining distribution. Intolerance is therefore indicated as not sensitive but with a low confidence.
Low Very high Very Low No change Moderate
The biotope occurs in harbours and the entrances to estuaries where turbidity may increase to high levels. Some clogging of feeding structures in many of the species that characterize this biotope may occur as a result of increased turbidity due to increased suspended sediment levels. Nevertheless, the likely outcome of clogging will be of decreased feeding and loss of condition.
Intermediate Very high Low Minor decline Low
The majority of species in the biotope are suspension feeders and, although there may be some reliance on the organic material associated with increased turbidity for nutrition, the reduced need for energy expenditure to clear silt may be beneficial. Decreased turbidity will result in increased light penetration and algal growth which may adversely affect the biotope at its shallowest extent. There may be some reduction in the shallow-water penetration of the biotope. However, it seems most likely that, at the level of the benchmark, species characteristic of the biotope will persist albeit overgrown by algae. Loss of some species characteristic of the biotope may occur but the biotope will still be recognised where algae colonize. Recoverability will be rapid as characterizing species will persist.
High High Moderate Decline Moderate
This biotope has been reported from areas that are exposed or moderately exposed to wave action, whereas Molgula manhattensis has been mainly reported from wave sheltered habitats and may, therefore, be intolerant of increase in wave exposure together with some other species that characterize this biotope. Should the wave exposure increase from exposed to extremely exposed, Molgula manhattensis and other ascidians in the biotope may be removed from examples of the biotope in shallow depths where wave action is most severe. Similarly, a proportion of the associated epifaunal species are also likely to be removed, being replaced by more wave tolerant species such as Alcyonium digitatum and erect bryozoans. There is a possibility that the biotope will change to one that is not characterized by solitary ascidians such as ECR.Alc.MaS (Alcyonium digitatum with massive sponges and Nemertesia antennina on moderately tide-swept exposed circalittoral rock). Therefore, an intolerance of high has been recorded. Recovery will depend on space being available for settlement but, bearing in mind the rapidity with which Molgula manhattensis at least settles and grows, a recoverability of high is suggested (see additional information below).
Tolerant* Not sensitive Rise Moderate
This biotope has been reported from areas of moderate wave exposure, whereas Molgula manhattensis has been reported from wave exposed to extremely wave sheltered habitats and is therefore relatively insensitive to changes in wave exposure within this range. Overall, the distribution of this biotope seems to be mainly influenced by tidal stream strength and to reflect the presence of silty conditions. A decrease in wave exposure, e.g. from moderately exposed to very sheltered is unlikely to increase siltation as tidal flow is the most important form of water movement to this biotope. However, the species composition of the epifauna is likely to change, favouring species tolerant of reduced wave action or water movement. Indeed, area subject to moderate tidal flow but little wave action are often much richer in species. Overall, the biotope is likely to remain as MCR.MolPol and not sensitive* has been recorded to reflect the possibility that the species composition may increase in richness and some of the more scarce species such as Axinella dissimilisand Axinella infundibuliformis might be favoured by calmer conditions. Recoverability has been recorded as not relevant as the biotope is expected to become more species rich and remain MCR.MolPol.
Tolerant Not relevant Not relevant Not relevant High
Few species within the biotope are likely to respond to noise or vibration at the benchmark level.
Tolerant Not relevant Not relevant Not relevant High
Few, if any, species within the biotope have a significant visual acuity, and are unlikely to respond to visual disturbance at the benchmark level.
Intermediate Moderate Moderate Major decline Moderate
It is likely that physical disturbance at the benchmark level would remove individuals from their substratum and damage others. Disturbance of the cohesive groups of individuals may strip away tracts of the biotope or create gaps or 'edges' that may allow peeling away of the ascidians by tidal streams or wave action.

Erect epifaunal species are particularly vulnerable to physical disturbance. Sponges, hydroids and bryozoans are likely to be uprooted or damaged by bottom trawling or dredging and some bryozoans repair damage slowly (Holt et al., 1995). Veale et al. (2000) reported that the abundance, biomass and production of epifaunal assemblages decreased with increasing fishing effort. The characteristic and dominant species in the biotope, the ascidians, are likely to colonize rapidly, other species may settle and establish, preventing re-establishment of the biotope. More importantly, some species in the biotope, for instance, Axinella dissimilisand Axinella infundibuliformis are long-lived and slow growing and would not be replaced rapidly.

Overall, physical disturbance at the benchmark level may remove or damage a proportion of the ascidian bed and its associated epifauna. Therefore, an intolerance of intermediate has been recorded. For recoverability, see additional information below.
High Moderate Moderate Major decline High
Most of the characteristic species in this biotope are sessile and will not reattach after displacement so that the biotope will not recover through re-attachment and new settlement will be needed.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Intermediate Moderate Moderate Decline Low
intolerance of component species of the biotope ranges greatly. One dominant species, Molgula manhattensis, is most likely tolerant of synthetic chemical pesticides. Weis & Weis (1992) found that the ascidian was commonly present, although in small numbers, on wood treated with chromated arsenate. In mesocosm experiments, Flemer et al. (1995) studied the effect of the pesticide endosulfan and found that the average abundance of Molgula manhattensis increased with increasing concentration of the pesticide possibly as a result of reduced competition with more susceptible organisms. The high abundance of the species in harbours where levels of tributyl tin are or were likely to be high also suggests tolerance. Molgula manhattensis may benefit from tolerance to synthetic pollutants by occupying space that would have been colonized by less tolerant species. On the other hand, Rees et al. (2001) reported that the abundance of epifauna (including bryozoans) had increased in the Crouch estuary in the five years since TBT was banned from use on small vessels. This last report suggests that bryozoans and ascidians may be at least inhibited by the presence of TBT. Hoare & Hiscock (1974) suggested that Polyzoa (Bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay, Anglesey and reported that Flustra foliacea did not occur less than 165m from the effluent source. Smith (1968) reported dead colonies of Alcyonium digitatumat a depth of 16m in the locality of Sennen Cove (Cornwall) resulting from the offshore spread and toxic effect of detergents sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill. At the level of the benchmark, it might be expected that some species would be adversely affected but that the biotope would persist albeit in a possibly impoverished form. On removal of contaminants, recovery to full species richness would depend on the individual tolerance of species and whether any long-lived and slow growing ones had been killed. Intolerance is assessed as intermediate but with low confidence. For recoverability, see additional information. Since information has not been found for species such as Axinella dissimilisand Axinella infundibuliformis, confidence in assessing recoverability is low.
Heavy metal contamination
Intermediate Moderate Moderate Minor decline Very low
Very little information has been found regarding the effects of heavy metals on species in the biotope. One of the dominant species, Molgula manhattensis, commonly lives in the entrance to harbours and estuaries so that it might be expected to be tolerant of heavy metals. Bryozoans are common members of the fouling community, and amongst those organisms most resistant to anti-fouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1979; Holt et al, 1995). Amongst the large number of species that occur in this biotope, some at least are likely to be intolerant of heavy metal pollution and so an intolerance of intermediate is suggested by with a very low confidence in the absence of evidence. The biotope will still be recognised and recoverability (see additional information below) refers to species richness in the biotope.
Hydrocarbon contamination
Intermediate High Low Minor decline Low
Subtidal populations are protected from the direct effects of oil spills by their depth but are likely to be exposed to the water soluble fraction of oils and hydrocarbons, or hydrocarbons adsorbed onto particulates. During the Torrey Canyon oil spill, Urticina felina were found to be alive even in intertidal areas (Smith, 1968). However, Smith (1968) reported dead colonies of Alcyonium digitatum at a depth of 16m in the locality of Sennen Cove (Cornwall) resulting from the offshore spread and toxic effect of detergents sprayed along the shoreline to disperse oil from the Torrey Cannon tanker spill (see synthetic chemicals). During the Sea Empress oil spill, surveys of the open Pembrokeshire coast (where this biotope commonly occurs) found no signs of adverse effects (SEEEC, 1998). Overall, because the biotope is circalittoral and because of lack of evidence of impacts from spills, an intolerance of intermediate is suggested indicating that some stress and possibly loss of intolerant crustaceans may occur. Recoverability is suggested to be high as the most intolerant species would most likely recolonize rapidly.
Radionuclide contamination
No information Not relevant No information Insufficient
information
Not relevant
No information found.
Changes in nutrient levels
Tolerant Not relevant Not relevant No change Moderate
Moderate increases in nutrient levels may benefit suspension feeding members of the community by increasing macroalgal and phytoplankton productivity, increasing the proportion of organic particulates and hence increasing the food supply. Similarly, increased availability of organic particulates may benefit the community. Nutrient enrichment may however lead to increased turbidity and decreased oxygen levels due to bacterial decomposition of organic material (see below). The species composition of the epifaunal community may also change as a result. However, suspension feeders would probably benefit from increased nutrients at the benchmark level.
Not relevant Not relevant Not relevant Not relevant High
The biotope is found on the open coast in full salinity and so increase in salinity is considered not relevant.
High Moderate Intermediate Major decline Moderate
The biotope is found on the open coast and includes some species such as sponges, anthozoans and some ascidians that might be intolerant of decrease in salinity. However, others including the dominant species are tolerant of decreased salinity. Van Name (1945; quoted in Kott, 1985), notes that Molgula manhattensis occurs in salinities equivalent to 20 to 36 psu whilst Hartmeyer (1923) quoted in Tokioka & Kado (1972) records Molgula manhattensis in brackish (16-30 psu) water of the Belt Sea. A fall in salinity from full to reduced would not therefore be expected to have an adverse effect on Molgula manhattensis but would on a significant number of other species in the biotope. Since the biotope is recorded only from open coast locations or the entrance to enclosed areas, it is expected that the biotope would not survive in low salinity conditions or at least would be greatly impoverished. Therefore an intolerance of high is recorded. For recoverability, see additional information below.
High Moderate Moderate Major decline Low
The biotope occurs on the open coast where oxygen is unlikely to be depleted and some species might be expected to be intolerant of low oxygen. For instance, Alcyonium digitatum mainly inhabits environments in which the oxygen concentration usually exceeds 5 ml l-1 and respiration is aerobic. Assimilation of oxygen occurs simply by diffusion through the epidermis of exposed tissues and transport to tissues is facilitated by hydroplasmic flow and ciliary activity (Hickson, 1901). However, Sagasti et al. (2000) demonstrated that Molgula manhattensis can withstand episodes of hypoxia and so intolerance is likely to be low amounting to some loss in condition. Some of the cushion sponges occur in Abereiddy Quarry in Pembrokeshire near to a zone affected by severe de-oxygenation (Hiscock & Hoare, 1973) and might be able to survive brief episodes of low oxygen conditions. Overall, in conditions of low oxygen, several species in the biotope may die and, whilst the dominant Molgula manhattensis might survive, it would cease to be that biotope. For recoverability, see additional Information below.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information Not relevant No information Not relevant Not relevant
Microbial pathogens are not known to have a severe adverse effect (causing extensive mortality) on any of the characterizing species but, in the absence of information, insufficient information is recorded.
Not relevant Not relevant Not relevant No change Moderate
There are no non-native species known to colonize this biotope although the author of this review speculates that Molgula manhattensis may have been a very early introduction to north-western Europe (see the species review) .
Not relevant Not relevant Not relevant Not relevant High
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 High

Additional information

Recoverability
Whilst the dominant species in the community (the ascidians) are likely to recolonize and grow very quickly (re-establishment within one year) if propagules are present at the time that bare rock is available, a different dominant species (for instance, Musculus discors) may settle and dominate the area for at least many years transforming the biotope to a different one. Some of the associated species (for instance, Nemertesia spp., Alcyonium digitatum, Pomatoceros triqueter, other ascidians) will colonize and grow within a few years. However, some of the species associated with the community most likely reproduce and settle infrequently and are slow growing (especially cushion and branching sponges). Little evidence is available for the longevity and growth of these sponges although Hiscock (1994) observes that Axinella dissimilis has a growth rate of less than 1 mm a year. Therefore, although recoverability to the same biotope is assessed as moderate (5-10 years) following a catastrophic event, recovery of full species richness may take much longer and will be very low.

Importance review

Policy/Legislation

- no data -

Exploitation

No exploitation of this biotope is known to take place.

Additional information

Whilst the majority of species in this biotope are likely to be robust and re-colonize quickly, some are long-lived, slow growing and slow to recruit.

Bibliography

  1. Connor, D.W., Dalkin, M.J., Hill, T.O., Holt, R.H.F. & Sanderson, W.G., 1997a. Marine biotope classification for Britain and Ireland. Vol. 2. Sublittoral biotopes. Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06., Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06.
  2. Davies, C.E. & Moss, D., 1998. European Union Nature Information System (EUNIS) Habitat Classification. Report to European Topic Centre on Nature Conservation from the Institute of Terrestrial Ecology, Monks Wood, Cambridgeshire. [Final draft with further revisions to marine habitats.], Brussels: European Environment Agency.
  3. Flemer, D.A., Stanley, R.S., Ruth, B.F., Bundrick, C.M., Moody, P.H. & Moore, J.C. 1995. Recolonization of estuarine organisms - effects of microcosm size and pesticides. Hydrobiologia, 304, 85-101.
  4. Hiscock, K., 1983. Water movement. In Sublittoral ecology. The ecology of shallow sublittoral benthos (ed. R. Earll & D.G. Erwin), pp. 58-96. Oxford: Clarendon Press.
  5. Hiscock, K., 1994. Marine communities at Lundy - origins, longevity and change. Biological Journal of the Linnean Society 51, 183-188.
  6. Hoare, R. & Hiscock, K., 1974. An ecological survey of the rocky coast adjacent to the effluent of a bromine extraction plant. Estuarine and Coastal Marine Science, 2 (4), 329-348.

  7. Holt, T.J., Jones, D.R., Hawkins, S.J. & Hartnoll, R.G., 1995. The sensitivity of marine communities to man induced change - a scoping report. Countryside Council for Wales, Bangor, Contract Science Report, no. 65.
  8. 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,
  9. Kott, P., 1985. The Australian Ascidiacea. Part I, Phlebobranchia and Stolidobranchia. Memoirs of the Queensland Museum, 23, 1-440.
  10. Magorrian, B.H. & Service, M., 1998. Analysis of underwater visual data to identify the impact of physical disturbance on horse mussel (Modiolus modiolus) beds. Marine Pollution Bulletin, 36, 354-359.
  11. Naranjo, S.A., Carballo, J.L., & Garcia-Gomez, J.C., 1996. Effects of environmental stress on ascidian populations in Algeciras Bay (southern Spain). Possible marine bioindicators? Marine Ecology Progress Series, 144 (1), 119-131.

  12. Rees, H.L., Waldock, R., Matthiessen, P. & Pendle, M.A., 2001. Improvements in the epifauna of the Crouch estuary (United Kingdom) following a decline in TBT concentrations. Marine Pollution Bulletin, 42, 137-144.
  13. Sagasti, A., Schaffner, L.C. & Duffy, J.E., 2000. Epifaunal communities thrive in an estuary with hypoxic episodes. Estuaries, 23, 474-487.
  14. SEEEC (Sea Empress Environmental Evaluation Committee), 1998. The environmental impact of the Sea Empress oil spill. Final Report of the Sea Empress Environmental Evaluation Committee, 135 pp., London: HMSO.
  15. Service, M., 1998. Recovery of benthic communities in Strangford Lough following changes in fishing practice. ICES Council Meeting Paper, CM 1998/V.6, 13pp., Copenhagen: International Council for the Exploration of the Sea (ICES).
  16. Smith, J.E. (ed.), 1968. 'Torrey Canyon'. Pollution and marine life. Cambridge: Cambridge University Press.
  17. Soule, D.F. & Soule, J.D., 1979. Bryozoa (Ectoprocta). In Pollution ecology of estuarine invertebrates (ed. C.W. Hart & S.L.H. Fuller), pp. 35-76.
  18. Tokioka, T. & Kado, Y., 1972. The occurrence of Molgula manhattensis (deKay) in brackish water near Hiroshima, Japan. Publications of the Seto Marine Biological Laboratory, Kyoto University, 21, 21-29.
  19. Veale, L.O., Hill, A.S., Hawkins, S.J. & Brand, A.R., 2000. Effects of long term physical disturbance by scallop fishing on subtidal epifaunal assemblages and habitats. Marine Biology, 137, 325-337.
  20. Weis, J.S. & Weis, P., 1992. Construction materials in estuaries: reduction in the epibiotic community on chromated copper arsenate. Marine Ecology Progress Series, 83, 45-53.

Citation

This review can be cited as:

Hiscock, K. 2002. Molgula manhattensis and Polycarpa spp. with erect sponges on tide-swept moderately 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/305

Last Updated: 31/05/2002