Crepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment

17-08-2001
Researched byWill Rayment Refereed byThis information is not refereed.
EUNIS CodeA5.422 EUNIS NameCrepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment

Summary

UK and Ireland classification

EUNIS 2008A5.422Crepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment
EUNIS 2006A5.422Crepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment
JNCC 2004SS.SMx.SMxVS.CreMedCrepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment
1997 BiotopeSS.IMX.EstMx.CreAphCrepidula fornicata and Aphelochaeta marioni in variable salinity infralittoral mixed sediment

Description

Variable salinity mixed sediment characterized by the slipper limpet Crepidula fornicata and the polychaete Aphelochaeta marioni. Shell debris and cobbles are colonized by the ascidians Ascidiella aspersa, Ascidiella scabra, Molgula sp. and Dendrodoa grossularia (the ascidians may not be recorded adequately by remote infaunal survey techniques). This biotope occurs in the lower estuary where currents allow a stable environment to develop. It is associated with oyster beds and relict oyster beds, (IMX.Ost), in southern England and Wales, separated from these by the superabundance of Crepidula fornicata. It may be found adjacent to or in conjunction with IMU.AphTub, again separated by the abundance of Crepidula fornicata and its sediment characteristics. It may be associated with IMX.VsenMtru and possibly forms a component of SCR.Aasp. (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

IMX.CreAph has been recorded from sheltered estuarine environments in south east England, southern England and south west Wales. There are no records from Ireland.

Depth range

-

Additional information

-

Listed By

Further information sources

Search on:

JNCC

Habitat review

Ecology

Ecological and functional relationships

  • This biotope occurs in the lower estuary where the hydrodynamic regime allows a suitable environment to develop. The presence of a suitable substratum is probably the primary structuring force, rather than the interspecific relationships. Mixed sediment provides a stable substratum for the epifauna such as Crepidula fornicata, Mytilus edulis and ascidians, and soft sediment for the infaunal annelids, crustaceans and bivalves.
  • Crepidula fornicata competes for nutrients with other suspension feeders, e.g. Mytilus edulis and ascidians. Where Crepidula fornicata is very abundant, trophic competition contributes to the competitive exclusion of commercially valuable species such as Ostrea edulis (Fretter & Graham, 1981; Blanchard, 1997). The faeces and pseudo-faeces produced by Crepidula fornicata contribute to the sediment requirements of the infauna (see 'habitat complexity') and also provide a food source for the deposit feeders, such as Aphelochaeta marioni.
  • Carcinus maenas is the most important predator in this biotope. It has been shown to significantly reduce the density of Eteone longa, Aphelochaeta marioni, Tubificoides sp. and Corophium volutator (Reise, 1985).
  • Nephtys hombergi and Eteone longa are active carnivorous annelids that operate at the trophic level below Carcinus maenas (Reise, 1985). They predate the smaller annelids, such as Exogone naidina, and crustaceans, such as Corophium volutator and Cumacea sp.
  • The amphipod, Corophium volutator, and the infaunal annelid species in this biotope probably interfere strongly with each other. Adult worms probably reduce amphipod numbers by disturbing their burrows, while high densities of Corophium volutator can prevent establishment of worms by consuming larvae and juveniles (Olafsson & Persson, 1986).

Seasonal and longer term change

Seasonal changes occur in the abundance of the fauna due to seasonal recruitment processes. The early reproductive period of Polydora ciliata often enables the species to be the first to colonize available substrata (Green, 1983). The settling of the first generation in April is followed by the accumulation and active fixing of mud continuously up to a peak during the month of May, when the substrata is covered with the thickest layer of Polydora mud. The following generations do not produce a heavy settlement due to interspecific competition and heavy mortality of the larvae (Daro & Polk, 1973). Variation in abundance is very pronounced in the polychaete Aphelochaeta marioni. For example, in the Wadden Sea, peak abundance occurred in January (71,200 individuals per m²) and minimum abundance occurred in July (22,500 individuals per m²) following maximum spawning activity between May and July (Farke, 1979). However, the spawning period varies according to environmental conditions and so peak abundances will not necessarily occur at the same time each year. For example, Gibbs (1971) reported Aphelochaeta marioni spawning in late autumn in Stonehouse Pool, Plymouth Sound. The adult densities of the bivalve Abra alba typically fluctuate widely from year to year due to variation in recruitment success (Rees & Dare, 1993). The other annelids and ascidians in the biotope are likely to exhibit seasonal variations in abundance, but, again, different areas have local spawning and recruitment characteristics. Crepidula fornicata is a relatively long lived species (8-9 years longevity), suffers low predation and therefore would not be expected to vary greatly in abundance through the year.
One of the key factors affecting benthic habitats is disturbance, which in shallow subtidal habitats increases in winter due to weather conditions. Storms may cause dramatic changes in distribution of macro-infauna by washing out dominant species, opening the sediment to recolonization by adults and/or available spat/larvae (Eagle, 1975; Rees et al., 1976; Hall, 1994) and by reducing success of recruitment by newly settled spat or larvae (see Hall, 1994 for review). For example, during winter gales along the North Wales coast large numbers of Abra alba were cast ashore and over winter survival rate was as low as 7% in the more exposed locations, whilst the survival rates of the polychaetes Eteone longa and Nephtys hombergi were 29% and 22% respectively (Rees et al., 1976). Hayward & Ryland (1995) reported that Crepidula fornicata is sensitive to movement of the substratum during periods of increased wave action and is often found cast ashore following storms. Soft bodied epifauna, such as ascidians, are likely to be very sensitive to storm damage and will probably suffer high mortality during winter storms. Rapid recolonization occurs in summer and therefore abundances are likely to vary considerably due to physical disturbance.

Habitat structure and complexity

The mixed sediment in this biotope is the important structural component, providing the complexity required by the associated community. Epifauna are attached to the cobbles and shell debris and infauna burrow in the soft underlying sediment. Sediment deposition, and therefore the spatial extent of the biotope, is initially dictated by the physiography and underlying geology coupled with the hydrodynamic regime (Elliot et al., 1998). However, once Crepidula fornicata becomes established, it strongly influences the nature of the sediment. Slipper limpets typically attach to a member of the same species, forming chains, which can comprise of up to 12 individuals. In suitable conditions, Crepidula fornicata can reach very high densities; up to 4770 individuals per m2 (de Montaduin & Sauriau, 1999). The resultant shell debris provides a hard substratum for attachment of juvenile Crepidula fornicata, hence perpetuating the population, and also for other epifauna, such as ascidians. Crepidula fornicata also has a major effect on the biotope through the deposition of faeces and pseudofaeces. The deposited sediment can smother other suspension feeders and render the substratum unsuitable for larval settlement (Fretter & Graham, 1981; Blanchard, 1997). In this way, settlement of Crepidula fornicata can initiate a shift away from the oyster beds biotope (IMX.Ost) towards IMX.CreAph. Indeed, this biotope often occurs on relict oyster beds. Conversely, the deposition of faeces and pseudofaeces by Crepidula fornicata can render the substratum more suitable for infauna and deposit feeders (Barnes & Hughes, 1992).

Productivity

Primary production in this biotope comes from benthic microalgae (microphytobenthos e.g. diatoms, flagellates and euglenoides) and water column phytoplankton. Photosynthetic processes may be light limited due to the turbidity of the water (Elliot et al., 1998) and hence primary production is usually low. Large allochthonous inputs of nutrients, sediment and organic matter come from the sea and from discharges of river water containing both naturally derived nutrients and anthropogenic nutrients (e.g. sewage) (Elliot et al., 1998). Secondary productivity in this biotope can therefore be very high and is reflected by the very large abundances obtained by the characterizing species. Crepidula fornicata, for example, can reach densities of 4770 individuals per m² (de Montaduin & Sauriau, 1999) and Aphelochaeta marioni of 108,000 individuals per m² (Gibbs, 1969).

Recruitment processes

Crepidula fornicata is a protandrous hermaphrodite. This means that the animals start their lives as males and then subsequently may change sex and develop into females. Although breeding can occur between February and October, peak activity occurs in May and June when 80-90% of females spawn. Most females spawn twice in a year, apparently after neap tides. Females can lay around 11,000 eggs at a time contained in up to 50 egg capsules (Deslou-Paoli & Heral, 1986). Laboratory experiments by Thain (1984) revealed that, following incubation, approximately 4000 larvae were released per female. Incubation of the eggs takes 2-4 weeks followed by a planktotrophic larval phase lasting 4-5 weeks (Fretter & Graham, 1981; Thouzeau, 1991). Due to the length of the planktonic phase, the potential for dispersal is high. Recruitment will be determined by the local hydrographic regime. For example, in sheltered bays the larvae may be entrapped and small scale eddies (e.g. over obstacles and inconsistencies in the surface of the substratum) may result in the concentration of larvae. The ability of Crepidula fornicata to disperse widely and colonize new areas is demonstrated by its spread through Europe following introduction from North America at the end of the 19th century (Fretter & Graham, 1981; Eno et al., 1997). The spat settle in isolation or on top of an established chain of Crepidula fornicata. Crepidula fornicata needs to be part of a chain in order to breed and therefore would be expected to settle preferentially where high densities of conspecifics already exist. High densities of suspension feeders and surface deposit feeders together with epibenthic predators and physical disturbance may result in high post settlement mortality rate of larvae and juveniles (Olafsson et al., 1994). Males reach sexual maturity 2 months after settlement (Fretter & Graham, 1981). If a male develops directly into a female, sexual maturity may be reached in 10 months (Nelson et al., 1983).
The lifecycle of Aphelochaeta marioni varies according to environmental conditions. In Stonehouse Pool, Plymouth Sound, Aphelochaeta marioni (studied as Tharyx marioni) spawned in October and November (Gibbs, 1971) whereas in the Wadden Sea, Netherlands, spawning occurred from May to July (Farke, 1979). The female spawns puddles of eggs onto the sediment surface adjacent to her burrow. Gibbs (1971) found that the number of eggs laid varied from 24-539 (mean=197) and was correlated with the female's number of genital segments, and hence, female size and age. The embryos develop lecithotrophically and hatch in about 10 days (Farke, 1979). Immediately after hatching, the juveniles dig into the sediment. Under stable conditions, juvenile Aphelochaeta marioni disperse by lateral burrowing (Farke, 1979). As there is no pelagic stage, dispersal and immigration to new areas must mainly occur during periods of erosion when animals are carried away from their habitat by water currents. At other times, recruitment must largely occur from local populations. Juvenile mortality is high (ca 10% per month) and most animals survive for less than a year (Farke, 1979). In the Wadden Sea, the majority of the cohort reached maturity and spawned at the end of their first year, although some slower developers did not spawn until the end of their second year (Farke, 1979). However, the population of Aphelochaeta marioni in Stonehouse Pool spawned for the first time at the end of the second year of life (Gibbs, 1971). There was no evidence of a major post-spawning mortality and it was suggested that individuals may survive to spawn over several years.
Most other macrofauna in the biotope breed several times in their life history (iteroparous) and are planktonic spawners producing large numbers of gametes. Dispersal potential is high. Overall recruitment is likely to be patchy and sporadic, with high spat fall occurring in areas devoid of adults, perhaps lost due to predation or storms.

Time for community to reach maturity

Cole & Hancock (1956) reported that following dredging of slipper limpets on estuarine oyster beds, it took up to 10 years for the species to reach pre-clearance population levels. The majority of the other species in the biotope are relatively short-lived and highly fecund and will probably reach mature community population levels rapidly. For example, ascidians exhibit annual episodic recruitment and are likely to achieve mature populations very quickly where suitable substrata and hydrographic conditions exist. The rapid recoverability of estuarine soft sediment infauna was reported by Hall & Harding (1997). Following suction dredging which resulted in 50% reduction in number of individuals of infauna, populations recovered to pre-dredging levels within 56 days. Therefore, assuming some colonization by Crepidula fornicata, a qualitative community would develop in a year or so, although recruitment to a mature community may take up to 10 years, taking account of the time taken for Crepidula fornicata to reach full abundance. It should be noted again that the IMX.CreAph biotope often occurs in association with declining or relict oyster beds and may be found in a transitional stage between IMX.Ost and IMX.CreAph.

Additional information

-

Preferences & Distribution

Recorded distribution in Britain and IrelandIMX.CreAph has been recorded from sheltered estuarine environments in south east England, southern England and south west Wales. There are no records from Ireland.

Habitat preferences

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

Additional Information

Both Crepidula fornicata and Aphelochaeta marioni, the species characterizing the biotope, are tolerant of a wide range of environmental conditions. For example, they are euryhaline, are found on a variety of substrata and tolerate variations in turbidity. However, they both achieve peak abundances in areas of muddy or mixed muddy sediments such as occur in the hydrographic regime of sheltered bays and lower estuaries (Gibbs, 1969; de Montaduin & Sauriau, 1999). The distribution of the biotope is probably limited by the geographic range of Crepidula fornicata, which only occurs in the southern half of the British Isles.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

-

Additional information

Sensitivity reviewHow is sensitivity assessed?

Explanation

Crepidula fornicata and Aphelochaeta marioni are both species which define this biotope. The loss of these species would result in the loss of the biotope. However, the loss of either of the species would be unlikely to have significant knock on effects for the rest of the community and therefore the species are ranked as 'important characterizing' not 'key'.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingAphelochaeta marioniA bristleworm
Important characterizingCrepidula fornicataSlipper limpet

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High High Moderate Major decline High
The majority of species in the biotope live either permanently attached to the substratum (epifauna) or buried in the underlying sediment (infauna). The physical removal of the substratum, e.g. as a result of channel dredging activities, would also remove the associated populations. Therefore, intolerance is recorded as high. For example, Ismail (1985) demonstrated that following suction dredging of the top few centimetres of sediment on oyster grounds in Delaware Bay, the Crepidula fornicata population was removed. Substratum loss is likely to result in the complete eradication of most species and therefore species richness in the biotope will experience major decline. Hall & Harding (1997) reported that following suction dredging in soft sediments, the species richness of infaunal communities was reduced by up to 30% and the numbers of individuals by up to 50%. Recoverability is recorded as high (see additional information below).
Low Very high Very Low Minor decline Low
The majority of species in the biotope live either infaunally or are capable of burrowing. They would be expected to tolerate an additional 5 cm layer of sediment and relocate to their preferred position. Aphelochaeta marioni, for example, deposit feeds at the surface by extending contractile palps from its burrow. The additional layer of sediment would result in a temporary cessation of feeding activity, and therefore growth and reproduction are likely to be compromised. However, Aphelochaeta marioni would be expected to quickly relocate to its favoured depth, with no mortality. The immobile epifauna in the biotope are likely to be more intolerant of smothering. Ascidians are active suspension feeders and rely on a through current of water for feeding and respiration. Smothering would be likely to cause severe inhibition of these activities and mortality would be expected to result within a few days. However, larger species such as Ascidiella aspersa would probably not be affected as they attach to protuberant surfaces and their siphons are a few centimetres clear of the sediment surface. Crepidula fornicata is also an active suspension feeder and it would be expected that the feeding and respiration structures would be susceptible to smothering. However, it has been demonstrated that Crepidula fornicata is capable of clearing its feeding structures at some energetic cost (Johnson, 1972). Furthermore, areas with large Crepidula fornicata populations do tend to become silted up through deposition of pseudofaeces, apparently with little effect on the species (Thouzeau et al., 2000) and the fact that Crepidula fornicata lives in chains of up to 12 individuals means that at least some of the chain would avoid the effects of smothering. Therefore, although there may be some energetic cost as a result of smothering, probably resulting in decreased growth and reproductive output, there is unlikely to be mortality.
Given the intolerance of the characterizing species, the overall intolerance for the biotope is recorded as low but there is likely to be a minor decline in species richness due to mortality of the smaller ascidian species. Once the infaunal species have relocated to the surface and feeding and respiration structures have been cleared, activity should return to normal and therefore a recoverability of very high is recorded.
Low Very high Very Low No change Moderate
The epifauna in the biotope are most likely to be affected by an increase in suspended sediment. Crepidula fornicata is an active suspension feeder, trapping food particles on a mucous sheet lying across the front surface of the gill filament. An increase in suspended sediment is therefore likely to interfere with the feeding and respiration structures. Johnson (1972) transplanted individual Crepidula fornicata to environments of varying turbidity and measured their shell growth rates. Growth rate was found to decrease as turbidity increased. These observations were verified in laboratory conditions by measuring water filtration rate at different turbidities. Filtration rate was found to decrease as turbidity increased with the greatest reduction in filtration occurring between 140-200 mg per litre. Decreased filtration rate was associated with increased production of pseudofaeces in order to keep the filtering mechanism clear of debris. Increased pseudofaeces production coupled with decreased food intake would lead to increased energy consumption that is likely to impair the survival of the species. The infauna and deposit feeders, such as Aphelochaeta marioni, are unlikely to be negatively affected by an increase in suspended sediment (Brenchley, 1981). An increased rate of siltation may result in an increase in food availability and therefore growth and reproduction may be enhanced. However, food availability would only increase if the additional suspended sediment contained a significant proportion of organic matter and the population would only be enhanced if food was previously limiting. Due to the intolerance of the suspension feeders, biotope intolerance is recorded as low. When suspended sediment returns to normal levels, feeding and respiration will return to normal and the only likely lag will be in reproductive output, i.e. it will take a period of time to replenish food reserves, during which reproductive output will not be at maximum levels. A recoverability of very high is therefore recorded.
Low Very high Not relevant No change Low
The majority of species in the biotope are either suspension feeders or deposit feeders and therefore rely on a supply of nutrients in the water column and at the sediment surface. A decrease in the suspended sediment would result in decreased food availability for suspension feeders. It would also result in a decreased rate of deposition on the substratum surface and therefore a reduction in food availability for deposit feeders. This would be likely to impair growth and reproduction. The benchmark states that this change would occur for one month and therefore would be unlikely to cause mortality. An intolerance of low is therefore recorded. As soon as suspended sediment levels increased, feeding activity would return to normal and hence recovery is recorded as immediate.
Low Very high Very Low Minor decline Low
The infaunal species in the biotope are likely to be able to avoid desiccation stress by burrowing into the sediment. Fine sediment contains a high silt content and retains a large amount of water. The epifauna, such as Crepidula fornicata, Mytilus edulis and the ascidians, are more likely to be affected by desiccation. Both the mollusc species would probably be able to retain water for extended periods by firm adherence to the substratum in the case of Crepidula fornicata and closure of the valves in the case of Mytilus edulis. The benchmark for desiccation is exposure to the air for one hour. It is likely that Crepidula fornicata and Mytilus edulis would be able to survive this exposure with only some loss of water. During the period of exposure they would not be able to feed and respiration would be compromised so there is likely to be some energetic cost. Intolerance for the biotope is therefore recorded as low. The solitary ascidians, however, are soft bodied and unlikely to be tolerant of desiccation. Exposure to the air for one hour would probably cause significant mortality, resulting in a minor decline in species richness.
Intermediate High Low Minor decline Low
IMX.CreAph predominantly occurs subtidally. However, the upper part of the biotope is exposed at low water spring tides and therefore an increase in emergence regime is relevant. The benchmark is an additional one hour of emergence every tidal cycle. During this time, exposed individuals of all species will not be able to feed and respiration of most will be compromised. Over the period of a year, the resultant energetic cost may cause the mortality of individuals exposed for the longest time. The overall intolerance of the biotope is therefore recorded as intermediate. Particularly intolerant species, such as ascidians, would be expected to suffer total mortality and therefore there would be a minor decline in species richness. Recoverability is recorded as high (see additional information below).
Tolerant* Not sensitive No change High
IMX.CreAph occurs in the subtidal zone and therefore would not be intolerant of a decreased emergence regime. It is possible that decreased emergence would allow the biotope to colonize further up the shore and extend its range.
Intermediate High Low Decline Low
IMX.CreAph occurs in wave protected areas where water flow is typically "moderately strong" or weaker (see glossary). An increase in water flow rate of two categories for one year would place the biotope in areas of strong or very strong flow. Increased water flow rate will change the sediment characteristics in which the biotope occurs, primarily by re-suspending and preventing deposition of finer particles (Hiscock, 1983). The underlying sediment in the biotope has a high silt content; a substratum which would not occur in very strong tidal streams. Therefore, the infaunal species, such as Aphelochaeta marioni, would be outside their habitat preferences and some mortality would be likely to occur. Additionally, the consequent lack of deposition of particulate matter at the sediment surface would reduce food availability for deposit feeders. The resultant energetic cost over one year would also be likely to result in some mortality. An intolerance of intermediate is therefore recorded and species richness is expected to decline. Recoverability is recorded as high (see additional information below).
Tolerant Not sensitive* No change High
IMX.CreAph occurs in areas of low water flow including the lowest category on the water flow scale ('very weak' - see glossary) (Connor et al., 1997a). Therefore, the biotope would be unlikely to be intolerant of decreases in water flow regime. However, it should be noted that decreased water flow rate could result in an increased settlement of suspended sediment (Hiscock, 1983) and deoxygenation. These factors are covered in their relevant sections.
Low Very high Very Low No change Low
Both the characterizing species in the biotope occur over a very wide geographic range. On the east coast of the Americas, Crepidula fornicata is found as far south as Mexico and therefore it must be able to tolerate higher temperatures than it experiences in northern Europe. The effect of temperature on larval development was investigated by Lucas & Costlow (1979). Larvae were found to tolerate daily temperature cycles of 5°C between 15°C and 30°C with little mortality. Over a 12 day period there was 0% mortality at 30°C but 100% mortality occurred by day 6 at 35°C. Thus, it seems that adult Crepidula fornicata are able to tolerate chronic change over time and larvae are able to tolerate acute change in the short term. Aphelochaeta marioni has been recorded from the Mediterranean Sea and Indian Ocean (Hartmann-Schröder, 1974; Rogall, 1977; both cited in Farke, 1979) and therefore must also be capable of tolerating higher temperatures than experienced in Northern Europe. Furthermore, Aphelochaeta marioni lives infaunally and so is likely to be insulated from rapid temperature change. For both the characterizing species, an increase in temperature would be expected to cause some physiological stress but no mortality and therefore an intolerance of low is recorded for the biotope. Metabolic activity should quickly return to normal when temperatures decrease and so a recoverability of very high is recorded. The majority of species in the biotope either live infaunally or are capable of burrowing and therefore would be insulated from rapid temperature change. Of the epifaunal species, Mytilus edulis is generally regarded as being eurythermal and the ascidians have a wide geographic range so are expected to tolerate variations in temperature. Hence, no decline in species richness is expected.
Intermediate High Low Minor decline High
During the severe winter of 1962-63 the British populations of marine invertebrates were subjected to an acute decrease in temperatures. Waugh (1964) recorded 25% mortality of Crepidula fornicata from the south coast and east coast of England where the recorded temperatures were 5-6°C and 3-4°C respectively below normal for a period of 2 months. Aphelochaeta marioni is more tolerant of decreases in temperature, probably because it lives infaunally. For example, in the Wadden Sea, the population was apparently unaffected by a short period of severe frost in I973 (Farke, 1979). The intolerance of Crepidula fornicata is in line with the benchmarks for temperature decrease and hence the intolerance of the biotope is recorded as intermediate. Recoverability is recorded as high (see additional information below). During the cold winter of 1962-63, severe mortalities of Carcinus maenas were recorded, while the infaunal species (e.g. Corophium volutator, Harmothoe impar, Nephtys hombergi) were largely unaffected (Crisp, 1964). Species richness in the biotope is therefore expected to show a minor decline.
Low Very high Very Low No change Low
IMX.CreAph occurs in turbid estuarine waters and therefore the species in the biotope are likely to be well adapted to turbid conditions. An increase in turbidity may affect primary production in the water column and therefore reduce the availability of diatom food, both for suspension feeders and deposit feeders. In addition, primary production by the microphytobenthos on the sediment surface may be reduced, further decreasing food availability for deposit feeders. However, primary production is probably not a major source of nutrient input into the system and, furthermore, phytoplankton will also immigrate from distant areas and so the effect may be decreased. As the benchmark turbidity increase only persists for a year, decreased food availability would probably only affect growth and fecundity of the intolerant species so a biotope intolerance of low is recorded. As soon as light levels return to normal, primary production will increase and hence recoverability is recorded as very high. There is not expected to be any mortality due to increased turbidity and hence the species richness is not expected to change.
Intermediate High Low Minor decline Very low
None of the species in the IMX.CreAph biotope require light and so therefore are not likely to be affected by a decrease in turbidity for light attenuation purposes. However, a decrease in turbidity will mean more light is available for photosynthesis by phytoplankton in the water column and phytobenthos on the sediment surface. Over the course of a year, this may lead to the development of a community of macroalgae which could potentially compete with some of the epifaunal species in the biotope, resulting in some mortality. Intolerance is therefore recorded as intermediate and there may be a minor decline in species richness. Recoverability is recorded as high (see additional information below).
High High Moderate Decline Low
IMX.CreAph occurs in sheltered areas such as estuaries and is characterized by a mixed substratum (Connor et al., 1997a). This suggests that the biotope would be intolerant of wave exposure to some degree. An increase in wave exposure by two categories for one year would be likely to affect the biotope in several ways. Fine sediments would be eroded (Hiscock, 1983) resulting in the likely reduction of the habitat of the infaunal species and a decrease in food availability for deposit feeders. Gravel and cobbles are likely to be moved by strong wave action resulting in damage and displacement of epifauna. For example, Crepidula fornicata is often found cast ashore following storms (Hayward & Ryland, 1995). Species may be damaged or dislodged by scouring from sand and gravel mobilized by increased wave action. Furthermore, strong wave action is likely to cause damage or withdrawal of delicate feeding and respiration structures of species within the biotope resulting in loss of feeding opportunities and compromised growth. It is likely that high mortality would result and therefore an intolerance of high is recorded and species richness is expected to decline. Recoverability is recorded as high (see additional information below).
Tolerant Not sensitive* No change High
IMX.CreAph occurs in 'extremely sheltered' environments (Connor et al., 1997a). The species present thrive in low energy environments and are tolerant of changes in chemical factors such as dissolved oxygen and salinity. The biotope, therefore, is unlikely to be intolerant of a further decrease in wave exposure and species richness is unlikely to change.
Tolerant Not relevant Not relevant No change Low
No information was found concerning the intolerance of the biotope or the characterizing species to noise. However, it is unlikely that the biotope will be affected by noise or vibrations caused by noise at the level of the benchmark.
Low Immediate Not sensitive No change High
The majority of species in the biotope are unlikely to be affected by visual disturbance. However, Farke (1979) noted the intolerance of Aphelochaeta marioni to visual disturbance in a microsystem in the laboratory. In order to observe feeding and breeding in the microsystem at night, the animals had to be gradually acclimated to lamp light. Even then, additional disturbance, such as an electronic flash, caused the retraction of palps and cirri and cessation of all activity for some minutes. Visual disturbance, in the form of direct illumination during the species' active period at night, may therefore result in loss of feeding opportunities, which may compromise growth and reproduction. On the basis of the reaction of Aphelochaeta marioni, an intolerance of low is recorded. When the visual disturbance is removed feeding activity should return to normal immediately.
Intermediate High Low Minor decline Low
Both the epifaunal and the infaunal species in the biotope are likely to be sensitive to physical disturbance due to dredging for scallops or oysters. Soft bodied epifauna, such as ascidians, are most vulnerable, and are likely to suffer high mortality. Sponges and hydroids attached to the slipper limpet bed are likely to be removed along the dredge track.

Crepidula fornicata has a robust body form and so individuals are likely to be resistant to the benchmark level of physical abrasion. However, the gregarious chain-forming characteristic of the species renders it susceptible to disturbance, as chains are more likely to be broken up, leaving some individuals exposed to predation.

De Montaudouin et al. (2001) (following Sauriau et al. , 1998) suggested that physical disturbance is a factor which could stimulate the presence of Crepidula fornicata. They noted that the species settles preferentially in the trails of trawl fishing gear, and that this may explain why Crepidula fornicata is not very abundant in the Arcachon Basin, France, as bottom trawling activities are prohibited here.

The infaunal annelids are predominantly soft bodied, live within a few centimetres of the sediment surface and may expose feeding or respiration structures where they could easily be damaged by a physical disturbance such as a passing dredge. The species with robust exoskeletons, such as bivalves and crustaceans, are likely to be the most resistant. The overall, a proportion of the slipper limpet bed, and its associated epifauna and infauna are likely to be removed or displaced. Therefore, an overall intolerance of intermediate has been recorded. For recoverability see additional information below.

Intermediate High Low Minor decline High
Effects of displacement on both the characterizing species in this biotope have been studied. Crepidula fornicata live in chains of up to 12 individuals, with the bottom individual being attached permanently to the substratum. Attachment is permanent as the shell takes on the shape of the substratum (Hoagland, 1979). Displacement would almost certainly lead to the mortality of the bottom individual in the chain as it would become very vulnerable to predation. However, other individuals in the chain would be unaffected by the displacement. Johnson (1972) demonstrated that transplanted individuals continue to grow normally. Farke (1979) noted the effects of displacement on Aphelochaeta marioni while performing experiments on intolerance to salinity changes. It was observed that when an individual was removed from its habitat and displaced to a similar habitat, it took approximately one minute to dig itself into the sediment. Aphelochaeta marioni is therefore recorded as not intolerant of displacement. The low level of mortality suffered by Crepidula fornicata suggests that the intolerance of the biotope to displacement is intermediate. Recoverability is recorded as high (see additional information below). Soft bodied, permanently attached epifauna, such as ascidians, are unlikely to survive displacement and therefore there would be a minor decline in species richness.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
High High Moderate Decline Low
Toxins, including synthetic chemicals such as dieldrin and poly-chlorinated biphenyls, tend to accumulate in low energy areas such as estuaries where the IMX.CreAph biotope occurs. Dispersion is low in these areas and the fine substrata act as a sink, retaining toxins for long periods of time (see review by Elliot et al., 1998). Therefore, the species which live infaunally in fine sediments, such as polychaetes, would be expected to be most vulnerable. Collier & Pinn (1998) investigated the effect on the benthos of ivermectin, a feed additive treatment for infestations of sea-lice on farmed salmonids. The polychaete Hediste diversicolor was particularly susceptible, exhibiting 100% mortality within 14 days when exposed to 8 mg/m² of ivermectin in a microcosm. Arenicola marina was also intolerant of ivermectin through the ingestion of contaminated sediment (Thain et al., 1998; cited in Collier & Pinn, 1998) and it was suggested that deposit feeding was an important route for exposure to toxins. Beaumont et al. (1989) investigated the effects of tri-butyl tin (TBT) on benthic organisms. At concentrations of 1-3 µg/l there was no significant effect on the abundance of Hediste diversicolor or Cirratulus cirratus after 9 weeks in a microcosm. However, no juvenile polychaetes were retrieved from the substratum and hence there is some evidence that TBT had an effect on the larval and/or juvenile stages of these polychaetes. No evidence was found on the effects of synthetic compounds specifically on Crepidula fornicata. However, there is a wealth of evidence concerning effects on related molluscs. For example, the effect of TBT from anti-fouling paints on gastropods is very well documented. Imposex, female mortality and the subsequent decline in population, has been described in Nucella lapillus (e.g. Bryan et al., 1986), Littorina littorea (Bauer et al., 1995), Ilyanassa obsoleta and Urosalpinx cinerea (Matthiessen & Gibbs, 1998). Limpets (Patellidae) are extremely intolerant of aromatic solvent based dispersants used in oil spill clean-up. During the clean-up response to the Torrey Canyon oil spill nearly all the limpets were killed in areas close to dispersant spraying. Viscous oil will not be readily drawn in under the edge of the shell by ciliary currents in the mantle cavity, whereas detergent, alone or diluted in sea water, would creep in much more readily and be liable to kill the limpet (Smith, 1968). For example, a concentration of 5ppm of dispersant killed half the patellid limpets tested in 24 hours (Southward & Southward, 1978; Hawkins & Southward, 1992). Thus, although no evidence was found concerning effects of synthetic chemicals on the biotope specifically, the intolerance of infaunal polychaetes and the likely intolerance of Crepidula fornicata, suggests that biotope intolerance is high and species richness will decline. Recoverability is recorded as high (see additional information below).
Heavy metal contamination
Low High Low Minor decline Moderate
As with synthetic chemicals, heavy metals tend to accumulate in the fine sediments present in biotopes such as IMX.CreAph (see review by Elliot et al., 1998). The intolerance of the characterizing species, Crepidula fornicata, has been well studied. In the Fal Estuary, Crepidula fornicata does occur in the Carrick Roads, an area where creek water polluted with heavy metals mixes with the open ocean (Bryan & Gibbs, 1983). In this area, concentrations of silver, cadmium, copper, lead and zinc were found to be higher than in 'control' estuaries (Bryan & Gibbs, 1983). This suggests that Crepidula fornicata is at least partially tolerant to heavy metal contamination. Laboratory trials have revealed specific responses to heavy metals. Thain (1984) investigated the effects of exposure to mercury. The adult and larval 96 hour LC50s (concentrations at which half the organisms die after 96 hours) were 330 and 60 µg/l respectively. As a reference, levels of mercury in UK waters at the time of these experiments were 104 to 105 below the 96 hour LC50 for adult Crepidula fornicata. Furthermore, sub-lethal concentrations of mercury were shown to impair growth and condition of young adult Crepidula fornicata and impair reproductive capacity at 0.25 µg/l. Nelson et al. (1983) investigated the effects of exposure to silver. Reproductive output was found to be impaired following exposure to the highest concentration of silver nitrate (10 µg/l) for 24 months. The evidence suggests that high concentrations of heavy metals will cause mortality in Crepidula fornicata. However, lower concentrations, which could realistically occur in situ impair growth, condition and reproductive output and will therefore affect the long term health of the population. The species intolerance is therefore recorded as low.
Evidence suggests that the other characterizing species in the biotope, Aphelochaeta marioni, is more tolerant of heavy metal contamination. It occurs in the heavily polluted Restronguet Creek (Bryan & Gibbs, 1983) and also is an accumulator of arsenic (Gibbs et al., 1983). Based on the intolerance of Crepidula fornicata, the intolerance of the biotope is recorded as low and there is likely to be an associated minor decline in species richness. Recoverability is recorded as high (see additional information below).
Hydrocarbon contamination
Intermediate Moderate Moderate Major decline Low
Oil spills resulting from tanker accidents can cause large-scale deterioration of communities in shallow subtidal sedimentary systems. The majority of benthic species often suffer high mortality, allowing a few tolerant opportunistic species to proliferate. For example, after the Florida spill of 1969 in Massachusetts, the entire benthic fauna was eradicated immediately following the spill and populations of the opportunistic polychaete Capitella capitata increased to abundances of over 200,000/m² (Sanders, 1978). The two characterizing species in the IMX.CreAph biotope are good examples of how species react differently to hydrocarbon pollution. No evidence could be found for the effect of hydrocarbons on Crepidula fornicata specifically. However, inferences can be drawn from other gastropods. Following the Torrey Canyon oil spill in 1967, total mortality of 3 Patella species was reported after one month of oil coming ashore at Porthleven reef (Smith, 1968). Other gastropod mortalities included Nucella lapillus, Nassarius incrassatus and Gibbula sp. Therefore, it is suggested that Crepidula fornicata would suffer high mortality when exposed to hydrocarbon contamination. Aphelochaeta marioni, however, seems to be mostly immune to oil spills, probably because the feeding tentacles are protected by a heavy secretion of mucus (Suchanek, 1993). This is supported by observations of the species following the Amoco Cadiz oil spill in March, 1978 (Dauvin, 1982, 2000). Prior to the spill, Aphelochaeta marioni was present in very low numbers in the Bay of Morlaix, western English Channel. Following the spill, the level of hydrocarbons in the sediment increased from 10 mg/kg dry sediment to 1443 mg/kg dry sediment 6 months afterwards. In the same period, Aphelochaeta marioni increased in abundance to a mean of 76 individuals/m², which placed it among the top five dominant species in the faunal assemblage. It was suggested that the population explosion occurred due to the increased food availability because of accumulation of organic matter resulting from high mortality of browsers. Six years later, abundance of Aphelochaeta marioni began to fall away again, accompanied by gradual decontamination of the sediments. This is an example of how invertebrate communities often react to oil spills. Initial massive mortality and lowered community diversity is followed by extreme fluctuations in populations of opportunistic mobile and sessile fauna (Suchanek, 1993).
As the biotope occurs subtidally, it is likely to avoid the worst impact of an oil spill and therefore the intolerance is recorded as intermediate. Recoverability of Crepidula fornicata is likely to be rapid (see additional information below), but recovery of the biotope to original species diversity and abundance may take longer and therefore, biotope recoverability is recorded as moderate.
Radionuclide contamination
Intermediate High Low Decline High
Information on intolerance to nuclear radiation is generally scarce. Greenberber et al. (1986) exposed larval Crepidula fornicata to doses of X-ray radiation between 500 and 20,000 Rad in total. After 20 days, there was a dose dependent decrease in larval shell growth rate and a significant increase in larval mortality following doses above 2000 Rad. These levels of radiation are extremely high compared to background levels in the environment. For reference, Polykarpov (1998) (cited in Cole et al., 1999) describes the natural levels of background radiation being equivalent to a dose of 0.005 Gy per year (equivalent to 0.5 Rad per year). Hence, high doses of radiation have been shown to significantly increase mortality while lower levels have sub-lethal effects on growth and reproduction. Based on the intolerance of Crepidula fornicata, the overall biotope intolerance is recorded as intermediate. Recoverability is recorded as high (see additional information below). There is little evidence concerning other species in the biotope.
Changes in nutrient levels
Intermediate High Low Minor decline Very low
Nutrient enrichment can lead to significant shifts in community composition in sedimentary habitats. Typically the community moves towards one dominated by deposit feeders and detritivores, such as polychaete worms (see review by Pearson & Rosenberg, 1978). The biotope includes several species tolerant of nutrient enrichment (e.g. Nephtys hombergi, Eteone longa, Corophium volutator) and typical of enriched habitats (e.g. Tubificoides sp., Mediomastus fragilis) (Pearson & Rosenberg, 1978). It is likely that these species would increase in abundance following nutrient enrichment, with an associated decline in suspension feeding species such as ascidians. The intolerance of the characterizing species Aphelochaeta marioni is difficult to ascertain from the available evidence. Raman & Ganapati (1983) presented evidence that Aphelochaeta marioni is not tolerant of eutrophication. However, nutrient enrichment would lead to increased food availability, the species is tolerant of low oxygen conditions (Broom et al., 1991) and has been recorded as proliferating following an oil spill which resulted in eutrophic conditions (Dauvin 1982, 2000). No information was found for the intolerance of Crepidula fornicata to nutrient enrichment. It seems likely that nutrient enrichment would result in a shift in community structure rather than a gross change in species composition and so biotope intolerance is recorded as intermediate, with a minor decline in species richness. Recoverability is recorded as high (see additional information below).
Tolerant Not relevant Not relevant No change High
IMX.CreAph occurs in estuaries and so the community is likely to be tolerant of variable salinities. Both characterizing species and the majority of other species in the biotope also occur on the open coast where sea water is at full salinity. Therefore the biotope is not likely to be intolerant of increases in salinity. No evidence was found concerning the reaction of the characterizing species to hypersaline conditions.
Low Very high Moderate No change Low
IMX.CreAph occurs in estuaries and so the community is likely to be tolerant of variable salinities. Aphelochaeta marioni, for example, has been recorded from brackish inland waters in the southern Netherlands with a salinity of 16 psu, but not in areas permanently exposed to lower salinities (Wolff, 1973). It also penetrates into areas exposed to salinities as low as 4 psu for short periods at low tide when fresh water discharge from rivers is high (Farke, 1979). The other species in the biotope do not display such tolerance. Despite being described as euryhaline (Blanchard, 1997), Crepidula fornicata is a marine organism and a drop in salinity to levels below 18 psu would be likely to cause water balance stress and therefore impair growth and reproduction. The same is likely to be true for the majority of the species in the biotope and hence an intolerance of low is recorded. Growth and reproduction should very quickly return to normal when salinity increases so recoverability is recorded as very high.
Intermediate High Low Minor decline Very low
The fauna in the biotope are all aerobic organisms and are therefore likely to be intolerant in some degree to lack of oxygen. No evidence was found for specific effects of reduced oxygenation on Crepidula fornicata but inferences can be drawn from the effects on other species. Jorgensen (1980) recorded the effects of low oxygen levels on benthic fauna in a Danish fjord. At dissolved oxygen concentrations of 0.2-1.0 mg/l the gastropod Hydrobia ulvae suffered mortality unless able to crawl to areas of higher oxygen concentration and the bivalves, Cardium edule and Mya arenaria, suffered mortality between 2 and 7 days. As Crepidula fornicata is not mobile, it is expected that some mortality would occur within a week at the benchmark level of 2 mg/l. Infaunal species which typically tolerate lower oxygen tensions than occur in the water column are likely to be less intolerant of reductions in dissolved oxygen. For example, Broom et al. (1991) recorded that Aphelochaeta marioni characterized the faunal assemblage of very poorly oxygenated mud in the Severn Estuary. They found Aphelochaeta marioni to be dominant where the redox potential at 4 cm sediment depth was 56 mV and, therefore, concluded that the species was tolerant of very low oxygen tensions. On the basis of the intolerance of epifauna such as Crepidula fornicata, the intolerance of the biotope is recorded as intermediate, with a minor decline in species richness. Recoverability is recorded as high (see additional information below).

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Low Very high Very Low No change Low
Gibbs (1971) recorded that nearly all of the population of Aphelochaeta marioni in Stonehouse Pool, Plymouth Sound, was infected with a sporozoan parasite belonging to the acephaline gregarine genus Gonospora, which inhabits the coelom of the host. No evidence was found to suggest that gametogenesis was affected by Gonospora infection and there was no apparent reduction in fecundity. However, any parasitic infection is likely to impair the host in some way so the intolerance of the species is recorded as low. If the parasite were to be removed, the host would be likely to return to normal health quickly so a recoverability of very high is recorded. No information was found concerning infection of the other characterizing species, Crepidula fornicata, by microbial pathogens.
Tolerant Not relevant Not relevant No change High
The biotope is dominated by Crepidula fornicata which is itself an alien species. It has spread widely through Europe following introduction from North America at the end of the 19th century (Fretter & Graham, 1981; Eno et al., 1997).
Intermediate Moderate Moderate Decline High
IMX.CreAph is associated with oyster beds and relict oyster beds, (A5.435), in southern England and Wales, separated from these by the superabundance of Crepidula fornicata (Connor et al., 1997b). Crepidula fornicata is a serious pest on oyster beds (Fretter & Graham, 1981) and therefore extraction of the species has occurred in an attempt to reduce the negative impact on the shellfishery in these areas. Cole & Hancock (1956) reported that over 8 tonnes/ha of slipper limpets were removed from oyster beds by dredging and that it takes up to 10 years to return to pre-clearance levels. Extraction of Crepidula fornicata would therefore be responsible for shifting the IMX.CreAph biotope back towards the IMX.Ost biotope from which it usually develops. Extent of the biotope would be expected to decrease and intolerance has therefore been recorded as intermediate. In this specific case, given the evidence for recovery time, recoverability is recorded as moderate. The effect of dredging for slipper limpets would be similar to removing the upper layer of the substratum and therefore a decline in species richness is expected.
Not relevant Not relevant Not relevant Not relevant Not relevant

Additional information

Recoverability
The recoverability of the important characterizing species is the principal factor in assessing the recoverability of the biotope.
  • The mode of reproduction of Crepidula fornicata gives the species strong powers of recoverability. Adults spawn at least once a year, large numbers of eggs are produced, there is a long planktotrophic larval stage and adults reach maturity within a year (Fretter & Graham, 1981; Deslou-Paoli & Heral, 1996). The ability of Crepidula fornicata to colonize new areas has been demonstrated by its spread through Europe following introduction from North America at the end of the 19th century (Fretter & Graham, 1981; Blanchard, 1997). Cole & Hancock (1956) reported that following clearance of slipper limpets from oyster beds by dredging, populations took up to 10 years to regain pre-clearance levels. However, given the species' reproductive characteristics and invasive record, it is likely that in most situations, populations would recover within 5 years and therefore recoverability is assessed as high.
  • Aphelochaeta marioni has no pelagic phase in its lifecycle, and dispersal is limited to the slow burrowing of the adults and juveniles (Farke, 1979). The blow lug, Arenicola marina, has similar dispersal capabilities and its recoverability has been well studied. It is therefore a suitable species to act as a guide for the recoverability of infaunal polychaetes. Heavy commercial exploitation in Budle Bay in winter 1984 removed 4 million worms in 6 weeks, reducing the population from 40 to <1 per m². Recovery occurred within a few months by recolonization from surrounding sediment (Fowler, 1999). However, Cryer et al. (1987) reported no recovery for 6 months over summer after mortalities due to bait digging. Beukema (1995) noted that the lugworm stock recovered slowly after mechanical dredging, reaching its original level in at least three years. Fowler (1999) pointed out that recovery may take a long time on a small pocket beach with limited possibility of recolonization from surrounding areas. Therefore, if adjacent populations are available recovery will be rapid. However where the affected population is isolated or severely reduced, recovery may be extended. Recoverability for Aphelochaeta marioni is therefore assessed as high.
  • As abundant epifauna in the biotope, the recoverability of ascidians should also be considered. Ascidians are fast growing, breed annually and disperse over short distances via a brief planktonic larval stage. Long distance dispersal may occur via drifting of adults attached to free floating objects. Ascidians are generally regarded to have low recoverability due to the brief larval stage. However, recoverability may be rapid if populations exist nearby and the hydrographic regime allows.
In light of the above information it is expected that the overall recoverability of the biotope would be high.

Importance review

Policy/Legislation

UK Biodiversity Action Plan PrioritySheltered muddy gravels

Exploitation

There is no evidence that any of the species in this biotope are exploited commercially.
In response to the invasion of shellfisheries by Crepidula fornicata, some management has been attempted. Sauriau et al. (1998) and Cole & Hancock (1956) reported dredging operations to clear slipper limpets from oyster beds, but concluded that further spread of the species could not be prevented.

Additional information

IMX.CreAph is related to the biotopes named in the Sheltered Muddy Gravels Habitat Action Plan.

Bibliography

  1. Anonymous, 1999iii. UK Biodiversity Group: tranche 2 action plans: volume V- maritime species and habitats. , English Nature, Peterborough, UK.
  2. Barnes, R.S.K. & Hughes, R.N., 1992. An introduction to marine ecology. Oxford: Blackwell Scientific Publications.
  3. Bauer, B., Fioroni, P., Ide, I., Liebe, S., Oehlmann, J., Stroben, E. & Watermann, B., 1995. TBT effects on the female genital system of Littorina littorea: a possible indicator of tributyl tin pollution. Hydrobiologia, 309, 15-27.
  4. Beaumont, A.R., Newman, P.B., Mills, D.K., Waldock, M.J., Miller, D. & Waite, M.E., 1989. Sandy-substrate microcosm studies on tributyl tin (TBT) toxicity to marine organisms. Scientia Marina, 53, 737-743.
  5. Beukema, J.J., 1995. Long-term effects of mechanical harvesting of lugworms Arenicola marina on the zoobenthic community of a tidal flat in the Wadden Sea. Netherlands Journal of Sea Research, 33, 219-227.
  6. Blanchard, M., 1997. Spread of the slipper limpet Crepidula fornicata (L.1758) in Europe. Current state and consequences. Scientia Marina, 61, Supplement 9, 109-118.
  7. Brenchley, G.A., 1981. Disturbance and community structure : an experimental study of bioturbation in marine soft-bottom environments. Journal of Marine Research, 39, 767-790.
  8. Broom, M.J., Davies, J., Hutchings, B. & Halcrow, W., 1991. Environmental assessment of the effects of polluting discharges: stage 1: developing a post-facto baseline. Estuarine, Coastal and Shelf Science, 33, 71-87.
  9. Bryan, G.W. & Gibbs, P.E., 1983. Heavy metals from the Fal estuary, Cornwall: a study of long-term contamination by mining waste and its effects on estuarine organisms. Plymouth: Marine Biological Association of the United Kingdom. [Occasional Publication, no. 2.]
  10. Bryan, G.W., Gibbs, P.E., Hummerstone, L.G. & Burt, G.R., 1986. The decline of the gastropod Nucella lapillus around south west England : evidence for the effect of tri-butyl tin from anti-fouling paints. Journal of the Marine Biological Association of the United Kingdom, 66, 611-640.
  11. Cole, H.A. & Hancock, D.A., 1956. Progress in oyster research in Britain 1949-1954, with special reference to the control of pests and diseases. Rapports du Conseils International Pour L'Exploration de la Mer, 140, 24-29.
  12. Collier, L.M. & Pinn, E.H., 1998. An assessment of the acute impact of the sea lice treatment Ivermectin on a benthic community. Journal of Experimental Marine Biology and Ecology, 230, 131-147.
  13. 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.
  14. Crisp, D.J. (ed.), 1964. The effects of the severe winter of 1962-63 on marine life in Britain. Journal of Animal Ecology, 33, 165-210.
  15. Cryer, M., Whittle, B.N. & Williams, K., 1987. The impact of bait collection by anglers on marine intertidal invertebrates. Biological Conservation, 42, 83-93.
  16. Dauvin, J.C., 1982. Impact of Amoco Cadiz oil spill on the muddy fine sand Abra alba - Melinna palmata community from the Bay of Morlaix. Estuarine and Coastal Shelf Science, 14, 517-531.
  17. Dauvin, J.C., 2000. The muddy fine sand Abra alba - Melinna palmata community of the Bay of Morlaix twenty years after the Amoco Cadiz oil spill. Marine Pollution Bulletin, 40, 528-536.
  18. 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.
  19. de Montaudouin, X. & Sauriau, P.G., 1999. The proliferating Gastropoda Crepidula fornicata may stimulate macrozoobenthic diversity. Journal of the Marine Biological Association of the United Kingdom, 79, 1069-1077.
  20. de Montaudouin, X., Labarraque, D, Giraud, K. & Bachelet, G., 2001. Why does the introduced gastropod Crepidula fornicata fail to invade Arcachon Bay (France) ? Journal of the Marine Biological Association of the United Kingdom, 81, 97-104.
  21. Deslou-Paoli, J.M. & Heral, M., 1986. Crepidula fornicata (L.) (Gastropoda, Calyptraeidae) in the bay of Marennes-Oleron: Biochemical composition and energy value of individuals and spawning. Oceanologica Acta, 9, 305-311.
  22. Eagle, R.A., 1975. Natural fluctuations in a soft bottom benthic community. Journal of the Marine Biological Association of the United Kingdom, 55, 865-878.
  23. 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.
  24. Farke, H., 1979. Population dynamics, reproduction and early development of Tharyx marioni (Polychaeta, Cirratulidae) on tidal flats of the German Bight. Veroffentlichungen des Instituts fur Meeresforschung in Bremerhaven, 18, 69-99.
  25. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

  26. Fowler, S.L., 1999. Guidelines for managing the collection of bait and other shoreline animals within UK European marine sites. Natura 2000 report prepared by the Nature Conservation Bureau Ltd. for the UK Marine SACs Project, 132 pp., Peterborough: English Nature (UK Marine SACs Project)., http://www.english-nature.org.uk/uk-marine/reports/reports.htm
  27. Fretter, V. & Graham, A., 1981. The Prosobranch Molluscs of Britain and Denmark. Part 6. olluscs of Britain and Denmark. part 6. Journal of Molluscan Studies, Supplement 9, 309-313.
  28. Gibbs, P.E., 1969. A quantitative study of the polychaete fauna of certain fine deposits in Plymouth Sound. Journal of the Marine Biological Association of the United Kingdom, 49, 311-326.
  29. Gibbs, P.E., 1971. Reproductive cycles in four polychaete species belonging to the family Cirratulidae. Journal of the Marine Biological Association of the United Kingdom, 51, 745-769.
  30. Gibbs, P.E., Langston, W.J., Burt, G.R. & Pascoe, P.L., 1983. Tharyx marioni (Polychaeta) : a remarkable accumulator of arsenic. Journal of the Marine Biological Association of the United Kingdom, 63, 313-325.
  31. Greenberber, J.S., Pechenik, J.A., Lord, A., Gould, L., Naparstek, E., Kase, K. & Fitzgerald, T.J., 1986. X-irradiation effects on growth and metamorphosis of gastropod larvae (Crepidula fornicata) : a model for environmental radiation teratogenesis. Archives of Environmental Contamination and Toxicology, 15, 227-234.
  32. Hall, S.J. & Harding, M.J.C., 1997. Physical disturbance and marine benthic communities: the effects of mechanical harvesting of cockles on non-target benthic infauna. Journal of Applied Ecology, 34, 497-517.
  33. Hall, S.J., 1994. Physical disturbance and marine benthic communities: life in unconsolidated sediments. Oceanography and Marine Biology: an Annual Review, 32, 179-239.
  34. Hawkins, S.J. & Southward, A.J., 1992. The Torrey Canyon oil spill: recovery of rocky shore communities. In Restoring the Nations Marine Environment, (ed. G.W. Thorpe), Chapter 13, pp. 583-631. Maryland, USA: Maryland Sea Grant College.
  35. 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.
  36. Hoagland, K.E., 1979. The behaviour of three sympatric species of Crepidula (Gastropoda : Prosobranchia) from the Atlantic, with implications for evolutionary ecology. Nautilus, 93, 143-149.
  37. Ismail, N.S., 1985. The effects of hydraulic dredging to control oyster drills on benthic macrofauna of oyster grounds in Delaware Bay, New Jersey. Internationale Revue der Gesamten Hydrobiologie, 70, 379-395.
  38. 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,
  39. Johnson, J.K., 1972. Effect of turbidity on the rate of filtration and growth of the slipper limpet, Crepidula fornicata. Veliger, 14, 315-320.
  40. Jorgensen, B.B., 1980. Seasonal oxygen depletion in the bottom waters of a Danish fjord and its effect on the benthic community. Oikos, 32, 68-76.
  41. Lucas, J.S. & Costlow J.D., 1979. Effects of various temperature cycles on the larval development of the gastropod mollusc Crepidula fornicata. Marine Biology, 51, 111-117.
  42. Matthiessen, P. & Gibbs, P.E., 1998. Critical appraisal of the evidence for tri-butyl tin mediated endocrine disruption in molluscs. Environmental Toxicology and Chemistry, 17, 37-43.
  43. Nelson, D.A., Calabrese, A., Greig, R.A., Yevich, P.P. & Chang, S., 1983. Long term silver effects on the marine gastropod Crepidula fornicata. Marine Ecology Progress Series, 12, 155-165.
  44. Olafsson, E.B. & Persson, L.E., 1986. The interaction between Nereis diversicolor (Muller) and Corophium volutator (Pallas) as a structuring force in a shallow brackish sediment. Journal of Experimental Marine Biology and Ecology, 103, 103-117.
  45. Pearson, T.H. & Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology: an Annual Review, 16, 229-311.
  46. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin., http://www.itsligo.ie/biomar/
  47. Raman, A.V. & Ganapati, P.N., 1983. Pollution effects on ecobiology of benthic polychaetes in Visakhapatnam Harbour (Bay of Bengal). Marine Pollution Bulletin, 14, 46-52.
  48. Rees, H.L. & Dare, P.J., 1993. Sources of mortality and associated life-cycle traits of selected benthic species: a review. MAFF Fisheries Research Data Report, no. 33., Lowestoft: MAFF Directorate of Fisheries Research.
  49. Reise, K., 1985. Tidal flat ecology. An experimental approach to species interactions. Springer-Verlag, Berlin.
  50. Sanders, H.L., 1978. Florida oil spill impact on the Buzzards Bay benthic fauna: West Falmouth. Journal of the Fisheries Board of Canada, 35, 717-730.
  51. Sauriau, P.G., Pichocki-Seyfried, C., Walker, P., De Montauduin, A., Pascual, A. & Heral, M., 1998. Crepidula fornicata L. (Mollusca, Gastropoda) in the Marennes-Oleron Bay : side-scan sonar mapping of subtidal and stock assessment. Oceanologica Acta, 21, 353-362.
  52. Smith, J.E. (ed.), 1968. 'Torrey Canyon'. Pollution and marine life. Cambridge: Cambridge University Press.
  53. Southward, A.J. & Southward, E.C., 1978. Recolonisation of rocky shores in Cornwall after use of toxic dispersants to clean up the Torrey Canyon spill. Journal of the Fisheries Research Board of Canada, 35, 682-706.
  54. Suchanek, T.H., 1993. Oil impacts on marine invertebrate populations and communities. American Zoologist, 33, 510-523.
  55. Thain, J.E., 1984. Effects of mercury on the prosobranch mollusc Crepidula fornicata : acute lethal toxicity and effects on growth and reproduction of chronic exposure. Marine Environmental Research, 12, 285-309.
  56. Thouzeau, G., 1991. Experimental collection of postlarvae of Pecten maximus (L.) and other benthic macrofaunal species in the Bay of Saint-Brieuc, France. 1. Reproduction and post larval growth of five mollusc species. Journal of Experimental Marine Biology and Ecology, 148, 181-200.
  57. Thouzeau, G., Chavaud, L., Grall, J. & Guerin, L., 2000. Do biotic interactions control pre-recruitment and growth of Pecten maximus (L.) in the Bay of Brest ? Comptes rendus - acadamies des sciences, Paris, 323, 815-825.
  58. Waugh, G.D., 1964. Effect of severe winter of 1962-63 on oysters and the associated fauna of oyster grounds of southern England. Journal of Animal Ecology, 33, 173-175.
  59. Wolff, W.J., 1973. The estuary as a habitat. An analysis of the data in the soft-bottom macrofauna of the estuarine area of the rivers Rhine, Meuse, and Scheldt. Zoologische Verhandelingen, 126, 1-242.

Citation

This review can be cited as:

Rayment, W.J. 2001. Crepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment. 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/52

Last Updated: 17/08/2001