MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Crepidula fornicata and Mediomastus fragilis in variable salinity infralittoral mixed sediment

17-08-2001
Researched byJohn Readman & Will 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 polychaetes Mediomastus fragilis and Aphelochaeta marioni. Other numerically important taxa include the oligochaetes Tubificoides benedii, syllids such as Exogone naidina and Sphaerosyllis, and Nephtys hombergii. Lepidonotus squamatus and Scoloplos armiger may also be common. 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).

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?

Sensitivity characteristics of the habitat and relevant characteristic species

Both SS.SMx.IMx.CreAsAn and SS.SMx.SMxVS.CreMed are characterized by the presence of the invasive Crepidula fornication infralittoral sediment and generally occur on the southern coast of England. 

SS.SMx.IMx.CreAsAn occurs on medium-coarse sands with gravel, shells, pebbles and cobbles on moderately exposed coasts.  In addition to Crepidula forincata,  a faunal community is present comprising ascidians (including Styela clava), anemones and bryozoans.  Polychaetes may also be found, but little information is available regarding the infauna (Connor et al., 2004).

SS.SMx.SMxVS.CreMed is similar, but occurs in mixed muddy sediments estuarine conditions, subject to variable salinity.  Crepidula fornicata tends to be found in greater abundances, the faunal community is less conspicuous and the polychaetes Mediomastus fragilis and Aphelochaeta marioni are considered characterizing (Connor et al., 2004).

This assessment focuses on the important characterizing Crepidula fornicata and the polychaetes Mediomastus fragilis and Aphelochaeta marioni.  The assessments also take into consideration faunal communities including ascidians and anemones where appropriate.

Resilience and recovery rates of habitat

Crepidula fornicata is a protandrous hermaphrodite that starts its life as male and then, subsequently, may change sex and develop into a female. Although breeding can occur between February and October, peak reproduction occurs in May and June when 80-90% of females spawn. Most females spawn twice in a year and can lay ca 11,000 eggs at a time, contained in up to 50 egg capsules (Deslou-Paoli & Heral, 1986). Thain (1984) reported that, following incubation, ca 4,000 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 is 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 fornicataCrepidula 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 a high post settlement mortality rate of larvae and juveniles (Olafsson et al., 1994). Males reach sexual maturity two 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).  Immediately after settlement, juvenile Crepidula fornicata are capable of slow crawling and locate a suitable site for attachment and growth. This is either a stone or a chain of other Crepidula fornicata (conspecifics). The shell then grows to fit the substratum and consequently most animals are incapable of further movement at the age of about two years (Fretter & Graham, 1981). Cole & Hancock (1956) reported that following clearance of slipper limpets from oyster beds, 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 five years.

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.

The characterizing polychaete Mediomastus fragilis is opportunistic species (small size, rapid maturation and short-life span of 1-2 years with production of large numbers of small propagules). It is likely to recolonize disturbed areas first, although the actual pattern will depend on recovery of the habitat, season of occurrence and other factors. Sardá et al. (1999) tracked annual cycles within a Spisula community in Bay of Blanes (north west Mediterranean sea, Spain) for 4 years. Macroinfaunal abundance peaked in spring, decreased sharply throughout the summer, with low density in autumn and winter.  The observed trends were related to a number of species, including the characterizing Mediomastus fragilis. The Spisula subtruncata populations were dominated by juveniles, with high abundances in spring followed by declines in summer, with very few survivors 3 months after recruitment. In comparison, Mediomastus fragilis had spring population peaks but more individuals persisted throughout the year. 

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. 

Both Crepidula fornicata and Aphelochaeta marioni, 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 Montadouin & 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.

Resilience assessment

Crepidula fornicata is an invasive, highly fecund species which matures in 2-10 months.  Larvae have a long pelagic phase (Fretter & Graham, 1981; Thouzeau, 1991) and the potential for dispersal is high.  Recruitment is likely to very rapid, however some studies have suggested that recover following almost complete removal may be longer, taking up to 10 years (Beukema (1995).  The polychaetes are likely to be opportunistic and recover rapidly from significant mortality.

Resilience is therefore likely to be ‘High’ for most levels of perturbation, although a resilience of ‘Medium’ ( recovery in 2-10 years) was recorded   for resistances of ‘None’, based on evidence following clearance of Crepidula fornicata.

Hydrological Pressures

 ResistanceResilienceSensitivity
High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

The characterizing species in the biotope occur over a very wide geographic range. Crepidula fornicata has a southerly distribution in the British Isles (NBN, 2015) and is found in the Mediterranean (Sciberras & Schembri, 2007). On the east coast of the Americas, Crepidula fornicata is found as far south as Mexico and, therefore, 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.

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 the British Isles.  Mediomastus fragilis has been recorded throughout the British Isles (NBN, 2015) and in the Mediterranean (Faulwetter, 2010).  However, the polychaetes live infaunally and are likely to be insulated from short term temperature change.

Sensitivity assessment

The important characterizing species occur in the Mediterranean and are probably resistant to an increase at the benchmark level.  Resistance has been recorded as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Low High Low
Q: Medium
A: Medium
C: Medium
Q: High
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

The distribution of Crepidula fornicata is generally limited to the south coast of England (NBN, 2015).  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 two months.   Crepidula fornicata populations in the Wadden Sea were strongly affected by cold winters, Thieltges et al. (2004) reported that mortality over two winters amounted to 56–64% with up to 97% on single mussel beds, in contrast to 11–14% yearly mortality in areas without frost in southern Europe. Thieltges et al.(2004) also found low larval abundances after an exceptionally severe winter and suggested that winter mortality was the main limiting factor for population increase in the study area.

The characterizing polychaetes are infauna, which would afford them some protection in the event of a short-term change in temperature.  Aphelochaeta marioni occurs throughout the British Isles (NBN, 2015) and is likely to tolerant decreases in temperature at the benchmark level. For example, in the Wadden Sea, the population was apparently unaffected by a short period of severe frost in I973 (Farke, 1979).

During the cold winter of 1962-63, infaunal species (e.g. Corophium volutator, Harmothoe impar, Nephtys hombergi) were largely unaffected (Crisp, 1964a). Species richness in the biotope is, therefore, expected to show a minor decline.

Sensitivity assessment

Evidence suggests that Crepidula fornicata is susceptible to cold temperatures and this is likely to a factor in limiting distribution of the species Thieltges et al.(2004).  Resistance is likely to be ‘Low’, resilience as ‘High’ and the sensitivity as ‘Low’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: Low
C: NR

SS.SMx.SMxVS.CreMed occurs in variable salinity and SS.SMx.IMx.CreAsAn occurs in full salinity.  An increase at the benchmark level would result in hypersalinity (>40 ppt ) which is likely to cause mortality.  However, ‘No evidence’ was found for the characterizing hypersaline conditions.

Medium High Low
Q: High
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: High
A: Medium
C: Medium

Despite being described as euryhaline (Blanchard, 1997), Crepidula fornicata is principally a marine organism and a decrease in salinity to levels below 18 psu would be likely to cause water balance stress and therefore impair growth and reproduction (Raiment, 2008).

Environmental fluctuations in salinity are only likely to affect the surface of the sediment, and not deeper organisms, since the interstital or burrow water is little affected.  Polychaetes are infaunal and are likely to have some resistance to decreases in salinity.

Aphelochaeta marioni, 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).

Whilst Styela clava is capable of surviving short term hyposalinity down to 8‰, it is suggested that this is due to closing its siphons (Sims, 1984), however, the species is generally not found in areas with estuarine conditions (Lützen, 1998). Sims (1984) reported that Styela clava has limited osmoregulatory capability in hyposaline media (poor vital functions and complete cessation of siphonal responses at 26.5‰). Kelly (1974) observed dramatic reduction in population density following  heavy rainfall during the winter of 1972/1973 in Newport Bay, California.

Lützen & Sorensen (1993) exposed Styela clava to a gradually salinity decrease from 31‰ to 18‰ over 40 days, with 17 of 24 animals having survived.  A decrease to 16‰ over 50 days  resulted in mortality in 6 of 12 specimens. Kashenko (1996) reported that larvae of Styela clava from the Sea of Japan were able to complete metamorphosis at salinities ranging from 32‰ to 20‰, but that salinities below 18‰ were deleterious.

Ryland (1970) stated that, with a few exceptions, the Gymnolaemata were fairly stenohaline and restricted to full salinity (30-35 ppt), noting that reduced salinities result in an impoverished bryozoan fauna. Flustra foliacea appears to be restricted to areas with high salinity (Tyler-Walters & Ballerstedt 2007; Budd 2008).  Dyrynda (1994) noted that Flustra foliacea and Alcyonidium diaphanum were probably restricted to the vicinity of the Poole Harbour entrance by their intolerance to reduced salinity. Although protected from extreme changes in salinity due to their subtidal habitat, severe hyposaline conditions could adversely affect Flustra foliacea colonies.

Sensitivity assessment: SS.SMx.IMx.CreAsAn occurs in full salinity and SS.SMx.SMxVS.CreMed occurs in variable salinity.  Decrease at the benchmark level to ‘reduced’ may cause mortality among the characterizing species.  It should be noted that a decrease from variable (18 -40 ppt ) to reduced (18 – 30 ppt) does not result in a lower range limit.  A change from full (CreAsAn) to variable (CreMed) would probably reduce the abundance of ascidians and anemones, so that CreAsAn would come to resemble CreMed.  Resistance is ‘Medium’, resilience is ‘High’ and sensitivity is ‘Low’ at the benchmark level. 

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

 

This biotope occurs in wave protected areas where water flow is typically moderately strong.

If water flow was to increase to strong or very strong, it is likely that physical damage to the bed would occur.  Erosion and re-suspension of the sediment could result in a change in substrata. Increased flow over the bed could potentially remover lighter sediment fractions, leaving only coarser sediment, boulders and bedrock.

Therefore, the infaunal species 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 could reduce food availability for deposit feeders. The resultant energetic cost over one year could also result in some mortality.

Crepidula fornicata is a cosmopolitan species but is found in greatest numbers in wave protected areas (Blanchard, 1997) and has only been recorded in biotopes that occur in moderately strong or weaker water flow (Connor et al., 2004). An increase in water flow outside the species' habitat preferences may cause mortality through interference with feeding and/or respiration.

Sensitivity assessment.  An increase in water flow rate may physically disturb the bed, where the change is outside the biotopes normal range of water flow. Examples of the habitat at the limits of the range of water flow are likely to be most sensitive to change. However, a change in water flow of 0.1-0.2 m/s, is unlikely to affect adversely the biotope.  Therefore, resistance and resilience are 'High' and the biotope is 'Not sensitive' at the benchmark level.

Low High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

This biotope can occur in the 0-5 m range.  Crepidula fornicata may be able to survive in the intertidal zone without resort to

anaerobiosis. Between 70 and 90% of the minimum aquatic oxygen requirements may be met by aerial gas exchange (Newell & Kofoed, 1977).  The infaunal polychaetes would have some resistance to emergence, however other species composing the faunal turf are restricted to the sublittoral and emergence would likely cause significant damage to the community. 

Sensitivity assessment: Whilst Crepidula fornicata would probably be tolerant of short term emergence, the faunal turf comprising sublittoral ascidians and bryozoans would suffer mortality and resistance is, therefore, assessed as ‘Low’.  Following return to normal conditions, the faunal turf species are likely to recover rapidly and resilience is therefore ‘High’, with ‘Low’ sensitivity.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

.SMx.SMxVS.CreMed  occurs in sheltered or extremely sheltered conditions, whereas SS.SMx.IMx.CreAsAn occurs in moderately exposed conditions (Connor et al., 2004). A significant increase in wave exposure could erode fine sediments (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. Crepidula fornicata has been reported washed up on the shore following storms (Hayward & Ryland, 1995b). 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.

Evidence for polychaetes is limited for the effects of wave exposure changes. Increased wave action results in increased water flow in the shallow subtidal. Wave mediated water flow tends to be oscillatory, i.e. moves back and forth (Hiscock, 1983), and may result in dislodgement or removal of individuals. The infaunal nature of the polychaetes is likely to provide some resistance to increases in wave exposure (Coosen et al., 1994), but if the change was significant enough to modify the sediment, it would result in a change in the infaunal community.   

Sensitivity assessment: Whilst significant increases in wave exposure (e.g. storms) have been linked with displacement of Crepidula fornicata, an increase in wave exposure at the benchmark level (3-5% change in significant wave height) is unlikely to result in mortality and resistance is therefore ‘High’, resilience is ‘High’ and the biotope is assessed as ‘Not sensitive’ at the benchmark level.

Chemical Pressures

 ResistanceResilienceSensitivity
Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

As with synthetic chemicals, heavy metals tend to accumulate in the fine sediments (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. Half the adults and larvae died after 96 hours following exposure to 330 and 60 µg/l respectively. 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.

Evidence suggests that the polychaetes present in this biotope, are more tolerant of heavy metal contamination. Aphelochaeta marioni  occurs in the heavily polluted Restronguet Creek (Bryan & Gibbs, 1983) and has also been reported to accumulate arsenic (Gibbs et al., 1983).

However, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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).

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 lapillusNassarius incrassatus and Gibbula sp. Based on the evidence for other gartopods, Crepidula fornicata would probably suffer high mortality when exposed to hydrocarbon contamination. 

Aphelochaeta marioni, however, has been reported to be highly resistant 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. Six years later, abundance of Aphelochaeta marioni began to decline, accompanied by gradual decontamination of the sediments.  Borja et al. (2000) recorded the relative sensitivity of Mediomastus fragilis as an ABMI Ecological Group III species ‘tolerates disturbance and excess organic content’.

Nevertheless, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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., 1997; 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 evidence concerning effects on other 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. Following the clean-up response to the Torrey Canyon oil, almost all 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 5 ppm of dispersant killed half the patellid limpets tested in 24 hours (Southward & Southward, 1978; Hawkins & Southward, 1992).

However, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with all relevant environmental protection standards.

High High Not sensitive
Q: Medium
A: Low
C: Low
Q: High
A: High
C: High
Q: Medium
A: Low
C: Low

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. 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 (equivalent to 20 Gy). 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. There is little evidence concerning other species in the biotope.

Sensitivity assessment. Evidence at the benchmark level is unavailable, however, Crepidula fornicata mortality at high levels of radiation has been reported.  Nevertheless, mortality as the benchmark level is unlikely and resistance is therefore ‘High’, resilience is ‘High’ and the biotope is ‘Not sensitive’.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No benchmark was proposed.  Therefore, sensitivity has been assessed as 'Not sensitive' at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

In general, respiration in most marine invertebrates does not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates this concentration is about 2 ml/l (Herreid, 1980; Rosenberg et al., 1991; Diaz & Rosenberg, 1995). Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l.

No direct evidence was found for specific effects of reduced oxygenation on adult Crepidula fornicata.  Brante et al. (2009) reported that whilst hypoxic conditions affected the growth rate of embryonic Crepidula fornicata during development, survival was not affected.  Borja et al. (2000) recorded the relative sensitivity of both Mediomastus fragilis and Crepidula fornicata as ABMI Ecological Group III species that ‘tolerate disturbance and excess organic content’.

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.

Sensitivity assessment. The characterizing species are likely to be resistant to hypoxic events. Resilience is therefore ‘High’, recoverability is ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Nutrient enrichment can lead to significant shifts in community composition in sedimentary habitats.   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.

Nevertheless, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

Whilst Raman & Ganapati (1983) presented evidence that Aphelochaeta marioni is not tolerant of eutrophication, organic enrichment would lead to increased food availability and the species is tolerant of low oxygen conditions (Broom et al., 1991).  It has also been recorded as proliferating following an oil spill which resulted in eutrophic conditions (Dauvin, 1982; 2000)

Borja et al. (2000) recorded the relative sensitivity of both Mediomastus fragilis and Crepidula fornicata as ABMI Ecological Group III species that ‘tolerate disturbance and excess organic content’.  Resistance is, therefore, assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Physical Pressures

 ResistanceResilienceSensitivity
None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’). Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described, confidence in this assessment is ‘High’ due to the incontrovertible nature of this pressure.

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

If sediment were replaced with rock or artificial substrata, this would represent a fundamental change to the biotope with reclassification necessary. Change from a mixed sediment substrata to rock would also result in loss of the infaunal component. Resistance to the pressure is considered ‘None’, and resilience ‘Very Low’. Sensitivity has been assessed as ‘High

None Very Low High
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

A change in one Folk class is considered to relate to a change in classification to adjacent categories in the modified Folk triangle (Long, 2006).  SS.SMx.IMx.CreAsAn occurs on medium coarse sands and SS.SMx.SMxVS.CreMed occurs on Mixed muddy sediment.

Sediment type is a key factor structuring the biological assemblage present in the biotope. Surveys over sediment gradients and before-and-after impact studies from aggregate extraction sites where sediments have been altered indicate patterns in change. The biotope classification (JNCC, 2015) provides information on the sediment types where biotopes are found and indicate likely patterns in change if the sediment were to alter. Long-term alteration of sediment type to finer more unstable sediments was observed six years after aggregate dredging at moderate energy sites (Boyd et al., 2005).

Differences in biotope assemblages in areas of different sediment type are likely to be driven by pre and post recruitment processes. Sediment selectivity by larvae will influence levels of settlement and distribution patterns. Snelgrove et al. (1999) demonstrated that capitellid polychaetes selected muddy sand over coarse sand, regardless of site. Both larvae selected sediments typical of adult habitats, however, some species were nonselective (Snelgrove et al., 1999) and presumably in unfavourable habitats post recruitment, mortality will result for species that occur in a restricted range of habitats. 

Sensitivity assessment: While the epifauna are unlikely to be affected, change in sediment at the benchmark level, (e.g. to coarser sediments) is likely to impact the infaunal polychaete community.  Resistance is assessed as ‘Low’, resilience as Very low (the pressure is a permanent change), and  sensitivity is, therefore, High. 

None High Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

Sedimentary communities are likely to be highly intolerant of substratum removal, which will lead to partial or complete defaunation, expose underlying sediment which may be anoxic and/or of a different character and lead to changes in the topography of the area (Dernie et al., 2003). Any remaining species, given their new position at the sediment   water interface, may be exposed to unsuitable conditions.

Removal of 30 cm of sediment will remove species that occur at the surface and within the upper layers of sediment including Crepidula fornicata, the faunal community and the majority of the polychaetes.

Recovery of the sedimentary habitat would occur via infilling, although some recovery of the biological assemblage may take place before the original topography is restored, if the exposed, underlying sediments are similar to those that were removed. Newell et al. (1998) indicate that local hydrodynamics (currents and wave action) and sediment characteristics (mobility and supply) strongly influence the recovery of soft sediment habitats.  It should be noted that the slipper limpets and ascidians are likely to rely on terrigenous debris in providing suitable for settlement.

Sensitivity assessment. Extraction of 30 cm of sediment will remove the characterizing biological component of the biotope. Resistance is assessed as ‘None’ and biotope resilience is assessed as ‘Medium’.   Sensitivity is, therefore, assessed as ‘Medium’.

Low High Low
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

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. Emergent epifauna are generally very intolerant of disturbance from fishing gear (Jennings & Kaiser, 1998).

Crepidula fornicata has a robust body form and so individuals are likely to be resistant of lighter abrasion events, although dredging has been used in clearance operations associated with protecting aquaculture (Sauriau et al., 1998; Cole & Hancock, 1956).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.

It has been suggested that physical disturbance is a factor which could stimulate the presence of Crepidula fornicata, with reports suggesting it settles preferentially in the trails of trawl fishing gear (Sauriau et al. , 1998; De Montaudouin et al., 2001). 

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 burrowing traits of the polychaetes may provide some tolerance of this pressure. However, Boldina and Beninger (2014) report decreases in naturally occurring aggregations of Arenicola marina in trawled areas suggesting consequences for basic biological characteristics such as reproduction, recruitment, growth and feeding. Ferns et al. (2000) reported a decline of 31% in populations of Scoloplos armiger (initial density 120 m−2) in muddy sands and an 83% decline in Pygospio elegans (initial density 1850 m−2) when a mechanical tractor towed harvester was used (in a cockle fishery). Pygospio elegans were significantly depleted for >100 days after harvesting (surpassing the study monitoring timeline). In a review of impacts of fishing activities on benthic communities, Collie et al. (2000) identified that well established sand and muddy sand intertidal communities suffered the greatest impact from bottom towed fishing activities. The review concluded that there were ecologically important impacts from removal of >50% of fauna from bottom towed fishing activity (dredge and trawls) (Collie et al., 2000).

Overall, a proportion of the slipper limpet bed, and its associated epifauna and infauna are likely to be removed or displaced.  

Sensitivity assessment. Evidence suggests a decline in all species present following abrasion type events and resistance is, therefore, assessed as ‘Low’, resilience as ‘High’ and sensitivity as ‘Low’.

Low High Low
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

Penetration and or disturbance of the substratum would result in similar, if not identical results as ‘abrasion’ for the epifaunal communities and Crepidula fornicata.  The infaunal polychaetes may be more exposed to penetration type damage.  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 burrowing traits of the polychaetes may provide some tolerance of this pressure. However, Boldina and Beninger (2014) report decreases in naturally occurring aggregations of Arenicola marina in trawled areas suggesting consequences for basic biological characteristics such as reproduction, recruitment, growth and feeding. Ferns et al. (2000) reported a decline of 31% in populations of Scoloplos armiger (initial density 120 m−2) in muddy sands and an 83% decline in Pygospio elegans (initial density 1850 m−2) when a mechanical tractor towed harvester was used (in a cockle fishery). Pygospio elegans were significantly depleted for >100 days after harvesting (surpassing the study monitoring timeline). In a review of impacts of fishing activities on benthic communities , Collie et al. (2000) identified that well established sand and muddy sand intertidal communities suffered the greatest impact from bottom towed fishing activities. Mean response in muddy sand communities was much more negative than other habitats and most negative responses were for the polychaetes Arenicola marina and Scoloplos armiger. Macoma balthica and Cerastoderma edule were also more negatively impacted, although this may be due to direct targeting of Cerastoderma edule by cockle fisheries. The review concluded that there were ecologically important impacts from removal of >50% of fauna from bottom towed fishing activity (dredge and trawls) (Collie et al., 2000).

Sensitivity assessment.  Resistance of the biotope is assessed as ‘Low’, although the significance of the impact for the bed will depend on the spatial scale of the pressure footprint.  Resilience is assessed as ‘Low’, and sensitivity is assessed as ‘High’.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

SS.SMx.SMxVS.CreMed occurs in lower estuarine waters and, therefore, the species in the biotope are likely to be well adapted to turbid conditions.  Wass et al. (1999) described suspended sediment maxima for ‘medium’ sized rivers as rarely exceeding 500 mg/l, with a few rivers (including the Don and the Swale) experiencing concentrations in excess of 1000 mg/l.  Langston et al. (2003) described annual mean suspended sediment concentrations in the Tamar as varying from 61 mg/l to 1039 mg/l in the upper estuary, 6 to 18 mg/l in the outer estuary and 2 to 9 mg/l beyond.  It should be noted that the values quoted are mean annual concentrations and the same report states that conditions could be ‘very turbid’ in the outer estuary.

The estuarine turbidity maximum (the point at which highest turbidity is experienced) can be highly variable and has been reported to move by ca 12 km down-estuary during the transition from neap to spring tides in the Humber estuary (Uncles et al., 2001).  Estuarine environments are likely to experience variable turbidity and the species present are probably tolerant of significant short term changes in suspended solid concentrations.

Long-term 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.  Johnson (1972) noted that an increase in suspended solids above 100 mg/l resulted in lower growth rate and reduced filtration rate in Crepidula fornicata. However, the study found that the species survived in concentrations above 600 mg/l by continuously expelling pseudofaeces.  The long term effects of this strategy on survival were questioned.

Sensitivity assessment: The biotope occurs in outer estuaries and is therefore probably subject to variable turbidity.  Crepidula fornicata is able to survive high turbidity events and is unlikely to be negatively affected by changes in turbidity at the benchmark level (the highest benchmark value is 300 mg/l).  The infaunal polychaetes are likely to be resistant to changes in turbidity.  Whilst an increase is therefore unlikely to have an impact on the biotope community, a significant, long-term decrease may lead to the development of a community of macroalgae which could potentially compete with some of the epifaunal species in the biotope, and result in loss of the biotope.  Assuming a turbidity value of ‘Intermediate’ (10-100 mg/l), an increase to ‘Medium’ (100 -300 mg/l) is unlikely to have an effect.  However a decrease to ‘Clear’ (<10 mg/l) could result in colonization from algal species.  Whilst mortality from changes in suspended sediment are unlikely, colonization by algae could result in fundamental change in biotope.  Given that the pressure benchmark is for one year, return to prevailing conditions would likely result in loss of the algae and full recovery to SS.SMx.SMxVS.CreMed or SS.SMx.SMxVS.CreAsAa.  Resistance is, therefore, ‘High’, resilience is ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Medium High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Stacks of adult Crepidula fornicata live attached to the substratum and are incapable of moving. They are active suspension feeders, generating a water current through the mantle cavity by ciliary action and trapping food particles on a mucous sheet lying across the front surface of the gill filament. Smothering with a 5 cm layer of sediment would be expected to clog the feeding and respiration structures. 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, considering that Crepidula fornicata lives in chains of up to 12 individuals, at least some of the chain may 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.

Polychaetes are infaunal, and deposition of fine material (e.g. continuous deposition) would be expected to lead to higher densities of macrobenthic organisms. For example, in the North Sea (Belgium) deposition of fine particle sediment, disturbed by scour around the base of a wind farm tower led to higher macrobenthic densities and created a shift in macrobenthic communities around the wind farm tower (influenced by the  direction fine material had settled) (Coates et al., 2014). Borja et al. (2000) classified the characterizing species Mediomastus fragilis as ‘Group III’ which ‘tolerate disturbance and excess organic content’.

The faunal community considered in this report are generally permanently attached to the substratum and are active suspension feeders. Because adult Styela clava typically reach 8-12 cm (although it has been recorded up to 20 cm) (Neish, 2007), smothering with 5 cm of sediment is likely to only affect a small proportion of the population. Recovery should be rapid, facilitated by the remaining adults. 

Sensitivity assessment. Removal of 5cm of sediment is likely to be occur and mortality among the characterizing species is unlikely. Therefore, resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Medium High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Stacks of adult Crepidula fornicata live attached to the substratum and are incapable of moving. They are active suspension feeders, generating a water current through the mantle cavity by ciliary action and trapping food particles on a mucous sheet lying across the front surface of the gill filament. Smothering with a 30 cm layer of sediment would bury the majority of the population, even after considering that Crepidula fornicata is capable of clearing its feeding structures at some energetic cost (Johnson, 1972).

It should be noted that 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), a burial event at this level is likely to cause some mortality.

Polychaetes are infaunal, and deposition of fine material (e.g. continuous deposition) would be expected to lead to higher densities of macrobenthic organisms. For example, in the North Sea (Belgium) deposition of fine particle sediment, disturbed by scour around the base of a wind farm tower led to higher macrobenthic densities and created a shift in macrobenthic communities around the wind farm tower (influenced by the  direction fine material had settled) (Coates et al., 2014). Within a Marine Biotic Index compiled by Borja et al. (2000), the characterizing species Mediomastus fragilis was classified as ‘Group III’ which tolerate disturbance and excess organic content.

The faunal community considered in this report are generally permanently attached to the substratum and are active suspension feeders. Styela clava typically reach 8-12 cm (although it has been recorded up to 20 cm) (Neish, 2007), smothering with 30 cm of sediment is likely bury the entire population

Sensitivity assessment: The evidence suggests that the characterizing Crepidula fornicata is quite resilient to sedimentation and burial, however, mortality could not be ruled out. Whilst the polychaetes are unlikely to be affected, the faunal community is likely to be entirely buried..  Where the biotope occurs in lower energy, removal of the sediment may be prolonged.  Resistance is, therefore, assessed as ‘Low’, resilience as ‘High’ and sensitivity as ‘Low’.

Not Assessed (NA) Not Assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

'No evidence' was found.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

'No evidence' was found.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

'No evidence' was found for effect of noise or vibrations on the characterizing species.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Whilst polychaetes have been reported to synchronize reproduction through light (Franke, 1986), introduction of light is unlikely to cause mortality among the characterizing species and resistance has been assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not Sensitive’.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

'Not relevant'

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

'Not relevant' to seabed habitats. NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

'Not relevant'.

Biological Pressures

 ResistanceResilienceSensitivity
Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Key characterising species within this biotope are not cultivated or trans-located. This pressure is therefore considered ‘Not relevant’ to this biotope group.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

These biotopes are dominated by Crepidula fornicata, which is itself an Invasive Non-Indigenous 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). The invasive ascidian Styela clava is also present in SS.SMx.IMx.CreAsAn.  This pressure is therefore ‘Not relevant’.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Gibbs (1971) reported that almost the entire population of Aphelochaeta marioni in Stonehouse Pool, Plymouth, UK 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.  No information was found concerning infections of Crepidula fornicata.

Sensitivity assessment: No evidence of mortality in the characterizing species was found.  Resistance is, therefore, assessed as ‘High’, resilience as ‘High’ and the biotope is assessed as ‘Not sensitive’.

Low High Low
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Medium
C: Medium

There is no evidence that any of the species in this biotope are exploited commercially.  Crepidula fornicata is considered a pest on oyster beds (Fretter & Graham, 1981), and in response to the invasion of shellfisheries, 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.  Suction dredging has been used in France, with removal of 30,000 t/yr from St Brieuc Bay and the Bay of Mont Saint-Michel (Fitzgerald, 2007).  The Bay of Mont Saint-Michel was reported to have a slipper limpet population of 100,000 tonnes in 1995-1996 which increased to 150,000 tonnes by 2005, despite the removal of 44,000 tonnes of slipper limpets during this period (Blanchard, 2009).  The effect of dredging for slipper limpets would be similar to removing the upper layer of the substrata and therefore a decline in species richness is expected.

Sensitivity assessment. Whilst dedicated removal programmes by dredging for Crepidula fornicata exist, these have typically focused on limiting expansion and eradication (Fitzgerald, 2007; Sauriau et al. 1998).  However, resistance is assessed as ‘Low’, resilience as ‘High’ and sensitivity as ‘Low’.

Low High Low
Q: Low
A: NR
C: NR
Q: Medium
A: Medium
C: Medium
Q: Low
A: Low
C: Low

Living infaunally, the polychaetes are unlikely to be affected directly from removal of Crepidula fornicata, however techniques for removing slipper limpets typically involve dredging or extraction, which would remove the top layer of the substrata and therefore be analogous to the penetration pressure assessed above.  Therefore, if the Crepidula fornicata bed was removed by accident (e.g. as by-catch), then resistance is assessed as ‘Low’, resilience as ‘High’ and sensitivity as ‘Low’.

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., 2009. Recent expansion of the slipper limpet population (Crepidula fornicata) in the Bay of Mont-Saint-Michel (Western Channel, France). Aquatic Living Resources, 22 (1), 11-19.
  7. 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.
  8. Boldina, I. & Beninger, P.G., 2014. Fine-scale spatial distribution of the common lugworm Arenicola marina, and effects of intertidal clam fishing. Estuarine Coastal and Shelf Science, 143, 32-40.
  9. Borja, A., Franco, J. & Perez, V., 2000. A marine biotic index to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments. Marine Pollution Bulletin, 40 (12), 1100-1114.
  10. Brante, A., Fernández, M. & Viard, F., 2009. Limiting factors to encapsulation: the combined effects of dissolved protein and oxygen availability on embryonic growth and survival of species with contrasting feeding strategies. Journal of Experimental Biology, 212 (14), 2287-2295.
  11. 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.
  12. 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.
  13. 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.]
  14. 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.
  15. Budd, G.C. 2008. Alcyonium digitatum Dead man's fingers. 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/species/detail/1187

  16. Coates, D.A., Deschutter, Y., Vincx, M. & Vanaverbeke, J., 2014. Enrichment and shifts in macrobenthic assemblages in an offshore wind farm area in the Belgian part of the North Sea. Marine Environmental Research, 95, 1-12.
  17. 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.
  18. Cole, S., Codling, I.D., Parr, W., Zabel, T., 1999. Guidelines for managing water quality impacts within UK European marine sites [On-line]. UK Marine SACs Project. [Cited 26/01/16]. Available from: http://www.ukmarinesac.org.uk/pdfs/water_quality.pdf
  19. Collie, J.S., Hall, S.J., Kaiser, M.J. & Poiner, I.R., 2000. A quantitative analysis of fishing impacts on shelf-sea benthos. Journal of Animal Ecology, 69 (5), 785–798.
  20. 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.
  21. Connor, D.W., Allen, J.H., Golding, N., Howell, K.L., Lieberknecht, L.M., Northen, K.O. & Reker, J.B., 2004. The Marine Habitat Classification for Britain and Ireland. Version 04.05. Joint Nature Conservation Committee, Peterborough. www.jncc.gov.uk/MarineHabitatClassification.

  22. 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.
  23. Coosen, J., Seys, J., Meire, P.M. & Craeymeersch, J.A.M, 1994. Effect of sedimentological and hydrodynamical changes in the intertidal areas of the Oosterschelde estuary (SW Netherlands) on distribution, density and biomass of five common macrobenthic species… (abridged). Hydrobiologia, 282/283, 235-249.
  24. 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.
  25. Cryer, M., Whittle, B.N. & Williams, K., 1987. The impact of bait collection by anglers on marine intertidal invertebrates. Biological Conservation, 42, 83-93.
  26. Daro, M.H. & Polk, P., 1973. The autecology of Polydora ciliata along the Belgian coast. Netherlands Journal of Sea Research, 6, 130-140.
  27. 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.
  28. 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.
  29. 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.
  30. 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.
  31. 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.
  32. Dernie, K.M., Kaiser, M.J., Richardson, E.A. & Warwick, R.M., 2003. Recovery of soft sediment communities and habitats following physical disturbance. Journal of Experimental Marine Biology and Ecology, 285-286, 415-434.
  33. 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.
  34. Diaz, R.J. & Rosenberg, R., 1995. Marine benthic hypoxia: a review of its ecological effects and the behavioural responses of benthic macrofauna. Oceanography and Marine Biology: an Annual Review, 33, 245-303.
  35. Dyrynda, P.E.J., 1994. Hydrodynamic gradients and bryozoan distributions within an estuarine basin (Poole Harbour, UK). In Proceedings of the 9th International Bryozoology conference, Swansea, 1992. Biology and Palaeobiology of Bryozoans (ed. P.J. Hayward, J.S. Ryland & P.D. Taylor), pp.57-63. Fredensborg: Olsen & Olsen.
  36. 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.
  37. Elliot, M., Nedwell, S., Jones, N.V., Read, S.J., Cutts, N.D. & Hemingway, K.L., 1998. Intertidal sand and mudflats & subtidal mobile sandbanks (Vol. II). An overview of dynamic and sensitivity for conservation management of marine SACs. Prepared by the Scottish Association for Marine Science for the UK Marine SACs Project.
  38. 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.
  39. 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.
  40. Ferns, P.N., Rostron, D.M. & Siman, H.Y., 2000. Effects of mechanical cockle harvesting on intertidal communities. Journal of Applied Ecology, 37, 464-474.
  41. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.
  42. 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
  43. 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.
  44. 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.
  45. 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.
  46. 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.
  47. Green, N.W., 1983. Key colonisation strategies in a pollution-perturbed environment. In Fluctuations and Succession in Marine Ecosystems: Proceedings of the 17th European Symposium on Marine Biology, Brest, France, 27 September - 1st October 1982. Oceanologica Acta, 93-97.
  48. 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.
  49. 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.
  50. Hall, S.J., 1994. Physical disturbance and marine benthic communities: life in unconsolidated sediments. Oceanography and Marine Biology: an Annual Review, 32, 179-239.
  51. 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.
  52. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.
  53. Herreid, C.F., 1980. Hypoxia in invertebrates. Comparative Biochemistry and Physiology Part A: Physiology, 67 (3), 311-320.
  54. 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.
  55. 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.
  56. 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.
  57. Jennings, S. & Kaiser, M.J., 1998. The effects of fishing on marine ecosystems. Advances in Marine Biology, 34, 201-352.
  58. 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,
  59. Johnson, J.K., 1972. Effect of turbidity on the rate of filtration and growth of the slipper limpet, Crepidula fornicata. Veliger, 14, 315-320.
  60. 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.
  61. Kelly, D.L., 1974. Aspects of the reproductive ecology of three solitary ascidians, Ciona intestinalis (L.), Styela plicata (L.), and Styela clava (H.), from Southern California. Master's thesis, California State University.
  62. Lützen, J., 1998. Styela clava Herdman (Urochordata, Ascidiacea), a successful immigrant to North West Europe: ecology, propagation and chronology of spread. Helgoländer Meeresuntersuchungen, 52 (3-4), 383-391.
  63. Lützen, J. & Sørensen, V., 1993. Udbredelse, økologi og forplantning i Danmark af den indslæbte østasiatiske søpung, Styela clava Herdman. Flora og Fauna, 99, 75-79.
  64. Langston, W.J., Chesman, B.S., Burt, G.R., Hawkins, S.J., Readman, J. & Worsfold, P., 2003. Characterisation of European Marine Sites. Poole Harbour Special Protection Area. Occasional Publication. Marine Biological Association of the United Kingdom, 12, 111.
  65. 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.
  66. 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.
  67. NBN, 2015. National Biodiversity Network 2015(20/05/2015). https://data.nbn.org.uk/
  68. Neish, A.H. 2007. Pachymatisma johnstonia A sponge. 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/species/detail/1885

  69. 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.
  70. Newell, R., Seiderer, L. & Hitchcock, D., 1998. The impact of dredging works in coastal waters: a review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed. Oceanography and Marine Biology: An Annual Review, 36, 127-178.
  71. 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.
  72. Olafsson, E.B., Peterson, C.H. & Ambrose, W.G. Jr., 1994. Does recruitment limitation structure populations and communities of macro-invertebrates in marine soft sediments: the relative significance of pre- and post-settlement processes. Oceanography and Marine Biology: an Annual Review, 32, 65-109
  73. 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.
  74. 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/
  75. 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.
  76. Rees, E., Nicolaidou, A. & Laskaridou, P., 1976. The effects of storms on the dynamics of shallow water benthic associations. In Proceedings of the 11th European Symposium on Marine Biology, Galway, 5-11 October, 1976. Biology of benthic organisms (ed. B.F., Keegan; P., O'Ceidigh & P.J.S., Boaden), pp. 465-474.
  77. 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.
  78. Reise, K., 1985. Tidal flat ecology. An experimental approach to species interactions. Springer-Verlag, Berlin.
  79. Rosenberg, R., Hellman, B. & Johansson, B., 1991. Hypoxic tolerance of marine benthic fauna. Marine Ecology Progress Series, 79, 127-131.
  80. Ryland, J.S., 1970. Bryozoans. London: Hutchinson University Library.
  81. 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.
  82. 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.
  83. Sims, L.L., 1984. Osmoregulatory capabilities of three macrosympatric stolidobranch ascidians, Styela clava Herdman, S. plicata (Lesueur), and S. montereyensis (Dall). Journal of Experimental Marine Biology and Ecology, 82 (2-3), 117-129.
  84. Smith, J.E. (ed.), 1968. 'Torrey Canyon'. Pollution and marine life. Cambridge: Cambridge University Press.
  85. 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.
  86. Suchanek, T.H., 1993. Oil impacts on marine invertebrate populations and communities. American Zoologist, 33, 510-523.
  87. 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.
  88. Thain, J.E., Davies, I.M., Rae, G.H. & Allen, Y.T., 1997. Acute toxicity of ivermectin to the lugworm Arenicola marina. Aquaculture, 159, 47-52.
  89. Thieltges, D.W., Strasser, M., Van Beusekom, J.E. & Reise, K., 2004. Too cold to prosper—winter mortality prevents population increase of the introduced American slipper limpet Crepidula fornicata in northern Europe. Journal of Experimental Marine Biology and Ecology, 311 (2), 375-391.
  90. 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.
  91. 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.
  92. Tyler-Walters, H. & Ballerstedt, S., 2007. Flustra foliacea Hornwrack. 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/species/detail/1609

  93. Uncles, R.J., Lavender, S.J. & Stephens, J.A., 2001. Remotely sensed observations of the turbidity maximum in the highly turbid Humber estuary, UK. Estuaries, 24, 745-755.
  94. 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.
  95. 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:

Readman, J.A.J. & Rayment, W.J. 2016. 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: 13/06/2016