Common razor shell (Ensis ensis)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help

Summary

Description

Razor shells have an elongated and fragile shell with valves gaping at both ends. The shell is smooth on the outside and whitish in colour with vertical and horizontal reddish-brown or purplish-brown markings separated by a diagonal line. The periostracum is olive-green. The inner surface is white with a purple tinge and the foot is pale red-brown. The presence of razor shells in the sand is indicated by keyhole-shaped openings made by the short, united siphons which extend just above the sediment surface when the animal is suspension feeding.

There are four native species of razor shell in Britain and Ireland: Ensis ensis, Ensis siliqua, Ensis minor (syn. siliqua var. minor), and Ensis magnus (syn. arcuatus) (Oliver et al., 2016). Ensis ensis is slender, with a slightly curved elongate shell up to 13 cm long. In Ensis siliqua both dorsal and ventral margins are straight and adults are up to 20 cm long. Ensis minor grows up to 15 cm long and both dorsal and ventral margins are straight.  Ensis magnus grows up to 15 cm long, the dorsal margin is straight and the ventral margin is curved. It may be particularly difficult to distinguish between species in juvenile individuals.

Recorded distribution in Britain and Ireland

Common on all British coasts.

Global distribution

From Norway to the Atlantic coast of Spain. Ensis ensis and Ensis siliqua found in some parts of the Mediterranean.

Habitat

Razor shells live in deep, vertical, permanent burrows in fine, sometimes muddy, sand from extreme low water to the shallow sublittoral. Ensis arcuatus lives in coarser sediment than either Ensis ensis or Ensis siliqua.

Depth range

to a depth of 60m

Identifying features

Ensis sp.

  • Anterior margin is rounded and the posterior is obliquely truncate.
  • Anterior and posterior ends gaping.
  • Left valve with two, projecting peg-like cardinal teeth, and two elongate, posterior laterals, situated above the other. Right valve with one short cardinal and a single, elongated posterior lateral.

Ensis ensis

  • The dorsal and ventral margins are evenly and equally curved.
  • Up to 13 cm long.
  • Large foot pale red-brown in colour.

Ensis siliqua

  • The dorsal and ventral margins of the shell are parallel and almost straight, and the anterior and posterior margins are obliquely truncate, with rounded corners.
  • Up to 20 cm long.
  • Foot creamy white with brown lines.

Ensis arcuatus

  • The dorsal margin of the shell is almost straight, the ventral margin curved, shell widest mid-length.
  • Length up to 15 cm.
  • Foot creamy white with brown lines

Additional information

  • Many intertidal populations have been reduced by over fishing and the species is in decline in many areas.
  • Razor fish are very sensitive to minor perturbations (for instance increased/decreased temperature and higher to lower salinity - salt is used as a method of dislodging them from their burrows).
  • There are two other species of razor shell common to Britain, both larger than Ensis ensis and typically occupying different sediment types: Ensis siliqua which has straight margins and is up to 20 cm in length, is found in fine sand on moderately exposed shores and Ensis arcuatus which is curved and up to 15 cm in length is found in coarse sand and fine gravel.
  • A non-native species Ensis americanus (synonym: Ensis directus) was found in 1989 on Holme beach, Norfolk (Howlett 1990). Currently it is found at sites along the British east coast south from the Humber and along the English Channel west as far as Rye Harbour, East Sussex. (Howlett 1990; J. Light & I. Killeen pers. comm.). It is also common in the Wash (JNCC, 1999).
  • Ensis ensis, (Linnaeus, 1758), MCS species index number W1999; Ensis arcuatus (Jeffreys, 1865), MCS species index number W1998
  • ; Ensis siliqua (Linnaeus, 1758), MCS species index number W2001.

The sensitivity and recoverability information has been compiled primarily using information regarding the common razor shell Ensis ensis.

Listed by

- none -

Biology review

Taxonomy

LevelScientific nameCommon name
PhylumMollusca
ClassBivalvia
OrderAdapedonta
FamilyPharidae
GenusEnsis
Authority(Linnaeus, 1758)
Recent Synonyms

Biology

ParameterData
Typical abundanceSee additional information
Male size rangeup to 13 cm
Male size at maturity>10 cm
Female size range>10 cm
Female size at maturity
Growth formBivalved
Growth rate2-4 cm/year
Body flexibilityNone (less than 10 degrees)
MobilityBurrower
Characteristic feeding methodActive suspension feeder
Diet/food sourcePlanktotroph
Typically feeds onSuspended organic detritus
SociabilitySolitary
Environmental positionInfaunal
DependencyNone.
SupportsIndependent
Is the species harmful?No

Ensis ensis is an edible species and therefore non-toxic. However, Ensis species are thought to be especially at risk of Amnesic Shellfish Poisoning (ASP) (Edward Fahy pers. comm.).

Biology information

Typical abundance. Abundance of Ensis sp. varies from high to low density. In favourable conditions - such as the lee of rocks, rocks and islands for Ensis arcuatus on the western coast, individuals are found in high densities in 'beds' which interchange individuals with the surrounding areas where they occur in a more dispersed pattern (Fahy et al. in press).

Size ranges. The size range given for Ensis ensis. Ensis siliqua males and females up to 20 cm and Ensis arcuatus males and females up to 15 cm.

Growth rates. Growth in the first winter is 2 to 4 cm. The three species have similar growth patterns but with different asymptotic lengths. In Ensis siliqua males grow faster than females. Growth rates are higher in the summer when the food supply is abundant, than in the winter when the temperature and food supply are both reduced. Ensis ensis also show a neap-spring lunar growth pattern with smaller growth bands during spring tides when animals are emersed for longer (Henderson & Richardson, 1994). The growth rate given is the maximum rate in the first year or two of life. Thereafter growth falls to 2 to 3 cm/year (Robinson & Richardson, 1998).

Habitat preferences

ParameterData
Physiographic preferences
Biological zone preferences
Substratum / habitat preferences
Tidal strength preferences
Wave exposure preferences
Salinity preferences
Depth rangeto a depth of 60m
Other preferences

No text entered

Migration PatternNon-migratory or resident

Habitat Information

Habitat. Ensis spp. occur virtually everywhere inshore but favourable conditions, such as the lee of reefs, rocks and islands make for high densities known as 'beds' which interchange individuals with the surrounding areas where they occur in a more dispersed pattern. Ensis ensis beds do occur at the extreme low water of spring tides but the species is much more common in depths of about 10 m (Holme, 1954). Single specimens have been collected from depths of 60 m in the Plymouth area. Ensis arcuatus lives in coarser sediment than either Ensis ensis or Ensis siliqua.

Migration. Henderson & Richardson (1994) observed a distribution of razor clam size classes on a shore in north Wales which may indicate that there is a gradual down-shore migration of juveniles into the adult population. They suggest that juveniles become established further up the shore because the low water mark is exposed to the strongest tidal currents.

Wave exposure. In moderate wave exposure, Ensis ensis may be replaced by the larger Ensis siliqua (Holme, 1954).

Life history

Adult characteristics

ParameterData
Reproductive type
Reproductive frequency Annual episodic
Fecundity (number of eggs)
Generation timeInsufficient information
Age at maturity3 years minimum
SeasonSummer - Summer
Life span11-20 years

Larval characteristics

ParameterData
Larval/propagule type-
Larval/juvenile development
Duration of larval stage1-2 months
Larval dispersal potential No information
Larval settlement period

Life history information

Lifespan. The lifespan of Ensis ensis is likely to be in excess of 10 years. The other two British species Ensis siliqua and Ensis arcuatus are also very long-lived, with a lifespan of up to 18 years (E. Fahy pers. Comm.).

Reproduction. Razor shells in Britain do not appear to breed before they are three years old (Henderson & Richardson, 1994). Breeding occurs during the summer but larval settlement is not successful every year, and recruitment of juveniles is irregular (Hayward et al., 1996). Breeding probably occurs during spring and the veliger larvae have a pelagic life of about a month (Fish & Fish, 1996). Studies on razor shells from North Wales showed that individuals of Ensis ensis were mature in July but were spent in August, indicating that spawning had occurred by the middle of the summer (Henderson & Richardson, 1994).

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

Use / to open/close text displayed

 IntoleranceRecoverabilitySensitivityEvidence / Confidence
Substratum loss [Show more]

Substratum loss

Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details

Evidence

Loss of the substratum will remove the resident population of the burrowing razor shell Ensis ensis and so intolerance is high. However, razor clams are very mobile bivalves and will rapidly migrate and recolonize favourable areas. In addition, razor shells have a pelagic larva, with annual spatfalls (E. Fahy pers. comm.) so it seems likely that populations could recover within a year. However, given the sporadic nature of the abundance of spatfalls, recovery may be more protracted and the age distribution of the population may be skewed towards younger individuals than before. In the Setubal region of Portugal, signs of recovery of Ensis siliqua populations was observed about 18 months after the cessation of fishing. However, yields were still low and it was recommended that the closure of fishing should remain for full recovery (Gaspar & Dias, 1999). However, it is likely that recovery should be complete within five years although beds of larger adults would probably take up to about 10 years.

High High Moderate Moderate
Smothering [Show more]

Smothering

Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details.

Evidence

Ensis ensis lives buried in sand, can extend its siphons and rise in its burrow and so is likely to tolerate smothering by 5 cm of sediment.

Tolerant Not relevant Not sensitive High
Increase in suspended sediment [Show more]

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Holme (1954) reports that Ensis ensis is the more silt tolerant of the British Ensis species and is generally found at sheltered localities or from offshore and in sediments with a silt percentage of up to 16%. A decrease in siltation may affect growth and fecundity if the supply of organic particulate matter declines.

Low High Low High
Decrease in suspended sediment [Show more]

Decrease in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

No information
Desiccation [Show more]

Desiccation

  1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
  2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

Ensis ensis is found in the intertidal at extreme low water so will be subject to desiccation only rarely. The shell gapes at both ends so that water loss cannot be prevented and the animal is therefore, likely to be highly intolerant of an increase in desiccation. If the animal is not surrounded by a burrow the shells open and the mantle splits. However, the species may burrow further into the sand during low tide to avoid desiccation although on a number of occasions Ensis ensis have been seen to come right out of the sand at low tide, and lie on the surface when a heavy mortality is likely to result (Holme, 1954). Ensis spp. may be held for some time out of water, provided the shells are kept closed (by being restrained by an elastic band for example) although periods are likely to be damaging. In years of good recruitment recolonization may occur within a year. However, recruitment is sporadic (see reproduction) and recovery may take longer but should be complete within five years.

High High Moderate Moderate
Increase in emergence regime [Show more]

Increase in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Ensis ensis is found in the intertidal at extreme low water being exposed briefly once or twice a month and is therefore likely to be highly intolerant of an increase in emergence. On a number of occasions Ensis ensis have been seen to come right out of the sand at low tide, and lie on the surface when a heavy mortality is likely to result. While some probably survive the exposure and burrow in again when the tide returns, many must be eaten by gulls (Holme, 1954). The species will probably tolerate a decrease in emergence which will probably allow the population to extend up the shore. In years of good recruitment recovery may occur within a year. However, recruitment is sporadic (see reproduction) and recovery may take longer but should be complete within five years.

High High Moderate High
Decrease in emergence regime [Show more]

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

No information
Increase in water flow rate [Show more]

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

In an investigation of an intertidal population of Ensis ensis in north Wales Henderson & Richardson (1994) found that the largest razor clams were found only at extreme low water, whilst smaller clams (<100mm) were collected further up the shore. The authors suggest that the area on the lower shore may be unsuitable for juveniles because they are exposed to the greatest tidal currents and may get washed away. Increased water flow is likely to make the sediment more mobile and individuals of Ensis ensis may be washed away. However, since the species is able to burrow deeper into the sediment during unsuitable conditions water flow rates would have to increase substantially to remove individuals and so intolerance is assessed as intermediate.

Intermediate High Low Moderate
Decrease in water flow rate [Show more]

Decrease in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

No information
Increase in temperature [Show more]

Increase in temperature

  1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
  2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

Populations of the razor shell Ensis siliqua in the warmer waters of Portugal spawn several months earlier in the year than UK populations and are sexually mature at only one year old (Gaspar & Monteiro, 1998; Henderson & Richardson, 1994) compared to three in the UK. Therefore, it is likely that temperature is important for growth and fecundity of Ensis ensis. However, the species extends north and south of British populations and so is likely to be tolerant of a long term change in temperature of 2°C. The species is likely to be more intolerant of a rapid change in temperature of 5°C outside its normal temperature range. During the cold winter of 1962-63 when air temperatures fell below freezing for several weeks Crisp (1964) recorded very high levels of mortality of Ensis ensis and suggests that the razor shells lost the ability to burrow at lowered temperatures, and so were left exposed at the surface. At some sites live individuals were later found by digging so some protection is afforded by burrowing position. Ensis spp. are known to emerge from the sediment when shallow inshore waters become warm as happened in Torbay in 1999 (K. Hiscock pers. comm.). In years of good recruitment recolonization may occur within a year, however, recruitment is sporadic and may take several years when recruitment is poor.

Intermediate High Low Moderate
Decrease in temperature [Show more]

Decrease in temperature

  1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
  2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

No information
Increase in turbidity [Show more]

Increase in turbidity

  1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
  2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Changes in light attenuation resulting from turbidity changes are not likely to affect the suspension feeding Ensis ensis. However, if increased turbidity is caused by silt particles additional feeding costs may be imposed and phytoplankton production may decline reducing food supplies. The species may benefit from increased nutritional value if turbidity is caused by organic particles.

Low High Low Moderate
Decrease in turbidity [Show more]

Decrease in turbidity

  1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
  2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

No information
Increase in wave exposure [Show more]

Increase in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

On exposed beaches where the sand is continually churned by waves, razor shells are absent. Wave scour caused by winter gales along the North Wales coast washed out some individuals of Ensis ensis although numbers were much lower than for some other fauna (Rees et al., 1976). Therefore, significant increases in wave exposure may cause the death of some individuals in a population and may limit individuals to below the low-water mark. On moderately wave exposed beaches Ensis ensis may be replaced by the larger Ensis siliqua (Holme, 1954). In years of good recruitment recolonization may occur within a year, however, recruitment is sporadic and may take several years when recruitment is poor.

Intermediate High Low Moderate
Decrease in wave exposure [Show more]

Decrease in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

No information
Noise [Show more]

Noise

  1. Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods.
  2. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details

Evidence

Ensis ensis can probably detect the vibration caused by predators and will withdraw its siphons. No information was found concerning the effect of noise or vibration on razor shell populations although the species is unlikely to be sensitive to noise or vibration.

Tolerant Not relevant Not sensitive Moderate
Visual presence [Show more]

Visual presence

Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details

Evidence

Razor shells are unlikely to be sensitive to visual disturbance.

Tolerant Not relevant Not sensitive Moderate
Abrasion & physical disturbance [Show more]

Abrasion & physical disturbance

Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details.

Evidence

Ensis ensis has a thin brittle shell and so is highly intolerant of abrasion and physical disturbance. Eleftheriou & Robertson (1992) observed large numbers of Ensis ensis killed or damaged by dredging operations and Gaspar (1998) reports high levels of damage in Ensis siliqua from fishing. Therefore, an intolerance of high has been recorded. In years of good recruitment recolonization may occur within a year. However, given the sporadic nature of the abundance of spatfalls, recovery may be more protracted and the age distribution of the population may be skewed towards younger individuals than before. In the Setubal region of Portugal, signs of recovery of Ensis siliqua populations was observed about 18 months after the cessation of fishing. However, yields were still low and it was recommended that the closure of fishing should remain for full recovery (Gaspar & Dias, 1999). However, it is likely that recovery should be complete within five years although beds of larger adults would probably take up to about 10 years.

High High Moderate High
Displacement [Show more]

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Razor shells displaced from their burrow onto the surface of the sediment, as may be caused by a storm, can rapidly reburrow on return to a suitable substratum and so can survive. However, if the method of removal is stressful the species ability to reburrow on return to a suitable substratum may be impaired. For example, live specimens removed by dredging and then replaced on the substratum took a long time to reburrow and many were consumed by predatory crabs (Robinson & Richardson, 1998). Therefore, intolerance has been assessed as intermediate.

Intermediate High Low High

Chemical pressures

Use [show more] / [show less] to open/close text displayed

 IntoleranceRecoverabilitySensitivityEvidence / Confidence
Synthetic compound contamination [Show more]

Synthetic compound contamination

Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:

  • evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity;
  • evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity;
  • evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity.

The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details.

Evidence

High levels of mortality of Ensis spp. were found at places distant from shores treated with dispersants following the Torrey Canyon oil spill (Smith, 1968). Almost complete mortality of razor shells was found at stations more than a kilometre from the shore at a depth of about 20m. Experiments have shown that Ensis species are intolerant of only 0.5 ppm of detergent with high intolerance to the solvent rather than the surfactant element (Smith, 1968). On return to normal conditions recovery may occur within a year if recruitment is good. However, recruitment is sporadic (see reproduction) and recolonization may take longer but should be complete within five years.

High High Moderate Moderate
Heavy metal contamination [Show more]

Heavy metal contamination

Evidence

No specific information on the effect of heavy metals to razor shells could be found. However, in investigations of faunal distribution in the metal contaminated Restronguet Creek in the Fal estuary bivalve molluscs appear to be the most vulnerable (Bryan, 1984). The bivalve Scrobicularia plana, for example, is absent from large areas of the intertidal muds where, under normal conditions, it would account for a large amount of the biomass (Bryan & Gibbs, 1983). Bryan (1984) also reports that metal-contaminated sediments can exert a toxic effect on burrowing bivalves and so intolerance has been assessed as intermediate. Embryonic and larval stages of bivalve molluscs are the most vulnerable to heavy metals (Bryan, 1984). On return to normal conditions recovery may occur within a year if recruitment is good. However, recruitment is sporadic (see reproduction) and recovery may take longer but should be complete within five years.

Intermediate High Low Low
Hydrocarbon contamination [Show more]

Hydrocarbon contamination

Evidence

Ensis ensis is reported to bioconcentrate aromatics and is highly intolerant of hydrocarbons. Four days after the Sea Empress oil spill moribund razor shells (mostly Ensis siliqua) were the first organisms observed to have been affected (SEEEC, 1998). Hundreds of razor shells were protruding from the sand and most died in that position over the next few days. Glegg & Rowland (1996) observed dead razor shells washed up on the shore a few days after the final break-up of the Braer wreck and about a million razor shells were seen after the Amoco Cadiz oil spill in Brittany (Southward, 1978). On return to normal conditions recolonization should be high. Although recruitment of Ensis ensis is sporadic recovery should be complete within five years. However, the age distribution of the population may be skewed towards younger individuals than before.

High High Moderate Moderate
Radionuclide contamination [Show more]

Radionuclide contamination

Evidence

Insufficient
information.

No information No information No information Not relevant
Changes in nutrient levels [Show more]

Changes in nutrient levels

Evidence

Although no specific information regarding the response of Ensis ensis to changes in nutrient levels the species is not characteristic of habitats at the upper end of the organic gradient and so is assessed as having intermediate intolerance.

Intermediate High Low Low
Increase in salinity [Show more]

Increase in salinity

  1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
  2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Ensis ensis does not occur in water of reduced salinity, although its absence from estuaries may sometimes be due to the lack of deposits of suitable grade (Holme, 1954). The species concentrates K and Ca (Kinne, 1971) and can probably tolerate a degree of salinity reduction because it will be subject to periodic precipitation in the intertidal. Intolerance has therefore, been assessed as intermediate. One means of collecting Ensis spp. is to sprinkle salt on their burrows causing them to rise to the surface.

Intermediate High Low Moderate
Decrease in salinity [Show more]

Decrease in salinity

  1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
  2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

No information
Changes in oxygenation [Show more]

Changes in oxygenation

Benchmark.  Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details.

Evidence

Ensis species typically occur in sands which are not black below the surface i.e. where conditions are oxygenated and not reducing. Where seaweed or other organic matter gets buried in and incorporated in the sand, resulting in a black layer containing ferrous sulphide, Ensis is absent. However, the species can tolerate sands which are slightly reducing, in which there is a grey layer below the surface, such as occurs on beaches of firm fine sand in which the organic content is not high, but there is little circulation of water (Holme, 1954), and so intolerance is assessed as intermediate.

Intermediate High Low Moderate

Biological pressures

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 IntoleranceRecoverabilitySensitivityEvidence / Confidence
Introduction of microbial pathogens/parasites [Show more]

Introduction of microbial pathogens/parasites

Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details.

Evidence

No information on diseases of Ensis spp. was found. However, mortalities of the Pacific razor clam Siliqua patula, explained by infection with Rickettsia-like organisms, have been reported in several locations in the US (Elston, 1986).

No information No information No information Not relevant
Introduction of non-native species [Show more]

Introduction of non-native species

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

The American razor shell Ensis americanus (synonym: Ensis directus) has spread from its point of introduction in the German Bight in 1978 into southern North Sea countries. The species, which is native to the Atlantic coast of North America was found in Britain in 1989 on Holme beach, Norfolk. The long-lasting pelagic larval stage is assumed to be transported with water currents and has spread rapidly in southern North Sea countries and is now found at sites along the British east coast south from the Humber and along the English Channel west as far as East Sussex (Eno et al., 1997). The species lives in brackish as well as marine conditions so may be filling a niche in estuaries not already occupied (Urk van, 1987). Ensis americanus is also found in much finer and unstable sand than Ensis ensis and so the two species may not be in direct competition. Armonies & Reise (1999) report that there were no significant interactions between Ensis americanus and resident species.

Intermediate High Low Moderate
Extraction of this species [Show more]

Extraction of this species

Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Traditionally Ensis ensis has been hand collected for food, bait and personal use. In Scotland, some subtidal razor clam beds are dense enough to be exploited commercially and recently the species has been harvested by suction dredger (Fowler, 1999; Robinson & Richardson, 1998). Ensis ensis has a pelagic larva so it seems likely that the population could recolonize within a year. However, given the sporadic nature of recruitment in Ensis ensis, recovery may be more protracted but should be complete within five years. However, the age distribution of the population may be skewed towards younger individuals than before. In the Orkneys for example, where Ensis arcuatus beds are subject to repeated dredging, populations have a significantly smaller average length than those at an un-fished site (Robinson & Richardson, 1998).

Intermediate High Low High
Extraction of other species [Show more]

Extraction of other species

Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Ensis ensis has no known obligate relationships with other species.

Not relevant Not relevant Not relevant Not relevant

Additional information

The intolerance and recoverability information has been compiled primarily using information regarding the common razor shell Ensis ensis.  Occasional mass mortalities of razor clams have occurred being attributable to several causes, among them storms (Tebble, 1966) and "adverse environmental conditions" (Howard, 1998). In western Ireland in the spring of 2001, there were mass mortalities of razor clams (Fahy, in press) over too wide an area to be explained by local environmental conditions. Histological and bacterial examinations were carried out but no pathological cause was identified. It is suggested that mortality is explained as a natural post-spawning phenomenon, which in 2001 was unusually severe, possibly exacerbated by an environmental factor.

Importance review

Policy/legislation

- no data -

Status

Non-native

ParameterData
NativeNative
Origin-
Date Arrived-

Importance information

Traditionally Ensis ensis has been hand collected for food, bait and personal use. Boats with hydraulic dredges and SCUBA diving have also been employed to collect up to a tonne of live razor clams each week (Allen, 1990) although it is unclear which species are being collected or how often they are fished commercially. More recently, in Scotland and Ireland, dense subtidal razor clam beds have been exploited commercially and the species is now harvested by hydraulic dredger (Fowler, 1999; Fahy, 1999). However, the vulnerability of the species to overfishing has been recognised with visible declines in stocks in some areas and absence of larger animals (Henderson & Richardson, 1994; Gaspar & Monteiro, 1998).

Bibliography

  1. Oliver, P.G., Holmes, A.M., Killeen, I.J. & Turner, J.A., 2016. Marine Bivalve Shells of the British Isles. Amgueddfa Cymru - National Museum Wales. Available from: http://naturalhistory.museumwales.ac.uk/britishbivalves [Cited:  3 July 2018].

Datasets

  1. Centre for Environmental Data and Recording, 2018. IBIS Project Data. Occurrence dataset: https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

  2. Cofnod – North Wales Environmental Information Service, 2018. Miscellaneous records held on the Cofnod database. Occurrence dataset: https://doi.org/10.15468/hcgqsi accessed via GBIF.org on 2018-09-25.

  3. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) data for Great Britain and Ireland - restricted access. Occurrence dataset: https://doi.org/10.15468/4bsawx accessed via GBIF.org on 2018-09-25.

  4. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) records for Great Britain and Ireland. Occurrence dataset: https://doi.org/10.15468/aurwcz accessed via GBIF.org on 2018-09-25.

  5. Environmental Records Information Centre North East, 2018. ERIC NE Combined dataset to 2017. Occurrence dataset: http://www.ericnortheast.org.ukl accessed via NBNAtlas.org on 2018-09-38

  6. Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01

  7. Fife Nature Records Centre, 2018. St Andrews BioBlitz 2015. Occurrence dataset: https://doi.org/10.15468/xtrbvy accessed via GBIF.org on 2018-09-27.

  8. Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: https://www.kentwildlifetrust.org.uk/ accessed via NBNAtlas.org on 2018-10-01.

  9. Lancashire Environment Record Network, 2018. LERN Records. Occurrence dataset: https://doi.org/10.15468/esxc9a accessed via GBIF.org on 2018-10-01.

  10. Merseyside BioBank., 2018. Merseyside BioBank (unverified). Occurrence dataset: https://doi.org/10.15468/iou2ld accessed via GBIF.org on 2018-10-01.

  11. National Trust, 2017. National Trust Species Records. Occurrence dataset: https://doi.org/10.15468/opc6g1 accessed via GBIF.org on 2018-10-01.

  12. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  13. Norfolk Biodiversity Information Service, 2017. NBIS Records to December 2016. Occurrence dataset: https://doi.org/10.15468/jca5lo accessed via GBIF.org on 2018-10-01.

  14. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-05-20

  15. Outer Hebrides Biological Recording, 2018. Invertebrates (except insects), Outer Hebrides. Occurrence dataset: https://doi.org/10.15468/hpavud accessed via GBIF.org on 2018-10-01.

  16. South East Wales Biodiversity Records Centre, 2018. SEWBReC Molluscs (South East Wales). Occurrence dataset: https://doi.org/10.15468/jos5ga accessed via GBIF.org on 2018-10-02.

Citation

This review can be cited as:

Hill, J.M. 2024. Ensis ensis Common razor shell. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 20-05-2024]. Available from: https://www.marlin.ac.uk/species/detail/1419

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Last Updated: 01/02/2024