The Marine Life Information Network

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

Bathyporeia pelagica lives infaunally in the uppermost 3 cm of sandy substrata. The removal of the substratum would also remove the resident population and therefore intolerance has been assessed to be high. Re-population is likely to be rapid (see additional information below).

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

Within amphipod crustaceans the most efficient adaptations of body form for a sand burrowing mode of life have occurred (Maurer et al., 1986). Bathyporeia pelagica would probably be unaffected by an additional covering of a sediment of a texture within its habitat preference (fine - medium sand, 0.125-0.5 mm median diameter, Wentworth scale), although there may be an energetic cost incurred by the additional burrowing activity required to attain a near-surface position for feeding and to swim. However, Maurer et al., (1986) observed curtailment of burrowing activity and reduced survivorship in another burrowing amphipod, Parahaustorius longimerus (Haustoriidae), when exposed to 'exotic' sediments with a greater silt/clay content. Therefore, Bathyporeia pelagica is likely to be more intolerant of smothering by both coarser and finer particles and viscous materials such as oil, through which burrowing is likely to be hindered. Consequently, the intolerance of Bathyporeia pelagica to smothering has been assessed to be intermediate. The species is likely to have a high capacity for recovery (see additional information, below).

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

Bathyporeia pelagica is an infaunal species whose feeding is not reliant upon a supply of suspended material, and it is unlikely that its swimming activity would be affected by an increase in the suspended matter in the water column, as it is a regular swimmer in the surf plankton, where the concentration of suspended particles would be expected to be higher (Fincham, 1970a). Furthermore, during the winter, when the species often extends its distribution into the mouths of estuaries, Bathyporeia pelagica may encounter concentrations of suspended sediment measurable in grams per litre (benchmark is mg/l) (Cole et al., 1999). However, in turn, as a result of increased suspended sediment, the quantity of material deposited on the substratum surface is likely to increase on the ebb tide. Bathyporeia pelagica appears to have a habitat preference for substrata of fine to medium sand with a silt/clay content of <5% (Fish & Fish, 1978). Increased deposition of finer particles may result in changes of the sediment composition, certainly of the surface layers, and could have a smothering effect on the infaunal population (see smothering). However, the effects of accretion of material are addressed under smothering (see above), and as Bathyporeia pelagica is a constituent of the surf plankton, intolerance has been assessed as low. The species is likely to have a very high capacity for recovery (see additional information, below).

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

Bathyporeia pelagica is an infaunal species whose feeding is not reliant upon a supply of suspended material. A reduced concentration of suspended matter may be indicative of an alteration of shore topography, resulting in the reduced deposition of material and habitat loss for the species. However, for the period of one month effects are not likely to be significant, and intolerance has been assessed to be low. The species is likely to have an immediate capacity for recovery and re-population (see additional information, below).

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

Desiccation is unlikely to prove a lethal factor to a species of an established beach fauna since the risk of drying up follows a regular pattern to which the species have evolved e.g. the development of physiological adaptations to withstand the risk of desiccation (Eltringham, 1971). Bathyporeia pelagica is an intertidal species, whose distribution typically extends from above mean tide level (MTL), into the shallow sublittoral on beaches of clean medium to fine sand. Medium to fine-grained sand remains damp throughout the tidal cycle (Connor et al. 1997b) and its uppermost distribution on the shore is apparently primarily determined by its intolerance to reduced salinity (Preece, 1970). It is also a mobile species able to migrate from intolerable environmental fluctuations. If Bathyporeia pelagica were exposed to a change in desiccation equivalent to a change in position of one vertical zone on the shore, its environmental position and physiology are likely to protect it from the effects of desiccation and Bathyporeia pelagica has been assessed not to be intolerant of the benchmark change in desiccation.

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

Bathyporeia pelagica is an intertidal species, found from slightly above the mean tide level (MTL) into the shallow sublittoral, consequently it experiences regular periods of emersion. During periods of emergence, birds such as the ringed plover, Charadrius hiaticula and grey plover,Pluvialis squatarola, exploit populations of intertidal animals. An additional hour of emergence would allow the birds to feed for longer and the viability of the population of Bathyporeia pelagica may be reduced. Intolerance has been assessed to be low, and recovery expected to be very high (see additional information, below).

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

Bathyporeia pelagica is an intertidal species that experiences regular periods of immersion and emersion. Its distribution extends into the shallow sublittoral where it remains immersed on all but the lowest spring tides. Therefore Bathyporeia pelagica has been assessed to be tolerant of a decrease in emergence.

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

An increase of two categories in the water flow rate for the duration of one year would probably result in the winnowing away of the finest fraction of sand, leaving a coarser surface layer. Bathyporeia pilosa, a closely related species to Bathyporeia pelagica (Fish & Fish, 1996), avoided burrowing into substrata with particles > 500µm median diameter (Khayrallah & Jones, 1978a). Thus it is likely that Bathyporeia pelagica would become exposed to conditions outside its habitat preference and would probably no longer be found at such a location. Intolerance has been assessed to be high. Recovery has been assessed to be high owing to the species distribution and reproductive pattern (see additional information below), although following return to prior conditions, it may take many months for the deposition of a substratum suitable for colonization by the species e.g. Scott (1960) witnessed the deposition of a sandy beach to take 5 months following its near complete removal during storms.

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

A decrease of two categories in the water flow rate for the duration of one year would, in the absence of wave action determining grain size, favour the deposition of finer sand, silts and clays. Bathyporeia pelagica demonstrated a habitat preference for clean, medium to fine grained sands with a minimum silt/clay content. Accumulation of finer sediments over the period of a year would alter not only the physical properties of the substratum, but also the chemical properties, especially the degree of oxygenation. Bathyporeia pelagica is probably intolerant of poorly oxygenated substrata, and smaller juveniles may be easily smothered by accretion of fine material. Again, assuming that tidal flow rate exerts an influence on sedimentation, Bathyporeia pelagica would become exposed to conditions outside its habitat preference and would probably no longer be found at such a location. Intolerance has been assessed to be high. Recovery has been assessed to be high owing to the species distribution and reproductive pattern (see additional information below), although following return to prior conditions, it may take many months for the substratum to obtain characteristics favourable for colonization by the species.

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

Hayward (1994) states that seawater temperatures vary little between day and night, and seasonal variations tend to be slow and gradual, allowing animals to respond through behavioural changes. However, at low tide air temperature becomes critically important to intertidal animals, and on sandy beaches the habitat, from the surface to a depth of several centimetres, can experience large variations in temperature during a single tidal cycle (Hayward, 1994). For instance, Khayrallah & Jones (1978b) reported the temperature range of sand at a depth of 1 cm during neap tide periods, to be from -2°C in February 1973 to a maximum of 25°C in July 1977. The effects of increased temperature are not necessarily direct, and may be related more to the resultant changes in other factors, especially oxygen (Eltringham, 1971; Hayward, 1994). For interstitial sand dwellers such as Bathyporeia pelagica, increased temperatures may be deleterious through an effect on oxygen levels. In the surface layer of the substratum, higher temperatures promote bacterial growth, especially on beaches with a higher organic content e.g. decaying seaweed, so that the interstitial water is rapidly depleted of oxygen for the period before it is replenished by the flood tide. An intolerance assessment of low has been made owing to the fact that the deleterious effects of high temperature upon a species are not necessarily direct, but rather related to the exacerbated influences of other factors e.g. depleted oxygen or salinity change.

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

Hayward (1994) states that seawater temperatures vary little between day and night, and seasonal variations tend to be slow and gradual, allowing animals to respond through behavioural changes. However, at low tide air temperature becomes critically important to intertidal animals, and on sandy beaches the habitat, from the surface to a depth of several centimetres, can experience large variations in temperature during a single tidal cycle (Hayward, 1994). For instance, Khayrallah & Jones (1978b) reported the temperature range of sand at a depth of 1 cm during neap tide periods, to be from -2°C in February 1973 to a maximum of 25°C in July 1977, but freezing of sediment was only encountered once in the three year period of study. The effect of an unusually cold winter on the interstitial fauna is a simple physical one, in which body fluids freeze, causing cell and tissue damage. However, whilst low temperature are likely to be physically damaging to interstitial animals, Crisp (1964) reported that other interstitial species of amphipod and isopods seemed to be unharmed by the severe winter of 1962-1963 and intolerance has been assessed to be low.

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

Bathyporeia pelagica is infaunal and is not likely to be affected by the light attenuating effects caused by an increase in turbidity.

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

Bathyporeia pelagica is infaunal and is not likely to be directly affected by increased light penetration of the water column caused by a decrease in turbidity.

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

The strength of wave action determines the topography, slope and width of the intertidal. An increase in wave exposure would alter the shore through increased erosion (which may not be compensated for by deposition) and leave a coarser substratum. Intolerance has been assessed to be high owing the potential loss of habitat and the alteration in the nature of the sediment outside the habitat preference of the species. Re-population is likely on return to prior conditions and recoverability has been assessed to be high (see additional information below).

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

The hydrodynamic regime has a significant effect on the distribution of sediments of different particle sizes and the slope of the shore. Decreases in wave exposure in relatively sheltered locations, may cause accretion of finer sands and even silt and clays. Bathyporeia pelagica demonstrates a habitat preference for clean, medium to fine grained sands with a minimum silt/clay content. Accumulation of finer sediments over the period of a year would alter not only the physical properties of the substratum, but also the chemical properties, especially the degree of oxygenation. Bathyporeia pelagica has been assessed to be intolerant of poorly oxygenated substrata, and smaller juveniles may be easily smothered by accretion of fine material. An intolerance assessment of high has been made. On return to prior conditions re-population is likely and recovery has been assessed to be high (see additional information below).

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

Bathyporeia pelagica may respond, e.g. wriggle, to vibrations caused by noise, but it is unlikely to be directly sensitive to noise at the benchmark level.

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

Bathyporeia pelagica is able to detect changes in light, which influences its endogenous swimming activity, but it is unlikely to have any visual acuity and has been assessed not to be sensitive to this factor.

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

Bathyporeia pelagica is infaunal and highly mobile so that is unlikely to be damaged by abrasion caused by the passing scallop dredge. Therefore, it has been assessed as tolerant.

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

Bathyporeia pelagica is a mobile species, which leaves the protection of the substratum regularly owing to its endogenous swimming rhythm and buries back into the substratum before low tide (see adult general biology). As displacement is a regular feature in the life of Bathyporeia pelagica, it has been assessed to be not sensitive to displacement from the substratum.

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

In general, crustaceans are widely reported to be intolerant of synthetic chemicals (Cole et al., 1999) and intolerance to some specific chemicals has been observed in amphipods. Gammaridean amphipods have been reported to be intolerant of TBT with 10 day LC₅₀ values of 1-48ng/l (Meador et al., 1993). Intolerance has been assessed to be high (in the absence of information to the contrary for this species) and recovery moderate owing to the possible persistence of contaminants in the substratum.

Heavy metal contamination

Evidence

For most metals, toxicity to crustaceans increases with decreased salinity and elevated temperature, consequently marine species living within their normal salinity range may be less susceptible to heavy metal pollution than those living in salinities near the lower limit of their salinity tolerance (McLusky et al., 1986).
High concentrations of mercury (Hg) in sediments have been reported by many authors (cited in Khayrallah, 1985). This is a feature which may be of direct importance for epistrate feeders such as Bathyporeia pelagica and of indirect importance for its fish and shorebird predators. Khayrallah (1985) investigated the effects of salinity and temperature on the toxicity of two mercuric compounds to Bathyporeia pilosa, which is closely related, and has a similar life-cycle to Bathyporeia pelagica (Fish & Fish, 1996). Khayrallah (1985) found the organic form (C₂H₅HgCl) to be more toxic than the inorganic form (HgCl) of mercury. The toxicity of both forms of Hg to Bathyporeia pilosa, was directly related to increasing concentration (range 0.04-0.75 mg/Hg/l (no sediment)) and temperature (1-20°C), and inversely related to salinity (10 & 20 psu) and age (adults were more tolerant than juveniles). The survival rate of Bathyporeia pilosa was found to be dependent on both the salinity and temperature of the medium, the effect being most pronounced in inorganic concentrations of Hg <0.09 mg/Hg /l, suggesting that the lower concentrations of Hg become important only under conditions of stress caused by some other factor. Bathyporeia pelagica is intolerant of salinity changes unlike Bathyporeia pilosa, so it is possible that Bathyporeia pelagica would be more intolerant of sub-lethal concentrations of both organic and inorganic mercury. Recovery is likely to be moderate owing to the possible persistence of contaminants in the substratum.

Hydrocarbon contamination

Evidence

Amphipods have been reported to be sensitive to oil (Suchanek, 1993). After the Amoco Cadiz oil spill there was a reduction in both the number of amphipod species and the number of individuals (Cabioch et al., 1978). Initially significant mortality would be expected, attributable to toxicity and the effects of smothering, therefore intolerance has been assessed to be high. Often populations do not return to pre-spill abundances for 5 or more years, which is most likely related to the persistence of oil within sediments (Southward, 1982), and recovery has been assessed to be moderate.

Radionuclide contamination

Evidence

Insufficient
information.

Changes in nutrient levels

Evidence

The sandy shore environment favoured by Bathyporeia pelagica has a characteristically low level of organic matter. As an epistrate feeder, Bathyporeia pelagica feeds upon the film of diatoms and bacteria adhering to individual sand particles. Nutrient enrichment would enhance the growth of episammic diatoms and bacteria as nutrients are probably limiting. A flourishing population of bacteria would utilize oxygen for the oxidization of the resulting organic matter, possibly causing hypoxia. Bathyporeia pelagica has been assessed to be intolerant of hypoxic conditions (see oxygenation below). Intolerance has been assessed to be high owing to the fact that an increase in nutrient levels would probably result in the species being exposed to conditions outside its habitat preferences. Recovery has been assessed to be moderate owing to the length of time it may take to return to prior conditions. For instance the normal fauna of clean sandy beaches had only partially recovered after three years after the opening of a sewage works and resultant reduction in organic enrichment in the Firth of Forth (Read et al., 1983).

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

Salinities higher than those of natural seawater are uncommon, although they could occur in surface pools of interstitial water on sand and mud flats in summer owing to surface evaporation. Bathyporeia pelagica is a stenohaline species and would be intolerant of exposure to hypersaline conditions, especially in conditions of elevated temperature. However, owing to the relatively well drained nature of the substratum populated by Bathyporeia pelagica, pooling of surface water is unlikely. In addition the species can, to some extent, avoid the factor by burrowing deeper into the sediment where changes of salinity are buffered. Therefore, intolerance has been assessed to be low. Recovery has been assessed to be high because it is unlikely that the entire population would be affected, e.g. individuals may burrow deeper into the sediment, and would rapidly attain a pre-impact population following reproduction.

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

Bathyporeia pelagica is an intertidal species restricted to the lower half of the tidal range by its intolerance to reduced salinity (Preece, 1970). An intolerance assessment of high would have been given except for the fact that as a mobile species Bathyporeia pelagica is able to migrate and avoid conditions of depressed salinity.
Salvat (1967), Fish & Preece (1970), Ladle (1975) and Fish & Fish (1978) have reported both the re-distribution of populations down the shore during spring and summer on open coasts, and the migration of Bathyporeia pelagica from sandy estuarine beaches to sites on the open coast. These authors recorded Bathyporeia pelagica in the sandy flats at the mouths of estuaries (west Wales and Northumberland) from September through to April, after which time the species disappeared, a pattern which was observed in each subsequent year. Fish & Fish (1978) concluded that the migration pattern was controlled by the combined effects of salinity and temperature, the species being better able to tolerate conditions of reduced salinity at cooler temperatures. Furthermore, although the extent of penetration by Bathyporeia pelagica into estuarine sandflats is ultimately limited by its salinity tolerance, populations that do so, are able to exploit the food resources, whether qualitative or quantitative, of the estuary. Fish & Fish (1978) found that in the population of Bathyporeia pelagica that over-wintered in the Dovey Estuary, the reproductive output was greater and specimens were larger. An intolerance assessment of low has been made, owing to the lack of evidence for mortalities arising from reduced salinities in the field and that the species is able to migrate. Recovery has been assessed to be immediate because it is unlikely that the entire population would be affected, e.g. individuals may burrow deeper into the sediment or may migrate seawards and would probably rapidly attain a pre-impact population owing to migration and reproduction.

Changes in oxygenation

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

Evidence

Brafield (1964) concluded that the most significant factor influencing the oxygenation was the drainage of the beach which, in turn, is controlled by the slope and the particle size. Oxygen depletion becomes a severe problem at all states of the tide on only the very finest grained beaches, and as a general rule, if the percentage of particles of less than 0.25 mm median diameter exceeds 10% of a sand, then the oxygen concentration of its interstitial water will be less than 20% of the air saturation level, and will drop rapidly during low tide periods. Oxygen depletion, variations in salinity and pH result in steep gradients of faunal change through the upper layers of the substrata. The infauna are generally restricted to the uppermost layers, where the interstitial water contains sufficient oxygen for the fauna, and for the oxidization of the organic waste products of the infauna and allochthonous detritus. Laboratory studies by Khayrallah (1977) on Bathyporeia pilosa, which is closely related, and has a similar life-cycle to Bathyporeia pelagica (Fish & Fish, 1996), revealed Bathyporeia pilosa to have a relatively poor resistance to conditions of hypoxia in comparison to other interstitial animals. It was also susceptible to hydrogen sulphide, supporting the conclusion that aerated deposits are a fundamental requirement of Bathyporeia pilosa and also probably Bathyporeia pelagica. It is likely, therefore, that Bathyporeia pelagica would be unable to endure hypoxic conditions for a week, that may result from smothering by impermeable/viscous materials, and intolerance has been assessed to be high.

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 concerning infestation or disease related mortalities was found.

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

No information concerning non-native species that might affect abundance or survival of Bathyporeia pelagica was found.

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

Bathyporeia pelagica is not a species targeted for extraction.

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

The cockle, Cerastoderma edule, is found in both muddy and clean sands, although it is frequently more abundant in the former. Specimens of marketable size may be harvested more efficiently using mechanical methods, such as tractor-powered harvesters and suction dredgers than by traditional methods. Ferns et al., (2000) examined the effects of a tractor-towed cockle harvester on the benthic invertebrates and predators of intertidal plots of muddy and clean sand. Harvesting resulted in the loss of a significant proportion of the most common invertebrates from both areas. In the muddy sand, the population of a similar species, Bathyporeia pilosa remained significantly depleted for more than 50 days, whilst the population in clean sand recovered more quickly. It is therefore likely that Bathyporeia pelagica would be similarly affected by the mechanical extraction of marketable shellfish in locations where populations co-occur. Intolerance has been assessed to be intermediate owing to the likelihood of a proportion of the population being killed and the reduced abundance of the remaining population. Recovery has been assessed to be very high owing to the likelihood of migration from other areas on the shore.