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

Hediste diversicolor is infaunal and is reliant upon a muddy / sandy sediment in which to burrow. Physical removal of the substratum e.g. as a result of channel dredging activities would remove with it the entire associated population of Hediste diversicolor. The ability of postlarvae and larger juveniles and adults of Hediste diversicolor to swim, burrow and be carried by bedload transport can aid the rapid recolonization of disturbed sediments (Shull, 1997). Davey & George (1986), found evidence that larvae of Hediste diversicolor were tidally dispersed within the Tamar Estuary over a distance of 3 km and well away from areas of dense adult populations. However, this dispersal may not always lead the larvae to a favourable area and it is likely that there will be some loss.

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

Hediste diversicolor inhabits depositional environments. It is capable of burrowing to depths of up to 0.3 m and reworking sub-surface modifications of its burrow through fine clays and sand. Smith (1955) found no appreciable difference in the population of a Hediste diversicolor colony which had been covered by several inches of sand through which the worms tunneled. It would not be adversely affected by smothering with additional sediments. However, smothering with impermeable materials would prevent Hediste diversicolor clearing the burrow to the sediment surface and prevent feeding. Larvae are more intolerant than adults as they are still acquiring the physical ability to burrow (see larval sensitivity).

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

Increased siltation maybe beneficial to feeding. As a surface-deposit feeder and suspension feeder Hediste diversicolor will be able to utilize suspended matter as a food resource. Increased deposition of silt onto the mudflats can raise the height of the mudflats and therefore increasing the exposure time of infaunal communities at low tide (Jones et al., 2000). At the benchmark level however, this is unlikely to have an adverse effect on Hediste diversicolor.

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

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

Hediste diversicolor inhabits a burrow within the sediment which may be up to 0.3m deep. The species retreats within the burrow during periods of exposure and thus away from the desiccating factors of sunlight and wind. Residual surface and interstitial water prevent the burrow and thus Hediste diversicolor from drying. Therefore Hediste diversicolor is largely able to avoid desiccation. Specimens found at the upper limits in the intertidal zone may become stressed by desiccation if the substratum begins to dry, but Hediste diversicolor is sufficiently mobile to retreat back to damper substrata . Consequently this species is considered to have a low intolerance to the benchmark change in desiccating factors.

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

Hediste diversicolor inhabits a burrow within the sediment which may be up to 0.3m deep. The species retreats within the burrow during periods of exposure and thus away from desiccating factors of sunlight and wind. Thus Hediste diversicolor can avoid some detrimental aspects of emergence (see desiccation). However, whilst in retreat within the burrow during extended periods of emergence, the ragworm is prevented from actively feeding at the surface and is likely to be prone to more intense predation pressure from wading birds as they have longer to search the mudflats. An increased emergence regime is also likely to cause a decline in the abundance of ragworms at the upper limits of the intertidal zone, as they may become stressed by desiccation if the substrata begin to dry and are prone to more extremes of temperature, but Hediste diversicolor is sufficiently mobile to gradually retreat back to damper substrata. Consequently, this species is considered to have a low intolerance to the benchmark change in emergence.

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

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

Hediste diversicolor characteristically inhabits littoral mudflats predominantly of clay (particles < 4 µm), silt (4-63 µm) and to a lesser extent very fine sand (63-125 µm) (Jones et al., 2000). The type direction and speed of the currents control sediment deposition within an area. A change in two categories in water flow rate from weak and negligible to moderately strong and strong would entrain and maintain particles in suspension and erode the mud. As a result the scouring and consequent redistribution of components of the substratum would alter the extent of suitable habitat available to populations of Hediste diversicolor. Recovery of this species would be influenced by the length of time it would take for the potential habitat to return to a suitable state for recolonization by adult and juvenile specimens from adjacent habitats, and the establishment of a breeding population. This may take between one and three years, as populations differ in reaching maturity (Dales, 1950; Mettam et al., 1982; Olive & Garwood, 1981), from the time that the habitat again becomes suited to the species.

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

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

The geographic range of Hediste diversicolor (see adult distribution) suggests that it is tolerant of a range of temperatures and a long term chronic temperature increase or decrease is unlikely to have an adverse effect on UK populations. Hediste diversicolor can tolerate temperatures from below zero under Baltic ice to high summer temperatures in Black Sea lagoons (Smith, 1977).
A decrease in temperature has been shown to be beneficial to Hediste diversicolor through reduction in numbers of their predators. A severe winter in the Wadden Sea in 1995/1996 saw an increased abundance of this species coinciding with a reduction in the numbers of Carcinus maenus and Crangon crangon (Armonies et al., 2001). A similar increase in abundance was noted in the same area between 1978 and 1987 after a series of cold winters: mean density increased from 24 / m² to 151 / m² respectively (Beukema, 1990).
Species dwelling in the sediments are likely to be protected from direct effects of temperature change at the surface, for instance Hediste diversicolor burrows deeper in very cold and frosty weather (Linke, 1939). In addition, insensitivity to temperature change is limited by the insulating properties of the mud in which it lives (M. Kendall, pers. comm.).
Temperature change may adversely affect reproduction. Bartels-Hardege & Zeeck (1990) demonstrated that an increase from 12°C and maintenance of water temperature at 16°C induced reproduction in specimens outside the normal period of spawning (see reproduction), and without a drop in temperature to simulate winter conditions the spawning period was prolonged and release of gametes was not synchronized. Poor synchronization of spawning could result in reduced recruitment, as gametes are wasted and mature specimens die shortly after gamete release. Therefore, an intolerance of intermediate has been recorded.

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

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

Hediste diversicolor characteristically inhabits estuaries where turbidity is typically higher than other coastal waters. Changes in the turbidity may influence the abundance of phytoplankton available as a food source that may be attained through filter feeding. However, Hediste diversicolor utilizes various other feeding mechanisms and, at the benchmark level, the likely effects of a change in turbidity are limited.

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

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

Hediste diversicolor is infaunal, inhabiting a burrow in which it seeks refuge from predators and may partially emerge to seek and capture food. In addition, it inhabits low energy depositional environments. An alteration of factors within the environment that increases wave exposure is likely to cause erosion of the substrata and consequently, loss of habitat.
Recovery would be influenced by the length of time it would take for the habitat to return to a suitable state for recolonization by adult and juvenile specimens from adjacent habitats, and the establishment of a breeding population. This may take between one and three years, as populations differ in reaching maturity (Dales, 1950; Mettam et al., 1982; Olive & Garwood, 1981), from the time that the habitat again becomes suited to the species.

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

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

Hediste diversicolor may be able to detect some noise vibration but is not known to exhibit a significant response at the benchmark levels. However, wildfowl which prey upon estuarine infauna such as Hediste diversicolor are known to be disturbed by noise, consequently predation pressure upon Hediste diversicolor may be reduced for the length of time that the disturbance continues.

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

Hediste diversicolor demonstrates a distinct movement towards darkness (skototaxis) and it has been shown that feeding sensitizes the worm to light and influences their response to a sudden increase in illumination (Herter, 1926; Evans, 1966, in Clay 1967(c)). Otherwise, Hediste diversicolor lacks the visual ability to be affected by the visual presence of moving objects not normally found in the marine environment.

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

The body of Hediste diversicolor may be physically damaged by mechanical interference as it has a fragile hydrostatic skeleton. Mechanical interference within the substratum, such as that caused by the dropping and dragging of an anchor or fishing gear, could physically damage ragworms within the path of the anchor and cause their displacement. Physical injury and displacement would hinder the ability of a ragworm to burrow rapidly back into the sediment to seek refuge from predation.
Regeneration of the lost body is often observed (M. Kendall, pers. comm.) however it is likely that some individuals may die and an intolerance of intermediate has been recorded.

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

Displacement from within the sediment to be left upon the sediment surface would increase the risk of Hediste diversicolor to predation but as a mobile burrowing species it is able to burrow rapidly back into the sediment and seek refuge. However, this is only possible if the animal is near its own burrow on a suitable substratum (M. Kendall, pers. comm.). The burrows of other worms are well defended through territorial behaviour.

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

Reports of the effects of synthetic chemicals on Hediste diversicolor illustrate that the intolerance of the species is highly dependent upon the molecular structure of the chemical, which determines the chemicals properties and use. For example:

1. Collier & Pinn (1998) observed significant differences in both the abundance and biomass of a benthic community from the Ythan Estuary, Scotland, experiencing contamination by Ivermectin. Ivermectin is the 22,23-dihydro derivative of avermectin ß which has been shown to be highly efficient in the treatment of sea lice. Hediste diversicolor was the most intolerant species to Ivermectin in the benthic community studied. A rapid decline in both abundance and total biomass of Hediste diversicolor occurred within 7 days and with increasing concentration. An Ivermectin concentration of 8.0 mg m² caused 100% mortality within 14 days. Davies et al., (1998) modelled factors influencing the concentration of Ivermectin reaching the seabed which ranged from 2.2 to 6.6 mg m². The upper limit of this range was only slightly less than the concentrations found to be toxic by Collier & Pinn (1998) and Black et al. (1997). Davies et al.(1998) concluded that there was a significant risk to benthic organisms within a radius of 50 m of salmon farms utilizing Ivermectin and that Ivermectin could accumulate (half life of Ivermectin in marine sediments > 100 days) within the sediment beyond a single treatment and reach toxic levels.
2. In contrast, Craig & Caunter (1990) examined the effects of the organosilicon compound, Polydimethylsiloxane (PDMS) in sediment on Hediste diversicolor. PDMS fluids are less dense than water and insoluble and form a discrete layer on the surface of the water. In an intertidal environment PDMS fluids are deposited upon the sediment surface at low tide and into contact with Hediste diversicolor. In laboratory tests, exposure to 10,000 mg PDMS per kg of sediment caused no deaths over 96 hours, and exposure to 1,000 mg PDMS per kg of sediment caused no deaths of Hediste diversicolor after 28 days.

Recovery of this species would be influenced by the length of time it would take for the potential habitat to return to a suitable state (e.g. factors such as the rate of decay of the synthetic chemical within the marine environment), recolonization by adult and juvenile specimens from adjacent habitats, and the establishment of a breeding population. This may take between one and three years, as populations differ in reaching maturity (Dales, 1950; Mettam et al., 1982; Olive & Garwood, 1981), from the time that the habitat again becomes suited to the species.

Heavy metal contamination

Evidence

Bryan (1984) reviewed metals in the marine environment and from the evidence available suggested that polychaetes were fairly resistant to heavy metals.
In Hediste diversicolor the acute toxicity is dependent on the rate of uptake of the metal, since this determines the speed with which the lethal dose is built up. The rate of intake is important because this determines whether the organism's detoxification mechanisms can regulate internal concentrations. The resistance of Hediste diversicolor is thought to be dependent on a complexing system which detoxifies the metal and stores it in the epidermis and nephridia (Bryan & Hummerstone, 1971; McLusky et al. 1986).

Hediste diversicolor has been found successfully living in estuarine sediments contaminated with copper ranging from 20 µm Cu/g in low copper areas to >4000 µm Cu/g where mining pollution is encountered e.g. Restronguet Creek, Fal Estuary, Cornwall (Bryan & Hummerstone, 1971). Attempts to change the tolerance of different populations of Hediste diversicolor to different sediment concentrations of copper have shown that it is not readily achieved suggesting that increased tolerance to copper has a genetic basis (Bryan & Hummerstone, 1971; Bryan & Gibbs, 1983).

Crompton (1997) reviewed the toxic effect concentrations of metals to marine invertebrates (see Table 5.12, Crompton, 1997). Annelid species, such as Hediste diversicolor were found to be at risk if metals exceeded the following concentrations during 4-14 days of exposure: >0.1 mg Hg l^-1, > 0.01 mg Cu l^-1, > 1 mg Cd l^-1, >1 mg Zn l^-1,>0.1 mg Pb l^-1, >1 mg Cr L^-1, >1 mg As l^-1 and >10 mg Ni l^-1.
In general, for estuarine animals heavy metal toxicity increases as salinity decreases and temperature increases (McLusky et al., 1986). For example, Fernandez & Jones (1990) calculated 96 hour LC₅₀ Zinc values for Hediste diversicolor at four salinities 5, 10, 17.5 and 30 psu at 12°C. The 96 hour LC₅₀ at 17.5 psu and 12°C was 38 mg Zn l^-1, while at 5 and 10 psu it was 7 and 19 mg Zn l^-1 respectively. Toxicity decreased with increasing salinity. When salinity remained constant at 17.5 psu, but temperature varied, the following 96 hour LC ₅₀ values for Zinc were recorded: 40 mg Zn l^-1 at 6°C, 32 mg Zn l^-1 at 12°C and 9.1mg Zn l^-1 at 20°C. Toxicity increased with increasing temperature. Accumulation of zinc was also greater at the lowest salinities and when the temperature was highest at 20°C. In a parallel experiment, the presence of sediment was found to reduce toxicity and body accumulation of zinc in Hediste diversicolor.
Recovery of this species would be influenced by the length of time it would take for the potential habitat to return to a suitable state (e.g. factors such as the decline of bioavailable metals within the marine environment), recolonization by adult and juvenile specimens from adjacent habitats, and the establishment of a breeding population. Since juveniles remain in the infauna throughout their development selection for metal tolerance can be expected to be operative from an early stage (Bryan & Gibbs, 1983).

Hydrocarbon contamination

Evidence

The 1969 West Falmouth (America) spill of Grade 2 diesel fuel documents the effects of hydrocarbons in a sheltered habitat (Suchanek, 1993). The entire benthic fauna including Hediste diversicolor was eradicated immediately following the spill and remobilization of oil that continued for a period > 1 year after the spill, contributed to much greater impact upon the habitat than that caused by the initial spill. Effects are likely to be prolonged as hydrocarbons incorporated within the sediment by bioturbation will remain for a long time owing to slow degradation under anoxic conditions. Oil covering the surface and within the sediment will prevent oxygen transport to the infauna and promote anoxia as the infauna utilize oxygen during respiration. Although Hediste diversicolor is tolerant of hypoxia and periods of anoxia, a prolonged absence of oxygen will result in the death of it and other infauna. McLusky (1982) found that petrochemical effluents released from a point source to an estuarine intertidal mudflat, caused severe pollution in the immediate vicinity. Beyond 500 m distance the effluent contributed to an enrichment of the fauna in terms of abundance and biomass similar to that reported by Pearson & Rosenberg (1978) for organic pollution, and Hediste diversicolor was found amongst an impoverished fauna at 250 m from the discharge.

Radionuclide contamination

Evidence

Beasley & Fowler (1976) and Germain et al., (1984) examined the accumulation and transfers of radionuclides in Hediste diversicolor from sediments contaminated with americium and plutonium derived from nuclear weapons testing and the release of liquid effluent from a nuclear processing plant. Both concluded that the uptake of radionuclides by Hediste diversicolor was small. Beasley & Fowler (1976) found that Hediste diversicolor accumulated only 0.05% of the concentration of radionuclides found in the sediment. Both also considered that the predominant contamination pathway for Hediste diversicolor was from the interstitial water. However, there is insufficient information available on the biological effects of radionuclides to comment further upon the intolerance of this species to radionuclide contamination.

Changes in nutrient levels

Evidence

Nutrient enrichment favours the growth of opportunistic green macro-algae blooms which can cause declines in some species and increases in others (Raffaelli, 2000). Evidence (Beukema, 1989; Reise et al., 1989; Jensen, 1992) suggested a doubling in the abundance of Hediste diversicolor in the Dutch Wadden Sea, accompanied by a more frequent occurrence of algal blooms that were attributed to marine eutrophication. Algae may be utilized by Hediste diversicolor in its omnivorous diet, so some effects of nutrient enrichment may be beneficial to this species.

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

Hediste diversicolor is an euryhaline species, able to tolerate a range of salinities from full sea water down to 5 psu or less (Barnes, 1994). Consequently a change of one category from the MNCR salinity scale (see benchmark) for a duration of one year would not be restrictive to adults of Hediste diversicolor. Specimens already at the extreme ends of their salinity tolerance would be more intolerant of a short term change of two categories on the MNCR salinity scale but are sufficiently mobile to retreat to more hospitable conditions. Low salinities (< 8 psu) can have an adverse effect on reproduction (Ozoh & Jones, 1990; Smith 1964) (see larval sensitivity).

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

Changes in oxygenation

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

Evidence

The littoral muds and muddy sands which Hediste diversicolor inhabits tend to have lower oxygen levels than other sediments. Hediste diversicolor is resistant to moderate hypoxia (Diaz & Rosenberg, 1995). The successful survival of this species under prolonged hypoxia was confirmed by the resistance experiments of Vismann (1990), which resulted in a mortality of only 15% during a 22 day exposure of Hediste diversicolor at 10% oxygen (ca. 2.8 mg O₂ per litre). Hediste diversicolor is active at the sediment/water interface where hydrogen sulphide concentrations increase during periods of hypoxia. Vismann (1990), also demonstrated that the high tolerance of Hediste diversicolor to hypoxia in the presence of sulphide is enabled by elevated sulphide oxidation activity in the blood. Hediste diversicolor may also exhibit a behavioural response to hypoxia by leaving the sediment (Vismann, 1990) which is enhanced in the presence of sulphide. After 10 days of hypoxia (10% oxygen saturation) with sulphide (172-187 µmM) only 35% of Hediste diversicolor had left the sediment compared to 100% of Nereis virens. Laboratory experiments in the absence of sediments, found that Hediste diversicolor could survive hypoxia for more than 5 days and that it had a higher tolerance to hypoxia than Nereis virens, Nereis succinea and Nereis pelagica (Theede, 1973; Dries & Theede, 1974; Theede et al., 1973).

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

Insufficient
information.

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

Insufficient
information.

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

Populations of Hediste diversicolor are dominated by females, males may constitute up to 40% of the population but several reports suggest that the proportion of males is frequently lower (< 20%) (see Clay, 1967(c.)). The sexes are externally indistinguishable except when approaching maturation and during spawning (see reproduction and adult general biology). Consequently extraction e.g. by bait digging, of 50% of the specimens from within an area is likely to remove more females than males. A reduction in the female proportion of the population prior to spawning could reduce recruitment to the population. The mechanical action of the digging, even if the worms were not actually taken, may also cause some damage to the bodies. Recovery is dependent on the reproductive success and survival of the remaining population and colonization by adults from unaffected areas.

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

Many species in addition to Hediste diversicolor are taken from the intertidal environment for personal or commercial use as fishing bait. Techniques for extraction include hand digging, bait pumping and worm dredging (Fowler, 1999). Heiligenberg (1987) reported upon the effects of both hand and mechanical digging in the Dutch Wadden Sea. Hand and mechanical digging operating at a level to achieve a 50% reduction in Arenicola marina, caused a significant reduction in many of the common species, including Hediste diversicolor. A total of 1.9 g of other benthic animals were removed for every 1 g of Arenicola marina.
Mechanical disturbance of the substrata will also displace Hediste diversicolor causing specimens to be susceptible to predation (see abrasion & displacement).
Recovery is dependent on the reproductive success and dispersion of the remaining population and colonization by adults from unaffected areas.