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

During its inactive (non-feeding) phase Eurydice pulchra buries infaunally in the uppermost 10 cm of sandy substrata, and the removal of the substratum would also remove the resident population. Intolerance has been assessed to be high. It is likely that the species would re-populate on return to prior conditions, including by immigration, and recovery has been assessed to be very high.

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

Eurydice pulchra would probably be unaffected by an additional covering of sediment of a texture within its preference. In an experiment to determine if Eurydice pulchra was selective of substratum particle size, Jones (1970b) observed Eurydice pulchra to demonstrate a strong preference for coarse particles (1.0 - 0.5 mm median diameter). It is likely that the grade of the substratum is an important factor determining the zonation and relative geographical distribution of the species. Jones (1970b, Table 6) also observed differences in the speed of burrowing and depth attained by Eurydice pulchra, which varied according to particle size. In the finest grades of particles (0.157 - 0.031 mm median diameter (silts, Wentworth scale)), Eurydice pulchra made little progress in its attempts at burial, achieving a depth of only 1 cm after 3 hours. Thus if Eurydice pulchra experienced difficulty when trying to bury into finer substrata, it is also likely that it would experience difficulty in burying out after smothering by fine particulate matter and would have to rely on displacement by tidal wave action. Furthermore, smothering by fine particulate matter would not only alter the physical properties of the substratum, but also the chemical properties, especially the degree of oxygenation. Eurydice pulchra was considered to be intolerant of poorly oxygenated substrata (see oxygenation below), and smaller juveniles may be easily smothered by accretion of fine material. Therefore Eurydice pulchra has been assessed to have a high intolerance to smothering by fine particulate matter and viscous materials such as oil, through which burrowing is likely to be hindered and cause changes to the habitat which are outside the species preference. The species is likely to have a high capacity for recovery on return to prior conditions (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

It is unlikely that the swimming and hunting activity of Eurydice pulchra would be affected by an increase in the suspended matter in the water column for a period of one month, as it is a regular swimmer in the surf plankton, where the concentration of suspended particles would be expected to be higher and variable according to the strength of wave action. The species has been assessed to be tolerant. The resultant light attenuation effects have been addressed under turbidity, end the effects of rapid settling out of suspended sediment have been addressed under smothering.

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

Eurydice pulchra is a regular swimmer in the surf plankton, where the concentration of suspended sediment would be expected to be variable according to wave action. The resultant light attenuation effects have been addressed under turbidity.

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

Should the species be stranded, it is likely to be adversely affected by desiccation. However, 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 behavioural and/or physiological adaptations (Eltringham, 1971). Eurydice pulchra is an intertidal species which lives on the upper half of the shore, generally being most abundant between mean tide level (MTL) and mean high water of neap tides (MHWN). It relies upon the cue of increasing wave action caused by the flood tide (Jones, 1970b) to initiate swimming from the substratum. It swims in search of food, and buries itself in the sand again as the tide ebbs. As the fortnightly spring tides carry water further up the shore, so Eurydice pulchra moves up, and it can be found in the sand up to the mean high water of spring tides. When the tidal cycles swings again towards neaps, the Eurydice population also moves downshore, and avoids being stranded above the neap high water mark (Fish, 1970), the synchronisation with the tide is maintained by its endogenous rhythm (see adult general biology). Therefore the behaviour of Eurydice pulchra is likely to prevent it from being exposed to the benchmark change (see benchmark) in desiccation, and it has been assessed to be tolerant.

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

Eurydice pulchra is an intertidal, infaunal species, that is most abundant between mean tide level (MTL) and mean high water of neap tides (MHWN), 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 (Pienkowski, 1983). An additional hour of emergence may allow the birds to feed for longer and the viability of the population, especially where it occurs in lower abundance, may be reduced. Intolerance has been assessed to be intermediate, 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

Eurydice pulchra is an intertidal species, which during periods of immersion swims amongst the surf plankton in order to hunt for food (see general biology). Consequently, an additional hour of immersion may benefit the species and it has been assessed to be not sensitive.

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

Eurydice pulchra demonstrated a preference for specific grades of sandy substrata (Jones, 1970b) (see smothering above). It is likely that Eurydice pulchra would be highly intolerant of an increase of two categories in the water flow rate for the duration of one year, e.g. owing to a straightening of channel flow over the sand flats at an estuary mouth. Although the species may not be directly exposed to the increased current, the effect would probably be to cause a redistribution/reduction of suitable substrata and the species population may become restricted or lost from a location. Re-population of an area is likely on return to prior conditions, and recovery has been assessed to be very high (see additional information below).

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

Eurydice pulchra demonstrated a preference for specific grades of sandy substrata (Jones, 1970b) (see smothering above). It is likely that Eurydice pulchra would be highly intolerant of a decrease of two categories in the water flow rate for the duration of one year, e.g. channel flow over the sand flats becoming more sinuous, sea defences shielding beaches. Although the species may not directly experience the decreased current, the effect would probably be to cause accretion of finer particulate matter to which the species is intolerant e.g. smothering (see smothering above). Re-population of an area is likely on return to prior conditions, and recovery has been assessed to be very high (see additional information below).

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 Eurydice pulchra extends to the south of Britain and Ireland, suggesting that the species would be tolerant of a long term chronic change in temperature of 2°C. At low tide air temperature becomes critically important to intertidal animals, and on sandy beaches the substratum, from the surface to a depth of several centimetres, can experience large variations in temperature during a single cycle and throughout the year (Hayward, 1994). For instance, Khayrallah & Jones (1978b) reported the temperature range of sand at a depth of 1 cm during neap tides to be from -2°C in February 1973, to a maximum of 25°C in July 1977. Jones (1970b) observed some differences in survival rate in Eurydice pulchra in response to extreme temperatures e.g. individuals started dying after 18 hours at 30°C and all specimens died after 12 hours at 38°C (fully aerated seawater). The effects of a temperature increase on the species are not necessarily direct and may be related more to the resultant changes in other factors, especially oxygen (Hayward, 1994; Eltringham, 1971). For infaunal sand dwellers, such as Eurydice pulchra, increased temperatures may become stressful through an effect upon oxygen levels, owing to enhanced bacterial growth and utilization of oxygen. However, since Eurydice pulchra prefers coarse grained, typically well oxygenated sand, oxygen is unlikely to become limiting in the period between low and high tide. In view of the experiment showing survival at high temperatures, the evidence of high temperatures in the usual habitat of Eurydice pulchra and the coarse well oxygenated nature of the sediment, intolerance has been assessed to be low.

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

The geographic range of Eurydice pulchra extends to the north of Britain and Ireland, suggesting that the species would be tolerant of a long term chronic change in temperature of 2°C.
At low tide air temperature becomes critically important to intertidal animals, and on sandy beaches the substratum, from the surface to a depth of several centimetres, can experience large variations in temperature during a single cycle and throughout the year (Hayward, 1994). For instance, Khayrallah & Jones (1978b) reported the temperature range of sand at a depth of 1 cm during neap tides to be from -2°C in February 1973, to a maximum of 25°C in July 1977. In the winter, Eurydice pulchra migrates into the sublittoral zone, thus escaping extreme temperatures (Jones, 1970b), a factor perhaps in part responsible the high survival rate of the species after the severe winter of 1962-1963 (Crisp, 1964). Intolerance has been assessed to be low as there is no evidence to suggest that the population would killed by decreased temperatures.

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

The light attenuating effects of an increase in turbidity may be beneficial to Eurydice pulchra during its active feeding phase. In the clearer waters of south-west France, Salvat (1966) noted that the feeding activity of Eurydice pulchra was suppressed during daylight. The isopod appeared in greater abundance on the night time tide, possibly as a behavioural mechanism to avoid predation by fish that hunt intertidally by sight. Eurydice pulchra has been assessed as tolerant of 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

In British waters Eurydice pulchra feeds during high tide, both day and night, relying upon the wave action of the flood tide to wash it out of the sand. A decrease in turbidity, perhaps associated with reduced wave action, may allow fish that hunt by sight to prey upon Eurydice pulchra more efficiently. Intolerance has been assessed to be intermediate. Recovery has been assessed to be very high (see additional information below).

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

Whilst wave action operates indirectly upon small infaunal animals during their inactive phase through its control of particle size and beach oxygenation, wave action also has a direct effect upon them during their active phase (Jones, 1970b). The active feeding phase is initiated as the rising tide reaches the sand in which the isopod is buried (Elmhirst, 1932; Watkin 1942; Salvat, 1966). In trying to confirm that wave action controls the emergence of Eurydice pulchra, Jones (1970b) found a direct relationship between the numbers of Eurydice pulchra swimming and the height of the waves. The depth of disturbance of sand by a wave is in direct proportion to its height, providing that the slope and the median particle size of the sand remain constant. King (1959) calculated that for a beach with a median grain diameter of 0.23 mm there is an approximate increase of 1 cm depth for every 1 ft of wave height, and that for a beach with a median grain diameter of 0.4 mm the increase of disturbance is about 3 cm depth for every 1 ft of wave height. Since Eurydice pulchra relies upon wave action to initiate swimming, it occurs in greatest abundance within the range of deepest penetration by wave action. The beaches populated by Eurydice pulchra tend to be moderately exposed in the first instance (see distribution) and the benchmark increase would result in the exposure of Eurydice pulchra to very wave exposed conditions. A greater proportion of the population would be washed out as the waves eroded the substratum. Whilst the higher concentration of suspended particulate matter and prey items resulting from the increased turbulence may result in enhanced feeding, ultimately the nature of the substratum would change becoming coarser and forming deposits of gravel or shingle rather than sand, creating conditions outside the species habitat preference. Intolerance has been assessed to be high as the species would probably no longer be found. Recovery has been assessed to be very high, for instance, at Village Bay in St Kilda, an island group far out into the Atlantic west of Britain, an expanse of sandy beach was removed offshore as a result of winter storms to reveal an underlying rocky shore (Scott, 1960). Yet in the following summer the beach was gradually replaced when wave action was less severe. Eurydice pulchra was a species reported to be a frequent member of the re-colonizing fauna, its recovery being aided by the ability to survive in the shallow sublittoral zone where substrata may be deposited.

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

Whilst wave action operates indirectly upon small infaunal animals during their inactive phase through its control of particle size and beach oxygenation, wave action will also have a direct effect upon the species during their active phase (Jones, 1970b) (see increase in wave exposure for additional information). The beaches populated by Eurydice pulchra tend to be moderately exposed in the first instance (see distribution) and the benchmark decrease would decrease exposure to very sheltered conditions. A smaller proportion of the population would be washed from the substratum on each flood tide, consequently limiting feeding activity. Jones (1970b) suggested that reduced wave action resulting in shortened available feeding times, allowed Eurydice affinis to compete more successfully with Eurydice pulchra on semi-exposed beaches in Britain and Ireland. In addition, the nature of the substratum would change becoming finer with deposits of finer sands and silts (see smothering). Intolerance has been assessed to be high owing to the creation of conditions outside the habitat preference of Eurydice pulchra. Recovery has been assessed to be very high on return to prior conditions (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

Eurydice pulchra may respond 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

Eurydice pulchra is able to detect changes in light. During the day, if disturbed, the species demonstrates photonegative behaviour and immediately buries back into the sand. Furthermore, as a predator it probably has sufficient visual acuity to distinguish between prey items in the surf plankton. However, at the benchmark level, it is unlikely that Eurydice pulchra would be sensitive to the visual presence of boats, machinery or humans, and has been assessed to be not sensitive.

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

Eurydice pulchra is a small, infaunal but highly mobile species that is regularly washed from the substratum by wave action of the flood tide and re-buries itself on the ebb tide. It is unlikely to be damaged by a passing scallop dredge or similar effect since it can readily avoid the impact and/or pass through the dredge, only to rebury rapidly. 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

Eurydice pulchra is a mobile species, which is regularly washed from the substratum by wave action of the flood tide and swims in response to its circasemilunar endogenous rhythm, it re-buries itself on the ebb tide. As displacement is a regular feature in the life of Eurydice pulchra 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 sensitive to synthetic chemicals (Cole et al., 1999). Powell (1979) infers from the known susceptibility of Crustacea to synthetic chemicals and other non-lethal effects, that there would probably also be a deleterious effect on isopod fauna as a direct result of synthetic chemical application.
Following the Torrey Canyon tanker oil spill (March, 1967), shore-spraying operations exposed intertidal animals to very high concentrations of the detergent BP 1002 for several hours. Smith (1968) conducted toxicity experiments and found that the concentration required to kill all Eurydice pulchra in 24 hours was 10 mg/BP 1002/l at 12°C. At 5 mg/BP 1002/l four out of five specimens survived when transferred to clean water, while all survived at lower concentrations. On Mawgan Porth beach, Cornwall, a concentration of 4 mg/BP 1002/l was found in seawater at either end of the bay on an incoming tide for at least 24 hours after spraying. However, it became apparent that some of the population of Eurydice pulchra had survived, despite exposure to lethal concentrations both in the sea water and in the sand, as specimens were collected during May 1967. The species had repopulated the entire beach by August of the same year. Recovery within 4 months may have been aided by the fact that during the summer Eurydice pulchra would have spent twice daily periods in almost uncontaminated water.
Other oil dispersing compounds, were found to be toxic to two other species of isopod. Kaim-Malka (1972a, b,c, cited in Powell, 1979) tested the tolerance of Idotea baltica and Sphaeroma serratum to various non-ionic detergents (which do not dissociate in solution to any significant degree) ranging from 0.1 to 800 mg/l. The individual detergents affected the two isopods differently: (a) acid-and ester-base detergents, inactive against Idotea baltica, were lethal to Sphaeroma serratum at concentrations of 10 to 25 mg/l; (b) ether-base detergents were four times more toxic to Idotea baltica than to Sphaeroma serratum; (c) alcohol-function detergents were twice as toxic to Sphaeroma serratum than to Idotea baltica; and (d) alkyl-aryl polyoxyethelenes were ten times more toxic to Idotea baltica as to Sphaeroma serratum.
Thus it is apparent that different isopod suborders differ greatly in their susceptibility to synthetic detergent formulas and that this may be related to their physiology (Powell, 1979). Consequently, owing to the diversity of chemicals to which Eurydice pulchra may be exposed and the intolerance of crustaceans in general, intolerance has been assessed to be high. Recovery has been assessed to be very high owing to the evidence of Smith (1968) when Eurydice pulchra repopulated a shore within 5 months following exposure to a chemical detergent.

Heavy metal contamination

Evidence

Jones, (1975b; 1973) found that mercury (Hg) and copper (Cu) react synergistically with changes in salinity and temperature, resulting in increased toxicity of the metals to marine and brackish water isopods. In an extensive study of six species of isopod, including Eurydice pulchra, Jones (1975) examined mortality caused by Cadmium (Cd) at two temperatures (5 & 10°C), two concentrations (10 and 20 mg/l), and at seven salinities (0.34-34psu). Maximum mortality for Eurydice pulchra occurred at the lowest salinities (20.4 & 13.6 psu) at both concentrations and at the higher temperature. At full salinity (34psu) at 5°C, with 10 mg/Cd/l 60% of Eurydice pulchra died within 4 days. However, Eurydice pulchra was more tolerant of zinc (Zn) at concentrations of 10 and 20 mg/Zn/l, even at the higher temperature of 10°C. Whilst the concentrations of heavy metals used in the work by Jones (1975, 1975b) are higher than those typically occurring in British waters (e.g. Preston (1973) gives values for heavy metal 'hotspots' e.g. Severn Estuary 7.7 µg/Cd/l and 26.6 µg/Zn/l; Tyne-Tees 0.8µg/Cd/l and 11.7 µg/Zn/l), the point was to obtain a comparative study of species over a short time scale. However, Jones (1975) suggested that owing to the accumulative nature of heavy metals, his experiments would provide a reasonable basis for predictions about the comparative effects of various metals at lower environmental concentrations. Intolerance has been assessed to be intermediate owing to the fact that alterations in salinity and temperature influence the effects of heavy metals on the species. The entire population may not be killed but could experience sublethal effects which may reduce the viability of the population. Recovery has been assessed to be moderate owing to the possible persistence of contaminants in the substratum.

Hydrocarbon contamination

Evidence

Toxic effects:
A proportion of the population of Eurydice pulchra on Mawgan Porth beach, Cornwall, was reported to survive the oil pollution caused by the Torrey Canyon tanker spill. In addition the population was observed to have recovered by the summer of the same year (Smith, 1968) (see synthetic chemicals above). However, evaluation of hydrocarbon toxicity impacts alone from the Torrey Canyon spill are nearly impossible owing to the quantity of dispersants used (at a ratio of 10,000 tons of dispersant to 14, 000 tons of oil) to disperse the oil (Suchanek, 1993).
Physical effects:
The crude oil from the Torrey Canyon washed into the sandy bays of Cornwall in drifts between 3-6 cm thick. Some sank into the sand, creating sticky layers, through which Eurydice pulchra would not be able to burrow (see smothering, above). Such areas of oil contaminated sand were scooped up and dumped inland (see substratum removal). Wave action also frequently buried untreated layers of brown oil a few centimetres under the surface and deeper, and the development of grey layers in the sand became an abnormal and conspicuous feature of oil contaminated beaches (Smith, 1968). The beaches populated by Eurydice pulchra are clean with a very low content of organic detritus, and, being generally devoid of silt, the sands are mobile and well aerated. The presence of a grey sulphide layer following oil contamination suggests that the interstitial oxygen concentration became limiting owing to oxidisation by bacteria. Eurydice pulchra is likely to be intolerant of a decrease in oxygenation of the substratum (see oxygenation, below). However, large individuals of Eurydice pulchra were also found at Sennen, Cornwall, during August of 1967, despite markedly grey layers in the sand below them (Smith, 1968). The intolerance of Eurydice pulchra to hydrocarbon contamination has been assessed to be intermediate owing to evidence for the reduced abundance of the species and the additive but indirect effects arising from the type of clean up operations that might be employed on a sandy shore following an oil spill.

Radionuclide contamination

Evidence

Insufficient
information.

Changes in nutrient levels

Evidence

The sandy shore environment inhabited by Eurydice pulchra has a characteristically low level of organic matter. Enhanced levels of organic matter would usually increase the secondary production of the shore, and on sandy shores organic enrichment may be revealed by a shift in species composition towards polychaetes and oligochaetes (Pearson & Rosenberg, 1978). However, the effects of organic enrichment are usually seen earlier and more obviously in meiofaunal populations. From survey work by Read et al. (1983) it may be inferred that Eurydice pulchra had a high intolerance to organic enrichment in the Firth of Forth, as it became established on the beaches of Seafield East and Portobello, only after the introduction of a new sewage treatment scheme for Edinburgh, which reduced the suspended solids content of the liquid effluent by 60%. Recovery has been assessed to be moderate owing to the fact that partial recovery occurred within five years, the pollution community was reduced to isolated patches and gradually replaced by species previously found, in the ten year period after the opening of the sewage works.

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 less common, although they can occur in surface pools of interstitial water on sand and mud flats in summer owing to surface evaporation. However as a burrower Eurydice pulchra is probably sufficiently mobile to avoid increased surface salinities resulting from evaporation and intolerance has been assessed to be low.

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

Jones (1970b) conducted salinity tolerance experiments with Eurydice pulchra and found that to some extent the species was euryhaline, tolerating a reduced salinity of 17psu for up to 5 days before death. Therefore, the species is likely to be highly intolerant of an acute change in salinity of two categories, from full salinity to low salinity (< 18psu) for the period of a week. However, an intolerance assessment of intermediate has been made owing to the fact that Eurydice pulchra is a mobile species and may avoid conditions outside its tolerance by migration e.g. Salvat (1966) observed the abundance of Eurydice spp. to decline where a freshwater stream crossed a beach in France. Recovery has been assessed to be very high (see additional information, below).

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 is the drainage of the beach which, in turn, is determined by the slope and particle size. Oxygen depletion becomes a severe problem at all states of the tide on only the finest grained beaches and as a general rule, if the percentage of particles of less than 0.25 mm in 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.
Jones (1970b) investigated the oxygen requirements of Eurydice pulchra. Its respiration rate was high in comparison with some other isopods, although not excessive when the small size and high activity rates of the species was taken into consideration. Jones (1970b) concluded that since the preferred habitat of Eurydice pulchra is generally well oxygenated, owing to the low percentage of fine sand, absence of silts and organic matter, that in normal conditions oxygenation had little influence upon its distribution. Thus it is unlikely that the species would be able to tolerate conditions of hypoxia for a week and intolerance has been assessed to be high. Recovery has been assessed to be high (see additional information below).

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 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

Eurydice pulchra 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

No other species are extracted from the habitat of Eurydice pulchra.