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

Limecola balthica inhabits the upper layers of sandy and muddy substrata in physiographic locations where activities causing substratum loss occur e.g. channel dredging. Consequently, removal of the substratum would remove the population of Limecola balthica from the area affected and so intolerance is assessed as high. Direct evidence of recovery by Limecola balthica following substratum loss is given by Bonsdorff (1984) (see additional information below) and recoverability is recorded as 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

Limecola balthica is an infaunal species that is able to burrow both vertically and horizontally through the substratum which it inhabits by use of its foot. It is likely that Limecola balthica is not sensitive to smothering by a layer of sediment 5 cm thick as it is a mobile species able to burrow upwards and surface from a depth of 5 - 6 cm (Brafield & Newell, 1961; Brafield, 1963; Stekoll et al., 1980).

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

Limecola balthica is known to practice two alternative modes of feeding. It either holds its feeding organ, the siphon, at a fixed position just above the sediment surface to filter out food particles suspended in the overlying water, or extends and moves its siphon around on the sediment above it to vacuum up deposited food particles (Peterson & Skilleter, 1994). Facultative switching between the modes of feeding in Limecola balthica is directly affected by food availability in the over-lying water (Lin & Hines, 1994). In turn, changes in feeding mode from suspension to deposit feeding directly affects burial depth and burrowing in the sediment is one of few defensive mechanisms Limecola balthica has against predators. In the laboratory, Lin & Hines (1994) observed specimens of Limecola balthica kept in estuarine water supplemented with 75 µg L^-1of algae to maintain a deeper burial position whilst suspension feeding, than those without an enhanced diet who deposit fed. Thus an increase of material in suspension will favour suspension feeding by Limecola balthica and indirectly reduce its vulnerability to lethal and sub-lethal siphon browsing by fish and decapods. Limecola balthica is therefore assessed as 'tolerant' with the potential for growth and reproduction to be enhanced by the increased food supply.

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

Limecola balthica is known to practice two alternative modes of feeding. It either holds its feeding organ, the siphon, at a fixed position just above the sediment surface to filter out food particles suspended in the overlying water, or extends and moves its siphon around on the sediment to vacuum up deposited food particles (Peterson & Skilleter, 1994). A reduction in suspended material is likely to decrease the availability of food attained efficiently by suspension feeding. Facultative switching between the modes of feeding in Limecola balthica is directly affected by food availability in the over-lying water (Lin & Hines, 1994). In turn, changes in feeding mode from suspension to deposit feeding directly affects its burial depth and burrowing in the sediment is one of few defensive mechanisms Limecola balthica has against predators. Thus a decrease in the amount of suspended material in the over-lying water is likely to initiate deposit feeding in Limecola balthica. In doing so, Limecola balthica may decrease the depth at which it resides in order to stretch its siphon over the substratum to feed efficiently. The exposure of its inhalent siphon (rather than just the tip) for deposit feeding is likely to increase the risk of lethal predation and non-lethal siphon browsing by fish and decapods. However, intolerance is assessed to be low since the benchmark change period is one month.

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

Limecola balthica is a bivalve and can close tightly by contraction of the adductor muscle, storing moisture inside the shell. The silty sediments in which the species lives have a high water content and are therefore resistant to desiccation. Furthermore, Limecola balthica is mobile and would be able to relocate further down the shore by burrowing (Bonsdorff, 1984) or floating (Sörlin, 1988) if exposed to desiccation stress. Limecola balthica has therefore been assessed as 'tolerant' to desiccation at the level of the benchmark.

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

Limecola balthica occurs in the upper regions of the intertidal (Tebble, 1976) and is therefore likely to be tolerant of prolonged emergence. It is a bivalve and can close tightly by contraction of the adductor muscle, storing moisture inside the shell. The silty sediments in which the species lives have a high water content and are therefore resistant to desiccation. Furthermore, Limecola balthica is mobile and able to relocate in the intertidal by burrowing (Bonsdorff, 1984) or floating (Sörlin, 1988). It would be expected to react to an increase in emergence by migrating down the shore to its preferred position. There may be an energetic cost to this migration but it is not expected that mortality would result and so intolerance is recorded as low. Limecola balthica should quickly recover from the energetic cost of relocation and so recoverability is assessed as very high.

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

Limecola balthica occurs in the intertidal and sublittorally down to depths of 190 m (Olafsson, 1986), although is more abundant intertidally, so would be expected to be tolerant of a decrease in emergence regime.

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

Limecola balthica thrives in low energy environments such as estuaries (Tebble, 1976) where the substratum has a high proportion of fine sediment. Increased water flow rate will change the sediment characteristics in which the species lives, primarily by re-suspending and preventing deposition of finer particles (Hiscock, 1983). This would result in erosion of the preferred habitat, which may cause mortality of some portion of the population of Limecola balthica. Green (1968) recorded that towards the mouth of an estuary where sediments became coarser and cleaner, Limecola balthica was replaced by another tellin species, Tellina tenuis. Intolerance is therefore recorded as intermediate. Recoverability is recorded as 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

Limecola balthica thrives in low energy environments such as estuaries (Tebble, 1976) where the substratum has a high proportion of fine sediment. The species is able to maintain a feeding and respiration current independent of ambient flow. As a result of decreased water flow, rate of siltation is likely to increase, making conditions more favourable for deposit feeders. Indeed, Newell (1965) (cited in Green, 1968) noted that Limecola balthica populations in the Thames Estuary, UK, were denser where the grade of deposit was finer, possibly due to greater food availability. Therefore, Limecola balthica is probably tolerant of a decrease in water flow rate.

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 Limecola balthica (see distribution) illustrates that the species is tolerant of a range of temperatures and probably becomes locally adapted. In Europe, the species occurs as far south as the Iberian Peninsula and hence would be expected to tolerate higher temperatures than experienced in Britain and Ireland. Oertzen (1969) reported that Limecola balthica (as Macoma balthica) could tolerate temperatures up to 49°C before thermal numbing of gill cilia occurred presumably resulting in death. Ratcliffe et al. (1981) reported that Limecola balthica from the Humber Estuary, UK, tolerated 6 hours of exposure to temperatures up to 37.5°C with no mortality. It seems likely therefore that the species could adapt to a chronic change and tolerate a large acute change with no mortality. The worst case scenario following an increase in temperature is an energetic cost associated with sub-optimal metabolic function and so intolerance is assessed as low. Metabolic activity should rapidly return to normal when temperatures fall to original levels so recoverability is assessed as very high.

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 geographical distribution of Limecola balthica suggests that it is very tolerant of low temperature. The species occurs in the Gulfs of Finland and Bothnia where the sea freezes for several months of the year (Green, 1968). It must therefore tolerate much lower temperatures than it experiences in Britain and Ireland. Furthermore, Limecola balthica was apparently unaffected by the severe winter of 1962/3 which decimated populations of many other bivalve species (Crisp, 1964), and De Wilde (1975) noted that Limecola balthica kept at 0°C maintained a high level of feeding activity. It is unlikely therefore that UK populations of Limecola balthica would be intolerant of decreases in temperature.

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

Limecola balthica does not require light and therefore is not directly affected by an increase in turbidity for the purposes of light attenuation. An increase in turbidity may affect primary production in the water column and therefore reduce the availability of phytoplankton food in suspension and deposited at the sediment surface. However, phytoplankton will also immigrate from distant areas and so the effect may be decreased. As the benchmark turbidity increase only persists for a year, decreased food availability would probably only affect growth and fecundity and an intolerance of low is recorded. As soon as light levels return to normal, primary production will increase and hence recoverability is recorded as very high. The effect of increased siltation is detailed in 'increase in suspended sediment' above.

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

Limecola balthica does not require light and therefore would not be affected by a decrease in turbidity for light attenuation purposes. It is possible that decreased turbidity would increase primary production in the water column and by micro-phyto benthos. The resultant increase in food availability may enhance growth and reproduction in Limecola balthica but only if food was previously limiting. The effect of decreased siltation is detailed in 'decrease in suspended sediment' above.

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

Limecola balthica characteristically inhabits fine sediments in low energy environments (Tebble, 1976). This suggests that it would, in some way, be intolerant of an increase in wave exposure. An increase in wave exposure by two categories for one year would be likely to affect the species in several ways. Fine sediments would be eroded (Hiscock, 1983) resulting in the likely reduction of the habitat of Limecola balthica. Strong wave action may cause damage or withdrawal of the siphons, resulting in loss of feeding opportunities and compromised growth. Furthermore, individuals may be dislodged by scouring from sand and gravel mobilized by increased wave action. For example, Ratcliffe et al. (1981) reported that juvenile Limecola balthica are susceptible to displacement by water currents due to their small mass and inability to bury deeply. For the above reasons, some mortality would be likely to occur and intolerance is recorded as intermediate. Recoverability is recorded as 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

Limecola balthica characteristically inhabits muddy sand in low energy environments (Tebble, 1976). It is capable of maintaining a feeding and respiration current by ciliary action. It is therefore unlikely to be affected by a decrease in wave exposure. However, it should be noted that decreased wave exposure will lead to changes in oxygenation and increased risk of smothering due to siltation. These factors are discussed in their relevant sections.

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

Limecola balthica is intolerant of shear-wave vibrations that propagate along the sediment surface in the frequency range 50-200 Hz (Franzen, 1995). When placed on the surface of the substratum and exposed to a shear-wave of typical velocity for unconsolidated muddy sand (15 meters per second), the response of Limecola balthica consisted of frequent and intense digging attempts (Franzen, 1995). It is likely that Limecola balthica will be not sensitive to the benchmark for underwater noise as it will either remain buried or take immediate avoidance reaction by burying without a detectable effect upon the species viability.

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

Limecola balthica does not have the visual acuity to detect objects and is unlikely to be sensitive to visual disturbance.

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

No evidence was found concerning the effect of physical abrasion on Limecola balthica. However, the species is not mobile enough to be able to avoid an object such as a dragging anchor or a scallop dredge and the shell is relatively thin and would probably be damaged by such an impact. It is expected that some mortality would result and therefore intolerance is assessed as intermediate. Recoverability is recorded as high (see additional information below).

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

Limecola balthica is likely to be tolerant of displacement as it is able to rebury itself within 17 minutes when placed on the surface of the substratum (McGreer, 1979). However, Limecola balthica individuals displaced to the sediment surface are likely to suffer an increased risk of predation and some mortality may result. Intolerance is therefore recorded as intermediate. Recoverability is recorded as high (see additional information below).

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

Beaumont et al. (1989) concluded that bivalves are particularly sensitive to tri-butyl tin (TBT), a toxic component of antifouling paints. For example, when exposed to 1-3 µg TBT/l, Cerastoderma edule and Scobicularia plana suffered 100% mortality after 2 weeks and 10 weeks respectively. There is also evidence that TBT causes recruitment failure in bivalves, either due to reproductive failure or larval mortality (Bryan & Gibbs, 1991). However, little evidence was found concerning the effects of synthetic chemicals specifically on Limecola balthica. Bryan & Gibbs (1991) recorded bioaccumulation of TBT by Limecola balthica (as Macoma balthica) to be similar to Cerastoderma edule and Scobicularia plana. Langston (1978) recorded bioaccumulation of a polychlorinated biphenyl in Limecola balthica (as Macoma balthica), levels of Aroclor 1242 reached 60 ppm in 40 days. Duinker et al. (1983) also reported bioaccumulation of PCBs by Limecola balthica (as Macoma balthica) but made no comment on toxicity to the species. In light of the intolerance of other bivalve species, the intolerance of Limecola balthica  to synthetic chemicals is recorded as high but with very low confidence. Recoverability is recorded as high (see additional information below).

Heavy metal contamination

Evidence

• Boisson et al. (1998) investigated the intolerance of Limecola balthica (as Macoma balthica) from two French estuaries to silver and mercury. They reported an LT₅₀ for 80µg Ag/l of 9.3 days and an LT₅₀ for 100µg Hg/l of 11.0 days. However, acute tests are not necessarily relevant, especially if the major route of exposure is via food /sediment (Langston, W.J., pers. comm.). They also noted that Limecola balthica from a contaminated estuary were more intolerant of silver than those from an uncontaminated estuary. The differing responses were attributed to the chronic stress of living in a polluted environment making clams more intolerant of subsequent exposure. Limecola balthica from the contaminated estuary also exhibited lower uptake rates of heavy metal stressors, which was suggested as an adaptive trait to avoid exposure to contaminants.
• Luoma et al. (1983) investigated the intolerance of Limecola balthica from different populations within San Francisco Bay to copper, in the form of seawater spiked with copper sulphate. The 10 day LC₅₀ varied between 210 µg/l and 1290 µg/l. They suggested that physiological and/or genetic adaptations could be responsible for the heterogeneity of the sensitivities and added that species survival depends more on the range of adaptive capacity within the species rather than identification of a single value of lethal or sublethal toxicant concentration.
• McGreer (1979) investigated the effect of heavy metal contaminated sediments on the burrowing and avoidance behaviour of Limecola balthica. Exposure to estuarine sediments containing high levels of heavy metals (Cu, Pb, Zn, Cr, Ag, Hg, Cd and Fe) caused inhibited burrowing behaviour in all contaminated sediments compared to the control. The time for 50% of the experimental population to burrow into the sediment core ranged from 0.17 hours in the control to 4.8 hours in the most contaminated substrata. Correlative evidence of the concentrations of individual metals in the sediment versus the burrowing response times suggests the inhibition of burrowing by Limecola balthica to be significant for Hg and Cd. The ecological significance of inhibited burrowing is very clear; exposure to predators and wave action. The significance of the avoidance response remains to be tested in the field but McGreer (1979) demonstrated that Limecola balthica may actively avoid sediments which become contaminated.
• Bryant et al. (1985 & 1985a) present evidence that the environmental variables of temperature and salinity should be considered when evaluating the toxicity of arsenic, nickel and zinc to Limecola balthica in the estuarine environment. The median survival time of Limecola balthica exposed to Ni and Zn (range 15 - 2000 ppm) decreased as salinity decreased (from 35 psu to 5 psu in 5 psu increments). Whilst, temperature changes had greater influence on the effect of As concentration upon Limecola balthica.

There is evidence, therefore, of lethal and sublethal effects of exposure to heavy metals. Intolerance of Limecola balthica is, therefore assessed as high. Recoverability is recorded as high, assuming contaminant levels return to normal. Please see additional information below. For reference, the lethal copper concentrations reported by Luoma et al. (1983) are similar to copper concentrations in freshwater inputs to the Fal Estuary, UK, reported by Bryan & Gibbs (1983).

Hydrocarbon contamination

Evidence

Stekoll et al. (1980) exposed Limecola balthica (as Macoma balthica) to Prudhoe Bay crude oil in flowing seawater for six months at three concentrations; low 0.03 mg/l, medium 0.3 mg/l and high 3.0 mg/l. Limecola balthica exhibited a range of behavioural, physical, physiological and biochemical changes prior to death at the highest concentration of oil.
Mortality:

• Total cumulative mortality of Limecola balthica in control tanks after six months was 3.1%.
• Limecola balthica in 0.03 mg/l oil had a similar mortality of 3.2% after six months exposure.
• In the 0.3 mg/l oil treatment the mortality rate was already significantly different from the control by day 120. Mortality reached 8% by day 180.
• Limecola balthica in 3.0 mg/l began to die by day 30 of the experiment and after six months mortality had reached 81%.

Other observations:

• Exposure to 0.03 mg/l of oil inhibited growth and caused reabsorption of the gametes, whilst exposure to 0.3 and 3.0 mg/l of oil caused abnormalities in the gonads.
• Limecola balthica exposed to 0.3 and 3.0 mg/l of oil fed less actively, whilst specimens in the 3.0 mg/l oil treatment rarely extended their siphons at all.
• After one week of exposure to 0.3 and 3.0 mg/l of oil Limecola balthica began to burrow upwards out of the sand. Those exposed to 3.0 mg/l of oil stayed on the surface and progressively more animals surfaced throughout the duration of the experiment so that 90% had surfaced by the end of the experiment. It was not until day 90 that Limecola balthica in the 0.3 mg/l oil treatment began to surface in significant numbers.
• Limecola balthica in 3.0 mg/l of oil were also less able to orientate themselves with respect to the surface of the sand. They extruded their feet in various directions but were unable to penetrate the sand.
• For a more detailed summary of other effects particularly those of a biochemical nature, refer to Table 4 in Stekoll et al., (1980).
  Stekoll et al. (1980) concluded that chronic exposure of Limecola balthica to oil-in-seawater concentrations even as low as 0.03 mg/l would in time lead to population decreases.
  Shaw et al. (1976) also reported mortality of Limecola balthica caused by exposure to crude oil following an experimental application of oil at a concentration of 1.2 µl oil/cm² and 5.0 µl oil/cm² to sediments which equated to oil spills of one ton /20 km² and one ton/100 km². Significant mortalities were observed after only two days following application of the oil at a concentration of 5.0 µl oil./cm². Some specimens of Limecola balthica survived the application of oil in these experiments but were weakened. The clams in the study of Stekoll et al. (1980) were not subjected to any of the stresses that normally occur in their natural environment on mudflats such as changes in salinity, temperature, oxygen availability and wave action, therefore it is possible that exposure of Limecola balthica to oil under field conditions results in higher mortality. Intolerance of Limecola balthica is therefore assessed as high. Recoverability is recorded as high assuming contamination removed (see additional information below).

Radionuclide contamination

Evidence

Hutchins et al. (1998) described the effect of temperature on bioaccumulation by Limecola balthica of radioactive americium, caesium and cobalt, but made no comment on the intolerance of the species. Insufficient
information was available to assess the intolerance of Limecola balthica to radionuclide contamination.

Changes in nutrient levels

Evidence

It has been suggested that Limecola balthica has the potential to be used as an indicator organism of organic pollution (Pearson & Rosenberg, 1978; Pekkarinen, 1983; Mölsa, 1986), as the species was reported to increase in abundance towards the sources of nutrient enrichment and to disappear when the organic loading became heavier (Anger, 1975 (a) & (b); Landner et al., 1977). Madsen & Jensen (1987) reported the population of Limecola balthica to increase in abundance and biomass at two localities in the Danish Wadden Sea experiencing nutrient enrichment caused by a waste water discharge. The increase in shell growth, productivity / biomass ratio and improvement in 'condition' index of Limecola balthica in the organically enriched areas was presumably due to the increased food supply (Madsen & Jensen, 1987). Owing to this evidence and that Limecola balthica is relatively tolerant to deoxygenation (an indirect effect of nutrient enrichment) it is likely that Limecola balthica will benefit from nutrient enrichment.

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

McLusky & Allan (1976) conducted salinity survival experiments with Limecola balthica (as Macoma balthica) over a period of 150 days. No deaths were reported in specimens of Limecola balthica maintained at 30.5 psu for the duration of the experiment. Limecola balthica is found in brackish and fully saline waters (although it is more common in brackish waters) (Clay, 1967(b)) so may tolerate a state of flux. McLusky & Allan (1976) reported that Limecola balthica failed to grow at 41 psu, but it is likely that Limecola balthica would be tolerant of increased salinity and intolerance to a change in this factor is likely to be low. Growth should quickly return to normal when salinity returns to original levels and so recoverability is recorded as very high.

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

McLusky & Allan (1976) conducted salinity survival experiments with Limecola balthica (as Macoma balthica) over a period of 150 days. Survival times declined with decreased salinity. At 12 psu specimens survived 78 days, whilst specimens at 8.5 psu survived 40 days. Some specimens of Limecola balthica survived 2.5 days at 0.8 psu, which was apparently due to the animals ability to clamp its valves shut in adverse conditions. McLusky & Allan (1976) also reported that Limecola balthica failed to grow (increase shell length) at 15 psu. Limecola balthica is found in brackish and fully saline waters (Clay, 1967(b)) so may tolerate a state of flux. Its distribution in combination with the experimental evidence of McLusky & Allan (1976) suggests that Limecola balthica is likely to be very tolerant to a decreased salinity over a short period. A decline in salinity in the long term may have implications for the species viability in terms of growth, and the distribution of the species may alter as specimens at the extremes retreat to more favourable conditions. Intolerance is therefore assessed as low. Metabolic function should quickly return to normal when salinity returns to original levels and so recoverability is recorded as very high. Decreased salinity may also affect the ability of Limecola balthica to tolerate contaminants such as heavy metals (see Bryant et al., 1985 & 1985a). Usually, contaminants become more toxic at low salinity (Langston, W.J. pers comm.).

Changes in oxygenation

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

Evidence

Limecola balthica appears to be relatively tolerant of deoxygenation. Brafield & Newell (1961) frequently observed that in conditions of oxygen deficiency (e.g. less than 1 mg O₂/l) Limecola balthica moved upwards to fully expose itself on the surface of the sand. Specimens lay on their side with the foot and siphons retracted but with valves gaping slightly allowing the mantle edge to be brought into full contact with the more oxygenated surface water lying between sand ripples. In addition, Limecola balthica was observed under laboratory conditions to extend its siphons upwards out of the sand in to the overlying water when water was slowly deoxygenated with a stream of nitrogen. The lower the oxygen concentration became the further the siphons extended. This behaviour, an initial increase in activity stimulated by oxygen deficiency, is of interest because the activity of lamellibranchs is generally inhibited by oxygen deficient conditions (Brafield & Newell, 1961). Dries & Theede (1974) reported the following LT₅₀ values for Limecola balthicaa maintained in anoxic conditions : 50 - 70 days at 5°C, 30 days at 10°C, 25 days at 15°C and 11 days at 20°C. Theede (1984) reported that the ability of Limecola balthica to resist extreme oxygen deficiency was mainly due to cellular mechanisms. Of considerable importance are sufficient accumulations of reserve compounds e.g. glycogen and the ability to reduce energy requirements for maintenance of life by reducing overall activity (Theede, 1984). Limecola balthica is therefore very tolerant of hypoxia, although it may react by reducing metabolic activity. Intolerance is therefore assessed as low. Metabolic function should quickly return to normal when normoxic levels are resumed and so recoverability is recorded as very 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

Limecola balthica is host to at least three gymnophallid trematodes; Lacunovermis macomae (Lebour), Gymnophallus gibberosus (Loos-Franc) and Parvatrema affinis which is known to cause sexual castration (Swennen & Ching, 1974). Specimens tend to be more infested at higher levels of the intertidal (1.0 m above mean low water) than at mean low water, and larger specimens tend to be more infested than smaller ones (Lim & Green, 1991). Lim & Green (1991) also suggest that increased exposure of Limecola balthica at the higher intertidal level to shore birds (the final host of the trematodes) is the reason for the differences in parasite load between the tidal levels. They found that the most parasitised specimens grew faster and larger than the less parasitised. Enhanced stomatic growth as a result of parasitic castration was proposed as a logical explanation to account for the faster growth rate of parasitised specimens. Recoverability is recorded as high (see additional information below).

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

There is no evidence to suggest that Limecola balthica is likely to be susceptible to displacement by invasive species.

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

Limecola balthica is not extracted commercially.

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

Commercial extraction of other infaunal species is likely to have an effect on Limecola balthica where their distributions overlap. Hall & Harding (1997) demonstrated that commercial cockle harvesting by suction dredging had significant effects on soft-sediment infaunal communities. Following dredging, species numbers were reduced by up to 30% and abundances by up to 50%. Bait harvesting has also been shown to impact infaunal bivalves. For example, mechanical harvesting for Arenicola marina resulted in drastic reduction in the population of Mya arenaria in the Wadden Sea (Beukema, 1995), and commercial digging of mudflats in Maine, USA, reduced total number of infaunal taxa (Brown & Wilson, 1997). Some mortality of Limecola balthica may occur therefore due to harvesting of other species so an intolerance of intermediate is recorded. Recoverability is recorded as high (see additional information below).