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

Nucula nitidosa lives infaunally in muddy /sandy sediments. Removal of the substratum would also remove the entire population of this species so intolerance has been assessed to be high with a high recoverability. See additional information for recoverability.

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

Nucula nitidosa can tolerate anaerobic conditions for several days and is able to thrive in poorly aerated sediments. Ranchor (1976) suggested that their ability to tolerant anaerobic conditions and their mobility, allowed them to survive when covered by sediments during stormy weather. Ranchor (1976) also reported that Nucula nitidosa was abundant in an area subject to sewage sludge dumping. Therefore, an intolerance of low has been recorded at the benchmark level. Intolerance to other factors such as oil may be higher.

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

Nucula nitidosa is a deposit feeder and therefore is not directly reliant on suspended matter as a food resource. Davis & Wilson (1983b) reported that the high levels of particulate matter in the water column suggested that turbidity was unlikely to be a factor that limited the distribution of Nucula nitidosa (Davis & Wilson, 1983b). However, an increase in suspended sediment will increase the rate of siltation at the sediment surface which may enhance the food supply for Nucula nitidosa . Therefore Nucula nitidosa is tolerant* of increases in suspended sediment at the benchmark level.

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

Nucula nitidosa is a deposit feeder and is therefore not directly reliant on suspended matter to be able to feed. However a decrease in siltation may result in a decreased rate of deposition on the substratum surface and therefore a reduction in food availability. The benchmark states that this change would occur for one month and therefore would be unlikely to cause mortality. Intolerance has been assessed as low and as feeding activity should return to normal as soon as the suspended sediment levels increase recoverability has been assessed as very high.

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

The effect of desiccation stress on Nucula nitidosa is likely to be minimal as it lives infaunally in muddy sand and is able to burrow into the sediments in order to avoid or reduce the effects of desiccation. Bivalves are also able to respond to desiccation stress by valve adduction i.e. during periods of emersion. Therefore an intolerance of low has been given with a high recoverability.

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

An increase in emergence may expose Nucula nitidosa to thermal stress and increase the risk of predation and dislodgement from the sediments. Nucula nitidosa is a burrowing bivalve that lives infaunally in the muddy sands and can be found at depths of 180 m. It is therefore unlikely that the benchmark level would cause mass mortalities. However, those clams further up the shoreline would be more at risk to desiccation stress and mortalities may occur. Therefore, an intolerance of intermediate is given with a high recoverability.

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

A decrease in emergence, is unlikely to stress Nucula nitidosa and may benefit the species, allowing it to colonize further up the shore and increase its habitat range. Periods of thermal stress, risk of predation and dislodgement would be reduced. Therefore, as decreased emergence may benefit this tolerant* is recorded for this species.

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

Nucula nitidosa lives in a mixture of fine muddy sand sediments. Increased water flow may cause the substrata to be disturbed and the sediment on the seabed to erode. This scouring of sand and gravel causes coarse sediments to become unstable and difficult to burrow. This may lead to dislodgement and abrasion of Nucula nitidosa. The sediments and the species within such as Nucula nitidosa may then be transported to another area (bedload transport) by increased water flow. It may also damage or prevent settlement of larvae that can lower recruitment levels and lower the population present (Hiscock, 1983). Therefore, an intolerance of intermediate has been assessed with high recoverability.

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

In areas exposed to less water flow, the sediments will be more stable (Hiscock, 1983) and particles may become finer and the substrata may become more muddy. However, a decrease in water flow over the benchmark level of 1 year may also cause the substrata to build up and become too muddy for Nucula nitidosa, which prefers muddy sand sediments. Therefore, intolerance has been assessed as intermediate with a high recoverability level.

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

Nucula nitidosa is distributed to the south of the British Isles and so is likely to be tolerant of warmer water temperatures than those it experiences round the British Isles.

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

Short term acute periods of extreme cold and icing conditions are likely to cause stress and some mortality in bivalve populations (Dame, 1996). During the extreme cold winter of 1962/1963 sea water temperatures near Helgoland (North Sea) fell to an abnormal low of -1.5 °C. Most invertebrates present suffered high mortalities except for Nucula nitidosa. A decrease in temperature may slow down the growth of Nucula nitidosa. Therefore it is likely that Nucula nitidosa would survive a decrease in temperature, but the viability of the population may be reduced. Hence, intolerance has been assessed as low with a very high recoverability.

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 on primary productivity resulting from an increase in turbidity are unlikely to directly affect Nucula nitidosa which is dependent on organic matter for its productivity. Davis & Wilson (1983b) reported that the high levels of particulate matter in the water column suggested that turbidity was unlikely to be a factor that limited the distribution of Nucula nitidosa (Davis & Wilson, 1983b). In addition, Nucula nitidosa lives within the sediment. Therefore, this factor is not relevant.

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

This factor is considered not relevant (see 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

Nucula nitidosa prefers depths less than 50 m in areas of wave action ranging from sheltered to very sheltered. Increased wave exposure will cause the sediment on the seabed to erode. The sediments and the species within, such as Nucula nitidosa, may then be transported to another area (bedload transport) reducing numbers of the population of present in an area. The dispersion and settlement of juvenile Nucula nitidosa may also be disrupted. Therefore, intolerance has been assessed as intermediate with a high recoverability.

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

Changes in wave exposure are likely to have marked effects on the sediment dynamics. If the wave exposure is decreased, sediments that are deposited will slowly consolidate becoming more fine and muddy. Decreased exposure could also increase siltation and the risk of smothering. Nucula nitidosa is specialised for its preferred habitat of muddy and fine sand, however a decrease in wave exposure over the benchmark period of 1 year may cause the substrata to become too muddy for Nucula nitidosa. Therefore, intolerance has been assessed as intermediate with a high recoverability.

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

No information was found concerning the intolerance levels of Nucula nitidosa to noise. This species is not expected to be sensitive at the level of the benchmark.

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

Nucula nitidosa probable has little visual acuity and was recorded to be not sensitive to this factor.

Abrasion & physical disturbance

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

Evidence

Fishing for demersal species will disturb the surface layer of sediment and any protruding or shallow burrowing species. Even though Nucula nitidosa has a small thick shell, it is probably vulnerable to physical damage from e.g. otter boards (Rumohr & Krost, 1991) but its small size relative to the meshes of commercial trawls may ensure survival of at least a moderate proportion of disturbed individuals that pass through the nets. The effects of trawl disturbance on a benthic community was investigated with a manipulative field experiment in a fine muddy habitat that had been closed to fishing for twenty five years (Tuck et al., 1998). A decline in the population density of Nucula nitidosa was reported after 5 months of trawling disturbance, which remained significantly lower than the reference control area after 10 months (Tuck et al., 1998). Therefore intolerance has been assessed as intermediate as mortality may occur, and recoverability has been assessed as high.

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

Nucula nitidosa has a small solid shell. Fishing for demersal species will disturb the surface layer of sediment and any protruding or shallow burrowing species. Nucula nitidosa has the ability to reburrow back down into the sediment when it is displaced to the surface therefore, it is probably relatively tolerant of displacement. However, when displaced the risk of predation by predators is increased which may lead to some mortalities of Nucula nitidosa. Storms or increased wave action may cause whole populations to be lifted along with the substrata and transported to a different area where they will settle. Sediment bed load transport can occur when wave action is increased causing large coarse muddy / sandy grains to roll, hop or saltate along the bottom as bedload (Snelgrove et al., 1994). Therefore, an intolerance of low has been recorded with a high recoverability assessment.

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

Synthetic chemicals, including tributyl-tin (TBT) have been shown to have detrimental effects in a variety of bivalve species (for examples see reviews of Abra alba, Macoma balthica, Mytilus edulis, Cerastoderma edule, Ostrea edulis and Mya arenaria. However, no specific information was found concerning the effect of synthetic chemicals on Nucula nitidosa, therefore intolerance and recoverability assessments could not be given.

Heavy metal contamination

Evidence

The capacity of bivalves to accumulate heavy metals in their tissues, far in excess of environmental levels, is well known. For example:

• Bryan (1984) states that Hg is the most toxic metal to bivalve molluscs while Cu, Cd and Zn seem to be most 'problematic' in the field; and
• reactions to sub-lethal levels of heavy metals include siphon retraction, valve closure, inhibition of byssal thread production, disruption of burrowing behaviour, inhibition of respiration, inhibition of filtration rate, inhibition of protein synthesis and suppressed growth (see review by Aberkali & Trueman, 1985).

However, no information specifically concerning the effects of heavy metal contamination on Nucula nitidosa was found therefore intolerance and recoverability could not be assessed.

Hydrocarbon contamination

Evidence

Nucula nitidosa may not come into direct contact with spilt oil but may be exposed to the water soluble components of oils, and oils adsorbed onto particulates. Suchanek (1993) reviewed the effects of oil on invertebrates. Information on the effects of oils and hydrocarbons on bivalves is included in reviews of Abra alba, Macoma balthica, Mytilus edulis, Cerastoderma edule, Ostrea edulis and Mya arenaria. However, no information concerning the effects of hydrocarbons specifically on Nucula nitidosa was found. Therefore intolerance cannot be assessed.

Radionuclide contamination

Evidence

No specific information was found concerning the effects of radionuclides on Nucula nitidosa.

Changes in nutrient levels

Evidence

Nucula nitidosa are considered to be indicators of organic enrichment (Walker & Rees, 1980). Nucula nitidosa was abundant in an area north of the Elbe estuary where colonization by other macrofauna was impaired due to the sewage sludge from Hamburg being regularly deposited in the estuary (Rachor, 1976). High densities of Nucula nitidosa were also recorded in Howth Harbour (Ireland) in an area that was subject to sewage sludge dumping (Davis & Wilson, 1983b). Therefore Nucula nitidosa has been assessed as tolerant*.

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

Nucula nitidosa is found in waters at full salinity. Therefore this factor is not relevant. However, no information concerning the effects of hypersaline conditions was found.

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

Nucula nitidosa is found in waters at full salinity. Ranchor (1976) successfully reared specimens in the laboratory at a salinity of 27 to 32 ppt. However, very little information on salinity tolerance was found. It is possible that a decrease in salinity may cause mortalities. Therefore, intolerance has been assessed as intermediate with a high recoverability at the benchmark level.

Changes in oxygenation

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

Evidence

Wilson & Davis (1984) suggested that Nucula nitidosa showed the greatest limitation in the protobranch gill and in its inability to regulate oxygen to any great extent in response to hypoxic conditions. Holmes et al. (2002) stated that all the literature with regards to the susceptibility of Nucula nitidosa to hypoxia are anecdotal in nature. For example:

• Trevallion (1965: cited in Wilson & Davis, 1984) showed that Nucula nitidosa has the ability to survive up to 72 hours under anoxic conditions, and
• Ranchor (1976) reported that Nucula nitidosa will withstand oxygen deficiency and reducing conditions in the sediment and will survive 7 days of anaerobic conditions (Ranchor, 1976), whereas
• Holmes et al.(2002) reported that Nucula nitidosa had a mean survival time of 3.53 days and suffered 100% mortality after 10 days under hypoxic conditions at 1.38 ml O₂/l (1.93 mg O₂/l).

A long term decline of populations of Nucula nitidosa in the German Bight was attributed to an increased frequency of hypoxic events (Diaz & Rosenberg, 1995; Holmes et al., 2002). Therefore, a decrease in oxygen concentration at the benchmark level is likely to result in some mortality, and an intolerance of intermediate has been recorded. Recoverability is likely to be high.

Introduction of microbial pathogens/parasites

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

Evidence

A number of parasites have been found in Nucula nitidosa.

• Nucula nitidosa is the sole intermediate host for the trematode Steringotrema pagelli. About 2% of Nucula nitidosa from western Kattegat were found to be infected (Køie, 1980). The gonad of the infected host is completely destroyed. Trematodes can reduce growth and fecundity within bivalves and in some instances may cause death (Dame, 1996).
• Monascus (Haplocladus) filiformis has its larval stage in Nucula nitidosa. The furcocercous cercariae, which occur in thick walled red brown sporocysts in the digestive gland and gonads, are unusually large measuring on average 970 X 340 µm. Køie, (1979) recorded these cercariae in 30% of about 200 Nucula nitidosa also from Kattegat.

Parasitic infections are likely to result in sub lethal effects but an intolerance of intermediate has been recorded to reflect the castrations in some individuals. Recoverability has been assessed as high.

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 regarding the effects of non- native species on Nucula nitidosa could be found therefore an intolerance assessment could not be made.

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

Nucula nitidosa are not targeted for extraction. Therefore, an intolerance assessment is not relevant.

Extraction of other species

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

Evidence

The effects of trawl disturbance on a benthic community was investigated with a manipulative field experiment in a fine muddy habitat that had been closed to fishing for twenty five years (Tuck et al., 1998). A decline in the population density of Nucula nitidosa was reported after 5 months of trawling disturbance and remained significantly lower than the reference control areas after 10 months (Tuck et al., 1998).
In areas of high population density it appears that trawling would be unlikely to remove a whole population, therefore intolerance has been assessed as intermediate with a high recovery level.