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

Removal of the substratum would cause removal of adult and juvenile dog whelks together with their egg capsules. Therefore, an intolerance of high has been recorded. Given their poor dispersal ability, recruitment from other populations is likely to be slow, therefore a recoverability of low has been recorded.

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

Little information on the effect of smothering was found. However, dog whelks are found at the mouths of highly turbid estuaries, such as the Severn Estuary where rock pools are often filled with silt. Dog whelks are therefore probably not adversely affected by temporary smothering. If smothering occurs, there will be an energetic expenditure involved in freeing itself from the smothering material. Hence, an intolerance of low has been recorded.

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

Nucella lapillus is found in turbid estuaries such as the Severn estuary, and is, therefore, unlikely to be adversely affected by an increase in suspended sediment concentration. However, the accumulation of silt or mud may restrict their distribution in silty estuaries such as the Severn. In addition, the abundance of their prey (barnacles and mussels) may be restricted by increased suspended sediment, reducing their food supply. Therefore, an intolerance of low has been recorded.

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

Nucella lapillus is found on a variety of shores from wave exposed to sheltered and is, therefore, unlikely to be affected by a decrease in suspended sediment concentration. Hence, Nucella lapillus has been recorded as 'tolerant' to a decrease in suspended sediment.

Desiccation

1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

Desiccation tolerance is dependant on the volume of water held inside the mantle cavity of the shell and hence the shell shape. Squat shells characteristic of some wave exposed shores have wider apertures and shorter spires which results in less water being retained within the shell when emersed and a greater rate of evaporation through the larger aperture.

• Boyle et al. (1979) demonstrated that the amount of water in the mantle cavity fell on drying at 20 °C for 6 hrs from 39% to 33% of the total water content of the animal, due to drainage and evaporation, with a resultant increase in ionic concentration. As expected higher shore animals, emersed for longer, showed a greater reduction in water volume on the shore. Etter (1988b) suggested that the evaporation of the mantle water resulted in cooling (see temperature below).
• Coombs (1973b) noted that desiccation was dependant on age and size. Small individuals (<16 mm, ca 1 year old) lost water more rapidly but survived a greater percentage water loss, and became comatose at a water loss of 50-55%; whereas large dog whelks (15-25 mm, ca 1-2 years old) became comatose after 35-40% water loss. Small and large individuals reach critical water loss after 6hr at 25 °C, however.
• During emersion dog whelks were able to maintain normal aerobic respiration. Individuals that retained the most water during emersion also exhibited a higher oxygen consumption than those that retained less (Sandison, 1968; Houlihan et al., 1981; Innes & Houlihan, 1985).
• Sandison (cited in Lewis, 1964) reported 100% mortality in dog whelks exposed to drying for 7 days at 18 °C.
• On sheltered shores, with relatively high temperatures the dog whelks are predominately white (Berry, 1983; Etter, 1988). Etter (1988b) reported that white shells reflected more light, and hence absorbed less heat, perhaps a mechanism for avoiding desiccation.

The effect of a change in desiccation will be dependent on the level of wave exposure. Increased desiccation on sheltered shores is likely to reduce the upper limit on dog whelks on the shore. Wave exposed shores are less susceptible to desiccation due to increase humidity due to wave action, however, the wave exposed shell form (squat shell shape) of Nucella lapillus is more intolerant of desiccation than the sheltered, elongate form. It should be remembered that on most shores of intermediate wave exposure, intermediate shell shapes will occur. Similarly, on shores with a large tidal range, the upper shores may experience a high level of desiccation since at low tide the sea is so far away that no spray reaches the upper shore (Crothers, pers comm.). Putting aside any migration downshore, desiccation at the level of the benchmark (see benchmark) is likely to result in high mortality.
An increase in desiccation is likely to reduce the upper limit of adult dog whelks on the shore and an intolerance of intermediate has been recorded. Gibbs et al. (1999) reported that dog whelks surviving a mass-kill were able to re-establish the population within 2 years but where there were few survivors, many years may be required. Therefore, a recoverability of high, to previous population levels, has been recorded (see additional information). Dog whelks displaced to the top of the shore (e.g. by wave action) will probably succumb to desiccation unless they are able to migrate to the lower shore before emersion.

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

The distribution of dog whelks on the shore is centred around the mid-tidal level and between 10-75% emersion (Fretter & Graham, 1994). Dog whelks extend higher upshore in Scotland or Norway than in south Britain (Dr John Crothers pers comm.), presumably because of the lower average air temperatures in more northern latitudes. In Norway, they can reach the uppermost Semibalanus and can eat-out their food supply.
Increased emersion would expose the population to increased risk of desiccation and a wider range of temperatures. Coombs (1973b) reported that dog whelks were unlikely to experience more than 3 -4 hours of emersion at their preferred shore height, but also reported that dog whelks became comatose and reached critical water loss after 6 hours at 25 °C, a temperature that may be experienced during a hot summer. Comatose animals are likely to be dislodged to lower on the shore, where they would escape the effects of increased emmersion best, since they become relaxed, become more prone to desiccation. Therefore, some mortality of individuals at the upper limits of their range may occur as a result of an increase in emergence regime, and therefore an intolerance of intermediate has been recorded.

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

The distribution of dog whelks on the shore is centred around the mid-tidal level between 10-75% emersion (Fretter & Graham, 1994). Decreased emergence would allow the population to follow their prey as they colonized further up the shore. However, it may also expose the individuals at the bottom of the shore to increased predation from crabs and starfish. It is likely that dogwhelks would migrate up the shore and the benefits of increased access to prey would balance out the possibility of increased predation, therefore an intolerance of tolerant has been recorded.

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

Change to water flow rate mostly relevant to subtidal area. Etter (1988a) demonstrated that the tenacity of dog whelks to resist water flow was proportional to the pedal surface area. Tenacity of dog whelks from sheltered shores was lower than dog whelks form wave exposed shores. He also demonstrated that dog whelks from sheltered shores would develop a larger foot when transplanted to wave exposed shores. Therefore, Nucella lapillus exhibits considerable phenotypic plasticity in response to wave exposure and most likely current flow. Although, the most elongate specimens are probably highly intolerant of increases in water flow rates, hatchlings and juveniles, which are still growing, will probably adapt to the increase water flow regime. Therefore, an overall intolerance of low has been recorded. A recoverability of very high has been recorded to represent the time taken for juveniles to recolonize and adapt (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

It is unlikely that a decrease in water flow rate will directly affect dog whelks even though the longer foot associated with strong flows becomes superfluous. However, the biotope may change and prey species, predominantly barnacles, become less abundant. Etter (1988a) demonstrated that the tenacity of dog whelks to resist water flow was proportional to the pedal surface area. A decrease in water flow may result in an increase in the mean shell length of the population (depending on wave exposure) but Nucella lapillus is otherwise probably tolerant of a decrease in water flow.

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

Largen (1967) reported that feeding rate was maximal between 20 -22 °C and fell steeply to zero at 25 °C whilst crawling reached zero at 27 °C. Sandison (1968); (reported unpublished in Lewis, 1964) noted that heat coma occurred in Nucella lapillus at 27 -28 °C, and death at 32 -33 °C. Largen (1967) noted that feeding rates were temperature dependant, dog whelks averaged consumption of 16 barnacles or 0.7 mussels per week at 20 °C but only 10.2 barnacles and 0.4 mussels per week at 15 °C. Newell (1979) noted that oxygen consumption (hence metabolic rate) fell with decreased temperature and starvation, being low in winter but high in summer. This resulted in a high scope for activity, and dog whelks responded rapidly to increases in temperature in the spring. Newell (1979) pointed out that dog whelks could adjust their metabolic rate with temperature and season. Stickle et al. (1985) also noted that feeding and ingestion rates decreased with decreasing temperature and salinity. Etter (1988b) noted that white shells reflected more light (reducing the rate of heating and the temperature reached within unit time) and that dog whelks were cooled by evaporation of the water retained within the shell during emersion.
Increased temperatures also increase the risk of desiccation (see above), especially on sheltered shores. However, dog whelks demonstrate behavioural adaptations depending on the type of shore they inhabit, e.g. dog whelks from sheltered shores forage less in sunny, warm weather, whereas animals from wave exposed shores (higher humidity) favoured calm periods even when sunny (Burrows & Hughes, 1989; Fretter & Graham, 1994). In southern Britain mortality form high temperatures is probably more likely than from low temperatures (Dr John Crothers, pers comm.). Crothers (1985) suggested that the southern limit of dog whelk distribution was temperature dependant and noted that in Portugal dog whelks live inside mussels clumps and in Massachusetts, where water temperature may reach 25 °C, dog whelks may spend summer below the tide mark. Therefore, Nucella lapillus is probably relatively tolerant of temperature change within the normal range for the UK, and is probably tolerant to a change of 2 °C over a year. However, an acute temperature change (e.g. 5 °C) will probably interfere with feeding activity and in summer may result in direct mortality or indirect mortality due to heat coma and desiccation. Therefore an intolerance of intermediate has been recorded.

Decrease in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

The northern geographical limit of Nucella lapillus is close to the 0 °C winter isotherm. Therefore, Crothers (1985) suggested that they were limited by ice, and that although dog whelks themselves could avoid ice in cracks and crevices, their prey (barnacles and mussels) could not avoid ice-scour. Cold torpor was apparent in dog whelks acclimated to 5 °C (Stickle et al., 1985). Speed of movement increases rapidly above 5 °C (Largen, 1967), and activity begins at 3 °C , however, Nucella lapillus is totally inactive at 0 °C and will fall off steep substrata (Largen, 1967; Crothers, 1985). Dog whelks crept into sheltered crevices in winter and probably effectively hibernate over winter (Moore, 1936; Largen, 1967). Cold torpor is likely, therefore, to increase this species risk of being washed offshore or of predation. Low temperatures make dog whelks less tolerant of low salinity (Dr John Crothers, pers comm.). Feeding and ingestion rates also decrease with temperature. Largen (1967) noted that spawning began once temperatures increased to 9-10 °C , and was interrupted by a fall in temperature. Largen (1967) reported that dog whelks averaged consumption of 16 barnacles or 0.7 mussels per week at 20 °C but only 10.2 barnacles and 0.4 mussels per week at 15 °C. Newell (1979) noted that oxygen consumption (hence metabolic rate) fell with temperature and starvation, being low in winter but high in summer. This resulted in a high scope for activity, and dog whelks responded rapidly to increases in temperature in the spring. Newell (1979) pointed out that dog whelks could adjust their metabolic rate with temperature and season. Stickle et al. (1985) also noted that feeding and ingestion rates decreased with decreasing temperature and salinity. During the severe winter of 1962/63, Nucella lapillus were reportedly unaffected in Anglesey, north Wales and the South Wales coast although many were reported killed in the Beaulieau River, Hampshire (Crisp ed., 1964). Overall, it appears that Nucella lapillus can survive temperatures as low as 3 °C and possibly 0 °C, although evidence for duration is lacking, the effects of low temperatures are sub-vital and an intolerance of low, at the level of the benchmark, has been recorded.

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

Nucella lapillus is an active carnivore and is unlikely to be adversely affected by increases or decreases in light attenuation due to turbidity and has been recorded as 'tolerant' to this factor.

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

Nucella lapillus is an active carnivore and is unlikely to be adversely affected by increases or decreases in light attenuation due to turbidity and has been recorded as 'tolerant' to this factor.

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

Dog whelks adapt to wave action through their shell shape and size of foot (Crothers, 1985). Etter (1988a) demonstrated that the tenacity of dog whelks to resist wave action was proportional to the pedal surface area. Tenacity of dog whelks from sheltered shores was lower than dog whelks from wave exposed shores. He also demonstrated that dog whelks from sheltered shores would develop a larger foot when transplanted to wave exposed shores. Therefore, Nucella lapillus exhibits considerable phenotypic plasticity in response to wave exposure and current flow. It is also found from very wave exposed to very sheltered shores. An increase in wave action, for example from sheltered to exposed (see benchmark) is likely to increase mortality due to dislodgement and result in loss of a proportion of the population. Very sheltered and sheltered shores are likely to be more intolerant of such an increase. Therefore, an intolerance of intermediate has been recorded. Recent juveniles colonizing the shore in autumn and winter in the UK, are likely to adapt their phenotype to the prevalent conditions. Therefore a recoverability of high (see additional information below) has been recorded.

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

Growth adaptations of the dog whelk to strong wave action result in a thinner shell and longer pedal opening. Therefore, although adhesion to the substrate will be more than adequate with an increase in shelter. However, wave exposed forms may be more liable to predation from crabs and to desiccation (see above). Therefore, an intolerance of intermediate has been recorded. Recent juveniles colonizing the shore in autumn and winter in the UK, are likely to adapt their phenotype to the prevalent conditions. Therefore a recoverability of high (see additional information below) has been recorded.

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

While Nucella lapillus is probably sensitive to local vibration within its vicinity, possibly similar to that caused by a predator, it is unlikely to be adversely affected by noise of the type or levels addressed in 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

Nucella lapillus bears light sensitive eyes on its tentacles. However, its visual acuity is probably low and it is unlikely to be adversely affected by movement or shading due to anthropogenic activities.

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

Shells of Nucella lapillus are likely to show signs of abrasion due to wave action or sediment scour. The flounces of Nucella lapillus var. imbricata may also be reduced due to abrasion. However, no information concerning the effect of abrasion such as trampling on dog whelks was found. It is likely that some individuals may be dislodged and some washed to deep water and lost as a result. The most adverse affect is likely to be indirect due to a loss of prey such as mussels or barnacles due to trampling or removal by an abrasive force. However, dog whelks are capable to switching to another prey source in the absence of their preferred prey, so an intolerance of low has been recorded.

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Displaced and dislodged individuals may become subject to increased desiccation if up turned, or washed to deep water and lost. However, Bryan (1968) reported that adults, presumably narcotized by oil and dispersants and washed below low water recolonized the shore within about 6 months, suggesting that displaced individuals could return to the intertidal. However, Nucella lapillus does not readily crawl across sediment, therefore individuals displaced to unsuitable substrata may not be able to return. Therefore, a precautionary intolerance of intermediate has been recorded. Recruitment from surviving adults and recolonization by juveniles from below water may result in recovery within about two years and a recoverability of high has been recorded (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

The effects of tributyl tin (TBT), used in anti-fouling paints, on Nucella lapillus have been extensively documented and represent one of the best known examples of the effects of chemical pollution. The following is based upon reviews by Hawkins et al. (1994) and Bryan & Gibbs (1991) to which the reader should refer for further detail.

• Nucella lapillus (and other stenoglossan gastropods) are particularly intolerant of TBT contamination. Imposex is initiated at TBT concentrations low as <0.5 ng Sn/l. A proportion of females are sterilised at 1-2 ng Sn/l, and virtually all females are sterile at 3-5 ng Sn/l. Oogenesis was suppressed at >10 ng Sn/l, testis development may occur at 20 ng Sn/l and the sperm ingesting gland in some females remains undeveloped at 100 ng Sn/l (Gibbs et al., 1988; Hawkins et al., 1994). These values can be compared with concentrations of 430 ng Sn /l in the Crouch estuary and >2 µg Sn/l in some marine sites (Waldock & Miller, 1983).
• Nucella lapillus has been effectively exterminated from many areas in its European range (Gibbs et al., 1991), especially in area of pleasure boating or shipping. In the south coast of England virtually all populations had been affected to some extent, and some were extinct (Bryan & Gibbs, 1991; Hawkins et al., 1994).
• Imposex is irreversible and recovery is dependant on recruitment of juveniles into the population.
• TBT has been banned from use of boats <20 m since 1987 since which time populations have begun to recover.
• Evans et al. (1996b) reported marked recovery of many populations from the North Sea and Clyde Sea and that although ports were 'hot spots' of TBT contamination the populations of Nucella lapillus were not sterile and produced enough offspring to survive. However, several populations is semi-enclosed areas with high boating activity in south west England had become extinct. Evans et al., (1996b) also suggested that extinction of populations in Tarbert Harbour, western Scotland, the Clyde Sea, Lerwick in Shetland, the Solent, Channel Islands, Isle of Wight and east coast of the North Sea were probably due to TBT contamination.
• Moore et al. (2000) reported recovery of Nucella lapillus from the effects of TBT contamination in Yell Sound, adjacent to the Sullom Voe oil terminal in Shetland, with only 28% of females showing signs of imposex in their 1999 survey. The population in Sullom Voe itself, especially close to the terminal, had improved since 1991 but still had a low reproductive capacity.
• Overall, Nucella lapillus is highly sensitive of TBT contamination, while females may be killed at concentrations above 5 ng Sn/l, imposex and hence reduced reproductive capacity can occur at lower concentration (above) and the population will decline due to natural mortality and poor recruitment. Where populations have become extinct, recovery is dependant on recolonization, and may take many years due to their poor dispersal capability (see additional information below). However, recoverability (sensu MarLIN) assumes that the impact has stopped or is removed. Bryan & Gibbs, (1991) and Hawkins et al. (1994), note that TBT is persistent in sediments and little recovery is likely until the ambient concentration of TBT falls below 4 ng/l.

Heavy metal contamination

Evidence

Bryan (1984) suggested that adult gastropod molluscs were relatively tolerant of heavy metal pollution. Bryan & Gibbs (1983) noted that Nucella lapillus accumulated Cu and Zn in the Fal estuary, but was excluded from the highly heavy metal contaminated Restronguet Creek. Food is the main route of uptake of iron (Fe) and zinc (Zn) in Nucella lapillus (Young, 1977). Nucella lapillus exhibits detoxification systems e.g. granules containing phosphate, calcium, zinc, magnesium (Mg) and copper occur in the digestive gland, which may explain their tolerance of high levels of Zn and copper (Cu), (Ireland, 1979; Bryan, 1984), Cadmium (Cd) is detoxified by storage as a metallothionien (Bryan, 1984). Therefore, an intolerance of low has been recorded.

Hydrocarbon contamination

Evidence

• The combination of oiling and subsequent treatment with dispersants after the Torrey Canyon oil spill ( in March 1967) resulted in loss of Nucella lapillus from affected shores, however, Smith (1968) noted that where less dispersants were used Nucella lapillus was amongst one of the most tenacious gastropods. Smith (1968) noted that the most resistant gastropods (such as Osilinus lineatus and to a lesser extent Nucella lapillus) were able to tightly close their shells with their operculum.
• The toxicity of the emulsifiers BP1002 (a non-ionic surfactant in an aromatic hydrocarbon solvent) has been examined by several workers. Smith (1968) reported that 10 ppm was adequate to inhibit crawling in gastropods and that Nucella lapillus was detached at this concentration. A concentration of >100 ppm was required to kill the majority of the dog whelk (after 24hr exposure at 12°C). Bryan (1968) noted that none died when exposed to 1ppm BP1002 and some survived longer than 2 hrs in neat BP1002. BP1002 was most toxic between 2.5-1000 ppm but less so above 1000ppm since the dog whelk was able to detect the emulsifier and close its shell. Surviving individuals recovered within 8 days. Crapp (1970a) reported that Nucella lapillus was severely affected by direct treatment with BP1002 in the field (exposed for ca. 6hrs at low tide). However, Crapp (1970b) reported that Nucella lapillus was relatively resistant, exhibiting a 1 hr LC₅₀ of between 10,000 -500,000 ppm, depending on season, being very resistant in winter. Crapp (1970b) also noted that individuals took longer to recover from exposure in winter.
• Exposure to petrol/water emulsions in Milford Haven as a result of the Dona Marika incident, caused gastropods to retract into their shells and resulted in a marked reduction in Nucella lapillus abundance, from Common to Rare. However, numbers increased within 9-11 months, mainly due to recolonization by adults that had presumably been narcotized or retracted, washed below low water and had taken some time to recover before returning to the shore (Blackman et al., 1973; Baker, 1976).
• Smith (1968) and Bryan (1968) report similar rapid re-colonization from low water. Bryan (1968) noted that the majority of the recruitment was by juveniles that had presumably been living below low water during the spill and that the population had recovered within 2 years. However, both Smith (1968) and Bryan (1968) suggested that in areas of heavy treatment by dispersants, recovery may take much longer.
• Gelder-Ottaway (1976a) noted that Nucella lapillus and Littorina littorea were un-able to crawl through crude oil films. Gelder-Ottaway (1976b) exposed several species of gastropod to various oil/ water emulsions. After 6hrs exposure at 17-20 °C the toxicities of different oil emulsions to Nucella lapillus was as follows (percentage mortalities in brackets) leaded gasoline (54) > Kuwait crude oil (18) > Kerosene (10) > diesel and No. 2 fuel oil (2-4). However, no indication of concentrations used was given.
• Stickle et al. (1984) reported that Nucella lima (as Thais lima was very tolerant of short term exposure to oil, but that tolerance declined with duration of exposure, e.g. the LC₅₀ to Cook Inlet crude oil after 7days was >3000 ppm, but between 961 ppm after 21 days and 818 ppm after 28 days exposure.
• Ebert & Lees (1996) noted that growth of Nucella lamellosa was depressed on sites oiled by the Exxon Valdez spill in comparison to un-oiled sites.
• Nelson-Smith (1968) reported the Nucella lapillus was significantly affected at the upper end of its range on one shore, and markedly reduced in abundance on another after oiling and subsequent emulsifier treatment after the Chrissi P. Goulandris crude oil spill in Milford Haven. After the spill most gastropods were absent with Steromphala umbilicalis, Steromphala cineraria, and Nucella lapillus only represented by a few dead animals lodged in crevices. In areas that received less of this oil, such as Porthcolhen (near Padstow) and Marazion, Nucella lapillus, top-shells and winkles (except Littorina littorea) were numerous and un-affected.

Overall, while Nucella lapillus is probably more resistant to oiling and emulsifiers than most gastropods (except Osilinus lineatus), the above evidence indicates that population are severely affected by oil but especially emulsifiers depending on concentration. Therefore, an intolerance of intermediate has been recorded. Where, adults survive or juveniles are represent below low water, recolonization may take up to 2 years (see additional information below).

Radionuclide contamination

Evidence

Insufficient
information.

Changes in nutrient levels

Evidence

Gibbs et al. (1999) reported a massive kill of Nucella lapillus in Bude Bay, north Cornwall. Gibbs et al. (1999) suggested that the mass mortalities may have been caused by eutrophication and summer algal blooms due to a new sewage outfall in the area that received only primary treated sewage. Nucella lapillus has been shown to be severely affected by toxic algal blooms. For example, Robertson (1991) reported up to 98-99% mortality of dog whelks exposed to a toxic bloom of Chrysochromulina polylepis in Gullmar Fjord, west Sweden in June 1988. As a result, the distribution and abundance were reduced, 1-2 yr. olds (three years recruitment) suffered heavy mortality and subsequent reproductive capacity was reduced (Robertson, 1991). Similarly, Nucella lapillus was shown to be severely affected by a bloom of Gyrodinium aureolum in south west Ireland in 1979 (Cross & Southgate, 1980) and strongly affected by a bloom of Chrysochromulina polylepis in the Kattegat, Skagerrak and Norwegian coast of the North Sea, May -June, 1988 (Underdal et al., 1989). Therefore, an intolerance of high has been recorded. Given their poor dispersal and recruitment from other populations, recovery may take many years (see additional information below).

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

Kirby et al. (1994b) simulated the effects of hyper-osmotic shock due to evaporation of mantle cavity retained seawater in Nucella lapillus. Exposure to 35, 45, 55, 65 and 75 psu over periods of 6, 12 and 24 hrs at 15 °C resulted in an increase in alanine production, with concomitant decrease in aerobic respiration and, on return to 35 psu, an increase in nitrogen excretion due to increased protein metabolism. However, no mortalities were observed during the experiment, although the dog whelks remained in their shells for the duration of the experiment (Kirby pers. comm.). Kirby et al. (1994b) noted that the wave exposed (short spired shell) form of Nucella lapillus suffered a greater decrease in aerobic respiration and increase in protein metabolism and hence greater stress than the sheltered site forms. Kirby et al. (1994b) also noted a correlation between the physiological effects of hyperosmotic shock and different alleles at the leucyl-amino peptidase (Lap) locus suggesting a genetic component to hyper-osmotic shock tolerance. Overall, it appears that Nucella lapillus would tolerate an acute, short term increase in salinity, albeit at metabolic cost, suggesting an intolerance of '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

Nucella lapillus is unable to feed under brackish conditions and are likely to be absent from areas of fresh water influence on the shore (Crothers, 1985). Feare (1970b) noted that in rock pools at full salinity 100% of egg capsules hatched, whereas only 27% hatched in areas subject to fresh water runoff at low tide. Stickle & Bayne (1985) reported that, at between 5 -20 °C, dog whelks over 20 mm in length tolerated between 14.2 and 16.2 psu, whether exposed abruptly or after acclimation. In their experiments smaller dog whelks were able to tolerate salinities as low as 12.7 psu. Stickle et al., 1985 noted that reduced salinity and temperature reduced feeding rates in Nucella lapillus, e.g. only 10% fed at 25 psu and 5 °C or 15 psu and 8.5 °C. They reported that Nucella lapillus was a poor volume regulator and did not quantitatively regulate their free amino acid pool. Crothers (1985) noted that Nucella lapillus is usually absent from estuaries and although found in the Severn Estuary it is restricted to the lower shore up-channel from Minehead where they presumably avoid reduced salinities. Therefore, a reduction in salinity below 18 psu is likely to adversely affect reproduction and feeding. Hence, a reduction in salinity at the benchmark level is likely to reduce the extent or abundance of Nucella lapillus and an intolerance of intermediate has been recorded. Gibbs et al. (1999) reported that dog whelks surviving a mass kill were able to re-establish the population within 2 years, except where mortalities were extensive, and a recoverability of high has been recorded (see additional information below).

Changes in oxygenation

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

Evidence

No information regarding tolerance to anoxic conditions was found. Nucella lapillus is able to maintain aerobic respiration when emmersed (Sandison, 1968; Houlihan et al., 1981; Innes & Houlihan, 1985) and unlikely to suffer anoxia at low tide. Nucella lapillus is reported to be capable of anaerobic respiration (Sandison, 1966 cited in Gibbs et al., 1999). Gibbs et al. (1999) suggested that its ability to respire aerobically at low tide would compensate for any anoxia experienced when immersed and that it is probably relatively tolerant of low oxygen conditions. Gelder-Ottaway (1976a) demonstrated mortalities (8-40%) in dog whelks held for 5 days in seawater under films of oil. Although the experiment was intended to demonstrate mortalities due to oil film, the death observed probably owed more to oxygen deficiency than the oil itself. Therefore, exposure to 2 mg/l O₂ for one week is likely to result in some mortality in dog whelk populations, and an intolerance of intermediate is recorded, although the ability to respire during emersion will probably keep mortalities to a minimum. Gibbs et al. (1999) reported that dog whelks surviving a mass kill were able to re-establish the population within 2 years, except where mortalities were extensive, and a recoverability of high has been recorded (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

Intertidal gastropods often act a secondary hosts for trematode parasites of sea birds. Nucella lapillus may be infected by cercaria larvae of the trematode Parorchis acanthus. Infestation causes castration and continued growth (Feare, 1970b; Kinne, 1980; Crothers, 1985). Infected individuals may exhibit a deformed and enlarged shell, additional rows of teeth in the aperture, and an additional seventh whorl (Feare, 1970b). Feare (1970b) reported 15% infestation in one sample, in which the shells showed 3-4 rows of teeth. In one population, however, Feare (1970b) reported an infestation rate of 69%. Kinne (1980) notes that Nucella lapillus may also be infested with larvae of Lepocreadium sp., which cause reduced or non-functional gonads and a reduction in penis size in males. Castration of a proportion of the population may result in a reduction in recruitment and a reduced decline in population size eventually. Therefore an intolerance of intermediate has been recorded. Recoverability is dependant on recruitment from within the population. Gibbs et al. (1995) noted that a small number of individuals surviving the effects of an algal bloom (see nutrients) in north Cornwall, were able to re-establish the population within two years but noted that it would probably take many years for the population to regain its former abundance. Therefore, a recoverability of high is reported.

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

The introduced American oyster drill Urosalpinx cinerea may feed on barnacles when not feeding on oyster spat and hence may compete with Nucella lapillus for either food or space. However, no further information 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

Nucella lapillus is not subject to targeted extraction in the UK. However, whelks (including the dog whelk) were once collected for the production of Tyrian purple (see Baker, 1974 for review; Crothers, 1985).

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

Mussels are subject to extraction (see Mytilus edulis) and are a major food species for dog whelks where they occur. However, dog whelks are able to switch to a more abundant prey, such as barnacles (albeit slowly) if necessary and are therefore, likely to suffer a brief interruption in feeding and possibly temporary reduction in reproductive capacity. Therefore, an intolerance of low has been recorded.