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

Osilinus lineatus is epifaunal so loss of the substratum would result in the loss of the population, and an intolerance of high has been recorded. Osilinus lineatus cannot survive on or move over substrate consisting of fine, mobile sediment. Recolonization, recruitment and recovery are possible once the substrate is restored, or to neighbouring areas of suitable habitat as the adults are capable of migration and the planktonic stage of the lifecycle will facilitate limited dispersal from neighbouring populations (see additional information below).

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

Smothering by 5 cm of sediment is highly likely to cause death. Respiration would be prevented and the microalgal food source would not grow under such conditions. Smothering of nursery areas under boulders would also prevent survival of juvenile recruits which depend on a coarse grained substrate to settle and over-winter on. Recruitment failure may result from a chronic deposition over a year or an acute episode coinciding with the peak juvenile settlement season in autumn. This is evident in Aberaeron, where regular recruitment occurred throughout the 1970s and 1980s (Kendal, 1987) but the population was severely reduced in 2002 due to heavy sedimentation of the habitat (Kendal et al. in submission). Recoverability is likely to be moderate (see additional information below).

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Deposition of suspended sediment may cause siltation of nursery areas, removing required habitat including nooks and crevices and prevent juveniles from settling and surviving. Recruitment failure may result from a chronic deposition over a year or an acute episode coinciding with the peak juvenile settlement season in autumn (see smothering above). Overall, an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).

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

Osilinus lineatus is unlikely to be adversely affected by a decrease in suspended sediment (editors addition).

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

Osilinus lineatus can fully retract into its shell and seal the opening with an operculum to minimize desiccation. This species can be mobile, feeding and walking during periods of low tide when the animal is exposed to air if conditions are damp or it is disturbed. It is tolerant of extended periods (days) exposed to air, and positions itself on the tops of boulders during sunny days when the desiccation risk is higher. It migrates upshore in the spring prior to spawning and remains there until the end of summer. This is an active movement into an area of increased desiccation stress which suggests that this species has a high tolerance. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).

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

Adults migrate upshore prior to spawning to a region where the emergence period is greater than lower down the shore. When specimens are returned to the laboratory they can survive for a week without submergence in seawater. The species can therefore tolerate a wide emergence regime.

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Water flow rates may become high enough to prevent animals from maintaining contact with the rock surface when moving and feeding at high tide. Increased flow rates may also move the boulder substrate around more, causing dislodgement and abrasion of the animals. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be 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

Osilinus lineatus is found in habitats with a range of flow rates including sheltered bays where flow rates are reduced. If the flow rate is too low and sediment drops out of suspension the habitat may be unsuitable for this species due to smothering of adults and nursery areas of juveniles (see smothering above). Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).

Increase in temperature

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

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

Evidence

Increasing air and sea temperatures allows Osilinus lineatus to colonize areas previously too cold. This is evident around British coasts as this species has increased its range during the current period of climate warming (Kendal et al., in submission). Osilinus lineatus has a distribution range from Morocco to North Wales, where it reaches its northern limits. The average temperature gradient is approximately 6 °C between these locations. Osilinus lineatus can also tolerate the wide range of air and sea temperatures it is exposed to in the intertidal zone.

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

A decrease in temperature may prevent regular successful recruitment within a population and could lead to a localized extinction. A sudden, sharp decrease in temperatures during the winter of 1962/63 resulted in the loss of many populations in Britain (Crisp, 1964). Some populations close to the northern limits have still not recovered. Overall, an intolerance of high to acute temperature decrease has been recorded. Recoverability is likely to be moderate (see additional information below).

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

Increases in turbidity will probably not have much of a direct effect on this species. Reduced irradiance may decrease the productivity of the microalgal food source.

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

Insufficient
information

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

Osilinus lineatus is typically found on moderately exposed shores but also occurs in small numbers on some shores where wave exposure is high. Individuals may survive an increase in wave exposure by becoming more cryptic in their habitat selection. If wave action is too strong the animals may not be able to maintain their hold on the rock surface and may be washed off. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be 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

Osilinus lineatus is also found in sheltered bays where there is little wave action. If the water movement is too low and sediment drops out of suspension the habitat may be unsuitable for this species due to smothering of adults and nursery areas of juveniles (see smothering above).

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

There is no evidence that noise adversely affects this species. They move towards localized drilling noise made by researchers on the shore (pers. obs.).

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

Adults do respond to visual presence by fully retracting into the shell, both when submerged and emersed. They do not close the operculum but remain attached to the rock by their foot. However, they re-emerge after a few minutes.

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

Abrasion can cause shell damage. The outer, thinner, dark layer of the shell is often abraded in older animals to the extent that the mother-of-pearl inner layer is evident on the top two or three whorls. Abrasion marks are more common on animals living on more exposed shores. Overall, 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

Animals displaced from the rock surface quickly reattach themselves if not carried away in the water column, when they may be lost. Animals that are displaced will attach to nearby substrate providing that it is suitable. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be 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

Insufficient
information

Heavy metal contamination

Evidence

Insufficient
information

Hydrocarbon contamination

Evidence

Adult Osilinus lineatus were seen to decline further in Milford Haven after the Sea Empress oil spill in 1996 (Little, 1999).

Radionuclide contamination

Evidence

Insufficient
information

Changes in nutrient levels

Evidence

It is unlikely that changes in nutrient levels will have a large effect on this species. Increase in the nutrient load of the water may lead to an increase in the microalgal food source. It has been suggested that toxic algal blooms may adversely affect this species but no direct evidence of this has been found.

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

This species is found on open ocean coasts adjacent to oceanic waters and can tolerate salinities of around 33-35, which are typical of large water bodies. They also inhabit rockpools in the high mid shore zone. These pools are exposed for around 6 hours every day and evaporation can cause the salinity of the remaining water to become very high. Osilinus lineatus can tolerate such an increase in salinity and an intolerance of low has been recorded.

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

This species is found in large estuaries such as the Bristol Channel where salinities are less than at open coast locations. It is also found higher up the shore where small trickles of freshwater occur on the rock.

Changes in oxygenation

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

Evidence

Osilinus lineatus has the ability to breathe in air as well as water, due to a well vascularised mantle cavity used for respiration along with their gill (Crothers, 2001). It actively removes itself from the water when the tide is retreating and the oxygen content of residual water decreases. This behaviour suggests a high intolerance to low oxygen content in water which has resulted in a behavioural adaptation.

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

Lichomolgid copepods have been recorded inside Osilinus lineatus. However, no information concerning the effect of such infestation was found.

Introduction of non-native species

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

Introduction of non-native topshells occupying a similar zone on the shore (e.g. Gibbula pennanti) may increase competition for food resources. Depending on which species is the competitive dominant, Osilinus lineatus may reduce the width of its zone or maintain its distribution and force the invasive species further down the shore into the low shore zone. Therefore, an intolerance of intermediate has been recorded. Recoverability would be dependent on the removal of the non-native species, which is probably unlikely to occur.

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

It is possible that Osilinus lineatus may be removed from the shore as misidentified Littorina littorea by winkle collectors due to their similar external appearance. On shores where Osilinus lineatus is rare or absent the topshell Steromphala umbilicalis can become more abundant in the mid shore zone where Osilinus lineatus would otherwise occur. This is likely to be the result of decreased competition for the detrital scraps of microalgae.

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

It is possible that Osilinus lineatus may be removed from the shore as misidentified Littorina littorea by winkle collectors due to their similar external appearance.