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

The species is epifaunal so loss of the substratum would also result in loss of the population. Individuals unattached to the substratum are very vulnerable to desiccation and to predation by birds and crabs. An intolerance of high has therefore been recorded. For recoverability, 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

A related limpet, Patella granularis, was found to survive no more than 3 days when smothered with sand. This effect was thought to be due to hypoxia caused by the sand preventing a normal current of water passing over the gills (Marshall & McQuaid, 1989). Also, inundation with sand is likely to affect locomotion and grazing and cause the limpet to starve (Professor Steve Hawkins, pers. comm.). Therefore an intolerance of high has been recorded. For recoverability, 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

Since Patella ulyssiponensis is a grazer on rocky shores, an increase in suspended sediment is unlikely to reduce its ability to find food. Predation rates are unlikely to be affected since its principal underwater predators (crabs and starfish) use senses other than sight to locate prey and birds (such as oystercatchers) prey on limpets when they are exposed by the tide. An increase in suspended sediment may clog the gills of limpets and lead to difficulties in extracting oxygen from the water. Intolerance is assessed as low.

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

Patella ulyssiponensis is not reliant on suspended sediment for food or shelter so a decrease is unlikely to affect this species. Therefore tolerant has been recorded.

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

Patella ulyssiponensis suffers 100% mortality at 40% water loss. In comparison, Patella vulgata suffers at most 30% mortality at the same water loss (Davies, 1969). Therefore, at the benchmark level, an intolerance of high has been recorded.

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

Patella ulyssiponensis is found on the lower shore and in rock pools in the mid-shore. If emergence increased adults may migrate down the shore although it is also possible that some individuals would stick to their home scars and die. Therefore an intolerance of intermediate has been recorded reflecting some mortality.

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

Some Patella ulyssiponensis occur subtidally, therefore an decrease in emergence would probably not affect this species. Therefore 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

Limpets are extremely tenacious and tests on one species, Lottia pelta, showed that they will only begin to be dislodged by water currents in excess of 13 m/s (25 knots) while stationary and 8 m/s (16 knots) while moving. To remove all the limpets from a surface would take current speeds in excess of 20 m/s (39 knots) (Denny, 1989). Tidal currents in the waters of Britain and Ireland do not exceed 10 knots in surface velocity. Therefore tolerant has been recorded.

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

If the reduction in water flow rate was concomitant with a reduction in wave exposure then Patella ulyssiponensis may become less abundant or disappear entirely. Under any other circumstances, a decrease in water flow rate is unlikely to affect this species. Therefore tolerant has been recorded.

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

Grazing activity in limpets is closely correlated with temperature: the warmer it is, the more time limpets spend grazing (Jenkins et al., 2001). A slight warming is likely to be beneficial to individual and population growth. Patella ulyssiponensis is less tolerant than Patella vulgata to changes in temperature. However, since it occurs in the sublittoral fringe and in rock pools in the mid-shore, changes in temperature at the benchmark level are likely to be buffered. Therefore tolerant has been recorded for an increase in temperature.

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 related species, Patella vulgata, loses adhesion at very low temperatures and become very vulnerable to crab and bird predation (see review of Patella vulgata). The water in a rock pool will buffer sudden and drastic changes in air temperature until the tide returns with warmer water and thus protect any organisms within the pools. In the very cold winter of 1962-63 Patella ulyssiponensis suffered less mortality than other limpets because it was protected by the warmer seawater because it was not exposed to the cold air temperatures for very long each day. An intolerance of intermediate has been recorded for a decrease temperature because extreme cold in winter is likely to kill a proportion of the population.

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

Increasing turbidity is unlikely to directly affect Patella ulyssiponensis but may reduce the amount of light reaching the epilithic algae at high tide. This will reduce the productivity of the epilithic algae and may affect the growth and reproductive output of the organisms which feed upon it (Langston et al., 2003). Therefore tolerant has been recorded.

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

A decrease in turbidity is likely to benefit to all rocky shore grazers by increasing the amount of light reaching the epilithic algae and increasing productivity which will probably increase the productivity of the grazers. Therefore tolerant* has been recorded.

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

Limpets are extremely tenacious and Patella ulyssiponensis occurs at the highest densities on the most wave exposed shores: up to 1000 m² on extremely exposed shores (Thompson, 1979). Therefore an increase in exposure is unlikely to affect this species.

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

Patella ulyssiponensis prefers wave exposed shores with little fucoid cover and is intolerant to a reduction in wave exposure (Evans, 1953). However the effect of a decrease in wave exposure on a population of Patella ulyssiponensis depends on the wave exposure before the decrease. The benchmark is a 2 rank change in the wave exposure of the shore. Therefore, if the Patella ulyssiponensis population started at extremely exposed and ended up at exposed, little change in the population would occur since fucoids only start to appear on moderately exposed/sheltered shores (Little & Kitching, 1996) and Patella ulyssiponensis is tolerant to sparse fucoid cover (Evans, 1953). However, if the population started on an exposed shore and ended up on a sheltered shore, the Patella ulyssiponensis are likely to become locally extinct in that area until the returns to its previous exposure grade. An intermediate intolerance of a reduction in wave exposure has therefore been recorded to take into account the worst case scenario described 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

Although limpets are not likely to be affected by atmospheric noise levels, vibrations near to the animal will cause the shell muscles to contract vigorously, clamping the limpet to the rock (Fretter & Graham, 1994), and potentially interfere with respiration and foraging in pools. This is unlikely to seriously affect Patella ulyssiponensis at the benchmark level and therefore tolerant has been recorded.

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

Patella ulyssiponensis has eyes and is sensitive to visual presence. The limpet may clamp down onto its home scar in response to, for example, the presence of humans on the shore. However, this reaction is short lived and is unlikely to adversely affect the viability of the species. Therefore tolerant has been recorded.

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

The adult has a tough shell that offers protection from abrading factors and any near vibration causes the shell muscles to contract vigorously, clamping the animal to the rock. A short, sharp knock may dislodge an individual leaving it vulnerable to predation and limpets may be crushed by wave driven debris or by seagoing vessels grounding on the shore. However, small individuals tend to occupy depressions, crevices, or pools that would provide protection from trampling or the scraping that would occur when a vessel goes ashore. Therefore, an intolerance of intermediate 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

Limpets are intolerant of being knocked off the rock by trampling on the shore and, if the foot is damaged, do not re-attach easily (Professor Steve Hawkins, pers. comm.). Displaced individuals with the foot exposed to the air are likely to become prone to predation and desiccation and may die. If individuals remain foot down on rock after displacement and are not damaged they may be able to become reattached. However, individuals removed several feet from their scars do not appear to make their way home again (Fretter & Graham, 1996) and so may be more vulnerable to desiccation without the tight fit to their 'home scar'. Therefore, an intolerance of intermediate has been recorded.

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

Limpets are extremely intolerant of fresh oil and any solvent based dispersants used in oil spill clean-up. During the clean-up response to the Torrey Canyon oil spill, nearly all the limpets were killed in areas close to dispersant spraying (Southward & Southward, 1978). Viscous oil will not be readily drawn in under the edge of the shell by ciliary currents in the mantle cavity, whereas detergent, alone, or diluted in sea water, would creep in much more readily and be liable to kill the limpet (Smith, 1968). A concentration of 5 ppm of chemical dispersant killed half the limpets tested in 24 hours (Southward & Southward, 1978; Hawkins & Southward, 1992).
Sub-lethal effects on limpets are also relevant. The limpets may be narcotized by the fresh oil which may render them incapable of clamping down on their home scar. Consequently they may be more vulnerable to predation since they would be easier to prize off the rocks. In addition, they may be more susceptible to dislodgment by, for example, wave exposure and wave driven debris. When limpets move around on the rock they leave a mucous trail which enables them to retreat back to their home scar. If contact with this mucous trail is broken it is unlikely that the limpet will successfully find its way back to its home scar. This will also leave the limpet more prone to predation.

 

Acidified sea-water affects the motility of Patella vulgata. At a pH of 5.5, motility was reduced whilst submerged but individuals recovered when returned to normal sea-water. At a pH of 2.5, total inhibition of movement occurred and when returned to normal sea-water half had died (Bonner et al., 1993). Reduced motility reduces time for foraging and may result in decreased survival of individuals. Acidified seawater can also change the shell composition which will lead to a decrease in its protective nature and hence survival (Bonner et al., 1993). Short periods (48 hours) are unlikely to have much effect on a population but long periods (1 year) may cause reduced grazing and an increase in algal growth. However, sea-water is unlikely to reach pH 2.5 therefore intolerance to slight changes in pH will be low. Gastropod molluscs are known to be intolerant of endocrine disruption from synthetic chemicals such as tri-butyl tin (Cole et al., 1999). However no information on the specific effects of tri-butyl tin on Patella vulgata was found. Hoare & Hiscock (1974) reported that in Amlwch Bay Patella vulgata was excluded from sites within 100-150 m of the discharge of acidified, halogenated effluent. Therefore an intolerance of high has been recorded.

 

Heavy metal contamination

Evidence

Limpets are regarded as good bioindicators of heavy metal pollution because they tend to accumulate metals at levels proportional to their environment (Catsiki et al., 1991). Limpets isolate and detoxify heavy metals by producing metallothioneins in response to heavy metal pollution (Bebianno et al., 2003). Metallothioneins are low molecular weight proteins that bind metal cations, their production allows an organism to tolerate heavy metal pollution but presumably have a metabolic cost that increases with greater heavy metal exposure. Limpets also adjust their physiology and behaviour in response to heavy metal exposure. Exposure of Patella ulyssiponensis to 0.5 ppm of copper caused the limpets' hearts to stop beating (probably to prevent metal absorbed through the gills travelling around the body) but heart activity returned to normal once the limpets were returned to clean seawater (De Pirro et al., 2001). Exposure to solutions of copper and zinc were found to suppress activity in Patella ulyssiponensis by causing them to clamp their shell onto the substratum and thus isolate them from the environment (Davies, 1992). In this way, Patella ulyssiponensis can tolerate short pulses of heavy metal input but longer term exposure will have energetic consequences for the limpets. In summary, limpets will be stressed by exposure to heavy metals but widespread mortality is unlikely and therefore their intolerance is recorded as low.

Hydrocarbon contamination

Evidence

The resistance of Patella ulyssiponensis to direct oiling is poor and causes high mortalities. Weathered oil that has been deposited on the bedrock of the shore gets scraped off during grazing by limpets and ends up in their digestive system. This does not seem to affect them, presumably because there is little of the lighter, more toxic fractions of the oil left (Southward & Southward, 1978).
Petpiroon & Dicks (1982) studied the long term effects an oil refinery discharge had on the surrounding shore communities in Littlewick Bay, Milford Haven. By combining their own field work with earlier studies in the same area it was evident that numbers of Patella species had fallen considerably at the two sample sites nearest the discharge pipe (the pipe being approximately 100 m away) since the 1960s. Individuals that were found within the vicinity of the pipe were comparatively much larger. In addition, no juveniles were found within about 45 m of the outfall suggesting that larval recruitment was affected either through the direct mortality of the larvae or by inhibiting larval settlement on the substratum surrounding the pipe. This would also explain the lack of younger, smaller individuals nearest the pipe. The maximum oil content in the effluent gradually decreased from 50 ppm at the start of the work to 25 ppm at the end of the study. Fieldwork in 1981 (the end of the study) found that some juveniles had settled at the two sampling stations nearest the pipe. However the reduction in oil content was not thought to have corresponded with any reduction in the biological effects of the effluent. Petpiroon & Dicks (1982) suggested that at least part of the observed effects resulted from the effluent effects on the larval stages as opposed to the adults directly. In addition, the low salinity of the effluent and the sheltered nature of the receiving waters had meant that the effluent floated after discharge and as a result made contact with all levels of the shore during each tide.

 

Overall, due to the lethal effect that direct oiling has on the limpets an intolerance of high has been recorded.

Radionuclide contamination

Evidence

No information found.

Changes in nutrient levels

Evidence

Limpets near sewage outfalls have a higher growth rate than those further away but mortality is higher. However the source of mortality was unknown (Tablado et al., 1994). In another study, there was a massive mortality of limpets 2-3 weeks after a nearby sewage outfall was shut off permanently: the nutrient enrichment from the outfall had led to a dense growth of sea lettuce, Ulva lactuca, which supported a very large population of limpets. Once the enrichment ceased, the Ulva lactuca could not recover from grazing damage as quickly as before and was eventually completely removed from the area around the outfall. With their food source eradicated, a large proportion of the limpets starved (Rogers, 2003). Limpets often benefit from nutrient enrichment (Rogers, 2003 and Tablado et al., 1994) and can survive extended periods the anoxia (Santini et al., 2001) that excludes many organisms from areas of organic enrichment. A drop in nutrient levels is more difficult to assess. Mass mortalities of limpets have been described when artificial enrichment is removed but this probably represents a return to an environmental equilibrium in place before the enrichment occurred. It can only be assumed that if nutrient decreased in an area with no previous enrichment that the limpets' growth would be slowed and that reproductive output would also be reduced. As nutrient further decreased, the population would presumably thin out as some individuals starved. Based upon the evidence of increasing population size with organic enrichment, an intolerance of tolerant* has been recorded.

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

In laboratory experiments, Patella ulyssiponensis survived 43psu for 24 minutes and was only killed when placed in 63 psu for 24 minutes. The metabolic rate of the limpets increased in increasing salinity and this was thought either to be a result of increased locomotion (an escape response) or maintenance of cell volume (De Pirro et al. 1999). Gastropods are osmoconformers, meaning that the salinity of their body fluids is equal to that of their surroundings but in high salinities, water will leave their cells so metabolism has to increase to pump water back into cells to maintain their volume. Because of the various ways Patella ulyssiponensis can cope with an increase in salinity, 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

Patella ulyssiponensis does not penetrate into estuaries although its tolerance of short periods of low salinities is high (Evans, 1953). Lack of penetration into estuaries may be because of increased shelter. Rainfall can significantly lower the salinity of the rock pools it inhabits. Patella ulyssiponensis survived 24 minute exposures at 23 psu without apparent physiological effect but there was 100% mortality when exposed to 3 psu for more than 20 minutes. The limpets' response to low salinity was the same as when exposed to high salinity i.e. metabolic rate increased (De Pirro et al., 1999). It seems that Patella ulyssiponensis occurs only in full and variable salinity. It is probably highly intolerant of decreases in salinity at the benchmark level.

Changes in oxygenation

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

Evidence

It was assumed for some time that limpets experience anoxia with emergence during every tide, due to the limpets clamping down their shells to avoid desiccation. However, it has been found that limpets will raise their shells to allow transfer of air but at the cost of water loss. Their gills are inefficient at absorbing oxygen from air and limpets are expected to be subject to moderate anaerobic conditions during low tide. In water, limpets can survive at least 18 hours in completely anoxic water by respiring anaerobically (the species studied was Patella caerula) (Santini et al., 2001). Given that limpets do well in areas of organic enrichment (Rogers, 2003; Tablado et al. 1994) which are often hypoxic due to bacterial respiration. Overall, an intolerance of low has been recorded.

Introduction of microbial pathogens/parasites

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

Evidence

No information 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

Patella ulyssiponensis is not known to compete with any non-native 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

The flesh of Patella ulyssiponensis is highly prized in the Azores and Azorean communities in the USA and, in 1985, was the sixth most important fishery in the Azores (Martins et al., 1987; Corte-Real et al., 2000). Azorean stocks of Patella ulyssiponensis began to decline in the 1970s when snorkel diving became the main means of collection. The fishery was stable as long as recruitment remained high and only individuals 40 mm long were taken so that the limpets matured and bred before extraction. On some of the central islands of the Azores, individuals as small as 20 mm were being taken and the population was in decline because recruitment from outlying populations was low (Martins et al., 1987). A ban on limpet extraction in these areas has probably saved these populations of Patella ulyssiponensis. Therefore Patella ulyssiponensis is probably sensitive to uncontrolled extraction and an intolerance of high has been recorded.

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

Patella ulyssiponensis has no known relationships with species subject to extraction fisheries.