Barnacles and Patella spp. on exposed or moderately exposed, or vertical sheltered, eulittoral rock

06-01-2001
Researched byJacqueline Hill Refereed byThis information is not refereed.
EUNIS CodeA1.113 EUNIS NameSemibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock

Summary

UK and Ireland classification

EUNIS 2008A1.113Semibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock
EUNIS 2006A1.113Semibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock
JNCC 2004LR.HLR.MusB.SemSemibalanus balanoides on exposed to moderately exposed or vertical sheltered eulittoral rock
1997 BiotopeLR.ELR.MB.BPatBarnacles and Patella spp. on exposed or moderately exposed, or vertical sheltered, eulittoral rock

Description

Exposed or moderately exposed upper and mid eulittoral bedrock and boulders are characterized by dense barnacles Semibalanus balanoides and the limpet Patella vulgata. In the south-west Chthamalus spp. can be the dominant barnacle. Patella ulyssiponensis predominates in the south-west, but in the north is restricted to very exposed conditions. The barnacles may be covered by Porphyra on the upper shore of exposed sites. Patches of Lichina pygmaea may be prominent, especially in the south, where this may form a distinct Lichina zone (ELR.BPat.Lic). Cracks and crevices in the rock provide a refuge for small mussels Mytilus edulis, winkles Littorina saxatilis and the dog whelk Nucella lapillus. Damp crevices are also frequently occupied by red algae, particularly Osmundea pinnatifida, Mastocarpus stellatus and encrusting coralline algae. With decreasing wave exposure Fucus vesiculosus is able to survive, gradually replacing the barnacles and Patella biotope (see MLR.FvesB). On such moderately exposed shores ELR.BPat may occur on steep and vertical faces, while fucoids dominate the flatter areas. It should not be confused with more exposed shores characterized by Fucus vesiculosus f. linearis and Chthamalus spp. (ELR.BPat.Fvesl). In areas of soft rock (e.g. shales), the barnacles may be scarce or absent and the rock dominated by Patella. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

Recorded from most coasts of Britain and Ireland except the south-east coast of Britain where there is an absence of hard substrata.

Depth range

Mid shore

Additional information

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Habitat review

Ecology

Ecological and functional relationships

While physical factors, such as wave exposure, as indicated in the title of the biotope, clearly influence the occurrence of this biotope, the interactions between physical and biological factors are responsible for much of the structure and dynamics within the biotope.
  • The diversity of species within the ELR.BPat biotope, and on rocky shores in general, increases towards the lower shore where the habitat is wet for longer. Damp crevices at the lower parts of the biotope may support macroalgae such as Mastocarpus stellatus, Osmundia pinnatifida and encrusting coralline algae as well as some faunal organisms.
  • Exposed conditions favour the growth of barnacles, limpets and mussels. Fucoid algae are largely excluded because of the effect of wave action, but also from grazing pressure on exposed shores. For example, in New England, where Patella is absent, fucoid plants extend into more exposed conditions. A dynamic balance probably exists between fucoids and limpets plus barnacles, and is mediated by wave action. In sheltered conditions the balance shifts in favour of fucoids and in exposure the balance shifts towards limpets, barnacles and mussels. Communities on exposed shores are more stable than those of moderately exposed shores (see MLR.BF) where a mosaic of patches of fucoid cover, dense barnacles and limpets are subject to small scale temporal variations.
  • Although there are relatively few species or abundance of predators on rocky shores predation can play a role in structuring the biotope. The most obvious predator, particularly in those exposed to wave action such as the ELR.Bpat biotope, is the dogwhelk Nucella lapillus, which feeds on mussels and barnacles. When present in high abundance the dog whelk can affect the density of mussels and barnacles on the shore. Birds, which invade the shore at high and low tide respectively, can also be important predators on the shore.
  • A dense covering of barnacle species is effective in limiting the efficiency of limpet grazing which adversely affects limpet growth. Bulldozing by grazing limpets may cause high post-settlement mortality of barnacles (Jenkins et al., 2000).

Seasonal and longer term change

Rocky shore communities are often highly variable in time, due to the combined influences of physical disturbance, competition, grazing, predation and variation in recruitment. However, exposed shores tend to be less variable than moderately exposed shores and are therefore more stable. Exposed conditions favour the development of a relatively stable covering of barnacles and limpets. The barnacle population can be depleted by the foraging activity of the dogwhelk Nucella lapillus from spring to early winter and replenished by settlement of Semibalanus balanoides in the spring and Chthamalus spp. in the summer and autumn. There will also be seasonal changes in the growth rates of the algae that may be present in the biotope.

Habitat structure and complexity

Apart from cracks and crevices in the bedrock and overhangs which provide refugia for a variety of species there is very little habitat complexity in the ELR.BPat biotope. Most of the surface of the bedrock or boulders in the biotope will be covered in barnacles and limpets to which few other species can attach. The barnacles may be covered by Porphyra sp. on the upper shore. Empty barnacle shells provide shelter for small littorinids such as Littorina neglecta and Littorina saxatilis.

Productivity

In the absence, or low abundance, of macroalgae primary production in this biotope will be limited to microalgae growing on rock surfaces so productivity in the ELR.BPat biotope is probably not as high as some other rocky shore biotopes. Detrital input will be important for the suspension feeding barnacles and mussels. Rocky shores can make a contribution to the food of many marine species through the production of planktonic larvae and propagules which contribute to pelagic food chains.

Recruitment processes

Most species present in the biotope possess a planktonic stage (gamete, spore or larvae) which float in the plankton before settling and metamorphosing into the adult form. This strategy allows species to rapidly colonize new areas that become available such as in the gaps often created by storms. Thus, for organisms such as those present in this biotope, it has long been evident that recruitment from the pelagic phase is important in governing the density of populations on the shore (Little & Kitching, 1996). Both the demographic structure of populations and the composition of assemblages may be profoundly affected by variation in recruitment rates.
  • Barnacle settlement and recruitment can be highly variable because it is dependent on a suite of environmental and biological factors, such as wind direction and success depends on settlement being followed by a period of favourable weather. Long term surveys have produced clear evidence of barnacle populations responding to climatic changes. During warm periods Chthamalus spp. predominate, whilst Semibalanus balanoides does better during colder spells (Hawkins et al., 1994). Release of Semibalanus balanoides larvae takes place between February and April with peak settlement between April and June. Release of larvae of Chthamalus montagui takes place later in the year, between May and August.
  • Recruitment of Patella vulgata fluctuates from year to year and from place to place. Fertilization is external and the larvae is pelagic for up to two weeks before settling on rock at a shell length of about 0.2mm. Winter breeding occurs only in southern England, in the north of Scotland it breeds in August and in north-east England in September.
Some of the species living in the biotope do not have pelagic larvae, but instead have direct development of larvae producing their offspring as 'miniature adults'. For example, many whelks such as Nucella lapillus and some winkles do this, as do all amphipods. Adult populations of these species are governed by conditions on the shore and will generally have a much smaller dispersal range. Nucella lapillus breeds throughout the year but there is a maximum in reproductive output in the spring and autumn. The species lays eggs in protective egg capsules on hard substrata in damp crevices and under stones.

Time for community to reach maturity

Bennell (1981) observed that barnacles that were removed when the surface rock was scraped off in a barge accident at Amlwch, North Wales returned to pre-accident levels within 3 years. However, barnacle recruitment can be very variable because it is dependent on a suite of environmental and biological factors, such as wind direction, so populations may take longer to recruit to suitable areas. Recolonization of Patella vulgata on rocky shores is rapid as seen by the appearance of limpet spat 6 months after the Torrey Canyon oil spill reaching peak numbers 4-5 years after the spill (Southward & Southward, 1978). However, it does seem likely that a barnacle-limpet community would reach maturity within five years.

Additional information

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Preferences & Distribution

Recorded distribution in Britain and IrelandRecorded from most coasts of Britain and Ireland except the south-east coast of Britain where there is an absence of hard substrata.

Habitat preferences

Depth Range Mid shore
Water clarity preferences
Limiting Nutrients Not relevant
Salinity Full (30-40 psu)
Physiographic Open coast
Biological Zone Eulittoral, Upper eulittoral
Substratum
Tidal Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.), Weak < 1 knot (<0.5 m/sec.)
Wave Exposed, Moderately exposed
Other preferences

Additional Information

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

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    Additional information

    Sensitivity reviewHow is sensitivity assessed?

    Explanation

    The biotope is characterized by a dense covering of barnacles, represented by Semibalanus balanoides (although the chthamalid barnacles Chthamalus montagui and Chthamalus stellatus can be the dominant barnacle in the south-west), and the limpet Patella vulgata. The dog whelk, Nucella lapillus, is a predator of barnacles and has been included because the species may influence the abundance of barnacles on the shore.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name
    Important functionalNucella lapillusDog whelk
    Key structuralPatella vulgataCommon limpet
    Key structuralSemibalanus balanoidesAn acorn barnacle

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
    High High Moderate Major decline High
    All key and important species in the biotope are highly intolerant of substratum loss. The barnacles are permanently attached to the substratum so populations would also be removed. Epifaunal grazers such as Patella vulgata, littorinid snails and the predatory dog whelk Nucella lapillus are epifaunal and also likely to be removed along with substratum because although mobile they cannot move rapidly enough to avoid the factor. Any individuals that do remain are likely to be at risk of increased desiccation and predation and so populations are unlikely to survive. Any algal species present will also be lost. Therefore, intolerance of the biotope to substratum loss is high because almost all faunal and floral groups will disappear. Recovery is likely to be high - see additional information below for rationale.
    High High Moderate Decline Moderate
    Sediment will have an especially adverse effect on the settlement of larvae and spat. Smothering would bury adult barnacles and prevent feeding although it is likely that barnacles can withstand smothering for some period of time because they are able to respire anaerobically. Smothering of limpets by 5cm of sediment for one month is likely to interfere with locomotion, grazing and respiration. If the sediment is fluid and mobile limpets are unlikely to be able to move through the layer of sediment and will probably die. Lower down the shore active suspension feeders such as sponges and mussels may be killed by smothering. Therefore, the intolerance of the biotope is recorded as high. However, on exposed shores strong wave action is likely to mobilise any sediment alleviating the effect of smothering. Most characterizing species have planktonic larvae and/or are mobile and so can migrate into the affected area so recovery should be high - see additional information below.
    Low Very high Very Low No change High
    Increased suspended sediment may reduce growth rates in barnacles due to the energetic costs of cleaning sediment particles from feeding apparatus. However, at the benchmark increase of 100mg/l for a month effects are likely to be minimal. Patella vulgata and Nucella lapillus also have low intolerance to an increase in suspended sediment because they are found in turbid estuaries where suspended sediment levels are high. Therefore, at the level of the benchmark, the biotope is considered to have low intolerance. On return to pre-impact conditions recovery will be rapid.
    Low High Moderate Decline Low
    A decrease in suspended sediment may reduce food supplies for suspension feeding barnacles which may affect growth rates. However, for a period of a month any effects are likely to be minimal. None of the other key species in the biotope require a supply of suspended sediment particles for feeding or for activities such as tube building so the biotope is likely to have low intolerance to a decrease in the levels of suspended sediment for a month. Normal feeding and growth rates will resume as soon as normal conditions return.
    Intermediate High Low No change Moderate
    A change in desiccation equivalent to a change in position of one vertical biological zone on the shore would adversely affect the biotope where it is already near its upper limit on the shore because the key species, although relatively tolerant of desiccation, can only tolerate an increase up to a critical level of water content. Semibalanus balanoides may be replaced by the more desiccation tolerant Chthamalus montagui at the upper limits of the biotope. The upper range of limpets and Nucella lapillus may be reduced as they move down the shore to avoid increasing desiccation. Thus the upper limit of the biotope is likely to be depressed down the shore to be replaced by a barnacle dominated community with an absence or very low abundance of limpets and whelks such as the biotope ELR.Bpat.Lic - Barnacles and Lichina pygmaea on steep exposed upper eulittoral rock. Since a part of the biotope over its normal extent is likely to be lost and replaced with another biotope intolerance is considered to be intermediate. See additional information for recovery.
    Low High Low No change High
    An increase of one hour in the period of emersion would subject the species in the biotope to greater desiccation and nutrient stress, leading to reduced growth and a depression in the upper limit of the species distribution on the shore is likely. Only those barnacles at the extremes of their physiological limits will die. Limpets are able to move down the shore although the loss of a home scar can increase the species vulnerability to predation. Thus, the biotope is likely to be lost only at the very upper limit of its range and so a rank of low has been recorded. A change in the level of emergence on the shore may also affect the lower distribution limit of all the key species as competition increases lower down the shore.
    Low High Low No change High
    A decrease in the period of emersion will immerse animals at the bottom of the biotope in seawater for longer which may increase growth rates as the supply of oxygenated water and nutrients increase. However, competition from other species may increase and the biotope could change to another more species rich biotope. The overall effect could simply be a moving of the biotope up the shore so intolerance is assessed as low.
    Low High Low No change Moderate
    The biotope is found in areas of weak to moderately strong tidal streams and is unlikely to be highly intolerant of an increase in water flow because of the tenacity of the key species. Barnacles can tolerate very high flow rates although feeding in very strong water flows may be impaired resulting in reduced growth and fecundity. The molluscs Patella vulgata and Nucella lapillus are able to attach very strongly to rock. Strong water flow may impair feeding but it seems likely that the biotope will survive and so an intolerance of low is reported.
    High High Intermediate Rise Moderate
    The biotope is found in areas of weak tidal streams such as found in lagoons and sea lochs. However, a certain degree of water flow is required to supply nutrients and remove waste products so a reduction in the water flow below a certain level may have an adverse effect on the species and hence the biotope. For example, barnacle growth rates are lower in reduced water flow and this may affect abundance within the biotope. However, the overall impact is not expected to be significant so the biotope considered to have low intolerance to decreased water flow.
    Low Very high Very Low No change High
    Increased temperature is likely to favour chthamalid barnacles rather than Semibalanus balanoides (Southward et al. 1995). Chthamalus montagui and Chthamalus stellatus are warm water species, with a northern limit of distribution in Britain so are likely to be tolerant of long term increases in temperature. Thus, an increase in temperature may lead to a change in the dominant species of barnacle. However, such a change will not alter the nature of the biotope. Patella vulgata and Nucella lapillus are hardy intertidal species that tolerate long periods of exposure to the air and consequently wide variations in temperature. Therefore, the impact on the biotope of temperature increases at the benchmark level are likely to be sub-lethal effects on growth and fecundity. Thus, the biotope is reported as having low intolerance to an increase in temperature. On return to normal temperatures original metabolic activity will rapidly resume so recoverability is set to very high.
    Low Very high Moderate No change High
    A decrease in temperature will favour Semibalanus balanoides rather than the chthamalid barnacles which may lead to change in species dominance. However, a change in the species of barnacle will not change the nature of the biotope. Patella vulgata is largely unaffected by short periods of extreme cold. Ekaratne & Crisp (1984) found adult limpets continuing to grow over winter when temperatures fell to -6°C, and stopped only by still more severe weather. Therefore, a benchmark decrease in temperature is likely to result in sub-lethal effects on growth and fecundity only. The biotope is therefore of low intolerance to a decrease in temperature. On return to normal temperatures original metabolic activity will rapidly resume so recoverability is set to very high.
    Tolerant Not relevant Not relevant No change High
    The biotope is predominantly an assemblage of faunal species so the light attenuation effects of an increase in turbidity would not significantly affect the community. However, there are some crustose and other algae in the biotope that may be affected. An increase in turbidity would reduce the light available for photosynthesis during immersion which could result in reduced biomass of the algae in the biotope. However, the biotope is found at the upper and mid-tide levels and so is subject to long periods of emersion during which time macroalgae can continue to photosynthesize as long as plants have a sufficiently high water content. Therefore, photosynthesis and consequently growth will be unaffected during this period. The overall effects on the overall community dynamics of the biotope are likely to be negligible so the biotope is considered to be not sensitive. Upon return to previous turbidity levels the photosynthesis rate would return immediately to normal.
    The impacts on suspension feeding organisms are addressed under 'suspended sediment' above.
    Tolerant Not sensitive* No change High
    The biotope is predominantly an assemblage of faunal species so the light attenuation effects resulting from a decrease in turbidity would not significantly affect the community. However, there are some crustose and other algae in the biotope so increased light availability for photosynthesis during immersion may increase the growth rates of these species. However, this is not likely to effect the overall community dynamics so the intolerance of the biotope is considered to be not sensitive.
    High High Moderate Minor decline Moderate
    The ELR.Bpat biotope is found on exposed or moderately exposed upper and mid eulittoral bedrock and boulders. In increasing wave action, to very or extremely exposed wave exposure, the few fucoids that may be present in the ELR.BPat biotope are likely to be removed and under conditions of very high exposure Patella vulgata may be limited to the upper region of the shore, its place being taken below mean tide level by Patella aspera (Blackmore, 1969). Also as wave exposure increases on rocky shores, barnacles and limpet numbers may decrease and may be replaced by mussel dominated communities. Thus, if wave exposure increases the biotope could be replaced by another, such as the mussel dominated biotope on extremely exposed shores (A1.111). Thus, intolerance of the biotope is assessed as high.
    High High Intermediate Rise Moderate
    The effect of changes in wave action on rocky shores is predominantly through its influence on the balance of the biological interactions. If wave exposure is reduced, fucoids are able to survive and this inhibits the settlement of barnacles by blocking larval recruitment mainly by fucoid fronds 'sweeping' the rock of colonizers. In further reducing wave exposure the fucoids are able to maintain a more or less total and permanent canopy (Hartnoll & Hawkins, 1985). Thus, if wave exposure decreases the biotope can rapidly disappear to be replaced by another, barnacles and fucoids on moderately exposed shores (A1.21) and dense fucoid cover on sheltered shores (SLR.F.Fser). On return to normal conditions fucoid cover would again disappear and the previous biotope re-establish itself. See additional information for recovery.
    Tolerant Not relevant Not relevant Not relevant High
    None of the selected key or important species in the biotope are recorded as sensitive to noise although limpets do respond to vibration. However, the biotope as a whole is not likely to be intolerant to changes in noise levels at the level of the benchmark.
    Tolerant Not relevant Not relevant Not relevant High
    Most macroinvertebrates have poor or short range visual perception and are unlikely to be affected by visual disturbance such as by boats or humans on the shore. The biotope is therefore, considered to be not sensitive to the factor.
    High High Moderate Minor decline High
    The biotope is susceptible to abrasion and physical disturbance from trampling. Light trampling pressure, of 250 steps in a 20x20 cm plot, one day a month for a period of a year, has been shown to damage and remove barnacles (Brosnan & Crumrine, 1994). Trampling pressure can thus result in an increase in the area of bare rock on the shore (Hill et al., 1998). Chronic trampling can affect community structure with shores becoming dominated by algal turf or crusts. Therefore, chronic trampling could result in loss of the biotope and an intolerance of high has been recorded.

    However, if trampling stops, recovery should be good. In Oregon for example, the algal-barnacle community recovered within a year after trampling stopped (Brosnan & Crumrine, 1994). Bennell (1981) observed the impact of abrasion of barnacles from a grounded barge at Amlwch, North Wales and subsequent recovery of barnacle populations at least within three years.

    High High Moderate Decline High
    intolerance to displacement is high because one of the key species in the biotope, Semibalanus balanoides is permanently attached to the substratum and cannot re-establish itself if detached. Loss of this key species results in loss of the biotope. The epifaunal species, such as Patella vulgata, Nucella lapillus and Littorina spp., can re-establish themselves if displaced although they may be at risk of increased desiccation and predation if they are not returned foot down. Algal species are permanently attached and so will have very high intolerance to displacement. Intolerance of the biotope is high because community composition will be significantly affected. See additional information below for recovery.

    Chemical Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    High High Moderate Minor decline High
    intolerance of the biotope is assessed as high because one the key species, Patella vulgata is highly intolerant of synthetic chemicals. Patella vulgata is extremely intolerant of aromatic solvent based dispersants such as those used in the Torrey Canyon oil spill clean-up (Smith, 1968). The effects of tributyl tin (TBT), used in anti-fouling paints, on Nucella lapillus has been extensively documented and represents one of the best known examples of the effects of chemical pollution which causes the development of male sexual characteristics in females, termed 'imposex' (Smith, 1980).
    Heavy metal contamination
    Low Very high Very Low No change Moderate
    intolerance of the biotope is low because the key species are fairly robust in terms of heavy metal pollution. Barnacles are able to concentrate heavy metals in their tissues and Patella vulgata is found living in conditions of fairly high metal contamination in the Fal estuary in Cornwall (Bryan & Gibbs, 1983). Adult fucoid plants appear to be fairly tolerant of heavy metal pollution although earlier life stages may be more sensitive (Holt et al., 1997). Recovery from sub-lethal effects will be very high as metabolism and growth return to normal.
    Hydrocarbon contamination
    High Moderate Moderate No change High
    The limpet Patella vulgata has a high intolerance to hydrocarbons. For example, in long term studies into the environmental effects of oil refinery effluent discharged into Littlewick Bay, Milford Haven, the number of limpets, usually found in substantial numbers on this type of shore, were considerably reduced in abundance on areas close to the discharge (Petpiroon & Dicks, 1982). A loss of limpets can have a profound impact on the rest of the community because limpet grazing excludes fucoids from exposed shores. This was demonstrated by the fucoid colonization of exposed shores after the Torrey Canyon oil spill killed all the limpets. The barnacle Semibalanus balanoides is relatively tolerant of oil pollution. Nucella lapillus has been observed to be fairly robust in the face of oil pollution. However, exposure to petrol/water emulsions in Milford Haven as a result of the Done 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 a 9-11 months, mainly due to recolonization by adults. Recovery is set to moderate because it can take much longer for the biotope to recover from the effects of oil pollution. The loss of limpets can enable a covering of fucoids to take hold, and so a return to barnacle and limpet dominance will probably take longer than five years and so has been set to moderate.
    Radionuclide contamination
    No information No information No information Not relevant Not relevant
    Insufficient
    information.
    Changes in nutrient levels
    Intermediate High Low Decline Low
    Little data exists on the effects of increased nutrients on the biotope. A slight increase in nutrient levels could be beneficial for barnacles by promoting the growth of phytoplankton levels and therefore increasing zooplankton levels. Limpets would also benefit from increased growth of benthic microalgae. However, Holt et al. (1995) predict that smothering of barnacles by ephemeral green algae is a possibility under eutrophic conditions and so the intolerance of the biotope is set at intermediate. Recovery of barnacles should be possible within five years.
    High High Moderate Decline Low
    The biotope occurs in areas of full salinity although will be subject to some variability because of rainfall in the intertidal. However, there are no reports of the biotope occurring in hypersaline areas such as rockpools where evaporation in the summer causes salinity to increase. In the laboratory, Semibalanus balanoides was found to tolerate salinities between 12 and 50 psu (Foster, 1970). However, in the field it seems likely that the biotope will be intolerant of a year long increase in salinity and so a rank of high is reported.
    High High Intermediate Decline Low
    The biotope occurs in areas of full salinity although will be subject to some variability because of rainfall in the intertidal. Therefore, most species are likely to be tolerant of a short term decrease in salinity and variable salinity. Although barnacles and limpets can tolerate moderately long term decreases in salinity a long term decrease, say from full to reduced salinity (18 - 30psu) for a period of year, is likely to result in the loss of many individuals so intolerance is assessed as high. See additional information below for recovery.
    Low Immediate Not sensitive No change Moderate
    There is no information of the effects of deoxygenation on the ELR.Bpat biotope. Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l. Semibalanus balanoides can respire anaerobically, so it can tolerate some reduction in oxygen concentration (Newell, 1979). When placed in wet nitrogen, where oxygen stress is maximal and desiccation stress is low, Semibalanus balanoides has a mean survival time of 5 days (Barnes et al., 1963). Therefore, most barnacles can probably survive low levels of oxygen for a week. In oxygen free water limpet metabolic rate gradually fell eventually resulting in death only after 36 hours (Grenon & Walker,1981). However, the biotope is intertidal, with species being able to respire in air, so will only be subject to low oxygen in the water column intermittently during periods of tidal immersion. Therefore, it is likely that many individuals will survive for one week at a water oxygen concentration of 2mg/l and so intolerance is reported to be low. In addition, in areas of high wave exposure low oxygen levels in the water are unlikely to persist for very long.

    Biological Pressures

     IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
    Low High Low Minor decline Moderate
    Barnacles are parasitised by a variety of organisms and, in particular, the cryptoniscid isopod Hemioniscus balani. Heavy infestation can cause castration of the barnacle. Levels of infestation within a population vary. Once infected recovery of an individual barnacle is unlikely. Nucella lapillus may be infected by several species. For example cercaria larvae of the trematode Parorchis acanthus causes castration and extended growth (Feare, 1970b; Kinne, 1980; Crothers, 1985) and the 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 barnacle and dog whelk populations may result in a reduction in recruitment and a decline in population numbers in the long term. There were no reported occurrences found of the biotope being affected by these or any other infestations so intolerance is reported to be low. However, there is always the potential for this to occur so intolerance may change.
    Low High Low No change Moderate
    The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second world war. The species does well in estuaries and bays, where it can displace Semibalanus balanoides and Chthamalus montagui. However, its overall effect on the dynamics of rocky shores has been small as Elminius modestus has simply replaced some individuals of a group of co-occurring barnacles (Raffaelli & Hawkins, 1999). Although no other species has been observed to compete with or prey upon the other species in the biotope there is always the potential for this to occur.
    Not relevant Not relevant Not relevant Not relevant Not relevant
    It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.
    Low High Low No change Moderate

    Additional information

    Recoverability
    Bennell (1981) observed that barnacle populations removed when the surface rock was scraped off in a barge accident at Amlwch, North Wales returned to pre-accident levels within 3 years. However, barnacle recruitment can be very variable because it is dependent on a suite of environmental and biological factors, such as wind direction and the presence of adults as an inducement for larvae to settle, therefore populations may take longer to recover. Recolonization of Patella vulgata on rocky shores is rapid as seen by the appearance of limpet spat 6 months after the Torrey Canyon oil spill reaching peak numbers 4-5 years after the spill (Southward & Southward, 1978). Most characterizing species have planktonic larvae and/or are mobile and so can migrate into the affected area. Therefore, it seems likely that within five years the community should be able to return to a pre-impact state so recovery is set to high.

    Importance review

    Policy/Legislation

    Habitats Directive Annex 1Reefs, Reefs
    UK Biodiversity Action Plan Priority

    Exploitation

    There are no species present that are likely to be harvested from the ELR.BPat biotope. Fucoid plants are not present in high enough abundance for exploitation to be viable. However, rocky shores are widely exploited for a range of recreational uses including rock pooling, angling and as a resource for students and scientific researchers. Trampling has been shown to have a significant impact on community structure.

    Additional information

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    Bibliography

    1. Airoldi, L. & Hawkins, S.J., 2007. Negative effects of sediment deposition on grazing activity and survival of the limpet Patella vulgataMarine Ecology Progress Series, 332, 235-240.
    2. Alfaro, A.C., 2006. Byssal attachment of juvenile mussels,Perna canaliculus, affected by water motion and air bubbles. Aquaculture, 255, 357-61
    3. Almada-Villela, P.C., Davenport, J. & Gruffydd, L.L.D., 1982. The effects of temperature on the shell growth of young Mytilus edulis L. Journal of Experimental Marine Biology and Ecology, 59, 275-288.
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    Citation

    This review can be cited as:

    Hill, J.M. 2001. Barnacles and Patella spp. on exposed or moderately exposed, or vertical sheltered, eulittoral rock. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/199

    Last Updated: 06/01/2001