Biodiversity & Conservation

LR.HLR.MusB.Cht

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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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.
Smothering
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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.
Increase in suspended sediment
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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.
Decrease in suspended sediment
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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.
Desiccation
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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.
Increase in emergence regime
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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.
Decrease in emergence regime
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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.
Increase in water flow rate
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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.
Decrease in water flow rate
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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.
Increase in temperature
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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.
Decrease in temperature
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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.
Increase in turbidity
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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.
Decrease in turbidity
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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.
Increase in wave exposure
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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 (£ELR.MytB£). Thus, intolerance of the biotope is assessed as high.
Decrease in wave exposure
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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 (£MLR.BF£) 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.
Noise
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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.
Visual Presence
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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.
Abrasion & physical disturbance
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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.

Displacement
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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 Factors

Synthetic compound contamination
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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
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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
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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
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Insufficient information.
Changes in nutrient levels
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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.
Increase in salinity
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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.
Decrease in salinity
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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.
Changes in oxygenation
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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 Factors

Introduction of microbial pathogens/parasites
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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.
Introduction of non-native species
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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.
Extraction
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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.

Additional information icon 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.

This review can be cited as follows:

Hill, J.M. 2001. Barnacles and Patella spp. on exposed or moderately exposed, or vertical sheltered, eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29/07/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=199&code=2004>