Biodiversity & Conservation


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 algae and barnacles are permanently attached to the substratum so populations would be lost. Epifaunal grazers like Patella vulgata and littorinid snails are epifaunal and most will be removed along with substratum loss. Those that do remain have an increased risk of desiccation and predation and so populations are unlikely to survive. Mobile species like the amphipod Hyale prevostii will be indirectly affected by the loss of fucoid plants as protection from desiccation is removed, as will sessile epiphytic flora and fauna. See additional information for recovery.
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Smothering by 5 cm of sediment, although unlikely to occur in this biotope, is likely to completely cover the species in the biotope, preventing photosynthesis and respiration. The individual key species have high intolerance to smothering. Algae may rot under smothering material and sessile and slow moving fauna may suffocate. Barnacle feeding is likely to be affected and limpet locomotion and grazing will probably be impaired. Sediment will have an especially adverse effect on young germling algae and on the settlement of larvae and spat. Suspension feeders such as mussels may be killed by smothering. However, since the biotope occurs in extremely exposed locations wave action will mobilize sediment alleviating the effect of smothering and so intolerance has been assessed as low. As sediment is removed photosynthesis, locomotion and feeding will return to normal so recovery will be rapid.
Increase in suspended sediment
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Increased suspended sediment may reduce growth rate in barnacles due to the energetic costs of cleaning sediment particles from feeding apparatus although if the organic content is high suspension feeders will benefit. Patella vulgata and Mytilus edulis also have low intolerance to an increase in suspended sediment because they are found in turbid estuaries where suspended sediment levels are high. Intertidal algae (which continue to photosynthesize when the tide is out) are not sensitive to levels of suspended sediment. Therefore, at the level of the benchmark, the biotope is considered to have low intolerance. On return to normal conditions feeding rates will return to pre-impact levels almost immediately and growth within a short time. Recovery is therefore reported to be very high.
Decrease in suspended sediment
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A decrease in suspended sediment, especially organic particulates, could potentially reduce the food available to suspension feeders such as the barnacles and Mytilus edulis and hence growth rates. For a period of a month however, the effect is not likely to be significant. None of the other species in the biotope require a supply of suspended sediment particles for feeding or for activities such as tube building. Therefore, an intolerance of low has been recorded.
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The fucoid species Fucus distichus and the more widespread form of Fucus spiralis both have high intolerance to desiccation stress. Fucus distichus is thought to be prevented from growing further south due to its poor tolerance of desiccation and inability to compete with plants growing further down the shore. The southern distribution of the species is also thought to be limited by day length as shorter day lengths are thought to stimulate the onset of receptacle formation (Bird & McLachlan, 1976). Fucus spiralis can tolerate desiccation until the water content has been reduced to 10-20 % (Lüning, 1990). However if water is lost beyond this critical level irreversible damage occurs. As Fucus spiralis lives close to the upper limit of it's physiological tolerance the species probably cannot tolerate increased desiccation. However, care is needed in extrapolating information on the physiological tolerances of the widespread form of Fucus spiralis to Fucus spiralis f. nana. Increased desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from the littoral fringe to the upper littoral fringe or supralittoral would cause the upper limit of both fucoid species distribution, and hence the biotope to become depressed. At the top of its range the biotope will probably become replaced by another biotope such as a lichen dominated one. However, the lower limit of the biotope may also move down the shore. Intolerance is therefore, reported to be intermediate. For recovery see additional information.
Increase in emergence regime
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A change in the level of emergence on the shore will affect the upper or lower distribution limit of all the key species. An increase 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 distribution limit. Changes in the numbers of important species are likely to have profound effects on community structure and may result in loss of the biotope at the extremes of its range. For example, at the upper limit the biotope may lose fucoid cover and so change to one dominated by barnacles and limpets or lichens. However, the more widespread form of Fucus spiralis can tolerate an emersion period of 1-2 days so an increase in time spent in air of 1 hour in per day may limit growth and fecundity rather than survival. Although care is needed in extrapolating information on the physiological tolerances of the widespread form of Fucus spiralis to Fucus spiralis f. nana it seems likely that only those species at the extremes of their physiological limits would 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 is reported. 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. Growth, condition and fecundity are likely to return within several months if pre-impact emersion levels return.
Decrease in emergence regime
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An 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 water flow rates in which the biotope occurs are not known. However, Fucus distichus and Fucus spiralis f. nana appear to attach very strongly to the substratum because they live in areas exposed to very high wave action. Barnacles can tolerate very high flow rates as they are unlikely to be washed off the substratum although feeding in very strong water flows may be impaired resulting in reduced growth and fecundity. The mollusc Patella vulgata is also able to attach very strongly to rock and populations can adapt to changing water currents through the development of different shell shape and profile. Thus, strong water flow may impair feeding of some fauna but it seems likely that the biotope will survive and so an intolerance of low is reported. Recovery will be immediate on return to normal conditions.
Decrease in water flow rate
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A decrease in water flow rates may affect the supply of particulate matter, nutrients and oxygenated water to the biotope. However, since wave exposure in this biotope is high wave action is also likely to bring fresh water supplies and so intolerance to a decrease in water flow rate is likely to be low.
Increase in temperature
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Schonbeck & Norton (1979) demonstrated that fucoids can increase tolerance in response to gradual change in a process known as 'drought hardening'. However, fucoids are intolerant of sudden changes in temperature and relative humidity with field observations of bleaching and death of plants during periods of hot weather (Hawkins & Hartnoll, 1985). Also, Fucus distichus reaches the southern limit of its distribution in the British Isles, so may be very intolerant of increases in temperature. However, day length is thought to be responsible for the southern limit of the species, which requires short day lengths to stimulate the onset of receptacle formation. However, a short-term increase of 5°C may result in the death of some algal plants, especially at the upper limit of the biotope. However, many plants are likely to survive this temperature increase for a period of only 3 days. The more widespread form of Fucus spiralis has low intolerance to temperature changes and so is not likely to be affected by an increase. Increased temperature is likely to favour chthamalid barnacles rather than Semibalanus balanoides (Southward et al. 1995). Chthamalus spp. are warm water species, with a northern limit of distribution in Britain so are likely to be tolerant of or favourably affected by long term increases in temperature. However, a change in the species of barnacle will not change the nature of the biotope. Patella vulgata is a hardy intertidal species that tolerates 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 the loss of some fucoid plants and sub-lethal effects on growth and fecundity of other plants and species. Thus, the biotope is reported as having low intolerance to the benchmark increases in temperature. On return to normal temperatures original metabolic activity will rapidly resume and new plants will soon recruit so recoverability is set to high.
Decrease in temperature
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Fucus distichus reaches the southern limit of its distribution in the British Isles so decreases in temperature would probably have little effect and also because the species distribution appears to be determined primarily by day length rather than temperature. and may allow the species to colonize further south. The species has been found to tolerate freezing in small rock pools in Maine (Pearson & Davison, 1994). Fucus spiralis also has low intolerance to temperature changes. A decrease in temperature will favour Semibalanus balanoides rather than Chthamalid barnacles which 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 have only minimal 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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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 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 intolerance is considered to be low. Upon return to previous turbidity levels the photosynthesis rate would return immediately to normal and growth rates would be restored within a few months. Recovery is therefore, set to very high. The impacts on suspension feeding organisms are addressed under 'suspended sediment' above.
Decrease in turbidity
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A decrease in turbidity would increase light availability for photosynthesis during immersion which may result in increased growth rates of the algal species. However, this is not likely to effect the overall community dynamics so the intolerance of the biotope is considered to be low. Upon return to previous turbidity levels the photosynthesis rate would return immediately to normal and growth rates within a few months.
Increase in wave exposure
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The ELR.Fdis biotope occurs on some of the most exposed coasts in Britain and so is very tolerant of extreme wave exposure. The short tufted form of the fucoids Fucus distichus and Fucus spiralis f. nana enable them to remain attached to the rock even when exposed to severe wave action. However, if wave exposure were to increase further it is likely that most algae and fauna would be lost leaving bare rock so intolerance is high. The biotope extends into some of the severest wave conditions existing around the British and Irish coasts so in reality wave exposure is not likely to increase. See additional information for recovery.
Decrease in wave exposure
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A shift to more sheltered conditions may allow other fucoid species to inhabit the shore which are faster growing and would out-compete Fucus distichus. The normal form of Fucus spiralis would predominate over the diminutive form. Barnacle and limpet abundance may increase and lead to the development of a different biotope such as MLR.BF barnacle and fucoid biotope commonly found on moderately exposed rocky shores. Thus intolerance is reported to be high as ELR.Fdis would be lost. See additional information for recovery.
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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 sensitive to changes in noise levels at the benchmark level.
Visual Presence
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Algae have no visual perception. Most macroinvertebrates have poor or short range perception and are unlikely to be affected by visual disturbance such as by boats or humans. Although limpets have eyes, visual perception is probably quite limited and as such the species is unlikely to be sensitive to the visual presence of humans on the shore, for example. The biotope is therefore, considered to be not sensitive to the factor.
Abrasion & physical disturbance
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The rocky intertidal is not at risk from boating or fishing activity except strandings but is susceptible to physical disturbance and abrasion from trampling. Even very light trampling on shores in the north east of England was sufficient to reduce the abundance of fucoids (Fletcher & Frid, 1996), which in turn reduced the microhabitat available for epiphytic species. 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, 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).
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intolerance to displacement is high because many of the key species in the biotope, including the fucoids and barnacles are permanently attached to the substratum and cannot re-establish themselves if detached. Epifaunal species such as limpets can re-attach to the substratum if displaced although removal from the home scar is likely to increase the likelihood of predation. Loss of the key species results in loss of the biotope. Recovery should be possible within a few years - see additional information.

Chemical Factors

Synthetic compound contamination
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There is no information available on the effects of chemicals on the biotope as a whole. However, there is some information on the effects of several chemicals on the species that make up the biotope. Fucoids in general, for example, are reported to exhibit high intolerance to chlorate and pulp mill effluents containing chlorate (Kautsky, 1992). Patella vulgata is extremely intolerant of aromatic solvent based dispersants such as those used in the Torrey Canyon oil spill clean-up (Smith, 1968). However, on rocky coasts of Amlwch in areas close to acidified halogenated effluent from a bromine plant the shore consisted almost entirely of bare rock but there was a fucoid-barnacle mosaic nearby (Hoare & Hiscock, 1974). Therefore, effects depend on the chemical under consideration and there is obviously tolerance to some chemicals. However, intolerance is assessed as high because some chemicals could lead to the loss of the biotope. See additional information for recovery.
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. Adult fucoid plants appear to be fairly tolerant of heavy metal pollution although earlier life stages may be more sensitive (Holt et al., 1997). 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). Recovery from sub-lethal effects will be very high as metabolism and growth return to normal.
Hydrocarbon contamination
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The loss of key herbivores, such as limpets and littorinids, and the subsequent prolific growth of ephemeral algal mats appears to be a fairly consistent feature of coastal oil spills (Hawkins & Southward, 1992). Species richness, diversity and evenness were all much lower in fucoid-barnacle communities at sites close to the Braer oil spill (Newey & Seed, 1995). In the absence of tarry masses of oil which cause physical smothering of sessile animals and mechanical damage to algae, adult fucoids and barnacles occupying primary space in the community are relatively resistant to damage from chemical properties of the oil itself, although some damage will inevitably occur. The most serious effects tend to occur among juvenile and newly settling recruits to the community. However, this biotope is subject to very strong wave action and therefore, oil is likely to be rapidly removed and not cause smothering effects. Intolerance of the biotope is considered to be low. See additional information for recovery.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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A reduction in the level of nutrients could reduce growth rates of algal species in the biotope. Nutrient availability is the most important factor controlling germling growth. A slight increase in nutrients may enhance growth rates but high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae and an increase in the number of grazers. The effect of sewage discharge on an extremely exposed rocky shore is likely to be low because water movements should limit the build up of particulates and prevent eutrophication. Fucoids appear to be relatively resistant to the input of sewage, and grow apparently healthily to within 20 metres of an outfall discharging untreated sewage in the Isle of Man (Holt et al., 1997). Intolerance of the biotope is therefore assessed as low. Recovery will be rapid as growth responds to changing nutrient levels.
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. Therefore, it seems likely that the biotope will be highly intolerant of a long term increase in salinity and a rank of high is reported. See additional information for recovery.
Decrease in salinity
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Barnacle and fucoid shores are able to tolerate short term variations in salinity because the littoral zone is regularly exposed to precipitation. Fucus distichus extends into estuaries on the coast of North America. so the biotope may tolerate long term reductions in salinity within its normal tolerance range although growth rates and fecundity are likely to be impaired. Intolerance is therefore, reported to be low. However, the biotope is only found on open exposed coasts.
Changes in oxygenation
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Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l. There is no information about key algae species tolerance to changes in oxygenation although Kinne (1972) reports that reduced oxygen concentrations inhibit both algal photosynthesis and respiration. However, since the biotope occurs in the upper eulittoral a proportion of time will be spent in air where oxygen is not limited so the metabolic processes of photosynthesis and respiration can take place. Therefore, for a period of a week reduced oxygenation in the water is likely to have minimal sub-lethal effects and so an intolerance rank of low is reported.

Biological Factors

Introduction of microbial pathogens/parasites
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The cryptoniscid isopod Hemioniscus balani is a widespread parasite of barnacles, found around the British Isles. Heavy infestation inhibits or destroys the gonads resulting in castration of the barnacle. High levels of infestation may reduce barnacle abundance and distribution which would impact on patch dominance although no reported cases of this were found. There were no reported occurrences found of the fucoid algae or 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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There are no non-native species at present in Britain likely to occur in this biotope.
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It is extremely unlikely that the species indicative of sensitivity would be targeted for extraction due to the fact that the biotope occurs on remote and dangerously wave exposed shores. We have no evidence for the indirect effects of extraction of other species on this biotope and not relevant has been suggested.

Additional information icon Additional information

Recovery of the biotope is high because recruitment of key species is fairly rapid and the biotope will look much as before within five years. For example, Fucus distichus (Ang, 1991) and Fucus spiralis have been observed to readily recruit to cleared areas (Hartnoll & Hawkins, 1985; Hawkins & Hartnoll, 1985) and have fast growth rates, so recovery rates are expected to be high. 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, 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. Therefore, it seems likely that the biotope should recover within five years.

This review can be cited as follows:

Hill, J.M. 2005. Fucus distichus and Fucus spiralis f. nana on extremely exposed upper shore rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 25/11/2015]. Available from: <>