The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Marine lichens are exposed to extremes of temperature from hot, dry summers to cold, frosty winters. Fletcher (1980) noted that few studies implicated high or low temperatures as a factor affecting seashore lichens, but that changes in temperature affect water relations. Increased temperature may increase desiccation (see emergence) although, other factors are involved, such as wind and wave action, precipitation, sunlight and shading. Fletcher (1980) suggested that the effect of temperature on littoral lichens was inconclusive. For example, Verrucaria maura is abundant on both sunny and shaded shores but is considered a shade tolerant plant from North Africa to France and in Scandinavia. Reid (1969; cited in Fletcher, 1980)  reported that Verrucaria mucosa had the similar temperature resistance to the algae with which it is ecologically associated but that Verrucaria maura was even less resistant. However, Fletcher (1980) also suggested that temperature was an important factor for water conservation, in combination with insolation, shade and wind, emersion and precipitation.

This biotope may contain a mix of Chthamalus and Semibalanus balanoides barnacles depending on location. Increased temperatures are likely to favour chthamalid barnacles (that dominate the south and south-west examples of this biotope) rather than Semibalanus balanoides (that dominates northern and eastern examples of this biotope) (Southward et al. 1995; Connor et al., 2004). Long-term time series show that successful recruitment of Semibalanus balanoides is correlated to sea temperatures (Mieszkowska et al., 2014) and that, due to recent warming, its range has been contracting northwards. Temperatures above 10 to 12°C inhibit reproduction (Barnes, 1957, 1963, Crisp & Patel, 1969) and laboratory studies suggest that temperatures at or below 10°C for 4-6 weeks are required in winter for reproduction, although the precise threshold temperatures for reproduction are not clear (Rognstad et al., 2014). Observations of recruitment success in Semibalanus balanoides throughout the south-west of England, strongly support the hypothesis that an extended period (4-6 weeks) of sea temperatures <10°C is required to ensure a good supply of larvae (Rognstad et al., 2014, Jenkins et al., 2000). During periods of high reproductive success, linked to cooler temperatures, the range of barnacles has been observed to increase, with range extensions in the order of 25 km (Wethey et al., 2011) and 100 km (Rognstad et al., 2014). Increased temperatures are 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. The range of Chthamalus stellatus and Chthamalus montagui has been extending northwards due to increasing temperatures. Breeding of Chthamalus stellatus in France occurs in April (Barnes, 1992), and correlates with mean air and sea temperatures of 11 - 12°C, and maximum temperatures of 14 °C. Barnes (1992) found that at an upper-temperature limit of 20 - 21°C in the sea and 24 - 25°C in the air reproductive activity decreased. Chthamalus suffers a failure of fertilization at temperatures of 9°C and below (Patel & Crisp, 1960), its lower critical temperature for feeding activity is 4.6°C (Southward, 1955). Semibalanus balanoides out-competes Chthamalus species for space, but recruitment declines and failures of Semibalanus balanoides in response to warmer temperatures benefit Chthamalus species by allowing them to persist and recruit (Mieszkowska et al., 2014).

Sensitivity assessment. The 'black lichen zone' (Ver) experiences the extremes of hot summers and cold frosty winters and is, therefore, adapted to extreme variation in temperature. It also occurs from North Africa to Scandinavia, so that it is unlikely to be adversely affected by changes in temperature at the benchmark level within Britain and Ireland. Similarly, chronic or acute change at the benchmark level may affect reproduction and survival or the difference barnacle species and affect the relative abundance of Semibalanus or Chthamalus. However, the biotope will remain as long as one of the characteristic barnacle species remains. Therefore, a resistance of High is suggested. Resilience is, therefore, likely to be High, and the biotope has been assessed as Not sensitive at the benchmark level. Ellis et al. (2007) modelled the effect of climate change scenarios on selected terrestrial lichens and identified potential threats to Northern montane and Boreal species, and uncertainties in the fate of species typical of the Atlantic coast margin, but no information on littoral species was found. Similarly, longer-term, broad-scale perturbations such as increased temperatures from climate change might have a greater effect on the relative abundance of the characteristic barnacles. 

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Marine lichens are exposed to extremes of temperature from hot, dry summers to cold, frosty winters. Fletcher (1980) noted that few studies implicated high or low temperatures as a factor affecting seashore lichens, but that changes in temperature affect water relations. Increased temperature may increase desiccation (see emergence) although, other factors are involved, such as wind and wave action, precipitation, sunlight and shading. Fletcher (1980) suggested that the effect of temperature on littoral lichens was inconclusive. For example, Verrucaria maura is abundant on both sunny and shaded shores but is considered a shade tolerant plant from North Africa to France and in Scandinavia. Reid (1969; cited in Fletcher, 1980)  reported that Verrucaria mucosa had the similar temperature resistance to the algae with which it is ecologically associated but that Verrucaria maura was even less resistant. However, Fletcher (1980) also suggested that temperature was an important factor for water conservation, in combination with insolation, shade and wind, emersion and precipitation.

This biotope may contain a mix of Chthamalus and Semibalanus balanoides barnacles depending on location. Decreased temperatures are likely to favour Semibalanus balanoides (that dominates northern and eastern examples of this biotope) rather than chthamalid barnacles (that dominate the south and south-west examples of this biotope) (Southward et al. 1995; Connor et al., 2004). Long-term time series show that successful recruitment of Semibalanus balanoides is correlated to sea temperatures (Mieszkowska et al., 2014) and that, due to recent warming, its range has been contracting northwards. Temperatures above 10 to 12°C inhibit reproduction (Barnes, 1957, 1963, Crisp & Patel, 1969) and laboratory studies suggest that temperatures at or below 10°C for 4-6 weeks are required in winter for reproduction, although the precise threshold temperatures for reproduction are not clear (Rognstad et al., 2014). Observations of recruitment success in Semibalanus balanoides throughout the south-west of England, strongly support the hypothesis that an extended period (4-6 weeks) of sea temperatures <10°C is required to ensure a good supply of larvae (Rognstad et al., 2014, Jenkins et al., 2000). During periods of high reproductive success, linked to cooler temperatures, the range of barnacles has been observed to increase, with range extensions in the order of 25 km (Wethey et al., 2011), and 100 km (Rognstad et al., 2014). The barnacle Semibalanus balanoides has a greater tolerance for cooler temperatures and a decrease in temperature may enhance recruitment success and replacement of Chthamalus spp. The tolerance of Semibalanus balanoides collected in the winter (and thus acclimated to lower temperatures) to low temperatures was tested in the laboratory. The median lower lethal temperature tolerance was -14.6°C (Davenport & Davenport, 2005).  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. The range of Chthamalus stellatus and Chthamalus montagui has been extending northwards due to increasing temperatures. Breeding of Chthamalus stellatus in France occurs in April (Barnes, 1992), and correlates with mean air and sea temperatures of 11 - 12°C, and maximum temperatures of 14°C. Barnes (1992) found that at an upper-temperature limit of 20 - 21°C in the sea and 24 - 25°C in the air reproductive activity decreased. Chthamalus suffers a failure of fertilization at temperatures of 9°C and below (Patel & Crisp, 1960), its lower critical temperature for feeding activity is 4.6°C (Southward, 1955). The cold winter of 2009-10 in France led to recruitment failure in Chthamalus species (Wethey et al., 2011). Semibalanus balanoides out-competes Chthamalus species for space, but recruitment declines and failures of Semibalanus balanoides in response to warmer temperatures benefit Chthamalus species by allowing them to persist and recruit (Mieszkowska et al., 2014).

Sensitivity assessment. The 'black lichen zone' (Ver) experiences the extremes of hot summers and cold frosty winters and is, therefore, adapted to extreme variation in temperature. It also occurs from North Africa to Scandinavia, so that it is unlikely to be adversely affected by changes in temperature at the benchmark level within Britain and Ireland. Similarly, chronic or acute change at the benchmark level may affect reproduction and survival or the difference barnacle species and affect the relative abundance of Semibalanus or Chthamalus. However, the biotope will remain as long as one of the characteristic barnacle species remains. Therefore, a resistance of High is suggested. Resilience is, therefore, likely to be High, and the biotope has been assessed as Not sensitive at the benchmark level. Ellis et al. (2007) modelled the effect of climate change scenarios on selected terrestrial lichens and identified potential threats to Northern montane and Boreal species, and uncertainties in the fate of species typical of the Atlantic coast margin, but no information on littoral species was found.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

The littoral fringe is likely to experience localised evaporation and a resultant increase in surface salinity during neap and low tides in hot summers and/or warm windy conditions. Fletcher (1980) noted that marine lichens in the lower littoral fringe died out in waters less than 20‰ while upper littoral fringe lichens were found in waters of 4-20‰ salinity.  However, Fletcher (1980) commented that loss of littoral lichens in estuaries can also be attributed to changes in pH, silt, reduced tidal range, and reduced wave exposure. Barnes & Barnes (1974) found that larvae from six barnacle species including Chthamalus stellatus and Semibalanus (as Balanus) balanoides, completed their development to nauplii larvae at salinities between 20-40% and some embryos exposed at later development stages could survive at higher and lower salinities.

Overall, littoral lichens receive regular inundation by seawater, unlike the supralittoral, and may not experience the extremes of salt spray. Nevertheless, there is not enough evidence to assess the sensitivity of the biotope to hypersaline conditions.

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

The littoral fringe is likely to experience localised evaporation and a resultant increase in surface salinity during neap and low tides in hot summers and/or warm windy conditions. Conversely, it is exposed to rainfall and freshwater runoff during low and neap tides. Fletcher (1980) noted that marine lichens in the lower littoral fringe died out in waters less than 20‰ while upper littoral fringe lichens were found in waters of 4-20‰ salinity. However, Fletcher (1980) commented that loss of littoral lichens in estuaries can also be attributed to changes in pH, silt, reduced tidal range, and reduced wave exposure.

Barnes & Barnes (1974) found that larvae from six barnacle species including Chthamalus stellatus and Semibalanus (as Balanus) balanoides, completed their development to nauplii larvae at salinities between 20-40% and some embryos exposed at later development stages could survive at higher and lower salinities. Barnes & Barnes (1965) found that in high suspended solids and low salinity there was a decrease in the number of eggs per brood of Chthamalus stellatus / Chthamalus montagui. If salinities decrease below 21 psu all cirral activity of barnacles normally associated with full salinity waters, ceases (Foster, 1971b). Semibalanus balanoides are tolerant of a wide range of salinity and can survive periodic emersion in freshwater, e.g. from rainfall or freshwater run-off, by closing their opercular valves (Foster, 1971b). They can also withstand large changes in salinity over moderately long periods of time by falling into a "salt sleep" and can be found on shores (example from Sweden) with large fluctuations in salinity around a mean of 24 (Jenkins et al., 2001).

Sensitivity assessment. The characteristic barnacles are probably adapted to changes in salinity. Hence, a reduction from full to reduced salinity may result in some mortality (resistance is 'Medium), although recovery is probably rapid (resilience is 'High'). However, the limited evidence suggests that littoral lichens would be adversely affected by a reduction of salinity and a resistance of 'Low' is suggested but at 'Low' confidence. Resilience is probably 'Medium', therefore, a sensitivity of 'Medium' is recorded.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

The littoral fringe is unlikely to be affected by changes in water flow as described in the pressure benchmark. Runoff due to heavy rainfall is possible but is outside the scope of the pressure. Therefore, the pressure is Not relevant.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

The emergence regime, that is the time covered or uncovered by the tide, is likely to change the frequency of drying and wetting of lichens, especially on sheltered shores. Fletcher (1980) noted that littoral lichens are emersed for several weeks during neap tides, during which time they are exposed to the hottest and dryest periods in summer and the coldest and most frost-prone periods in winter. The levels of moisture and relative duration of wet and dry periods are the most important factors controlling vertical zonation in marine lichens.  Rates of evaporation and hence desiccation is dependent on the slope and drainage of the shore, the rock type and its porosity, temperature and hence insolation and aspect, and wind exposure. Any activity that changes the exposure of the shore to wind, wave, rain or sunlight is likely to affect littoral lichen communities.

• Littoral lichens lost water faster than they absorbed it, over periods of up to 200 hrs, but that the reverse was true of supralittoral species (Fletcher, 1980). 
• Verrucaria mucosa (which occurs lower on the shore) is less efficient at water conservation than Verrucaria maura (Fletcher, 1980).
• Verrucaria maura is the only littoral lichen species found above the littoral fringe, although it is restricted to crevices that retain water (Fletcher, 1980).
• Littoral lichens were able to maintain photosynthesis after 35 days of immersion.
• All littoral species needed to be 30-50% water saturated for respiration and 40% saturated for photosynthesis but achieved maximum photosynthesis at 100% saturation.
• Fletcher (1976; cited in Fletcher, 1980) found no difference in photosynthesis and respiration between Verrucaria maura and Verrucaria mucosa after two days drought at 0% relative humidity but that the littoral lichens died quickly when exposed to cycles of 21 hr drought, and 3 days submersion over a period of 14 days.

Some regional variation occurs in the distribution of Chthamalus on the shore and its vertical zonation will be affected by wave splash and shore steepness. On shores in west Scotland, Chthamalus stellatus and Chthamalus montagui are restricted to high shores as Semibalanus balanoides, the northern species, is competitively superior at these latitudes (Connell, 1961a,b). Further south in the UK, the two genera coexist in the mid-shore (Crisp et al., 1981). Increased emergence would reduce the feeding time for attached suspension feeders within the biotope and the increased desiccation. It is likely that the distribution of Chthamalus stellatus will move further up the shore, with no noticeable difference in the range. Chthamalus stellatus / Chthamalus montagui are very tolerant of high periods of emersion, yet Patel & Crisp (1960) found that when barnacles which were brooding eggs were kept out of the water, a second batch of eggs was not produced. Decreased emergence is likely to lead to the habitat the biotope is found in becoming more suitable for the lower shore species generally found below the biotope, leading to replacement. Adults of Chthamalus stellatus can survive permanent submersion (Barnes, 1953). However, competition between Semibalanus balanoides is likely to play an important role in the changes in species distribution. Semibalanus balanoides is less tolerant of desiccation stress than Chthamalus barnacles species but is considered to out-compete Chthamalus spp. in the mid and lower shore.

Sensitivity assessment.  Water relations (Fletcher 1980) are vital to the zonation of marine lichens and the 'black lichen belt' exists in a distinct balance between immersion and emersion.  A decrease in emersion (increased inundation) would probably allow the 'black lichen belt' to extend up the shore (where suitable substratum exists) and replace supralittoral lichens at the bottom of the supralittoral. However, the lower littoral fringe would probably be lost to competition from macroalgae or barnacles, depending on the exposure of the shore, and the abundance of the characteristic barnacles would probably increase. Conversely, an increase in emersion (reduced inundation) would probably result in loss of the upper limit of the Verrucaria maura belt and its replacement by supralittoral lichens typical of the yellow-orange belt (e.g. Caloplaca spp.). Therefore, a decrease in emersion is likely to result is a slow shift in the biotope up the shore but an increase in emergence is likely to result in a rapid loss of Verrucaria spp. at its upper limit, based on observations by Fletcher (1976; cited in Fletcher, 1980).  Hence, a resistance of 'Low' is suggested. As resilience is probably 'Medium', a sensitivity of 'Medium' is recorded.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

LR.FLR.Lic.Ver and Ver.Ver are recorded from very wave exposed to very wave sheltered conditions while Ver.B is only recorded from wave exposed conditions (Connor et al., 2004). The 'black lichen band' tends to be wider in more wave exposed conditions, as the influence of wave action and splash are carried further up the shore.  Therefore, changes in wave exposure may either increase or decrease the width of the 'black lichen band' depending on the nature of the shore.  The extent of the band (especially Ver.B.) may extend on sheltered shore exposed to increased wave action but be reduced on wave exposed shores where the wave action is reduced, which suggests a Low resistance to change. Ver.B may be particularly sensitive to reduced wave exposure as it is only recorded from wave exposed shores. However, a change in significant wave height of 3-5% (the benchmark) is probably not significant on wave exposed shores, and might only be of minor benefit in the long-term on very sheltered shores. Therefore, a resistance of High is recorded, so that, a resilience of High and sensitivity of Not sensitive are recorded at the benchmark level.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

Lichens are known indicators of heavy metals in the environment, especially iron (Seaward, 2008). Seashore lichens often indicate environmental concentrations of heavy metals or accumulate them, frequently to very high levels (Fletcher, 1980). The accumulation of high levels of heavy metals may deter grazers (Gerson & Seaward, 1977). For example, Verrucaria maura was reported to accumulate Fe to 2.5 million times over the concentration in seawater, and Zn by a factor of 8000. Some species accumulate lead (Pb) to 100 ppm and cadmium (Cd) to 2 ppm of thallus dry weight (Fletcher, 1980). Heavy metals may be derived from rainfall, and dust as well as seawater (Fletcher, 1980). Gerson & Seaward (1977) noted that accumulated heavy metals could potentially accumulate up lichen-based food webs, e.g. the lichen to caribou to man food chain in Alaska. However, no information on bioaccumulation through littoral lichen communities was found. Overall, the ability of lichens to accumulate heavy metals to such high levels suggests a 'High' resistance to the heavy metal ions studied. Therefore, the lichen community is probably 'Not sensitive to heavy metal contamination.

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

Several studies have documented the effects of oil spills on marine lichen communities, although in many cases is difficult to separate the effects of oiling from the effects of dispersants.

• Ranwell (1968) noted that Verrucaria maura and Verrucaria mucosa were killed after the Torrey Canyon' due to oiling but especially emulsifiers (Kerosene based).
• Cullinane et al. (1975) recorded an oily film on the surface of Verrucaria maura but no apparent damage after the oil spill in Bantry Bay.
• Oiling and subsequent clean-up cause loss of (unspecified) lichen cover after the Sea Empress oil spill (Moore, 2006) but noted that high pressure washing did not kill Verrucaria maura.

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available. Several studies have documented the effects of oil spills on supralittoral lichen communities, although in many cases is difficult to separate the effects of oiling from the effects of dispersants. Most studies concluded that the decontamination methods, (including dispersants) were more toxic to lichens than the oil itself (see Hydrocarbon and PAH contamination above).

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

Lichens have also been reported to accumulate radionuclides in a similar manner to other heavy metals (see above) (Gerson & Seaward, 1977; Fletcher, 1980). Radionuclides could potentially accumulate up food webs based on lichen species, however, no further evidence was found.

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

The littoral fringe is rarely inundated and is often exposed to the air.  For example, Fletcher (1980) noted that Lichina confinis, a species that occurs at the top of the littoral fringe, spent a maximum of 1% of time submerged each year while Verrucaria striatula, a species that occurs in the lower littoral fringe below the Verrucaria maura, spent a maximum of 44% of time submerged each year.  Therefore, the 'black lichen belt' characterized by Ver.Ver and Ver.B are exposed to the air for the majority of the time. Even if the water lapping over the littoral fringe was deoxygenated, wave action and turbulent flow over the rock surface would probably aerate the water column. Hence, the biotope is unlikely to be exposed to deoxygenated conditions and 'Not relevant' is recorded.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

Nutrient levels are a determining factor in supralittoral lichen zonation (Fletcher, 1980) but the evidence of the importance of nutrient in the in the littoral fringe is less clear. Wootton (1991) examined the effects of bird guano on rocky shore lichens in the San Juan archipelago, Washington. Verrucaria mucosa cover declined in areas affected by guano but the decline was only significant in wave exposed sites where the cover of Prasiola meridionalis increased.  Connor et al. (2004) noted that Prasiola and opportunistic algae (e.g. Ulva and Porphyra) grow over the Verrucaria belt. However, no evidence on the effects on Verrucaria maura was found. Holt et al. (1995) suggested that smothering of barnacles by ephemeral green algae is a possibility under eutrophic conditions.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

Nutrient levels are a determining factor in supralittoral lichen zonation (Fletcher, 1980) but the evidence of the importance of nutrient in the in the littoral fringe is less clear. Wootton (1991) examined the effects of bird guano on rocky shore lichens in the San Juan archipelago, Washington. Verrucaria mucosa cover declined in areas affected by guano but was only significant in wave exposed sites where the cover of Prasiola meridionalis increased. Guano provides nitrates, phosphates, potassium and some salts (Wootton, 1991) but may introduce some organic material. In addition, organic-rich runoff, e.g. from agriculture and livestock, could introduce organic carbon to the littoral fringe.  Organic-rich runoff would probably result in Prasiola growth over the 'black lichen belt', where wave exposure allowed.  However, no direct evidence on the effects of organic enrichment in the littoral fringe was found and not sensitivity assessment was made.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very low’). Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’.  Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

The lichen community typical of this biotope is only found on hard substrata and dominates rocks in the littoral fringe. A change to a sedimentary substratum, however unlikely, would result in the permanent loss of the biotope. Therefore, the biotope has a resistance of 'None', with a 'Very low' resilience (as the effect is permanent) and, therefore, a sensitivity of 'High'. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

Not Relevant on hard rock biotopes.

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

Not Relevant on hard rock biotopes.

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Fletcher (1980) reported that the species diversity of lichens decreased in areas subject to mechanical damage, such as trampling, the passage of boats or vehicles, mining or physical removal due to building works.  In disturbed areas, the 'normal' lichen flora is replaced by disturbance tolerant species, typically faster-growing species. For example, the littoral zone is dominated by Arthopyrenia halodytes in disturbed areas (Fletcher, 1980). Dethier (1994) noted that Verrucaria mucosa was less susceptible to experimental brushing with 'steel brush' than other crustose species in the littoral, but that it became more susceptible to damage from a steel and a nylon brush when completely submerged. However, no information on Verrucaria maura was found. Verucaria maura was not killed by high pressure washing during the Sea Empress oil spill cleanup (Moore, 2006) but was removed by bulldozing of the shore after the Esso Bernica oil spill (Rolan & Gallagher, 1991), although it was removed because the surface of the rock itself was removed or damaged.

The effects of trampling on barnacles appear to be variable with some studies not detecting significant differences between trampled and controlled areas (Tyler-Walters & Arnold, 2008). However, this variability may be related to differences in trampling intensities and abundance of populations studied. The worst case incidence was reported by Brosnan & Crumrine (1994) who reported that a trampling pressure of 250 steps in a 20x20 cm plot one day a month for a period of a year significantly reduced barnacle cover at two study sites. Barnacle cover reduced from 66% to 7% cover in 4 months at one site and from 21% to 5% within 6 months at the second site. Overall barnacles were crushed and removed by trampling. Barnacle cover remained low until recruitment the following spring. Long et al. (2011) also found that heavy trampling (70 humans km^-1 shoreline h^-1) led to reductions in barnacle cover.  Single step experiments provide a clearer, quantitative indication of sensitivity to direct abrasion. Povey & Keough (1991) in experiments on shores in Mornington Peninsula, Victora, Australia, found that in single step experiments 10 out of 67 barnacles, (Chthamalus antennatus about 3mm long),  were crushed. However, on the same shore, the authors found that limpets may be relatively more resistant to abrasion from trampling. Following step and kicking experiments, few individuals of the limpet Cellana trasomerica, (similar size to Patella vulgata)  suffered damage or relocated (Povey & Keough, 1991). One kicked limpet (out of 80) was broken and 2 (out of 80) limpets that were stepped on could not be relocated the following day (Povey & Keough, 1991). Trampling may lead to indirect effects on limpet populations, Bertocci et al. (2011) found that the effects of trampling on Patella sp. increased the temporal and spatial variability of in abundance. The experimental plots were sited on a wave-sheltered shore dominated by Ascophyllum nodosum. On these types of shore, trampling in small patches, that removes macroalgae and turfs, will indirectly enhance habitat suitability for limpets by creating patches of exposed rock for grazing.  

Shanks & Wright (1986) found that even small pebbles (<6 cm) that were thrown by wave action in Southern California shores could create patches in Chthamalus fissus aggregations and could smash owl limpets (Lottia gigantea). Average, estimated survivorship of limpets at a wave exposed site, with many loose cobbles and pebbles allowing greater levels of abrasion was 40% lower than at a sheltered site. Severe storms were observed to lead to the almost total destruction of local populations of limpets through abrasion by large rocks and boulders.

Sensitivity assessment. There is little direct evidence on the effect of surface abrasion on the 'black lichen belt'.  Verucaria maura is crustose and closely adherent to the rock surface so may resist abrasion and only be removed where the abrasion destroys the rock surface.  However, the observation that fast growing lichen species come to dominate areas subject to disturbance (Fletcher, 1980) suggests that the 'black lichen belt' may be sensitive. Gastropods would probably be removed by abrasion and barnacle crushed, except where they occur in crevices.  Overall, a resistance of Medium is suggested to represent localised damage of the rock surface or long-term disturbance but with 'Low' confidence. As resilience is probably Medium and sensitivity assessment of Medium is recorded.

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Penetration is unlikely to be relevant to hard rock substrata. Therefore, the pressure is Not relevant. 

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

The littoral fringe is rarely submerged and is often exposed to the air. For example, Fletcher (1980) noted that Lichina confinis, a species that occurs at the top of the littoral fringe, spent a maximum of 1% of time submerged each year while Verrucaria striatula, a species that occurs in the lower littoral fringe below the Verrucaria maura, spent a maximum of 44% of time submerged each year.  Therefore, the 'black lichen belt' characterized by Ver.Ver and Ver.B are exposed to the air for the majority of the time. Hence, an increase in turbidity may not adversely affect the availability of light. Nevertheless, Fletcher (1980) noted that littoral fringe lichens die back in estuarine conditions but that loss of littoral lichens in estuaries can also be attributed to changes in salinity, pH, silt, reduced tidal range, or reduced wave exposure.  Therefore, an increase in turbidity due to suspended solids (at the benchmark) may be detrimental to the characteristic Verrucaria maura and a resistance of 'Medium' is suggested but at Low confidence. As resilience is probably 'Medium', sensitivity is assessed as 'Medium' at the benchmark level.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

No evidence on the effect of siltation or smothering by sediment on littoral lichens was found. The lack of littoral lichens in estuaries was attributed to siltation amongst other factors by Fletcher (1980) but not to smothering alone.  The barnacles that characterize this biotope are found permanently attached to hard substrata and are suspension feeders. They have no ability to escape from silty sediments that would bury individuals and prevent feeding and respiration.  However, no direct evidence for sensitivity to siltation was found. Therefore, no sensitivity assessment was made.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

No evidence on the effect of siltation or smothering by sediment on littoral lichens was found. The lack of littoral lichens in estuaries was attributed to siltation amongst other factors by Fletcher (1980) but not to smothering alone.  The barnacles that characterize this biotope are found permanently attached to hard substrata and are suspension feeders. They have no ability to escape from silty sediments that would bury individuals and prevent feeding and respiration.  However, no direct evidence for sensitivity to siltation was found. Therefore, no sensitivity assessment was made.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

No evidence was found. 

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

Not relevant

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

Verrucaria maura is well developed on both shaded and sunny coasts in Britain and Ireland but is considered a shade plant in North Africa, France and Scandinavia (Fletcher, 1980). Verrucaria mucosa and green forms of Verrucaria striatula increase in abundance on shaded shores and may, therefore, increase in abundance in the 'black lichen belt'.

Semibalanus balanoides sheltered from the sun grew bigger than unshaded individuals (Hatton, 1938; cited in Wethey, 1984), although the effect may be due to indirect cooling effects rather than shading. Barnacles are also frequently found under algal canopies suggesting that they are tolerant of shading. Light levels have also been demonstrated to influence a number of phases of the reproductive cycle in Semibalanus balanoides.  In general, light inhibits aspects of the breeding cycle. Penis development is inhibited by light (Barnes & Stone, 1972) while Tighe-Ford (1967) showed that constant light inhibited gonad maturation and fertilization. Davenport & Crisp (unpublished data from Menai Bridge, Wales, cited from Davenport et al., 2005) found that experimental exposure to either constant darkness, or 6 h light: 18 h dark photoperiods induced autumn breeding in Semibalanus. They also confirmed that very low continuous light intensities (little more than starlight) inhibited breeding. Latitudinal variations in the timing of the onset of reproductive phases (egg mass hardening) have been linked to the length of darkness (night) experienced by individuals rather than temperature (Davenport et al., 2005). Changes in light levels associated with climate change (increased cloud cover) were considered to have the potential to alter the timing of reproduction (Davenport et al., 2005) and to shift the range limits of this species southward.

However, it is not clear how these findings may reflect changes in light levels from artificial sources, and whether observable changes would occur at the barnacle population as a result. The artificial increase in light or shade may not adversely affect the littoral fringe, although seasonal opportunistic algae may be excluded and complete shade (darkness) may exclude even the lichens in the long-term. Therefore, resistance is probably 'High' albeit with 'Low' confidence, so that resilience is 'High' and the biotope is probably 'Not sensitive' at the benchmark level.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Not relevant

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

The pressure definition is not directly applicable to the littoral fringe so Not relevant has been recorded.  Collision via ship groundings or terrestrial vehicles is possible but the effects are probably similar to those of abrasion above.

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Lichens have no visual receptors, and the visual acuity of barnalces is probably limited to detecting shading by predators, so the pressure is Not relevant.

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

No evidence on the translocation, breeding or species hybridization in lichens or the characterizing barnacle species was found.

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

Essl & Lambdon (2009) reported that that only five species of lichen were thought to be alien in the UK, which is ca 0.3% of the UK's lichen flora.  All five species were Parmelia spp. epiphytes and unlikely to occur in the supralittoral. Essl & Lambdon (2009) note that no threat to competing natives has yet been demonstrated.  Although they note that information on the presence or spread of non-indigenous lichens is unclear due to the lack of data on lichen distribution across Europe.

The Australasian barnacle Austrominius (previously Elminius) modestus was introduced to British waters on ships during the second world war. However, its overall effect on the dynamics of rocky shores has been small as Austrominius modestus has simply replaced some individuals of a group of co-occurring barnacles (Raffaelli & Hawkins, 1999).  Although present, monitoring indicates it has not outnumbered native barnacles in the Isle of Cumbrae (Gallagher et al., 2015) it may dominate in estuaries where it is more tolerant of lower salinities than Semibalanus balanoides (Gomes-Filho et al., 2010). The degree of wave exposure experienced by this biotope will limit colonization by Austrominius modestus, which tends to be present in more sheltered biotopes.  These results may be applicable to Chthamalus sp.

Sensitivity assessment. Overall, there is little evidence of this biotope being adversely affected by non-native barnacle species and limited evidence on the effect of non-native lichens. Therefore, there is currently not enough evidence on which to base an assessment.

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

No evidence on disease or pathogens mediated mortality in lichens was found. The characterizing barnacles and the limpet Patella vulgata are considered subject to persistent, low levels of infection by pathogens and parasites.  For example, Patella vulgata has been reported to be infected by the protozoan Urceolaria patellae (Brouardel, 1948) at sites sheltered from extreme wave action in Orkney. Baxter (1984) found shells to be infested with two boring organisms, the polychaete Polydora ciliata and a siliceous sponge Cliona celata.

Sensitivity assessment. Based on the characterizing species and the lack of evidence for widespread, high-level mortality due to microbial pathogens the biotope is considered to have 'High' resistance to this pressure and therefore 'High' resilience (by default), the biotope is therefore considered to be 'Not sensitive'. 

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

No information concerning the use of marine lichens was found. Extraction of lichens will undoubtedly reduce their abundance but probably not the extent of the supralittoral zone.  However, No evidence of targeted removal was found. Similarly, barnacles are not subject to targeted removal.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

Verrucaria spp. are crustose lichens, thin and closely attached to the surface of hard rocks.  Similarly, barnacles are closely adherent to the rock surface. It is unlikely that they would be removed accidentally by any fishery activity at a commercial or recreational scale. Physical removal from rock by abrasion, or by removal of pieces of rock could occur during oil spill cleanup by high-pressure washing or bulldozing (Rolan & Gallagher, 1991; Moore, 2006) but physical abrasion is addressed under the relevant pressure above. Therefore, this pressure was considered to be Not relevant.