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

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. Dethier (1994) reported that Verrucaria mucosa transplanted to a high shore pool consistently died in the summer months. In addition, control transplantations in emergent shaded areas all survived while transplantations into emergent sunny areas all died (Dethier, 1994). This suggests, therefore, that Verrucosa mucosa is sensitive to the effect of direct insolation but it is unclear whether this is due to desiccation or temperature.  Nevertheless, Verrucaria mucosa is recorded from around the coasts of the British Isles, north to Iceland and south to the Cape Verde islands (OBIS 2016), and in Washington State, USA (Dethier, 1994). 

Hildenbrandia rubra is found from the littoral fringe down to the subtidal and has a cosmopolitan distribution from Iceland, Alaska and Baffin Bay in the north to South America, South Africa, India and Australia in the south (OBIS, 2016).  Kim & Garbary (2006). reported that Hildenbrandia rubra was one of the most physiologically tolerant seaweed tested.  In laboratory tests, Hildenbrandia rubra thalli were exposed to temperatures between -17 to 27°C, from fully hydrated to extremely desiccated, from full seawater to 4 psu and back again over a period of 13 days, without any apparent long-term effects to the photosynthetic apparatus, and no significant difference in photosynthesis (Kim & Garbary, 2006). 

Both species are likely to be exposed to a range of temperatures across their range and are probably resistant to temperature change at the benchmark level. Hence, a resistance of High is suggested, so that resilience is also High, and the biotope is assessed as Not sensitive at the benchmark level, albeit with Low confidence.

Temperature decrease (local)

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

Evidence

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. Nevertheless, Verrucaria mucosa is recorded from around the coasts of the British Isles, north to Iceland and south to the Cape Verde islands (OBIS, 2016), and in Washington State, USA (Dethier, 1994). 

Hildenbrandia rubra is found from the littoral fringe down to the subtidal and has a cosmopolitan distribution from Iceland, Alaska and Baffin Bay in the north to South America, South Africa, India and Australia in the south (OBIS, 2016).  Kim & Garbary (2006). reported that Hildenbrandia rubra was one of the most physiologically tolerant seaweed tested.  In laboratory tests, Hildenbrandia rubra thalli were exposed to temperatures between -17 to 27°C, from fully hydrated to extremely desiccated, from full seawater to 4 psu and back again over a period of 13 days, without any apparent long-term effects to the photosynthetic apparatus, and no significant difference in photosynthesis (Kim & Garbary, 2006). 

Both species are likely to be exposed to a range of temperatures across their range and are probably resistant to temperature change at the benchmark level. Hence, a resistance of High is suggested, so that resilience is also High, and the biotope is assessed as Not sensitive at the benchmark level, albeit with Low confidence.

Salinity increase (local)

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

Evidence

This biotope occurs on the ceilings and walls of caves, depending on their size and degree of wave exposure (and hence spray, and splash) and probably represent an extension of lower littoral fringe and upper littoral into caves. The littoral fringe and upper littoral are likely to experience localised evaporation and resultant increased surface salinity during neap and low tides in hot summers and/or warm windy conditions. However, the cave environment could protect species from wind and insolation (depending on size and aspect) and, hence, protect the habitat from increased salinity due to the evaporation of seawater and spray. 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. Similarly, Hildenbrandia rubra is recorded from fully marine and estuarine conditions, as well freshwater seeps (Peckol & Searles, 1983; Irvine & Chamberlain, 1994).  Nevertheless,  there is not enough evidence to assess their sensitivity 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

This biotope occurs on the ceilings and walls of caves, depending on their size and degree of wave exposure (and hence spray, and splash) and probably represent an extension of lower littoral fringe and upper littoral into caves. The littoral fringe and upper littoral are likely to experience localised evaporation and resultant increased surface salinity during neap and low tides in hot summers and/or warm windy conditions. However, the cave environment could protect species from wind and insolation (depending on size an aspect) and, hence, protect the habitat from increased salinity due to the evaporation of seawater and spray. 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. Similarly, Hildenbrandia rubra is recorded from fully marine and estuarine conditions, as well freshwater seeps (Peckol & Searles, 1983; Irvine & Chamberlain, 1994). Lüning (1990) reported that Hildenbrandia rubra was one of a few algae that could survive mesohaline (18-8‰) conditions. Kim & Garbary (2006) reported that Hildenbrandia rubra was one of the most physiologically tolerant seaweed tested.  In laboratory tests, Hildenbrandia rubra thalli were exposed to temperatures between -17 to 27°C, from fully hydrated to extremely desiccated, from full seawater to 4 psu and back again over a period of 13 days, without any apparent long-term effects to the photosynthetic apparatus, and no significant difference in photosynthesis (Kim & Garbary, 2006). 

Overall, a reduction from 'full' to 'reduced' salinity may result in loss of a proportion of the Verrucaria mucosa population in the upper intertidal while Hildenbrandia rubra is probably resistant. As this biotope occurs in shaded, moist caves and can extend to the ceilings of caves, its inundation and emergence are probably highly variable between caves.  Therefore, a resistance of Medium is suggested to represent the loss of the proportion of the population of Verrucaria mucosa most exposed to inundation. Resilience is probably Medium so that 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

Tidal influence in mid-littoral to supralittoral caves is probably is probably limited to the floor and sides of the caves, and the upper walls and ceilings only receive spray and splash. However, water movement, splash, spray in caves are probably wave mediated rather than due to tidal streams. Therefore, the biotope is unlikely to be affected by water flow as described by the benchmark and 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

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 is less efficient at water conservation than Verrucaria maura (which occurs higher on the shore, but can occur in this biotope) (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 of 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.
• Dethier (1994) reported that Verrucaria mucosa transplanted to a high shore pool consistently died in the summer months. In addition, control transplantations in emergent shaded areas all survived while transplantations into emergent sunny areas all died (Dethier, 1994). This suggests, therefore, that Verrucosa mucosa is sensitive to the effect of direct insolation but it is unclear whether this is due to desiccation or temperature.

Dethier (1994) also noted that Hildenbrandia rubra was tolerant of a range of intertidal stresses, and survived in high emergent rock and in’ desiccated mid-south areas’ but that it grew more slowly when transplanted to the highest zones examined and experienced only partial mortality compared to the other algal crusts tested. Kim & Garbary (2006) reported that Hildenbrandia rubra was one of the most physiologically tolerant seaweed tested.  In laboratory tests, Hildenbrandia rubra thalli were exposed to temperatures between -17 to 27°C, from fully hydrated to extremely desiccated, from full seawater to 4 psu and back again over a period of 13 days, without any apparent long-term effects to the photosynthetic apparatus, and no significant difference in photosynthesis (Kim & Garbary, 2006). 

Sensitivity assessment. Water relations (Fletcher 1980) are vital to the zonation of marine lichens and Hildenbrandia rubra is limited to the upper littoral and littoral fringe.  In this cave biotope, the shape and aspect of the cave presumably allows the wave surge, splash and spray to reach a greater height depending on exposure and emergence while providing protection from wind and insolation, so that the evaporation is reduced and moisture (humidity) is high, relative open rock.  A decrease in emersion (increased inundation) would probably allow the biotope to extend up to ceilings of caves, where suitable substratum exists. However, the lower littoral fringe would probably be lost to competition from macroalgae (see CvOv.AudCla) or barnacles, depending on the exposure of the shore. Conversely, an increase in emersion (reduced inundation) would probably result in loss of the upper limit of the biotope belt and its replacement by green algal films (see CvOv.GCv). 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

This biotope reaches upper walls and ceilings of caves directly affected by wave action (Connor et al., 2004), where wave surge, splash and spray keep the rock surface moist. It is recorded from caves that experience moderately wave exposed and wave exposed conditions. Therefore, an increase in wave exposure may increase the extent of the biotope, but a decrease in wave exposure is likely to result in loss of extent.  However, a 3-5% change in significant wave height is unlikely to be significant in wave exposed conditions. Therefore, the biotope is probably Not sensitive (resistance and resilience are High) 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 to 100 ppm and cadmium to 2 ppm of thallus dry weight (Fletcher, 1980). Heavy metals may be derived from rainfall, and dust as well as seawater (Fletcher, 1980). No information on the effects of heavy metals on Hildenbrandia rubra 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) reported that oil was absorbed onto the thallus of Verrucaria mucosa but not onto the surrounding crust of Hildenbrandia spp. after the oil spill in Bantry Bay and concluded that gelatinous (e.g. Verrucaria mucosa) or non-crustose lichens absorb oil and were easily damaged.
• 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). But no information on Hildenbrandia spp. was found.

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

In this cave biotope, the shape and aspect of the cave presumably allow wave surge, splash and spray to reach a greater height depending on exposure and emergence while providing protection from wind and insolation, so that the evaporation is reduced and moisture (humidity) is high, relative open rock. The biotope is probably an extension of the lower littoral fringe. The littoral fringe is 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, this biotope is probably 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 the pressure is assessed as 'Not relevant. 

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 in the intertidal.  In dark moist caves, while the moisture may allow Prasiola or other opportunitic algae to grow, the light regime may restrict their growth. However, no evidence on the effects on Hildenbrandia rubra was found. Nevertheless, this biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with good status as defined by the WFD.

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 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 in the intertidal.  In dark moist caves, while the moisture may allow Prasiola or other opportunitic algae to grow, the light regime may restrict their growth.  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 and algal crust community typical of this biotope is only found on hard substrata. This biotope is not recorded from chalk. 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. Hildenbrandia rubra was negatively affected by steel brushing in the field but lost less area than any other crust tested, other than the Petrocelis phase of Mastocarpus (Dethier (1994). In the laboratory, Hildenbrandia rubra it was one of the most resistant crusts tested (Dethier 1994). 

Verrucaria maura was not killed by high pressure washing during the Sea Empress oil spill clean-up (Moore, 2006) but Verrucaria spp. 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.

Sensitivity assessment. There is little direct evidence on the effect of surface abrasion as described by the pressure definition on this biotope or its characteristic species. Both Verrucaria mucosa and Hildenbrandia rubra are crustose and closely adherent to the rock surface so may resist abrasion and only be removed where the abrasion destroys the rock surface. The work of Dethier (1994) suggests that abrasion (e.g. by chains or cables) may be detrimental. However, the observation that fast growing lichen species come to dominate areas subject to disturbance (Fletcher, 1980) suggests that the biotope 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 abrasion and 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

This biotope occurs in mid to upper littoral and littoral fringe and reaches upper walls and ceilings of caves, probably only exposed to wave splash and rarely inundated. 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, an increase in turbidity due to suspended solids (at the benchmark) is unlikely to adversely affect the biotope and Not relevant is recorded.

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

The ceilings and upper, vertical walls of caves are unlikely to be subject to smothering, but the inner reaches of caves with shallow slopes or horizontal ledges may be.  In the wave exposed conditions experienced by this biotope, 5 cm of sediment may be removed quickly from the entrance but may persist in the inner reaches of the cave, depending on the shape of the cave. 

Algal crusts are considered to dominate in areas of disturbance, grazing or sand scour.  In experiments, Hildenbrandia occidentalis was partially covered by an opaque disk (Dethier & Steneck, 2001). It persisted ‘remarkably well’, paled slightly and showed only a small reduction in growth after one year.  Dethier & Steneck (2001) reported that Hildenbrandia spp. was found under barnacles and mussels that were several years old.  In similar experiments, Underwood (2006) Hildenbrandia rubra crusts covered partially or completely by black discs showed reduced growth, but the reduction was greatest when its thallus was separated from any unshaded thallus. However, after 13 months the crusts were alive in all plots even with a reduction in area of 44-98%. It was only eliminated in one site (Underwood, 2006). Underwood (2006) noted that Hildenbrandia rubra crusts could withstand overgrowth for some considerable time. In field experiments, crusts of Hildenbrandia rubra overgrown by foliose algae still had 55-65% cover (compared to 80-90% cover in controls) after 18 months (Underwood, 1980, 2006). Fletcher (1980) noted that littoral fringe lichens die back in estuarine conditions but that loss of littoral lichens in estuaries could also be attributed to changes in salinity, pH, silt, reduced tidal range or reduced wave exposure.

Sensitivity assessment.  The above evidence suggests that Hildenbrandia rubra would survive smothering by 5 cm of sediment, and it is probably resistant of scour.  The loss of littoral fringe lichens in estuaries suggests that siltation, scour or smothering may be involved, but is inconclusive.  In wave exposed conditions, if the smothering sediment is removed quickly, then Verrucaria mucosa would probably survive. Therefore, a resistance of High is suggested but with Low confidence. Therefore, resilience is recorded as High and the biotope is probably Not sensitive at the benchmark level.

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

The ceilings and upper, vertical walls of caves are unlikely to be subject to smothering, but the inner reaches of caves with shallow slopes or horizontal ledges may be. A deposit of 30 cm of fine sediment in caves is likely to remain in place for some time, depending on the degree of wave exposure. In the wave exposed conditions experienced by this biotope, 30 cm of sediment may be removed quickly from the entrance but may persist in the inner reaches of the cave.

 Algal crusts are considered to dominate in areas of disturbance, grazing or sand scour.  In experiments, Hildenbrandia occidentalis was partially covered by an opaque disk (Dethier &Steneck, 2001). It persisted ‘remarkably well’, paled slightly and showed only a small reduction in growth after one year.  Dethier & Steneck (2001) reported that Hildenbrandia spp. was found under barnacles and mussels that were several years old.  In similar experiments, Underwood (2006) Hildenbrandia rubra crusts covered partially or completely by black discs showed reduced growth, but the reduction was greatest when its thallus was separated from any unshaded thallus. However, after 13 months the crusts were alive in all plots even with a reduction in area of 44-98%. It was only eliminated in one site (Underwood, 2006). Underwood (2006) noted that Hildenbrandia rubra crusts could withstand overgrowth for some considerable time. In field experiments, crusts of Hildenbrandia rubra overgrown by foliose algae still had 55-65% cover (compared to 80-90% cover in controls) after 18 months (Underwood, 1980, 2006). Fletcher (1980) noted that littoral fringe lichens die back in estuarine conditions but that loss of littoral lichens in estuaries could also be attributed to changes in salinity, pH, silt, reduced tidal range or reduced wave exposure.

Sensitivity assessment.  The above evidence suggests that Hildenbrandia rubra would survive smothering by 5 cm of sediment, and it is probably resistant of scour.  The loss of littoral fringe lichens in estuaries suggests that siltation, scour or smothering may be involved, but is inconclusive.  Therefore, a resistance of Medium (<25% loss) is suggested to represent to the potential loss of Verrucaria mucosa from this biotope but with Low confidence. Therefore, resilience is recorded as Medium and sensitivity as Medium.

Litter

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

Evidence

Not assessed. Caves, especially high on the shore, may accumulate litter blown into the cave by the wind. Large pieces of marine debris blown around by wind or wave action may cause abrasion of the cave wall communities (see above). However, No evidence on the effects of litter was found. 

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

This biotope occurs at the entrances of wave exposed caves and forms a distinct band in dark moist conditions.  Fletcher (1980) noted that Verrucaria mucosa appeared black in sunlit areas but green in shaded areas, was black in summer and olive-green in winter, and that is increased in abundance on shaded shores, even in areas of wave exposure.

In experiments, Hildenbrandia occidentalis was partially covered by an opaque disk (Dethier &Steneck, 2001). It persisted ‘remarkably well’, paled slightly and showed only a small reduction in growth after one year.  Dethier & Steneck (2001) reported that Hildenbrandia spp. was found under barnacles and mussels that were several years old.  In similar experiments, Underwood (2006) Hildenbrandia rubra crusts covered partially or completely by black discs showed reduced growth, but the reduction was greatest when its thallus was separated from any unshaded thallus. However, after 13 months the crusts were alive in all plots even with a reduction in area of 44-98%. It was only eliminated in one site (Underwood, 2006). Underwood (2006) noted that Hildenbrandia rubra crusts could withstand overgrowth for some considerable time. In field experiments, crusts of Hildenbrandia rubra overgrown by foliose algae still had 55-65% cover (compared to 80-90% cover in controls) after 18 months (Underwood, 1980, 2006). Therefore, Hildenbrandia rubra is unlikely to be affected by shading.

Sensitivity assessment. The biotope is probably unaffected by shading (although a complete absence of light is detrimental to all algae and lichens).  An increase in sunlight may be detrimental but no evidence on the effect of artificial lighting in littoral caves was found. In terrestrial caves know for their archaeology artificial lights contribute to the increase in green algal growth but their environment is probably very different. Therefore, a resistance of High is recorded, so that resilience is High and the biotope is probably Not sensitive to this pressure.

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 caves, 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

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 algal crusts 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 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.  However, 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. Similarly, no information on non-native algal crustose species was found. Therefore, there is not enough evidence currently 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 was found.

Removal of target species

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

Evidence

Extraction of lichen and algal crusts will undoubtedly reduce their abundance.  But given their thin, encrusting and adherent form, extraction is unlikely.  However, No evidence of targetted removal was found.

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 and Hildenbrandia rubra is a crustose algae; both are thin and closely attached to the suface of hard rocks.  It is very 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.