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

Supralittoral 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 (splash and spray), precipitation, dew, sunlight and shading.  The characterizing lichen species are widely distributed around Britain and Ireland and unlikely to be adversely affected by changes in temperature at the benchmark level. 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 supralittoral species was found.

Temperature decrease (local)

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

Evidence

Supralittoral lichens are exposed to extremes of temperature from hot, dry summers to cold, frosty winters. The characterizing lichen species are widely distributed around Britain and Ireland and unlikely to be adversely affected by changes in temperature at the benchmark level. However, a decrease in temperature is likely to decrease the risk of desiccation (see above) and increase the average humidity of the shore. Fletcher (1980) suggested that the lower average temperatures and increased rainfall of the shores of western Scotland resulted in a reduced xeric-supralittoral zone (the Ramalina siliquosa belt). Overall, the biotope will remain, and although the relative extent of the supralittoral lichen zones and species composition is likely to change in the long-term. 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. 

Salinity increase (local)

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

Evidence

The mesic-supralittoral is the only supralittoral zone subject to direct inundation by seawater. The supralittoral is exposed to a harsh regime of fluctuating salt (ionic) concentration due to deposition of wave splash or sea spray, subsequent evaporation and increased concentration, and the freshwater influences of rain, dew and runoff. Fluctuations in salt concentration and saline influence are important determinants of supralittoral zonation (Fletcher, 1980) Therefore, an increase in saline influence, e.g. via increased sea spray deposition is likely to have similar effects to that of increased wave exposure; an increase in the height of supralittoral zones, especially the xeric, on the shore, as the terrestrial lichens are pushed further inland.  Supralittoral lichen zones are likely to increase in extent, although it may take more than a year (see benchmark) for the effects to be observable and, therefore, a resistance of 'High' is recorded. As resilience is  'High' (by default), the biotope is assessed as 'Not sensitive'. (Please note the benchmark is not directly applicable to the supralittoral). 

Salinity decrease (local)

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

Evidence

A decrease in the extent of the biotope in estuaries is probably more related to the reduction of wave action and sea spray, and the lack of suitable substrata than a reduction in salinity itself. Increased freshwater runoff or rainfall is likely to allow halophilic terrestrial lichens and vegetation to colonize further down the shore, forming lichen communities similar to those of shaded shores. For example, Fletcher (1980) reported that the xeric-supralittoral zone was better represented in south west Britain and Ireland than western Scotland, where even wind exposed shores bear halophobic terrestrial species. Fletcher (1980) suggested that the increased rainfall and lower temperatures in western Scotland mitigated the effect of salinity and sea spray.

A reduction in saline influence is likely to allow more terrestrial species to colonize further down the shore, increasing species richness but reducing the extent of the biotope. The availability of water, salinity and pH are important factors in the zonation of supralittoral lichen communities, so that the biotope probably has a Medium sensitivity (a Medium resistance and resilience) to changes in salinity. However, it may take more than a year (see benchmark) for the effects to be observable and, therefore, a resistance of 'High' is recorded. As resilience is  'High' (by default), the biotope is assessed as 'Not sensitive'. (Please note the benchmark is not directly applicable to the supralittoral). 

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 supralittoral 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 amount of wave or wind driven spray and splash deposited on the supralittoral zone and, hence, the frequency of drying and wetting of lichens, especially on sheltered shores, The levels of moisture and relative duration of wet and dry periods are the most important factors controlling vertical zonation in supralittoral lichens. Water is supplied by tidal inundation, wave splash or sea spray at the bottom of the shore but by rainfall and runoff at the top of the shore. Rates of evaporation and hence desiccation is dependent of 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 supralittoral communities.

• The xeric-supralittoral receives the least amount of water from sea or land together with the greatest degree of evaporation and is, therefore, the driest and most drought-prone zone (Fletcher, 1980).
• The number of lichen species decreases on wind exposed shores, due to the loss of foliose species (e.g. Parmelia sp.), xeric-supralittoral and terrestrial lichens, and total lichen cover is reduced.
• Supralittoral lichens take up water faster than it is lost, unlike their littoral counterparts (Fletcher, 1980).
• Growth form and thallus structure affects desiccation rates with crustose and closely appressed forms having lower rates of water loss (Fletcher, 1980).
• Supralittoral lichens were reported to respire at 5-20% water saturation and photosynthesize at 10-30% although littoral species required 30-50% to respire and greater than 40% water saturation to photosynthesize (for further details see Fletcher, 1980).
• Exposure to 21 hr drought and 3 hr submersion for 14 days in supralittoral lichens broke down their symbiosis resulting in liberation of the microalgal symbiont. Fletcher (1980) concluded that the lichen symbiosis required a suitable balance of dry and wet periods for each species.

Although supralittoral lichens are probably highly tolerant of high levels of desiccation when compared to littoral species, each species probably lives within a narrow range of environmental conditions and are intolerant of changes in the moisture levels and desiccation (Jones et al., 1974; Holt et al., 1995).

An increase in emergence will reduce the inundation of the mesic and submesic supralittoral and littoral fringe, and reduce the upper extent of sea spray, especially on sheltered shores. Johannesson (1989) attributed the zone of bare rock (devoid of marine and terrestrial life) found on non-tidal rocky shores in Sweden, to prolonged periods of submergence and emergence due to changes in tidal height by atmospheric pressure. An increase in emergence could potentially allow the mesic and xeric supralittoral zones to increase in extent down the shore while halophilic terrestrial lichens may colonize the upper supralittoral. However, in one year (see benchmark) little difference is likely to be observed since lichens grow and colonize slowly, and the effects only manifest themselves if the change in emergence is prolonged.

A decrease in emergence will increase the inundation of the lower supralittoral (mesic and submesic zones) and may increase the effects of wave splash further up the shore.  In a one year period (see benchmark) the mesic and submesic species are likely to be reduced in extent while the littoral fringe communities are likely to increase in extent. If the decrease in emergence is prolonged the upper limit of the mesic and submesic zones is likely to increase while the extent of the xeric will decrease.

The classification of acarid mites into maritime, nomadic or terrestrial species is partly related to their response to inundation by seawater (Pugh & King, 1985b). The zonation of different species of acarid mites is partly determined by their tolerance to desiccation (Pugh & King, 1985b) so that the acarid species composition will probably change, with an increase in the number of terrestrial species.

Sensitivity assessment. Overall, the extent of the biotope in the lower supralittoral and its species richness is likely to decrease due to a decrease in emergence (increased inundation) and loss of the lower supralittoral so that the biotope probably has a Medium sensitivity (a Medium resistance and resilience) to changes in salinity.

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

The biotope has been recorded from very wave exposed to wave sheltered environments. Increased wave exposure raises the height of the lichen zones, reduces the number of species present and the overall lichen cover, and reduces the lower limit of terrestrial vegetation (Fletcher, 1973b,1980) due to an increase in the amount of wave splash and sea spray. As a result, the mesic and xeric zones increase in vertical extent. Increased wave action may remove some species, e.g. Xanthoria parietina which becomes restricted to fissures and crevices on wave exposed shores. On very wave exposed shores, littoral fringe and mesic-supralittoral lichen species may extend into the terrestrial zone. Overall, an increase in wave exposure is likely to increase the extent of the biotope, although species richness will decline. The extent of the area affected by sea spray (seawater droplets and salt) is also affected by wind exposure (see additional information below). It should be noted that the effects will probably take more than a year to become observable.

Lichen cover increases on shores sheltered from wave or wind generated sea spray but the vertical extent of the supralittoral zones are much reduced in extent due to downward penetration of terrestrial vegetation. The mesic-supralittoral is poorly represented on sheltered shores (Fletcher, 1973b, 1980). Therefore, a decrease in wave exposure is likely to reduce the extent of the supralittoral lichens zone, although the abundance of individual species present may increase, and a recognisable biotope remain.

Sensitivity assessment. Therefore, the supralittoral lichen communities are likely to exhibit a Medium resistance to changes wave exposure, with a Medium resilience and hence Medium sensitivity.  However, a 3-5% change in significant wave height (the benchmark) is unlikely to be significant except in the most sheltered examples of the biotope, where even a minor increase in wave action may allow the supralittoral lichens to increase in extent. Therefore, a resistance of High is recorded. Hence, resilience is High and the biotope is Not sensitive.

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). 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 supralittoral 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 supralittoral lichen communities, although in many cases is difficult to separate the effects of oiling from the effects of dispersants.

• Ranwell (1968) reported 19 species of lichens that were killed by oil or dispersants, including the characterizing species Lichina sp., Caloplaca marina, Caloplaca thallincola, Tephromela atra, Ochrolechia parella, Ramalina siliquosa, and Xanthoria parietina.
• Smith (1968) reported that Xanthoria parietina grew even under a covering of weathered oil while Crump & Moore (1997) noted that Caloplaca marina survived 10 months under weathered oil.
• Oil inundation caused discoloration of the thallus (e.g. Xanthoria parietina became dark brown), especially of the fruiting bodies, or bleaching of the thallus, while brittle tough thalli of Ramalina siliquosa and Lichina pygmaea became flaccid, soft and slimy (Cullinane et al., 1975).
• In Bantry Bay, Cullinane et al. (1975) reported that a spill of crude oil affected fructicose species most of all, crustose species the least while foliose species were affected at an intermediary level. Gelatinous and crustose lichens absorbed the oil and were removed from the substratum. Xanthoria parietina was the most severely affected species, while Ramalina siliquosa, Lichina pygmaea and Dermatocarpon miniatum were obviously affected (Cullinane et al., 1975). Cullinane et al. (1975) listed nine species of lichen damaged by oil.
• Crump & Moore (1997) reported that oiling with crude oil followed by fuel oil from the Sea Empress spill, severely damaged Ramalina siliquosa and Xanthoria parietina, resulting in necrosis, bleaching and peeling from the substratum. Almost all the Xanthoria parietina surviving after the spill in September 1996 had died by February 1997. Caloplaca thallincola was also damaged.
• Moore (2006) reported that the recovery of supralittoral lichen cover after the Sea Empress oil spill was faster in sunny sites than in shaded sites but varied with location, based on observations of quadrats ten years after the spill in west Angle Bay and Hopgang, south Wales. Moore (2006) reported that Caloplaca sp. grew quickly and showed signs of recovery soon after the oil had been removed while Xanthoria parietina could grow at 1 cm/year but Ochroleuca parella growth was slow at ca 1mm/year.
• On sunny south facing supralittoral rocks in West Angle Bay were 'covered in lichens' within five years but shaded north facing areas had large areas of bare rock ten years after the spill, although Caloplaca colonies grew back quickly (Moore, 2006). However, at Sawdern Point, Caloplaca colonization and growth was faster on areas that were left alone than areas subject to high pressure washing (Moore, 2006).
• At Hopgang, recovery of Ochroleucia parella was slow (Moore, 2006).

Several of the characterizing species are probably highly sensitive of oiling while others demonstrate sublethal effects and are likely to be damaged by oiling, depending on the type and weathering of the oil. Oiling is likely to have adverse effects of the invertebrate fauna, either through toxicity or smothering and especially through loss of the lichen habitat.

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.

Dispersants and detergents. 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.

• Ranwell (1968) reported 19 species of lichens that were killed by oil or dispersants, including the characterizing species Lichina sp., Caloplaca marina, Caloplaca thallincola, Tephromela atra, Ochrolechia parella, Ramalina siliquosa, and Xanthoria parietina.
• In Bantry Bay, walls washed with the detergent (dispersant ) BP1100X were very clean. Although crustose species were little affected, Caloplaca citrina had turned green, Physcia sp. and other foliose species were absent and Xanthoria parietina thalli had changed colour and were peeling off (Cullinane et al., 1975).
• Laboratory treatment (24hr) of lichens with dispersants resulted in discoloration, loss of chlorophyll and algal cells in several species (Brown, 1974).
• Heavy use of dispersants in Caerthillian Cove, after the Torrey Canyon oil spill, was reported to have 'annihilated' the lichen flora, and subsequent recolonization did not begin until 7 years later (Brown, 1974).
• Lichen communities were also reported to be affected by trampling during clean up and to be highly intolerant of high pressure spray washing techniques (see abrasion above) (Ranwell, 1968; Cullinane et al., 1975; Crump & Moore, 1997; Menot et al., 1998).

Air pollution. The effects of air pollutants on terrestrial lichens and their use as indicator species have been studied extensively (Holt et al., 1995) although few studies refer to maritime species (see reviews and bibliographies by Henderson (1999), Richardson (1992), NHM (2002), Nash, 2008). Fletcher (1980) suggested that supralittoral lichens were less resistant of air pollution than littoral species, and had disappeared in the Clyde estuary and north eastern England. Studies of terrestrial locations suggest that Xanthoria parietina was more resistant of air pollution than other lichens, although germination and growth were inhibited (Holt et al., 1995; Dobson, 2000). Jones et al. (1974) attributed dying Ramalina siliquosa, Verrucaria maura, Caloplaca marina and Lichina pygmaea, and a reduced cover of Xanthoria parietina in Bull Bay, Anglesey to fumes from a nearby petroleum plant, which were also reported to make working on the shore unpleasant.

Overall, lichen species sensitivities vary, many of the characterizing species are intolerant of atmospheric pollution and synthetic chemicals.

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 supralittoral is rarely inundated and is, therefore, permanently exposed to the air. The biotope is unlikely to be exposed to deoxygenated conditions.
 

Nutrient enrichment

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

Evidence

Nutrient levels are a determining factor in supralittoral lichen zonation. Nutrient-rich, acid runoff from terrestrial habitats influences the top of the supralittoral while saline, basic conditions dominate at the bottom of the shore. Heavy bird manuring can result in loss of the xeric-supralittoral to submesic lichen species such as Xanthoria parietina, Xanthoria candelaria and Caloplaca verruculifera (Fletcher, 1980). However, Xanthoria parietina is considered to be a nitrophilous species (Fletcher, 1980; Wootton, 1991; Armstrong, 1994; Honeggar, 1996). Wootton (1991) reported that the presence of guano on the shores of Washington State resulted in the loss of grey lichens allowing the orange lichens (Caloplaca marina and Xanthoria elegans) to colonize further up the shore (Wootton, 1991; Holt et al., 1995). The lichen Aspicilia leprosescens is exclusively associated with bird perches on siliceous rocks (Fletcher, 1980). Large populations of the lichen Candelariella vitellina on the shore are indicative of nutrient enrichment (Fletcher, 1980; Holt et al., 1995). Siliceous rocks are nutrient poor and dominated by grey lichens e.g. Ramalina siliquosa. It is likely that an increase in nutrients may promote lichen communities of more nutrient rich calcareous rocks or halophilic terrestrial lichen species.

Sensitivity assessment. Nutrient enrichment by bird manuring is likely to result in an increase in 'orange belt' submesic species but the biotope will still be identifiable. An increase in nutrient runoff from the terrestrial zone, e.g. due to agricultural fertilizer and sprays may allow the halophilic terrestrial lichens species or species typical of calcareous rocks to colonize further down the shore, reducing the extent of the supralittoral lichen zone. Therefore, the biotope may exhibit a Medium resistance to nutrient enrichment, albeit at low confidence. However, 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

Little evidence of the effects of organic enrichment was found. Wotton (1991) demonstrated an increase in the extent of orange lichens, and loss of grey lichens due to guano from seabirds (see nutrient enrichment), although guano is a rich source of nitrogen and phosphorus rather than organic materials. Similarly, Favero-Longo et al. (2011) described the major changes in coastal lichens (mainly terrestrial species) due to excretion by fur seals in the South Orkney Islands attributed to elevated levels of nitrogen. Fletcher (1980) noted that the organic content of water increases further up the shore in the xeric zone, due to runoff from terrestrial habitats.

Sensitivity assessment. No evidence on the effects of organic enrichment on supralittoral lichen communities was found and no 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 supralittoral lichen communities typical of this biotope are only found on hard substrata and dominate rocks in the supralittoral. 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

The biotope is susceptible to trampling by birds (in heavily populated sites), animals and man, animal rubbing and the physical abrasion caused by the wind.

• Physical abrasion by wind may discourage large foliose and fructicose lichens (Fletcher, 1980).
• Fletcher (1980) noted that large specimens of lichens, e.g. Ramalina siliquosa, were only found on vertical rocks inaccessible to animals, including man.
• James & Syratt (1987) noted that rubbing by animals (e.g. sheep) damaged lichens resulting in loss of parts of some thalli and loss of Ramalina siliquosa at some sites while it showed signs of regeneration at some sites.
• Trampling damage is greatest when the thallus is wet, causing it too peel from the surface, while when dry, some fragments are likely to remain to propagate the lichen (Fletcher, 1980).
• Physical disturbance of the lichen flora or substratum may reduce species richness and favour more rapid growing, disturbance tolerant species, e.g. Lecanora dispersa, Candelariella vitellina and Rinodina gennerii (Fletcher, 1980)
• Extreme physical abrasion due to high pressure water cleaning techniques (used to clear oil after spills), damaged lichens even at low pressures, especially Ramalina siliquosa, Xanthoria sp. and Caloplaca marina, and removed all supralittoral lichens at high pressures (Crump & Moore, 1997; Menot et al., 1998).

Sensitivity assessment. Animal trampling and rubbing are likely to remove a proportion of lichen thalli in the short-term, and alter the lichen communities in the long-term. Therefore, a resistance of Low has been recorded. Resilience is likely to be Low so that sensitivity is probably High.

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 supralittoral is rarely covered in water, except at its lowest extent on the shore and extreme high tides.  It is unlikely to be exposed to changes in water clarity due to changes in suspended sediment. Therefore, the pressure is 'Not relevant'.
 

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

Fletcher (1980) noted that littoral lichens were eliminated by silt deposition. But most supralittoral species are unlikely to be smothered by sediment. Smothering by wind-blown sediment and dust may occur on sloping surfaces. Smith (1968) noted that Xanthoria sp. survived when smothered by weathered oil in the splash zone, and Crump & Moore (1997) noted that Verrucaria maura and Caloplaca marina survived for 10 months under weathered oil. No information on the effects of smothering on the invertebrate fauna was found, although smothering by oil is probably detrimental. Overall, smothering will probably reduce photosynthesis and growth rates of lichens. Therefore, the biotope would probably survive and a resistance of High has been recorded. Hence, resilience is 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

Fletcher (1980) noted that littoral lichens were eliminated by silt deposition. But most supralittoral species are unlikely to be smothered by sediment. Smothering by wind-blown sediment and dust may occur on sloping surfaces. Smith (1968) noted that Xanthoria sp. survived when smothered by weathered oil in the splash zone, and Crump & Moore (1997) noted that Verrucaria maura and Caloplaca marina survived for 10 months under weathered oil. No information on the effects of smothering on the invertebrate fauna was found, although smothering by oil is probably detrimental. Overall, smothering will probably reduce photosynthesis and growth rates of lichens. Therefore, the biotope would probably survive and a resistance of High has been recorded. Hence, resilience is High and the biotope is probably Not sensitive at the benchmark level.

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 on the effects of electromagnetic fields 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

No evidence on the effects of noise or vibration was found. 

Introduction of light or shading

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

Evidence

Aspect and hence light intensity and duration affect lichen communities primarily by affecting temperature and hence moisture levels. Sunny shores tend to be dominated by orange and white photophilic lichens while shaded shores are dominated by greyer, shade-loving lichen species (see ecology). The supralittoral zones are reduced in height on shaded shores and the xeric-supralittoral is replaced by terrestrial lichens, resulting in an increase in species richness (Fletcher, 1980). However, the extent of the biotope is likely to be markedly reduced by shading. Therefore, a resistance of Low is suggested. Resilience is probably Low so that the biotope probably has a High sensitivity to shading, within the footprint of the activity or structure responsible.

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. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores.  But spore dispersal is not considered under the pressure definition and benchmarks, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores. But spore dispersal is not considered under the pressure definition and benchmark.

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 supralittoral 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, 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 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. 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

Lichens e.g. Ochrolechia parella, have been collected in the past for the manufacture of dyes. The collection of lichens to prepare lichen-dyed tweed has largely stopped (Richardson & Young, 1977), however, no information concerning the use of coastal lichens was found. Extraction of lichens will undoubtedly reduce their abundance but probably not the extent of the supralittoral zone.  However, No evidence on 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

No commercial or recreational activities thought to occur in the supralittoral are likely to remove lichens as by-catch or by accident. Recreational activities that traverse the supralittoral (e.g. recreational angling, access to the shore, or coasteering) are likely to result in physical abrasion, addressed above (see abrasion). Therefore, this pressure was considered to be Not relevant.