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.

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. 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.

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.

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. 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.

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 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

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.

Overall, the limited evidence suggests that littoral lichens would be adversely affected by a reduction of salinity, for example from full to reduced 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.

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. 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 his 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 increase 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. 

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.

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 no 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.

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 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.  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.  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'. However, 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 at 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, 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 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. 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 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

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 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, thin and closely attached to the surface 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.