MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Audouinella purpurea and Cladophora rupestris on upper to mid-shore cave walls

25-01-2007
Researched byDr Harvey Tyler-Walters & Karen Riley Refereed byThis information is not refereed.
EUNIS CodeA1.444 EUNIS NameAudouinella purpurea and Cladophora rupestris on upper to mid-shore cave walls

Summary

UK and Ireland classification

EUNIS 2008A1.444Audouinella purpurea and Cladophora rupestris on upper to mid-shore cave walls
EUNIS 2006A1.444Audouinella purpurea and Cladophora rupestris on upper to mid-shore cave walls
JNCC 2004LR.FLR.CvOv.AudClaAudouinella purpurea and Cladophora rupestris on upper to mid-shore cave walls
1997 BiotopeLR.LR.Ov.RhoCvRhodothamniella floridula in upper littoral fringe soft rock caves

Description

Vertical and steeply-sloping upper walls at the entrances and inner reaches of upper to mid-shore caves that are partially sheltered from direct wave action characterised by a turf of the 'velvety' red seaweed Audouinella purpurea. Patches of green filamentous seaweed Cladophora rupestris can be present. The fauna is generally limited to limpets Patella spp., the winkle Littorina saxatilis and the barnacle Semibalanus balanoides, while they usually occur in low abundance. Filamentous or crust forming brown seaweeds may occur mixed with Audouinella purpurea, often becoming a zone in its own right (AudPil) above the AudCrup biotope. Other shade-tolerant red seaweed such as Catenella caespitosa and Lomentaria articulata may occur (but at lower abundance), and where freshwater seepage occurs, Ulva intestinalis can form patches. Some variation in the species composition of the individual caves must be expected depending on local conditions. Audouinella purpurea can be the only seaweed present in caves on the Thanet coast in south-east England. This biotope is known to occur in hard rock caves in north-east England and chalk caves in south-east England. In hard rock caves, this biotope is generally found on the upper walls above the CvOv.ScrFa and CvOv.FaCr biotopes and beneath the biotopes dominated by green and/or brown crusts (CvOv.GCv; CvOv.AudPil). In chalk caves, CvOv.AudCla may cover the lower and upper walls while it is usually found below CvOv.GCv and/or CvOv.AudPil.  (Information from Connor et al., 2004). Please note that Audouinella purpurea is now synonymous with Rhodochorton purpureum and Pilinia maritima is now synonymous with Pleurocladia lacustris.

Recorded distribution in Britain and Ireland

Recorded from the Northumberland coast, Thanet coast and south east England, south west England and the Llyn Peninsula, Wales in hard rock or chalk caves.

Depth range

Mid shore, Upper shore

Additional information

Both of the Rhodochorton purpureum (syn. Audouinella purpurea) biotopes LR.FLR.CvOv.AudCla and CvOV.AudPil  are very similar cave habitats and both are dominated by Rhodochorton purpurea. While other macroalgae or algal films may also occur, Rhodochorton purpureum is the dominant species. Therefore, the following sensitivity review represents both biotopes. Where relevant, differences in the sensitivity of Cladophora rupestris or Pleurocladia lacustris (syn Pilinia maritima) are highlighted. 

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JNCC

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

The biotopes LR.FLR.CvOv.AudCla and CvOv.AudPil are dominated by the velvety growth of Rhodochorton purpureum (syn. Audouinella purpurea). In CvOv.AudCla, Cladophora rupestris may be present while Pleurocladia lacustris (syn Pilinia maritima) occurs in CvOV.AudPil.  CvOV.AudPil usually occurs above CvOV.AudCla (Connor et al., 2004). Grazers such as Littorina saxatilis and Patella spp. occur and probably graze the macroalgae and microalgae present in the biotope. The dominance of Rhodochorton purpureum probably depends on the correct environmental conditions of the cave or cliff walls, of light, moisture versus desiccation, and hence wave splash or spray, that prevents competition from other macroalgae (e.g. Ulva, Fucus) and overgrazing. The presence of these biotopes below the green algal film biotope (CvOv.GCv) but above faunal turf biotope (CvOV.ScaFa and CvOV.FaCr) suggests they occur in lower to upper littoral fringe or supralittoral conditions (see also Conway & Knaggs, 1966). Therefore, Rhodochorton purpureum is the dominant important characterizing species in both biotopes, and is used to indicate the sensitivity of the biotope in the following review. Where relevant, differences in the sensitivity of Cladophora rupestris or Pleurocladia lacustris (syn Pilinia maritima) are highlighted.

Resilience and recovery rates of habitat

Rhodochorton purpureum (syn. Audouinella purpurea) has a triphasic life cycle that alternates between a gametophyte, tetrasporophyte and carposporophtye stage. The gametophyte and tetrasporophyte phases produce monospores, capable of replacing the parent plant. Gamateophytes produce sexual spores (sperm and carpospores) while the tetrasporophyte produced tetrapsores that give rise to gametophytes (Conway & Knaggs, 1966; Stegenga, 1978). All spores are typically non-motile.  Growth and sporulation were greatest at high light intensities (up to 5000 lux) but lowest at low intensity (150 lux) (West, 1972). Vegetative growth was greatest in long day lengths, yet sporulation was greatest in short day lengths (e.g. winter months) (West, 1972). Rhodochorton purpureum spores attach to the substratum via a sticky rhizoid (Pearlmutter & Vadas, 1978). However, Rhodochorton purpureum can regenerate from fragmented filaments and vegetative growth (Pearlmutter & Vadas,1978). In culture, regeneration was detected within 24-48 hrs, and new cells developed with 20 days in 89% of samples. Filaments may also be transported by grazers. Breeman & Hoeksema (1987) noted that grazers fragmented the thallus but more importantly, carried viable filaments through their digestive tracts and deposited them within their faeces, from which filaments could then grow. They also found small tufts of Rhodochorton purpureum on bare substratum growing from sticky detritus rich faecal pellets (Breeman & Hoeksema,1987).

Little information on recruitment or the life history of Pleurocladia lacustris (syn Pilinia maritima) was found. Wilce (1966) suggested that it was more widespread and common than thought. It is seasonal in the Artic (Wilce, 1966) present in the Arctic summer suggesting that it can recruit annually. Many species of epifauna, such as Patella spp. and Littorina saxatlis and polychaetes that may be associated with rock crevices, have long lived pelagic larvae and/or are highly motile as adults.

Information on the ecology of reproduction and propagation of the genus Cladophora is limited. Reproduction is achieved by the release of quadriflagellate zoospores and biflagellate isogametes (‘swarmers’) formed in the terminal cells of fronds. The life history consists of an isomorphic (indistinguishable except for the type of reproductive bodies produced) alternation of gametophyte and sporophyte generations, the plants are dioecious (Burrows, 1991). Both zoospores and gametes can be found at most times of the year. Archer (1963, cited in Burrows, 1991) was unable to find any correlation between the time of reproduction, the state of tide or environmental conditions. these basal holdfasts may serve as resistant structures from which new growths can arise. Therefore, it is likely that Cladophora rupestris will have a considerable capacity for recovery. The species is widespread around the British Isles and Ireland, and may be found in reproductive condition all year round. Numerous motile 'swarmers' (reproductive propagules) are released and in the water column they can be dispersed over considerable distances. In addition to recruitment by swarmers, new growth may arise from the resistant multicellular branching rhizoids (van den Hoek, 1982) that may remain in situ. For instance, after the Torrey Canyon tanker oil spill in mid-March 1967, recolonization by sporelings of Ulva and Cladophora had colonized by the end of April (Smith, 1968).  

Resilience assessment. Although Rhodochorton purpureum spores are non-motile, they are numerous. It can also be transported by fragmentation and by grazers.  It is recorded from the eulittoral, the supralittoral and ‘almost terrestrial’ habitats with maritime influence (Conway & Knaggs, 1966). It is also widely distributed in the North East Atlantic (OBIS, 2016) and recorded from Chile, California, Washington and Alaska (West, 1972). Therefore, its life history and distribution suggests that is could recolonize suitable habitat rapidly, although no information on growth rates was found.  Similarly, Cladophora spp. are probably an opportunistic species capable of rapid recruitment and growth. Although, no direct evidence on Pleurocladia lacustris was found, many Ectocarpales are opportunistic species.  Therefore, recovery of the dominant species Rhodochorton purpureum is probably rapid, even after significant damage, and resilience has been assessed as High.

Hydrological Pressures

 ResistanceResilienceSensitivity
High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

The percentage of plants of Rhodochorton purpureum sporulating was greatest at 10°C from Washington and Alaska, but greatest at 15°C in plants from California but plants from Chile sporulated between 10 and 15°C (West, 1972). But sporulation was 'strikingly' inhibited above or below these optima. Gametogenesis was greatest at 15°C but reduced below 10 (West, 1972). Tetrasporophytes survived at 25°C in the laboratory but exhibited aberrant growth (Stegenga, 1978). In the Shetland Isles, Conway & Knaggs (1966) recorded Rhodochorton purpureum along the top of cliffs 200 feet high, suggesting that it can tolerate supralittoral conditions, exposed to high summer temperatures and low winter temperatures.  It is also widely distributed in the North East Atlantic, and occurs in California, suggesting that it would be resistant of an increase in temperature at the benchmark level within the UK. In addition, the biotopes occur in the darker or shaded areas of caves, protected from strong sunlight and, in the presumably humid or moist areas of caves, protected from desiccation due to the sun and the wind.

Fortes & Lüning (1980) and Lüning (1984) reported that Cladophora rupetrsis from Helgoland were able to survive at temperatures between 0 -28°C (for a period of a week), so the species is likely to tolerate the benchmark acute increase in temperature, the species is also characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days. The biotope CvOv.AudPil also occurs on the upper littoral level of cliffs, where is could receive heating from sunlight. However, Pleurocladia lacustis is recorded from Devon Island in the Arctic, Greenland, Novaya Zemlya, south to the Baltic and the French Mediterranean (Wilce, 1966).

Overall, the important characterizing species are probably resistant of an increase in temperature at the benchmark level within the UK. Therefore, a resistance of High is recorded, so that resilience is also High and the biotope is assessed as Not sensitive.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

The percentage of plants of Rhodochorton purpureum sporulating was greatest at 10°C from Washington and Alaska, but greatest at 15°C in plants from California but plants form Chile sporulated between 10 and 15°C (West, 1972). But sporulation was 'strikingly' inhibited above or below these optima. Gametogenesis was greatest at 15°C but reduced below 10 (West, 1972). In the Shetland Isles, Conway & Knaggs (1966) recorded Rhodochorton purpureum along the top of cliffs 200 feet high, suggesting that it can tolerate supralittoral conditions, exposed to high summer temperatures and low winter temperatures. It is also widely distributed in the North East Atlantic, and occurs in California, suggesting that it would be resistant of an increase in temperature at the benchmark level within the UK. In addition, the biotopes occur in the darker or shaded areas of caves, protected from strong sunlight and, in the presumably humid or moist areas of caves, protected from desiccation due to the sun and the wind.

Fortes & Lüning (1980) and Lüning (1984) reported that Cladophora rupetrsis from Helgoland were able to survive at temperatures between 0 -28°C (for a period of a week), so the species is likely to tolerate the benchmark acute increase in temperature, the species is also characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days. The biotope CvOv.AudPil also occurs on the upper littoral level of cliffs, where is could receive heating from sunlight. However, Pleurocladia lacustis is recorded from Devon Island in the Arctic, Greenland, Novaya Zemlya, south to the Baltic and the French Mediterranean (Wilce, 1966).  In addition, Wilce (1966) noted that it must be able to withstand the intense freezing and thawing associated with the start of the growing season in the Arctic.

Overall, the important characterizing species are probably resistant of a decrease in temperature at the benchmark level within the UK. Therefore, a resistance of High is recorded, so that resilience is also High and the biotope is assessed as Not sensitive.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

Rhodochorton purpureum is recorded as an epiphyte on laminarian stipes in the subtidal, and a lithophyte under fucoids in the littoral, in caves in the littoral or littoral fringe, on cliffs and cliff tops in the supralittoral, and in a freshwater waterfall in a shallow cave (Shetland) (Conway & Knaggs, 1966; Connor et al., 2004; Guiry & Guiry, 2015). In experiments, West (1972) noted that clones of Rhodochorton purpureum from the upper littoral showed little response to a change in salinity, and were able to sporulate at 10‰, and 20‰ but that clones from the mid-littoral showed the poorest ability to sporulate at the salinities tested (10, 20 and 30‰). Nevertheless, Rhodochorton purpureum found on cave walls is probably resistant of a wide range of salinities as it occupies a littoral fringe or supralittoral position on the shore.

Cladophora rupestris found in intertidal rock pools can withstand 5-30 psu (Jansson, 1974) and as the species is successful in the high intertidal zone it is likely that the species has a broad salinity tolerance (Dodds & Gudder, 1992). However, Thomas et al. (1988) found that, at extreme temperatures, Cladophora rupestris had a reduced salinity tolerance range, e.g. the most marked inhibition of photosynthesis occurred in conditions of low salinity (0 psu) and high temperatures (25 - 30°C). Pleurocladia lacustris was reported from the upper littoral of limestone shores, exposed to freshwater runoff and rainfall until the breakup of the ice sheet, after which conditions are fully marine (Wilce, 1966).  

Sensitivity assessment. The important characterizing species are typical of upper littoral and supralittoral habitats. Therefore, they are probably exposed to a wide range of salinities, from running freshwater and rainfall, for fully marine and salt deposited by spray and splash, especially on cliffs. The biotopes are probably resistant of a change in salinity from full to reduced or low. Therefore, resistance is assessed as High, so that resilience is High and the biotope assessed as Not sensitive.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

Rhodochorton purpureum is recorded as an epiphyte on laminarian stipes in the subtidal, under fucoids in the littoral, in caves in the littoral or littoral fringe, on cliffs and cliff tops in the supralittoral, and in a freshwater waterfall in a shallow cave (Shetland) (Conway & Knaggs, 1966; Connor et al., 2004; Guiry & Guiry, 2015). In experiments, West (1972) noted that clones of Rhodochorton purpureum from the upper littoral showed little response to a change in salinity, and were able to sporulate at 10‰, and 20‰ but that clones from the mid-littoral showed the poorest ability to sporulate at the salinities tested (10, 20 and 30‰). Nevertheless, Rhodochorton purpureum found on cave walls is probably resistant of a wide range of salinities as it occupies a littoral fringe or supralittoral position on the shore.

Cladophora rupestris found in intertidal rock pools can withstand 5-30 psu (Jansson, 1974) and as the species is successful in the high intertidal zone it is likely that the species has a broad salinity tolerance (Dodds & Gudder, 1992). However, Thomas et al. (1988) found that, at extreme temperatures, Cladophora rupestris had a reduced salinity tolerance range, e.g. the most marked inhibition of photosynthesis occurred in conditions of low salinity (0 psu) and high temperatures (25 - 30°C). Pleurocladia lacustris was reported from the upper littoral of limestone shores, exposed to freshwater runoff and rainfall until the breakup of the ice sheet, after which conditions are fully marine (Wilce, 1966).  

Sensitivity assessment. The important characterizing species are typical of upper littoral and supralittoral habitats. Therefore, they are probably exposed to a wide range of salinities, from running freshwater and rainfall, for fully marine and salt deposited by spray and splash, especially on cliffs. The biotopes are probably resistant of a change in salinity from marine to reduced, or reduced to low. Therefore, resistance is assessed as High, so that resilience is High and the biotope assessed as Not sensitive.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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.

Low High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Rhodochorton purpureum (syn. Audouinella purpurea) is recorded from s recorded as an epiphyte on laminarian stipes in the subtidal, and a lithophyte under fucoids in the littoral, in caves in the littoral or littoral fringe, on cliffs and cliff tops in the supralittoral, and in a freshwater waterfall in a shallow cave (Shetland) (Conway & Knaggs, 1966; Connor et al., 2004; Guiry & Guiry, 2015). It is, therefore, found in a variety of emergence regimes.  Cladophora rupestris is also recorded from the sublittoral fringe to the supralittoral (Connor et al., 1997a) while Pleurocladia lacustris (syn Pilinia maritima) is primarily recorded from upper littoral or littoral fringe habitats (Wilce, 1966). However, the Rhodochorton purpureum dominated biotopes only occur in shaded areas of caves, sheltered from wave action, or on cliff faces, presumably moist and shaded enough to support the biotope. Changes in emergence will probably affect the degree of splash and spray, and, hence, moisture, desiccation and salinity experienced by the biotopes. Therefore, a change in wave exposure will probably affect the upper and lower extent of the biotopes, and result in loss of extent.  Therefore, a resistance of Low is recorded. Resilience is probably High (albeit at Low confidence), therefore, a sensitivity of Low is recorded.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

These biotopes (CvOv.AudCla and CvOv.AudPil) occur on the entrances and inner reaches of upper to mid-shore caves that are partially sheltered from direct wave action, in moderately wave exposed to wave sheltered shores (Connor et al., 2004). Wave surge, splash and spray keep the rock surface moist while the cave habitat maintains the humidity. AudPil can also occur on upper littoral cliffs. Changes in wave action will probably affect the degree of splash and spray, and, hence, moisture, desiccation and salinity experienced by the biotopes. Therefore, a change in wave exposure will probably affect the upper and lower extent of the biotopes, and 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.

Chemical Pressures

 ResistanceResilienceSensitivity
Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Smith (1968) reported Cladophora rupestris to be amongst algae of unhealthy appearance following exposure to oil dispersants. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/dispersant mixtures, with little difference between adults, sporelings, diploid or haploid stages (Grandy, 1984, cited in Holt et al., 1995). In addition, Cole et al. (1999) suggested that the herbicides Atrazine, Simazine, Diuron, Linuron and the insecticide Dimethoate were probably very toxic to algae. However, this biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The littoral fringe and supralittoral and cave ceilings are rarely inundated and are, therefore, permanently exposed to the air. The biotope is unlikely to be exposed to deoxygenated conditions.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Maritime cliff plant and algae communities are probably nutrient poor, i.e. lack nutrients. An increase in nutrients in the form of runoff from adjacent agricultural land may benefit the communities. The opportunistic filamentous algae such as Ulothrix sp. and Urospora sp. may overgrow these biotopes. However, no evidence concerning the effects of nutrient enrichment on these communities was found.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Maritime cliff plant and algae communities are probably nutrient poor, i.e. lack nutrients. An increase in nutrients in the form of runoff from adjacent agricultural land may benefit the communities. The opportunistic filamentous algae such as Ulothrix sp. and Urospora sp. may overgrow these biotopes. However, no evidence concerning the effects of nutrient enrichment on these communities was found.

Physical Pressures

 ResistanceResilienceSensitivity
None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

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.

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

These biotopes require hard or soft rock substrata. 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.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not Relevant on hard rock biotopes. Where present, it is unlikely that chalk would be replaced by sediment in the littoral fringe or supralittoral.  Therefore, this pressure is Not relevant. However, change in substratum type is address above.

None High Medium
Q: High
A: High
C: High
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Extraction of sediment, as described under this pressure, is not relevant in hard rock habitats. However, soft rocks could suffer extraction due to tunnelling, mining or construction. Therefore, removal of chalk from the cliff or caves would remove the surface resulting in loss of the biotope. Resistance would, therefore, be None where it occurs on chalk or other soft rocks. But if the existing substratum (chalk) remains in the same habitat (upper littoral fringe to supralittoral) then the biotope would recover rapidly and resilience is probably High, therefore, sensitivity to extraction is probably Medium.

Low High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

The characterizing species are filamentous, lithophytes, and probably fairly soft and fragile.  These algal communities are likely to be removed as a result of any abrasion, e.g. from vessel grounding, the abrasion from chains or cables, or recreational access and trampling, especially where the friable (e.g. chalk) rock surface is removed. Therefore, resistance is probably Low (depending on the scale of the impact). However, recovery is likely to be rapid if suitable substratum remains so that resilience is probably High and sensitivity is probably Low.

Low High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Penetration by mobile fishing gear is unlikely to occur in caves or on vertical chalk cliffs. However, soft rock, by definition, can be damaged by other penetrative activities, for example during construction. Therefore, where these biotopes occur on chalk (e.g. CvOv.AudPil) resistance is probably Low (depending on the scale of the impact). However, recovery is likely to be rapid if suitable substratum remains so that resilience is probably High and sensitivity is probably Low.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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

Medium High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

The 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.  The fine 'velvety' mat of Rhodochorton purpureum, filaments of Cladophora rupestris or Pleurocladia lacustris may trap sediment and result in localised anoxia near the base of the plant. This may cause death, where the slope of the rock is sufficient for sediment to be deposited and the wave action so limited that sediment is not removed quickly.  It is possible, therefore, that a proportion of the biotope (on shallow sloping or horizontal surfaces) could be lost and a resistance of Medium is recorded. Resilience is probably High, so that a sensitivity of Low is suggested, albeit at Low confidence.

Medium High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

The 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, 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.  The fine 'velvety' mat of Rhodochorton purpureum, filaments of Cladophora rupestris or Pleurocladia lacustris may trap sediment and result in localised anoxia near the base of the plant. This may cause death, where the slope of the rock is sufficient for sediment to be deposited and the wave action so limited that sediment is not removed quickly.  It is possible, therefore, that a proportion of the biotope (on shallow sloping or horizontal surfaces) could be lost and a resistance of Medium is recorded. Resilience is probably High, so that a sensitivity of Low is suggested, albeit at Low confidence.

Not Assessed (NA) Not Assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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. 

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found. 

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No relevant

Medium High Low
Q: Low
A: NR
C: NR
Q: Low
A: NR
C: NR
Q: Low
A: Low
C: Low

Red algae are more shade tolerant than their green or brown equivalents. West (1972) noted that vegetative growth and gametogenesis of Rhodocorton purpureum was greatest in long day lengths (summer months), that sporulation and growth were greatest at highest light intensity tested (5000 lux), yet spermatangia and carpogonia production was greatest in short days (winter months), but concluded that the observations were not true photoperiodism. It may be that long summer days promote growth and asexual reproduction while short days and winter months promote sexual reproduction.  No evidence on the effects of light on the other characteristic species was found. 

These biotopes are characteristic of shaded or dark, moist caves, presumably because green algae would out-compete the dominant species at higher light levels. If artificial lighting was introduced to a cave where this biotope occurred, then it might adversely affect the biotopes by promoting green algal growth. Increased shaded might allow the biotope to increase in extent, or reduce light levels below those needed for the algae to survive. Therefore, a resistance of Medium is suggested at Low confidence. However, resilience is probably High, so that sensitivity is Low.

 

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant has been recorded. 

Biological Pressures

 ResistanceResilienceSensitivity
No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found to suggest that the macroalgae that characterize these biotopes were subject to translocation, nor that they were subject to genetic modification or hybridization with other similar species.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence was found.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The algal communities characteristic of these biotopes are unlikely to be targetted by any commercial or recreational fishery or harvest.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Incidental removal the dominant characteristic species would result in loss of the entire biotope. Where present, mobile invertebrate or gastropod fauna are probably not entirely dependent on the biotope for food or habitat and would forage elsewhere.  However, soft rock and hard rock cave communities are unlikely to be targetted by any commercial or recreational fishery or harvest. Accidental physical disturbance due to access (e.g. trampling) or grounding is examined under abrasion above.

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Citation

This review can be cited as:

Tyler-Walters, H. & Riley, K. 2016. Audouinella purpurea and Cladophora rupestris on upper to mid-shore cave walls. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/39

Last Updated: 25/03/2016