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

Faunal crusts on wave-surged littoral cave walls



UK and Ireland classification


The inner walls of caves, predominantly in the mid shore in wave-surged conditions dominated by barnacles Semibalanus balanoides, and Verruca stroemia, with patches of encrusting sponges such as Halichondria panicea and Grantia compressa and occasional patches of the mussel Mytilus edulis. Increased moisture allows a denser faunal population than LR.FLR.CVOV.ScrFa to develop within the cave. The limpet Patella vulgata, the sponge and spirorbid tube-forming polychaetes can be present. The hydroid Dynamena pumila and anemones such as Metridium dianthus and Actinia equina may occur towards the lower reaches of the cave. Where a dense faunal turf of barnacles or bryozoan crusts cover the cave walls, the biotope can also extend to cover the ceiling and may be accompanied by the bryozoan Alcyonidium diaphanum. Variations of this biotope may occur in mid and lower shore scoured caves in south Wales the rock is dominated by dense Sabellaria alveolata. In south-west England the rock can be completely covered by the barnacle Perforatus perforatus. There may be a variation in the species composition from cave to cave, depending on local conditions. (Information taken from the revised Marine Habitat Classification, Version 04.05: Connor et al., 2004.)

Depth range

Mid shore, Lower shore

Additional information


Listed By

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Habitat review


Ecological and functional relationships


Seasonal and longer term change


Habitat structure and complexity




Recruitment processes


Time for community to reach maturity


Additional information


Preferences & Distribution

Habitat preferences

Depth Range Mid shore, Lower shore
Water clarity preferencesNo information found
Limiting Nutrients Data deficient, No information found
Salinity preferences Full (30-40 psu)
Physiographic preferences
Biological zone preferences Eulittoral
Substratum/habitat preferences Bedrock, Caves
Tidal strength preferences No information
Wave exposure preferences Exposed, Moderately exposed, Sheltered
Other preferences Sheltered to exposed coasts.

Additional Information

This biotope is found on the vertical walls and ceilings of dark, damp caves. The caves must be damp in order to sustain the various soft bodied faunal and floral crusts.

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope


    Additional information

    A full species list was unavailable for this biotope. However, given the extreme habitat with which it is associated, species diversity is likely to be quite low with a noticeable absence of erect algal species.

    Sensitivity review


    This biotope is characterized by a transient and ephemeral community that is likely to change both spatially and temporally. As a result, the species chosen as indicative to sensitivity have all been listed as 'important other', since other designations suggest the species plays a permanent central role in the biotope. A representative of the groups of organisms most likely to be found in the biotope at a given time has been selected. Where relevant, species particularly prevalent in certain areas have also been included. For example, the acorn barnacle, Balanus perforatus, has been listed because in southwest records of this biotope, this species can reportedly completely cover the rock (Connor et al., 2004). In addition, the honeycomb worm Sabellaria alveolata may dominate the rock in wave scoured caves in south Wales.

    Overall, the acorn barnacle Semibalanus balanoides is reported to dominate this biotope (Connor et al., 2004). However, it does not necessarily characterize the biotope as the species composition associated with these cave walls is likely to change from cave to cave. Its presence is likely to competitively exclude other species in terms of space. The remaining six 'important other' species represent a further six phyla and are the representatives of such phyla that are likely to be most frequently associated with this biotope. The encrusting algae and sponge may cover large areas of the rock.

    Species indicative of sensitivity

    Community ImportanceSpecies nameCommon Name

    Physical Pressures

     IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
    High High Moderate Major decline Moderate
    All the key and important species associated with this biotope are permanently attached to the substratum and are unable to reattach themselves. Loss of the substratum would result in the loss of the entire biotope and, accordingly, intolerance has been assessed as high. Recoverability is expected to be high as the fauna associated with this biotope are ephemeral and no 'climax community' is known per se (see additional information).
    Tolerant Not relevant Not sensitive Not relevant Moderate
    This biotope is associated with wave surged areas. Such periodic surges would serve to flush clean the biotope and, therefore, any smothering would be short-lived. Furthermore, most of the substratum will be vertical or overhanging thereby preventing smothering. This biotope is likely to be tolerant to smothering at the benchmark level.
    Intermediate High Low Minor decline Low
    The effect of an increase in the amount of suspended sediment will depend partly on the nature of the sediment. An increase in coarse, sandy sediment, combined with the wave-surged nature of the habitat, could serve to scour species such as hydroids and bryozoans off the rock, especially in the lower reaches of the cave. It may also interfere with the delicate feeding apparatus of the suspension feeders. Furthermore, the feeding activity of suspension feeders on emergent rock, that rely on immersion by wave surges for feeding opportunities, may be prevented altogether if, in that short time, they spend all the time trying to clean their feeding apparatus. At the benchmark level it is likely that, over the course of one month, feeding opportunities will be reduced. This may be reflected in a reduced scope for growth and reproductive potential in the faunal crusts and other species. Delicate or annual species may experience some mortality. In contrast, an increase in the amount of suspended sediment will be beneficial to the establishment of Sabellaria alveolata which need the sediment for tube construction.

    Overall, however, intolerance has been assessed as intermediate with a high recovery (see additional information).

    Tolerant High Not relevant No change Moderate
    A decrease in suspended sediment could reduce the scour effect of particles on both the floral and faunal components of this biotope. In addition, it is likely that suspension feeding community may become more efficient as there would be fewer inorganic particles to clog and interfere with the feeding apparatus. Assuming that the decrease in suspended sediment refers to inorganic particles, a reduction in ingestion in the suspension feeding component of this biotope is not expected. Therefore, tolerant has been assessed.
    Intermediate High Low Minor decline Low
    An increase in desiccation at the benchmark level would mean that this biotope change its position by one vertical biological zone on the shore. However, due to that fact that this biotope is found in caves, the effects of such a transition are likely to be reduced since the majority of walls of the cave will remain damp. In addition, the fact that all the species associated with this biotope are intertidal means that they are adapted to some degree of cyclical desiccation. Nevertheless, where the cave walls are exposed to sunshine and wind, such as at the entrance to the caves, some species may experience some mortality. For example, the damp crevices that may otherwise support the beadlet and plumose anemones, may become much drier and therefore unsuitable for these two species. Semibalanus balanoides has a lower tolerance to desiccation than the chthamalid species, due to a greater permeability of the shell plates, and it is likely that, in some areas, this barnacle may be replaced by other barnacle species over the course of the benchmark. The edges of colonies of the breadcrumb sponge and encrusting algae may experience some bleaching and death. Furthermore, a change in height within the cave may mean that some species are out of reach of the wave surges and will therefore experience reduced feeding opportunities in addition to increased desiccation. However, mass mortality is unlikely and intolerance has been assessed as intermediate. Recoverability is likely to be high (see additional information).
    High High Moderate Major decline Low
    Intertidal biotopes such as LR.FLR.CVOV.FaCr are adapted to a certain degree of cyclical immersion and emersion and the associated changes in salinity, desiccation and temperature. In a damp dark cave within which this biotope is found, many of these stresses will be reduced. However, feeding opportunities for much of the suspension feeding community will be reduced. Since many of them are annual species, mortality is likely. For longer living species such as Pomatoceros triqueter, Halichondria panicea and Lithophyllum incrustans, a decrease in abundance may occur. The barnacles are likely to persist since they can respire anaerobically as desiccation increases (Barnes et al., 1963) although the proportion of the various barnacle species may vary as an increase in the period of emersion would cause increased competition from chthamalid barnacles. The upper limit of the biotope is likely to be depressed and, due to the fact that, the biotope may already extend to the cave floor, this reduction may not be counterbalanced by a downward extension of the lower limit. This mean the overall extent of the biotope will be reduced and accordingly, intolerance has been assessed as high but with a high recovery (see additional information).
    Tolerant* Not sensitive Not relevant Low
    A decrease in emergence would increase feeding opportunities for all filter feeders, the dominant fauna within this biotope. Both the upper limit of rock covered in faunal crusts and the total area covered may increase. The density of Pomatoceros triqueter, anemones, sponges and encrusting algae may increase on the lower reaches of the cave walls. Due to the fact that there is not one particular characteristic community associated with this biotope, it is difficult to assess whether such a change would be 'beneficial'. However, species diversity is likely to increase and therefore tolerant* has been suggested.
    Not relevant Not relevant Not relevant Not relevant High
    An increase in water flow rate is not considered relevant as the forces associated with a wave surged environment, such as in this biotope, are likely to be far greater than those that would be experienced by an increase in water flow rate at the benchmark level.
    High High Intermediate Major decline Low
    A decrease in water flow rate is not considered relevant because the forces associated with a wave surged environment, such as in this biotope, are likely to exceed any caused by water flow.
    Low High Low Minor decline Moderate
    The geographical distribution of the species associated with this biotope are such that an increase in temperature at the benchmark level is unlikely to adversely affect the majority of them e.g. Lithophyllum incrustans, Halichondria panicea and Sabellaria alveolata. However, Semibalanus balanoides is a boreal species, adapted to cool environments. Its southern limits are controlled by high temperatures which prevent final maturation of gametes and mean monthly sea temperature must fall below 7.2 °C in order for the barnacles to breed. In southern occurrences of this biotope where Semibalanus balanoides may be rare anyway, it may give way completely to chthamalid barnacles. However, although Semibalanus balanoides may experience a decline in abundance, the resultant community would still be typical of this biotope. Therefore, intolerance has been assessed as low. Recovery is expected to be high (see additional information).
    Intermediate High Low Decline Low
    Although many of the species associated with this biotope may be able to tolerate a chronic decrease in temperature, fewer species are likely to be tolerant of an acute drop in temperature. Sabellaria alveolata growth is inhibited below 5 °C and below 7 °C, Pomatoceros triqueter is unable to build calcareous tubes (Thomas, 1940). These are both temperatures that can reasonably be expected in the intertidal in the British Isles. Crisp (1964) noted frost damage to colonies of Halichondria panicea during the severe winter of 1962-63 and other sponges may be similarly affected. In contrast, Semibalanus balanoides was not affected during the severe winter of 1962-63 in most areas (Crisp, 1964). Lithophyllum incrustans is also likely to be able to tolerate decreased temperature since it occurs in a wide geographical range in temperatures that are much colder (air and water) than in Britain and Ireland. On balance, intolerance has been assessed as intermediate with a high recovery (see additional information).
    Tolerant Not relevant Not sensitive Not relevant Moderate
    An increase in turbidity is not likely to adversely affect the species associated with this biotope. The faunal component will not be affected and the encrusting coralline algae are tolerant of low light levels. At the benchmark level, no adverse affects are expected and accordingly, this biotope has been assessed as being tolerant to turbidity.
    Tolerant* Not sensitive No change Moderate
    An increase in turbidity may have the potential to increase phytoplankton production and may also increase light availability for photosynthesis in the encrusting coralline algae. The biotope may therefore benefit from such a reduction and accordingly tolerant* has been suggested.
    Intermediate High Low Decline Low
    An increase in exposure, in combination with the tunneling effect the cave can have on the wave surges, would result in an extremely high energy environment. Erect bryozoans such as Alcyonidium diaphanum would almost certainly be lost. If other filter feeders survived, such as the anemones and hydroids, they may experience feeding difficulties in the powerful surges. Over time this would lead to reduction in ingestion and, therefore, a reduced scope for growth.
    The barnacle Semibalanus balanoides thrives in extremely wave exposed conditions and may come to dominate this biotope over the course of the benchmark. Colonies of Lithophyllum incrustans also appear to thrive in conditions exposed to strong water movement. Irvine & Chamberlain (1994) observe that the species is best developed on wave exposed shores. Sabellaria alveolata and Pomatoceros triqueter can be found in very wave exposed and extremely wave exposed conditions respectively, although the tunneling effects of the surges in the cave may lead to the dislodgement and subsequent loss of parts of the Sabellaria alveolata colony.
    Overall, some mortality among various species is likely and species diversity will probably decline. Therefore, an intolerance of intermediate has been suggested with a high recovery.
    High High Intermediate Major decline Low
    A decrease in wave exposure could result in the biotope experiencing extremely wave sheltered conditions. This may have a deleterious effect on the biotope community since the dampness sustaining many of the species is reliant on the wave surges to splash the walls and ceiling of the cave. A reduction of wave exposure of this magnitude would mean that the upper reaches of the biotope may be too dry to support the species normally found there and it is likely that the upper limits of the biotope may be suppressed. The reduced upper limit would probably be set by barnacles that may come to dominate the biotope given their ability to competitively outcompete lower shore species in the face of desiccation. Furthermore, without regular and significant wave surges, many of the suspension feeders would be unable to feed and would therefore perish. The biotope would no longer be 'wave surged'. In the lower reaches of the cave, where the walls may be permanently submerged, species more characteristic of sheltered conditions may proliferate. Erect bryozoans may increase in abundance, for example. Competition for space may increase in this area since the biotope will have been 'squeezed' and it is likely that there will be a reduction in the number of species frequently associated with this biotope and an increase in other species. The majority of the biotope coverage is likely to be lost and therefore, intolerance has been assessed as high with a high recovery.
    Tolerant Not relevant Not sensitive Not relevant Low
    The fauna associated with this biotope are unlikely to have effective mechanisms for detecting noise and will most likely be tolerant of noise at the benchmark level.
    Tolerant Not relevant Not sensitive Not relevant Low
    The fauna associated with this biotope are unlikely to have effective mechanisms for detecting visual presence and will most likely be tolerant of visual presence at the benchmark level.
    Intermediate High Low Minor decline Moderate
    Due to the fact that this biotope is associated with cave habitats, abrasion and physical disturbance in this biotope is likely to come in the form of cobbles taken into suspension. Trampling and boats running aground are unlikely. Both the flora and fauna associated with this biotope are characterized by low lying crust forming species and therefore the effects of abrasion will most likely be the removal of, for example, small patches of sponge and bryozoan colonies or encrusting algae. Individual anemones may be killed but mass mortality is unlikely. In a study looking at the compressive strengths of several barnacles (Gubbay, 1983), Semibalanus balanoides was found to be weaker than Balanus perforatus and repeated physical disturbance in areas where these two co-existed could reduce the abundance of the weaker species thus altering the relative abundances of barnacles. In the lower reaches of the cave, suspended cobbles could scour the walls creating bare patches among the crusts and this area is likely to be more adversely affected than higher up the walls. Intolerance has been recorded as intermediate to reflect some mortality. Due to the fact that a proportion of each species will remain, recoverability is likely to be high.
    High High Moderate Major decline High
    The majority of key and important species associated with this biotope are permanently attached to the substratum and are unable to reattach themselves if displaced. In contrast, many anemones can reattach themselves once displaced. Wahl (1984) observed that Metridium dianthus detached from the substratum in the Inner Flensburg Fjord may drift away and eventually resettle. However, anemones in isolation are not indicative of LR.FLR.CVOV.FaCr and in general, this factor is thought to have a similar effect to substratum loss. Accordingly, intolerance is likely to be high. Recoverability will be high (see additional information).

    Chemical Pressures

    Intermediate High Low Decline Low
    Information concerning the effects of synthetic chemicals was not available for all the important species in this biotope and some of the information was conflicting.

    Hoare & Hiscock (1974) recorded that 'lithothamnia' was absent from the rocky shore up to 150 m distance from an acidified halogenated effluent. They also suggested that Polyzoa (Bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay. However, Soule & Soule (1979) and Holt et al. (1995) reported that bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints.

    Barnacles have a low resilience to chemicals such as dispersants, dependant on the concentration and type of chemical involved (Holt et al., 1995) . Most Semibalanus balanoides were killed in areas treated with dispersants (Smith, 1968). Hawkins & Southward (1992) suggested that the communities on shores heavily treated with dispersants had taken 5-8 years to recover, while some had not recovered after 10 years. Where oil had gone largely untreated, recovery was almost complete within 3 years (Hawkins & Southward, 1992).

    On balance, it is likely that some species will experience some mortality and, therefore, intolerance has been assessed as intermediate. Recovery is likely to be high (see additional information). The wave surged nature of the habitat may assist in flushing the contaminants from the biotope.
    Heavy metal contamination
    Low High Low Minor decline Low
    Information concerning the effects of heavy metals was not available for all the important species in this biotope.

    Barnacles accumulate heavy metals and store them as insoluble granules. Clarke (1947) investigated the intolerance of Semibalanus balanoides to copper, mercury, zinc and silver. He found that 90% of barnacles died when held in 0.35 mg/l Cu carbonate for two days. Zinc, mercury and silver killed 90 % of barnacles in two days at concentrations of 32 mg/l, 1 mg/l and 0.4 mg/l respectively. Pyefinch & Mott (1948) recorded median lethal concentrations of 0.32 mg/l copper and 0.36 mg/l mercury over 24 hours for this species. Barnacles may tolerate fairly high level of heavy metals in nature, for example they are found in Dulas Bay, Anglesey, where copper reaches concentrations of 24.5 µg/l, due to acid mine waste (Foster et al., 1978).

    Bryozoans are common members of the fouling community and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints. Bryozoans were also shown to bioaccumulate heavy metals to a certain extent (Soule & Soule, 1979; Holt et al., 1995). Bryozoans and hydroids may only manifest sublethal effects due to heavy metal contamination.

    On balance, an intolerance of low has been suggested. Recovery should be high, especially since the wave surged habitat may flush out some contaminants from the biotope.
    Hydrocarbon contamination
    High High Moderate Major decline Moderate
    The nature of the habitat with which this biotope is associated means that the associated community has the potential to collect oil. For example, if an oil spill was to occur, oil may be splashed onto the walls of the cave. Subsequent splashes of water may be insufficient to wash the oil off the rocks.

    Littoral barnacles have a high resistance to oil (Holt et al., 1995). However, after the Torrey Canyon oil spill, some mortality of barnacles was caused by the oil although most had been able to form a hole in the covering of oil and were 'in good order' (Smith, 1968). Significant reductions in densities of Semibalanus balanoides were observed after the Exxon Valdez oil spill (1989), especially at high and mid shore (Highsmith et al., 1996). Experimentally, Semibalanus balanoides has been found to tolerate exposure to the water-accommodated fraction of diesel oil at 129.4 µg/l for two years (Bokn et al., 1993). Recovery rates appear to be variable. They depend on the level of settlement and the survival rate of spat, both of which vary with a suite of environmental and biological factors. Lightly oiled shores have been observed to take 7 to 9 years to reach the previous normal state and more heavily oiled shores take longer (Holt et al., 1995).

    Where exposed to direct contact with fresh hydrocarbons, encrusting coralline algae appear to have a high intolerance. Crump et al. (1999) describe "dramatic and extensive bleaching" of 'Lithothamnia' following the Sea Empress oil spill. Observations following the Don Marika oil spill (K. Hiscock, own observations) were of rockpools with completely bleached coralline algae. However, Chamberlain (1996) observed that although Lithophyllum incrustans was quickly affected by oil during the Sea Empress spill, recovery occurred within about a year. The oil was found to have destroyed about one third of the thallus thickness but regeneration occurred from thallus filaments below the damaged area.

    Membranipora spp. (encrusting bryozoans) and Bugula spp. (erect bryozoans) were reported to be lost or excluded from areas subject to oil spills (Mohammad, 1974; Soule & Soule, 1979). Soule & Soule (1979) reported that Bugula neritina was lost from breakwater rocks in the vicinity of the 1976 Bunker C oil spill in Los Angeles Harbour, and had not recovered within a year. However, Bugula neritina had returned to a nearby area within 5 months even though the area was still affected by sheens of oil. Houghton et al. (1996) also reported a reduction in the abundance of intertidal encrusting bryozoans (no species given) at oiled sites after the Exxon Valdez oil spill. No information was found concerning the effects of hydrocarbon contamination on the erect bryozoan Alcyonidium diaphanum.

    Very little information has been found about the effects of oil on the sponges associated with this biotope although it appears that Halichondria panicea survived in areas affected by the Torrey Canyon oil spill (Smith, 1968), although few observations were made.

    Overall, an intolerance of high has been suggested. Recoverability will depend on the ability of the habitat to clean itself but it is expected to be high.

    Radionuclide contamination
    No information No information No information Insufficient
    Not relevant
    information was available on the effects of radionuclides on the community associated with LR.FLR.CVOV.FaCr.
    Changes in nutrient levels
    Tolerant* Not relevant Not sensitive* No change Low
    No information was found concerning the specific effects of nutrient enrichment on the community associated with this biotope. However, it is possible that the suspension feeding community, the dominant trophic group, will benefit. Phytoplankton production may increase thereby increasing the availability of organic particulate matter on which to feed. The risk of oxygen reduction and reduced light, often associated with plankton blooms, are extremely low given the wave surged nature of the habitat. Tolerant* has therefore been suggested.
    Not relevant Not relevant Not relevant Not relevant Moderate
    An increase in salinity is not considered relevant since the biotope is found in variable and full salinity areas. There is no great risk of hypersalinity either considering the walls of the cave will invariably stay damp and there is probably insufficient sunshine and wind to create patches of evaporated salt crust.
    Low High Low No change Moderate
    A chronic decrease in salinity at the benchmark level (i.e. down to reduced salinity, 18-30) for one year is unlikely to affect this biotope since it already occurs in areas of variable salinity which can be as low as 18. However, an acute drop in salinity could mean that the biotope experiences salinities less than 18 for one week. There may already be some freshwater penetration into this biotope through seepage and cracks and fissures in the ceiling of the cave and so some species may be tolerant. For example, both the breadcrumb sponge Halichondria panicea and the beadlet anemone Actinia equina can be found in low salinity conditions. The beadlet anemone is often found in the rills of freshwater that sometimes occur on beaches at low water (Manuel, 1988).

    Barnacles can survive periodic emersion in freshwater, e.g. from rainfall or fresh water run off, by closing their opercular valves (Foster, 1971b). They can also withstand large changes in salinity over moderately long periods of time by falling into a "salt sleep". In this state motor activity ceases and respiration falls, enabling animals to survive in freshwater for three weeks (Barnes, 1953). Semibalanus balanoides can tolerate salinities down to 12 psu, below which cirral activity ceases (Foster, 1970).

    Sabellaria alveolata and Pomatoceros triqueter only occur in fully marine environments any may therefore be intolerant of a sudden decrease in salinity. However, the loss of these two species may not necessarily affect the recognizable biotope. Furthermore, all the species in this biotope are intertidal and will therefore be adapted, to some extent, to short term acute declines in salinity from rainfall and freshwater runoff. Therefore, intolerance has been assessed as low with a high recovery.
    Low High Low No change Low
    Semibalanus balanoides can respire anaerobically, so it can tolerate some reduction in oxygen concentration (Newell, 1979). When placed in wet nitrogen, where oxygen stress is maximal and desiccation stress is low, Semibalanus balanoides has a mean survival time of 5 days (Barnes et al., 1963). Insufficient
    information was available concerning the effects of reduced oxygen on the other species. However, Cole et al. (1999) suggested possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l. Given that the benchmark level is exposure to dissolved oxygen concentration of 2mg/l for 1 week, intolerance has been assessed as low with a high recovery.

    Biological Pressures

    No information No information No information Insufficient
    Not relevant
    Barnacles are parasitised by a variety of organisms and, in particular, the cryptoniscid isopod Hemioniscus balani. Heavy infestation can cause castration of the barnacle and, once infected recovery, of an individual barnacle is unlikely. However, levels of infestation within a population vary and the probability of barnacles in this biotope being infected is not known.
    Tolerant Not relevant Not sensitive Not relevant Moderate
    The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second World War. The species does well in estuaries and bays, where it can displace Semibalanus balanoides. However, on exposed shores the native species out-compete this invasive species (Raffaelli & Hawkins, 1999). Therefore, tolerant has been assessed.
    Not relevant Not relevant Not relevant Not relevant Not relevant
    Sabellaria alveolata is occasionally collected for bait although the intertidal cave habitats in this biotope are such that exploitation is likely to be minimal. Furthermore, this species is only associated with variations of this biotope in south Wales and this factor is, therefore, not considered to be relevant. It is highly unlikely that any of the other species indicative of sensitivity would be subject to extraction.
    Not relevant Not relevant Not relevant Not relevant Not relevant

    Additional information

    The community associated with this biotope is dominated by ephemeral and fast growing species that can colonize rapidly space created by wave energy. For this reason, the progression of recoverability will depend on what time of year disturbances occur. However, as mentioned previously, the LR.FLR.CVOV.FaCr community will vary both spatially and temporally and it is therefore difficult to identify a ‘climax’ community as such. Furthermore, because there are no key functional, structural or characterizing species, any combination of faunal crust species could, theoretically, determine the biotope community. Nevertheless, the majority of the flora and fauna normally associated with LR.FLR.CVOV.FaCr will recolonize the areas within a year or two and recoverability is expected to be high.

    In Sebens' study of recolonization of vertical rock wall in Maine (Sebens, 1986), epifaunal and algal crust species were shown to re-colonize cleared areas quickly. For example encrusting bryozoans, tubeworms, tubicolous amphipods and worms, erect hydroids and bryozoans were reported to cover cleared areas within 1-4 months in spring, summer and autumn (Sebens, 1986). Pomatoceros triqueter is fairly widespread, reaches sexual maturity within 4 months (Hayward & Ryland, 1995b; Dons, 1927) and longevity has been recorded to be between 1.5 and 4 years (Hayward & Ryland, 1995b; Castric-Fey, 1983; Dons, 1927). Larvae are pelagic for about 2-3 weeks in the summer and about 2 months in the winter (Hayward & Ryland, 1995b), enabling them to disperse widely. Recovery is therefore likely to be high. Actinia equina is also likely to recover fairly rapidly from surrounding areas.

    The remaining species associated with this biotope may take longer to recover although it should still be within about three years. Bennell (1981) observed that, after barnacles were scraped off the surface rock in a barge accident at Amlwch in North Wales, barnacle populations returned to pre-accident levels within 3 years. However, barnacle recruitment can be very variable because it is dependent on a suite of environmental and biological factors. Jenkins et al. (2000) reported variation in settlement and recruitment of Semibalanus balanoides at all spatial scales studied (10s, 1000s of metres and 100s of km) in Sweden, the Isle of Man, southwest Ireland and southwest England and between 2 years, 1997 and 1998. Substantial variation in settlement and recruitment occurred between sites and variation in settlement explained 29 -99% of variation in recruitment across all sites, although not all variation in recruitment was explained by settlement at all sites.

    Sebens (1985) reported that Halichondria panicea had reached previous cover within two or more years. It was slow to recolonize the cleared areas, only appearing after about a year, although it is relatively fast growing.

    Sabellaria alveolata spawning occurs each July but actual recruitment levels vary considerably from year to year so recovery could take several years. The presence of some remaining adults will assist in larval settlement as this is the preferred substratum (Wilson, 1929). However, this species is only dominant south Wales and not the majority of records of this biotope.

    Encrusting coralline algae (e.g. Lithothamnion and Phytomatolithon took 1-2 years to recolonize cleared areas (Sebens, 1985; 1986) and with their slow growth rates probably take many years to recover their original abundance. Recoverability of Lithophyllum incrustans will be slow because although spores will settle and new colonies will arise rapidly on bare substratum, growth rate is slow (2-7 mm per annum - see Irvine & Chamberlain 1994).


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    This review can be cited as:

    Readman, J.A.J., Tillin, H.M., C.E. Marshall 2016. Faunal crusts on wave-surged littoral 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. [cited 19-06-2018]. Available from:

    Last Updated: 08/08/2016