MarLIN

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

Alcyonium digitatum and faunal crust communities on vertical circalittoral bedrock

08-11-2016

Summary

UK and Ireland classification

UK and Ireland classification

Description

This biotope typically occurs on the vertical faces and overhangs of exposed to moderately exposed lower infralittoral and upper circalittoral bedrock subject to moderately strong to weak tidal streams. Due to the large numbers of the urchin Echinus esculentus often recorded, this biotope tends to have a grazed appearance, and the bedrock is often encrusted with pink coralline algae, encrusting bryozoans such as Parasmittina trispinosa and the calcareous tubeworm Spirobranchus triqueter. Dense aggregations of dead mans fingers Alcyonium digitatum may be present along with the cup coral Caryophyllia smithii. Other species present include the echinoderms Asterias rubens, Ophiothrix fragilis and Antedon bifida, the ascidians Clavelina lepadiformis, Ciona intestinalis and Ascidia mentula, the anthozoans Urticina felina, Cortynactis viridis, Metridium senile and Sagartia elegans, the gastropod Calliostoma zizyphinum and the crustacean Cancer pagurus. Three regional variations of this biotope have been recorded. One variant found typically off the north-east coast of Scotland and around the Northern Isles, has a very impoverished appearance dominated by anthozoans. A second variant occurs along the west coast of Scotland, extending to Rockall in the west, and the Northern Isles in the north-east, and has a more fauna, characterized by hydroids, sponges, anthozoans and echinoderms. A third variant occurs along the north-east coast of England (Northumberland) up to the Northern Isles and is dominated by Alcyonium digitatum, brittlestars and Echinus esculentus. (Information from Connor et al., 2004).

Depth range

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Additional information

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Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

The biotope occurs on vertical faces and overhangs and is characterized by a heavily grazed faunal crust of encrusting bryozoans such as Parasmittina trispinosa with dense aggregations of Alcyonium digitatum.       

Grazing by the sea urchin Echinus esculentus is considered significant in preserving the nature of this biotope and loss of this species is likely to significantly affect the biotope to the extent that reclassification would be necessary.  For this sensitivity assessment Alcyonium digitatum and Echinus esculentus are the primary focus of research as the important characterizing species defining CR.MCR.EcCr.AdigVt, with species making up the faunal crust (such as the bryozoan Parasmittina trispinosa) considered where appropriate. Other species present in these biotopes are considered transient, mobile or ubiquitous and are therefore not considered significant to assessment of the sensitivity of these biotopes.  However, information on the sensitivity of other characterizing species is included where appropriate. 

Resilience and recovery rates of habitat

Alcyonium digitatum is a colonial species of soft coral with a wide distribution in the North Atlantic, recorded from Portugal (41°N) to Northern Norway (70°N) as well as on the east coast of North America (Hartnoll, 1975; Budd, 2008). Colonies consist of stout “finger like” projections (Hartnoll, 1975), which can reach up to 20 cm tall (Budd, 2008) and can dominate circalittoral rock habitats (as in CR.HCR.FaT.CTub.Adig; Connor et al., 2004). Alcyonium digitatum colonies are likely to have a lifespan that exceeds 20 years as colonies have been followed for 28 years in marked plots (Lundälv, pers. comm., in Hartnoll, 1998).  Colonies that were 10-15 cm in height were aged at between 5 and 10 years old (Hartnoll, unpublished). Most colonies are unisexual, with the majority of individuals being female.  Sexual maturity is predicted to occur, at its earliest, when the colony reaches its second year of growth. However, the majority of colonies are not predicted to reach maturity until their third year (Hartnoll, 1975).  Alcyonium digitatum spawns from December and January. Gametes are released into the water where fertilization occurs. The embryos are neutrally buoyant and float freely for seven days, when they give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within 1 or 2 further days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). In laboratory experiments, several larvae of Alcyonium digitatum failed to settle within 10 days, presumably finding the conditions unsuitable. These larvae were able to survive for 35 weeks as non-feeding planulae. After 14 weeks some were still swimming and after 24 weeks the surface cilia were still active although they rested on the bottom of the tanks. By the end of the experiment, at 35 weeks, the larvae had shrunk to a diameter of 0.3 mm. The ability to survive for long periods in the plankton may favour the dispersal and eventual discovery of a site suitable for settlement (Hartnoll, 1975).  The combination of spawning in winter and the long pelagic lifespan may allow a considerable length of time for the planulae to disperse, settle and metamorphose ahead of the spring plankton bloom. Young Alcyonium digitatum will consequently be able to take advantage of an abundant food resource in spring and be well developed before the appearance of other organisms that may otherwise compete for the same substrata.  In addition, because the planulae do not feed whilst in the pelagic zone they do not suffer by being released at the time of minimum plankton density.  They may also benefit by the scarcity of predatory zooplankton which would otherwise feed upon them (Hartnoll, 1975).  Alcyonium digitatum was first observed one year after the sinking of the HMS Scylla and took one year to grow to nearly full size.  By early 2009 (5 years after the sinking of the HMS Scylla) , Alcyonium digitatum had become a visually dominant part of the reef community (Hiscock et al., 2010).

Echinus esculentus is a sea urchin found within the north-east Atlantic, recorded from Murmansk Coast, Russia to Portugal (Hansson, 1998). Echinus esculentus is estimated to have a lifespan of 8-16 years (Nichols, 1979; Gage, 1992) and reaches sexual maturity within 1-3 years (Tyler-Walters, 2008). Maximum spawning occurs in spring although individuals may spawn over a protracted period throughout the year.  Gonad weight is at its maximum in February/March in English Channel (Comely & Ansell, 1988) but decreases during spawning in spring and then increases again through summer and winter until the next spawning season. Spawning occurs just before the seasonal rise in temperature in temperate zones but is probably not triggered by rising temperature (Bishop, 1985). Echinus esculentus is a broadcast spawner, with a complex larval life history which includes a blastula, gastrula and a characteristic four armed echinopluteus stage, which forms an important component of the zooplankton. MacBride (1914) observed planktonic larval development could take 45-60 days in captivity.

Recruitment is sporadic or variable depending on locality, for example Millport populations showed annual recruitment, whereas few recruits were found in Plymouth populations during Nichols’ studies between 1980-1981 (Nichols, 1984). Bishop & Earll (1984) suggested that the population of Echinus esculentus at St Abbs had a high density and recruited regularly whereas the Skomer population was sparse, ageing and had probably not successfully recruited larvae in the previous six years (Bishop & Earll, 1984). Comely & Ansell (1988) noted that the largest number of Echinus esculentus occurred below the kelp forest.

Echinus esculentus is a mobile species and could therefore migrate and re-populate an area quickly if removed. For example, Lewis & Nichols (1979a) found that adults were able to colonize an artificial reef in small numbers within three months and the population steadily grew over the following year.  If completely removed from a site and local populations are naturally sparse, then recruitment may be dependent on larval supply, which can be highly variable. As suggested by Bishop & Earll (1984), the Skomer, Wales Echinus esculentus population had most likely not successfully recruited for six years, which would suggest the mature population would be highly sensitive to removal and may not return for several years. The Prestige oil tanker spilled 63 000t of fuel 130 nautical miles off Galicia, Spain in November 2002. High wave action and strong weather systems increased mixing of the oil to “some” depth within the water column, causing sensitive faunal communities to be effected. The biological community of Guéthary, France was monitored preceding and for nine years following the oil spill. Following the oil spill, taxonomic richness decreased significantly from 57 recorded species to 41, which included the loss of Echinus esculentus from the site. Two to three years after the oil spill, taxonomic richness had increased to pre-spill levels and Echinus esculentus had returned (Castège et al., 2014).

Coralline crusts, Parasmittina trispinosa and Caryophyllia smithii are also important within the CR.MCR.EcCr.AdigVt biotope. Studies by Edyvean & Ford (1984a; 1986; 1987) of populations of coralline crusts, namely Lithophyllum incrustans, suggest that reproduction may be sexual or asexual (on average early in the third year), and spores are released throughout the year with seasonal variation as less spores were produced in the summer. The authors also found that spore survival was extremely low and young mortality was high, but individuals after the age of 10 appear relatively long-lived (up to 30 years). Some repair of damaged encrusting coralline occurs through vegetative growth, so recolonization by propagules may also be an important mechanism for rapid recovery (Chamberlain, 1996; Airoldi, 2000).

There is sparse information regarding the life history traits of Parasmittina trispinosa. Eggleston (1972a) noted in the Isle of Man, a peak in reproductive and vegetative growth was not well markedand the number of embryos present is fairly constant throughout the year, indicating that Parasmittina trispinosa could potentially reproduce annually within the UK. Caryophyllia smithii is a small (max 3 cm across) solitary coral common within tide swept sites of the UK (Wood, 2005). It was suggested by Fowler & Laffoley (1993) that Caryophyllia smithii was a slow growing species, which suggests that inter-specific spatial competition with colonial faunal or algae species are important factors in determining local abundance (Bell & Turner, 2000). Caryophyllia smithii reproduces sexually with gamete release most likely triggered by seasonal temperature increases (typically from January-April) (Tranter et al., 1982). The pelagic stage of the larvae may last up to 10 weeks, which provides this species with a good dispersal capability (Tranter et al., 1982). 

Resilience assessment. Echinus esculentus can reportedly reach sexual maturity within 1-2 years (Tyler-Walters, 2008), however as highlighted by Bishop & Earll (1984) and Castège et al. (2014) recovery may take 2-6 years (possibly more if local recruitment is poor).  Alcyonium digitatum can recruit onto bare surfaces within 2 years, however may take up to 5 years to become a dominant component of the community (Whomersley & Picken, 2003; Hiscock et al., 2010). The faunal crust is heavily grazed by Echinus esculentus and, together with the evidence presented, is likely to be quite resilient.   If the community significantly declined (resistance of ‘None’ or ‘Low’) resilience would be assessed as ‘Medium’ (recovery in 2-10 years). However, where resistance was assessed as ‘Medium’ or ‘High’ then resilience would be assessed as ‘High’.

Hydrological Pressures

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

Alcyonium digitatum is described as a northern species by Hiscock et al. (2004), but is distributed from northern Norway (70°N) to Portugal (41°N) (Hartnoll, 1975; Budd, 2008) and is commonly found across the British Isles (Fish  & Fish, 1992).  Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Ursin (1960) reported Echinus esculentus occurred at temperatures between 0-18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11-19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24 hr exposure to 15°C but normally at 4, 7 and 11°C (Tyler & Young 1998).  Parasmittina trispinosa is commonly found across the whole of the British Isles (NBN, 2015) and is distributed from the Northern coast of Norway to the Mediterranean (Hayward & Ryland, 1990). 

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over 9 years.  High temperature events were recorded, the first causing mass mortality among a number of species.  Decline in Pentapora fascialis colony cover between 11 and 22m depth following unusually warm summer in 1999 (temperature at 11m of 23.87 ± 1.4 °C and resulted in a 86% reduction in live colony portion) with larger colonies most affected.  Gradual recovery took place, with deeper communities recovering to pre-disturbance levels within 4 years.

Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Ursin (1960) reported Echinus esculentus occurred at temperatures between 0-18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11-19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24 hr exposure to 15°C but normally at 4, 7 and 11°C (Tyler & Young 1998).  High temperature (up to 31 °C) had little effect on the growth, survival and boring rate of the sponge Cliona celata (Duckworth & Bradley, 2012).  

Sensitivity assessment. Whilst Alcyonium digitatum and Parasmittina trispinosa are likely to tolerate an increase in temperature at the benchmark level, evidence suggests that Echinus esculentus may be affected. Resistance has been assessed as ‘Medium’, resilience has been assessed as ‘High’ and sensitivity has been assessed as ‘Low’.

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

Alcyonium digitatum is described as a northern species by Hiscock et al. (2004), but is distributed from Northern Norway (70°N) to Portugal (41°N) (Hartnoll, 1975; Budd, 2008).   Alcyonium digitatum was also reported to be apparently unaffected by the severe winter of 1962-1963 where air temperature reached -5.8°C (Crisp, 1964a). Parasmittina trispinosa is commonly found across the whole of the British Isles (NBN, 2015) and is distributed from the northern coast of Norway to the Mediterranean (Hayward& Ryland, 1990).

Ursin (1960) reported Echinus esculentus occurred at temperatures between 0-18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11-19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24 hr exposure to 15°C but normally at 4, 7 and 11°C (Tyler & Young 1998).  Echinus esculentus has been recorded from the Murmansk Coast, Russia. Due to the high latitude at which Echinus esculentus can occur, it is unlikely to be affected by a decrease in temperature at the pressure benchmark.

Sensitivity assessment. None of the characterizing species are at their southern distribution limit and are unlikely to suffer mortality by a decrease in temperature at the benchmark level.  Resistance is therefore recorded as ‘High’, resilience as ‘High’ and the biotope is ‘Not Sensitive’ at the benchmark level.

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

Echinoderms are generally stenohaline and possess no osmoregulatory organ (Boolootian, 1966) and lack the ability to osmo- and ion-regulate (Stickle & Diehl, 1987). The inability of echinoderms to osmoregulate extracellularly causes body fluid volume to decrease when individuals experience higher external salinity.  Protracted hypersalinity is likely to result in the decline of echinoderm populations. Echinoderm larvae have a narrow range of salinity tolerance and will develop abnormally and die if exposed to increased salinity (Tyler-Walters, 2008).   Alcyonium digitatum distribution and the depth at which it occurs also suggest it would not likely experience regular salinity fluctuations and therefore not resists significant increases in salinity.  CR.MCR.EcCr.AdigVt occurs in full salinity (Connor et al., 2004), it is therefore possible that an increase in salinity may cause a decline in the abundance of Alcyonium digitatum, Echinus esculentus and the faunal crust.

Sensitivity assessment. It is likely that Echinus esculentus is stenohaline and hypersaline conditions would probably affect the species.  Resistance has been assessed as ‘Low’, resilience as ‘Medium’, and sensitivity has been assessed as ‘Medium’.  Due to the lack of information regarding salinity effects on the characterizing species, confidence in this assessment has been assessed as low.

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

Alcyonium digitatum is found at the entrances to sea lochs (Budd, 2008) and estuaries (Braber & Borghouts, 1977) where salinity may vary occasionally. Furthermore, Alcyonium digitatum is found within a number of variable salinity biotopes, e.g. MCR.BYH.Flu.Hocu (Connor et al., 2004).  However, its distribution and the depth, at which it occurs suggest that Alcyonium digitatum would not likely often experience salinity fluctuations and is, therefore, unlikely to survive significant reductions in salinity (Budd, 2008).

Echinoderms are generally unable to tolerate low salinity (stenohaline) and possess no osmoregulatory organ (Boolootian, 1966). At low salinity urchins gain weight, and the epidermis loses its pigment as patches are destroyed; prolonged exposure is fatal. However, within Echinus esculentus there is some evidence to suggest intracellular regulation of osmotic pressure due to increased amino acid concentrations. Echinus esculentus is found within a number of variable and reduced salinity biotopes, e.g. IR.LIR.KVS.LsacPsaVS (Connor et al., 2004).

Sensitivity assessment. CR.MCR.EcCr.AdigVt is recorded exclusively in full marine conditions (30-35 ppt) (Connor et al., 2004). Records from the MNCR suggest Alcyonium digitatum and Echinus esculentus can occur in reduced salinity habitats, however the evidence suggests that these species would decrease in abundance.  In addition, a reduction in salinity may result in a reduction in species richness of the biotope anTherefore, resistance has been assessed as ‘Low’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

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

The biotope (EcCr.AdigVT) occurs in extremely to moderately wave exposed conditions in areas of moderately strong to negligible water flow at 5-50m depth (Connor et al., 2004).  The biotope is structured by grazing, especially by Echinus esculentus.  The biotope probably occurs at a critical range of water movement that allows the Echinus population to remain in high enough abundance to structure the biotope.  Deep examples probably depend on water flow or extreme wave action, while shallow examples depend on wave action or water flow.

Alcyonium digitatum and the bryozoans are suspension feeders relying on water currents to supply food. These taxa, therefore, thrive in conditions of vigorous water flow e.g. around Orkney and St Abbs, Scotland, where the community may experience tidal currents of 3 and 4 knots (1.5 and 2 m/s) during spring tides (De Kluijver, 1993).

Echinus esculentus occurred in kelp beds on the west coast of Scotland in currents of about 0.5 m/sec. Outside the beds, specimens were occasionally seen being rolled by the current (Comely & Ansell, 1988), which may have been up to 1.4 m/sec. Echinus esculentus are also displaced by storm action. After disturbance Echinus esculentus migrates up the shore, an adaptation to being washed to deeper water by wave action (Lewis & Nichols, 1979a). Therefore, increased water flow may remove the population from the affected area, probably to deeper water, however individuals would probably not be killed in the process and could recolonize the area quickly.

Sensitivity assessment. This biotope occurs negligible water flow, so a reduction in water flow would therefore not affect the biotope.  All characterizing species are likely to be tolerant of an increase at the benchmark level (0.1-0.2 m/s), being present in biotopes with stronger water flow. Resistance is therefore ‘High’, resilience is ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

Changes in emergence are ‘Not relevant’ to this biotope as it is restricted to fully subtidal/circalittoral conditions - the pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

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

The biotope (EcCr.AdigVT) occurs in extremely to moderately wave exposed conditions in areas of moderately strong to negligible water flow at 5-50 m depth (Connor et al., 2004).  The biotope is structured by grazing, especially by Echinus esculentus.  The biotope probably occurs at a critical range of water movement that allows the Echinus population to remain in high enough abundance to structure the biotope.  Deep examples probably depend on water flow or extreme wave action, while shallow examples depend on wave action or water flow.

Alcyonium digitatum are suspension feeders relying on water currents to supply food. These taxa therefore thrive in conditions of vigorous water flow. As a circalittoral biotope (recorded from 5 - 50 m), the depth at which these biotopes occur may therefore also reduce the direct physical effects of a localised change in wave height; wave attenuation is directly related to water depth (Hiscock, 1983).

Echinus esculentus occurred in kelp beds on the west coast of Scotland in currents of about 0.5 m/sec. Outside the beds, specimens were occasionally seen being rolled by the current (Comely & Ansell, 1988), which may have been up to 1.4 m/sec. Urchins are removed from the stipe of kelps by wave and current action. Echinus esculentus are also displaced by storm action. After disturbance, Echinus esculentus migrates up the shore, an adaptation to being washed to deeper water by wave action (Lewis & Nichols, 1979a). Keith Hiscock (pers. comm.) reported Echinus esculentus occurred in significant numbers as shallow as 15 m below low water at the extremely wave exposed site of Rockall, Scotland.

Sensitivity assessment. Whilst storm events may have an impact on the biotope, a change at the benchmark level is not likely to have a significant effect on the characterizing species. Resistance has been assessed as ‘High’, resilience has been assessed as ‘High’ and the biotope is assessed as ‘Not sensitive’ 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

Little is known about the effects of heavy metals on echinoderms. Bryan (1984) reported that early work had shown that echinoderm larvae were sensitive to heavy metals contamination, for example Migliaccio et al. (2014) reported exposure of Paracentrotus lividis larvae to increased levels of cadmium and manganese caused abnormal larval development and skeletal malformations. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu).

No information was found on the direct biological effects of heavy metal contamination on Alcyonium digitatum. Possible sub-lethal effects of exposure to heavy metals, may result in a change in morphology, growth rate or disruption of reproductive cycle. The vulnerability of this species to concentrations of pollutants may also depend on variations in other factors e.g. temperature and salinity conditions outside the normal range.

Bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1979; Holt et al., 1995). Bryozoans were shown to bioaccumulate heavy metals to a certain extent (Holt et al., 1995). For example, Bowerbankia gracialis and Nolella pusilla accumulated Cd, exhibiting sublethal effects (reduced sexual reproduction and inhibited resting spore formation) between 10-100 µg Cd /l and fatality above 500 µg Cd/l (Kayser, 1990).

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

Echinus esculentus was reported absent after the oil spill however returned after 2-5 years. Large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m in the vicinity of Sennen cove, presumably due to a combination of wave exposure and heavy spraying of dispersants following the Torrey Canyon oil spill (Smith, 1968). Smith (1968) also demonstrated that 0.5 -1ppm of the detergent BP1002 resulted in developmental abnormalities in its echinopluteus larvae. Echinus esculentus populations in the vicinity of an oil terminal in La Coruna Bay, Spain, showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gommez & Miguez-Rodriguez, 1999).

Oil pollution is mainly a surface phenomenon, so its impact upon circalittoral turf communities is likely to be limited. However, as in the case of the Prestige oil spill off the coast of France, high swell and winds can cause oil pollutants to mix with the seawater and potentially negatively affect sub-littoral habitats (Castège et al., 2014). Smith (1968) reported dead colonies of Alcyonium digitatum at a depth of 16m in the locality of Sennen Cove, Cornwall which was likely a result of toxic detergents sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill (Budd, 2008).  Little information on the effects of hydrocarbons on bryozoans could be found. Ryland & De Putron (1998) did not detect adverse effects of oil contamination on the bryozoan Alcyonidium spp. in Milford Haven or St. Catherine's Island, south Pembrokeshire although it did alter the breeding period.  Echinus esculentus is subtidal and unlikely to be directly exposed to oil spills. However, as with the ‘Prestige’ oil spill rough seas can cause mixing with the oil and the seawater, and therefore sub-tidal habitats can be affected by the oil spill. Castège et al., (2014) recorded the recovery of rocky shore communities following the Prestige oil spill which impacted the French Atlantic coast. Rough weather at the time of the spill increased mixing between the oil and seawater, causing sub-tidal communities/habitats to be affected.

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 dead colonies of Alcyonium digitatum at a depth of 16 m in the locality of Sennen Cove, Cornwall resulting from the offshore spread and toxic effect of detergents (a mixture of a surfactant and an organic solvent). Possible sub-lethal effects of exposure to synthetic chemicals may result in a change in morphology, growth rate or disruption of reproductive cycle. The vulnerability of this species to concentrations of pollutants may also depend on variations in other factors e.g. temperature and salinity conditions outside the normal range (Budd, 2008).

Hoare & Hiscock (1974) suggested that polyzoa (bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay, Anglesey and reported that Flustra foliacea did not occur less than 165m from the effluent source. The evidence therefore suggests that Parasmittina trispinosa would be sensitive to synthetic compounds.

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' was found.

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

No benchmark was proposed.  Therefore, sensitivity has been assessed as 'Not sensitive' at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

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

Mass mortality of species including Echinus esculentus was observed due to a stratified hypoxic event below 8 m caused by a phytotplankton bloom ( Griffiths et al., 1979).  Hiscock & Hoare (1975) reported an oxycline forming in the summer months (Jun-Sep) in a quarry lake (Abereiddy, Pembrokeshire) from close to full oxygen saturation at the surface to <5% saturation below ca 10 m.  During these summer events, no echinoderms were recorded at depths below 10 - 11 m.  At the time of writing there was insufficient evidence on which to assess this pressure. There is anecdotal evidence to suggest that Alcyonium digitatum is sensitive to hypoxic events. However, because the degree of de-oxygenation wasn’t quantified the evidence cannot be compared to the pressure benchmark.  In general, respiration in most marine invertebrates does not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates this concentration is about 2 ml/l, or even less (Herreid, 1980; Rosenberg et al., 1991; Diaz & Rosenberg, 1995).  Alcyonium digitatum mainly inhabits environments in which the oxygen concentration usually exceeds 5 ml/l and respiration is aerobic (Budd, 2008). In August 1978 a dense bloom of a dinoflagellate, Gyrodinium aureolum occurred surrounding Geer Reef in Penzance Bay, Cornwall and persisted until September that year. Observations by local divers indicated a decrease in underwater visibility (<1 m) from below 8 m. It was also noted that many of the faunal species appeared to be affected, e.g. no live Echinus esculentus were observed whereas on surveys prior to August were abundant, Alcyonium sp. and bryozoans were also in an impoverished state. During follow up surveys conducted in early September Alcyonium sp. were noted to be much healthier and feeding. It was suggested the decay of Gyrodinium aureolum either reduced oxygen levels or physically clogged faunal feeding mechanisms. Adjacent reefs where also surveyed during the same time period and the effects of the Gyrodinium aureolum bloom were less apparent. It was suggested that higher water agitation in shallow water on reefs more exposed to wave action were less effected by the phytoplankton bloom (Griffiths et al., 1979).   CR.MCR.EcCr.AdigVt is recorded from very weak to moderately strong tidal streams (negligible to 1.5 m/sec) (Connor et al., 2004). Whilst mixing with surrounding oxygenated water is likely to occur in examples of this biotope that experience moderate water movement (Dennis, 1979), de-oxygenation is likely to become a chronic factor in examples where there is negligible water movement.

Sensitivity assessment. The characterizing species are likely to suffer significant mortality in a hypoxic event at the benchmark level, especially in examples of the biotope that occur with negligible water flow in which it may take longer for the oxygen levels to recover.  Whilst the majority of assessed species are sessile, Echinus esculentus is mobile and may escape the hypoxic event (depending on extent and conditions). Resistance is assessed as ‘Low’, Resilience as ‘Medium’ (assuming recovery to normal oxygen conditions) and sensitivity as ‘Medium’.

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

It was suggested by Comely & Ansell (1988) that Echinus esculentus could absorb dissolved organic material for the purposes of nutrition. Nutrient enrichment may encourage the growth of ephemeral and epiphytic algae and therefore increase sea-urchin food availability. Lawrence (1975) reported that sea urchins had persisted over 13 years on barren grounds near sewage outfalls, presumably feeding on dissolved organic material, detritus, plankton and microalgae, although individuals died at an early age.  Alcyonium digitatum is a suspension feeders of phytoplankton and zooplankton. Nutrient enrichment of coastal waters that enhances the population of phytoplankton may be beneficial to these species in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). High primary productivity in the water column combined with high summer temperature and the development of thermal stratification (which prevents mixing of the water column) can lead to hypoxia (see de-oxygenation).  Nutrient enrichment could also lead to algal blooms.

This biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with good status as defined by the WFD.

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

It was suggested by Comely & Ansell (1988) that Echinus esculentus could absorb dissolved organic material for the purposes of nutrition. Organic enrichment may encourage the growth of ephemeral and epiphytic algae and therefore increase sea-urchin food availability. Lawrence (1975) reported that sea urchins had persisted over 13 years on barren grounds near sewage outfalls, presumably feeding on dissolved organic material, detritus, plankton and microalgae, although individuals died at an early age. Alcyonium digitatum is a suspension feeders of phytoplankton and zooplankton. Organic enrichment of coastal waters that enhances the population of phytoplankton may be beneficial to these species in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). High primary productivity in the water column combined with high summer temperature and the development of thermal stratification (which prevents mixing of the water column) can lead to hypoxia, (see de-oxygenation)

Sensitivity assessment.  ‘No evidence’ of the effects of organic enrichment in circalittoral faunal crusts 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

If rock were replaced with sediment, this would represent a fundamental change to the physical character of the biotope and the species would be unlikely to recover. The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very low’. Sensitivity has been assessed as ‘High’.

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’ to biotopes occurring on bedrock.

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 species characterizing this biotope are epifauna or epiflora occurring on rock and would be sensitive to the removal of the habitat. However, extraction of rock substratum is considered unlikely and this pressure is considered to be ‘Not relevant’ to hard substratum habitats.

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

Alcyonium digitatum, Echinus esculentus and Parasmittina trispinosa are sessile or slow moving species that might be expected to suffer from the effects of abrasion. Boulcott & Howell (2011) conducted experimental Newhaven scallop dredging over a circalittoral rock habitat in the sound of Jura, Scotland and recorded the damage to the resident community. Only 13% of photographic samples showed visible damage to Alcyonium digitatum. Where Alcyonium digitatum damage was evident it tended to be small colonies that were ripped off the rock. The authors highlight physical damage to faunal turfs (erect bryozoans and hydroids) was difficult to quantify in the study. However, the faunal turf communities did not show large signs of damage and were only damaged by the scallop dredge teeth, which was often limited in extent (approximately 2 cm wide tracts). The authors indicated that species such as Alcyonium digitatum and faunal turf communities were not as vulnerable to damage through trawling as sedimentary fauna and whilst damage to circalittoral rock fauna did occur it was of an incremental nature, with loss of species such as Alcyonium digitatum and faunal turf communities increasing with repeated trawls.  Species with fragile tests, such as Echinus esculentus were reported to suffer badly as a result of scallop or queen scallop dredging (Bradshaw et al., 2000; Hall-Spencer & Moore, 2000a). Kaiser et al. (2000) reported that Echinus esculentus were less abundant in areas subject to high trawling disturbance in the Irish Sea. Jenkins et al. (2001) conducted experimental scallop trawling in the North Irish sea and recorded the damage caused to several conspicuous megafauna species.  The authors used simultaneous assessment of both bycatch and organisms left on the seabed to estimate capture efficiency for both target and non-target organisms. This found 16.4% of Echinus esculentus were crushed or dead, 29.3% had >50% spine loss/minor cracks, 1.1% had  <50% spine loss and the remaining 53.3% were in good condition. Sea urchins can rapidly regenerate spines, e.g. Psammechinus miliaris were found to re-grow all spines within a period of 2 months (Hobson, 1930).  The trawling examples mentioned above were conducted on sedimentary habitats and thus the evidence is not directly relevant to rock based, however it does indicate the likely effects of abrasion on Echinus esculentus.

Sensitivity assessment. Whilst abrasion pressures tend to heavily impact sessile or slow moving marine species, the evidence suggests that mortality amongst the characterizing species is ‘Medium’ (<25% loss) for the characterizing  Alcyonium digitatum and Echinus esculentus.  It should be noted that this is dependent on the abrasion activity and heavier gears may well cause more damage.  Based on the evidence for the characterizing species, resistance is ‘Medium’, resilience as ‘High’ and sensitivity as ‘Low’. Please note, Boulcott & Howell (2011) did not mention the abrasion caused by fully loaded collection bags on the new haven dredges. A fully loaded Newhaven dredge may cause higher damage to community than indicated in their study.

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 species characterizing this biotope group are epifauna or epiflora occurring on rock which is resistant to subsurface penetration.  The assessment for abrasion at the surface only is therefore considered to equally represent sensitivity to this pressure. This pressure is considered to be ‘Not Relevant’ to hard rock biotopes.

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

Alcyonium digitatum and Parasmittina trispinosa are not thought to be highly susceptible to changes in water clarity due to the fact they are suspension feeding organisms and are not directly dependent on sunlight for nutrition. Alcyonium digitatum has been shown to be tolerant of high levels of suspended sediment. Hill et al. (1997) demonstrated that Alcyonium digitatum sloughed off settled particles with a large amount of mucous. Alcyonium digitatum is also known to inhabit the entrances to sea lochs (Budd, 2008) or the entrances to estuaries (Braber & Borghouts, 1977) where water clarity is likely to be highly variable.  Also, Moore (1977a) suggested that Echinus esculentus was unaffected by turbid conditions. Echinus esculentus is an important grazer in CR.MCR.EcCr.AdigVt but also feeds on detritus or dissolved organic material (Lawrence, 1975, Comely & Ansell, 1988). 

Sensitivity assessment. The biotope is faunally dominated and circalittoral and is therefore not dependent on light, so a change in suspended sediment is unlikely to affect the characterizing species and Resistance is therefore assessed as ‘High’, Resilience as ‘High’ and the biotope is ‘Not sensitive’.

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

CR.MCR.EcCr.AdigVt occurs on vertical faces and overhangs which would afford the characterizing species protection in the event of sediment deposition.  Alcyonium digitatum is sessile and thus would be unable to avoid the deposition of a smothering layer of sediment, however, colonies can attain a height of up to 20 cm (; Budd, 2008; Edwards, 2008), so would still be able to feed in the event of sediment deposition. Parasmittina trispinosa is an encrusting species and would thus likely be smothered, and depending on sediment retention, could block larval settlement. Echinus esculentus are mobile, large globular urchins which can reach a diameter of 17 cm (Tyler-Walters, 2000).  Comely & Ansell (1988) recorded large Echinus esculentus from kelp beds on the west coast of Scotland in which the substratum was seasonally covered with "high levels" of silt. This suggests that Echinus esculentus is unlikely to be killed by smothering, however, smaller specimens and juveniles may be less resistant. A layer of sediment may interfere with larval settlement.  If retained within the host biotope for extended periods a layer of 5 cm of the sediment may negatively affect successive recruitment events, however this is unlikely given the typically vertical nature of the biotope.

Sensitivity assessment. CR.MCR.EcCr.AdigVt occurs on vertical faces and overhangs and sedimentation would be unlikely, with removal likely to be rapid.  Areas at the base of the rock could be affected, but overall, resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

CR.MCR.EcCr.AdigVt typically occurs on vertical faces and overhangs which would afford the characterizing species some protection in the event of sediment deposition. 

Alcyonium digitatum is sessile and thus would be unable to avoid the deposition of a smothering layer of sediment.  However Alcyonium digitatum colonies can attain a height of up to 20 cm (; Budd, 2008; Edwards, 2008), so would still be able to feed in the event of sediment deposition. However, Parasmittina trispinosa is an encrusting species and would thus likely be smothered, and depending on sediment retention, could block larval settlement. Echinus esculentus are mobile, large globular urchins which can reach a diameter of 17 cm (Tyler-Walters, 2000).  Comely & Ansell (1988) recorded large Echinus esculentus from kelp beds on the west coast of Scotland in which the substratum was seasonally covered with "high levels" of silt. This suggests that Echinus esculentus is unlikely to be killed by smothering, however, smaller specimens and juveniles may be less resistant. A layer of sediment could interfere with larval settlement.  If sediment is retained within the host biotope for extended periods a layer sediment may negatively affect successive recruitment events, however given that the biotope tends to occur on vertical faces and overhangs, this is unlikely.

Sensitivity assessment. CR.MCR.EcCr.AdigVt occurs on vertical faces and overhangs and sedimentation would be unlikely, with removal likely to be rapid.  Smothering at the base of rocks could result in burial of the encrusting bryozoans and would affect Alcyonium digitatum which grows to 20 cm tall (Budd, 2008; Edwards, 2008). A cautious assessment of ‘Medium’ resistance is applied. Resilience is ‘High’ and sensitivity is ‘Low’.

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

'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

Echinus esculentus, Alcyonium digitatum and Parasmittina trispinosa have no hearing perception but vibrations may cause an impact, however there is ‘No evidence’ to support an assessment.   

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

There is some evidence that the basiepithelial nerve plexus below the entire outer skins of echinoderms is sensitive to light (Hill, 2008). There is no evidence to suggest that algal species would benefit if exposed to anthropogenic light sources. CR.MCR.EcCr.AdigVt is a circalittoral biotope and therefore defined as occurring at low light levels due to depth. Increased shading (e.g. by construction of a pontoon, pier etc) could be beneficial to the characterizing species within these biotopes and

Sensitivity assessment. Resistance is assessed as 'High', with 'High' resilience and the biotope is '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

‘Not relevant’ as barriers and changes in tidal excursion are not relevant to biotopes restricted to open waters.

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 to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

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

Biological Pressures

 ResistanceResilienceSensitivity
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

Echinus esculentus was identified by Kelly & Pantazis (2001) as a species suitable for culture for the urchin roe industry. However, at present no evidence could be found to suggest that significant Echinus esculentus mariculture was present in the UK. If industrially cultivated it is feasible that Echinus esculentus individuals could be translocated. ‘No evidence’ of cultivation or translocation of Alcyonium digitatum and Parasmittina trispinosa 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

Styela clava was first recorded in the UK at Plymouth in 1952 (Eno et al., 1997). Where Styela clava and Ciona intestinalis co-occur they may compete for space and food (Jackson, 2008).

Didemnum vexillum is an invasive colonial sea squirt native to Asia which was first recorded in the UK in Darthaven Marina, Dartmouth in 2005. Didemnum vexillum can form extensive mats over the substrata it colonizes; binding boulders, cobbles and altering the host habitat (Griffith et al., 2009). Didemnum vexillum can also grow over and smother the resident biological community. Recent surveys within Holyhead Marina, North Wales have found Didemnum vexillum growing on and smothering native tunicate communities, including Ciona intestinalis (Griffith et al., 2009). Due to the rapid-re-colonization of Didemnum vexillum eradication attempts have to date failed. 

Presently, Didemnum vexillum is isolated to several sheltered locations in the UK (NBN, 2015). However Didemnum vexillum has successfully colonized the offshore location of the Georges Bank, USA (Lengyel et al., 2009) which is more exposed than the locations which Didemnum vexillum have colonized in the UK. It is therefore possible that Didemnum vexillum could colonize more exposed locations within the UK and could therefore pose a threat to these biotopes.  A number of invasive bryozoans are of concern including Schizoporella japonica (Ryland et al., 2014) and Tricellaria inopinata (Dyrynda et al., 2000; Cook et al., 2013b).

However, there is ‘No evidence’ regarding known invasive species colonizing this biotope.  Due to the constant risk of new invasive species, the literature for this pressure should be revisited.

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

Echinus esculentus is susceptible to 'Bald-sea-urchin disease', which causes lesions, loss of spines, tube feet, pedicellariae, destruction of the upper layer of skeletal tissue and death. It is thought to be caused by the bacteria Vibrio anguillarum and Aeromonas salmonicida. Bald sea-urchin disease was recorded from Echinus esculentus on the Brittany Coast. Although associated with mass mortalities of Strongylocentrotus franciscanus in California and Paracentrotus lividus in the French Mediterranean it is not known if the disease induces mass mortality (Bower, 1996).

Alcyonium digitatum acts as the host for the endoparasitic species Enalcyonium forbesi and Enalcyonium rubicundum (Stock, 1988). Parasitisation may reduce the viability of a colony but not to the extent of causing mortality.  No further evidence was found to substantiate this suggestion.

Stebbing (1971b) reported that encrusting epizoites reduced the growth rate of Flustra foliacea by ca 50%. The bryozoan Bugula flabellata produces stolons that grow in and through the zooids of Flustra foliacea, causing "irreversible degeneration of the enclosed polypide" (Stebbing, 1971b). No evidence of Parasmittina trispinosa disease could be found.

Sensitivity assessment. However, whilst evidence of disease in the characterizing species could be found, ‘No evidence’ of mass-mortality through disease could be 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

Despite historic extraction as a curio (Jangoux, 1980; Nichols, 1984), Echinus esculentus is not thought to be currently targeted. 'No evidence' for the targeted removal of Alcyonium digitatum or bryozoans could be found.

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

The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of non-target species on this biotope. Alcyonium digitatum goes through an annual cycle, from February to July all Alcyonium digitatum colonies are feeding, from July to November an increasing number of colonies stop feeding. During this period a large number of polyps can retract and a variety of filamentous algae, hydroids and amphipods can colonize the surface of colonies epiphytically. From December-February the epiphytic community is however sloughed off (Hartnoll, 1975). If Alcyonium digitatum were removed the epiphytic species would likely colonize rock surfaces and are therefore not dependent on Alcyonium digitatum.

While recovery of the characterizing species should be possible within 2-10 years following non-targeted removal (e.g. from static or mobile gears), loss of Echinus esculentus from the biotope subsequent loss of grazing pressure would result in increasing competition from algae and increased competition for space, which could lead to a change in biotope classification e.g. to XFa biotopes with a more .  Alcyonium digitatum and faunal turf communities (which include bryozoans such as Parasmittina trispinosa) are probably resistant to abrasion through bottom fishing (see abrasion pressure).

Sensitivity assessment. Decrease in Alcyonium digitatum would result in a decline in the biotope richness.  However, removal of Echinus esculentus could result in restructuring of the biotope.  If both are lost, reclassification would be necessary.  Resistance has therefore been assessed as ‘None’, resilience as ’Medium’ and sensitivity as ‘Medium’.

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Citation

This review can be cited as:

Readman, J.A.J., 2016. [Alcyonium digitatum] and faunal crust communities on vertical circalittoral bedrock. 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/1097

Last Updated: 31/05/2016