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Alcyonium digitatum with Securiflustra securifrons on tide-swept moderately wave-exposed circalittoral rock

Distribution MapBIO Map Legend

Summary

UK and Ireland classification

Description

This variant is typically found on the upper and vertical faces of moderately wave-exposed circalittoral bedrock subject to moderately strong to weak tidal streams. The rock surface is dominated by Alcyonium digitatum and the bryozoan Securiflustra securifrons. The rock between these species appears fairly sparse and grazed, with expanses of encrusting red algae. The sea urchin Echinus esculentus is frequently seen, and in collaboration with the light attenuating effects of depth, is probably the principal reason for the lack of algal turf. Other species found include the hydroids Abietinaria abietina, Nemertesia antennina, Thuiaria thuja, the bryozoans Cellepora pumicosa, Parasmittina trispinosa, Flustra foliacea, Alcyonidium diaphanum and other bryozoan crusts. Encrusting species such as the polychaete Spirobranchus triqueter and the barnacle Balanus balanus are frequently observed. Other species present include Asterias rubens, Antedon bifida, Ophiura albida, Ophiothrix fragilis, Caryophyllia smithii, Urticina felina, Clavelina lepadiformis, Calliostoma zizphinium and Pandalus montagui.

Above this biotope, you tend to find exposed kelp forest and park (LhypR). There is a tendency for slight scouring to occur in this biotope. However, if this scour increases further, for example if water movement increases, mobilising more sand, this biotope may graduate into UrtScr. In more silty sites, there is a tendency for Securiflustra securifrons to be replaced by Flustra foliacea as the dominant bryozoan, turning the biotope into FaAlCr.Flu. The great majority of species in this variant are most likely present throughout the year but Clavelina lepadiformis grows in spring and may show great variation in abundance from year to year. (Information from Connor et al., 2004; JNCC, 2015). 

Depth range

10-20 m, 20-30 m

Additional information

-

Listed By

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Sec, CR.MCR.EcCr.FaAlCr.Spi & CR.MCR.EcCr.FaAlCr.Car are within the “Faunal and algal crusts on exposed to moderately wave-exposed circalittoral rock” FaAlCr habitat complex.  All these biotopes have a sparse appearance due to grazing, mainly by Echinus esculentus, which combined with water depth, is thought to be a limiting factor controlling the growth of algal and increasing the dominance of faunal turfs. Alcyonium digitatum is common to all biotopes however colonies are generally smaller and have lower biomass within CR.MCR.EcCr.FaAlCr.Spi. Securiflustra securifrons is also an important erect faunal species within CR.MCR.EcCr.FaAlCr.Sec. In CR.MCR.EcCr.FaAlCr.Car Caryophyllia smithii is an important characterizing species.  Encrusting fauna such as Spirobranchus triqueter (syn. Pomatoceros triqueter) and the bryozoan Parasmittina trispinosa are also important characterizing species across these biotopes (Connor et al., 2004).

For this sensitivity assessment Alcyonium digitatum, Caryophyllia smithii, Echinus esculentus, the encrusting bryozoan Parasmittina trispinosa, Securiflustra securifrons and Spirobranchus triqueter and are the primary foci of research as the key characterizing species defining CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Sec, CR.MCR.EcCr.FaAlCr.Spi & CR.MCR.EcCr.FaAlCr.Car.  Grazing pressure is the most important structuring feature of the biotope after depth.  Therefore, the sensitivity of grazers, e.g. Echinus esculentus is probably crucial to the sensitivity of the biotope. Other erect hydroids and bryozoans, e.g. Abietinaria abietina, Nemertesia antennina, Thuiaria thuja and Cellepora pumicosa are also thought important to the character of these biotopes, however, were not assessed within this review.

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 between five and ten 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 several days when they give rise to actively swimming lecithotrophic planulae which may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). In laboratory experiments, several larvae of Alcyonium digitatum failed to settle within ten days, presumably finding the conditions unsuitable. These larvae were able to survive 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 from the scarcity of predatory zooplankton which would otherwise feed upon them (Hartnoll, 1975).

Securiflustra securifrons is an erect bryozoan with a wide distribution across the North East Atlantic, recorded from Kongsfjorden, Svalbard (Gontar et al., 2001) to the Iberian Peninsula, Spain (Ramos, 2010) and within the eastern Mediterranean (Antoniadou et al., 2010). Colonies form an erect fan-like structure that can grow to approximately 10 cm in length (Porter, 2012). Antoniadou et al. (2010) recorded the successional community on settlement panels deployed in Porto Koufo Bay, Mediterranean Sea. Among other early pioneer species. After 1-2 years of immersion, the panels were colonized by further faunal species including Securiflustra securifrons. Little further information was found on the life history or recovery rates of Securiflustra securifrons. Where information regarding Securiflustra securifrons was not available evidence has been inferred from the life history traits of closely related species Flustra foliacea and Chartella papyracea. Please note, there are stark differences in the life history traits of Flustra foliacea and Chartella papyracea, for example, Flustra foliacea fronds can survive for up to 12 years whereas Chartella papyracea fronds survive for 2-3 years (Dyrynda & Ryland, 1982). Due to this variability where sensitivity assessments are based on the recovery of Flustra foliacea and/or Chartella papyracea, as proxy species for Securiflustra securifrons, confidence is assessed as low.

Flustra foliacea and Chartella papyracea are perennial species that brood their larvae (Eggleston, 1972; Dyrynda & Ryland, 1982). The brooded lecithotrophic larvae of bryozoans have a short pelagic lifetime of about 12 hours, and may therefore have poor dispersal capabilities (Ryland, 1976). Chartella papyracea and Flustra foliacea colonies begin as encrusting sheets (Tyler-Walters & Ballerstedt, 2007). Colonies have a growing season from late April–October, however new frond growth typically occurs in early Autumn.  The first larvae can be released when fronds are approximately one year old (Eggleston, 1972).  Once larval production has begun it can continue throughout the growing season however there is a major peak in Autumn and a minor peak in Spring (Dyrynda & Ryland, 1982). Larval settlement is probably related to surface contour, chemistry and the proximity of conspecific colonies (Tyler-Walters & Ballerstedt, 2007). Stebbing (1971) noted that Flustra foliacea colonies regularly reached six years of age, although 12 year old specimens were reported off the Gower peninsula, Wales.

Fariñas-Franco et al. (2014) recorded the colonization of an artificial reef constructed of 16 tonnes of king scallop shells (Pecten maximus) deployed in Strangford Loch in February 2010. The reef was then seeded with translocated Modiolus modiolus in March 2010. Among other species, Flustra foliacea had colonized the reef within six months of the reef construction. Flustra foliacea was also recorded locally prior to the construction of the reef, and therefore, recruitment may have a local source. An example of where recruitment was longer term, includes that of the RV Robert (Hiscock, 1981). Four years after sinking, the wreck of a small coaster, the M.V. Robert, off Lundy was found to be colonized by erect bryozoans and hydroids, including occasional Flustra foliacea (Hiscock, 1981). The wreck was several hundreds of metres from any significant hard substrata, and hence a considerable distance from potentially parent colonies (Hiscock, 1981 and pers comm.).

Spirobranchus triqueter and Parasmittina trispinosa are two visually dominant encrusting species within CR.MCR.EcCr.FaAlCr.Sec & CR.MCR.EcCr.FaAlCr.Spi & CR.MCR.EcCr.FaAlCr.Adig. Spirobranchus triqueter is a species of serpulid worm that forms encrusting tubes, typically 2-3cm long, on rock and shell surfaces. Once settled onto the substratum the worm forms a temporary delicate semi-transparent tube. Mature tubes are formed by the secretion of calcium carbonate. Growth rates have been observed by Dons (1927) to be 1.5 mm per month, although this varies with external conditions. Hayward & Ryland (1995) and Dons (1927) stated that sexual maturity is reached in approximately four months. Spirobranchus triqueter is also a visually dominant species within mobile and/or disturbed biotopes e.g. SS.SCS.CCS.SpiB (Connor et al., 2004), indicating this species is either highly resilient to physical disturbance or has a rapid recolonization rate. In agreement, Hiscock (1983) noted that a community, under conditions of scour and abrasion from stones and boulders moved by storms, developed into a community consisting of fast growing species such as Spirobranchus triqueter. Off Chesil Bank, the epifaunal community dominated by Spirobranchus triqueter, Balanus crenatus and Electra pilosa, decreased in cover in October, was scoured away in winter storms, and was recolonized in May to June (Warner, 1985). Hayward & Ryland (1995) noted that Spirobranchus triqueter lived approximately 1.5 years (Hayward & Ryland, 1995). Spirobranchus triqueter are broadcast spawners and are therefore likely to have a large dispersal capacity. Larvae are pelagic for about 2-3 weeks in the summer, however, in the winter this amount of time increases to about two months (Hayward & Ryland, 1995). The time of reproduction is variable, Hayward & Ryland (1995) and Segrove (1941) suggested that Spirobranchus triqueter reproduction probably takes place throughout the year, but peaks in spring and summer. However, Moore (1937) noted Spirobranchus triqueter breeding only took place in April in Port Erin, Isle of Man. Castric-Fey (1983) studied variations in settlement rate and concluded that, although the species settled all year round, very rare settlement was observed during winter and maximum settlement occurred in April, June, August and Sept-Oct. Studies in Bantry Bay revealed a single peak in recruitment during summer (especially July and August) with very little recruitment at other times of the year (Cotter et al., 2003).

Caryophyllia smithii is a small (max 3cm across) solitary coral common within tide swept sites of the UK (Wood, 2005), distributed from Greece (Koukouras, 2010) to the Shetland Islands and southern Norway (NBN, 2015). It was suggested by Fowler & Laffoley (1993) suggested that Caryophyllia smithii was a slow-growing species (0.5-1 mm in the horizontal dimension of the corallum per year), which in turn suggested that inter-specific spatial competition with colonial faunal or algae species are important factors in determining the local abundance of Caryophyllia smithii (Bell & Turner, 2000). Caryophyllia smithii reproduces sexually; sessile polyps discharge gametes typically from January-April, gamete release is most likely triggered by seasonal temperature increases, gametes are fertilized in the water column and develop into a swimming planula that then settles onto suitable substrata. The pelagic stage of the larvae may last up to ten weeks, which provides this species with a good dispersal capability (Tranter et al., 1982).

Whomersley & Picken (2003) documented epifauna colonization of offshore oil platforms in the North Sea from 1989-2000. On all platforms, Mytilus edulis dominated the near surface community. For the first three years, hydroids and tubeworms dominated the community below the mussel band. However, the hydroid community were later out-competed by other more climax communities.  Recruitment of Alcyonium digitatum and Metridium senile (as senile) began at two to five years (dependent on the oil rig).  The community structure and zonation differed between the four rigs, however generally after four years Metridium senile had become the dominant organism below the mussel zone to approximately 60-80 m Below Sea Level (BSL). Zonation differed between oil rigs but Alcyonium digitatum was the dominant organism from approximately 60-90 m BSL.

The HMS Scylla was intentionally sunk on the 27th March 2004 in Whitsand Bay, Cornwall to act as an artificial reef. Hiscock et al. (2010) recorded the succession of the biological community on the wreck for five years following the sinking of the ship. Initially, the wreck was colonized by opportunistic species /taxa, e.g. filamentous algae, hydroids, serpulid worms and barnacles. Tubularia sp. were early colonizers, appearing within a couple of months after the vessel was sunk. Metridium senile appeared late in the summer of the first year but didn’t become visually dominant until 2007 (three years after the vessel was sunk). Cylista elegans was recorded within the summer of 2005, and by the end of 2006 was well established. Corynactis viridis was first recorded in the summer of the first year and quickly formed colonies via asexual reproduction. Urticina felina was first recorded at the end of august 2006 (two years after the vessel was sunk), and by summer 2008 had increased in abundance. Alcyonium digitatum was first recorded in early summer 2005, a year after the vessel was sunk.  Within one year of growth colonies had grown to nearly full size, however, did not become a visually dominant component of the community until 2009 (five years after the vessel had been sunk). The authors noted that erect branching Bryozoa (such as Securiflustra securifrons) are not a common part of rocky reef communities to the west of Plymouth and at the time of writing had not colonized to any great extent on ‘Scylla’ by the end of the study, although several species were recorded which included Chartella papyracea in 28/08/2006 (two years after the vessel was sunk). Caryophyllia smithii was noted to colonize the wreck a year after the vessel was sunk.

Parasmittina trispinosa is an encrusting bryozoan which is described as having a “cosmopolitan” distribution by Powell (1971), in the North East Atlantic recorded from all coasts of the British Isles (NBN, 2015) to the Iberian Peninsula (Ramos, 2010). Parasmittina trispinosa is also recorded from the Panama Cana (Powell (1971) to the Gulf of Alaska (Soule, 2002) in the Pacific Ocean. At the time of writing sparse information regarding the life history traits of Parasmittina trispinosa. Eggleston (1972) noted In the Isle of Man, a peak in reproductive and vegetative growth was not well marked in Parasmittina trispinosa, and the number of embryos present is fairly constant throughout the year (Eggleston, 1972). Indicating that Parasmittina trispinosa could potentially reproduce annually within the UK. However, due to the lack of available literature regarding Parasmittina trispinosa, resilience cannot be assessed with sufficient confidence.

Echinus esculentus is a sea urchin found within Northeast 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 reach 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, 1989) 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 that 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, e.g., 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 (1979) 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. On 19th November 2002, the Prestige oil tanker spilt 63 000t of fuel 130 nautical miles off Galicia, Spain. High wave exposure and strong weather systems increased the mixing of the oil to “some” depth within the water column, causing sensitive faunal communities to be affected. Preceding and for nine years following the oil spill, the biological community of Guéthary, France was monitored. Following the oil spill, taxonomic richness decreased significantly from 57 recorded species to 41, which included the loss of Echinus esculentus from the site. Spill taxonomic richness had increased to pre-spill levels 2-3 years after the oil and Echinus esculentus had returned (Castège et al., 2014).

Resilience assessment. Colonization experiments on artificial reefs and shipwrecks also indicate that Flustra foliacea and Chartella papyracea can colonize substrata within a period of six months to two years (Hiscock et al., 2010; Fariñas-Franco et al., 2014).  Securiflustra securifrons is closely related, with a similar life history and (in the absence of other evidence) may recruit at a similar rate.  Spirobranchus triqueter can reach maturity within approximately four months and is often a dominant component of physically disturbed habitats, indicating rapid colonization rates (<1 year). Echinus esculentus can reportedly reach sexual maturity within 1-2 years (Tyler-Walters, 2008), however, recovery may take two to six years (possibly more if local recruitment is poor) (Bishop & Earll,1984; Castège et al., 2014). Alcyonium digitatum can recruit onto bare surfaces within two years, however, may take up to five years to become a dominant component of the community (Whomersley & Picken, 2003; Hiscock et al., 2010). Alcyonium digitatum is a common characterizing species across CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Sec and CR.MCR.EcCr.FaAlCr.Spi, without which the character of these biotopes would change and may be un-recognisable. As a result, the resilience assessments within this review are largely based on the recovery of Alcyonium digitatum.  If the community was completely removed from the habitat (resistance of ‘None’ or ‘Low’) resilience would be assessed as ‘Medium’. However, where resistance was assessed as ‘Medium’ or ‘High’ then resilience would be assessed as ‘High’.

Climate Change Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
Low Very Low High
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the north-west Atlantic coasts, at sea surface temperatures between 5 and 20°C but mostly between 10 and 15°C (www.obis.org).  Across this latitudinal gradient species are likely to experience a range of temperatures from approximately 5 and 18°C (Sea temperature, 2015). 

Alcyonium digitatum spawns during the winter months (Hartnoll, 1975). Gametes are fertilized while in the water column and the embryos give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975). However, laboratory experiments have observed settlement failure to occur in unsuitable conditions (Hartnoll, 1975). As spawning occurs when sea temperatures are low there is the probability that spawning and settlement could be correlated to climatic conditions, therefore global warming could impact the reproduction and recruitment of Alcyonium digitatum. However, 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 (Hartnoll, 1975).

The duration, dispersal and survival of planktonic larvae are dependent on several factors including temperature (O’Connor et al., 2007). O’Connor et al. (2007) reported planktonic larval duration to increase with temperature, therefore cold-water species could see an increase in planktonic larval duration under global warming trends. Larval survival has been reported to decrease exponentially with time (planktonic larval duration) (O’Connor et al., 2007). Elevated temperatures may increase the occurrence of octocoral diseases caused by pathogens that act opportunistically to attack hosts that are under stressful conditions. For example, Cerrano et al. (2000) reported that ecosystems in the Mediterranean are rapidly declining from extensive attacks by microorganisms correlating to elevated seawater temperatures.

Caryophyllia smithii is a temperate cup coral that has a wide distribution from Norway to the Mediterranean and South Africa in the Atlantic, found in both shallow and deep water, with records of this species between temperatures of 5 and 30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982).

Echinus esculentus is a sea urchin distributed across the North East Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Echinus esculentus is common on most coasts of the British Isles but absent from most of the east coast of England, the eastern English Channel and some parts of north Wales. 

Echinus esculentus has been recorded primarily between sea temperatures of 5 and 15°C (www.obis.org). Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark (Ursin 1960). Temperature, photoperiod and food availability are considered to be factors that control the reproduction of echinoids (Kelly, 2001). Bishop (1985) noted that gametogenesis proceeded at temperatures between 11 and 19 °C although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after 24 hr at 15°C (Tyler & Young 1998) but normally at the other temperatures tested (4, 7 and 11°C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Therefore, Echinus esculentus is likely to be intolerant of chronic long term temperature change but would probably be more intolerant of sudden or short term acute change (e.g. 5°C for one week) in temperature. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and is expected to affect calcification (Smith, 2014; Moreno, 2020). The bryozoan Securiflustra securifrons has a northern distribution, recorded at temperatures from -5-15°C (www.obis.org). Therefore, Securiflustra securifrons is highly likely to be affected by long-term changes in temperature. However, the bryozoan Parasmittina trispinosa has been recorded from Britain, north to western Norway, the Faroe Isles, northwestern Atlantic coasts, the Californian coast and the Gulf of Mexico. Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, however, there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and 22.27 ± 1.2°C at 22 m) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm2) at 11m deep survived after the first disturbance.

Spirobranchus triqueter occurs as far south as the Mediterranean. Therefore, the species will be subject to a wider range of temperatures than experienced in the British Isles (www.obis.org). Castric-Fey (1983) found that animals settling during spring showed the best growth rate and the best larval settlement occurred in the summer months. Therefore, it is assumed that Spirobranchus triqueter has some tolerance to increased temperatures. 

Sensitivity assessment. Under the middle, high and extreme emission scenarios seawater temperatures are expected to rise by 3-5°C, with potential southern summer temperatures of 22-24°C. While no evidence on the impacts of ocean warming on the characterizing species Alcyonium digitatum and Securiflustra securifrons was found, biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). The distribution of Alcyonium digitatum and Securiflustra securifrons suggests that these species may be impacted by ocean warming, as populations of these species are reported where seawater temperatures range up to 20°C and 15°C respectively (www.obis.org). Spirobranchus triqueterParasmittina trispinosa and red algae communities are found in geographical locations with higher temperatures than in the UK. Therefore these species are unlikely to be affected by an increase in seawater temperature within the UK. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods. A reduction in grazing due to loss of Echinus esculentus may result in loss of the biotope if it is replaced by a more abundant and diverse faunal turf, eg. FaT.CTub.Adig. As CR.MCR.EcCr.FaAlCr.Car is a grazed biotope and the main characterizing species Alcyonium digitatum is unknown to tolerate high temperatures resistance is assessed as ‘Low’ and resilience as ‘Very low’ so that sensitivity is assessed as 'High' at levels predicted for the end of this century.

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

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the north-west Atlantic coasts, at sea surface temperatures between 5 and 20°C but mostly between 10 and 15°C (www.obis.org).  Across this latitudinal gradient species are likely to experience a range of temperatures from approximately 5 and 18°C (Sea temperature, 2015). 

Alcyonium digitatum spawns during the winter months (Hartnoll, 1975). Gametes are fertilized while in the water column and the embryos give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975). However, laboratory experiments have observed settlement failure to occur in unsuitable conditions (Hartnoll, 1975). As spawning occurs when sea temperatures are low there is the probability that spawning and settlement could be correlated to climatic conditions, therefore global warming could impact the reproduction and recruitment of Alcyonium digitatum. However, 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 (Hartnoll, 1975).

The duration, dispersal and survival of planktonic larvae are dependent on several factors including temperature (O’Connor et al., 2007). O’Connor et al. (2007) reported planktonic larval duration to increase with temperature, therefore cold-water species could see an increase in planktonic larval duration under global warming trends. Larval survival has been reported to decrease exponentially with time (planktonic larval duration) (O’Connor et al., 2007). Elevated temperatures may increase the occurrence of octocoral diseases caused by pathogens that act opportunistically to attack hosts that are under stressful conditions. For example, Cerrano et al. (2000) reported that ecosystems in the Mediterranean are rapidly declining from extensive attacks by microorganisms correlating to elevated seawater temperatures.

Caryophyllia smithii is a temperate cup coral that has a wide distribution from Norway to the Mediterranean and South Africa in the Atlantic, found in both shallow and deep water, with records of this species between temperatures of 5 and 30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982).

Echinus esculentus is a sea urchin distributed across the North East Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Echinus esculentus is common on most coasts of the British Isles but absent from most of the east coast of England, the eastern English Channel and some parts of north Wales. 

Echinus esculentus has been recorded primarily between sea temperatures of 5 and 15°C (www.obis.org). Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark (Ursin 1960). Temperature, photoperiod and food availability are considered to be factors that control the reproduction of echinoids (Kelly, 2001). Bishop (1985) noted that gametogenesis proceeded at temperatures between 11 and 19 °C although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after 24 hr at 15°C (Tyler & Young 1998) but normally at the other temperatures tested (4, 7 and 11°C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Therefore, Echinus esculentus is likely to be intolerant of chronic long term temperature change but would probably be more intolerant of sudden or short term acute change (e.g. 5°C for one week) in temperature. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and is expected to affect calcification (Smith, 2014; Moreno, 2020). The bryozoan Securiflustra securifrons has a northern distribution, recorded at temperatures from -5-15°C (www.obis.org). Therefore, Securiflustra securifrons is highly likely to be affected by long-term changes in temperature. However, the bryozoan Parasmittina trispinosa has been recorded from Britain, north to western Norway, the Faroe Isles, northwestern Atlantic coasts, the Californian coast and the Gulf of Mexico. Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, however, there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and 22.27 ± 1.2°C at 22 m) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm2) at 11m deep survived after the first disturbance.

Spirobranchus triqueter occurs as far south as the Mediterranean. Therefore, the species will be subject to a wider range of temperatures than experienced in the British Isles (www.obis.org). Castric-Fey (1983) found that animals settling during spring showed the best growth rate and the best larval settlement occurred in the summer months. Therefore, it is assumed that Spirobranchus triqueter has some tolerance to increased temperatures. 

Sensitivity assessment. Under the middle, high and extreme emission scenarios seawater temperatures are expected to rise by 3-5°C, with potential southern summer temperatures of 22-24°C. While no evidence on the impacts of ocean warming on the characterizing species Alcyonium digitatum and Securiflustra securifrons was found, biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). The distribution of Alcyonium digitatum and Securiflustra securifrons suggests that these species may be impacted by ocean warming, as populations of these species are reported where seawater temperatures range up to 20°C and 15°C respectively (www.obis.org). Spirobranchus triqueterParasmittina trispinosa and red algae communities are found in geographical locations with higher temperatures than in the UK. Therefore these species are unlikely to be affected by an increase in seawater temperature within the UK. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods. A reduction in grazing due to loss of Echinus esculentus may result in loss of the biotope if it is replaced by a more abundant and diverse faunal turf, eg. FaT.CTub.Adig. As CR.MCR.EcCr.FaAlCr.Car is a grazed biotope and the main characterizing species Alcyonium digitatum is unknown to tolerate high temperatures resistance is assessed as ‘Low’ and resilience as ‘Very low’ so that sensitivity is assessed as 'High' at levels predicted for the end of this century.

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

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the north-west Atlantic coasts, at sea surface temperatures between 5 and 20°C but mostly between 10 and 15°C (www.obis.org).  Across this latitudinal gradient species are likely to experience a range of temperatures from approximately 5 and 18°C (Sea temperature, 2015). 

Alcyonium digitatum spawns during the winter months (Hartnoll, 1975). Gametes are fertilized while in the water column and the embryos give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975). However, laboratory experiments have observed settlement failure to occur in unsuitable conditions (Hartnoll, 1975). As spawning occurs when sea temperatures are low there is the probability that spawning and settlement could be correlated to climatic conditions, therefore global warming could impact the reproduction and recruitment of Alcyonium digitatum. However, 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 (Hartnoll, 1975).

The duration, dispersal and survival of planktonic larvae are dependent on several factors including temperature (O’Connor et al., 2007). O’Connor et al. (2007) reported planktonic larval duration to increase with temperature, therefore cold-water species could see an increase in planktonic larval duration under global warming trends. Larval survival has been reported to decrease exponentially with time (planktonic larval duration) (O’Connor et al., 2007). Elevated temperatures may increase the occurrence of octocoral diseases caused by pathogens that act opportunistically to attack hosts that are under stressful conditions. For example, Cerrano et al. (2000) reported that ecosystems in the Mediterranean are rapidly declining from extensive attacks by microorganisms correlating to elevated seawater temperatures.

Caryophyllia smithii is a temperate cup coral that has a wide distribution from Norway to the Mediterranean and South Africa in the Atlantic, found in both shallow and deep water, with records of this species between temperatures of 5 and 30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982).

Echinus esculentus is a sea urchin distributed across the North East Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Echinus esculentus is common on most coasts of the British Isles but absent from most of the east coast of England, the eastern English Channel and some parts of north Wales. 

Echinus esculentus has been recorded primarily between sea temperatures of 5 and 15°C (www.obis.org). Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark (Ursin 1960). Temperature, photoperiod and food availability are considered to be factors that control the reproduction of echinoids (Kelly, 2001). Bishop (1985) noted that gametogenesis proceeded at temperatures between 11 and 19 °C although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after 24 hr at 15°C (Tyler & Young 1998) but normally at the other temperatures tested (4, 7 and 11°C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Therefore, Echinus esculentus is likely to be intolerant of chronic long term temperature change but would probably be more intolerant of sudden or short term acute change (e.g. 5°C for one week) in temperature. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and is expected to affect calcification (Smith, 2014; Moreno, 2020). The bryozoan Securiflustra securifrons has a northern distribution, recorded at temperatures from -5-15°C (www.obis.org). Therefore, Securiflustra securifrons is highly likely to be affected by long-term changes in temperature. However, the bryozoan Parasmittina trispinosa has been recorded from Britain, north to western Norway, the Faroe Isles, northwestern Atlantic coasts, the Californian coast and the Gulf of Mexico. Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, however, there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and 22.27 ± 1.2°C at 22 m) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm2) at 11m deep survived after the first disturbance.

Spirobranchus triqueter occurs as far south as the Mediterranean. Therefore, the species will be subject to a wider range of temperatures than experienced in the British Isles (www.obis.org). Castric-Fey (1983) found that animals settling during spring showed the best growth rate and the best larval settlement occurred in the summer months. Therefore, it is assumed that Spirobranchus triqueter has some tolerance to increased temperatures. 

Sensitivity assessment. Under the middle, high and extreme emission scenarios seawater temperatures are expected to rise by 3-5°C, with potential southern summer temperatures of 22-24°C. While no evidence on the impacts of ocean warming on the characterizing species Alcyonium digitatum and Securiflustra securifrons was found, biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). The distribution of Alcyonium digitatum and Securiflustra securifrons suggests that these species may be impacted by ocean warming, as populations of these species are reported where seawater temperatures range up to 20°C and 15°C respectively (www.obis.org). Spirobranchus triqueterParasmittina trispinosa and red algae communities are found in geographical locations with higher temperatures than in the UK. Therefore these species are unlikely to be affected by an increase in seawater temperature within the UK. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods. A reduction in grazing due to loss of Echinus esculentus may result in loss of the biotope if it is replaced by a more abundant and diverse faunal turf, eg. FaT.CTub.Adig. As CR.MCR.EcCr.FaAlCr.Car is a grazed biotope and the main characterizing species Alcyonium digitatum is unknown to tolerate high temperatures resistance is assessed as ‘Low’ and resilience as ‘Very low’ so that sensitivity is assessed as 'High' at levels predicted for the end of this century.

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

Marine heatwaves are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). No studies on the impacts of marine heatwaves on Alcyonium digitatum were found. However, this species appears to be restricted to colder waters and occurs in seawater temperatures between 5 and 20°C (www.obis.org).  Therefore, Alcyonium digitatum is likely to be impacted by heatwaves under both scenarios. 

Caryophyllia smithii is a temperate cup coral that has a wide distribution and is found in both shallow and deep water, with records of this species between temperatures of 5 and 30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982). Therefore, marine heatwaves could impact the reproduction and recruitment of Caryophyllia smithii. 

Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate resulting in metabolic stress (Bishop 1985). Bishop (1985) observed gametogenesis to occur between 11 and 19°C however, continued exposure to 19°C disrupted gametogenesis. In addition, embryos and larvae developed abnormally after 24hr exposure to 15°C (Bishop, 1985). Therefore, marine heatwaves have the potential to impact the reproduction, recruitment and survival of Echinus esculentus. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Leveroni, 2020). No evidence on the impacts of marine heatwaves on Securiflustra securifrons was found, however as this species occurs between -5 and 15°C (www.obis.org), therefore there is a high chance of the species being affected by heatwaves. Similarly, no evidence on the impacts of marine heatwaves on Parasmittina trispinosa was found. Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, but there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature in the UK, as Parasmittina trispinosa is likely to acclimate to temperatures with time. However, the occurrence of marine heatwaves could cause mass mortality to populations that have not been acclimated to warmer temperatures.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years.  The marine heatwave events caused mass mortality among a number of species. A warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm2) at 11 m deep survived after the first disturbance.  

Spirobranchus triqueter is recorded as abundant from the Iberian Peninsula, Spain (Ramos, 2010) as well as from the Alexandria coast of Egypt, Mediterranean Sea (Sarah, 2010). Across this latitudinal gradient, Spirobranchus triqueter is likely to experience a range of temperatures from approximately 5-28°C (Sea temperature, 2015), and is therefore unlikely to be affected by marine heatwaves. 

Sensitivity assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Under the high emission scenario, if heatwaves occurred every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C. There is no experimental evidence of the impact of marine heatwaves on the characteristic species of this biotope, however, as Alcyonium digitatum is not known to tolerant seawater temperatures >20°C and the bryozoan Securiflustra securifrons is found between temperatures of -5 and 15°C. As CR.MCR.EcCr.FaAlCr.Sec is a grazed biotope and the primary grazer Echinus esculentus cannot tolerate high temperatures, under the middle and high emissions scenario resistance is assessed as “Low”, and resilience is assessed as “Low”, so the biotope is assessed as “High” sensitivity.

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

Marine heatwaves are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). No studies on the impacts of marine heatwaves on Alcyonium digitatum were found. However, this species appears to be restricted to colder waters and occurs in seawater temperatures between 5 and 20°C (www.obis.org).  Therefore, Alcyonium digitatum is likely to be impacted by heatwaves under both scenarios. 

Caryophyllia smithii is a temperate cup coral that has a wide distribution and is found in both shallow and deep water, with records of this species between temperatures of 5 and 30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982). Therefore, marine heatwaves could impact the reproduction and recruitment of Caryophyllia smithii. 

Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate resulting in metabolic stress (Bishop 1985). Bishop (1985) observed gametogenesis to occur between 11 and 19°C however, continued exposure to 19°C disrupted gametogenesis. In addition, embryos and larvae developed abnormally after 24hr exposure to 15°C (Bishop, 1985). Therefore, marine heatwaves have the potential to impact the reproduction, recruitment and survival of Echinus esculentus. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Leveroni, 2020). No evidence on the impacts of marine heatwaves on Securiflustra securifrons was found, however as this species occurs between -5 and 15°C (www.obis.org), therefore there is a high chance of the species being affected by heatwaves. Similarly, no evidence on the impacts of marine heatwaves on Parasmittina trispinosa was found. Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, but there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature in the UK, as Parasmittina trispinosa is likely to acclimate to temperatures with time. However, the occurrence of marine heatwaves could cause mass mortality to populations that have not been acclimated to warmer temperatures.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years.  The marine heatwave events caused mass mortality among a number of species. A warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm2) at 11 m deep survived after the first disturbance.  

Spirobranchus triqueter is recorded as abundant from the Iberian Peninsula, Spain (Ramos, 2010) as well as from the Alexandria coast of Egypt, Mediterranean Sea (Sarah, 2010). Across this latitudinal gradient, Spirobranchus triqueter is likely to experience a range of temperatures from approximately 5-28°C (Sea temperature, 2015), and is therefore unlikely to be affected by marine heatwaves. 

Sensitivity assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Under the high emission scenario, if heatwaves occurred every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C. There is no experimental evidence of the impact of marine heatwaves on the characteristic species of this biotope, however, as Alcyonium digitatum is not known to tolerant seawater temperatures >20°C and the bryozoan Securiflustra securifrons is found between temperatures of -5 and 15°C. As CR.MCR.EcCr.FaAlCr.Sec is a grazed biotope and the primary grazer Echinus esculentus cannot tolerate high temperatures, under the middle and high emissions scenario resistance is assessed as “Low”, and resilience is assessed as “Low”, so the biotope is assessed as “High” sensitivity.

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

Increasing levels of CO2 in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005). In general, it is thought that calcifying invertebrates will be more sensitive to ocean acidification than non-calcifying invertebrates, which appear to have a more mixed response (Hofmann et al., 2010). It must be noted that many species show variation in their response to pCOindependent of their taxonomic group or habitat preferences (Widdicombe & Spicer, 2008; Kroeker et al., 2013).

No evidence of the impacts of ocean acidification on Alcyonium digitatum was found. However, studies on the impacts of ocean acidification on octocorals reported various responses (Conci et al., 2021). Gomez et al. (2014) found a significant negative correlation between calcification and CO2 concentrations for Eunicea flexuosa at a pH range of 8.1–7.1. But another study on Eunicea flexuosa observed no significant differences in branch extension and sclerite structure at pH 7.75 and suggested that Eunicea flexuosa had a degree of resilience to ocean acidification (Enochs et al., 2016). Similarly, ocean acidification did not significantly impact the octocorals Ovabunda macrospiculata, Heteroxenia fuscescens and Sarcophyton sp. with no effects on polyp weight and protein concentration, nor any significant differences in chlorophyll abundance or density of zooxanthellae at pH 7.6 and 7.3 when compared to controls at pH 8.2. The findings suggested that the octocoral’s tissue may provide a protective role against acidification (Gabay et al., 2013; Gabay et al., 2014).

The planktonic larval stage is often thought to be the most sensitive stage to ocean acidification in benthic organisms (Kurihara, 2008, Chan et al., 2015).  The embryos of Alcyonium digitatum are neutrally buoyant and float freely for several days before they give rise to actively swimming lecithotrophic planulae which may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). In laboratory experiments, larvae of Alcyonium digitatum failed to settle within ten days, presumably finding the conditions unsuitable (Hartnoll, 1975), however, the water conditions were not recorded. 

Ocean acidification has negative impacts on numerous species of coral; however, laboratory evidence has shown that the temperate cup coral Caryophyllia smithii might have some resistance to ocean acidification. Rodolfo-Metalpa et al. (2015) exposed Caryophyllia smithii samples to elevated CO2 conditions expected for the end of this century for several months. All of the corals survived the treatment and no significant differences in respiration or gross and net calcification rates were observed under high seawater pCO2

Dupont et al. (2010) analysed the literature and suggested that echinoderms were generally robust to ocean acidification, although different life stages and species were affected differently. Limited evidence on the impacts of ocean acidification on Echinus esculentus was found. However, near future CO2-driven ocean acidification (-0.4 units for the end of this century) had negative impacts on the survival and developmental dynamics of Echinus esculentus (Dupont and Thorndyke, personal communication, 2009). Evidence on the reproduction or early life stages of Echinus esculentus was not found, however, studies have found a variety of responses to ocean acidification depending on the species of sea urchin. Dworjanyn & Byrne (2018) found acidification to decrease the gonad index of Tripneustes gratilla, with almost no gonads in urchins at pH 7.6 regardless of temperature. Clark et al. (2009) observed the effects of lowered pH on larvae from tropical (Tripneustes gratilla), temperate (Pseudechinus huttoniEvechinus chloroticus), and a polar species (Sterechinus neumayeri) of sea urchin. The results indicated that the survival of larvae may not be directly affected by the pH levels predicted for 2100, but the low pH may cause reduced growth and calcification, which could compromise survival. Lee et al. (2019) observed metabolic rates of Strongylocentrotus purpuratus larvae to increase with decreasing pH and reach a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Therefore, ocean acidification could have detrimental effects on the survival, reproduction and recruitment of Echinus esculentus. 

NeverthelessSuckling et al. (2014) emphasized that studies that presented stressors in a shock-type exposure (as above) may reflect stress response outcomes rather than the results of gradual change in the climate. Cross generation echinoderm studies observed a variety of responses to the progeny produced by adults that have been exposed to low pH. The evidence indicated that the effect on progeny depended on the level of acidification and the conditioning duration of the parents (Byrne et al., 2019). Suckling et al. (2014) found that when Psammechinus miliaris larvae were raised from parents pre-exposed to low pH conditions (pH 7.7 compared to control pH of 7.98), settlement rates were similar to control larvae, and the test (i.e. the urchin shell) diameter was larger, which suggested that this species can acclimate and possibly adapt to low pH conditions. Similarly, Clark et al. (2019) observed that gene expression profiles associated with transgenerational plasticity contributed to Psammechinus miliaris larval resilience when the adults were conditioned to low pH.

From observations at natural vent sites, Connell et al. (2018) observed that increased CO2 enrichment reduced the abundance and feeding rates of primary grazers (urchin Evechinus chloroticus), allowing turf algae to increase in abundance. Therefore, ocean acidification could cause changes to community structure. 

Bryozoans are invertebrate calcifiers, therefore they are potentially highly sensitive to ocean acidification (Smith, 2009). The decrease in water pH from global climate change could cause corrosion, changes in mineralogy and decrease the survival of bryozoans (Smith, 2014). No evidence on the impacts of ocean acidification on the characterizing bryozoan species Parasmittina trispinosa or Securiflustra securifrons were found. However, Swezey et al. (2017) observed that populations of bryozoans raised under high CO2 (1254 μatm; pH 7.60) conditions grew faster, invested less in reproduction and produced lighter skeletons when compared to genetically identical clones raised under current surface atmospheric CO2 values (400 μatm; pH 8.04). In addition, the bryozoans under high COaltered Mg/Ca ratio of skeletal calcite, which could be a protective mechanism against acidification (Swezey et al., 2017). 

Lombardi et al. (2011) investigated the impacts of ocean acidification on the growth, organic tissue and protein profile of bryozoan Myriapora truncata along a gradient of different pH levels in a natural volcanic CO2 vent site. At sites with normal pH levels (mean pH 8.10),  Myriapora truncata produced new and complete zooids. However, at the intermediate (pH 7.83) and low pH (pH 7.32) sites neither partial nor complete zooids were produced. At the intermediate pH sites, Myriapora truncata increased its skeleton thickness suggesting a protective defence against dissolution, but at the low pH sites, there was a decrease in skeletal weights and corrosion of skeletal structures. Additionally, at intermediate and low pH sites Myriapora truncata upregulated protein production to potentially overcome the low pH conditions, however, the upregulation came at a cost, and fitness was reduced resulting in mortality particularly in the lower pH sites. 

Studies on the impacts of ocean acidification on the calcareous tube structure of serpulidae polychaete worms observed reductions of tube elongation, elasticity and strength when exposed to reduced pH conditions (Chan et al., 2012; Li et al., 2014; Dıáz-Castanẽda et al., 2019). Dıáz-Castanẽda et al. (2019) observed pH to affect trochophore size and post-settlement tube growth, with post-settlement tubes half the size of those at current ocean pH levels. Li et al. (2014) observed changes to the structure, volume and density of the tubes, with reductions in hardiness and elasticity, in addition to a 64% reduction in tube crushing force. The reduction in tube size and hardiness could impact the survival of the species with increased predation and reduction in the ability to withstand wave force (Chan et al., 2012; Li et al., 2014). 

Sensitivity assessment. While no evidence of the effect of ocean acidification on Alcyonium digitatum was found, the effects of ocean acidification on other species of octocoral show some resilience to low pH. Though, Alcyonium digitatum larvae settlement had been reported to be sensitive to environmental conditions, though the conditions were not verified. Ocean acidification studies have shown negative impacts on the health and reproduction of sea urchins. In addition, bryozoans appear to be highly sensitive to ocean acidification, with impacts on health, survival and reproduction.  Unfortunately, at present, there are no studies to determine whether Alcyonium digitatum, Securiflustra securifrons, Parasmittina trispinosa or Echinus esculentus can adapt or acclimate to future pH conditions, but on the evidence available, Parasmittina trispinosa, Securiflustra securifrons and Echinus esculentus could be lost from this biotope under the predicted emissions scenarios. Therefore, as CR.MCR.EcCr.FaAlCr.Sec is a grazed biotope, under both the middle and high emission scenarios (0.15 and 0.35 pH unit decrease, respectively) the biotope is assessed as having a resistance level of ‘Low’, and a resilience level of ‘Very low’ because of the long-term nature of ocean acidification, leading to a sensitivity assessment of ‘High’ at the benchmark level, albeit with ‘Low’ confidence.

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

Increasing levels of CO2 in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005). In general, it is thought that calcifying invertebrates will be more sensitive to ocean acidification than non-calcifying invertebrates, which appear to have a more mixed response (Hofmann et al., 2010). It must be noted that many species show variation in their response to pCOindependent of their taxonomic group or habitat preferences (Widdicombe & Spicer, 2008; Kroeker et al., 2013).

No evidence of the impacts of ocean acidification on Alcyonium digitatum was found. However, studies on the impacts of ocean acidification on octocorals reported various responses (Conci et al., 2021). Gomez et al. (2014) found a significant negative correlation between calcification and CO2 concentrations for Eunicea flexuosa at a pH range of 8.1–7.1. But another study on Eunicea flexuosa observed no significant differences in branch extension and sclerite structure at pH 7.75 and suggested that Eunicea flexuosa had a degree of resilience to ocean acidification (Enochs et al., 2016). Similarly, ocean acidification did not significantly impact the octocorals Ovabunda macrospiculata, Heteroxenia fuscescens and Sarcophyton sp. with no effects on polyp weight and protein concentration, nor any significant differences in chlorophyll abundance or density of zooxanthellae at pH 7.6 and 7.3 when compared to controls at pH 8.2. The findings suggested that the octocoral’s tissue may provide a protective role against acidification (Gabay et al., 2013; Gabay et al., 2014).

The planktonic larval stage is often thought to be the most sensitive stage to ocean acidification in benthic organisms (Kurihara, 2008, Chan et al., 2015).  The embryos of Alcyonium digitatum are neutrally buoyant and float freely for several days before they give rise to actively swimming lecithotrophic planulae which may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). In laboratory experiments, larvae of Alcyonium digitatum failed to settle within ten days, presumably finding the conditions unsuitable (Hartnoll, 1975), however, the water conditions were not recorded. 

Ocean acidification has negative impacts on numerous species of coral; however, laboratory evidence has shown that the temperate cup coral Caryophyllia smithii might have some resistance to ocean acidification. Rodolfo-Metalpa et al. (2015) exposed Caryophyllia smithii samples to elevated CO2 conditions expected for the end of this century for several months. All of the corals survived the treatment and no significant differences in respiration or gross and net calcification rates were observed under high seawater pCO2

Dupont et al. (2010) analysed the literature and suggested that echinoderms were generally robust to ocean acidification, although different life stages and species were affected differently. Limited evidence on the impacts of ocean acidification on Echinus esculentus was found. However, near future CO2-driven ocean acidification (-0.4 units for the end of this century) had negative impacts on the survival and developmental dynamics of Echinus esculentus (Dupont and Thorndyke, personal communication, 2009). Evidence on the reproduction or early life stages of Echinus esculentus was not found, however, studies have found a variety of responses to ocean acidification depending on the species of sea urchin. Dworjanyn & Byrne (2018) found acidification to decrease the gonad index of Tripneustes gratilla, with almost no gonads in urchins at pH 7.6 regardless of temperature. Clark et al. (2009) observed the effects of lowered pH on larvae from tropical (Tripneustes gratilla), temperate (Pseudechinus huttoniEvechinus chloroticus), and a polar species (Sterechinus neumayeri) of sea urchin. The results indicated that the survival of larvae may not be directly affected by the pH levels predicted for 2100, but the low pH may cause reduced growth and calcification, which could compromise survival. Lee et al. (2019) observed metabolic rates of Strongylocentrotus purpuratus larvae to increase with decreasing pH and reach a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Therefore, ocean acidification could have detrimental effects on the survival, reproduction and recruitment of Echinus esculentus. 

NeverthelessSuckling et al. (2014) emphasized that studies that presented stressors in a shock-type exposure (as above) may reflect stress response outcomes rather than the results of gradual change in the climate. Cross generation echinoderm studies observed a variety of responses to the progeny produced by adults that have been exposed to low pH. The evidence indicated that the effect on progeny depended on the level of acidification and the conditioning duration of the parents (Byrne et al., 2019). Suckling et al. (2014) found that when Psammechinus miliaris larvae were raised from parents pre-exposed to low pH conditions (pH 7.7 compared to control pH of 7.98), settlement rates were similar to control larvae, and the test (i.e. the urchin shell) diameter was larger, which suggested that this species can acclimate and possibly adapt to low pH conditions. Similarly, Clark et al. (2019) observed that gene expression profiles associated with transgenerational plasticity contributed to Psammechinus miliaris larval resilience when the adults were conditioned to low pH.

From observations at natural vent sites, Connell et al. (2018) observed that increased CO2 enrichment reduced the abundance and feeding rates of primary grazers (urchin Evechinus chloroticus), allowing turf algae to increase in abundance. Therefore, ocean acidification could cause changes to community structure. 

Bryozoans are invertebrate calcifiers, therefore they are potentially highly sensitive to ocean acidification (Smith, 2009). The decrease in water pH from global climate change could cause corrosion, changes in mineralogy and decrease the survival of bryozoans (Smith, 2014). No evidence on the impacts of ocean acidification on the characterizing bryozoan species Parasmittina trispinosa or Securiflustra securifrons were found. However, Swezey et al. (2017) observed that populations of bryozoans raised under high CO2 (1254 μatm; pH 7.60) conditions grew faster, invested less in reproduction and produced lighter skeletons when compared to genetically identical clones raised under current surface atmospheric CO2 values (400 μatm; pH 8.04). In addition, the bryozoans under high COaltered Mg/Ca ratio of skeletal calcite, which could be a protective mechanism against acidification (Swezey et al., 2017). 

Lombardi et al. (2011) investigated the impacts of ocean acidification on the growth, organic tissue and protein profile of bryozoan Myriapora truncata along a gradient of different pH levels in a natural volcanic CO2 vent site. At sites with normal pH levels (mean pH 8.10),  Myriapora truncata produced new and complete zooids. However, at the intermediate (pH 7.83) and low pH (pH 7.32) sites neither partial nor complete zooids were produced. At the intermediate pH sites, Myriapora truncata increased its skeleton thickness suggesting a protective defence against dissolution, but at the low pH sites, there was a decrease in skeletal weights and corrosion of skeletal structures. Additionally, at intermediate and low pH sites Myriapora truncata upregulated protein production to potentially overcome the low pH conditions, however, the upregulation came at a cost, and fitness was reduced resulting in mortality particularly in the lower pH sites. 

Studies on the impacts of ocean acidification on the calcareous tube structure of serpulidae polychaete worms observed reductions of tube elongation, elasticity and strength when exposed to reduced pH conditions (Chan et al., 2012; Li et al., 2014; Dıáz-Castanẽda et al., 2019). Dıáz-Castanẽda et al. (2019) observed pH to affect trochophore size and post-settlement tube growth, with post-settlement tubes half the size of those at current ocean pH levels. Li et al. (2014) observed changes to the structure, volume and density of the tubes, with reductions in hardiness and elasticity, in addition to a 64% reduction in tube crushing force. The reduction in tube size and hardiness could impact the survival of the species with increased predation and reduction in the ability to withstand wave force (Chan et al., 2012; Li et al., 2014). 

Sensitivity assessment. While no evidence of the effect of ocean acidification on Alcyonium digitatum was found, the effects of ocean acidification on other species of octocoral show some resilience to low pH. Though, Alcyonium digitatum larvae settlement had been reported to be sensitive to environmental conditions, though the conditions were not verified. Ocean acidification studies have shown negative impacts on the health and reproduction of sea urchins. In addition, bryozoans appear to be highly sensitive to ocean acidification, with impacts on health, survival and reproduction.  Unfortunately, at present, there are no studies to determine whether Alcyonium digitatum, Securiflustra securifrons, Parasmittina trispinosa or Echinus esculentus can adapt or acclimate to future pH conditions, but on the evidence available, Parasmittina trispinosa, Securiflustra securifrons and Echinus esculentus could be lost from this biotope under the predicted emissions scenarios. Therefore, as CR.MCR.EcCr.FaAlCr.Sec is a grazed biotope, under both the middle and high emission scenarios (0.15 and 0.35 pH unit decrease, respectively) the biotope is assessed as having a resistance level of ‘Low’, and a resilience level of ‘Very low’ because of the long-term nature of ocean acidification, leading to a sensitivity assessment of ‘High’ at the benchmark level, albeit with ‘Low’ confidence.

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

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Evidence appears to suggest that impacts of sea-level rise on exposure or tidal energy will be non-linear and site-specific (Pickering et al., 2012, Li et al., 2016).  This biotope occurs on mixed sediment, in moderately exposed to sheltered areas, subject to strong to weak tidal streams and, therefore, should be reasonably robust to any changes which occur. Furthermore, this biotope occurs at depths of 10-30 m around the UK, and sea-level rises predicted for the end of this century should have limited impacts on this biotope.

Sensitivity assessment. As this biotope CR.MCR.EcCr.FaAlCr.Sec can occur from 10-30 m depth, in a range of different energy environments, it is assumed that a sea-level rise of 50 cm, 70 cm or 107 cm (middle and high emission, and extreme scenarios) would have limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. 

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

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Evidence appears to suggest that impacts of sea-level rise on exposure or tidal energy will be non-linear and site-specific (Pickering et al., 2012, Li et al., 2016).  This biotope occurs on mixed sediment, in moderately exposed to sheltered areas, subject to strong to weak tidal streams and, therefore, should be reasonably robust to any changes which occur. Furthermore, this biotope occurs at depths of 10-30 m around the UK, and sea-level rises predicted for the end of this century should have limited impacts on this biotope.

Sensitivity assessment. As this biotope CR.MCR.EcCr.FaAlCr.Sec can occur from 10-30 m depth, in a range of different energy environments, it is assumed that a sea-level rise of 50 cm, 70 cm or 107 cm (middle and high emission, and extreme scenarios) would have limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. 

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

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Evidence appears to suggest that impacts of sea-level rise on exposure or tidal energy will be non-linear and site-specific (Pickering et al., 2012, Li et al., 2016).  This biotope occurs on mixed sediment, in moderately exposed to sheltered areas, subject to strong to weak tidal streams and, therefore, should be reasonably robust to any changes which occur. Furthermore, this biotope occurs at depths of 10-30 m around the UK, and sea-level rises predicted for the end of this century should have limited impacts on this biotope.

Sensitivity assessment. As this biotope CR.MCR.EcCr.FaAlCr.Sec can occur from 10-30 m depth, in a range of different energy environments, it is assumed that a sea-level rise of 50 cm, 70 cm or 107 cm (middle and high emission, and extreme scenarios) would have limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. 

Hydrological Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
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). Securiflustra securifrons is recorded from Kongsfjorden, Svalbard (Gontar et al., 2001) to the Iberian peninsula in both Spain and Portugal (Ramos, 2010). Across this latitudinal gradient both species are likely to experience a range of temperatures from approximately 5-18°C (Seatemperature, 2015).

Spirobranchus triqueter is described as a temperate species by Kupriyanova & Badyaev (1998). Spirobranchus triqueter is recorded as abundant in sub-tidal habitats of Trondheimsfjord (63°N) (Kukliński & Barnes, 2008), no survey reports could be found further north. The most southerly records are from the Iberian peninsula, Spain (Ramos, 2010) as well from the Alexandria coast of Egypt, Mediterranean Sea (Dorgham et al., 2013). Across this latitudinal gradient, Spirobranchus triqueter is likely to experience a range of temperatures from approximately 5-28°C (Seatemperature, 2015).

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).

Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns. Mature examples of Caryophyllia smithii can be recorded in Greece

CR.MCR.EcCr.FaAlCr.Adig & CR.MCR.EcCr.FaAlCr.Pom are restricted to the north of the British Isles; CR.MCR.EcCr.FaAlCr.Sec is also recorded in the north of the British Isles, however, there are some records from Pembrokeshire, Wales. Sea surface temperature across this distribution ranges from northern to southern Sea Surface Temperature (SST) of 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013).

Sensitivity assessment. Spirobranchus triqueter records from the Alexandria coast of Egypt, Mediterranean Sea (Dorgham et al., 2013) indicate the species is unlikely to be affected at the benchmark level. An increase in sea surface temperature of 2°C for a period of 1 year combined with high temperatures may approach the upper temperature threshold of Alcyonium digitatum, Echinus esculentus, and/or Securiflustra securifrons, and may, therefore, cause minor declines in abundance. Biotopes in the North of the UK are unlikely to be affected at the benchmark level. There was insufficient evidence to assess the effect of a short-term increase in temperature of 5°C on Alcyonium digitatum however it may disrupt Echinus esculentus spawning in southern examples of this biotope. Resistance has been assessed as ‘Medium’, resilience has been assessed as ‘High’. Sensitivity has been assessed as ‘Low’.

High High Not sensitive
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). Across this latitudinal gradient, both species are likely to experience a range of temperatures from approximately 5-18°C. Alcyonium digitatum was also reported to be apparently unaffected by the severe winter of 1962-1963 where air temperature reached -5.8°C (Crisp, 1964). Securiflustra securifrons is recorded from Kongsfjorden, Svalbard (Gontar et al., 2001) to the Iberian peninsula in both Spain and Portugal (Ramos, 2010).

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 at the pressure benchmark. 

Spirobranchus triqueter is described as a temperate species by Kupriyanova & Badyaev (1998). Spirobranchus triqueter is recorded as abundant in sub-tidal habitats of Trondheimsfjord (63°N) (Kukliński & Barnes, 2008), no survey reports could be found further north. Averaged across several years the lowest winter temperature within Trondheimsfjord is 4.9°C (Seatemperature, 2015). Below 7°C Spirobranchus triqueter is unable to build calcareous tubes (Thomas, 1940). Mature adults may survive a decrease at the pressure benchmark however larvae may not be able to attach to the substate (Riley & Ballerstedt, 2005) if a temperature decrease co-occurred with cold winter temperatures in the UK. However, settlement is reportedly low within winter (See resilience section), and therefore the effects on recruitment are likely to be minor.

CR.MCR.EcCr.FaAlCr.Adig & CR.MCR.EcCr.FaAlCr.Pom core records are restricted to the north of the British Isles; CR.MCR.EcCr.FaAlCr.Sec is also recorded in the north of the British Isles, however, there are some records from Pembrokeshire, Wales. Sea surface temperature across this distribution ranges from northern to southern Sea Surface Temperature (SST) ranges of 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013).

Sensitivity assessment. Alcyonium digitatum, Echinus esculentus & Securiflustra securifrons have northern/boreal distributions and are unlikely to be affected at the benchmark level. Spirobranchus triqueter is unable to build calcareous tubes at low temperatures, however during winter, this is unlikely to have any significant effects on recruitment. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’.

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

Lyster (1965) tested the tolerance of Spirobranchus triqueter larvae to various hyper and hypo salinity treatments. Larvae were placed in cultures ranging from 0-90‰ and notes were made on the time taken for larvae to die or begin displaying abnormal behaviour. Spirobranchus triqueter larvae were tolerant of salinities ranging from 20-50‰, above 50‰ caused high mortality. Spirobranchus triqueter is therefore unlikely to be affected at the pressure benchmark.

Echinoderms are generally stenohaline and possess no osmoregulatory organ (Boolootian, 1966). Therefore, an increase in salinity may cause Echinus esculentus mortality. Alcyonium digitatum’ distribution and the depth at which it occurs also suggest it would not likely experience regular salinity fluctuations and therefore tolerate significant increases in salinity. CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom and CR.MCR.EcCr.FaAlCr.Sec are restricted to full salinity (Connor et al., 2004), it, therefore, seems likely that an increase in salinity to >40‰ may cause a decline in the abundance of Alcyonium digitatum, Echinus esculentus & Securiflustra securifrons.

Sensitivity assessment. Resistance has been assessed as ‘Low’, resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’. Due to the lack of information regarding salinity effects on Alcyonium digitatum, Echinus esculentus & Securiflustra securifrons confidence in this assessment has been assessed as low. 

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

Alcyonium digitatum does inhabit situations such as the entrances to sea lochs (Budd, 2008) or the entrances to estuaries (Braber & Borghouts, 1977) where salinity may vary occasionally. Furthermore, as highlighted the Marine Nature Conservation Review (MNCR) records of 23rd Oct 2014 show Alcyonium digitatum is found within a number of variable salinity biotopes, e.g. MCR.BYH.Flu.Hocu,. However, its distribution and the depth at which it occurs suggest that Alcyonium digitatum would not likely often experience salinity fluctuations and 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. Furthermore, as highlighted the Marine Nature Conservation Review (MNCR) records of 23rd Oct 2014 show Echinus esculentus is found within a number of variable and reduced salinity biotopes, e.g. IR.LIR.KVS.SlatPsaVS.

Ryland (1970) stated that with a few exceptions, the Gymnolaemata (the class of Bryozoans which Securiflustra securifrons is part of) were fairly stenohaline and restricted to full salinity (35 psu) and noted that reduced salinities result in an impoverished bryozoan fauna. Similarly, Dyrynda (1994) noted that Flustra foliacea were probably restricted to the vicinity of the Poole Harbour entrance by their intolerance to reduced salinity. Although protected from extreme changes in salinity due to their subtidal habitat, the introduction of freshwater or hyposaline effluents may adversely affect Flustra foliacea colonies.

Lyster (1965) tested the tolerance of Spirobranchus triqueter larvae to various hyper and hypo salinity treatments. Larvae were placed in cultures ranging from 0-90‰ and notes were made on the time taken for larvae to die or begin displaying abnormal behaviour. Spirobranchus triqueter larvae can survive very well in salinities down to 20‰, and can tolerate salinities down to 10‰. Adults are tolerant of salinities as low as 3‰, and can be found in areas were salinity ranges from 18-23‰ (Alexander et al., 1935).

Sensitivity review. CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are recorded exclusively in full marine conditions (30-40 ‰) (Connor et al., 2004). The lack of records within “Reduced” salinity (18-30‰) suggests the community would not persist/be recognisable if salinity was reduced. Securiflustra securifrons is unlikely to tolerate low salinity environments. Spirobranchus triqueter is likely to be able to tolerate reduced salinity, Records from the MNCR suggest Alcyonium digitatum & Echinus esculentus can occur in reduced salinity habitats, however, the general evidence suggests that these species would decrease in abundance. Resistance has been assessed as ‘Low’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

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

CR.MCR.EcCr.FaAlCr.Adig is recorded from weak-strong tidal streams (0.5-3 m/sec), CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are recorded from weak-moderately strong tidal streams (<0.5-1.5m/sec) (Connor et al., 2004). Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter 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 during spring tides (Kluijver, 1993).

Flustra foliacea colonies are flexible, robust and reach high abundances in areas subject to strong currents and tidal streams (Stebbing, 1971; Eggleston, 1972; Knight-Jones & Nelson-Smith, 1977; Hiscock, 1983, 1985; Holme & Wilson, 1985). Dyrynda (1994) suggested that mature fronded colonies do not occur on unstable substratum due to the drag caused by their fronds, resulting in rafting of colonies on shells or the rolling of pebbles and cobbles, resulting in the destruction of the colony. Dyrynda (1994) reported that the distribution of Flustra foliacea in the current swept entrance to Poole Harbour was restricted to circalittoral boulders, on which it dominated as nearly mono-specific stands.

Spirobranchus triqueter has been recorded in areas with very sheltered to exposed water flow rates (Price et al., 1980). Wood (1988) observed Spirobranchus sp. in strong tidal streams and Hiscock (1983) found that in strong tidal streams or strong wave action where abrasion occurs, fast growing species such as Spirobranchus triqueter occur.

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, 1979). Therefore, increased water flow may remove the population from the affected area; probably to deeper water although individuals would probably not be killed in the process and could recolonize the area quickly.

Sensitivity assessment. Due to the range of tidal streams in which CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom and CR.MCR.EcCr.FaAlCr.Sec are recorded (<0.5-3 m/sec) a decrease in tidal velocity of 0.1-0.2 m/s is not likely to have a significant effect on the biological community within these biotopes. Echinus esculentus may become dislodged but are unlikely to be killed and may recolonize quickly. Resistance has been assessed as ‘High’, resilience has been assessed as ‘High’. Sensitivity has been 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

Changes in emergence are not relevant to CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec, which are restricted to fully subtidal/circalittoral conditions-The pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

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.FaAlCr.Adig is recorded from extremely wave exposed-moderately wave exposed sites. CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are recorded from exposed to moderately exposed sites (Connor et al., 2004). Alcyonium digitatum, Securiflustra securifrons, Spirobranchus triqueter are suspension feeders relying on water currents to supply food. These taxa, therefore, thrive in conditions of vigorous water flow.

CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are predominantly circalittoral habitats, CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom are recorded from 5-50 m and CR.MCR.EcCr.FaAlCr.Sec 5-30 m (Connor et al., 2004). The depth at which these biotopes are recorded may therefore also negate 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, 1979). Keith Hiscock (pers. comm.) reported Echinus esculentus occurred in significant numbers as shallow as 15m below low water at the extremely wave exposed site of Rockall, Scotland. Therefore, localised increases in wave height may remove the population from the affected area; probably to deeper water although individuals would probably not be killed in the process and could recolonize the area quickly.

Sensitivity assessment. Wave action is a fundamental environmental variable controlling the biological community of sub-littoral biotopes. A large and significant change in wave height may fundamentally alter the character of CR.MCR.EcCr.FaAlCr.Aug, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec. However, a change in near shore significant wave height of 3-5% is not likely to have a significant effect on the biological community. Resistance has been assessed as ‘High’, resilience has been assessed as ‘High’. Sensitivity has been assessed as ‘Not sensitive’.

Chemical Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
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

This pressure is Not assessed but evidence is presented where available.

No information 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 the 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.

Based on the available evidence for several species Bryan (1984) suggested that polychaetes are fairly resistant to heavy metals.

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, 1977; Holt et al., 1995). Bryozoans were shown to bio accumulate 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).

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).

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

This pressure is Not assessed but evidence is presented where available.

CR.MCR.EcCr.FaAlCr, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are sub-tidal biotopes (Connor et al., 2004). Oil pollution is mainly a surface phenomenon 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 sublittoral 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).

At the time of writing little information on the effects of hydrocarbons on bryozoans was found. Ryland & 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.

Large numbers of dead polychaetes and other fauna were washed up at Rulosquet marsh near Isle de Grand following the Amoco Cadiz oil spill in 1978 (Cross et al., 1978). However, no information was found relating to Spirobranchus triqueter in particular.

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, subtidal 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 subtidal communities/habitats to be affected. The urchin 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 A 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) (Gomez & Miguez-Rodriguez 1999).

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

This pressure is Not assessed but evidence is presented where available.

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) e.g. BP 1002 sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill. Possible sub-lethal effects of exposure to synthetic chemicals may result in a change in morphology, growth rate or disruption of the 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).

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). Bryan & Gibbs (1991) reported that there was little evidence regarding TBT toxicity in bryozoa with the exception of the encrusting Schizoporella errata, which suffered 50% mortality when exposed for 63 days to 100ng/l TBT. Rees et al. (2001) reported that the abundance of epifauna (including bryozoans) had increased in the Crouch estuary in the 5 years since TBT was banned from use on small vessels. This last report suggests that bryozoans may be at least inhibited by the presence of TBT. 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 165 m from the effluent source. The evidence, therefore, suggests that Securiflustra securifrons would be sensitive to synthetic compounds.

Large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m in the vicinity of Sennen, presumably due to a combination of wave exposure and heavy spraying of dispersants in that area 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 echinopluteus larvae of Echinus esculentus. Echinus esculentus populations in the vicinity of an oil terminal in A 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) (Gomez & Miguez-Rodriguez 1999).

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 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

This pressure is Not assessed.

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

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. There is insufficient evidence to assess the sensitivity of Securiflustra securifrons or Spirobranchus triqueter.

In general, respiration in most marine invertebrates do not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates, this concentration is about 2 ml l-1, 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-1 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 Below Sea Level. 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 were 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 affected by the phytoplankton bloom (Dennis, 1979).

CR.MCR.EcCr.FaAlCr.Adig is recorded from weak-strong tidal streams (0.5-3 m/sec), CR.MCR.EcCr.FaAlCr.Pom and CR.MCR.EcCr.FaAlCr.Sec are recorded from weak-moderately strong tidal streams (<0.5-1.5m/sec) (Connor et al., 2004). The high water movement which is indicative of these biotopes is likely to increase mixing with surrounding oxygenated water (Dennis, 1979) and may, therefore, decrease the effects of deoxygenation.  However, the evidence from Dennis (1979) suggests that grazing echinoderms such as Echinus may be affected. Therefore, a resistance of Medium is suggested.  Resilience is probably High so that sensitivity is assessed as Low.

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 good status as defined by the WFD.

Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter are suspension feeders of phytoplankton and zooplankton. Nutrient enrichment of coastal waters that enhances the population of phytoplankton may be beneficial to Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). The survival of Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter may be influenced indirectly. 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 of the bottom waters which faunal species are likely to be highly intolerant of (see de-oxygenation pressure).

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types.

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. 

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

Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter are suspension feeders of phytoplankton and zooplankton. Organic enrichment of coastal waters that enhances the population of phytoplankton may be beneficial to Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). The survival of Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter may be influenced indirectly. 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 of the bottom waters which faunal species are likely to be highly intolerant of (see de-oxygenation pressure).

Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types.

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.

Sensitivity assessment. Organic enrichment is not likely to directly negatively affect the characterizing species within this biotope, however, chronic organic enrichment may cause secondary effects such as hypoxia. Resistance has been assessed as ‘Medium’, Resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Physical Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
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

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: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are subtidal habitats (Connor et al., 2004). Therefore abrasion is most likely to be a result of bottom or pot fishing gear, cable laying etc. which may cause localised mobility of the substrata and mortality of the resident community. The effect would be situation dependent however if bottom fishing gear were towed over a site it may mobilise a high proportion of the rock substrata and cause high mortality in the resident community.

Alcyonium digitatum, Echinus esculentus, Securiflustra securifrons & Spirobranchus triqueter are sedentary or slow moving species that might be expected to suffer from the effects of dredging. 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. The results indicated that the sponge Pachymatisma johnstoni was highly damaged by the experimental trawl. However, 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. 2cm 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 the 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, 2000). 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, both when caught as bi-catch and when left on the seabed. The authors predicted 16.4% of Echinus esculentus were crushed/dead, 29.3% would have >50% spine loss/minor cracks, 1.1% would have <50% spine loss and the remaining 53.3% would be 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 the rock based biotopes- CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec, however, does indicate the likely effects of abrasion on Echinus esculentus.

Sensitivity assessment. Resistance has been assessed ‘Medium’, resilience has been assessed as ‘High’. Sensitivity has been assessed 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 as 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 not thought relevant to hard rock biotopes.

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

Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter are not thought 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.

Moore (1977) suggested that Echinus esculentus was unaffected by turbid conditions. Echinus esculentus is an important grazer of red macro-algae within CR.MCR.EcCr. Increased turbidity and resultant reduced light penetration is likely to negatively affect algal growth. However, Echinus esculentus can feed on alternative prey, detritus or dissolved organic material (Lawrence, 1975, Comely & Ansell, 1988).

Increased turbidity will reduce light penetration and hence phytoplankton productivity. Small phytoplankton are probably an important food source in the shallow subtidal, although, Flustra foliacea is also found at greater depths, where organic particulates (detritus) are probably more important.

According to Bacescu (1972), sabellids are accustomed to turbidity and silt. Spirobranchus triqueter has also recently been recorded by De Kluijver (1993) from Scotland in the aphotic zone, indicating that the species would not be sensitive to an increase in turbidity.

Sensitivity assessment. Resistance has been assessed as ‘High’, Resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’. 

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

Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter are sessile and thus, would be unable to avoid the deposition of a smothering layer of sediment. Some Alcyonium digitatum colonies can attain a height of up to 20 cm (Edwards, 2008), Securiflustra securifrons colonies can attain a height of 10 cm (Porter, 2012) so would still be able to feed in the event of sediment deposition. However, Spirobranchus triqueter are an encrusting species and would thus likely be smothered, and depending on sediment retention could block larval settlement.

Holme & Wilson (1985) examined the bottom fauna in a tide-swept region of the central English Channel. Flustra foliacea dominated communities were reported to form in areas subject to sediment transport (mainly sand) and periodic, temporary, submergence by thin layers of sand (ca <5 cm).

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 5cm of the sediment may negatively affect successive recruitment events.

CR.MCR.EcCr.FaAlCr.Adig is recorded from weak-strong tidal streams (0.5-3 m/sec), CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are recorded from weak-moderately strong tidal streams (<0.5-1.5 m/sec) (Connor et al., 2004). Due to the high tidal energy within these biotopes, 5 cm of deposited sediment is likely to be removed from the biotope within a few tidal cycles.

Sensitivity assessment. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has therefore been assessed as ‘Not Sensitive’.

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

Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter are sessile and thus, would be unable to avoid the deposition of a smothering layer of sediment. Alcyonium digitatum colonies can attain a height of up to 20 cm (Edwards, 2008), Securiflustra securifrons colonies can attain a height of 10 cm (Porter, 2012) and Spirobranchus triqueter are encrusting species. Echinus esculentus are large globular urchins which can reach a diameter of 17 cm (Tyler-Walters, 2000). Therefore, it is likely that all characterizing species within CR.MCR.EcCr.FaAlCr.Adig, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec would be totally inundated.

Holme & Wilson (1985) examined the bottom fauna in a tide-swept region of the central English Channel. Flustra foliacea dominated communities were reported to form in areas subject to sediment transport (mainly sand) and periodic, temporary, submergence by thin layers of sand (ca <5 cm). If inundated by 30cm of sediment respiration and larval settlement are likely to be blocked until the deposited sediment is removed.

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 5cm of the sediment may negatively affect successive recruitment events.

CR.MCR.EcCr.FaAlCr.Adig is recorded from weak-strong tidal streams (0.5-3 m/sec), CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are recorded from weak-moderately strong tidal streams (<0.5-1.5 m/sec) (Connor et al., 2004). Due to the high tidal energy within these biotopes, 30 cm of deposited sediment is likely to be removed from the biotope within a year.

Sensitivity assessment. Resistance has been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has therefore been assessed as ‘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

Not assessed. CR.MCR.EcCr.FaAlCr.Adig is recorded from weak-strong tidal streams (0.5-3 m/sec), CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec are recorded from weak-moderately strong tidal streams (<0.5-1.5m/sec) (Connor et al., 2004). Therefore, if anthropogenic litter were deposited it would likely be removed within a few tidal cycles.

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

At the time of writing there is no evidence on which to assess 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

Alcyonium digitatum, Echinus esculentus, Securiflustra securifrons & Spirobranchus triqueter have no hearing perception but vibrations may cause an impact, however no studies exist to support an assessment (where relevant).

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

There is no evidence to suggest that If exposed to anthropogenic light sources algal species would benefit. CR.MCR.EcCr.FaAlCr, CR.MCR.EcCr.FaAlCr.Pom and CR.MCR.EcCr.FaAlCr.Sec are also circalittoral biotopes and are thus by definition naturally shaded environments with low light levels. Increased shading (e.g. by the construction of a pontoon, pier etc) could be beneficial to the characterizing species within these biotopes.

Sensitivity assessment. Resistance is probably 'High', with a 'High' resilience and a sensitivity of '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: 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

Use / to open/close text displayedResistanceResilienceSensitivity
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

Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter are not cultivated or translocated. Echinus esculentus was identified by Kelly & Pantazis (2001) as a species suitable for culture for the urchin Roe industry. However, at the time of writing 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. This pressure is therefore considered ‘Not relevant’ at the time of writing.

Translocation also has the potential to transport pathogens to uninfected areas (see pressure ‘introduction of microbial pathogens’). The sensitivity of the ‘donor’ population to harvesting to supply stock for translocation is assessed for the pressure ‘removal of target 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

There was no evidence regarding known invasive species which may pose a threat to CR.MCR.EcCr.FaAlCr, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec.

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 smother native tunicate communities (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 CR.MCR.EcCr.FaAlCr, CR.MCR.EcCr.FaAlCr.Pom & CR.MCR.EcCr.FaAlCr.Sec.

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

There was 'no evidence' to suggest that any of the characterizing species within CR.MCR.EcCr.FaAlCr, CR.MCR.EcCr.FaAlCr.Pom and CR.MCR.EcCr.FaAlCr.Sec are sensitive to current/known microbial pathogens.

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

Thomas (1940) recorded parasites of Spirobranchus triqueter. Trichodina pediculus (a ciliate) was observed in high numbers moving over the branchial crown. However, this relationship is symbiotic, not parasitic. Parasites found in the worm include gregarines & ciliated protozoa and parasites that had the appearance of sporozoan cysts. However, no information was found about the effects of microbial pathogens on Spirobranchus triqueter.

Stebbing (1971) 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, 1971). There is however no evidence of disease which can cause significant mortality at a population or biotope level within Flustra foliacea or Securiflustra securifrons.

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).

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

At the time of writing none of the characterizing species within CR.MCR.EcCr.FaAlCr, CR.MCR.EcCr.FaAlCr.Pom and CR.MCR.EcCr.FaAlCr.Sec are commercially exploited. This pressure is considered ‘Not Relevant’.

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

Alcyonium digitatum and faunal turf communities (which include bryozoans such as Securiflustra securifrons) are probably resistant to abrasion through bottom fishing (see abrasion pressure).

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 to 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.

Within CR.MCR.EcCr Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter spatially compete, however, there wasn’t any evidence to suggest other interspecific relationships or dependencies between these species. Therefore, removal of 1 or a number of these species would provide colonization space and most likely benefit the species with rapid colonization rates (e.g. Spirobranchus triqueter). Echinus esculentus is an important red algae grazer within CR.MCR.EcCr (Connor et al., 2004), without which the abundance of red algae may increase and possibly displace some of the faunal turf species. If Alcyonium digitatum, Securiflustra securifrons & Spirobranchus triqueter were removed this would alter the character of the biotope.

Sensitivity assessment. Resistance has been assessed as ‘Low’, resilience has been assessed as ’Medium’. Sensitivity has been assessed as ‘Medium’.

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Citation

This review can be cited as:

Stamp, T.E. & Williams, E.. 2021. Alcyonium digitatum with Securiflustra securifrons on tide-swept moderately wave-exposed circalittoral rock. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 10-12-2022]. Available from: https://www.marlin.ac.uk/habitat/detail/15

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