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

Mixed turf of hydroids and large ascidians with Swiftia pallida and Caryophyllia (Caryophyllia) smithii on weakly tide-swept circalittoral rock

08-11-2016

Summary

UK and Ireland classification

UK and Ireland classification

Description

Circalittoral rock subject to slight tidal currents, with the seafan Swiftia pallida and various erect branching and cup sponges, including Axinella infundibuliformis, Stelligera spp. and Raspailia spp. The rocky surfaces usually have a sparse turf of hydroids including Aglaophenia tubulifera and Schizotricha frutescens, bryozoans Bugula spp., Caryophyllia smithii, Porella compressa and occasionally Alcyonium glomeratum and Diazona violacea. The feather stars Antedon bifida and Antedon petasus (the latter more numerous in deeper water than the former) and large solitary ascidians Ascidia mentula and Polycarpa pomaria (see AmenCio) are also characteristic of the less exposed sites with this biotope. Rock surfaces often with Novocrania anomala - found both in Irish and Scottish examples of this biotope. Short verticals and overhangs occasionally with Parazoanthus anguicomus. Mycale lingua recorded in deep water at some of the sites in Scottish sealochs. There are a few records from Kenmare River in SW Ireland which have Swiftia and Eunicella at the same sites. These records have been included in ErSEun although there were several other biotopes in Kenmare River which share close links with those from Scottish sealochs.

Depth range

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Additional information

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Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

CR.HCR.XFa.SwiLgAs is similar to the CR.MCR.EcCr.CarSwi biotope complex as they are characterized by dense aggregations of the cup coral Caryophyllia smithii and the northern sea fan Swiftia pallida on rock or boulders with a thin layer of silt.  This assessment focuses on the characterizing Caryophyllia smithii and Swiftia pallida.  The faunal turf of CR.HCR.XFa.SwiLgAs is typical of circalittoral environements and composed of typically opportunistic species, but is considered where appropriate.

Given the lack of information on Swiftia pallida, evidence for other sea fans, including Eunicella verricosa is presented where applicable.  Evidence is also sparse for Alcyonium glomeratum and assessments are based on the similar Alcyonium digitatum.

Other species present are considered opportunistic colonizers, ephemeral or not important characterizing within the biotopes.

Resilience and recovery rates of habitat

Caryophyllia smithii is a small (max 3 cm across) solitary coral, common within tide swept sites of the UK (Wood, 2005), and distributed from Greece (Koukouras, 2010) to the Shetland Islands and Orkney (NBN, 2015; Wilson, 1975). It was suggested by Fowler & Laffoley (1993) that Caryophyllia smithii was a slow growing species (0.5-1 mm in horizontal dimension of the corallum per year), which in turn suggested that inter-specific spatial competition with colonial faunal or algae species were important factors in determining local abundance of Caryophyllia smithii (Bell & Turner, 2000). Caryophyllia smithii reproduces between January and March and spawning occurs from March to June (Tranter et al., 1982). The pelagic stage of the larvae may last up to 10 weeks, which provides this species with a good dispersal capability (Tranter et al., 1982) Asexual reproduction and division is also commonly observed (Hiscock & Howlett, 1976).  Bell (2002) reported that juvenile Caryophyllia smithii have variable morphology which gives them an advantage in colonizing a wide range of habitats.

Sea fans are sessile colonial cnidarians that grow erect from the substratum, with each colony formed of many small polyps, each with tentacles that may be either extended or retracted. Swiftia pallida is a small sea fan that forms slender colonies with infrequent branching, up to 20 cm tall but usually 7- 10 cm. Branches are irregularly orientated and twig-like (Manuel, 1988; Hiscock, 2007).

Populations of Swiftia pallida are thought to be self-sustaining, with short lived larvae and limited potential for larval dispersal. It is thought that colonization of the Shetland Islands has been prevented by geographical barriers (Hiscock et al., 2001). Reproduction is likely to be annual and may be triggered by either summer high or winter low temperatures (Hiscock et al., 2001).

Although Swiftia pallida has not been specifically studied, the average number of eggs per polyp in other gorgonians increases with increasing colony size. The number of eggs released from larger colonies can be orders of magnitude higher than for smaller colonies (Beiring & Lasker, 2000). It has been suggested that when large colony size is attained, more energy is available for reproduction because relative colony growth decreases (Beiring & Lasker, 2000). Swiftia pallida abundance may be up to three colonies per metre (Minchin, 1987c). Growth rates for this species are unknown, however, the pink sea fan Eunicella verrucosa has highly variable growth. A population of Eunicella verrucosa at Lundy Island had growth rates of approximately 1 cm/year, which may be similar to Swiftia pallida.  The lifespan of Swiftia pallida is estimated to be between 10 and 20 years (Hiscock et al. 2001; Wilding & Wilson, 2009).  Very little information was found on the recovery potential of this species.  The ability to recolonize an area following mass mortality is likely to be restricted (Hiscock et al., 2001).

Little information was available for Alcyonium glomeratum and resilience was assessed based on the similar Alcyonium digitatumAlcyonium digitatum colonies are likely to have a lifespan that exceeds 20 years as colonies have been followed for 28 years in marked plots (Lundälv, pers. comm., in Hartnoll, 1998). Colonies that were 10-15 cm in height were aged at between 5 and 10 years old (Hartnoll, unpublished). 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 7 days, when they give rise to actively swimming lecithotrophic planulae which may have an extended pelagic life before they eventually settle (usually within 1 or 2 further days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). Larvae have been reported to survive for up to 35 weeks as non-feeding planulae and may favour the dispersal and eventual discovery of a site suitable for settlement (Hartnoll, 1975).  Alcyonium digitatum can recruit onto bare surfaces within 2 years, but may take up to 5 years to fully recover following significant mortality (Whomersley & Picken, 2003; Hiscock et al., 2010).

The lifecycle of hydroids typically alternates between an attached solitary or colonial polyp generation and a free-swimming medusa generation.  Planulae larvae produced by hydroids typically metamorphose within 24 hours and crawl only a short distance away from the parent plant (Sommer, 1992).  Gametes liberated from the medusae (or a vestigial sessile medusae) produce gametes which fuse to form zygotes that develop into free-swimming planula larvae (Hayward & Ryland, 1994) that are present in the water column between 2-20 days (Sommer, 1992).  It has also been suggested that rafting on floating debris as dormant stages or reproductive adults (or on ships hulls or in ship ballast water), together with their potentially long lifespan, may have allowed hydroids to disperse over a wide area in the long-term and explain the near cosmopolitan distributions of many hydroid species (Cornelius, 1992; Boero & Bouillon 1993). Hydroids are therefore classed as potential fouling organisms, rapidly colonising a range of substrata placed in marine environments and are often the first organisms to colonize available space in settlement experiments (Gili & Hughes, 1995).  For example, hydroids were reported to colonize an experimental artificial reef within less than 6 months, becoming abundant in the following year (Jensen et al., 1994).  In similar studies, Obelia species recruited to the bases of reef slabs within three months and the slab surfaces within six months of the slabs being placed in the marine environment (Hatcher, 1998).  Bradshaw et al., (2002) observed that reproduction in Nemertesia antennina occured regularly, with three generations per year. It was also observed that presence of adults stimulate larval settlement, therefore if any adults remain, reproduction is likely to result in local recruitment. 

The recolonization of epifauna on vertical rock walls was investigated by Sebens (1985, 1986).  He reported that rapid colonizers such as encrusting corallines, encrusting bryozoans, amphipods and tubeworms recolonized within 1-4 months.  Ascidians such as Dendrodoa carnea, Molgula manhattensis and Aplidium spp. achieved significant cover in less than a year, and, together with Halichondria panicea, reached pre-clearance levels of cover after two years.  A few individuals of Alcyonium digitatum and Metridium senile colonized within four years (Sebens, 1986) and would probably take longer to reach pre-clearance levels.

Resilience assessment: The hydroids that characterize this biotope are likely to recover from damage very quickly. Based on the available evidence, resilience for the hydroid species assessed is ‘High’ (recovery within two years) for any level of perturbation (where resistance is ‘None’, ‘Low’, ‘Medium’ or ‘High’). Depending on the season of the impact and level of recovery, recovery could occur within six months. Caryophyllia smithii colonized the wreck of the Scylla within a year, however this may be due to the time of the vessel sinking and if removed recovery may take longer.   Alcyonium glomeratum is likely to recruit fairly rapidly, however full recovery following a significant decline may take longer.  Swiftia pallida  is likely to be the slowest to recover and if a population was completely removed from the habitat (resistance of ‘None’) resilience has been assessed as ‘Low’ (recovery in 10-25 years) because of the low larvae dispersal, probable importance of self-sustaining communities and slow growth rate of Swiftia pallida (Hiscock et al., 2001). For resistance assessments of ‘Low’ or ‘Medium’, resilience has been assessed as ‘Medium’ (recovery in 2-10 years).

Hydrological Pressures

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

Mitchell et al. (1983) suggested that the Scottish and Irish populations of Swiftia pallida were at the southern limit of the species range.  It should be noted that there are reports of Swiftia pallida in deep waters (518-766 m depth) in the Mediterranean (Mastrototaro et al., 2010), however distribution in the British Isles appears to be limited to the Atlantic coasts of Scotland and Ireland (NBN, 2015).  Hiscock et al. (2001) predicted the loss of all populations occurring in the Inner Hebrides and mainland western Scotland with a 2°C increase in summer surface temperatures over a 20 year period. 

Caryophyllia smithii is found across the British Isles (NBN, 2015) and has been recorded in Greece (Koukouras, 2010).  It is therefore unlikely to be significantly affected by an increase at the benchmark level. However, 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.

Alcyonium glomeratum has been recorded from Scotland to the Bay of Biscay (Hayward & Ryland, 1995b) and would probably tolerate an increase at the benchmark level.

Other species present in the biotope are widespread across the British Isles or are not important to the classification of this biotope.

Sensitivity assessment

The CR.MCR.EcCr.CarSwi biotope complex generally has a northern distribution within the British Isles, with the characterizing Swiftia pallida being intolerant of warmer conditions.  Resistance is likely to be ‘Low’, resistance is therefore ‘Medium’ and sensitivity is ‘Medium’.

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

Caryophyllia smithii is a southern species (Fish & Fish, 1992) with a northern range limit in the Shetland isles (NBN, 2015).  It is therefore likely to be close to its northerly range limit and therefore likely to be negatively affected by decrease in temperature at the benchmark level.

Swifita pallida is classed as a northerly species and is recorded in Scotland, south-west Ireland (e.g. Kenmare Bay) on the west coasts of Norway and Sweden and in deep water from the Bay of Biscay and the Mediterranean (Wilding & Wilson, 2009).

Alcyonium glomeratum has been recorded from Scotland to Biscay (Hayward & Ryland, 1995b) and, being close to it northerly distribution limit, is likely to experience a significant decline.

Sensitivity assessment

Caryophyllia smithii and Alcyonium glomeratum are already close to their northern range limit and a decrease would likely significantly affect the northern populations of the species and hence the biotope.  Resistance is assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’.

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

CR.HCR.XFa.SwiLgAs is a circalittoral biotope complex and an increase at the benchmark would result in change from full to hyper salinity.  No records of the characterizing Caryophyllia smithii or Swiftia pallida in hypersaline conditions was found. 

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

This biotope occurs in full salinity.  Caryophyllia smithii has been recorded in biotopes from Full to Low salinity (Connor et al., 2004) and would probably tolerate a change at the benchmark level. Swiftia pallida has only been recorded in full salinity biotopes (Connor et al., 2004) and is likely to be intolerant of a decrease in salinity. Resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity has been assessed as ‘Medium’.

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

Alcyonium digitatum, Caryophyllia smithii, Spirobranchus triqueter and sponges are suspension feeders, relying on water currents to supply food (Hiscock, 1983). These taxa therefore thrive in conditions of vigorous water flow e.g. around Orkney and St Abbs, Scotland, where Alcyonium digitatum dominated biotopes may experience tidal currents of 3 and 4 knots (approximately 1.5 m/sec) during spring tides (De Kluijver, 1993). Caryophyllia smithii in particular is described as favouring sites with high tidal flow (Bell & Turner, 2000; Wood, 2005).

This biotope consists mainly of species firmly attached to the substratum, which would be unlikely to be displaced by an increase in the strength of tidal streams at the benchmark level.

Sea fans are found in strong tidal streams but probably retract their polyps when current velocity gets too high for the polyps to retain food. Tidal streams exert a steady pull on the colonies and are therefore likely to detach only very weakly attached colonies. Colonies rely on high water flow rates to bring food and to remove silt (Hiscock, 2007).  Caryophyllia smithii has been recorded in biotopes from negligible to strong water flow (0-6 knots) (Connor et al., 2004)

No evidence for Swiftia pallida was found, however, Bunker (1986) reported that the sea fan Eunicella verrucosa was present in areas subject to at least moderate tidal stream, but was most abundant in strong tidal streams.  There is a tendency for Eunicella verrucosa to grow aligned across the direction of the prevailing current (Bunker, 1986).

Sensitivity assessment

The CR.MCR.EcCr.CarSwi biotope complex is found from negligible to moderately strong water flow (0-3 knots), but can be found from extremely exposed to sheltered wave exposure.  It is likely that the biotope exists in moderate energy, with either water flow or wave action prevailing.  Change in water flow is therefore probably only relevant to wave sheltered examples.  The characterizing species (including gorgonians, soft corals and Caryophyllia smithii) are generally associated with moderate to high energy environments. However a change at the benchmark level is unlikely to be significant. Resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not Sensitive’ at the benchmark level.

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

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

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

Dead sea fans have been recorded washed up along Chesil Beach (UK) following winter storms (Hatcher & Trewhella, 2006). However, Bunker (1986) reported that Eunicella verrucosa was most abundant in moderately exposed locations.

Caryophyllia smithii has been recorded in very sheltered to extremely exposed biotopes (Connor et al., 2004).  Bell (2002) reported that Caryophyllia smithii near Lough Hyne (Ireland) exposed to strong wave action on open coasts were relatively small, possibly down to juvenile morphological variability, as Caryophyllia smithii found deeper and in sediment were thinner and taller.

Sensitivity assessment

The CR.MCR.EcCr.CarSwi biotope complex is extremely exposed to sheltered from wave action, but can be found from negligible to moderately strong water flow (0-3 knots).  It is likely that the biotope exists in moderate to high energy, with either water flow or wave action prevailing.  Change in wave exposure is therefore probably only relevant to habitats that experience weak water flow.  The characterizing species (including gorgonians and Caryophyllia smithii) are generally associated with moderate to high energy environments. However a change at the benchmark level is unlikely to be significant. Resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not Sensitive’ at the benchmark level.

Chemical Pressures

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

Chan et al. (2012) studied the response of the gorgonian Subergorgia suberosa to heavy metal-contaminated seawater from a former coastal mining site in Taiwan.  Cu, Zn, and Cd each showed characteristic bioaccumulation. Metallic Zn accumulated, but rapidly dissipated. In contrast, Cu easily accumulated, but was slow to dissipate, and Cd was only slowly absorbed and dissipated. Associated polyp necrosis, mucus secretion, tissue expansion, and increased mortality were reported in Subergorgia suberosa exposed to water polluted with heavy metals.

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

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

CR.MCR.EcCr.CarSwi is a sub-tidal biotope complex (Connor et al., 2004). Oil pollution is mainly a surface phenomenon and 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 could potentially negatively affect sub-littoral habitats (Castège et al., 2014).

Filter feeders are highly sensitive to oil pollution, particularly those inhabiting the tidal zones which experience high exposure and show correspondingly high mortality, as are bottom dwelling organisms in areas where oil components are deposited by sedimentation (Zahn et al., 1981). White et al. (2012) reported on deep water gorgonian communities, including Swiftia pallida six months after the Deep Water Horizon oil spill.  Stress in the gorgonians was observed including excessive mucous production, retracted polyps and smothering of brown flocculent material (floc) which contained oil from the Macondo well. Hsing et al. (2013) reported that, following smothering by floc associated with the Deepwater Horzion spill, recovery of corals and gorgonians was inversely correlated with floc presence.

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

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

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

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

'No evidence'.

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

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

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

In general, respiration in most marine invertebrates does not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates this concentration is about 2 ml/l (ca 2.66 mg/l) (Herreid, 1980; Rosenberg et al., 1991; Diaz & Rosenberg, 1995). Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l.

Little information on the effects of oxygenation on bryozoans was found.  No evidence was found concerning the effects of hypoxia for Swiftia palida. However, as a species that lives in fully oxygenated waters in conditions of flowing waters, it is expected that it would be intolerant to decreased oxygen levels. Bell (2002) reported that a oxycline at Lough Hyne (<5 % surface concentration) limited vertical colonization by Caryophillia smithii.

Sensitivity assessment

Despite limited evidence, Swiftia pallida and Caryophyllia smithii are unlikely to tolerate hypoxic events given their preference for moderate water movement. Resistance is ‘Low’, resilience is ‘Medium’ and sensitivity is ‘Medium’.  It should be noted that, as these biotopes occur in high energy, low oxygen events are likely to be short lived.

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

Echavarri-Erasun et al. (2007) described the effects of deepwater sewage outfall discharges on the relative abundance of rocky reef communities.  Species typical of hard substrata (including Caryophyllia smithii and bryozoans) increased in total richness and abundance near the outfall.

Whilst Swifita pallida could be at risk of competition from algae in shallow waters due to nutrient enrichment, this biotope occurs in the circalittoral below the depth suitable for most macroalgae. If nutrient enrichment resulted in algal blooms, then their subsequent death could result in deposition of dead algae on the sea bed and resultant localised hypoxia (see above).

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

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

Echavarri-Erasun et al. (2007) described the effects of deepwater sewage outfall discharges on the relative abundance of rocky reef communities.  Species typical of hard substrata (including Caryophyllia smithii and bryozoans) increased in total richness and abundance near the outfall.

Sensitivity assessment

Evidence for some of the characterizing species suggests some tolerance, or even increased abundance, when exposed to organic enrichment in the circalittoral.  However, ‘No evidence’ for for the important characterizing Swiftia pallida could be found.

Physical Pressures

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

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very low’). Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

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

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

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

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

Not relevant’ to biotopes occurring on bedrock.

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

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

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

Physical disturbance by fishing gear has been shown to adversely affect emergent epifaunal communities with hydroid and bryozoan matrices reported to be greatly reduced in fished areas (Jennings & Kaiser, 1998). Heavy mobile gears could also result in movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998). Whilst no evidence for Swiftia pallida was found, reviews have considered the sea fan Eunicella verrucosa to be sensitive to abrasion (MacDonald et al., 1996; Hall et al., 2008; Tillin et al., 2010).  Other studies suggest that Eunicella verrucosa may be more resistant to abrasion pressures.  Eno et al. (2001) conducted experimental potting on areas containing fragile epifaunal species in Lyme Bay, south west England. Divers observed that pink sea fan ‘flexed and bent before returning to an upright position under the weight of pots’. Although relatively resistant to a single event it was not clear whether repeated exposure could cause further damage or whether injuries had been inflicted that could lead to deterioration (Eno et al., 2001). Observation of pots suggested that these were dragged along the bottom when wind and tidal streams were strong, however little damage to epifauna was observed.  Eunicella verrucosa were patchily distributed in areas subject to potting damage, but the study could not determine whether this was due to damage from potting (Eno et al., 2001). A further four year study on potting in the Lundy Marine Protected Area detected no significant differences in Eunicella verrucosa between areas subject to commercial potting and those where this activity was excluded (Sheehan et al., 2013).

However, Tinsley (2006) observed flattened sea fans ,that  had continued growing, with new growth being aligned perpendicular to the current, so clearly even colonies of Eunicella verrucosathat are damaged can continue to survive. Healthy Eunicella verrucosa are able to recover from minor damage and scratches to the coenenchyme (Tinsley, 2006), and the coenenchyme covering the axial skeleton will regrow over scrapes on one side of the skeleton in about one week (Hiscock, pers. comm.)  Hinz et al. (2011) reported that Eunicella verrucosa did not show a significant negative response with respect to abundance and average body size to the intensity of scallop dredging.

A study by Boulcott & Howell (2011) on the effects of scallop dredging in rocky substrata suggested that associated epifaunal communities, such as bryozoans, hydroids, soft corals and sponges were removed by a passing scallop dredge.  However on hard, uneven rock damage, damage to more resistant epifauna, whilst in evidence, was restricted.  The study also recorded that mobile substrata present was likely to be moved and turned by of the passing dredge, leading to further damage to the epifaunal communities. 

Sensitivity assessment

Swifita Pallida is sessile and epifaunal and, based on evidence for Eunicella verrucosa, is likely to be severely damaged by heavy gears, such as scallop dredging (MacDonald et al., 1996).  However, some studies suggest the sea fan Eunicella verrucosa may be more resistant, particularly to low intensity lighter abrasion pressures, such as pots and associated anchor damage (Eno et al. 2001; Sheehan et al., 2013), and this could be the case for Swiftia pallida.  Therefore, a resistance of ‘Low’ is recorded. Resilience is assessed as ‘Medium’ and sensitivity is ‘Medium’.

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 thought ‘Not Relevant’ to hard rock biotopes

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

Bell & Turner (2000) studied populations of Caryophyllia smithii at three sites of differing sedimentation regime in Lough Hyne, Ireland. Calyx size was largest at the site of least sedimentation and smallest at the site of most sedimentation. In contrast, height of individuals was greatest at the site of most sedimentation and smallest at the site of least sedimentation. The height of individuals correlated with the level of surrounding sediment. High density correlated with high sedimentation and depth (Bell & Turner, 2000). 

While siltation may inhibit feeding, colonies of the sea fan Eunicella verrucosa produce mucus to clear themselves of silt (Hiscock, 2007) and sea fans are probably tolerant of increases in suspended sediment (Hiscock et al., 2004).  Bunker (1986) reported that Eunicella verrucosa were mostly observed on bedrock or boulders, but did occur at sites up to ‘moderately silted’.

Sensitivity assessment

CR.MCR.EcCr.CarSwi occurs on bedrock in the circalittoral and is unlikely to experience highly turbid conditions.  From the evidence presented above, the characterizing species tolerate some siltation and a change at the benchmark level is unlikely to cause mortality.  Resistance is recorded as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

Caryophyllia smithii is small (approx. <3 cm height from the seabed) and would therefore likely be inundated in a 'light' sedimentation event. However, Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of 'moderate' sedimentation (7 mm ± 0.5 mm) in Lough Hyne. It is therefore likely that Caryophyllia smithii would be resistant to periodic sedimentation. If 5 cm of sediment were removed rapidly, via tidal currents, Caryophyllia smithii would likely remain within the biotope.  Burton et al. (2005) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover.  Bell (2002) reported that juvenile Caryophyllia smithii are morphologically variable and initially undergo rapid growth with tall and thin forms in deeper, sheltered, relatively sedimented conditions near Lough Hyne, Ireland.  It was concluded that this was to escape the thin layer of sediment present.  

Swiftia pallida generally grows to a height of about 7-10 cm (Wilson, 2007).  It is found on rocks covered with a fine layer of silt (Mitchell et al., 1983). While siltation may inhibit feeding, colonies of the sea fan Eunicella verrucosa produce mucus to clear themselves of silt (Hiscock, 2007). It is however thought that smothering causes mortality (Hiscock et al., 2004).  Bunker (1986) reported that Eunicella verrucosa were mostly observed on bedrock or boulders, but did occur at sites up to ‘moderately silted’.

Sensitivity assessment

Smothering by 5 cm would cover the majority of Caryophyllia smithii and the smallest examples of the other characterizing species and could result in limited mortality.  Caryophyllia smithii has been reported as quite tolerant of temporary burial and the biotope occurs in moderate water flow and the sediment would likely be removed rapidly.  Resistance was assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

Caryophyllia smithii is small (approx. <3 cm height from the seabed) and would therefore likely be inundated in a “light” sedimentation event. However, Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of “moderate” sedimentation (7 mm ± 0.5 mm) in Lough Hyne. It is therefore likely that Caryophyllia smithii would be resistant to periodic sedimentation. If the sediment was removed rapidly, via tidal currents, Caryophyllia smithii would likely remain within the biotope.  Burton et al. (2005) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover.  Bell (2002) reported that juvenile Caryophyllia smithii are morphologically variable and initially undergo rapid growth with tall and thin forms in deeper, sheltered, relatively sedimented conditions near Lough Hyne, Ireland.  It was concluded that this was to escape the thin layer of sediment present.  

Swiftia pallida generally grows to a height of about 7-10 cm (Wilson, 2007).  It is found on rocks covered with a fine layer of silt (Mitchell et al., 1983). While siltation may inhibit feeding, colonies of the sea fan Eunicella verrucosa produce mucus to clear themselves of silt (Hiscock, 2007). It is however thought that smothering causes mortality (Hiscock et al., 2004).  Bunker (1986) reported that Eunicella verrucosa were mostly observed on bedrock or boulders, but did occur at sites up to ‘moderately silted’.

Sensitivity assessment

Smothering by 30 cm of sediment would likely bury the majority of characterizing species, with only those individuals on boulders and vertical surfaces escaping burial.  The biotope occurs in moderate water flow and it is likely that the sediment would probably be removed rapidly.  Resistance was assessed as ‘Medium’, resilience as ‘Medium’ and sensitivity as ‘Medium’.

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

‘No evidence’ was found

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

‘No evidence’ was found

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

Whilst no evidence could be found on the effects of noise or vibrations on the characterizing species, it is unlikely that these species would be adversely affected by noise.  This pressure ‘Not relevant’.

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

Whilst no evidence could be found for the effect of light on the characterizing species of these biotopes, it is unlikely that these species would be impactedThe biotope is circalittoral, occurs below 10 m and is dependent on secondary rather than primary productivity. Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive' at the benchmark level.

 

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

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

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

‘Not relevant’ to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

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

‘Not relevant’.

Biological Pressures

 ResistanceResilienceSensitivity
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 for the characterizing species could be found.

Therefore, there is currently ‘No evidence’ on which to assess this pressure..

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

This biotope is classed as circalittoral and therefore no algal species have been considered.  Solidobalanus fallax barnacles are an invasive southern species only recently recorded in south west England (Southward et al. 2004) and have been observed fouling (primarily damaged or diseased) gorgonians (Hall-Spencer et al., 2007).

Resistance is therefore assessed as ‘Medium’, resilience as ‘Medium’ and sensitivity as ‘Medium’.  Due to the constant risk of new invasive species, the literature for this pressure should be revisited.

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

Whilst no evidence of disease in Swifita pallida could be found, the first recorded incidence of cold-water coral disease was noted in the sea fan Eunicella verrucosa, in south west England in 2002 (Hall-Spencer et al., 2007).  Video surveys of 634 separate colonies at 13 sites revealed that disease outbreaks were widespread in south west England from 2003 to 2006. Coenenchyme became necrotic in diseased specimens, leading to tissue sloughing and exposing skeletal gorgonin to settlement by fouling organisms. Sites where necrosis was found had significantly higher incidences of fouling. No fungi were isolated from diseased or healthy tissue, but significantly higher concentrations of bacteria occurred in diseased specimens. Vibrio’s isolated from Eunicella verrucosa did not induce disease at 15°C, but at 20°C controls remained healthy and test gorgonians became diseased. Bacteria associated with diseased tissue produced proteolytic and cytolytic enzymes that damaged Eunicella verrucosa tissue and may be responsible for the necrosis observed. Monitoring at the site where the disease was first noted showed new gorgonian recruitment from 2003 to 2006; some individuals had died and become completely overgrown, whereas others had continued to grow around a dead central area (Hall-Spencer et al., 2007).

No evidence for disease in the characterizing bryozoans could be found.

Sensitivity assessment

Based on reports of mortality linked to disease in the sea fan Eunicella verrucosa, disease may result in mortality of Swifita pallida.  It should be noted that the colder temperatures in which Swiftia pallida occurs may confer some resistance.  Resistance is assessed as ‘Medium’, resilience as ‘Medium’ and sensitivity as ‘Medium’. 

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

Eunicella verrucosa was collected historically as a curio by divers and was collected until recently in the British Isles (Wells et al., 1983; Bunker, 1986). It is now protected under schedule 5 of the Wildlife and Countryside Act 1981, no evidence of harvesting of the sea fan Swifita pallida or any of the other characterizing species was found. 

As there is historical evidence of harvesting of other sea fans, the sessile, epifaunal Swifita pallida would have no resistance to harvesting by divers.  Resistance has been assessed as ‘None’, resilience as ‘Low’ and sensitivity is therefore ‘High’.

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

The characteristic species probably compete for space within the biotope, so that loss of one species would probably have little if any effect on the other members of the community. However, removal of the characteristic epifauna due to by-catch is likely to remove a proportion of the biotope and change the biological character of the biotope.  As sessile epifauna, the characterizing species and likely to be severely damaged by heavy gears, such as scallop dredging (MacDonald et al., 1996).  However,  some studies suggests that sea fans may be more resistant, particularly to low intensity, lighter abrasion pressures, such as pots and associated anchor damage (Eno et al. 1996; Sheehan et al., 2013)  Taking all the evidence into account, a resistance of ‘Low’ is recorded, albeit with a low confidence value owing to the lack of consensus in the literature. Resilience is assessed as ‘Medium’ and sensitivity is ‘Medium’.

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Citation

This review can be cited as:

Readman, J.A.J., 2016. Mixed turf of hydroids and large ascidians with [Swiftia pallida] and [Caryophyllia (Caryophyllia) smithii] on weakly tide-swept circalittoral rock. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/34

Last Updated: 07/07/2016