The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

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, its 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. Holt (pers. comm.) also suggested that long-term increases in temperature due to climate change may allow the parasitic barnacle Adna anglica to extend its range northwards and overlap the range of this biotope. Adna anglica is a southern species limited to the southwest of Britain where it parasitizes Caryophillia and has probably contributed to the decrease in abundance of Leptopsammia (Holt pers. comm.). It may impact the abundance of Caryophyllia if climate change allowed it to extend its range northwards (Holt pers. comm.).

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 generally has a northern distribution within the British Isles, with the characterizing Swiftia pallida being intolerant of warmer conditions.  Therefore, resistance is likely to be ‘Low’, resistance is probably ‘Medium’ and sensitivity is assessed as ‘Medium’.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

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 a decrease in temperature at the benchmark level. Swiftia 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 its 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’.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

CR.MCR.EcCr.CarSwi is a circalittoral biotope and an increase at the benchmark would result in a change from full to hypersalinity.  No records of the characterizing Caryophyllia smithii or Swiftia pallida in hypersaline conditions was found. 

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

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’.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

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 a 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 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 assessed as ‘Not Sensitive’ at the benchmark level.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

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.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

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 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 assessed as ‘Not Sensitive’ at the benchmark level.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

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 deepwater 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 Horizon spill, recovery of corals and gorgonians was inversely correlated with floc presence.

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

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

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

'No evidence'.

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

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 pallida. 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 an 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 habitats and low oxygen events are likely to be short-lived.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

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.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

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 the important characterizing Swiftia pallida could be found.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

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.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

If the 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’.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

Not relevant’ to biotopes occurring on bedrock.

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

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.

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

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).  Swiftia pallida has been observed tangled in lobster pot netting and detached in the vicinity of lobster pots (Holt, pers comm.). 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 verrucosa that 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 were likely to be moved and turned by of the passing dredge, leading to further damage to the epifaunal communities. 

This biotope is also characterized by the bryozoan Porella compressa. Porella compressa is a delicate, 'stony' and brittle, erect bryozoan that is likely to be damaged by abrasion (Holt pers. comm.). However, its loss from the biotope would not result in loss of the biotope.

Sensitivity assessment. Swiftia 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 as ‘Medium’.

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

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

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

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, the 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.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

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.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

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’.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

‘No evidence’ was found

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

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’.

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

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 impacted.  The biotope is circalittoral, occurs below 10 m and is dependent on secondary rather than primary production. 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.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

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

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

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

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

‘Not relevant’.

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

No evidence of translocation or genetic modification of populations of the characterizing species was found. Therefore, there is currently ‘No evidence’ on which to assess this pressure.

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

This biotope is classed as circalittoral and therefore no algal species have been considered. Crepidula fornicata larvae require hard substrata for settlement. It prefers muddy gravelly, shell-rich, substrata that include gravel, or shells of other Crepidula, or other species e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. But it also recorded from rock, artificial substrata, and Sabellaria alveolata reefs (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Helmer et al., 2019; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Tillin et al., 2020). Close examination of the literature (2023) shows that evidence of its colonization and density on bedrock in the infralittoral or circalittoral was lacking. Tillin et al. (2020) suggested that Crepidula could colonize circalittoral rock due to its presence on tide-swept rough grounds in the English Channel (Hinz et al., 2011). However, Hinz et al. (2011) reported that Crepidula fornicata only dominated one assemblage (with an average of 181 individuals per trawl) on gravel substratum with boulders. Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas dominated by boulders, and Bohn et al. (2013a, 2013b, 2015) and Preston et al. (2020) showed that while Crepidula could settle on slate panels or ‘stone’ it preferred shell, especially that of conspecifics. In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats. It was only recorded at low density (0.1-0.9/m²) in one faunal turf biotope (CR.MCR.CFaVS.CuSpH.As) (JNCC, 2015). Faunal turfs are dominated by suspension feeders so larval predation is probably high, which may prevent colonization by Crepidula. Also, faunal turf species actively compete for space and many are fast growing and opportunistic, so may out-compete Crepidula for space even if it gained a foothold in the community. Therefore, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats or infralittoral or circalittoral rock habitats. Hence, there is 'Insufficient evidence' to suggest that the circalittoral rock biotopes are sensitive to colonization by Crepidula fornicata and further evidence is required. 

Hesperibalanus (syn. Solidobalanus) fallax is an invasive southern species of barnacle only recently recorded in southwest England (Southward et al., 2004).  It has been observed fouling (primarily damaged or diseased) gorgonians (Hall-Spencer et al., 2007). However, it has not yet been recorded in Scottish waters (NBN, 2023). Therefore, resistance to fouling by this barnacle is assessed as ‘Medium’ as a precaution based on its potential to foul sea fans but with 'Low' confidence. Hence, resilience is assessed as ‘Medium’ and sensitivity as ‘Medium’. Due to the constant risk of new invasive species, the literature on this pressure should be revisited and the confidence for this assessment is 'Low'. 

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

Whilst no evidence of disease in Swiftia 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. Vibrios 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, a disease may result in mortality of Swiftia 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’. 

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

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’.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

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 suggest 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 as ‘Medium’.