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

Eunicella verrucosa has been recorded in the Western Mediterranean and off north-west Africa (Wells et al., 1983 cited in Koomen & Helsdingen, 1996) so that an increase in temperature is not likely to negatively affect the species. However, during the last decades, mass mortality events related to high seawater temperature anomalies have been reported within the Western Mediterranean basin. A mass mortality event in 1999 affected many gorgonians, although Eunicella verrucosa near Gallinaria Island was ‘little affected’ (Cerrano et al. 2000).  ‘Occassional’ mortality was observed in the shallowest populations along the Provence coast (at 37-38 m) during a high temperature event in 1999 where sea temperature was 23-24°C throughout the water column to 40m depth (Perez et al. 2000). In 2003, the pink sea fan populations were affected in the Gulf of Genoa but not along the Provence coast (Garrabou et al. 2009). Although total mortality was not explicitly reported for this species, a certain reduction in population size could be suspected, due to delayed mortality of colonies affected by high levels of injury, as observed in some other Mediterranean gorgonians (e.g. Linares et al.,2005; Coma et al., 2006).

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

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 at the benchmark. 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.

There is no information available about the tolerance of Axinella dissimilis to increases in temperature. In the British Isles, it has a mainly southern and western distribution. The species is found in warmer waters as far south as Spain. It is replaced in the Mediterranean by the very similar species, Axinella polypoides (Howson & Picton, 1997). Long-term increases in temperature may cause extension of the British Isles populations and decreases in temperature may result in population shrinkage. 

Sensitivity assessment

Eunicella verrucosa, Pentapora foliacea, Caryophyllia smithii, and Axinella dissimilis are distributed throughout the UK, with the distribution of some of the species as far south as the Mediterranean. A long-term increase in temperature may result in an increase in abundance of some of the characterising species.  Resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope assessed as ‘Not sensitive’ at the benchmark level.

Temperature decrease (local)

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

Evidence

Eunicella verrucosa is a southern species, distribution is generally limited to the south west of the British Isles (Hayward & Ryland, 1990; NBN, 2015).  A decrease in temperature is likely to result in mortality. However, A live specimen collected from shallow depths off North Devon in 1973 exhibited growth rings that demonstrated that the colony had survived the 1962/63 cold winter(Hiscock, pers comm.). Also, large colonies were collected (for sale as souvenirs) from Lundy in the late 1960's suggesting no significant loss in 1962/63 (Hiscock, 2007). Assuming that temperature decrease reduces recruitment, the population size might decline for a year but recovery would occur following successful recruitment.

Pentapora foliacea is found as far north the Minch off western Scotland (Lombardi et al., 2010). Patzold et al. (1987) recorded the formation of growth bands in Pentapora foliacea during times of reduced reproduction, which appeared during periods of colder water temperatures.  Once established, colonies are most likely able to withstand occasional lower or higher than normal temperatures, but long-term decreases in temperature may cause distribution range to shrink.

Whilst Caryophyllia smithii is a southern species (Fish & Fish, 1996) it occurs in the Shetland Isles (NBN, 2015) whereas CR.HCR.Xfa.ByErSp.Eun is concentrated in the south and west of the UK.

The British Isles is at the northern distribution limit of Axinella dissimilis (Ackers et al., 1992). Apparent shrinkage of individual sponges (negative growth rate) observed in Lundy in some years was attributed to particularly cold winters, notably between 1985 and 1986 (Hiscock, 1993). Long-term increases in temperature may cause extension of the British Isles populations and decreases in temperature may result in population shrinkage. 

Sensitivity assessment

Eunicella verrucosa, already close to its northern distribution limit, would likely suffer mortality in the event of a decrease in temperature, however, it appears to have survived the 1962/3 winter and may have some resistance to temporary changed. Apparent shrinkage of individual Axinella dissimilis (negative growth rate) was observed in Lundy in some years and was attributed to particularly cold winters, notably between 1985 and 1986 (Hiscock, 1993).  Resistance is therefore assessed as ‘Medium’, resilience as ‘Very Low’ 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.HCR.XFa.ByErSp.Eun is a circalittoral biotope and an increase in salinity at the benchmark level would result in a change from full to hypersaline conditions.  No records of Eunicella verrucosa, Caryophyllia smithii, or Axinella dissimilis in hypersaline conditions was found.  Chesher (1975) monitored the species surrounding a desalination outfall with brine effluent at 52‰ salinity, together with variable concentrations of copper and nickel.  As a group gorgonians were noted to survive brief exposure to 4-5% effluent, however, long-term survival decreased in relation to proximity to the outfall.  

Whilst no evidence for the characterizing species was found, there is evidence of gorgonian mortality due to hypersaline effluent.  Resistance is therefore probably ‘Low’, resilience ‘Very Low’ and sensitivity is ‘High’.

Salinity decrease (local)

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

Evidence

Ryland (1970) stated that, with a few exceptions, the Gymnolaemata were fairly stenohaline and restricted to full salinity (30-35 ppt), noting that reduced salinities result in an impoverished bryozoan fauna. For example, Flustra foliacea appears to be restricted to areas with high salinity (Tyler-Walters & Ballerstedt, 2007; Budd, 2008). Dyrynda (1994) noted that Flustra foliacea and Alcyonidium diaphanum 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, severe hyposaline conditions could adversely affect  Flustra foliacea colonies.  However, Novosel et al. (2004) described large colonies of Pentapora fascialis growing inside the plumes of marine freshwater springs (3 psu lower than water outside of the channel). Eunicella verrucosa has only been recorded in Full salinity biotopes while 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.  No information was found for Axinella dissimilis in water with salinity below 30-40.

Sensitivity assessment.  Pentapora foliacea, Eunicella verrucosa (together with associated species), and Axinella dissimilis would probably be affected adversely by a decrease in salinity at the benchmark level and resistance is ‘Low’, resilience is ‘Very low’ and sensitivity is ‘High’.

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

CR.HCR.XFa.ByErSp.Eun consists mainly of species firmly attached to the substratum and 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 most likely 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 water flow to bring food and to remove silt (Hiscock, 2007). 

Water flow has been shown to be important for the development of bryozoan communities and the provision of suitable hard substrata for colonization (Eggleston, 1972b; Ryland, 1976). In addition, areas subject to the high mass transport of water such as the Menai Strait and tidal rapids generally support large numbers of bryozoan species (Moore, 1977a). Although bryozoans are active suspension feeders, feeding currents are probably fairly localized and they are dependent on water flow to bring adequate food supplies within reach (McKinney, 1986). A substantial decrease in water flow will probably result in impaired growth due to a reduction in food availability, and an increased risk of siltation (Tyler-Walters, 2005). Caryophyllia smithii, is a suspension feeder, 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).  Riisgard et al. (1993) discussed the low energy cost of filtration for sponges and concluded that passive current-induced filtration may be of insignificant importance for sponges. However, water movement is probably required to ensure supply of food (particulates and dissolved organic matter) as well as oxygen. The sponges Axinella spp. were recorded in biotopes that experienced very weak flow to moderate (0-1.5 m/s) (Connor et al., 2004). Eunicella verrucosa, Caryophyllia smithii and Pentapora foliacea have been recorded in biotopes ranging from very weak to strong water flow (0-3 m/s) (Connor et al., 2004).

Sensitivity assessment. CR.HCR.XFa.ByErSp.Eun is found in moderately strong water flow (1-3 knots) and, whilst a significant decrease could result in less favourable conditions for Eunicella verrucosa,  a change at the benchmark level (0.1-0.2 m/s) is unlikely to affect the characterizing species.  Resistance is therefore ‘High’, resilience is ‘High’ and the biotope is ‘Not Sensitive’.

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

Eunicella verrucosa occurs in biotopes that are extremely wave exposed (Connor et al., 2004).  Bunker (1986) reported that Eunicella verrucosa was most abundant in moderately exposed locations. However, dead sea fans have been recorded washed up along Chesil Beach (UK) following winter storms (Hatcher and Trewhella, 2006 cited in Wood, 2015b).

Caryophyllia smithii has been recorded in very sheltered to extremely exposed biotopes (Connor et al., 2004). Pentapora foliacea is recorded as occurring in biotopes experiencing moderate to extreme wave exposure (Connor et al., 2004). However, extreme wave action (storms) has been noted to cause widespread destruction of colonies (Cocito et al., 1998a). Significant increases in wave exposure may, therefore, cause damage to colonies.  Hiscock (2003) suggested that ‘prolonged Easterly gales in 1985’ might account for the loss of Axinella dissimilis specimens at Lundy.  Nevertheless, following severe gales in 2013/1014, the abundance of sea fans, Pentapora fascialis, and associated branching sponges on stable rocky habitats appeared much as always (Hiscock, pers. comm.)

Sensitivity assessment. CR.HCR.XFa.ByErSp.Eun occurs across a number of wave exposures, from moderate to extremely exposed.  A decrease in wave exposure, e.g. due to artificial barriers, may be detrimental as the biotope is dependent on strong water flow.  While storms may cause mortality, a 3-5% change in significant wave height is unlikely to result in any impact in a wave exposed biotope. Resistance is ‘High’, resilience is ‘High’ and the biotope is ‘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.

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.HCR.XFa.ByErSp.Eun is a sub-tidal biotope complex (Connor et al., 2004). Oil pollution is mainly a surface phenomenon and its impact on circalittoral turf communities is likely to be limited. However, as in the case of the Prestige oil spill off the coast of France, high swell and winds can cause oil pollutants to mix with the seawater and potentially negatively affect sub-littoral habitats (Castège et al., 2014).

Filter feeders are highly sensitive to oil pollution, particularly those inhabiting the tidal zones that 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). There is little information on the effects of hydrocarbons on bryozoans. 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. Banks & Brown (2002) found that exposure to crude oil significantly impacted recruitment in the bryozoan Membranipora savartii. No evidence for Eunicella verrucosa was found, although 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 mucus production, retracted polyps and smothering by brown flocculent material (floc).

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.

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). 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.

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. Sagasti et al. (2000) reported that epifaunal communities, including the dominant bryozoans, were unaffected by periods of moderate hypoxia (ca 0.35 -1.4 ml/l) and short periods of anoxia (<0.35 ml/l) in the York River, Chesapeake Bay, although bryozoans were more abundant in the area with generally higher oxygen. However, estuarine species are likely to be better adapted to periodic changes in oxygenation. 

Bell (2002) reported that an oxycline at Lough Hyne (<5 % surface concentration) limited vertical colonization by Caryophillia smithii.

No evidence was found concerning the effects of hypoxia for Eunicella verrucosa. 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.

No evidence was found for Axinella dissimilis.  Hiscock & Hoare (1975) reported an oxycline forming in the summer months (Jun-Sep) in a quarry lake (Abereiddy, Pembrokeshire) from close to full oxygen saturation at the surface to <5% saturation below ca 10 m. No Tethya aurantia, Kirchenpaueria pinnata, Hymeniacidon pereleve, or Polymastia boletiformis were recorded at depths below 10 - 11 m. Gunda & Janapala (2009) investigated the effects of variable oxygen levels on the survival of the marine sponge, Haliclona pigmentifera. Under hypoxic conditions (1.5-2.0 ppm), Haliclona pigmentifera with intact ectodermal layers and subtle oscula survived for 42 ± 3 days. Sponges with prominent oscula, foreign material, and damaged pinacoderm exhibited poor survival (of 1-9 days) under similar conditions. Complete mortality of the sponges occurred within 2 days under anoxic conditions (<0.3 ppm O2).

Sensitivity assessment

Despite limited evidence, Eunicella verrucosa, Axinella dissimils, and Caryophyllia smithii are unlikely to tolerate hypoxic events given their preference for moderate water movement and based on general information for marine invertebrates. Resistance is ‘Low’, resilience is 'Very Low’ and sensitivity is ‘High’.

Nutrient enrichment

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

Evidence

Whilst little information on Pentapora spp. was found, O’Dea & Okamura (2000) found that annual growth of the bryozoan Flustra foliacea in western Europe has substantially increased since 1970.  They suggest that this could be due to eutrophication in coastal regions due to organic pollution, leading to increased phytoplankton biomass (see Allen et al., 1998).    Echavarri-Erasun et al. (2007) described the effects of deep water sewage discharge 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 Eunicella verrucosa could be at risk of competition from algae in shallow waters due to nutrient enrichment, CR.HCR.XFa.ByErSp.Eun is a circalittoral biotope and flora are not considered in this review.  

Nutrient enrichment could result in greater exposure to microbial pathogens, leading to disease and loss of characterising species.  Microbial pathogens are considered below, along with evidence of bacterial damage to Eunicella verrucosa. 

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

Cocito et al. (2013) demonstrated the ability of Eunicella verrucosa and other gorgonians to feed on both suspended organic matter and zooplankton.  Whilst little information on Pentapora spp. was found, O’Dea & Okamura (2000) found that annual growth of the bryozoan Flustra foliacea in western Europe has substantially increased since 1970.  They suggest that this could be due to eutrophication in coastal regions due to organic pollution, leading to increased phytoplankton biomass (see Allen et al., 1998).   Novosel et al. (2004) described large colonies of Pentapora fascialis growing inside the plume of marine freshwater springs.  The plumes had significantly higher concentrations of NO₃^-, SiO₄, NH₄⁺, NO₂^- and PO₄^3-.  Echavarri-Erasun et al. (2007) described the effects of deep water sewage discharge 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.  No evidence was found for Axinella dissimilis.  

Sensitivity assessment. All characterizing species are sessile filter feeders and the evidence suggests that all tolerate, or increase in abundance when exposed to organic enrichment in the circalittoral.  Resistance is ‘High’ resilience is ‘High’ and the biotope is ‘Not sensitive’.

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

Sensitivity assessment. Resistance to this 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) and sensitivity of Eunicella verrucosa to abrasion events has been assessed High in previous reviews (MacDonald, 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, long-term deterioration or the effects of repeated exposure were not clear (Eno et al., 2001). Observation of pots suggested that they 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.   However Tinsley (2006) observed flattened sea fan that had continued growing, with new growth being aligned perpendicular to the current, so clearly even colonies of Eunicella verrucosa that are damaged can 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 re-grow over scrapes on one side of the skeleton in about one week (Hiscock, pers. comm, cited in Hiscock, 2007.)  While Hinz et al. (2011) reported that abundance and average body size of Eunicella verrucosa were not significantly affected by scallop dredging intensity, there is evidence of Eunicella verrucosa detached by mobile gear (Hiscock, pers. comm.)

Some large Pentapora foliacea individuals were observed to be badly smashed by potting (Eno et al., 2001).  

Sensitivity assessment. Eunicella verrucosa is a sessile epifauna and is likely to be severely damaged by heavy gears, such as scallop dredging (MacDonald et al., 1996, Hiscock, pers. comm.).  However,  some studies suggest that the species may be more resistant, particularly to low intensity lighter abrasion pressures, such as pots and associated anchor damage (Eno et al. 1996).  Axinella dissimilis is likely to be damaged by towed fishing gear (Hinz et al., 2011, Hiscock, 2014) Taking all the evidence into account, resistance is ‘Low’. Resilience is ‘Very Low’ and sensitivity as ‘High’.

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

While high levels of suspended solids may inhibit feeding, colonies of the sea fan Eunicella verrucosa produce mucus to clear themselves of silt (Hiscock, 2007) and is probably tolerant of increases in suspended sediment (Hiscock et al., 2004b).  Bunker (1986) reported that Eunicella verrucosa were mostly observed on bedrock or boulders, but occurred at sites described as  ‘moderately silted’.

Populations of Caryophyllia smithii were studied at three sites of differing sedimentation regimes in Lough Hyne, Ireland (Bell & Turner, 2000).  The height, length, width and density of individuals were measured along with the depth of accumulated sediment on the rock substratum at each site. 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. Caryophyllia smithii was more abundant in areas with higher sedimentation (Bell & Turner, 2000).

Bryozoans are suspension feeders that may be adversely affected by increases in suspended sediment, due to clogging of their feeding apparatus. 

Axinella dissimilis is mainly found on upward facing clean or silty rock and whilst it tends to prefer clean oceanic water, it is tolerant of silt (Ackers et al., 1992).

Sensitivity assessment

CR.HCR.XFa.ByErSp.Eun occurs on bedrock in moderate water flow in the circalittoral and is unlikely to experience highly turbid conditions.  From the evidence presented above, the characterizing species would probably tolerate some siltation and a change at the benchmark level is unlikely to cause mortality.  Resistance is ‘High’, resilience is ‘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

While high levels of suspended sediment 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., 2004b). Bunker (1986) reported that Eunicella verrucosa were mostly observed on bedrock or boulders but occurred at sites up to ‘moderately silted’.  Eunicella verrucosa forms large colonies which branch profusely up to 30 cm in height (Picton & Morrow, 2005).

Colonies of Pentapora fascialis can reach a height of 30 cm in the British Isles (Hayward & Ryland, 1979).  Partial mortality due to siltation has been recorded in the Mediterranean (Cocito et al., 1998a) although recovery was observed in all but one colony (which fragmented into two smaller colonies).

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 (7mm ± 0.5mm) in Lough Hyne. It is therefore likely that Caryophyllia smithii would be resistant to periodic sedimentation. If 5cm of sediment were removed rapidly, via tidal currents, Caryophyllia smithii would likely remain within the biotope.  Lock et al. (2006) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover.

Ackers et al. (1992) described Axinella dissimilis as preferring clean oceanic water but tolerating silt. Hiscock & Jones (2004) reported that Axinella dissimilis (as Axinella polypoides) grew up to a height of ca 30 cm.

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 sensitivity as ‘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

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., 2004b). Bunker (1986) reported that Eunicella verrucosa were mostly observed on bedrock or boulders but occurred at sites up to ‘moderately silted’.  Eunicella verrucosa forms large colonies which branch profusely up to 30 cm in height (Picton & Morrow, 2005).  Colonies of Pentapora fascialis can reach a height of 30 cm in the British Isles (Hayward & Ryland, 1979).  Partial mortality due to siltation has been recorded in the Mediterranean (Cocito et al., 1998a) although recovery was observed in all but one colony (which fragmented into two smaller colonies). Caryophyllia smithii is small (approx. <3 cm height from the seabed) and would therefore likely be inundated in a “heavy” sedimentation event. Whilst Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of “moderate” sedimentation (7mm ± 0.5mm) in Lough Hyne, it is unlikely that Caryophyllia smithii would survive.  Burton et al. (2005) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover.  Ackers et al. (1992) described Axinella dissimilis as preferring clean oceanic water but tolerating silt. Hiscock & Jones (2004) reported that Axinella dissimilis (as Axinella polypoides) grew up to a height of ca 30 cm.

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 high energy environments and it is likely that the sediment would be removed.  However, the damage to the resident community would depend on the time taken for the deposited sediment to be removed. Therefore, resistance was assessed as ‘Low’ as the worst-case scenario. Hence, resilience is probably ‘Very Low’ and sensitivity is assessed as ‘High’.

Litter

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

Evidence

Not assessed. Ghost fishing by discarded fishing gear, lines and pots may cause some damage to the community, especially the tall erect epifauna, where discarded lines may catch the upright epifauna and increase drag, especially in stormy weather. Fishing lines can cause lesions to the gorgonian coenenchyme, leading to greater aggregates of epibionts which can eventually cause the branch to rupture (Bo et al., 2014).

Electromagnetic changes

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

Evidence

No evidence

Underwater noise changes

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

Evidence

Stanley et al. (2014) studied the effects of vessel noise on fouling communities and found that the bryozoans Bugula neritina, Watersipora arcuate and Watersipora subtorquata responded positively.  More than twice as many bryozoans settled and established on surfaces with vessel noise (128 dB in the 30–10,000 Hz range) compared to those in silent conditions.  Growth was also significantly higher in bryozoans exposed to noise, with 20% higher growth rate in encrusting and 35% higher growth rate in branching species.

Sensitivity assessment. 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. Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive'. 

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.  Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive'. 

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

Not relevant: 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 for the characterizing species could be found.

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 classified 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. 

Several invasive bryozoans are of concern including Schizoporella japonica (Ryland et al., 2014) and Tricellaria inopinata (Dyrynda et al., 2000; Cook et al., 2013b), although 'No evidence' of these affecting CR.HCR.XFa.ByErSp.Eun was found.

Sensitivity assessment. The circalittoral rock characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata due to the extremely wave exposed to moderately wave exposed conditions, in which wave action and storms may mitigate or prevent the colonization by Crepidula at high densities, although Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats or infralittoral or circalittoral rock habitats. At present, there is 'Insufficient evidence' to suggest that the circalittoral rock biotopes are sensitive to colonization by Crepidula fornicata or other invasive species; further evidence is required. 

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

The first recorded incidence of cold-water coral disease was noted in Eunicella verrucosa, in south-west England in 2002 (Hall-Spencer et al., 2007).  Video surveys in south-west England from 2003 to 2006 of 634 separate colonies at 13 sites revealed that disease outbreaks were widespread and 9% of colonies had tissue necrosis.  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 isolated from Eunicella verrucosa did not induce disease at 15°C, but, at 20°C, controls remained healthy and test gorgonians became diseased, regardless of whether Vibrio was isolated from diseased or healthy colonies. 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; 5 of the 18 necrotic colonies videoed in 2003 had died and become completely overgrown, whereas others had continued to grow around a dead central area (Hall-Spencer et al., 2007).  No evidence of disease in the characterizing bryozoan could be found.

Gochfeld et al. (2012) found that diseased sponges hosted significantly different bacterial assemblages compared to healthy sponges, with diseased sponges also exhibiting a significant decline in sponge mass and protein content. Sponge disease epidemics can have serious long-term effects on sponge populations, especially in long-lived, slow-growing species (Webster, 2007). Numerous sponge populations have been brought to the brink of extinction including cases in the Caribbean with 70-95% disappearance of sponge specimens (Galstoff, 1942), the Mediterranean (Vacelet, 1994; Gaino et al.,1992). Decaying patches and white bacterial film were reported in Haliclona oculata and Halichondria panicea in North Wales, 1988-89 (Webster, 2007). Specimens of Cliona spp. have exhibited blackened damage since 2013 in Skomer. Preliminary results have shown that clean, fouled and blackened Cliona all have very different bacterial communities. Blackened Cliona are effectively dead and have a bacterial community similar to marine sediments. The fouled Cliona have a very distinct bacterial community which may suggest a specific pathogen caused the effect (Burton, pers comm; Preston & Burton, 2015). 

Sensitivity assessment. Sponge diseases have caused limited mortality in some species in the British Isles (although no evidence was found for axinellid sponges), mass mortality and even extinction have been reported further afield.  Based on this evidence, together with mortality linked to disease in Eunicella verrucosa, resistance is assessed as ‘Medium’, resilience as ‘Very Low’ sensitivity as ‘Medium’. Confidence is 'Low'.

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 has historically been harvested as a curio by divers and was collected until recently in the British Isles (Bunker, 1986; Wells et al., 1983 cited in Koomen & Helsdingen, 1996), however, it is now protected under schedule 5 of the Wildlife and Countryside Act 1981 and harvesting is illegal.  No evidence of harvesting of the other characterizing species was found.  

Hiscock (2003) stated that the greatest loss of Axinella dissimilis at Lundy might have been due to collecting during scientific studies in the 1970s. No indication of recovery was evident. Axinella damicornis was harvested in Lough Hyne during the 1980s (for molecular investigations) and the populations were reduced to very low densities, which subsequently recovered very slowly, although they are now considered to be back to their original densities (Bell, 2007).

Sensitivity assessment. The characterizing Eunicella verrucosa and the sponge Axinella dissimilis are sessile, epifaunal and would have no resistance to harvesting.  Resistance has been assessed as ‘None’, resilience as ‘Very 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

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. For example, Eunicella verrucosa and, in particular, Axinella dissimilis, are sessile epifauna and are likely to be severely damaged by heavy gears, such as scallop dredging (MacDonald et al., 1996; Hinz et al., 2011).  

This biotope may be removed or damaged by static or mobile gears that are targeting other species. These direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of non-target species in this biotope. The unintentional removal of the important characterizing species will result in loss of the biotope. Therefore, 

Sensitivity assessment. Therefore, resistance is ‘Low’, resilience is ‘Very Low’ and sensitivity is ‘High’