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

Murina (1997) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe which extends into the warmer waters of Portugal and Italy (Pardal et al., 1993; Sordino et al., 1989). In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata in temperatures of 7.5 to 11.5°C and in Whitstable in Kent, where sea temperatures varied between 0.5 and 17°C (Dorsett, 1961). Growth rates may increase if temperature rises. For example, at Whitstable in Kent, Dorsett (1961) found that a rapid increase in growth of Polydora ciliata coincided with the rising temperature of the seawater during March.

Sensitivity assessment: Typical surface water temperatures around the UK coast vary, seasonally from 4-19°C (Huthnance, 2010). No information was found on the maximum temperature tolerated by Polydora ciliata. However, it is likely that the species is able to resist a long-term increase in temperature of 2°C and may resist a short-term increase of 5°C. Resistance and resilience are therefore assessed as High and the biotope is judged as Not Sensitive.

Temperature decrease (local)

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

Evidence

Murina (1997) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe. In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata in temperatures of 7.5 to 11.5°C and in Whitstable in Kent abundance was high when winter water temperatures dropped to 0.5°C (Dorsett, 1961). During the extremely cold winter of 1962/63 Polydora ciliata was apparently unaffected, when temperature anomalies of between 2.5-5.8°C where observed (Crisp, 1964).

Sensitivity assessment: Typical surface water temperatures around the UK coast vary, seasonally from 4-19°C (Huthnance, 2010). Polydora ciliata is likely to be able to resist a long-term decrease in temperature of 2°C and may resist a short-term decrease of 5°C.  Temperature may act as a spawning cue and an acute or chronic decrease may result in some delay in spawning, however this is not considered to impact the adult population and may be compensated by later spawning events. Resistance and resilience are therefore assessed as High and the biotope judged as Not Sensitive.

Salinity increase (local)

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

Evidence

Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. However, there are no records of the species or the biotope occurring in hypersaline waters.

Sensitivity assessment: A long-term increase in salinity at the pressure benchmark level is likely to result in the death of many individuals. Resistance is therefore assessed as Low and resilience is likely to be High so the biotope is considered to have Low sensitivity to an increase in salinity at the pressure benchmark level.

Salinity decrease (local)

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

Evidence

Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. In an area of the western Baltic Sea, where bottom salinity was between 11.1 and 15.0psu Polydora ciliata was the second most abundant species with over 1000 individuals per m² (Gulliksen, 1977).

Sensitivity assessment: Records indicate CR.MCR.SfR.Pol occurs in areas of variable (18-35 ppt) salinity (Connor et al., 2004). Polydora ciliata is therefore likely to resist a decrease in salinity at the pressure benchmark level. Resistance is therefore assessed as High and resilience as High (by default) and the biotope is considered Not Sensitive to a decrease in salinity at the pressure benchmark level.

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.MCR.SfR.Pol is recorded in a range of tidal streams, including strong (1.5-3 m/s), moderately strong (0.5-1.5 m/s) and weak tidal stream conditions (<0.5 m/s) (Connor et al., 2004).

Polydora ciliata colonized test panels in Helgoland in three areas, two exposed to strong tidal currents and one site sheltered from currents (Harms & Anger, 1983). Very strong water flows may sweep away Polydora colonies, where these are present as a thick layer of mud on a hard substratum.

The most damaging effect of increased flow rate (above the pressure benchmark) could be the erosion of the soft rock substratum as this could eventually lead to loss of the habitat.

Sensitivity assessment: CR.MCR.SfR.Pol is recorded in a range of tidal streams, including strong, moderately strong and weak tidal stream conditions (Connor et al., 2004). A change in water flow at the benchmark level of 0.1-0.2 m/s is therefore likely to fall within the normal range of water flows experienced by the biotope. Resistance and resilience are therefore considered to be High and the biotope is assessed as Not Sensitive to a change in water flow rate at the pressure 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 the biotope, which 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

The biotope is found in moderately exposed sites (Connor et al., 2004). Feeding of Polydora ciliata may be impaired in strong wave action and changes in wave exposure may also influence the supply of particulate matter for tube building activities. Decreases in wave exposure may influence the supply of particulate matter because wave action may have an important role in re-suspending the sediment that is required by the species to build its tubes. Food supplies may also be reduced affecting growth and fecundity of the species.

Potentially the most damaging effect of increased wave heights would be the erosion of the soft rock substratum as this could eventually lead to loss of the habitat.

Sensitivity assessment. Some erosion will occur naturally and storm events may be more significant in loss and damage of soft rocks than changes in wave height at the pressure benchmark. The biotope is therefore considered to have High resistance to changes at the pressure benchmark where these do not lead to increased erosion of the substratum. Resilience is therefore assessed as High and the biotope is considered to be Not Sensitive, at the pressure benchmark.

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

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

Experimental studies with various species suggest that polychaete worms are quite resistant to heavy metals (Bryan, 1984). Polydora ciliata occurs in an area of the southern North Sea polluted by heavy metals but was absent from sediments with very high heavy metal levels (Diaz-Castaneda et al., 1989).

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.

In analysis of kelp holdfast fauna following the Sea Empress oil spill in Milford Haven the fauna present, including Polydora ciliata, showed a strong negative correlation between numbers of species and distance from the spill (SEEEC, 1998). After the extensive oil spill in West Falmouth, Massachusetts, Grassle & Grassle (1974) followed the settlement of polychaetes in the disturbed area. Species with the most opportunistic life histories, including Polydora ligni, were able to settle in the area. This species has some brood protection which enables larvae to settle almost immediately in the nearby area (Reish, 1979).

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.

Polydora ciliata was abundant at polluted sites close to acidified, halogenated effluent discharge from a bromide-extraction plant in Amlwch, Anglesey (Hoare & Hiscock, 1974). Spionid polychaetes were found by McLusky (1982) to be relatively resistant of distilling and petrochemical industrial waste in Scotland.

Radionuclide contamination

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

Evidence

No evidence was found

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

Polydora ciliata is frequently found at localities with oxygen deficiency (Pearson & Rosenberg, 1978). For example, in polluted waters in Los Angeles and Long Beach harbours Polydora ciliata was present in the oxygen range 0.0-3.9 mg/l and the species was abundant in hypoxic fjord habitats (Rosenberg, 1977). Furthermore, in a study investigating a polychaete community in the north west Black Sea, Polydora ciliata was observed in all four study sites, including those severely affected by eutrophication and hypoxia as a result of discharges of wastewaters (Vorobyova et al., 2008). However, Polydora ciliata is unlikely to be able to resist anoxic conditions. Hansen et al. (2002) reported near total extinction of all metazoan in the Mariager Fjord (Denmark), including Polydora spp. after a severe hypoxia event that resulted in complete anoxia in the water column for two weeks. Additionally, Como & Magni (2009) investigated seasonal variations in benthic communities known to be affected by episodic events of hypoxia. The authors observed that abundance of Polydora ciliata varied seasonally, decreasing during the summer months, and suggested it could be explained by the occurrence of hypoxic/anoxic conditions and sulphidic sediments during the summer. No details of the levels of dissolved oxygen leading to these community responses were provided.

Sensitivity assessment: Polydora ciliata is frequently found at localities with oxygen deficiency (Pearson & Rosenberg, 1978) and seems to only be affected by severe de-oxygenation episodes. Resistance to de-oxygenation at the pressure benchmark level is likely to be High. Opportunistic Polydora spp. have also repeatedly been reported amongst the first to recover hypoxia events (Hansen et al., 2002; Van Colen et al., 2010) so resilience is likely to also be High. The biotope is therefore considered Not Sensitive to exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for 1 week.

Nutrient enrichment

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

Evidence

Polydora ciliata is often found in environments subject to high levels of nutrient input. For example, the species was abundant in areas of the Firth of Forth exposed to high levels of sewage pollution (Smyth, 1968), in nutrient rich sediments in the Mondego estuary, Portugal (Pardal et al., 1993) and the coastal lagoon Lago Fusaro in Naples (Sordino et al., 1989). The extensive growths of Polydora ciliata in mat formations were recorded at West Ganton, in the Firth of Forth, prior to the introduction of the Sewage Scheme (Read et al., 1983). The abundance of the species was probably associated with their ability to use the increased availability of nutrients as a food source and silt for tube building.

Sensitivity assessment: The characterizing species of this biotope is likely to be able to resist nutrient enrichment. The biotope is considered 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

In colonization experiments in an organically polluted fjord receiving effluent discharge from Oslo, Polydora ciliata had settled in large numbers within the first month (Green, 1983; Pardal et al., 1993). However, Callier et al. (2007) investigated the spatial distribution of macrobenthos under a suspended mussel culture, in eastern Canada, where the sedimentation of organic matter to the bottom was approx. 1-3 gC/m²/d. Polydora ciliata was recorded as absent in the sites under the suspended mussel farm after one year and as dominant in reference areas of the study.  It should be noted that the organic matter input from the mussel farm exceeds the pressure benchmark.

Como & Magni (2009) investigated seasonal variations in benthic communities known to be affected by episodic events of sediment over-enrichment. The authors observed that abundance of Polydora ciliata varied seasonally, and suggested this could be a result of major accumulation of organic C-bounding fine sediments in the study site.

Studies by Almeda et al. (2009) and Pedersen et al. (2010) investigated larval energetic requirements for Polydora ciliata, and suggested maximum growth rates were reached at food concentrations ranging from 2.5 to 1.4 μg C/ml depending on larval size, energetic carbon requirements of 0.09 to 3.15 μg C l/d, respectively.

Polydora ciliata can also occur in organically poor areas (Pearson & Rosenberg, 1978).

Borja et al. (2000) and Gittenberger & van Loon (2011) in the development of an AMBI index to assess disturbance (including organic enrichment) both assigned Polydora ciliata to their Ecological Group IV ‘Second-order opportunistic species present in slight to pronounced unbalanced situations’.

Sensitivity assessment: The evidence presented suggests Polydora ciliata may not be able to resist organic enrichment that exceeds the pressure benchmark level (Callier et al., 2007) but may not be affected by at the benchmark level. Resistance and resilience are therefore assessed as High and the biotope is considered Not Sensitive to organic enrichment (deposit of 100 gC/m²/yr).

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

CR.MCR.SfR.Pol is characterized by the soft rock substratum which supports populations of Polydora sp. tubes. A change to a sedimentary, hard rock or artificial substratum would result in the loss of Polydora, significantly altering the character of the biotope. The biotope would be lost and/or re-classified.

Sensitivity assessment: Resistance to the pressure is considered None, and resilience Very Low based on the loss of suitable substratum to support the community of the characterizing species of Polydora. Sensitivity has been assessed as 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 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

Removal of the substratum to 30 cm would result in the loss of Polydora sp. tubes.  Resistance to the pressure is considered None, and resilience Very Low based on the loss of suitable substratum to support the community of the characterizing species of Polydora. Sensitivity has been assessed as High. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

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

This biotope is characterized by epifauna occurring on hard rock substratum. The tubes of Polydora spp. are likely to be removed by abrasion as these project above the surface and are not physically robust. Other epifauna associated with this biotope are also likely to be damaged and/or removed by surface abrasion. Some species such as anemones and sponges may be able to rapidly repair damage while others may recolonize rapidly, e.g. barnacles.  

Sensitivity assessment.  The characterizing Polydora community in this biotope, is considered likely to be damaged and removed by abrasion. As a soft bodied species, Polydora ciliata is likely to be crushed and killed by an abrasive force or physical blow. Erect epifauna are directly exposed to this pressure which would displace, damage and remove individuals. Resistance to abrasion is considered None. However, Polydora is likely to be able to re-establish the lost community rapidly, so resilience of the biotope is assessed as High with the biotope considered to have Medium sensitivity to abrasion or disturbance of the surface of the seabed. The substratum is unable to recover from damage and therefore the biotope would be considered highly sensitivity to abrasion that damaged or removed the soft rock substratum.

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

Activities that disturb the surface of the mat and penetrate below the surface would remove a significant proportion of the Polydora tubes within the direct area of impact. Biotope resistance is therefore assessed as None and recovery is assessed as High based on the assumption that the suitable substratum to support the community of the characterizing species of Polydora would only be damaged, not lost. Sensitivity is therefore assessed as Medium. The substratum is unable to recover from damage and therefore the biotope would be considered highly sensitivity to physical disturbance that damaged or removed the soft rock substratum. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

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

CR.MCR.SfR.Pol tends to occur in highly turbid areas (Connor et al., 2004). In the Firth of Forth, Polydora ciliata formed extensive mats in areas that had an average of 68 mg/l suspended solids and a maximum of approximately 680 mg/l, indicating the species is able to tolerate different levels of suspended solids (Read et al., 1982; Read et al., 1983). Occasionally, in certain places siltation is speeded up when Polydora ciliata is present because the species actually produces a 'mud' as it perforates soft rock and chalk habitats and larvae settle preferentially on substrates covered with mud (Lagadeuc, 1991).

Suspended sediment and siltation of particles is important for tube building in Polydora ciliata so a decrease in suspended solids may reduce tube building or the thickness of the mud surrounding the 'colonies'. Daro & Polk (1973) reported that the success of Polydora is directly related to the quantities of muds of any origin carried along by rivers or coastal currents.

An increase in turbidity, reducing light availability may reduce primary production by phytoplankton in the water column. A reduction in primary production in the water column may result indirectly in reduced food supply to the detritus feeding Polydora which in turn may affect growth rates and fecundity.

Sensitivity assessment: An increase in suspended solids at the pressure benchmark level is unlikely to affect the characterizing species of this biotope. However, a decrease in suspended matter in the biotope could result in limitation of material for tube building activity of Polydora and also in the substrate no longer being suitable for colonization by new recruits. Resistance of the biotope is therefore considered to be Low (loss of 25-75%) and resilience is High (following a return to normal conditions) so the biotope is considered to have Low sensitivity to a decrease in suspended solids at the pressure 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

Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates (Lagadeuc, 1991). A Polydora mud can be up to 50 cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes to reach the surface, or leave them to rebuild close to the surface.

Munari & Mistri (2014) investigated the spatio-temporal variation pattern of a benthic community following deposition of dredged material, at a maximum thickness of 30–40 cm. Polydora ciliata was amongst the first colonizers of the newly deposited sediments. The authors suggested that it was possible that the individuals migrated vertically through the deep layer of dredged sand. This was based on the results of Roberts et al. (1998) who suggested 15 cm as the maximum depth of overburden through which benthic infauna can successfully migrate. After one year, no adverse impact of sand disposal on the benthic fauna was detected on the study site.

Sensitivity assessment: Based on the evidence presented by Munari & Mistri (2014), Polydora ciliata is considered likely to resist smothering by 5 cm of sediment. Resistance and resilience are therefore assessed as High and the biotope is considered Not Sensitive to a ‘light’ deposition of up to 5 cm of fine material in a single discrete event.

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

Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates (Lagadeuc, 1991). A Polydora mud can be up to 50 cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes, or leave them to rebuild close to the surface.

Munari & Mistri (2014) investigated the spatio-temporal variation pattern of a benthic community following deposition of dredged material, at a maximum thickness of 30–40 cm. Polydora ciliata was amongst the first colonizers of the newly deposited sediments. The authors suggested that it was possible that the individuals migrated vertically through the deep layer of dredged sand. This was based on the results of Roberts et al. (1998) who suggested 15 cm as the maximum depth of overburden through which benthic infauna can successfully migrate. After one year, no adverse impact of sand disposal on the benthic fauna was detected on the study site.

Sensitivity assessment: Polychaete species have been reported to migrate through depositions of sediment greater that the benchmark (30 cm of fine material added to the seabed in a single discrete event) (Maurer et al., 1982). However, it is not clear whether Polydora ciliata is likely to be able to migrate through a maximum thickness of fine sediment that would compare to that investigated by Munari & Magni (2014) because muds tend to be more cohesive and compacted than sand. Some mortality of the characterizing species is likely to occur. Resistance is therefore assessed as Low and resilience as High and the biotope is considered to have Low sensitivity to a ‘heavy’ deposition of up to 30 cm of fine material in a single discrete event.

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 is available on which to assess this pressure.

Underwater noise changes

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

Evidence

Polydora ciliata may respond to vibrations from predators or bait diggers by retracting their palps into their tubes. However, the species is unlikely to be affected by noise pollution and so the biotope is assessed as Not Sensitive.

Introduction of light or shading

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

Evidence

CR.MCR.SfR.Pol is a circalittoral biotope (Connor et al., 2004) and therefore, not directly dependent on sunlight. 

Sensitivity assessment. Although Polydora spp. can perceive light, this pressure is not considered relevant. The biotope is considered to have High resistance and, by default, High resilience and therefore is Not Sensitive to the introduction of light.

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 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

Polydora ciliata exhibits shadow responses and withdraws its palps into its burrow, which is believed to be a defence against predation. The withdrawal of the palps interrupts feeding and possibly respiration, although the species also shows habituation of the response (Kinne, 1970).  Polydora is unlikely to be sensitive to visual disturbance caused by passing shipping but may respond to passing divers at close range. Resistance and resilience are, therefore, assessed as 'High' and the biotope judged as 'Not Sensitive' to visual disturbance.

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

The key characterizing species in the biotope are not cultivated or likely to be translocated. This pressure is therefore considered Not relevant.

Introduction or spread of invasive non-indigenous species

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

Evidence

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. 

Sensitivity assessment. The circalittoral rock characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata due to the 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

Introduced organisms (especially parasites or pathogens) are a potential threat in all coastal ecosystems. However, so far, no information was found on microbial pathogens affecting Polydora ciliata.

Sensitivity assessment. The biotope is judged to have High resistance to this pressure. By default resilience is assessed as High and the biotope is classed as Not Sensitive.

Removal of target species

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

Evidence

CR.MCR.SfR.Pol is currently not targeted by commercial fisheries and hence not directly affected by this pressure. This pressure is therefore considered Not Relevant.

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

Direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures, while this pressure considers the ecological or biological effects of by-catch. Species in this biotope, including the characterizing species Polydora ciliata, may be damaged or directly removed by static or mobile gears that are targeting other species (see abrasion and penetration pressures). Loss of Polydora species and the mat of tubes would alter the character of the biotope resulting in re-classification. Loss of Polydora spp. and the associated epifauna would alter the physical structure of the habitat and result in the loss of the ecosystem functions such as secondary production performed by these species.

Sensitivity assessment. Removal of the characterizing species would result in the biotope being lost or re-classified. Thus, the biotope is considered to have a resistance of None to this pressure and to have High resilience, resulting in the sensitivity being judged as Medium.