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

No evidence was found for the characterizing cumacean species.

Scoloplos armiger is a species complex as is Chaetozone setosa. Both are widely distributed but populations may be sibling species and exhibit different tolerances. Until recently, Chaetozone setosa was considered cosmopolitan with records world-wide, from the intertidal zone to the deep sea. It is now known that there are several species of eyeless Chaetozone spp. in the north-east Atlantic but the worldwide distribution is unclear. Chambers et al. (2007) assessed numerous records of Chaetozone setosa in the north-east Atlantic, and identified habitat preferences Chatezone setosa  was frequently found in habitats where the mean minimum winter bottom temperature is 5-10°C and the summer maximum is >10°C (Chambers et al., 2007)

Bamber & Spencer (1984) observed that Eteone longa were present in summer in an area affected by thermal discharge in the River Medway estuary. The species is clearly tolerant of temperature fluctuations as the sediments were exposed to the passage of a temperature front of approximately 10°C between heated effluent and estuarine waters during the tidal cycles (Bamber & Spencer, 1984).

Sensitivity assessment. No information was found on the maximum temperatures tolerated by the characterizing species, Chaetozone setosa and the cumaceans. This pressure is not assessed due to lack of evidence.

Temperature decrease (local)

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

Evidence

No evidence was found for the characterizing cumacean species.

Scoloplos armiger is a species complex as is Chaetozone setosa. Both are widely distributed but populations may be sibling species and exhibit different tolerances. Until recently, Chaetozone setosa was considered cosmopolitan with records world-wide, from the intertidal zone to the deep sea. It is now known that there are several species of eyeless Chaetozone in the north-east Atlantic and the worldwide distribution is unclear. Chambers et al. (2007) assessed numerous records of Chaetozone setosa in the north-east Atlantic. The species is frequently found in habitats where the mean minimum winter bottom temperature is 5-10°C and the summer maximum is >10°C.

Sensitivity assessment. No information was found on the maximum temperatures tolerated by the characterizing species, Chaetozone setosa and the cumaceans. This pressure is not assessed due to lack of evidence.

Salinity increase (local)

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

Evidence

This biotope occurs in full salinity habitats (30-35 ppt) (JNCC, 2015). An increase at the pressure benchmark refers to an increase to hypersaline conditions (>40 ppt).

No direct evidence was found to assess sensitivity of the characterizing species. The cumacean Iphinoe canariensis, was absent from the discharge point of brine effluents at 47-50 psu in the Canary Islands (Riera et al., 2012). Scoloplos armiger was found at low abundances at the discharge point (Riera et al., 2012). However, in the western Baltic Sea Scoloplos armiger abundance was greatest between 12 psu and 17 psu and reduced abundance with increasing salinity was observed (Gogina et al., 2010). As Scoloplos armiger is a species complex and is not a cosmopolitan species there may be differences in tolerances between populations.

Sensitivity assessment. Although short-term increases in  salinity may be tolerated, a persistent increase in one MNCR salinity category above the usual range of the biotope may reduce species richness and abundance. Biotope resistance is assessed as ’Low’ and recovery as ‘High’ (following restoration of habitat conditions). Biotope sensitivity is assessed as ‘Low’.

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 habitats (30-35 ppt) (JNCC, 2015). A decrease at the pressure benchmark refers to a decrease to variable salinity conditions (18-35 ppt). This biotope occurs in shallow habitats and inputs of freshwater from rain or land run-off may lower salinities.

Cumaceans are marine species with a few exceptions found in brackish water. Therefore, changes in salinity may be detrimental, although no specific information for the characterizing species was found to develop a sensitivity assessment.

Scoloplos armiger shows a lower salinity limit of 10.5 psu (Gogina et al., 2010), suggesting the species is tolerant of a decrease from full to reduced salinity and even the low salinity category in the MNCR scale.

Sensitivity assessment. No direct evidence was found to assess sensitivity of the characterizing cumaceans and Chaetozone setosa, both species are present in fully marine habitats and a reduction at the pressure benchmark is likely to result in the loss of these species and species replacement by more tolerant taxa, such as Bathyporeia spp. Biotope resistance is assessed as ’Low’ and recovery as ‘High’ (following restoration of habitat conditions). Biotope sensitivity is assessed as ‘Low’.

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

This biotope is recorded in areas where tidal flow is moderately strong (0.5-1.5 m/s) and weak (>0.5 m/s) (JNCC, 2015). Sands are less cohesive than mud sediments and a change in water flow at the pressure benchmark may alter sediment transport patterns within the biotope. Hjulström (1939) concluded that fine sand (particle diameter of 0.3-0.6 mm) was easiest to erode and required a mean velocity of 0.2 m/s. Erosion and deposition of particles greater than 0.5 mm require a velocity >0.2 m/s to alter the habitat. The topography of this habitat is shaped by currents and wave action that influence the formation of ripples in the sediment. Specific fauna may be associated with troughs and crests of these bedforms.  may form following an increase in water flow, or disappear following a reduction in flow.

Christie (1985) describe that Chaetozone setosa prefers stable and sheltered sediments and that therefore changes in water flow that increase sediment mobility may reduce habitat suitability.

Sensitivity assessment. This biotope occurs in areas subject to moderately strong water flows and these are a key factor maintaining the clean sand habitat. Changes in water flow may alter the topography of the habitat and may cause some shifts in abundance. However, a change at the pressure benchmark (increase or decrease) is unlikely to affect biotopes that occur in mid-range flows and biotope sensitivity is therefore assessed as ‘High’ and resilience is assessed as ‘High’ so that the biotope is considered to be ‘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

This biotope occurs in the shallow sublittoral and changes in emergence are 'Not relevant'.

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

This biotope occurs in habitats that are moderately exposed to wave action (JNCC, 2015). Increases in wave exposure that exceed species disturbance tolerance may result in a change to a Glycera lapidum dominated biotope (JNCC, 2015). In areas of weaker wave action, more bivalves and other species that prefer more stable conditions may colonize and the biotope classification could alter to SS.SSa.IMuSa.FfabMag or SS.SSa.CMuSa.AalbNuc (JNCC, 2015).

The cumaceans and polychaete species are protected within the sediment. Populations may be indirectly affected by changes in water movement where these impact the movements of adults, particularly cumaceans that migrate out of sediments into the water column or where the supply of larvae is affected. No specific evidence was found to assess this pressure. As the biotope SS.SCS.ICS.CumCset occurs in habitats that are exposed moderately exposed and sheltered from wave action (JNCC, 2015) but exposed to tidal streams it is more likely that currents and substratum, rather than wave action are significant factors determining species composition

Sensitivity assessment. No direct evidence was found to assess this pressure.  At the pressure benchmark the biotope is likely to have ‘High’ resistance and by default ‘High’ resilience to a change in significant wave height at the pressure benchmark. The biotope is therefore classed as ‘Not sensitive’.

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.

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.

Gray et al. (1990) found that Scoloplos armiger were a dominant species in uncontaminated soft sediments at a case study site adjacent to the Ekofisk oil field but were not present at contaminated sites.

Eteone were described by Hiscock et al. (2005, from Levell et al., 1989) as a very tolerant taxa, found in enhanced abundances in the transitional zone along hydrocarbon contamination gradients surrounding oil platforms.

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

No evidence..

Nutrient enrichment

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

Evidence

This pressure relates to increased levels of nitrogen, phosphorus and silicon in the marine environment compared to background concentrations. The pressure benchmark is set at compliance with Water Framework Directive (WFD) criteria for good status, based on nitrogen concentration (UKTAG, 2014).  

Sensitivity assessment. As this biotope is structured by sediment disturbance rather than nutrient enrichment and is not characterized by macroalgae (although some may be present), the biotope is considered to have ‘High’ resistance to this pressure and ‘High’ resilience, (by default) and is assessed as ‘Not sensitive’.

Organic enrichment

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

Evidence

Chaetezone setosa and cumaceans were typical of enriched sites off the coast of Barcelona that were subject to effluents and sludge disposal from treatment plants (Corbera & Cardell, 1995).

Borja et al. (2000) assessed relative sensitivity of Scoloplos armiger as an ABMI Ecological Group II species (indifferent/tolerant to enrichment). Field studies have also identified Scoloplos armiger as a ‘progressive’ species, i.e. one that shows increased abundance under slight organic enrichment (Leppakoski, 1975 cited in Gray, 1979).

Eteone longa have been characterized as AMBI Group III: 'Species tolerant to excess organic matter enrichment. These species may occur under normal conditions, but their populations are stimulated by organic enrichment (slight unbalance situations). They tend to be surface deposit-feeding species' (Borja et al., 2010; Gittenberger & Van Loon 2011). Eteone longa was an early colonizer at a sewage sludge disposal site off the Tyne mouth (Khan 1991, cited from Herrando-Perez & Frid, 2001 and references therein) where levels of nutrient enrichment and  organic matter are likely to be high.

Sensitivity assessment. The presence of the characterizing species in organically enriched areas indicates that biotope 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

The biotope is characterized by the sedimentary habitat (JNCC, 2015), a change to an artificial or rock substratum would alter the character of the biotope leading to reclassification and the loss of the sedimentary community including the characterizing bivalves, polychaetes and echinoderms that live buried in the sediment.

Sensitivity assessment. Based on the loss of the biotope, resistance is assessed as ‘None’, recovery is assessed as ‘Very Low’ (as the change at the pressure benchmark is permanent and sensitivity is 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

This biotope is found in medium to very fine sand with gravel and pebbles (JNCC, 2015). The change referred to at the pressure benchmark is a change in sediment classification (based on Long, 2006) rather than a change in the finer-scale original Folk categories (Folk, 1954). 

An assessment of distribution records of Chaetozone setosa in the North Sea concluded that the species is usually associated with fine sediments (Chambers et al., 2007). The polychaetes Scoloplos armiger and Eteone longa both have relatively  broad sediment preferences. Scoloplos armiger is a burrower and changes in sediment composition that alter the grade of sediment this species must move through can affect the suitability of the habitat. An increase in coarse composition to gravels would be expected to negatively impact this burrowing species. Eteone longa is found in sediments with a wide range of median grain sizes: the species is only absent in very fine (<100 µm) and very coarse sediments (>500 µm). Eteone longa is also found in empty tubes and on oyster banks. Well-sorted types of sediments are favoured (Hartmann-Schröder, 1971; Wolff, 1973 cited in Holtmann et al., 1996).The association of Eteone longa with a range of coarse substrata/sediments indicate that it would be able to tolerate (but possibly with population impacts) an increase in sediment coarseness (e.g. where shells and larger sediments accumulate). However, a transition to a fully coarse sediment type is likely to negatively impact this species as the habitat becomes sub-optimal. Degraer et al. (2006) indicate that a change to a very fine sediment would exclude this species.

Sensitivity assessment. Although the characterizing species generally have broad sediment preferences a change to either a finer muddy sediment or a coarser sediment, would be likely to lead to loss of the biotope (based on the JNCC description) and the characterizing species. Resistance is assessed as ‘None’, recovery is assessed as ‘Very Low’ (as the change at the pressure benchmark is permanent and sensitivity is assessed as ‘High’.

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

Biotope resistance to extraction of sediment and characterizing species is assessed as ‘None. Resilience is assessed as ‘High’, as sediment recovery will be enhanced by wave action and mobility of sand. The characterizing species are likely to recover through transport of adults in the water column or migration from adjacent patches. Biotope sensitivity is therefore assessed as ‘Medium’.

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 occurs in mobile sands that are likely to experience frequent wave disturbance and periodic sediment disturbance that prevents the development of bivalve assemblages typical of more stable areas. The species present are likely to either be resistant of some physical disturbance or to recover rapidly (JNCC, 2015).

No evidence was found to assess sensitivity to abrasion of the characterizing cumacean species. During the day when these are buried within sediments, they are likely to be protected from abrasion at the surface. The infaunal polychaetes that characterize this biotope are typical of disturbed and mobile sediments and their infaunal position provides protection from abrasion at the surface. Juveniles and adults of Scoloplos armiger stay permanently below the sediment surface and freely move without establishing burrows. While juveniles are only found a few millimetres below the sediment surface, adults may retreat to 10 cm depth or more (Reise, 1979; Kruse et al., 2004). The egg cocoons are laid on the surface and hatching time is 2-3 weeks during which these are vulnerable to surface abrasion. 

Sensitivity assessment. Abrasion may damage a proportion of the populations of the characterizing species but is unlikely to result in significant removal and damage. Biotope resistance is assessed as ’Medium’ and resilience as ‘High’ so that sensitivity is assessed as ‘Low’.

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

This biotope occurs in mobile sands that are likely to experience frequent wave disturbance and periodic sediment disturbance that prevents the development of bivalve assemblages typical of more stable areas. The species present are likely to either be resistant of some physical disturbance or to recover rapidly (JNCC, 2015).

Physical disturbance reduces the abundance of Eteone longa (Southern Science, 1992 cited from Hiscock et al., 2005). The mobile polychaete Eteone longa is found in mobile sand areas and should, therefore, have some tolerance for shallow and surface disturbance, being able to re-burrow or avoid shallow disturbance. In the access lanes associated with oyster culture on trestles, De Grave et al. (1998) found higher abundances of Eteone longa. These areas may have been subject to vehicle access and the results provide some circumstantial support for the evidence for Eteone as an opportunistic species that preferentially colonizes disturbed areas (Rees, 1978 quoted in Hiscock et al., 2002).

Eteone longa has been categorised through literature and expert review, as AMBI Fisheries Review Group III, defined as: ‘Species insensitive to fisheries in which the bottom is disturbed. Their populations do not show a significant decline or increase’ (Gittenberger & Van Loon, 2011). The cumacean Diastylis bradyi and the polychaete Scoloplos armiger were assessed as AMBI Fisheries Group II defined as: ‘Species sensitive to fisheries in which the bottom is disturbed, but their populations recover relatively quickly’ (Gittenberger & Van Loon, 2011).

Sparks-McConkey & Watling (2001) identified Chaetozone setosa as a common species that declined in abundance in response to experimental trawling. Tuck et al. (1998) found that following trawl disturbance, abundances of Chaetozone setosa had recovered and became greater at treatment sites than undisturbed sites 10 months after disturbance. Scoloplos armiger, however, had declined at disturbed sites.

The cumacean Diastylis lyrifera was present at a wreck site that prevented fishing disturbance and absent from fished sites in the Irish Sea (Ball et al., 2000b), suggesting indirectly that these species may be sensitive to activities that lead to subsurface disturbance. Direct mortality (percentage of initial density) of cumaceans and gammarids from a single pass of a beam trawl was estimated from experimental studies on sandy and silty grounds as 22% and 28% respectively Bergman & Van Santbrink (2000a). Direct mortality of Scoloplos armiger was estimated as 18% (Bergman & Van Santbrink, 2000a).  Experimental intertidal dredging for cockles reduced the abundance of Scoloplos armiger in disturbed plots compared to control sites. These differences persisted for 56 days (Hall & Harding, 1997). Ferns et al. (2000) reported a decline of 31% in intertidal populations of Scoloplos armiger  in muddy sands when a mechanical tractor towed harvester was used (in a cockle fishery) (surpassing the study monitoring timeline). Scoloplos armiger demonstrated recovery >50 days after harvesting in muddy sands. 

Sensitivity assessment. Penetration and disturbance are likely to result in decreased abundance of the characterizing Chaetozone setosa, Scoloplos armiger and cumaceans. Eteone longa may be more tolerant. Based on the evidence from fisheries biotope resistance is assessed as ‘Low’ and resilience is assessed as ‘High’ as the characterizing species rapidly colonize disturbed areas. Biotope sensitivity is, therefore ‘Low’. 

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

No evidence was found to assess this pressure. This biotope is found in shallow sandy habitats where wave and other sediment disturbing factors are likely to frequently re-suspend sediments. Where this biotope is found in the mouths of estuaries it is also likely to be exposed to high suspended solids from riverine inputs. The characterizing species are largely infaunal (although cumaceans migrate into the water column). 

The abundance of the cumacean Eudorellopsis deformis is linked to benthic primary productivity (Schuckel et al., 2010). Schuckel et al. (2010) found that highest abundances occurred where increased abundance of pelagic and epipelic diatoms occurred. Increased turbidity that limited the growth of microalgae associated with sand grains could negatively affect cumacean feeding.

Sensitivity assessment. The biotope is not considered directly sensitive to a decrease or increase in suspended solids. An increase in suspended solids may lead to decreased primary productivity. Biotope resistance is assessed as ‘Medium’ as some effects on feeding and diatom productivity may occur from increases in suspended solids, resilience is assessed as ‘High’, following a return to usual conditions and sensitivity is assessed as ‘Low’. This more precautionary assessment is presented in the table Indirect effects such as deposition, erosion and associated sediment change that may result from changes in suspended solids in the long-term are assessed separately. 

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

No evidence.

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

No evidence was found to assess the sensitivity of cumaceans to this pressure and it is unclear whether the characterizing species would be able to escape the deposition of 5cm of fine sediments. Chaetezone setosa occurs in areas subject to high natural rates of sedimentation where other benthic macrofauna were excluded (Wlodarska-Kowalczuk et al., 2007) although this is likely to be due to rapid recolonization rather than survival.

Bijkerk (1988, results cited from Essink 1999) indicated that the maximal overburden through which Scoloplos could migrate was 50 cm in sand and mud. No further information was available on the rates of survivorship or the time taken to reach the surface. Warner (1971) simulated the effects of dredge disposal of different thicknesses on animals in aquaria or plastic cores for 2 weeks. In core experiments at temperatures ranging from 14 to 18°C and 20 to 21°C, there was a relationship between vertical migration distance and sediment depth for the congener Scoloplos fragilis. This species could vertically migrate through 30 cm of sand. In other core experiments in silt-clay at temperatures of 17°C to 18°C, there was a suggestion of reduced efficiency of burrowing in finer grained sediment where even the smallest amount of silt-clay proportion tested (20%) affected the burrowing ability of this species.

Sensitivity assessment. Although Scoloplos armiger is considered to be able to migrate vertically, this may be limited where the overburden consists of fine sediments (based on Maurer et al., 1978). Biotope resistance is assessed as ‘Low’. Resilience is assessed as ‘High’ and sensitivity is ‘Low’.  

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.

Underwater noise changes

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

Evidence

'Not relevant'.

Introduction of light or shading

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

Evidence

Cumaceans feed on small diatoms and other organic matter present on sand grains (Ghiold, 1982). Benthic primary production is an important factor relating to food sources and so population density. The Eudorellopsis deformis occurs in higher densities where pelagic and epipelic diatoms occur (Schuckel et al., 2010). Changes in light that alter food supply may affect abundances but it should be noted that cumacean species also occur in deep waters where light penetration is limited.

Sensitivity assessment. No evidence was found to suggest that artifical light affected benthic microalgal abundance, and shading is probably localised.  Therefore, biotope resistance is assessed as ‘High’ (with 'Low' confidence') and resilience is assessed as ‘High’ (by default) and the biotope is 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

The characterizing polychaete species produce pelagic larvae as do many pf the polychaete species. Barriers that reduce the degree of tidal excursion may alter larval supply to suitable habitats from source populations. Conversely, the presence of barriers may enhance local population supply by preventing the loss of larvae from enclosed habitats. As the bivalve species characterizing the biotope are widely distributed and produce large numbers of larvae capable of long distance transport and survival, resistance to this pressure is assessed as 'High' and resilience as 'High' by default. This biotope is therefore considered to be 'Not sensitive'.

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'. Chaetozone setosa are eyeless (Chambers et al., 2007) and visual disturbance is unlikely to affect the other species that are predominantly infaunal.

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

Key characterizing species within this biotope are not cultivated or translocated. This pressure is therefore considered ‘Not relevant’ to this biotope group.

Introduction or spread of invasive non-indigenous species

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

Evidence

The American slipper limpet Crepidula fornicata was introduced to the UK and Europe in the 1870s from the Atlantic coasts of North America with imports of the eastern oyster Crassostrea virginica. It was recorded in Liverpool in 1870 and the Essex coast in 1887-1890. It has spread through expansion and introductions along the full extent of the English Channel and into the European mainland (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 1999, 2018; Helmer et al., 2019; Hinz et al., 2011; McNeill et al., 2010; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015).

Crepidula fornicata is recorded from shallow, sheltered bays, lagoons and estuaries or the sheltered sides of islands, in variable salinity (18 to 40) although it prefers ca 30 (Tillin et al., 2020). 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 in a wide variety of habitats including clean sands, artificial substrata, Sabellaria alveolata reefs and areas subject to moderately strong tidal streams (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015; Tillin et al., 2020). 

High densities of Crepidula fornicata cause ecological impacts on sedimentary habitats. The species can form dense carpets that can smother the seabed in shallow bays, changing and modifying the habitat structure. At high densities, the species physically smothers the sediment, and the resultant build-up of silt, pseudofaeces, and faeces is deposited and trapped within the bed (Fitzgerald, 2007, Blanchard, 2009, Stiger-Pouvreau & Thouzeau, 2015; Tillin et al., 2020). The biodeposition rates of Crepidula are extremely high and once deposited, form an anoxic mud, making the environment suitable for other species, including most infauna (Blanchard, 2009; Stiger-Pouvreau & Thouzeau, 2015). For example, in fine sands, the community is replaced by a reef of slipper limpets, that provide hard substrata for sessile suspension-feeders (e.g., sea squirts, tube worms and fixed shellfish), while mobile carnivorous microfauna occupy species between or within shells, resulting in a homogeneous Crepidula dominated habitat (Blanchard, 2009). Blanchard (2009) suggested the transition occurred and became irreversible at 50% cover of the limpet. De Montaudouin et al. (2018) suggested that homogenization occurred above a threshold of 20-50 Crepidula /m². 

Impacts on the structure of benthic communities will depend on the type of habitat that Crepidula colonizes. De Montaudouin & Sauriau (1999) reported that in muddy sediment dominated by deposit-feeders, species richness, abundance and biomass increased in the presence of high densities of Crepidula (ca 562 to 4772 ind./m²), in the Bay of Marennes-Oléron, presumably because the Crepidula bed provided hard substrata in an otherwise sedimentary habitat. In medium sands, Crepidula density was moderate (330-1300 ind./m²) but there was no significant difference between communities in the presence of Crepidula. Intertidal coarse sediment was less suitable for Crepidula with only moderate or low abundances (11 ind./m²) and its presence did not affect the abundance or diversity of macrofauna. However, there was a higher abundance of suspension–feeders and mobile Crustacea in the absence of Crepidula (De Montaudouin & Sauriau, 1999). The presence of Crepidula as an ecosystem engineer has created a range of new niche habitats, reducing biodiversity as it modifies habitats (Fitzgerald, 2007). De Montaudouin et al. (1999) concluded that Crepidula did not influence macroinvertebrate diversity or density significantly under experimental conditions, on fine sands in Arcachon Bay, France. De Montaudouin et al. (2018) noted that the limpet reef increased the species diversity in the bed, but homogenised diversity compared to areas where the limpets were absent. In the Milford Haven Waterway (MHW), the highest densities of Crepidula were found in areas of sediment with hard substrata, e.g., mixed fine sediment with shell or gravel or both (grain sizes 16-256 mm) but, while Crepidula density increased as gravel cover increased in the subtidal, the reverse was found in the intertidal (Bohn et al., 2015). Bohn et al. (2015) suggested that high densities of Crepidula in high-energy environments were possible in the subtidal but not the intertidal, suggesting the availability of this substratum type was beneficial for its establishment. Hinz et al. (2011) reported a substantial increase in the occurrence of Crepidula off the Isle of Wight, between 1958 and 2006, at a depth of ca 60 m, on hard substrata (gravel, cobbles, and boulders), swept by strong tidal streams. Presumably, Crepidula is more tolerant of tidal flow than the oscillatory flow caused by wave action, which may be less suitable (Tillin et al., 2020). 

Sensitivity assessment. The sediments characterizing this biotope are likely to be too mobile or otherwise unsuitable for most of the invasive non-indigenous species currently recorded in the UK. The above evidence suggests that Crepidula fornicata could colonize coarse sediment habitats in the subtidal, typical of this biotope. Bohn et al. (2015) demonstrated that Crepidula had a preference for gravelly habitats, while De Montaudouin & Sauriau (1999) and Bohn et al. (2015) noted that Crepidula densities were low in intertidal coarse sediments. Therefore, Crepidula has the potential to colonize, and modify the habitat and its associated community due to the introduction of Crepidula shell biomass, silt, pseudofaeces and faeces (Blanchard, 2009; Tillin et al., 2020), as occurs in maerl gravels (Grall & Hall-Spencer, 2003) resulting in the loss of the biotope. This is a moderate energy habitat, in which storms may mobilise the sediment (JNCC, 2022), which may mitigate or prevent colonization by Crepidula at high densities, although it has been recorded from areas of strong tidal streams (Hinz et al., 2011). Therefore, the habitat may be more suitable for Crepidula where water movement is meditated by tidal flow rather than wave action, e.g., the deeper examples of the biotope. However, Crepidula reduced the density of suspension feeders and mobile Crustacea in coarse sediment even at low densities (De Montaudouin & Sauriau, 1999). 

Therefore, resistance is assessed as 'Medium' in examples where wave action is high and subject to storms but 'Low' in areas dominated by tidal flow. Resilience is assessed as 'Very low' as it would require the removal of Crepidula, probably by artificial means. Hence, sensitivity is assessed as 'High' based on the worst-case scenario. Crepidula has not yet been reported to occur in this biotope so the confidence in the assessment is 'Low' and 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

No evidence.

Removal of target species

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

Evidence

No species within the biotope are targeted by commercial or recreational fishers or harvesters. 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 these biotopes, including the characterizing species, may be damaged or directly removed by static or mobile gears that are targeting other species (see abrasion and penetration pressures). Loss of these species would alter the character of the biotope resulting in re-classification, and would alter the physical structure of the habitat resulting in the loss of the ecosystem functions such as secondary production performed by these species.

Sensitivity assessment. Species within the biotope are relatively sedentary or slow moving although the infaunal position may protect some burrowing species from removal. Biotope resistance is therefore assessed as ‘Low’ and resilience as ‘High’ as cumaceans and Chaetozone setosa are likely to recolonize rapidly. Biotope sensitivity is assessed as 'Low'.