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

Sabella pavonina can be found in both the subtidal and the intertidal throughout the British Isles (NBN, 2016).  The ability to withstand repeated and rapid temperature changes on the intertidal shore suggests that this species does have some tolerance to an increase in temperature.  However, those Sabella pavonina that are found on the intertidal are likely to be acclimatized to those environmental conditions.  When investigating the environmental factors which initiate spawning in Sabella pavonina Murray et al. (2011) found temperature fluctuated considerably at spawning times over the three year study period.  Temperatures were found to vary from 13-18°C.  This study suggests further supports the idea that the species can tolerate a range of temperatures.  Tompsett (2003) suggested that one of the reasons that Sabella pavonina went through a period of severe decline within the Fal and Helford estuaries in the 1980’s could be high summer temperatures.  However, there was a lack of evidence to link the decline in Sabella pavonina with a period of high summer temperatures.

All characterizing sponges (Halichondria panacea, Amphilectus fucorum, Haliclona oculata) are widely distributed across the coasts of the British Isles and are all found from the Channel Isles to northern Scotland (NBN, 2016).  Berman et al. (2013) monitored sponge communities off Skomer Island, UK, over three years with all characterizing sponges for this biotope assessed.  seawater temperature, turbidity, photosynthetically active radiation and wind speed were all recorded during the study.  It was concluded that, despite changes in species composition, primarily driven by the non-characterizing Hymeraphia, Stellifera and Halicnemia patera, no significant difference in sponge density was recorded in all sites studied.  Many sponges rely on a holobiont of many synergistic microbes (Webster et al.,2008, 2011; Webster & Taylor, 2012; Preston &Burton, 2015).  Webster et al. (2011) described a much higher thermal tolerance to sponge larval holobiont when compared with adult sponges.  Lemoine et al. (2007) studied the effects of thermal stress on the holobiont of the sponge Halichondria bowerbanki collected from Virginia, USA.  Whilst no apparent change in density or diversity of symbionts was detected over the range of temperatures (29 °C, 30 °C and 31 °C), presence of particular symbionts was temperature dependent.  Barthel (1986) reported that reproduction and growth in Halichondria panicea in the Kiel Bight were primarily driven by temperature, with higher temperatures corresponding with highest growth. 

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore.  This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay.  Larvae, but not adults, have been recorded from the Mediterranean.  There is no further information available on the temperature tolerance of Cerianthus lloydii.

Urticina felina has a more northern distribution and is absent from warmer Mediterranean and equatorial waters.  Urticina felina has a boreal-arctic distribution and possibly a circumpolar distribution (Carlgren, 1949; Manuel, 1981).  It is found throughout Europe from northern Russia to the Bay of Biscay (Fautin, 2016).  Gosse (1860) observed that Urticina felina (as Actinia crassicornis) was "one of the most difficult [anemones] to keep in an aquarium" and that "the heat of the summer is generally fatal to our captive specimens".  It is therefore likely that local warming in summer may adversely affect individuals and that some mortality might occur.

Sensitivity assessment.  At the pressure benchmark the Sabella pavonina and most other characterizing species are unlikely to be negatively affected.  There may be a reduction in the abundance of Urticina felina in the more southerly example of this habitat, as this anemone is a more northerly species.  The resistance and resilience are assessed as ‘High’, resulting in the biotope being assessed as ‘Not sensitive’ at the pressure benchmark. 

Temperature decrease (local)

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

Evidence

Sabella pavonina can be found in both the subtidal and the intertidal throughout the British Isles (NBN, 2016).  The ability to withstand repeated and rapid temperature changes on the intertidal shore means that this species does have some tolerance to a decrease in temperature.  However, those Sabella pavonina that are found on the intertidal are likely to be acclimatized to those environmental conditions.  Tompsett (2003) suggested that one of the reasons that intertidal Sabella pavonina populations went through a period of severe decline in Cornwall in the 1963 could be low winter temperatures.  However, there was a lack of evidence to link the decline in Sabella pavonina with this period of unusually cold weather.  Tompsett (2003) did suggest that juvenile Sabella pavonina are likely to be more vulnerable to the cold as they are nearer to the air land interface and would be more exposed to changing temperatures.

All characterizing sponges (Halichondria panacea, Amphilectus fucorum, Haliclona oculata) are widely distributed across the coasts of the Bristish Isles and are all found from the Channel Isles to Northern Scotland (NBN 2016).  Berman et al. (2013) monitored sponge communities off Skomer Island, UK over three years with all characterizing sponges for this biotope assessed.  seawater temperature, turbidity, photosynthetically active radiation and wind speed were all recorded during the study.  It was concluded that, despite changes in species composition, primarily driven by the non-characterizing Hymeraphia Stellifera and Halicnemia patera, no significant difference in sponge density was recorded in all sites studied.  Some sponges do exhibit morphological strategies to cope with winter temperatures e.g.  Halichondria bowerbanki goes into a dormant state below 4°C, characterized by major disintegration and loss of choanocyte chambers with many sponges surviving mild winters in more protected areas from where it can recolonize (Vethaak et al., 1982).  Crisp (1964a) studied the effects of an unusually cold winter (1962-3) on the marine life in Britain, including Porifera in North Wales.   Whilst difficulty in distinguishing between mortality and delayed development was noted, Crisp found that Pachymastia johnstonia and Halichondria panicea were wholly or partly killed by frost, and several species appeared to be missing including Amphilectus fucorum. Others, including Hymeniacidon perleve were unusually rare and a few species, including Polymastia boletiformis, were not seriously affected.  It should be noted that Crisp’s general comments on all marine life state that damage decreased the deeper the habitat and that the extremely cold temperatures (sea temperatures between 4-6°C colder than the 5 year mean over a period of 2 months) is more extreme than the benchmark level for assessment.  Barthel (1986) reported that Halichondria panicea in the Kiel Bight degenerated and disintegrated after reproduction before winter, however young colonies observed from September.

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore.  This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay.  No further information is available on the temperature tolerance of Cerianthus lloydii.

Urticina felina has a more northern distribution and is absent from warmer Mediterranean and equatorial waters.  Urticina felina has a boreal-arctic distribution and possibly a circumpolar distribution (Carlgren, 1949; Manuel, 1981).  It is found throughout Europe from northern Russia to the Bay of Biscay (Fautin, 2016).  Although Urticina felina was apparently unaffected by the extremely cold winter of 1962/3 (Crisp, 1964a), Gosse (1860) observed that ‘after the intense and protracted frost of February 1855, the shores of South Devon were strewn with dead and dying anemones, principally of this species’.  Bearing in mind the equivocal observations from two cold winters, it is suggested that at least some individuals might be killed by extreme cold (exceeding the pressure benchmark).

Sensitivity assessment.  Much of the evidence given for the characterizing species Sabella pavonina comes from intertidal population observations.  The intertidal creates more extreme temperature conditions that the subtidal where temperatures tend to be more stable.  Therefore at the level of the benchmark it is unlikely that there will be a decrease in the population of this species as it is known to tolerate far more challenging environmental conditions.  The other species within this biotope are also tolerant to changes in temperature and can be found throughout the British Isles.  Bearing in mind that localized populations will be acclimatized to their own environmental conditions.  The resistance and resilience of this biotope to a decrease in temperature is assessed as ‘High’, so at the level of the benchmark this biotope is ‘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

This biotope is only found within fully marine conditions (Connor et al., 2004).  Any increase in the salinity regime would create hypersaline conditions.  No evidence could be found on the hypersaline tolerance of Sabella pavonina, the characterizing sponges, Cerianthus lloydii, or Urticina felina.  Some of these species can be found in deep rock pools around the low water mark, but no higher on the shore.  This situation may expose them to short-term small increases in salinity.  This suggests that the species are not resistant of an increase in salinity regime above full salinity for the stated time period.

Sensitivity assessment.  The resistance of this biotope to an increase in salinity regime is ‘None’ and the resilience is ‘Medium’, giving the biotope a sensitivity of ‘Medium’.

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 is only found within fully marine conditions (Connor et al., 2004).  Any increase in the salinity regime would create hypersaline conditions.  No evidence could be found on the hypersaline tolerance of Sabella pavonina, the characterizing sponges, Cerianthus lloydii, or Urticina felina.  Some of these species can be found in deep rock pools around the low water mark, but no higher on the shore.  This situation may expose them to short-term small increases in salinity.  This suggests that the species are not resistant of an increase in salinity regime above full salinity for the stated time period.

Sensitivity assessment.  The resistance of this biotope to an increase in salinity regime is ‘None’ and the resilience is ‘Medium’, giving the biotope a sensitivity of ‘Medium’.

Water flow (tidal current) changes (local)

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

Evidence

The water flow recorded within this biotope ranges from strong (3-6 knots) to moderately strong (1-3 knots) (Connor et al., 2004).  There is very little information on the tolerance of Sabella pavonina of difference water flow rates, however, the gregarious nature of tube dwelling polychaetes can produce complex hydrodynamic environments.  These complex hydrodynamic flows have been shown to affect larval settlement and food availability (Eckman, 1983; Merz, 1984; Miron et al., 1996; Walters et al., 1997).

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.  Pumping and filtering occurs in choanocyte cells which generate water currents in sponges using flagella (de Vos et al., 1991).

Evidence for the effect of changes in water flow on Cerianthus lloydii is unavailable.  This species is recorded from biotopes with a wide range of water flow regimes.  Therefore, it is likely to have a high tolerance to an increase in water flow rates.  However, a decrease in the water flow rate within this biotope will create almost entirely still conditions.  The effect of such low water flow rates on this species are not clear.

Urticina felina favours areas with strong tidal currents (Holme & Wilson, 1985; Migné & Davoult, 1998), although it is also found in calmer and sheltered areas as well as deep water.  Biotopes characterized by Urticina felina range from very weak (negligible) to very strong (negligible to >3 m/s), suggesting that a change in water flow eat the pressure benchmark would not have negative effects (Tillin & Tyler-Walters, 2014).  Similarly, Spirobranchus triqueter is found in biotopes that are exposed to flow speeds varying from very weak to moderately strong (negligible - >1.5m/s) (Tillin & Tyler-Walters, 2014).

Sensitivity assessment.  Although water flow can have a significant impact on a wide number of aspects of marine organisms lives, at the low level of the benchmark there is unlikely to be an effect.  The resistance and resilience of this biotope are assessed to be ‘High’, giving the biotope an assessment of ‘Not sensitive’ at the pressure benchmark. 

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 does not occur in the intertidal, and consequently an increase in emergence is considered not relevant to this biotope.

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 is found in moderately exposed to extremely sheltered habitats (Connor et al., 2004).  It is unclear how tolerant Sabella pavonina, Cerianthus lloydii, and the sponges found within this biotope are to a change in wave exposure at the pressure benchmark.

Urticina felina is firmly attached to the substratum and are unlikely to be dislodged by an increase in wave action at the pressure benchmark.  It is found in biotopes that experience a range of wave exposures, from extremely sheltered to very exposed, (Tillin & Tyler-Walters, 2014).  The crustose corallines associated with this biotope have a flat growth form and are unlikely to be dislodged by increased wave action.

Sensitivity assessment.  Although there is very little evidence to support an assessment of how the pressure may affect the species within this biotope, the benchmark is so low that it is very unlikely that there would be any effect on the characterizing species.  Therefore, resistance and resilience have been assessed as ‘High’, giving the biotope an overall assessment of ‘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.

Synthetic compound contamination

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

Evidence

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

Radionuclide contamination

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

Evidence

No evidence.

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

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

Evidence

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

Sabella pavonina can’t survive in oxygen levels below 4% for longer than four days (Tompsett, 2003).  Demosponges maintained under laboratory conditions can tolerate hypoxic conditions for brief periods, (Gunda & Janapala, 2009) investigated the effects of variable DO levels on the survival of the marine sponge, Haliclona pigmentifera.  Under hypoxic conditions (1.5-2.0 ppm DO), 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 DO).

No information was available on the tolerance of Cerianthus lloydii or Urticina felina to de-oxygenation.

Sensitivity assessment.  At the benchmark Sabella pavonina will die on the fourth day of the low oxygen event, although there is a lack of documentation on the laboratory experiments to back up this statement.  There is a lack of direct evidence for the tolerance of the other characterizing species in this biotope.  It appears that sponges may have some tolerance to deoxygenation, however, this is not certain for the characterizing species.  The resistance and resilience of this biotope to the pressure at the benchmark are assessed as ‘Medium’, giving the biotope a sensitivity of ‘Medium’.

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 nutrient enrichment of a marine environment leads to organisms no longer being limited by the availability of certain nutrients.  The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta-analysis of the effect of contaminants on species richness and evenness in the marine environment.  Of the 47 papers reviewed relating to nutrients as a contaminant, over 75% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect.  Due to the ‘remarkably consistent’ effect of marine pollutants on species diversity this finding relevant to this biotope (Johnston & Roberts, 2009).  It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009).  Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant.  These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls (Johnston & Roberts, 2009).

Moderate nutrient enrichment, especially in the form of organic particulates and dissolved organic material, is likely to increase food availability for all the suspension feeders within the biotope.  However, long-term or high levels of organic enrichment may result in eutrophication and have indirect adverse effects, such as increased turbidity, increased suspended sediment, increased risk of deoxygenation and the risk of algal blooms.

Sensitivity assessment.  A slight increase in nutrients may enhance food supply to the characterizing species in this biotope and increase growth rates in the species.  At the pressure benchmark there shouldn’t be a negative impact on the biotope.  Therefore, the resistance and resilience have been assessed as ‘High’, resulting in an assessment of ‘Not Sensitive’.

Organic enrichment

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

Evidence

Organic enrichment leads to organisms no longer being limited by the availability of organic carbon.  The consequent changes in ecosystem function can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) and decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).  Indirect adverse effects associated with organic enrichment include increased turbidity, increased suspended sediment and the increased risk of deoxygenation.  

Johnston & Roberts (2009) undertook a review and meta-analysis of the effect of contaminants on species richness and evenness in the marine environment.  Of the 49 papers reviewed relating to sewage as a contaminant, over 70% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect.  Due to the ‘remarkably consistent’ effect of marine pollutants on species diversity this finding relevant to this biotope (Johnston & Roberts, 2009).   It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009).  Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant.  These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls.

Borja et al., (2000) and Gittenberger & van Loon (2011) in the development of the AZTI Marine Biotic Index (AMBI) index to assess disturbance (including organic enrichment) both assigned Cerianthus lloydii to their Ecological Group I, (species very sensitive to organic enrichment and present under unpolluted conditions (initial state).  The basis for their assessment and relation to the pressure benchmark is not clear (Tillin & Tyler-Walters, 2014).

Sensitivity assessment.  Little empirical evidence was found to support an assessment of this biotope at this benchmark.  The lack of direct evidence for the characterizing species has resulted in this pressure being assessed as ‘No evidence’.

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 substratum within this biotope is not characterized by any bedrock.  If any kind of rock substratum were to be introduced into this biotope then the physical character of the biotope would have been changed,  which would lead to a loss of the biotope altogether.

Sensitivity assessment.  The resistance of this biotope to the introduction of rock substrata is ‘None’,  this change would lead to a loss of the biotope which in most cases is likely to be permanent.  Therefore, resilience is ‘Very low’, which results in the biotope having a ‘High’ sensitivity to this pressure at the benchmark. 

Physical change (to another sediment type)

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

Evidence

The substratum associated with this biotope is muddy, gravelly sand with pebbles (Connor et al., 2004).  The characterizing species Sabella pavonina creates its tube from sediment particles.  Sabella pavonina were absent from areas of the Fal Estuary where very fine sediments were found (Tompsett, 2003).  Murray et al. (2011) also found that Sabella pavonina were associated with larger size particle fractions.  Greater densities of Sabella pavonina in larger sediment fractions could also be linked to a requirement for anchorage and stability (Murray et al., 2011).  Tompsett, (2003) described the attachment of coarse material at the posterior end of Sabella pavonina tubes.

Tillin & Tyler-Walters (2014) Urticina felina was reported from a variety of substratum types including fine (muddy sand, sandy mud and fine sands) and coarse sediments, where some hard surfaces (such as pebbles or shells) are present.  Urticina felina, has been observed on the submerged ex-HMS Scylla (Hiscock et al., 2010).  But evidence for substratum preferences for this characterizing species is limited.

Cerianthus lloydii is found within a range of biotopes with different substrata compositions.  If each of the constituent substratum types within this biotope was to shift one grade of Folk class, it is unlikely to have a significant negative effect on this species due to the wide range of substratum types within which this biotope can be found.

Sensitivity assessment.  At the benchmark of this pressure, a decrease in one Folk class may have a significant effect on the tube building ability of the characterizing species Sabella pavonina.  This species has been reported to decrease in abundance as sediment fractions get smaller.  The other characterizing species are unlikely to be affected by a change in the pressure at the benchmark.  An increase in the Folk class is unlikely to have a negative effect of the species within this biotope, as many of them are recorded from a wide range of sediment types (Connor et al., 2004).  Resistance is assessed as ‘Medium’.  Resilience is assessed as Very low (the pressure is a permanent change), and sensitivity is, therefore, Medium. 

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 characterizing species within this biotope are all found within the top 30 cm of the substratum.  Therefore, the process of extraction is considered to remove all of these characterizing species as well as a large number of the other species present within this biotope group.  No direct evidence for resistance and recovery to this pressure was found and the sensitivity assessment is therefore based on expert judgement.

Sensitivity assessment.  Resistance is assessed as ‘None’ based on expert judgment but supported by the literature relating to the position of these species on or within the seabed.  At the pressure benchmark the exposed sediments are considered to be suitable for recolonization almost immediately following extraction.  Recovery will be mediated by the scale of the disturbance and the suitability of the sedimentary habitat.  Recovery is most likely to occur via larval recolonization.  Resilience is considered to be ‘Medium’.  Sensitivity based on resistance and resilience is therefore categorised 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

There is a lack of information regarding the impact of abrasion on Sabella pavonina.  However, a recent study on bait digging in Tunisia found that a month after disturbance Sabella pavonina disappeared from the surrounding intertidal benthic area (Mosbahi et al., 2015).  Other studies including Rossi et al. (2007) and Navon & Dauvin (2013) show that intertidal macrofauna are sensitive to disturbance.  These studies were undertaken in the intertidal

Freese et al. (1999) studied the effects of trawling on seafloor habitats and associated invertebrates in the Gulf of Alaska.  They found that a transect following a single trawling event showed significantly reduced ‘vase’ sponges (67% expressed damage), ‘morel’ sponges (total damage could not be quantified as their brittle nature meant that these sponges were completely torn apart and scattered).   The ‘finger’ sponges, the smallest and least damaged of the sponges assessed, were damaged by being knocked over (14%).  Van Dolah et al. (1987) studied the effects on sponges and corals of one trawl event over a low-relief hard bottom habitat off Georgia, US.  The densities of individuals taller than 10 cm of three species of sponges in the trawl path and in adjacent control area were assessed by divers, and were compared before, immediately after and 12 months after trawling.  Of the total number of sponges remaining in in the trawled area, 32% were damaged.  Most of the affected sponges were the barrel sponges Cliona spp., whereas Haliclona oculta and Ircina campana were not significantly affected.  12 months after trawling, the abundance of sponges had increased to pre-trawl densities, or greater. 

No direct evidence was found to assess the sensitivity Cerianthus lloydii to surface abrasion.  The burrowing life habit of the species specifically assessed would confer some protection from surface disturbance although individuals would be more exposed when close to the surface feeding.  Cerianthus lloydii inhabits a soft tube, which can be up to 40 cm long and is permanently buried.  The anemone can move freely within the tube and can retract swiftly if required (Tillin & Tyler-Walters, 2014).

The abundance of Urticina felina increased in gravel habitats on the Georges Bank, (Canada) closed to trawling by bottom gears (Collie et al., 2005) which suggested that this species was sensitive to fishing.  In a recent review, assigning species to groups based on tolerances to bottom disturbance from fisheries, the anemone Urticina felina and the sponge Halichondria panacea were assigned to AMBI Fisheries Group II, described as ‘species sensitive to fisheries in which the bottom is disturbed, but their populations recover relatively quickly’ (Gittenberger & van Loon, 2011).

Sensitivity assessment.  The species specific information on the effect of this pressure is limited but suggests.  However, that abrasion can have negative impacts on the characterizing species within this biotope.  Both Sabella pavonina and Cerianthus lloydii are tube dwelling and have some natural protection from abrasion if they can withdraw into their tubes.  Resistance is assessed as ‘Low’, and resilience is assessed as ‘Medium’, giving an overall sensitivity of ‘Medium’.

Penetration or disturbance of the substratum subsurface

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

Evidence

Penetration and or disturbance of the substratum would result in similar results as abrasion (see above) or removal of this biotope.  Damage to the tube dwelling species Sabella pavonina and Cerianthus lloydii would be greater within this pressure, as their ability to retract within their tubes would be limited.

Sensitivity assessment.  Resistance of the biotope is assessed as ‘Low’, although the significance of the impact for the bed will depend on the spatial scale of the pressure footprint.  Resilience is assessed as ‘Medium’, and sensitivity is assessed as ‘Medium’.

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

This biotope is dominated by suspension feeders. A change in the level of suspended solids in the water column is likely to affect food availability for these species.  The water flow regime within this biotope is strong (3-6 knots) to moderately strong (1-3knots) (Connor et al., 2004).  An increase in sediment in the water column has the potential to cause a greater scour effect.  There will also be a change in light availability, however, this is not deemed important for the characterizing species as none of them photosynthesize.

Sabella pavonina is a filter feeding species.  High particles loads can stimulate the secretion of mucus from the branchial filaments and bulky strings of mucus with entangled particles are produced (Moore, 1977a).  Sabella pavonina was found occasionally in suitable areas of the River Roach where waters were clearer (Mistakidis, 1951).  Yet in the more turbid waters of Southward Laying, in the River Crouch no Sabella pavonina were found (Mistakidis, 1951).  In other filter feeding organisms an increase in the level of suspended solids can have wide ranging effects.  An increase in organic matter in the water column will provide more food for the organism.  However, greater suspended solids mean that more sediment will be captured in the organisms filter feeding organ.  This could lead to greater energy expenditure to keep the branchial plume clear.

Despite sediment being considered to have a negative impact on suspension feeders (Gerrodette & Flechsig 1979), many encrusting sponges appear to be able survive in highly sediment conditions (Schönberg, 2015; Bell & Barnes 2000; Bell & Smith 2004).  No evidence on the effect of a change in turbidity on Ceriathus lloydii could be found.

Urticina felina is found in highly turbid areas associated with biotopes such as CR.MCR.SfR.Pol (Connor et al., 2004) and is therefore considered to be unaffected by an increase in turbidity at the benchmark.  Increases in siltation may begin to cover the anemone or interfere with feeding. An energetic cost will result from efforts to clean off the silt particles, e.g. through mucus production and sloughing.  Repeated energetic expenditure in cleaning off silt particles may cause sublethal effects.  

Sensitivity assessment.  An increase in the pressure at the benchmark is may increase energy expenditure in the characterizing species, Sabella pavonina.  Suspended sediment which is trapped in the branchial plume of this species results in mucus secretion to remove the sediment (Moore, 1977a).  If more sediment is present more mucus may have to be produced to keep the organism clean.  This will increase energy expenditure which may cause the organism to decrease in health.  The other species found within this biotope are found in conditions which suggest that they are able to tolerate an increase in the pressure at the benchmark.  A decrease in the level of suspended sediment may reduce the amount of food available to the filter feeding, and cause a decrease in health.  The resistance and resilience of this biotope are considered to be ‘High’, giving the biotope an overall assessment of ‘Not sensitive’.

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

The effect of smothering by sediment on Sabella pavonina is not well documented.  The impact of a 5 cm deposit will have a negative effect on the young and juvenile individuals as they are likely to be entirely smothered by this pressure.  Being smothered entirely will stop them from being able to extend their branchial plume to feed and will also reduce the availability of oxygen which could lead to asphyxiation (see deoxygenation pressure).  This species is immobile and can’t leave its tube at any stage in its life (Tompsett, 2003), so the worm is unable to avoid this pressure.  Adults may not be entirely smothered by this pressure, as their tube can protrude up to 10 cm from the sediment surface. 

Wulff (2006) described mortality in three sponge groups following four weeks of complete burial under sediment, in which  16% of Amphimedon biomass died compared with 40% and 47% in Iotrochota and Aplysina respectively.  The complete disappearance of ‘associated sponges’ in the Black Sea near the Kerch Strait was attributed to siltation (Terent'ev, 2008 cited in Tillin & Tyler-Walters, 2014).   Ackers, (1992) reported that Halichondria bowerbanki can be partly embedded in mud.  It should also be noted that some of the characterizing sponges are likely to be totally buried by 5 cm of sediment. 

Cerianthus lloydii can move rapidly within its tube but no information was found for the ability of this species to extend the tube through a 5 cm deposit of sediment to reach the surface.

Communities dominated by the anemone Urticina felina were described on tide swept seabed, exposed to high levels of suspended sediment, sediment scour and to periodic smothering by thin layers of sand, up to ca 5 cm in the central English Channel (Holme & Wilson, 1985).  Urticina felina is abundant in the sediment-scoured, silty rock communities CR.HCR.XFa.FluCoAs and CR.MCR.EcCr.UrtScr (Connor et al., 2004).

Sensitivity assessment.  There is little direct evidence available on which an assessment of this pressure can be made.  However, it is likely that there will be mortality of some of the characterizing species at the level of the benchmark.  There can be high level of water flow within this biotope (<6 knots) which will aid the removal of the sediment.  The may reduce the negative effect of sediment deposition in the biotope.  The resistance and has been assessed as ‘Low’, and the resilience is assessed as ‘Medium’ this results in an overall sensitivity of ‘Medium’.

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

The effect of smothering by sediment on Sabella pavonina is not well documented.  Gaseous exchange occurs through the branchial crown and body surfaces (Tompsett, 2003), 30 cm of sediment deposition would entirely cover the organism.  The tubes created by Sabella pavonina will protrude up to 10 cm from the sediment surface.  So even the large individuals would be covered.  This species is entire immobile and can’t leave its tube at any stage in its life (Tompsett, 2003), so the worm is unable to avoid this pressure. 

Wulff (2006) described mortality in three sponge groups following four weeks of complete burial under sediment, in which  16% of Amphimedon biomass died compared with 40% and 47% in Iotrochota and Aplysina respectively.  The complete disappearance of ‘associated sponges’ in the Black Sea near the Kerch Strait was attributed to siltation (Terent'ev, 2008 cited in Tillin & Tyler-Walters, 2014).   Ackers, (1992) reported that Halichondria bowerbanki can be partly embedded in mud.  It should also be noted that some of the characterizing sponges are likely to be totally buried by 5cm of sediment. 

Cerianthus lloydii can move rapidly within its tube but no information was found for the ability of this species to extend the tube through a 30 cm deposit of sediment to reach the surface.  It is extremely unlikely that this species will be able to burrow through this depth of sediment, consequently, death is likely.

Communities dominated by the anemone Urticina felina were described on tide swept seabed, exposed to high levels of suspended sediment, sediment scour and to periodic smothering by thin layers of sand, up to ca 5 cm in the central English Channel (Home & Wilson, 1985).  Urticina felina is abundant in the sediment-scoured, silty rock communities CR.HCR.XFa.FluCoAs and CR.MCR.EcCr.UrtScr (Connor et al., 2004).

Sensitivity assessment.  There is little direct evidence available on which an assessment of this pressure can be made.  However, it is likely that there will be mortality of most of the characterizing species at the level of the benchmark.  There can be high level of water flow within this biotope (<6 knots) which will aid the removal of the sediment.  The may reduce the negative effect of sediment deposition in the biotope.  The resistance and has been assessed as ‘Low’, and the resilience is assessed as ‘Medium’ this results in an overall sensitivity of ‘Medium’.  The recovery of this biotope will depend on the total removal of the deposited sediment.  If the deposited sediment is not suitable for recolonization by the characterizing species of this biotope the biotope will be lost permanently. 

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

Species characterizing this habitat do not have hearing perception but vibrations may cause an impact, however, no studies exist to support an assessment.  Therefore this assessment is considered to be ‘Not relevant’. 

Introduction of light or shading

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

Evidence

No evidence.

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 – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit propagule dispersal.  But propagule dispersal is not considered under the pressure definition and benchmark.

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 – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit propagule dispersal.  But propagule dispersal is not considered under the pressure definition and benchmark.

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 effect of this pressure on the characterizing species within this biotope 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

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., 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 (Tillin et al., 2020, Fitzgerald, 2007, Blanchard, 2009, Stiger-Pouvreau & Thouzeau, 2015). 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 (Stiger-Pouvreau & Thouzeau, 2015, Blanchard, 2009). 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 is 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 and unsuitable for most of the invasive non-indigenous species currently recorded in the UK. However, the above evidence suggests that Crepidula could colonize mixed sediment habitats in the subtidal, typical of this biotope, due to the presence of gravel, shells, cobbles, or any other hard substrata embedded in the substratum that can be used for larvae settlement (Tillin et al., 2020). 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 moderately exposed to very sheltered habitat, so storms may mobilise the sediment (JNCC, 2022), which may also 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 in wave sheltered areas of the biotope and where water movement is mediated by tidal flow rather than wave action, e.g., the deeper examples of the biotope. 

Therefore, resistance is assessed as 'Medium' in examples where wave action is high and subject to storms but 'Low' in wave sheltered 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 due to the constant risk of new invasive species.

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 for the effect of microbial pathogens on the characterizing species within this biotope could be found.

Removal of target species

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

Evidence

No evidence to suggest that the characterizing species within this biotope are targeted by commercial fisheries, and therefore and assessment of ‘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 from harvesting are assessed through the abrasion and penetration of the seabed pressures.  The characterizing species within n this biotope could easily be incidentally removed from this biotope as by-catch when other species are being targeted.  The loss of these species and other associated species would decrease species richness and negatively impact on the ecosystem function.

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope.  The resistance to removal is ‘None’ due to the easy accessibility of the biotopes location and the inability of these species to evade collection. The resilience is ‘Medium, with recovery only being able to begin when the harvesting pressure is removed altogether. This gives an overall sensitivity score of ‘Medium’.