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

Echinocardium cordatum is found from Norway to South Africa, Mediterranean, Australasia and Japan, and Ensis ensis is widely distributed in the north west of Europe. Both species are therefore likely to experience seasonal changes in water temperatures by as much as 10°C from summer to winter, although growth and fecundity could probably be affected. A study by Kashenko (2007) of the combined effects of temperature and salinity on the development of the sea urchin Echinocardium cordatum, in the Vostok Bay of the Sea of Japan suggested that fertilization and embryonic development were completed successfully at a range of temperatures (12-20 and 8-20°C, respectively). Results presented by Kirby et al. (2007), suggested that the increased abundance and spatial distribution in the North Sea of the larvae of Echinocardium cordatum, could have been caused by an increase in sea temperature after 1987 and that the key stages of reproduction, gametogenesis and spawning, appeared to be influenced by winter and spring sea temperature. These results suggest that Echinocardium cordatum’s recruitment may benefit from local increases in temperature. Populations of the razor shell Ensis siliqua in the warmer waters of Portugal spawn several months earlier in the year than UK populations and are sexually mature at only one year old (Gaspar & Monteiro, 1998; Henderson & Richardson, 1994) compared to three in the UK (Hill, 2006). Recruitment of Ensis spp. in this biotope is therefore likely to be affected by an increase in temperature. Some protection may be afforded by burrowing position.

Infaunal species are not subjected to the larger temperature variations experienced in the intertidal and so many of the other species in the biotope may be less resistant to changes, leading to a decline in species diversity. Temperature may also affect microbial activity within the sediment which could alter the depth at which the anoxic layer appears. There can be mass mortality of Echinocardium cordatum on sandy shores following oxygen depletion during extreme low water tides on hot days, as a result of high temperatures causing suffocation (D. Nichols pers. comm., cited in Hill, 2008).

Sensitivity assessment: The cosmopolitan distribution of the two species means they may be resistant to local increases in temperature at the pressure benchmark level. Resistance and resilience are, therefore, assessed as High and the group is considered Not Sensitive at the pressure benchmark level.

Temperature decrease (local)

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

Evidence

Echinocardium cordatum is found from Norway to South Africa, Mediterranean, Australasia and Japan, and Ensis ensis is widely distributed in the north west of Europe. Both species are therefore likely to experience seasonal changes in water temperatures by as much as 10°C from summer to winter. However, mortality of both species was observed in the very cold winter of 1962-63 (Crisp, 1964) and growth and fecundity could probably be affected. A study by Kashenko (2007) of the combined effects of temperature and salinity on the development of sea urchin Echinocardium cordatum, in Vostok Bay of the Sea of Japan, suggested that resistance of Echinocardium cordatum to fluctuations in temperature varied in the course of individual development, but fertilization and embryonic development were completed successfully at a range of temperatures (12-20 and 8-20°C, respectively). However, embryonic development did not occur as fast at lower temperatures. Additionally, changes in temperature may have cascading effects on the entire food web, potentially affecting all stages of benthic organisms (Schückel et al., 2010, cited in Kröncke et al., 2013a). Kröncke et al. (2013a) reported mortality of macrofauna species during and after the cold winters of 1978/1979 and 1995/96 that affected species biomass and abundance in the study area (the southern North Sea), including of the characterizing and other species of this biotope. Although the effects of the 1995/96 winter on macrofauna diversity was considered minor compared with 78/79, as the later was followed by three cold winters in the early 80’s, the cold winters seemed to have caused biological regime shifts in the years following the cold events. For example, the proportion of northern species increased and opportunistic species that feed on organic detritus thrived from feeding on decaying benthic organisms (Kröncke et al., 2013a).  

Temperature may also affect microbial activity within the sediment which could alter the depth at which the anoxic layer appears.

Sensitivity assessment: The characterizing species of this biotope have a cosmopolitan distribution, and Kashenko (2007) suggested some plasticity in recruitment of Echinocardium cordatum to varying temperature parameters. However, individual adults of the key characterizing species may be adversely affected by decreases in temperature as suggested by Kröncke et al. (2013a), who reported mortality of the key characterizing species at -2°C anomalies in sea-surface temperature. Resistance is therefore assessed as Medium and resilience assessed as High and the biotope is considered to have Low sensitivity to this pressure at the benchmark level.

Salinity increase (local)

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

Evidence

The biotope is only recorded in fully marine conditions so is unlikely to be resistant to changes in salinity. Echinoderms, such as Echinocardium cordatum, are stenohaline species owing to the lack of an excretory organ and a poor ability to osmo- and ion-regulate (Stickle & Diehl, 1987; Russell, 2013). A review by Russell (2013) on echinoderms responses to variable salinities did not report observations of Echinocardium cordatum in hypersaline conditions, hence this species is unlikely to be able to resist wide fluctuations in salinity. Salting is often used as a method of dislodging razor shells from their burrows, suggesting that Ensis spp. are unlikely to resist hypersaline conditions.

Sensitivity assessment: No direct evidence was found on the resistance of the characterizing species of the biotope to increased salinity. Long-term changes in salinity are likely to result in the loss of some species, and also result in decrease of species richness. Resistance of the biotope is assessed as Low and resilience as Medium, but with low confidence. The biotope is therefore considered to have Medium sensitivity to increases 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

The biotope is found in fully marine conditions so is unlikely to be resistant to changes in salinity. Echinoderms, such as Echinocardium cordatum, are stenohaline species owing to the lack of an excretory organ and a poor ability to osmo- and ion-regulate (Stickle & Diehl, 1987; Russell, 2013). Although Wolff (1968) reported populations of Echinocardium cordatum occuring at 27‰ in The Netherlands, studies by Kashenko (2006, 2007) suggested that the species is unable to resist fluctuations in salinity. Embryos seemed to only tolerate a narrow range of salinity between 36‰ and 28‰ (Kashenko, 2007), while adults were reported to only tolerate a salinity range between 33 and 28‰ (Kashenko, 2006).

Ensis ensis does not occur in water of reduced salinity, although its absence from estuaries may sometimes be due to the lack of sediments of suitable grade (Holme, 1954). The species concentrates K and Ca (Kinne, 1971b) and may be able to resist a degree of salinity reduction because it will be subject to periodic precipitation in the intertidal. Darriba & Miranda (2005) concluded that salinity decreases interrupted gonadal development in the razor clam Ensis magnus.

Sensitivity assessment: Long-term changes in salinity are likely to result in the loss of the characterizing species of this biotope. The evidence suggests that Echinocardium cordatum is unlikely to survive reduced salinities (18-30‰) for a year and Ensis spp. may suffer reproductive disruption. Resistance of the biotope is therefore assessed as None and resilience as Medium. The biotope is therefore considered to have Medium sensitivity to decreases 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

Changes in the water flow rate are likely to change the sediment structure and have concomitant effects on the community. The biotope is found in sediments of medium to fine sand or muddy fine sand in moderate to very weak tidal steams (Connor et al., 2004). An increase in water flow rate may remove smaller sediment particles leaving coarser elements behind which may be unsuitable for some of the burrowing fauna in the biotope. Individuals of Echinocardium cordatum and Ensis ensis are often washed out by increased water flow (Lawrence, 1996; Henderson & Richardson, 1994). A decrease in species diversity is likely to be observed, with the loss of the two key species and the loss of other small invertebrates such as bivalves that inhabit the burrows of Echinocardium cordatum. However, since Ensis ensis is able to burrow deeper into the sediment during unsuitable conditions, water flow rates would have to increase substantially to remove individuals.

A decrease in water flow could likely favour muddy sediments, which could result in change of species composition and loss of Ensis spp. and Echinocardium cordatum in favour of more muddy species, which would result in reclassification of the biotope to AreISa (Connor et al., 2004).

Sensitivity assessment: The assessment is based largely on the Hjulström-Sundborg diagram (Sundborg, 1956). This relates current velocity to deposition, erosion and transport. While this model has largely been superseded in by  more recent models that take into account other factors such as shear stress and water depth, these newer models are more complex, site specific and do not relate sediment transport to water velocity. The curve is therefore used to assess generally the potential effects of changes in water velocity but it should be recognized that a number of other factors will mediate effects. The biotope is found in sediments of medium to fine sand or muddy fine sand in moderate to very weak tidal steams (Connor et al., 2004). A change in water flow could potentially change the sediment type. However, a change at the benchmark level of 0.1-0.2 m/s is likely to fall within the range 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

The biotope extends from the very low shore to the shallow subtidal so an increase in emergence is likely to affect only the upper range of the biotope. Species like Ensis ensis and Echinocardium cordatum have little protection from desiccation when exposed and are likely to be lost if the length of time of exposure increases. Other species like crabs and errant polychaetes are likely to be able to migrate to unaffected areas. An increase in desiccation may cause some individuals to be lost at the extreme upper limit of the biotope although most species are able to re-burrow if exposed to air. However, Sievers et al. (2014) observed predation behaviour of carrion crows (Corvus corone) feeding on spatangoid sea urchins (Echinocardium cordatum) during low tide on two different beaches in Brittany, France, and suggested that sea urchin size and predation pressure could be linked. Thus, changes in emergence regime are likely to change exposure to predation by birds, with potential impacts on the biotope’s biological community. A decrease in emergence may enable the biotope to extend its range up-shore.

Sensitivity assessment: Although a change in emergence regime may affect the biological community on the upper range of the biotope, the sublittoral element of the biotope is not likely to be lost and the overall species richness of the biotope is not likely to change. A change in emergence regime experienced by mid-range populations are unlikely to be affected, so resistance and resilience are considered to be High and the biotope is assessed as Not Sensitive at the pressure benchmark level.

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

One of the key factors affecting benthic habitats is disturbance, which in shallow subtidal habitats will increase in winter due to weather conditions. Storms may cause dramatic changes in distribution of benthic communities by reducing success of recruitment by newly settled spat or larvae (Hall, 1994). The biotope is found in wave exposed, moderately wave exposed and sheltered areas (Connor et al., 2004). According to the wave exclusion hypothesis proposed by Paavo et al. (2011, cited in Armonies et al., 2014), the community of benthic organism found in the surf zone is not excluded by wave action. The depth at which this biotope occurs (from lower shore up to 20 m) suggests that the biological community present would not be excluded by wave action and is therefore likely to be able to resist disturbance. An increase in wave exposure is likely to disturb the fine sediment that characterizes this biotope, and may even displace some species as to change the composition of species present in the biotope. However, Echinocardium cordatum has been recorded from a range of wave exposure conditions, including extremely sheltered, very sheltered, sheltered, moderately exposed, exposed, very exposed (Tillin & Tyler-Walters, 2014). Furthermore, Wolff (1968) and Guillou (1985) have reported the species in coastal waters of The Netherlands in the tidal zone on some sandflats exposed to wave-action, and in the bay of Douarnenez, Brittany in areas of fine sand dominated by high sediment instability, respectively. On the other hand, razor shells seem to be absent on exposed beaches where the sand is continually churned by waves and Rees et al. (1976) reported that wave scour caused by winter gales may have caused some individuals of Ensis ensis to be washed out along the north Wales coast. Therefore, an increase in wave exposure may remove some individuals of Ensis ensis in a population.

Sensitivity assessment: An increase in wave action is likely to increase the coarseness of the sediment.  If muddy sands were replaced by medium to fine sand, then the biotope would probably survive although the infaunal community would change. However, an increase in storminess could result in loss of areas of sand and hence the biotope. Conversely a reduction in wave action, may result in muddy sediments, depending on water flow conditions, and loss of the biotope. However, the biotope is found in wave exposed, moderately wave exposed and sheltered areas (Connor et al., 2004) and change at the pressure benchmark level is likely to fall within the range experienced by the biotope. Resistance is therefore considered to be High and resilience is considered to be High (by default) and the biotope judged Not Sensitive to a change in nearshore significant wave height >3% but <5%.

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.

No details about the effects of heavy metals specific to Echinocardium cordatum and razor shells were found, and different members of the same community are likely to vary in their resistance. Bryan (1984) suggested that metal-contaminated sediments can exert a toxic effect on burrowing bivalves and echinoderms, especially at larval stages, and that polychaetes were fairly resistant. Possible suggested effects of this toxicity were reduced growth, abundance and abnormalities in areas of heavy pollution. Kanakaraju et al. (2008) found that, of the heavy metal contents analysed (Pb, Fe, Zn, Cu, Cd and Mn) razor clams of the Solen spp. in Malasya concentrated higher levels of Fe and Zn in their tissues, and Pb and Mn in their shells. These results suggest that razor clams potentially are likely to bio-accumulate toxic heavy-metals from their environment, but no biological effects of this bio-accumulation were suggested.

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.

Oil spills resulting from tanker accidents can cause large-scale deterioration of communities in intertidal and shallow subtidal sedimentary systems. The two key species in the biotope, Echinocardium cordatum and Ensis ensis suffered mass mortality after the Torrey Canyon and Amoco Cadiz oil spills (Southward & Southward, 1978; Southward, 1978; Cabioch et al., 1978), which suggests low resistance oil pollution. Many other species in the biotope are also likely to be affected. For example, after the West Falmouth, Florida spill of 1969 the entire benthic fauna was eradicated immediately following the spill and populations of the opportunistic polychaete Capitella capitata increased to abundances of over 200,000/m² (Sanders, 1978). Ensis ensis is reported to bio-concentrate aromatics and is highly likely to be sensitive to hydrocarbons. Four days after the Sea Empress oil spill moribund razor shells (mostly Ensis siliqua) were the first organisms observed to have been affected (SEEEC, 1998). Glegg & Rowland (1996) observed dead razor shells washed up on the shore a few days after the final break-up of the Braer wreck. Echinoderms have not been found to be resistant to the toxic effects of oil, likely because of the large amount of exposed epidermis (Suchanek, 1993). Reduced abundance of Echinocardium cordatum was also detectable up to > 1000 m away one year after the discharge of oil-contaminated drill cuttings in the North Sea (Daan & Mulder, 1996). However, invertebrate communities respond to severe chronic oil pollution in much the same way. Initial massive mortality and lowered community diversity is followed by extreme fluctuations in populations of opportunistic mobile and sessile fauna (Suchanek, 1993). Oscillations in population numbers slowly dampen over time and diversity slowly increases to original levels. Infaunal communities, such as those characterizing this biotope are highly likely to be adversely affected by an event of oil pollution, but the biological effects of accumulation of PAHs are likely to depend on the length of time exposed (Viñas et al., 2008).

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.

High levels of mortality of both Echinocardium cordatum and Ensis spp. resulted from the use of dispersants following the Torrey Canyon oil spill (Smith, 1968). Almost complete mortality of razor shells was found at stations more than a kilometre from the shore at a depth of about 20 m. The toxicity of TBT to Echinocardium cordatum is similar to that of other benthic organisms and echinoderms do not tend to be resistant of various types of marine pollution (Newton & McKenzie, 1995). Sea urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al., 1988). It is likely therefore, that Echinocardium cordatum and especially its larvae are highly sensitive to synthetic contaminants. Other species in the biotope, in particular polychaete worms, are generally more resistant of a range of marine pollutants so a change in the faunal composition may be expected if chemical pollution increases. Polluted areas would be characterized by biotopes with lower species diversity and a higher abundance and density of pollution resistant species such as polychaetes.

Radionuclide contamination

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

Evidence

Monitoring studies by Sohtome et al. (2014) of radioactive concentration in invertebrates of the benthic food web community within the Fukushima area confirm that echinoderm Echinocadium cordatum is likely to uptake contaminated sediments into their digestive tract. Carvalho (2011) determined the concentrations of ²¹⁰Po and ²¹⁰Pb in marine organisms from the seashore to abyssal depths, as these two radioactive elements tends to be higher in the marine environment. The author’s results showed that concentrations varied greatly, even between organisms of the same biota, mainly related with the trophic levels occupied by the species, suggesting that the more levels between a species and the bottom of the food chain, the more likely that the concentrations of radioactive elements were likely to be diluted. This may have great implications for the detritus and filter feeders that characterize this biotope. There was no information available about the effect of this bioaccumulation.

Sensitivity assessment: Although species in this biotope are likely to bio-accumulate radionuclides with potential impacts on the biological community, no information concerning the effects of such bioaccumulation was found. Therefore, there is insufficient evidence to assess this pressure against the benchmark.

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

Oxygen-deficient marine areas are characterized by a decline in the number and diversity of species. A decrease in oxygenation is likely to see the loss of the key species in the biotope. For example, in the south-eastern North Sea, a period of reduced oxygen resulted in the death of many individuals of Echinocardium cordatum (Niermann, 1997) and during periods of hypoxia the species migrates to the surface of the sediment (Diaz & Rosenberg, 1995). Low resistance of Echinocardium cordatum has also been demonstrated in laboratory experiments. Over a 21 day-long experiment, individuals appeared on the sediment surface at 4 mg/l and many were dead at a concentration of 2.4 mg/l (Nilsson & Rosenberg, 1994). Ensis ensis is likely to be more resistant than Echinocardium cordatum, and tolerate sands that are slightly reducing, in which there is a grey layer below the surface, but is likely to eventually die in low oxygenated areas (Holme, 1954).

Sensitivity assessment: A decrease in oxygenation at the pressure benchmark level is likely to result in significant (25-75%) mortality of the characterizing species of this biotope. With the loss of these species, the biotope would likely be lost. Community composition would likely become dominated by fewer species that are resistant of hypoxic conditions, such as some polychaete worms, so that the overall species richness would decline significantly. Resistance is therefore assessed as Low and resilience as Medium, and the biotope is judged as having Medium sensitivity to de-oxygenation at the pressure benchmark level.

Nutrient enrichment

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

Evidence

Increases in organic content can result in significant change in the community composition of sedimentary habitats. An increasing level of nutrients in the sediment is likely to result in a reduction in the abundance of the key species, in particular the heart urchin Echinocardium cordatum, which is generally associated with sediments of low organic content (Buchanan, 1966). Pearson & Rosenberg (1976) described the changes in fauna along a gradient of increasing organic enrichment by pulp fibre.  Echinocardium cordatum was absent from all but distant sediments with low organic input (Pearson & Rosenberg, 1976). Growth levels of this species have been observed to be lower in sediments with high organic content although it is suggested that this may be due to higher levels of intra-specific competition (Duineveld & Jenness, 1984). Echinocardium cordatum was also absent from an area in the southern North Sea into which large quantities of sewage sludge from Hamburg had been dumped and the species was never seen to settle in the area (Caspers, 1980). Townsend (2007) investigated the relationship between biodiversity, ecosystem functioning and nutrient cycling (nitrite, nitrate, ammonium, silicate and phosphate fluxes) in subtidal marine benthic ecosystems, using mesocosm systems. The author found that species responded to changing sediment conditions and to the presence of other species. Echinocardium cordatum performed differently according to sediment types, and was found to over yield (i.e. a more efficient use of available resources due to their complementarity or facilitation) when found in benthic assemblages with Amphiura filiformis and Nereis virens, which consequently increased nutrient exchange (Townsend, 2007). Although no specific information regarding the response of Ensis ensis to changes in nutrient levels was found, as filter-feeders, Ensis spp. are likely to benefit from some nutrient enrichment.

Sensitivity assessment: The overall species diversity in this biotope is likely to decline and the habitat becomes modified as numbers of bioturbating species decline. The community, and hence the biotope, may change to one dominated by nutrient enrichment resistant species, in particular polychaete worms such as Capitella capitata. However, these changes generally refer to gross nutrient enrichment. A decrease in nutrient availability may result in impaired growth and fecundity although species diversity is not likely to be affected significantly. Nevertheless, the biotope is considered to be Not Sensitive at the pressure benchmark that assumes compliance with good status as defined by the WFD.

Organic enrichment

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

Evidence

Typically, an increasing gradient of organic enrichment results in a decline in the suspension feeding fauna and an increase in the number of deposit feeders, in particular polychaete worms (Pearson & Rosenberg, 1978), which could result in significant change in the community composition of sedimentary habitats. An increasing level of nutrients in the sediment is likely to result in a reduction in the abundance of the key species, in particular the heart urchin Echinocardium cordatum, which is generally associated with sediments of low organic content (Buchanan, 1966). Pearson & Rosenberg (1976) described the changes in fauna along a gradient of increasing organic enrichment by pulp fibre.  Echinocardium cordatum was absent from all but distant sediments with low organic input (Pearson & Rosenberg, 1976). Growth levels of this species have been observed to be lower in sediments with high organic content although it is suggested that this may be due to higher levels of intra-specific competition (Duineveld & Jenness, 1984). Echinocardium cordatum was also absent from an area in the southern North Sea into which large quantities of sewage sludge from Hamburg had been dumped and the species was never seen to settle in the area (Caspers, 1980). Although no specific information regarding the response of Ensis ensis to changes in organic content was found, as filter-feeders, Ensis spp. are likely to benefit from some organic enrichment. Osinga et al. (1997) assessed the effects of sub-surface bacterial production on Echinocardium cordatum by adding up to 90 gC/m² in one event to sediment surfaces in experimental mesocosms. No detrimental effects on Echinocardium cordatum individuals were reported. Borja et al. (2000) and Gittenberger & van Loon (2011) in the development of the AZTI Marine Biotic Index (AMBI), a biotic index to assess disturbance (including organic enrichment), assigned Echinocardium cordatum and Ensis spp. to different Ecological Groups. Borja et al. (2000) considered that both species belonged to Ecological Group I ‘species very sensitive to organic enrichment and present under unpolluted conditions’. However, Gittenberger & van Loon (2011) considered that both species belonged to Ecological Group II ‘species indifferent to enrichment, always present in low densities with non-significant variations with time’. Although the unpublished Gittenberger & van Loon (2011) report is an update on Borja et al. (2000), the former is a peer reviewed publication.

Although no specific information regarding the response of Ensis ensis to changes in nutrient levels was found, as filter-feeders, Ensis spp. are likely to benefit from some organic enrichment.

Sensitivity assessment: The evidence presented based on the AMBI scores conflicts and is considered with caution. The biotope is generally found in areas with some water movement and this is likely to disperse organic matter reducing organic material load. However, the characterizing species of this biotope are likely to adversely suffer from an event of organic enrichment (Borja et al., 2000) and resistance is therefore  assessed as Low (loss of 25-75%) and resilience as Medium. Thus, the biotope is considered to have Medium sensitivity to organic enrichment, although the animals found within the biotope may be able to utilize some of the input of organic matter as food.

Physical loss (to land or freshwater habitat)

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

Evidence

All marine habitats and benthic species are considered to have a Resistance of None to this pressure and to be unable to recover from a permanent loss of habitat (Resilience is Very Low). Sensitivity within the direct spatial footprint of this pressure is therefore High. Although no specific evidence is described confidence in this assessment is High, due to the incontrovertible nature of this pressure.
 

Physical change (to another seabed type)

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

Evidence

If the muddy fine sand that characterizes this biotope was replaced with soft or hard rock substrata, this would represent a fundamental change to the physical character of the biotope. Additionally, the infaunal community that occurs and characterizes the biotope could no longer be supported. The biotope would therefore be lost and/or re-classified.

Sensitivity assessment: Resistance to the pressure is considered None, and resilience Very Low. Sensitivity has been assessed as High.

Physical change (to another sediment type)

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

Evidence

Records indicate that SS.SSa.IMuSa.EcorEns occurs on muddy fine sand and medium to fine sand (Connor et al., 2004). Echinocardium cordatum, occurs in a range of substrata, including fine to very fine muddy sand; sandy mud; fine to very fine sand with a fine silt fraction; medium to fine sand; slightly muddy sand; sand with some gravel; sand with gravel, pebbles and/or shingle (Tillin & Tyler-Walters, 2014). Additionally, although this assessment is largely based on Ensis ensis, the biotope also supports populations of other species of razor shells. Ensis siliqua and Ensis arcuatus are the other two species of razor shells occurring in the British Isles, which are found in fine sand, coarse sand and fine gravel (Hill, 2006). Furthermore, Connor et al. (2004) suggested that the infaunal community of EcorEns is likely to overlap a number of other biotopes such as FfabMag, NcirBat, AalbNuc and AreISa. Each of these biotopes supports slightly different infaunal communities depending on the nature of the substratum based on variations from fine muddy sand, to medium to very fine sand, muddy sand and slightly mixed sediment, and fine sand and muddy sand, respectively.

Sensitivity assessment: The characterizing species of this biotope are likely to be resistant to a change in one Folk class from, for example, muddy sand to sandy mud. However, this would probably represent a fundamental change in the character of the biotope, and a change in the abundance of the characteristic species, resulting in the loss and/or re-classification of the biotope. Resistance is, therefore, assessed as None and resilience is Very low (the pressure is a permanent change) 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

Muddy sand communities are highly unlikely to be resistant of substratum loss because most species are infaunal and extraction of substratum to 30 cm is likely to result in the removal of the biological community along with substrata, including the characterizing species. A few mobile demersal species like the crab Liocarcinus depurator may be able to avoid the factor but even fast moving polychaetes are likely be removed during substratum loss. For example, dredging operations, were shown to affect large infaunal and epifaunal species, decrease sessile polychaetes and reduce numbers of burrowing heart urchins (Eleftheriou & Robertson, 1992). Furthermore, Hall et al. (1990) conducted a study to analyse the interaction between fishing and natural disturbance events. As a result of suction dredging for razor clam Ensis spp., 3.5 x 0.6 m pits were dug into the sediment, and significant reductions in the abundance of large proportions of the species on site were observed.

Sensitivity assessment. Due to the nature of this pressure it is highly likely that a large amount of the sediment would be removed along with the biological community, resulting in the removal of the biotope. Resistance is therefore assessed as None and resilience as Medium with a sensitivity of Medium to extraction of substratum to 30 cm.

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

The two key species in the biotope, Echinocardium cordatum and Ensis ensis are infaunal found close to the sediment surface. This life habit provides some protection from abrasion at the surface only. Echinocardium cordatum has a fragile test that is likely to be damaged by an abrasive force, such as movement of trawling gear over the seabed. Bergman & van Santbrink (2000) suggested that Echinocardium cordatum was one of the most vulnerable species to trawling, and substantial reductions in the numbers of the species due to physical damage from scallop dredging have been observed (Eleftheriou & Robertson, 1992). Echinocardium cordatum was reported to suffer between 10 and 40% mortality due to fishing gear, depending on the type of gear and sediment after a single trawl event (Bergman & van Santbrink, 2000), with mortality possibly increasing to 90% in summer when individuals migrate to the surface of the sediment during their short reproductive season.

Bivalves such as Ensis spp., together with starfish have been reported to be relatively resistant (Bergman & van Santbrink, 2000). However, Eleftheriou & Robertson (1992) observed large numbers of Ensis ensis killed or damaged by dredging operations and Gaspar et al. (1998) reported high levels of damage in Ensis siliqua from fishing.

Upper burrow structures of species occupying the sediment may collapse by passing fishing gear, and although they may be rapidly reconstructed (Atkinson pers. com., cited in Jennings & Kaiser, 1998), the energetic costs of repeated burrow reconstruction may have long-term implications for the survivorship of individuals (Jennings & Kaiser, 1998). In the event of damage caused to species such as heart urchins, molluscs and crustaceans as a result of this pressure, damaged or undamaged animals are likely to experience increased predation pressure either at low (birds) or high tide (fish and crabs).

SS.SSa.IMuSa.EcorEns occurs in medium to fine sand and slightly muddy sand (Connor et al., 2004). Abrasion events caused by a passing fishing gear, or scour by objects on the seabed surface are likely to have marked impacts on the substratum and cause turbulent re-suspension of surface sediments. When used over fine muddy sediments, trawls are often fitted with shoes designed to prevent the boards digging too far into the sediment (M.J. Kaiser, pers. obs., cited in Jennings & Kaiser, 1998). The effects may persist for variable lengths of time depending on tidal strength and currents and may result in a loss of biological organization and reduce species richness (Hall, 1994; Bergman & van Santbrink, 2000; Reiss et al., 2009) (see change in suspended solids and smothering pressures).

Sensitivity assessment. The infaunal position provides some protection but the characterizing species of the biotope may suffer some damage as a result of surface abrasion. Resistance is therefore assessed as Low and resilience as Medium so the biotope’s sensitivity is assessed as Medium. 

Penetration or disturbance of the substratum subsurface

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

Evidence

The two key species in the biotope, Echinocardium cordatum and Ensis ensis are infaunal found close to the sediment surface. The biotope occurs in medium to fine sand and slightly muddy sand (Connor et al., 2004). Penetrative activities (e.g. anchoring, scallop or suction dredging) and damage to the seabed’s sub-surface is likely to remove and/or damage the infaunal community, including the characterizing species of the biotope, given the fragility of the tests and that bottom fishing gears penetrate deeper into softer sediments (Bergman & van Santbrink, 2000). Bergman & van Santbrink (2000) suggested that Echinocardium cordatum was one of the most vulnerable species to trawling, and substantial reductions in the numbers of the species due to physical damage from scallop dredging have been observed (Eleftheriou & Robertson, 1992). Echinocardium cordatum was reported to suffer between 10 and 40% mortality due to fishing gear, depending on the type of gear and sediment after a single trawl event (Bergman & van Santbrink, 2000), with mortality possibly increasing to 90% in summer when individuals migrate to the surface of the sediment during their short reproductive season.

Bivalves such as Ensis spp., together with starfish have been reported to be relatively resistant possibly given their ability to burrow deeper into the sediment (Bergman & van Santbrink, 2000). However, Eleftheriou & Robertson (1992) observed large numbers of Ensis ensis killed or damaged by dredging operations and Gaspar et al. (1998) reported high levels of damage in Ensis siliqua from fishing. A study by Haunton et al. (2007) analysed the correlation between hydraulic dredge efficiency and razor clam population annual production and found that gears of the current design are highly efficient and remove approx. 90% of the population in a single tow, which is likely to result in total removal of the population in the towed area.

In the event of damage caused to species such as heart urchins, molluscs and crustaceans as a result of this pressure, damaged or undamaged animals are likely to experience increased predation pressure either at low (birds) or high tide (fish and crabs).

Penetrative events caused by a passing fishing gear are also likely to have marked impacts on the substratum and cause turbulent re-suspension of surface sediments. When used over fine muddy sediments, trawls are often fitted with shoes designed to prevent the boards digging too far into the sediment (M.J. Kaiser, pers. obs., cited in Jennings & Kaiser, 1998). The effects may persist for variable lengths of time depending on tidal strength and currents and may result in a loss of biological organization and reduce species richness (Hall, 1994; Bergman & van Santbrink, 2000; Reiss et al., 2009) (see change in suspended solids and smothering pressures).

Sensitivity assessment: The biotope could be lost or severely damaged, depending on the scale of the activity (see abrasion pressure). Therefore, a resistance of None is suggested. Resilience is probably Medium, and therefore the biotope’s sensitivity to this pressure if likely to be 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

Changes in suspended sediment and siltation rate (resulting from changes in the hydrographic regime, run-off from the land or coastal construction) are likely to result in changes in the sediment composition of the surface layers and hence the communities present. Increased suspended sediment may lead to decreased light penetration, possible clogging of feeding organs of suspension feeders such as Ensis ensis, and the possibility of smothering of whole organisms (see smothering pressure). However, community members of this biotope live beneath the sediment surface or are mobile, and are unlikely to be directly exposed to changes in suspended solids. Probert (1981) reported Echinocardium cordatum in high numbers in the Bay of Mevagissey, Cornwall, for example, where fine-grained mineral waste from the china clay industry was dumped over many years, suggesting that this species is likely to be resistant to increases in siltation. In addition, studies by Gilbert et al. (2007) on sediment re-working coefficients reported that Echinocardium cordatum is capable of high sediment re-working rates, suggesting that this species is therefore likely to play an important role in mitigating the effects of increased siltation, that may result from an increase in suspended solids in the biotope.

An increase in turbidity, reducing light availability will reduce primary production in the biotope. However, the majority of productivity in SS.SSa.IMuSa.EcorEns is secondary (detritus) and so is not likely to be significantly affected by changes in turbidity. Nevertheless, primary production by pelagic phytoplankton and microphytobenthos do contribute to benthic communities and long-term increases in turbidity may reduce the overall organic input to the detritus. Species such as Echinocardium cordatum feeds on detritus that accumulate on the bottom and so its growth consequently relies on the regular supply of detritus (Ridder de et al., 1991).

Holme (1954) reported that Ensis ensis is the more silt resistant of the British Ensis species and is generally found at sheltered localities or from offshore and in sediments with a silt percentage of up to 16%. However, an increased in suspended solids in the water can considerably reduce the quantity of dissolved oxygen, as well as increase the production of mucous to protect the gills from clogging, which consequently can impair metabolism of filter-feeding bivalves, such as Ensis spp. (Moore, 1977). A decrease in siltation may equally affect growth and fecundity if the supply of organic particulate matter declines, given that the particles taken are not discriminated upon nutritional value (Moore, 1977 references therein).

Sensitivity assessment: The key species in the biotope, Echinocardium cordatum and Ensis ensis, are likely to be resistant to changes in suspended sediment and the species composition of the biotope is not likely to be drastically affected at the benchmark level. Resistance is assessed as High and resilience as High (by default). The biotope is therefore assessed as Not Sensitive 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

The biotope is characterized by burrowing species such as the heart urchin Echinocardium cordatum, razor shells Ensis spp., polychaete worms and bivalves, and mobile species such as crabs, fish and other molluscs, that are likely to be able to burrow upwards and therefore unlikely to be adversely affected by smothering of 5 cm sediment. Bijkerk (1988, results cited from Essink, 1999) indicated that the maximal overburden through which Echinocardium cordatum could migrate was approximately 30 cm in sand, but no further information was available on the rates of survivorship or the time taken to reach the surface. Ensis spp. have a large foot and are rapid, deep burrowers (Fish & Fish, 1996), and are therefore likely to be able to adapt their positioning in the substratum in response to a deposition of sediment. The character of the overburden would however determine the degree of the impact on the biotope. For example, smothering by other material, especially oil, could result in the death of most species in the biotope. Furthermore, the biotope occurs within a range of wave exposure conditions from sheltered to exposed, and a range of tidal streams from very weak to moderately strong (Connor et al., 2004). Dispersion of fine sediments may be rapid, and this could mitigate the magnitude of this pressure by reducing the time exposed, as ‘light’ deposition of sediments is likely to be cleared in a few tidal cycles in areas of higher water flow.

Sensitivity assessment: The characterizing species in this biotope are burrowers and therefore likely to be able to move within the sediment deposited as a result of a deposition of 5 cm of sediment. Resistance is assessed as High and resilience as High (by default) and the biotope is considered Not Sensitive to this pressure at the benchmark level.

Smothering and siltation rate changes (heavy)

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

Evidence

The biotope is characterized by burrowing species such as the heart urchin Echinocardium cordatum, razor shells Ensis spp., polychaete worms and bivalves, and mobile species such as crabs, fish and other molluscs, that are likely to be able to burrow upwards or escape. Bijkerk (1988, results cited from Essink, 1999) indicated that the maximal overburden through which Echinocardium cordatum could migrate was approximately 30 cm in sand, but no further information was available on the rates of survivorship or the time taken to reach the surface. Ensis spp. have a large foot and are rapid, deep burrowers (Fish & Fish, 1996), and are therefore likely to be able to adapt their positioning in the substratum in response to a deposition of sediment. The character of the overburden would however determine the degree of the impact on the biotope. For example, smothering by other material, especially oil, could result in the death of most species in the biotope. Furthermore, the biotope occurs within a range of wave exposure conditions from sheltered to exposed, and a range of tidal streams from very weak to moderately strong (Connor et al., 2004). Dispersion of fine sediments resulting from a ‘heavy’ deposition of sediment may take longer than a few tidal cycles to clear in the more sheltered examples of the biotope.

Sensitivity assessment: The characterizing species in this biotope are burrowers and therefore likely to be able to move within deposited sediment. However, a deposition of 30 cm of fine sediment is likely to result in a significant overburden of the infaunal species and there may be some mortality of the characterizing species as a result. Resistance is therefore assessed as Medium and resilience as High and the biotope is considered to have Low sensitivity to this pressure at the benchmark level.

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

No Evidence was 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

No relevant evidence of sound or vibration reception in echinoids was found. Ensis ensis may respond to sound vibrations, retracting into the sediment, but the species is unlikely to be sensitive to noise disturbance at the pressure benchmark level.

Introduction of light or shading

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

Evidence

SS.SSa.IMuSa.EcorEns is a sublittoral biotope, only occasionally occurring on the lower shore (Connor et al., 2004). Although eelgrass Zostera marina may occasionally occur in low densities (Connor et al., 2004), the biotope is not characterized by the presence of primary producers and is, therefore, not directly dependent on sunlight.

Barrier to species movement

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

Evidence

Not Relevant. Barriers and changes in tidal excursion are not relevant to biotopes restricted to open waters.

Death or injury by collision

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

Evidence

Not Relevant to seabed habitats.

Visual disturbance

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

Evidence

With the exception of mobile predators, most of the species in this biotope are infaunal and therefore, not likely to be sensitive to visual disturbance. Mobile predators, like Liocarcinus depurator, are likely to be very sensitive and respond to shadows and movement as an adaptive response to predation. However, this is unlikely to significantly affect the nature of the biotope, nor its characterizing species composition.

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 in the British Isles 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

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).

The availability of hard substrata (e.g., gravel) may only restrict initial colonization as higher densities of Crepidula function as substrata for subsequent colonization (Thieltges et al., 2004; Blanchard, 2009). However, Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas of homogenous fine sediment and areas dominated by boulders. Bohn et al. (2015) suggested that wave action (exposure) probably prevented the establishment of large numbers of Crepidula in high-energy areas. Blanchard (2009) noted that sandy areas in the Bay of Saint-Mont Michel were not colonized by Crepidula because of surface sand mobility. Thieltges et al. (2003) also noted that storm events removed some clumps of mussels and presumably Crepidula onto tidal flats where they disappeared, which caused their abundance to fluctuate. Similarly, Crepidula was absent from sandy substrata in Swansea Bay but was most abundant in the shelter of the breakwater at the Swansea east site (Powell-Jennings & Calloway, 2018). Powell-Jennings & Calloway (2018) noted that Crepidula is killed by sudden burial and possibly burial due to deposition, which could mitigate Crepidula density.

The North American razor shell Ensis directus (syn. Ensis americanus) was introduced into Britain via Europe and was found in Norfolk in 1989 (Palmer, 2004). Although it is widespread and has successfully established large populations, no direct impacts on native species or communities have been reported (Armonies & Reise, 1999; Palmer, 2004). Nevertheless, should local species be replaced by the American razor shell the nature of the biotope should be little altered. No other alien species are known to represent a threat to characterizing species in the biotope at present.

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 fornicata could colonize muddy fine sand habitats, typical of this biotope, due to the small amounts of pebbles, shells, gravel, or any other hard substrata that can be used for larvae settlement (Tillin et al., 2020), but in low densities due to the mobility of the substrata. This habitat is recorded from wave sheltered to wave exposed conditions, in which wave action and storms may mobilise the sediment (JNCC, 2022), which may mitigate or prevent colonization by Crepidula at high densities. However, Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). Therefore, the habitat may be more suitable for Crepidula in more sheltered examples of the biotope and where hard substrata occur but only in low densities due to the low levels of hard substrata present. Therefore, resistance is assessed as 'Medium', where low levels of hard substrata occur and in sheltered examples of the biotope. Resilience is assessed as 'Very low', as it would require the removal of Crepidula, probably by artificial means. Hence, the biotope sensitivity is assessed as 'Medium' 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

There is little information on microbial pathogen effects on the characterizing species of this biotope. The occurrence of several parasitic gregarine protozoans, such as Urospora neapolitana, have been observed in the body cavity of Echinocardium cordatum (Coulon & Jangoux, 1987) although no reports of disease related mortalities were found. Viruses similar to Papillomavirus and Polyomavirus were detected in the digestive glands of Ensis magnus (syn. Ensis arcuatus) in Spain (Ruíz et al., 2011, cited in López et al., 2012). Disseminated neoplasms (a type of tumour) were also reported in Ensis siliqua in Spain (López et al., 2011) including gonadal types (germinomas) in Ensis magnus (syn. Ensis arcuatus) and Ensis siliqua. However, epidemic mortalities seem to have not been observed (López et al., 2011). The limited field observations suggest that germinomas display slow progression, with a low mortality rate, and that the most significant damage produced is a reduction in the capacity to reproduce (Ruiz & López, 2012). No information regarding disease and pathogens on Ensis spp. in the British Isles was found. Liocarcinus depurator is known to suffer from Black Necrotic disease caused by a bacteria, although no information was available on mortality effects. If numbers are reduced predatory effects may decrease but this is not likely to have an impact on overall species diversity.

Sensitivity assessment: No evidence of losses of this biotope due to disease were found and it is likely that microbial pathogens will have only a minor possible impact on this biotope. Resistance and resilience are therefore assessed as High and the biotope judged as Not Sensitive to the introduction of microbial pathogens.

Removal of target species

Benchmark. Removal of species targeted by 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 sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of target species on this biotope. Razor shell clams have high economic value and are often targeted by fisheries. Fishing methods include hand digging, ‘salting’, diving, traditional and hydraulic dredging. A study by Haunton et al. (2007) analysed the correlation between fishing efficiency and population annual production and found that gears of the current design are highly efficient and remove approx. 90% of the population  in a single tow. Their analysis suggested that a high catch efficiency, together with the relatively slow growth of these species was likely to represent a real danger to the sustainability of this fishing industry and for Ensis populations. In Scotland, some subtidal razor shell beds are dense enough to be exploited commercially and the species has been harvested by suction dredges (Fowler, 1999). Although Echinocardium cordatum is not targeted by fisheries, dredging operations may adversely affect this species by removal or damage. Crabs such as Liocarcinus depurator are often extracted as a by-catch species in benthic trawling. A reduction in the density of predators may affect species abundance but is not likely to have a significant effect on overall species diversity.

Sensitivity assessment: Loss of either or both of the characterizing species is likely to result in the loss of the biotope. Resistance is therefore assessed as None (loss of >75% of selected species) and resilience as Medium resulting in the biotope being considered to have Medium sensitivity to removal of targeted species.

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. Echinocardium cordatum and Ensis spp., the characterizing species of this biotope, may be damaged or directly removed by static or mobile gears that are targeting other species, with reports of high levels of mortality of both characterizing species (see abrasion and penetration of the seabed pressures).

Commercial fisheries may discard damaged or dead non-target species, which could result in increased available food supply to detritus feeding Echinocardium cordatum that may have survived in the area targeted by fisheries, but may also attract mobile predators and scavengers including fish and crustaceans which may alter predation rates in the biotope.

Sensitivity assessment. Unintentional removal of the characterizing species would substantially alter the character of the biotope leading to re-classification. For example, Bergman & van Santbrink (2000) reported 10-40% mortality of Echinocardium cordatum due to fishing gear after one trawl event, possibly increasing to 90% in summer when individuals migrate to the surface of the sediment during their short reproductive season; and  Eleftheriou & Robertson (1992) observed large numbers of Ensis ensis killed or damaged by dredging operations. Thus, the biotope is considered to have Low resistance to this pressure and to have Medium resilience. Sensitivity is therefore Medium.