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information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Modiolus modiolus beds on open coast circalittoral mixed sediment

08-11-2016

Summary

UK and Ireland classification

UK and Ireland classification

Description

Muddy gravels and coarse sands in deeper water of continental seas may contain venerid bivalves with beds ofModiolus modiolus. The clumping of the byssus threads of the M. modiolus creates a stable habitat that attracts a very rich infaunal community with a high density of polychaete species including Glycera lapidumParadoneis lyraAonides paucibranchiata, Laonice bahusiensis, Protomystides bidentataLumbrineris spp., Mediomastus fragilis and syllids such as Exogone spp. and Sphaerosyllis spp. Bivalves such as Spisula ellipticaTimoclea ovata and other venerid species are also common. Brittlestars such as Amphipholis squamata may also occur with this community. This biotope is very similar to SMX.PoVen and the 'boreal off-shore gravel association' and the 'deep Venus community' described by previous workers (Ford 1923; Jones 1951). Similar Modiolus beds (though with a less diverse infauna) on open coast stable boulders, cobbles and sediment are described under MCR.ModT (JNCC, 2015).

Depth range

50-100 m

Additional information

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Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

Horse mussels (Modiolus modiolus) may occur as isolated individuals nesting in the sediment, scattered clumps or aggregations, with densities reaching up to 400 individuals/m2 (Lindenbaum et al., 2008) and stretching patchily for between several square metres to kilometres of the subtidal shelf  (Dinesen & Morton, 2014, and references therein).  OSPAR (2009) indicates that patches extending over >10m2 with >30% cover by mussels should definitely be classified as “bed”. However, mosaics also occur where frequent smaller clumps of mussels influence ecosystem functioning so that for conservation and management purposes lower thresholds can be accepted for defining beds (Rees, 2009). 

Studies have identified between 100 and 200 macrofaunal taxa associated with Modiolus modiolus, while overall species numbers may reach ≥ 400 (Göransson & Karlsson, 1998; Rees et al., 2008; Göransson et al. 2010) at sites with soft substrates. Few of these species are endemic to Modiolus beds and have a facultative rather than obligate relationship with Modiolus beds. The sensitivity assessments, therefore, focus on Modiolus modiolus as the main characterizing species and bioengineer with the habitat. Grazing species may be important in controlling algal growth which can increase drag by water currents on the bed and result in Modiolus being swept away. As the biotope definition refers to circalittoral beds where conditions are unsuitable for algae,  grazing is a less important factor and, therefore, infralittoral grazers are discussed only for completeness, where applicable. 

Resilience and recovery rates of habitat

Evidence for the length of time for Modiolus modiolus beds to recover from impacts is limited and for many of the pressures assessed no direct evidence was found. In general, observations on disturbed beds, manipulative experiments and life history characteristics suggest that recruitment to adult populations varies and that time to recover may be prolonged.  It should be noted that the recovery rates are only indicative of the recovery potential.  Recovery of impacted populations will always be mediated by stochastic events and processes acting over different scales including, but not limited to, local habitat conditions, further impacts and processes such as larval-supply and recruitment between populations.

Witman (1984, cited in Suchanek 1985) cleared 115 cm2 patches in a New England Modiolus modiolus bed. None of the patches were recolonized by the horse mussel after 2 years, 47% of the area being colonised by laminarian kelps instead (Witman pers. comm., cited in Suchanek 1985).  On Georges Bank in the Northwestern Atlantic, Modiolus modiolus larvae recruited onto test panels within two years (Collie et al. 2009), although, due to slow growth (and recruitment) of the species it would take 10–15 years for clusters of large individuals to form. Similarly Mair et al. (2000) reported recruitment into disturbed sediments a few years after pipeline was laid (cited from OSPAR, 2009)  Anwar et al. (1990) reported a substantial population on the legs of an oil rig, 10 years after installation, it was suggested that growth was enhanced in this situation due to a lack of predation (OSPAR, 2009). The results suggest that in areas that are artificially cleared or free of predators, recruitment may be relatively rapid where there is a supply of larvae. However, the results refer to the dense settlement of juveniles rather than the development of reefs and such settlements may be relatively ephemeral or in habitats that are not suitable for the long-term establishment of a bed.

Modiolus modiolus is long-lived.  Individuals of 100 mm shell length from Northern Ireland were estimated to be between 14 and 29 years old (Seed & Brown, 1975, 1978). Individuals from Shetland of 100 mm shell length were estimated to be between 11 and 17 years old (Comely, 1981), and those from Norway were 10–18 (13–19) years old (Wiborg, 1946). Anwar et al. (1990) report that the oldest individual studied, from the northern North Sea at a depth of 73–77 m, was ∼48 years old. In Norway, Modiolus modiolus has been reported to become sexually mature at 3 years of age, although most individuals do so at an age of 5–6 (and up to 8) years (Wiborg 1946). Around the Isle of Man, the youngest mature individuals were 3–4 years old (Jasim & Brand, 1989). In Canada, the earliest mature individuals were four years old, and most individuals did not reach maturity until the age of 7–8 years (Rowell, 1967). In Northern Ireland, most individuals mature at a shell length of 40–50 mm (∼4–6 years), but some were already mature at a shell length of 10–20mm (Seed & Brown, 1977).

Reproduction and spawning duration vary between depth and location. Dinesen & Morton (2014), compared gametogenesis and spawning season in four subtidal populations of Modiolus modiolus from a depth of 15 m and showed that both may occur simultaneously. In Strangford Lough, gametogenesis and spawning may occur throughout the year, with peak months varying between years (Brown, 1984). Geographic differences play an important role in the timing of maturity and there appear to be differences between populations even within short distances at similar depths. Similarly, populations in the same area but at different depths show variation (Dinesen & Morton, 2014).

 The larvae require  ∼4 weeks from fertilization to competency (Dinesen & Morton, 2014). Comely (1978) observed that spat settled on established adults, and larger individuals were found within the byssus thread where they had either settled or migrated to after shell settlement.  Dinesen & Ockelmann (unpublished data, cited in Dinesen & Morton, 2014) observed that competent larvae settle preferentially in response to the exhalant water of adults. Translocation of horse mussels Modiolus modiolus, to areas of ‘cultch’ (broken scallop shells) in Strangford Lough, Northern Ireland as part of a programme of work to restore populations destroyed by scallop dredging, also  indicated that settlement of Modiolus modiolus larvae was directly enhanced by the presence of adults on the sea floor (Davoult et al., 1990). Where beds are cleared or reduced in size, recolonization may, therefore, be hampered by the lack of adults.

Sources of and sink areas for recruitment are influenced by prevailing hydrographic conditions and current dynamics. The Strangford Lough populations appear to be self-recruiting (Brown 1990; Elsässer et al. 2013). In open areas with free water, movement larvae are probably swept away from the adult population, and such populations are probably not self-recruiting but dependant on recruitment from other areas, which is in turn dependant on the local hydrographic regime (Holt et al. 1998).

Resilience assessment. Recruitment in Modiolus modiolus is sporadic and highly variable seasonally, annually or with location (Holt et al., 1998).  Dinesen & Morton (2014) state that, post impact recovery times are long and dependent on local and mega-population distributions. Any factor that reduces recruitment is likely to adversely affect the population in the long-term. However, any chronic environmental impact may not be detected for some time in a population of such a long -lived species and populations may survive as ‘relicts’ in habitats that are now unsuitable (OSPAR, 2009).

Overall, therefore, while some populations are probably self-sustaining it is likely that a population that is reduced in extent or abundance will take many years to recover to a mature bed, and any population destroyed by an impact will require a very long time to re-establish and recover, especially since larvae depend on adults for settlement cues and juveniles require the protection of adults to avoid intense predation pressure.

The available evidence for Modiolus modiolus suggests that recovery from significant impacts could be inhibited by the lack of adults to provide settlement cues and protection to larvae and juveniles.  Therefore, where resistance is assessed as ‘None’, resilience is assessed as ‘Very Low’ (>25 years). Resilience is assessed as ‘Low’ (10 to 25 years) where resistance is assessed as ‘Low’ (removal of 25-75% of individuals). Resilience is assessed as ‘Medium’ (2-10 years) where less than 25% of the bed is removed ('Medium' resistance) and the habitat remains suitable for recolonization.  It should be noted that these recovery rates pertain to beds of Modiolus modiolus, not biotopes where sparse individuals occur.

Hydrological Pressures

 ResistanceResilienceSensitivity
High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: Low
C: High
Q: Low
A: Low
C: Low

Modiolus modiolus is a boreal species that reaches its southern limit in UK waters and forms beds of large individuals only in the north of Britain and Ireland (Hiscock et al. 2004). The depth range of Modiolus modiolus increases at higher latitudes with intertidal specimens more common on northern Norwegian shores where air temperatures are lower (Davenport & Kjørsvik, 1982). Little direct information on temperature tolerance in Modiolus modiolus was found, however, its upper lethal temperature is lower than that for Mytilus edulis (Bayne, 1976) by about 4°C (Henderson, 1929, cited in Davenport & Kjørsvik, 1982). Subtidal populations are protected from major, short term changes in temperature by their depth. However, Holt et al. (1998) suggested that because Modiolus modiolus reaches its southern limit in British waters it may be susceptible to long term increases in summer water temperatures. Hiscock et al. (2004) suggest that warmer seas may prevent recovery of damaged beds and recruitment to undamaged beds so that decline in the occurrence of beds can be expected at least in the south of their range. Declines of horse mussel beds in Strangford Lough (Magorrian, 1995) may be linked to increased water temperatures but other factors such as trawling have also contributed to changes.

Sensitivity assessment. Modiolus modiolus is a boreal species, and the fact that dense aggregations seem to reach their southerly limit around British shores suggests this species would be sensitive to long-term increases in temperature. Adult populations may be unaffected at the pressure benchmark and, in such long-lived species, an unfavourable recruitment may be compensated for in the following year. Resistance to an acute and chronic change in temperature at the pressure benchmark is therefore assessed as ‘High’ and recovery as ‘High’ (by default) and the biotope is considered ‘Not Sensitive’.  it should be noted that the timing of acute changes may lead to greater impacts, temperature increases in the warmest months may exceed thermal tolerances whilst changes in colder periods may stress individuals acclimated to the lower temperatures. Sensitivity to longer-term, broad-scale perturbations such as increased temperatures from climate change would, however, be greater, based on the extent of the impact. 

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Modiolus modiolus is a boreal species that reaches its southern limit in UK waters and forms beds of large individuals only in the north of Britain and Ireland (Hiscock et al., 2004). Davenport and Kjørsvik (1982) suggested that its inability to tolerate temperature change was a factor preventing the horse mussel from colonising the intertidal in the UK. Intertidal specimens were more common on northern Norwegian shores (Davenport & Kjørsvik, 1982). Subtidal populations are protected from major, short term changes in temperature by their depth. 

Sensitivity assessment. Modiolus modiolus is a boreal species with beds in higher latitudes exposed to colder temperatures than experienced at the southern limit of its range in the UK. Beds of Modiolus modiolus are therefore considered to have 'High' resistance to decreased temperatures at the benchmark.  Resilience is assessed as 'High' (by default) and this biotope is considered to be 'Not sensitive'. 

Low Low High
Q: Low
A: NR
C: NR
Q: High
A: Low
C: High
Q: Low
A: Low
C: Low

Modiolus modiolus is an osmoconformer.  In short-term fluctuating salinities, valve closure limits exposure to salinity changes in the surrounding waters, although slow diffusion through the byssal aperture means that the osmolarity of fluids will eventually increase ( Shumway, 1977; Davenport & Kjørsvik, 1982). Experimental evidence for short-term tolerances of M. modiolus to increased salinities is provided by Pierce (1970). Modiolus modiolus was exposed to a range of salinities between 1.5 and 54 psu and survived for 21 days (the duration of the experiment) at salinities between 27 and 41 psu (Pierce, 1970).  

Sensitivity assessment. The only evidence to support this assessment is provided by short-term experiments. As this biotope has only been recorded from areas of full salinity (Connor et al., 2004)  a change at the pressure benchmark refers to an increase to hypersalinity (>40 ppt). No direct evidence was available to support this assessment but over the course of a year, an increase in salinity may lead to mortality of Modiolus modiolus. Biotope resistance is, therefore, assessed as 'Low' and resilience as 'Low' so that sensitivity is assessed as 'High'.

Low Low High
Q: High
A: Medium
C: Medium
Q: High
A: Low
C: High
Q: High
A: Low
C: Medium

Local populations may be acclimated to the prevailing salinity regime and may, therefore, exhibit different tolerances to other populations subject to different salinity conditions and therefore, caution should be used when inferring tolerances from laboratory experiments and from populations in different regions. The sensitivity of  Modiolus modiolus to changes in salinity at the benchmark can be inferred from distribution information and from laboratory experiments that have exposed individuals to decreased salinities.

Some populations of Modiolus modiolus are present in areas where salinities are lower than typical, fully marine conditions. From the Baltic Sea distribution pattern, Dinesen & Morton, (2014 and references therein) inferred that the lower, long-term salinity tolerance of adult Modiolus modiolus is likely to be ∼26. This is supported by observations of Davenport & Kjørsvik (1982) who reported the presence of large horse mussels in rock pools at 16 psu in Norway, subject to freshwater inflow and noted that they were probably exposed to lower salinities.  By keeping the shell valves closed, the fluid in the mantle cavity of two individuals was found to be at a salinity of 28–29 despite some hours of exposure (Davenport & Kjørsvik, 1982).  Short-term tolerances to a salinity of 15 were similarly identified for Modiolus modiolus from the White Sea, north west Russia (where salinity is typically 25), whereas salinity levels of between 30 and 35 appeared optimal.    However, after a winter and spring of extremely high rainfall, populations of Modiolus modiolus at the entrance to Loch Leven (near Fort William) were found dead, almost certainly due to low salinity outflow (K. Hiscock, pers. comm). Holt et al. (1998) reported that dense populations of very young Modiolus modiolus do occasionally seem to occur sub tidally in estuaries, but the species is more poorly adapted to fluctuating salinity than many other mussel species (Bayne, 1976) and dense populations of adults are not found in low salinity areas. The biotope records suggest that this biotope only occurs in the UK in full salinity (30-40 ppt) habitats (Connor et al., 2004).

Laboratory experiments exposing Modiolus modiolus to reduced salinity water have demonstrated short term effects.  Pierce (1970) exposed Modiolus sp. to a range of salinities between 1.5 and 54 psu and reported that Modiolus modiolus survived for 21 days (the duration of the experiment) between 27 and 41 psu. Shumway (1977) exposed individual Modiolus modiolus to simulated tidal, (sinusoidal)  fluctuations between full seawater (salinity 32 ‰) and 50% fresh water and to more abrupt changes in salinity in laboratory experiments. Individual Modiolus modiolus that was able to close their valves survived 10 days exposure to salinity changes compared with individuals which had their shells wedged open that survived for 3 days of the experiment only. Exposure to reduced salinities has been observed to lead to reduced ctenidial ciliary stroke, (after 3 days at a salinity of 15 and 10°C, Schlieper et al., 1958) and increased intracellular liquid/water (Gainey, 1994).

Sensitivity assessment. The available evidence indicates that Modiolus modiolus is an osmoconformer able to tolerate decreases in salinity for a short period. However, a decrease in salinity at the pressure benchmark from full salinity to variable (18-35 ppt) would be considered to result in the mortality of all adults within the biotope over the course of a year. This assessment is supported by observed distribution across different salinity regimes (Connor et al., 2004, Dineson & Morton, 2014) and laboratory experiments (Shumway, 1977, Pierce, 1970) which suggest that a change at the pressure benchmark would exceed the lower threshold tolerance of adults over the course of a year). 

High High Not sensitive
Q: High
A: Low
C: Medium
Q: High
A: High
C: High
Q: High
A: Low
C: Medium

Holt et al. (1998) suggested water movement was important in the development of dense reefs and beds of Modiolus modiolus.  It is likely therefore that there is an optimum range of water flows, currently unknown, which are strong enough to disperse larvae and provide food but are not so strong that the current removes the bed, prevents settlement of larvae within beds (which is key for self-recruiting populations) or prevents the extension of feeding siphons. Conversely, decreased flow rates may inhibit larval settlement and the supply of suspended food and allow greater siltation on beds.

Adult M. modiolus occur commonly in areas with moderate to high water exchange in Nova Scotia (Wildish & Peer, 1983; Wildish & Kristmanson, 1985, 1994; Wildish & Fader, 1998; Wildish et al.,1998), and low field densities have been correlated with low current regimes and reduced food availability.   Densities of up to 220 individuals/m2 have been recorded from the Faroese shelf (Dinesen, 1999) where maximal tidal current speed has been estimated to be between 79 and 98 cm/s at two M. modiolus sites (Nørrevang et al., 1994: BIOFAR Stn. 661 & 662, cited from Dinesen & Morton, 2014). Mair et al. (2000) also observed that in Scottish sites with Modiolus modiolus beds, densities were greater where there were high tidal currents.

Comely (1978) suggested that areas exposed to strong currents required an increase in byssus production, at energetic cost, and resulted in lower growth rates.  At water velocities exceeding 16 cm/s in a flume tank, Carrington et al., (2008) observed that M. modiolus individuals could not extend the foot beyond the shell to form and attach byssus threads.  However, the mussel bed reduces water flow rates by increasing drag through friction. Carrington et al., (2008) observed that mussel beds of Mytilus trossulus and M. galloprovincialis in laboratory and field studies were able to reduce flow rates between 0.1 and 10% of free-stream velocity.  This modification of flow may enhance suspension feeding in areas of high current flow and allow byssus production to continue (Carrington et al., 2008).

Wildish et al., (2000) examined suspension feeding in M. modiolus in a flume tank and noted that individuals kept the exhalant and inhalant siphons open over the range of flow rates studied, from 0.12-0.63 m/s. However, the inhalant siphon closed by about 20% in currents above 0.5m/s.

Fouling by epifauna and algae in the infralittoral may also decrease the population’s resistance to increased water flow. Witman (1984, cited in Suchanek, 1985) found that over 11 months in New England, 84% of fouled mussels were dislodged in comparison with 0% of unfouled individuals. As the beds described by the biotope group occur in the circalittoral algal overgrowth is not relevant but the presence of high levels of epifauna on circalittoral beds may similarly increase dislodgement.

Changes in water flow may also be a spawning cue, although the available evidence does not strongly support this hypothesis. Schweinitz & Lutz, (1976) observed spontaneous, spawning in a group of M. modiolus individuals kept in a tank when the water flow stopped while previous attempts to induce spawning by various methods had failed. However, subsequent attempts to induce spawning by stopping the water flow failed (De Schweinitz & Lutz, 1976). A similar spawning response in Mytilus edulis to the cessation of flow (Williamson, 1997) was cited (De Schweinitz & Lutz, 1976).

Sensitivity assessment.  Flow rates are an important factor for Modiolus modiolus which may be sensitive to both increases and decreases in flow. Direct evidence is not available to identify the optimal range and increases may be moderated by the bed structure which will depend on the degree of recession into sediments and the size and type of associated epifauna (if any).  Adult M.modiolus may have ‘High’ resistance to changes in water flow rates at the pressure benchmark. Changes in flow rates that alter larval recruitment, however, may lead to the presence of beds, composed of ageing adults, that are not sustainable in the long-term. Resistance to changes in water flow is therefore assessed as ‘Medium’ (loss of <25%) to reflect potential minor changes in recruitment with the eventual decline and recovery is assessed as ‘’Medium’ so that sensitivity to this pressure is assessed as ‘Medium.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The majority of populations are subtidal, however, intertidal populations in rock pools or shallow subtidal populations occasionally exposed at extreme low water may occur and be vulnerable to increased emergence and hence, exposure to desiccation and temperature extremes. Modiolus modiolus has a lower tolerance of exposure than other Mytilidae such as Mytilus edulis, although whether this is due to the effects of desiccation, fluctuating temperatures or reduced feeding times is not clear (Dinesen & Morton, 2014). Gillmor (1982) showed that growth rate of juvenile  Modiolus modiolus (SL < 20 mm), was zero at aerial exposure times of 20–25. Gillmor (1982) also recorded 100% mortality of Modiolus modiolus at 40% aerial exposure.

Sensitivity assessment. Modiolus modiolus is considered to be ‘Not sensitive’ to a decrease in emergence or an increase in sea level, which would, theoretically, increase habitat suitability for this species. The available evidence indicates that Modiolus modiolus would be sensitive to increased emergence and decreases in sea level where exposed, but these pressures are considered to be not relevant to this biotope group which is restricted to circalittoral subtidal habitats. 

High High Not sensitive
Q: High
A: Medium
C: Medium
Q: High
A: High
C: High
Q: High
A: Medium
C: Medium

The majority of Modiolus modiolus populations are subtidal and unlikely to be affected by wave action directly. However, increased wave action results in increased water flow in the shallow subtidal. Wave mediated water flow tends to be oscillatory, i.e. move back and forth (Hiscock, 1983), and may result in dislodgement or removal of individuals. Mytilus edulis was shown to increase byssus production in response to agitation (Young, 1985) and Modiolus modiolus may respond similarly. However, horse mussels attached to hard substrata are probably more intolerant of wave action than Mytilus edulis due to their larger size and hence increased drag. The intolerance of semi-infaunal or infaunal populations probably owes more to the nature of the substratum rather than their attachment. Populations on mobile sediment may be removed by strong wave action due to removal or changes in the substratum. No information concerning storm damage was found. Shallow, nearshore subtidal populations in Strangford Lough were exposed to wave mediated flows of 0.1 m/s (Elsäßer et al., 2013).   Decreased wave action may allow horse mussel beds to extend into shallower depths, however, the rates of increase in bed size are likely to be slow, probably much longer than the benchmark level.

Sensitivity assessment. No direct evidence was found to assess sensitivity to changes at the pressure benchmark. Circalittoral beds in mixed sediment were assessed as ‘High’ resistance and ‘High’ resilience at the pressure benchmark to increases and decreases in wave height and are, therefore, assessed as ‘Not Sensitive’.

Chemical Pressures

 ResistanceResilienceSensitivity
Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

High High Not sensitive
Q: High
A: Low
C: NR
Q: High
A: High
C: High
Q: High
A: Low
C: Low

Theede et al. (1969) examined the relative tolerance of gill tissue from several species of bivalve to exposure to 0.21 mg/l O2 with or without 6.67 mg of sulphide (at 10°C and 30 psu). Modiolus modiolus tissue was found to be the most resistant of the species studied, retaining some ciliary activity after 120 hours compared with 48hrs for Mytilus edulis.

Sensitivity assessment. While it is difficult to extrapolate from tissue resistance to whole animal resistance (taking into account behavioural adaptations such as valve closure) the evidence suggests that horse mussels are more, or at least similarly, tolerant of hypoxia and hydrogen sulphide than the common mussel. In addition, most bivalve molluscs exhibit anaerobic metabolism to some degree. Therefore, a resistance of 'High' has been recorded at the benchmark level and resilience is assessed as 'High' (based on no effect to recover from). Modiolus beds are therefore considered to be 'Not sensitive' at the pressure benchmark. 

Not relevant (NR) Not relevant (NR) Not sensitive
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Modiolus modiolus is not considered sensitive at the pressure benchmark that assumes compliance with good status as defined by the WFD.

High High Not sensitive
Q: Medium
A: Medium
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

Little direct evidence was available to support the assessment of this pressure, which is largely based on expert judgement. In areas of strong tidal flow where some Modiolus modiolus beds are found, deposits of organic matter may be removed fairly rapidly mitigating the impact, although some deposits will be trapped within crevices and spaces where they may be utilised by the infaunal deposit feeding community. Where currents are weaker, as in some of the sheltered lochs and similar areas where beds occur, organic deposits may be removed more slowly and impacts may be greater. The persistence of a Modiolus modiolus population in the vicinity of a sewage sludge dumping site (Richardson et al., 2001) suggests that the species is tolerant of high levels of organic matter. Beds of Modiolus modiolus enrich the surrounding sediment via faeces and pseudofaeces so that the bed accumulates deposits rich in organic matter and increases in height compared to the surrounding seabed.  At the pressure benchmark, which refers to enrichment rather than gross organic pollution (Tillin & Tyler-Walters, 2014), the extra rate of organic matter accumulation may not far exceed the natural background level, particularly in sheltered areas.

Sensitivity assessment. At the pressure benchmark, which refers to enrichment rather than gross organic pollution, Modiolus modiolus is considered to have 'High' resistance and hence, 'High' resilience. This biotope group is therefore considered to be 'Not Sensitive'.

Physical Pressures

 ResistanceResilienceSensitivity
None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

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.  

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

The introduction of artificial hard substratum is considered at the pressure benchmark level and it is noted that Modiolus modiolus can colonise bedrock and artificial structures.  On Georges Bank in the Northwestern Atlantic, Modiolus modiolus larvae recruited onto test panels within two years (Collie et al. 2009). Anwar et al. (1990) reported a substantial population on the legs of an oil rig, 10 years after installation. It was suggested that growth was enhanced in this situation due to a lack of predation (OSPAR, 2009). The results suggest that on suitable surfaces recruitment may be relatively rapid where there is a supply of larvae. However, the results refer to a dense settlement of juveniles rather than the development of reefs and such settlements may be relatively ephemeral or in habitats that are not suitable for the long-term establishment of a bed. Modiolus modiolus is also found on natural bedrock.

Sensitivity assessment.   The resistance of the biotope is, therefore, assessed as ‘None’ (loss of >75% of extent), resilience (following habitat recovery) is assessed as ‘Very Low’ (at least 25 years).  Sensitivity, based on combined resistance and resilience is assessed as ‘High’. The more precautionary assessment for the biotope, rather than the species, is presented in the table as it is considered that any change to a sedimentary habitat from a rock reef habitat would alter the biotope classification and hence the more sensitive assessment is appropriate.

None Very Low High
Q: Low
A: NR
C: NR
Q: High
A: Low
C: High
Q: Low
A: Low
C: Low

The change in one Folk class is considered to relate to a change in classification to adjacent categories in the modified Folk triangle (Long, 2006).  For the mixed sediments that characterize this biotope the sediment changes considered may be to coarser or finer sediments.  Modiolus modiolus is found on and in a variety of substrata ranging from fine mud with shells and gravel to bedrock. Comely (1978) found Modiolus modiolus in different types of sediment at varying densities, with low densities (mean 4 individuals/m2) in clean gravel, stones and small boulders and at higher densities (mean 10 individuals/m2 in fine muddy sand and silty sand with coarse gravel overlain by clean coarse sand with boulders) . Based on ROV and SCUBA survey in Strangford Lough, Elsässer et al. (2013) modelled suitable habitat and found that substratum type was a key predictor of distribution, occurrence of the remaining beds was strongly linked to the presence of finer substrata such as sand and mud and negatively correlated with coarser substratum types  such as bedrock, boulders and cobbles.

Sensitivity assessment. Given the wide range of substratum types occupied by this species, a change in sediment type is not considered to negatively impact habitat suitability at the level of the individual. However, the biotope group refers specifically to beds of Modiolus modiolus occurring in mixed sediments rather than individuals. Based on the available evidence a change to coarse sediments may be more detrimental to the biotope than a change to finer sediments.  As the biotope classification refers specifically to mixed sediments an increase in fine or coarse sediments to the degree that sediments are re-classified would severely reduce habitat suitability.  Resistance is therefore assessed as ‘None’ (loss of >75% of extent), resilience (following habitat recovery) is assessed as ‘Very Low’ (10 -25 years) as a change at the pressure benchmark is permanent.

None Low High
Q: High
A: High
C: High
Q: High
A: Low
C: High
Q: High
A: Low
C: High

Modiolus modiolus is found on and in a variety of substrata ranging from fine mud with shells and gravel to bedrock. The process of extraction is considered to remove all members of the biotope group as beds of Modiolus modiolus are sessile and occur either on or within the sediment. No direct evidence for resistance and recovery to this pressure was found and the sensitivity assessment is therefore based on expert judgement.

Sensitivity assessment. The process of extraction is considered to remove all members of the biotope group as Modiolus modiolus are sessile. Resistance is therefore 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. Local migration of adults could re-populate very small defaunated patches and passive transport of adults via water movements may occur, however, recovery is most likely to occur via larval recolonisation. Resilience is considered to be ‘Low for Modiolus modiolus (10-25 years) although the caveats outlined in the recovery section regarding preferential settlement within beds and prolonged or no recovery without suitable larval supply should be noted. Sensitivity based on resistance and resilience is therefore categorised as ‘High’.

 

 

Low Low High
Q: High
A: Medium
C: Medium
Q: High
A: Low
C: High
Q: High
A: Low
C: Medium

Impacts from towed fishing gear (e.g. scallop dredges) are known to flatten clumps and aggregations and may break off sections of raised reefs and probably damage individual mussels (Holt et al., 1998) as described below in the ‘penetration and abrasion pressure’ which assesses the impacts of abrasion and sub-surface damage. Older individuals can be very brittle due to infestations of the boring sponge Cliona celata (Comely 1978).

Sensitivity assessment.  Abrasion at the surface only is considered likely to flatten clumps and dislodge and break individuals. Resistance is assessed as ‘Low’ (damage or loss to 25-75% of the population), although the significance of the impact for the bed will depend on the spatial scale of the pressure footprint. Resilience is assessed as ‘Low’ (10-25 years), and sensitivity is assessed as ‘High’. Epifauna associated with the bed is also likely to be damaged and removed.

Low Low High
Q: High
A: High
C: Medium
Q: High
A: Low
C: High
Q: High
A: Low
C: Medium

As Modiolus modiolus are large, sessile and shallowly buried, individuals are unable to escape from penetration and disturbance of the substratum and clear evidence exists for declines in the extent and density of beds exposed to activities that lead to this pressure.   The associated attached epifauna and infauna are also likely to be damaged and removed by this pressure.

Evidence for long-term decline in response to abrasion and sub-surface penetration pressures resulting from mobile gears has been found from surveys and monitoring in areas where beds have been impacted. Horse mussel beds in Strangford Lough in Northern Ireland have suffered notable declines in extent.  Magorrian & Service (1998) reported that queen scallop trawling resulted in flattening of horse mussel beds and disruption of clumps of horse mussels and removal of emergent epifauna in Strangford Lough. They suggested that the emergent epifauna were more intolerant than the horse mussels themselves but were able to identify different levels of impact, from impacted but largely intact to few Modiolus modiolus intact with lots of shell debris (Service & Magorrian 1997; Magorrian & Service 1998).  Recent comparison of dive survey data sets collected in 1975-1983 and 2005-2007, demonstrated further declines in Modiolus modiolus, the bivalves Aequipecten irregularis and Chlamys varia and some erect sessile fauna between the survey periods (Strain et al., 2012). Strain et al. (2012) concluded that the epifaunal assemblage in Strangford Lough had shifted due to the period of intensive fishing for the queen scallop (Aequipecten irregularis) between 1985 and 1995. Strain et al. (2012) noted that although all mobile fishing gear was banned in 2004, there were no detectable differences, indicating recovery of epifaunal communities between 2003 and 2007 surveys, seven years after the period of intensive fishing for queen scallops.

Cook et al. (2013) were able to examine the effects of a single pass by an otter trawl on Modiolus modiolus beds off the Lleyn Peninsula and a scallop dredge on the northeast of the Isle of Man. The tracks from the mobile gears were observed during routine bed monitoring and the observations are based on normal fishing activities rather than designed experiments. The trawl resulted in a 90% reduction in the number of epifauna while the scallop dredge resulted in a 59% reduction. At both sites mean Modiolus modiolus abundance declined, with visible flattening of clumps in response to dredging.  No evidence of recovery was recorded at the Isle of Man site a year after impact was first recorded.

Kenchington et al. (2006) examined the effects of multiple passes of an otter trawl on benthic communities on the Western Bank on Canada’s Scotian shelf in the northwest Atlantic. The community was dominated (76%) by Modiolus modiolus attached to rocks, embedded in the seabed or in small groups but was not considered to represent a Modiolus reef habitat. The transect was trawled 12-14 times, on three occasions over a 20 month period. As a result, the epifauna was reduced (from 90% to 77% contribution to the community). The most marked decline was in Modiolus modiolus abundance, which declined by approximately 80% to 60% of the community, (a reduction in biomass from approximately 2753 g before trawling in 1997 to 987 g after trawling in 1999) due to direct damage from the trawl and subsequent consumption by predators and scavengers.

Sensitivity assessment.  Based on the available evidence, resistance is assessed as ‘Low’ (loss of 25-75%), and resilience is assessed as ‘Low’ (10-25 years). Sensitivity is, therefore assessed as ‘High’.

High High Not sensitive
Q: Medium
A: Low
C: NR
Q: High
A: High
C: High
Q: Medium
A: Low
C: Low

Changes in light penetration or attenuation associated with this pressure are not relevant to Modiolus modiolus biotopes, however, alterations in the availability of food or the energetic costs in obtaining food or changes in scour could either increase or decrease habitat suitability for Modiolus modiolus beds. Modiolus modiolus is found in a variety of turbid and clear water conditions (Holt et al., 1998).  Muschenheim & Milligan (1998) noted that the height of the horse mussel beds in the Bay of Fundy positioned them within the region of high quality seston while avoiding high levels of re-suspended inorganic particulates (2.5-1500 mg/l) at the benthic boundary layer.  Decreases in turbidity may increase phytoplankton productivity and potentially increase food availability. Therefore, horse mussel beds may benefit from reduced turbidity.

Sensitivity assessment.  No directly relevant empirical evidence was found to assess this pressure.  Resistance to this pressure is assessed as 'High' as an increase in turbidity may impact feeding and growth rates but not result in mortality of adults. Resilience is assessed as 'High' (by default) and the biotope is assessed as 'Not Sensitive' to changes in turbidity at the benchmark level.

Low Low High
Q: High
A: High
C: NR
Q: High
A: Low
C: High
Q: High
A: Low
C: Low

In areas of strong tidal flow where some Modiolus modiolus beds are found, deposits of silt may be removed fairly rapidly, although some silts will be trapped within crevices and spaces. Where currents are weaker, as in some of the sheltered lochs and similar areas where beds occur, deposits may be removed more slowly and impacts may be greater.  Mass Accumulation Rates of  0.63±0.09 g cm2 year-1 following bottom trawling in Strangford Lough were suggested to act as a driver for potential negative effects on the physiological condition of remnant populations of Modiolus modiolus by Strong & Service (2008). In a series of burial experiments, Hutchison et al. (2016) tested the response of individuals to burial under three depths of sediment (2, 5 and 7cm), three sediment fractions (coarse-1-2mm; medium-fine-0.25-0.95 mm and fine-0.1-0.25 mm) and five burial durations (2, 4, 8, 16, 32 days). Modiolus modiolus could not re-emerge from sediments and mortality increased with duration of smothering and the proportion of fine particles in the smothering material, the depth of burial did not alter mortality rates. Buried individuals survived for 8 days without apparent mortality but by 16 days cumulative mortality was greater than 50% (Hutchison et al., 2016).

Sensitivity assessment. The experiments by Hutchison et al., (2016) show that duration of burial is a key factor determining survival, burial under even small amounts of fine sediment (2 cm) for longer than 8 days could lead to significant mortality. Site-specific hydrodynamics that influence the mobility of deposited sediments will mediate resistance. As this biotope may occur in sheltered conditions, resistance is assessed as 'Low' as some mussels may be smothered for longer than a week and begin to die before the overburden is removed. Resilience is assessed as 'Low' and sensitivity is, therefore, categorised as 'High'.

Low Low High
Q: High
A: High
C: NR
Q: High
A: Low
C: High
Q: High
A: Low
C: Low

In areas of strong tidal flow where some Modiolus modiolus beds are found, deposits of silt may be removed fairly rapidly, although some silts will be trapped within crevices and spaces. Where currents are weaker, as in some of the sheltered lochs and similar areas where beds occur, deposits may be removed more slowly and impacts may be greater.  Mass Accumulation Rates of  0.63±0.09 g cm2 year-1) following bottom trawling in Strangford Lough were suggested to act as a driver for potential negative effects on the physiological condition of remnant populations of Modiolus modiolus by Strong & Service (2008). In a series of burial experiments, Hutchison et al. (2016) tested the response of individuals to burial under three depths of sediment (2, 5 and 7cm), three sediment fractions (coarse-1-2mm; medium-fine-0.25-0.95 mm and fine-0.1-0.25 mm) and five burial durations (2,4,8,16,32 days). Modiolus modiolus could not re-emerge from sediments and mortality increased with duration of smothering and the proportion of fine particles in the smothering material, the depth of burial did not alter mortality rates. Buried individuals survived for 8 days without apparent mortality but by 16 days cumulative mortality was greater than 50% (Hutchison et al., 2016).

Sensitivity assessment. The experiments by Hutchison et al., (2016) show that duration of burial is a key factor determining survival, burial under even small amounts of fine sediment (2 cm) for longer than 8 days could lead to significant mortality. Site-specific hydrodynamics that influence the mobility of deposited sediments will mediate resistance, as the deposit at the pressure benchmark is substantial (30 cm) it is likely that the deposit will persist for some time (particularly if it consists of cohesive, fine particles) before removal. As this biotope may occur in sheltered conditions, resistance is assessed as 'Low' as some mussels may be smothered for longer than a week and begin to die before the overburden is removed. Resilience is assessed as 'Low' and sensitivity is therefore categorised as 'High'.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not assessed.

No evidence (NEv) No evidence (NEv) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant.

No evidence (NEv) No evidence (NEv) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not evidence.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant’ to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not relevant.

Biological Pressures

 ResistanceResilienceSensitivity
No evidence (NEv) No evidence (NEv) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Habitat restoration projects may translocate stock to repopulate areas of suitable habitat (Elsässer et al., 2013). No evidence was found for detrimental effects arising from this practice, although there is potential for the movement of pathogens and non-indigenous, invasive species. 

No evidence (NEv) No evidence (NEv) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence.

No evidence (NEv) No evidence (NEv) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Brown & Seed (1977) reported a low level of infestation (ca 2%) with pea crabs Pinnotheres sp. in Port Erin, Isle of Man and Strangford Lough. Comely (1978) reported that ca 20% of older specimens, in an ageing population, were damaged or shells malformed by the boring sponge Cliona celata. Infestation by the boring sponge reduces the strength of the shell and may render the population more intolerant of physical disturbance (see above). However, little other information concerning the effects of parasites or disease on the condition of horse mussels was found.

Shumway (1990) reviewed the effects of algal blooms on shellfish and reported that a bloom of Gonyaulax tamarensis(Protogonyaulax) was highly toxic to Modiolus modiolus. Shumway (1990) also noted that both Mytilus spp. and Modiolus spp. accumulated paralytic shellfish poisoning (PSP) toxins faster than most other species of shellfish, e.g. horse mussels retained Gonyaulax tamarensis toxins for up to 60 days (depending on the initial level of contamination). Landsberg (1996) also suggested that there was a correlation between the incidence of neoplasia or tumours in bivalves and outbreaks of paralytic shellfish poisoning in which bivalves accumulate toxins from algal blooms, although a direct causal effect required further research.

The parasites Martelia refringens or other Marteilia sp. can cause significant bivalve infections. Although these have been reported to infect Modiolus modiolus (Bower et al. 2004), no evidence was available to assess the scale of impact and therefore there is not enough evidence to assess sensitivity. 

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Artisanal fisheries have targeted Modiolus modiolus as bait for the long-line fishery (Jeffreys 1863; Wiborg 1946) and, more locally, for human consumption around the British Isles (Jeffreys 1863; Holt et al. 1998) and the Faroe Islands (Dinesen & Ockelmann 2005). Modiolus modiolus is not currently directly targeted in the UK and hence this pressure is considered to be ‘Not relevant’. While removal of targeted species, such as scallops, will reduce species richness the loss of targeted species is unlikely to adversely affect the Modiolus modiolus bed through biological effects. The physical effects of dredging for scallops and other targeted species are discussed through the abrasion and penetration pressures. The removal of target species that predate on Modiolus modiolus would potentially be beneficial allowing the recruitment of juveniles to the adult population. However, such effects are not directly documented and could not be included in the assessment.

Low Low High
Q: High
A: High
C: High
Q: High
A: Low
C: High
Q: High
A: Low
C: High

Removal of Modiolus modiolus within this biotope, as bycatch, will alter the physical structure of the biotope and reduce habitat complexity: these are considered ecological impacts and hence this biotope group is considered to be sensitive to this pressure, at the pressure benchmark. Epifauna associated with the bed is also likely to be damaged and removed as bycatch (Magorrian & Service, 1998) altering the structural complexity of the bed.

Sensitivity assessment. Resistance is assessed as ‘Low’ (damage or loss to 25-75% of the population), although the significance of the impact for the bed will depend on the spatial scale of the pressure footprint. Resilience is assessed as ‘Low’ (2-10 years), and sensitivity is assessed as ‘High’. Epifauna associated with the bed is also likely to be damaged and removed.

Bibliography

  1. Anwar, N.A., Richardson, C.A. & Seed, R., 1990. Age determination, growth rate, and population structure of the horse mussel Modiolus modiolus. Journal of the Marine Biological Association of the United Kingdom, 70, 441-457.

  2. Bishop, G.M. & Earll, R., 1984. Studies on the populations of Echinus esculentus at the St Abbs and Skomer voluntary Marine Nature Reserves. Progress in Underwater Science, 9, 53-66.

  3. Bishop, G.M., 1985. Aspects of the reproductive ecology of the sea urchin Echinus esculentus L. Ph.D. thesis, University of Exeter, UK.

  4. Bower, S.M., 1996. Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Bald-sea-urchin Disease. [On-line]. Fisheries and Oceans Canada. [cited 26/01/16]. Available from: http://www.dfo-mpo.gc.ca/science/aah-saa/diseases-maladies/bsudsu-eng.html

  5. Brown, R.A. & R. Seed., 1976. Modiolus modiolus (L.) - an autoecological study. In Proceedings of the 11th European Symposium on Marine Biology, Galway, 5-11 October, 1976. Biology of Benthic Organisms (ed. B.F. Keegan, P.O. Ceidigh & Boaden, P.J.S.), pp. 93-100.

  6. Brown, R.A., 1984. Geographical variation in the reproduction of the horse mussel, Modiolus modiolus (Mollusca: Bivalvia). Journal of the Marine Biological Association of the United Kingdom, 64, 751-770.

  7. Brown, R.A., 1990. Strangford Lough. The wildlife of an Irish sea lough. The Institute of Irish Studies, Queens University of Belfast.

  8. Bryan, G.W. & Gibbs, P.E., 1991. Impact of low concentrations of tributyltin (TBT) on marine organisms: a review. In: Metal ecotoxicology: concepts and applications (ed. M.C. Newman & A.W. McIntosh), pp. 323-361. Boston: Lewis Publishers Inc.

  9. Bryan, G.W., 1984. Pollution due to heavy metals and their compounds. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters, vol. 5. Ocean Management, part 3, (ed. O. Kinne), pp.1289-1431. New York: John Wiley & Sons.

  10. Cole, S., Codling, I.D., Parr, W. & Zabel, T., 1999. Guidelines for managing water quality impacts within UK European Marine sites. Natura 2000 report prepared for the UK Marine SACs Project. 441 pp., Swindon: Water Research Council on behalf of EN, SNH, CCW, JNCC, SAMS and EHS. [UK Marine SACs Project.], http://www.ukmarinesac.org.uk/

  11. Collie, J.S., Hermsen, J.M. & Valentine, P.C., 2009. Recolonization of gravel habitats on Georges Bank (northwest Atlantic). Deep-Sea Research Part II, 56 (19-20), 1847-1855.

  12. Comely, C.A., 1978. Modiolus modiolus (L.) from the Scottish West coast. I. Biology. Ophelia, 17, 167-193.

  13. Comely, C.A., 1981. The physical and biological condition of Modiolus modiolus (L.) in selected Shetland voes. Proceedings of the Royal Society of Edinburgh, Series B, 80, 299-321.

  14. Connor, D.W., Allen, J.H., Golding, N., Howell, K.L., Lieberknecht, L.M., Northen, K.O. & Reker, J.B., 2004. The Marine Habitat Classification for Britain and Ireland. Version 04.05. Joint Nature Conservation Committee, Peterborough. www.jncc.gov.uk/MarineHabitatClassification.

  15. Connor, D.W., Dalkin, M.J., Hill, T.O., Holt, R.H.F. & Sanderson, W.G., 1997a. Marine biotope classification for Britain and Ireland. Vol. 2. Sublittoral biotopes. Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06., Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06.

  16. Cook, R., Fariñas-Franco, J. M., Gell, F. R., Holt, R. H., Holt, T., Lindenbaum, C.,  Porter, J.S., Seed, R., Skates, L.R., Stringell, T.B. & Sanderson, W.G., 2013. The substantial first impact of bottom fishing on rare biodiversity hotspots: a dilemma for evidence-based conservation. PloS One, 8 (8), e69904.

  17. Crisp, D.J. (ed.), 1964. The effects of the severe winter of 1962-63 on marine life in Britain. Journal of Animal Ecology, 33, 165-210.

  18. Davenport, J. & Kjørsvik, E., 1982. Observations on a Norwegian intertidal population of the horse mussel Modiolus modiolus (L.). Journal of Molluscan Studies, 48, 370-371.

  19. Davies, C.E. & Moss, D., 1998. European Union Nature Information System (EUNIS) Habitat Classification. Report to European Topic Centre on Nature Conservation from the Institute of Terrestrial Ecology, Monks Wood, Cambridgeshire. [Final draft with further revisions to marine habitats.], Brussels: European Environment Agency.

  20. Davoult, D., Gounin, F. & Richard, A., 1990. Dynamique et reproduction de la population d'Ophiothrix fragilis (Abildgaard) du détroit du Pas de Calais (Manche orientale). Journal of Experimental Marine Biology and Ecology, 138, 201-216.

  21. Dinesen, G.E., & Morton, B., 2014. Review of the functional morphology, biology and perturbation impacts on the boreal, habitat-forming horse mussel Modiolus modiolus (Bivalvia: Mytilidae: Modiolinae). Marine Biology Research, 10 (9), 845-870.

  22. Dinesen, G.E., Ockelmann, K.W. 2005. Spatial distribution and species distinction of Modiolus modiolus and syntopic Mytilidae (Bivalvia) in Faroese waters (NE Atlantic). BIOFAR Proceedings 2005. Annales Societas Scientarium Færoenses (Fróðskapparit), 41, 125-136.

  23. Eleftheriou, A. & Robertson, M.R., 1992. The effects of experimental scallop dredging on the fauna and physical environment of a shallow sandy community. Netherlands Journal of Sea Research, 30, 289-299.

  24. Elsäßer, B., Fariñas-Franco, J.M., Wilson, C.D., Kregting, L. & Roberts, D., 2013. Identifying optimal sites for natural recovery and restoration of impacted biogenic habitats in a special area of conservation using hydrodynamic and habitat suitability modelling. Journal of Sea Research, 77, 11-21.

  25. Erwin, D.G., Picton, B.E., Connor, D.W., Howson, C.M., Gilleece, P. & Bogues, M.J., 1990. Inshore Marine Life of Northern Ireland. Report of a survey carried out by the diving team of the Botany and Zoology Department of the Ulster Museum in fulfilment of a contract with Conservation Branch of the Department of the Environment (N.I.)., Ulster Museum, Belfast: HMSO.

  26. Göransson, P., Karlsson, M., 1998. Knähagen Reef - Pride of the Öresund. A 100 Year Perspective of Biological Diversity in a Marine Coastal Area. Helsingborg. Report to the Malmöhus County Board and the Environmental Agency of Helsingborg City,

  27. Gili, J-M. & Hughes, R.G., 1995. The ecology of marine benthic hydroids. Oceanography and Marine Biology: an Annual Review, 33, 351-426.

  28. Gillmor, R.B., 1982. Assessment of intertidal growth and capacity adaptations in suspension-feeding bivalves. . Marine Biology, 68, 277-286.

  29. Gommez, J.L.C. & Miguez-Rodriguez, L.J., 1999. Effects of oil pollution on skeleton and tissues of Echinus esculentus L. 1758 (Echinodermata, Echinoidea) in a population of A Coruna Bay, Galicia, Spain. In Echinoderm Research 1998. Proceedings of the Fifth European Conference on Echinoderms, Milan, 7-12 September 1998, (ed. M.D.C. Carnevali & F. Bonasoro) pp. 439-447. Rotterdam: A.A. Balkema.

  30. Griffiths, A.B., Dennis, R. & Potts, G.W., 1979. Mortality associated with a phytoplankton bloom off Penzance in Mount's Bay. Journal of the Marine Biological Association of the United Kingdom, 59, 515-528.

  31. Hammer, L., 1972. Anaerobiosis in marine algae and marine phanerograms. In Proceedings of the Seventh International Seaweed Symposium, Sapporo, Japan, August 8-12, 1971 (ed. K. Nisizawa, S. Arasaki, Chihara, M., Hirose, H., Nakamura V., Tsuchiya, Y.), pp. 414-419. Tokyo: Tokyo University Press.

  32. Hartnoll, R.G., 1983. Substratum. In Sublittoral ecology. The ecology of the shallow sublittoral benthos (ed. R. Earll & D.G. Erwin), pp. 97-124. Oxford: Clarendon Press.

  33. Henderson, J.T., 1929. Lethal temperatures of Lamellibranchiata. Contributions to Canadian Biology and Fisheries, 4, 395-412.

  34. Hickson, J.S., 1901. Liverpool Marine Biological Committee Memoirs Number V. Alcyonium. Proceedings and Transactions of the Liverpool Biological Society, 15, 92-113.

  35. Hill, A.S., Brand, A.R., Veale, L.O. & Hawkins, S.J., 1997. Assessment of the effects of scallop dredging on benthic communities. Final Report to MAFF, Contract CSA 2332, Liverpool: University of Liverpool

  36. Hiscock, K., 1983. Water movement. In Sublittoral ecology. The ecology of shallow sublittoral benthos (ed. R. Earll & D.G. Erwin), pp. 58-96. Oxford: Clarendon Press.

  37. Hoare, R. & Hiscock, K., 1974. An ecological survey of the rocky coast adjacent to the effluent of a bromine extraction plant. Estuarine and Coastal Marine Science, 2 (4), 329-348.

  38. Holt, T.J., Jones, D.R., Hawkins, S.J. & Hartnoll, R.G., 1995. The sensitivity of marine communities to man induced change - a scoping report. Countryside Council for Wales, Bangor, Contract Science Report, no. 65.

  39. Holt, T.J., Rees, E.I., Hawkins, S.J. & Seed, R., 1998. Biogenic reefs (Volume IX). An overview of dynamic and sensitivity characteristics for conservation management of marine SACs. Scottish Association for Marine Science (UK Marine SACs Project), 174 pp.

  40. Hutchison, Z.L., Hendrick, V.J., Burrows, M.T., Wilson, B. & Last, K.S., 2016. Buried Alive: The Behavioural Response of the Mussels, Modiolus modiolus and Mytilus edulis to Sudden Burial by Sediment. PLoS ONE, 11 (3), e0151471.

  41. Jasim, A.K.N. & Brand, A.R., 1989. Observations on the reproduction of Modiolus modiolus in the Isle of Man. Journal of the Marine Biological Association of the United Kingdom, 69, 373-385.

  42. Jeffreys, J.G., 1863. British conchology, or an account of the mollusca which now inhabit the British Isles and surrounding seas, vol. 1-5. London: John van Voorst.

  43. Johansson ,G., Eriksson, B.K., Pedersen, M. & Snoeijs, P., 1998. Long term changes of macroalgal vegetation in the Skagerrak area. Hydrobiologia, 385, 121-138.

  44. Jones, L.A., Hiscock, K. & Connor, D.W., 2000. Marine habitat reviews. A summary of ecological requirements and sensitivity characteristics for the conservation and management of marine SACs. Joint Nature Conservation Committee, Peterborough. (UK Marine SACs Project report.). Available from: http://www.ukmarinesac.org.uk/pdfs/marine-habitats-review.pdf

  45. Julshamn, K. & Andersen, K-J., 1983. Subcellular distribution of major and minor elements in unexposed molluscs in western Norway-III. The distribution and binding of ..................in the kidney and the digestive system of the horse mussel Modiolus modiolus. Comparative Biochemistry and Physiology, 75A, 17-20.

  46. Kain, J.M., 1975a. Algal recolonization of some cleared subtidal areas. Journal of Ecology, 63, 739-765.

  47. Kain, J.M., & Norton, T.A., 1990. Marine Ecology. In Biology of the Red Algae, (ed. K.M. Cole & Sheath, R.G.). Cambridge: Cambridge University Press.

  48. Kaiser, M.J. & Spencer, B.E., 1995. Survival of by-catch from a beam trawl. Marine Ecology Progress Series, 126, 31-38.

  49. Kenchington, E.L.R., Gilkinson, K.D., MacIsaac, K.G., Bourbonnais-Boyce, C., Kenchington, T.J., Smith, S.J. & Gordon Jr, D.C., 2006. Effects of experimental otter trawling on benthic assemblages on Western Bank, northwest Atlantic Ocean. Journal of Sea Research, 56 (3), 249-270.

  50. Landsberg, J.H., 1996. Neoplasia and biotoxins in bivalves: is there a connection? Journal of Shellfish Research, 15, 203-230.

  51. Lindenbaum, C., Bennell, J.D., Rees, E.I.S., McClean, D., Cook, W., Wheeler, A.J. & Sanderson, W.G., 2008. Small-scale variation within a Modiolus modiolus (Mollusca: Bivalvia) reef in the Irish Sea: I. Seabed mapping and reef morphology. Journal of the Marine Biological Association of the UK, 88 (01), 133-141.

  52. Livingstone, D.R. & Pipe, R.K., 1992. Mussels and environmental contaminants: molecular and cellular aspects. In The mussel Mytilus: ecology, physiology, genetics and culture, (ed. E.M. Gosling), pp. 425-464. Amsterdam: Elsevier Science Publ. [Developments in Aquaculture and Fisheries Science, no. 25]

  53. Long, D., 2006. BGS detailed explanation of seabed sediment modified Folk classification. Available from: http://www.emodnet-seabedhabitats.eu/PDF/GMHM3_Detailed_explanation_of_seabed_sediment_classification.pdf

  54. Mackie, A.S.Y., Oliver, P.G. & Rees, E.I.S., 1995. Benthic biodiversity in the southern Irish Sea. Studies in Marine Biodiversity and Systematics from the National Museum of Wales. BIOMOR Reports, no. 1.

  55. Magorrian, B.H. & Service, M., 1998. Analysis of underwater visual data to identify the impact of physical disturbance on horse mussel (Modiolus modiolus) beds. Marine Pollution Bulletin, 36, 354-359.

  56. Mair, J.M., Moore, C.G., Kingston, P.F. & Harries, D.B. , 2000. A review of the status, ecology and conservation of horse mussel Modiouls modiolus beds in Scotland. Scottish Natural Heritage Commissioned Report.   F99PA08.

  57. May, S.J. & Pearson, T.H., 1995. Effects of oil-industry operations on the macrobenthos of Sullom Voe. Proceedings of the Royal Society of Edinburgh, 103B, 69-97.

  58. Migné, A. & Davoult, D., 1997b. Carbon dioxide production and metabolic parameters in the ophiurid Ophiothrix fragilis. Marine Biology, 127, 699-704.

  59. Muschenheim, D.K. & Milligan, T.G., 1998. Benthic boundary level processes and seston modification in the Bay of Fundy (Canada). Vie et milieu, Paris, 48, 285-294.

  60. Navarro, J.M. & Thompson, R.J., 1996. Physiological energetics of the horse mussel Modiolus modiolus in a cold ocean environment. Marine Ecology Progress Series, 138, 135-148.

  61. Navarro, J.M. & Thompson, R.J., 1997. Biodeposition by the horse mussel Modiolus modiolus (Dillwyn) during the spring diatom bloom. Journal of Experimental Marine Biology and Ecology, 209, 1-13.

  62. Newton, L.C. & McKenzie, J.D., 1995. Echinoderms and oil pollution: a potential stress assay using bacterial symbionts. Marine Pollution Bulletin, 31, 453-456.

  63. Nichols, D., 1984. An investigation of the population dynamics of the common edible sea urchin (Echinus esculentus L.) in relation to species conservation management. Report to Department of the Environment and Nature Conservancy Council from the Department of Biological Sciences, University of Exeter.

  64. Norton, T.A., 1992. Dispersal by macroalgae. British Phycological Journal, 27, 293-301.

  65. O'Brien, P.J. & Dixon, P.S., 1976. Effects of oils and oil components on algae: a review. British Phycological Journal, 11, 115-142.

  66. Ojeda, F.P. & Dearborn, J.H., 1989. Community structure of macroinvertebrates inhabiting the rocky subtidal zone in the Gulf of Maine: seasonal and bathymetric distribution. Marine Ecology Progress Series, 57, 147-161.

  67. OSPAR Commission. 2009. Background document for Modiolus modiolus beds. OSPAR Commission Biodiversity Series. OSPAR Commission: London. Available from: http://www.ospar.org/documents?v=7193

  68. Pierce, S.K., 1970. The water balance of Modiolus (Mollusca: Bivalvia: Mytilidae): osmotic concentrations in changing salinities. Comparative Biochemistry and Physiology, 36, 521-533.

  69. Ramsay, K., Kaiser, M.J., Rijnsdorp, S.D., Craeymeersch, J.A. & Ellis, J., 2000. Impact of trawling on populations of the invertebrate scavenger Asterias rubens. In Effects of fishing on non-target species and habitats. Biological, conservation and socio-economic issues (ed. M.J. Kaiser & S.J. de Groot), pp. 151-162.

  70. Rees, E.I.S., Sanderson, W.G., Mackie, A.S.Y. & Holt, R.H.F., 2008. Small-scale variation within a Modiolus modiolus (Mollusca: Bivalvia) reef in the Irish Sea. III. Crevice, sediment infauna and epifauna from targeted cores. Journal of the Marine Biological Association of the United Kingdom, 88 (01), 151-156.

  71. Rees, I., 2009. Assessment of Modiolus modiolus beds in the OSPAR area. Prepared on behalf of Joint Nature Conservation Committee.

  72. Richardson, C.A., Chensery, S.R.N. & Cook, J.M., 2001. Assessing the history of trace metal (Cu, Zn, Pb) contamination in the North Sea through laser ablation - ICP-MS of horse mussel Modiolus modiolus shells Marine Ecology Progress Series, 211, 157-167.

  73. Rietema, H., 1993. Ecotypic differences between Baltic and North Sea populations of Delesseria sanguinea and Membranoptera alata. Botanica Marina, 36, 15-21.

  74. Rowell, T.W., 1967. Some aspects of the ecology, growth and reproduction of the horse mussel Modiolus modiolus. , MSc Thesis. Queens' University, Ontario

  75. Sebens, K.P., 1985. Community ecology of vertical rock walls in the Gulf of Maine: small-scale processes and alternative community states. In The Ecology of Rocky Coasts: essays presented to J.R. Lewis, D.Sc. (ed. P.G. Moore & R. Seed), pp. 346-371. London: Hodder & Stoughton Ltd.

  76. Seed, R. & Brown, R.A., 1975. The influence of reproductive cycle, growth, and mortality on population structure in Modiolus modiolus (l.), Cerastoderma edule (L.) and Mytilus edulis L. (Mollusca: Bivalvia). In Proceedings of the 9th European Marine Biology Symposium, Dunstaffnage Marine Laboratory, Oban, 2-8 October, 1974, (ed. H. Barnes), pp. 257-274.

  77. Seed, R. & Brown, R.A., 1977. A comparison of the reproductive cycles of Modiolus modiolus (L.), Cerastoderma (=Cardium) edule (L.), and Mytilus edulis L. in Strangford Lough, Northern Ireland. Oecologia, 30, 173-188.

  78. Seed, R. & Brown, R.A., 1978. Growth as a strategy for survival in two marine bivalves, Cerastoderma edule and Modiolus modiolus. Journal of Animal Ecology, 47, 283-292.

  79. Service, M. & Magorrian, B.H., 1997. The extent and temporal variation of disturbance to epibenthic communities in Strangford Lough, Northern Ireland. Journal of the Marine Biological Association of the United Kingdom, 77, 1151-1164.

  80. Service, M., 1998. Recovery of benthic communities in Strangford Lough following changes in fishing practice. ICES Council Meeting Paper, CM 1998/V.6, 13pp., Copenhagen: International Council for the Exploration of the Sea (ICES).

  81. Shumway, S.E., 1977. Effect of salinity fluctuations on the osmotic pressure and Na+, Ca2+ and Mg2+ ion concentrations in the hemolymph of bivalve molluscs. Marine Biology, 41, 153-177.

  82. Shumway, S.E., 1990. A review of the effects of algal blooms on shellfish and aquaculture. Journal of the World Aquaculture Society, 21, 65-104.

  83. Smaal, A.C., 1994. Theme V: The response of benthic suspension feeders to environmental changes. The Oosterschelde Estuary (The Netherlands): A case study of a changing ecosystem. Hydrobiologia, 282-283, 355-357.

  84. Smith, J.E. (ed.), 1968. 'Torrey Canyon'. Pollution and marine life. Cambridge: Cambridge University Press.

  85. Stachowitsch, M., 1984. Mass mortality in the Gulf of Trieste: the course of community destruction. Marine Ecology, Pubblicazione della Statione Zoologica di Napoli, 5, 243-264.

  86. Strain, E. M. A., Allcock, A. L., Goodwin, C. E., Maggs, C. A., Picton, B. E., & Roberts, D. 2012. The long-term impacts of fisheries on epifaunal assemblage function and structure, in a Special Area of Conservation. Journal of Sea Research, 67(1), 58-68.

  87. Suchanek, T.H., 1985. Mussels and their role in structuring rocky shore communities. In The Ecology of Rocky Coasts: essays presented to J.R. Lewis, D.Sc., (ed. P.G. Moore & R. Seed), pp. 70-96.

  88. Suchanek, T.H., 1993. Oil impacts on marine invertebrate populations and communities. American Zoologist, 33, 510-523.

  89. Theede, H., Ponat, A., Hiroki, K. & Schlieper, C., 1969. Studies on the resistance of marine bottom invertebrates to oxygen-deficiency and hydrogen sulphide. Marine Biology, 2, 325-337.

  90. Tillin, H. & Tyler-Walters, H., 2014. Assessing the sensitivity of subtidal sedimentary habitats to pressures associated with marine activities. Phase 2 Report – Literature review and sensitivity assessments for ecological groups for circalittoral and offshore Level 5 biotopes. JNCC Report No. 512B,  260 pp. Available from: www.marlin.ac.uk/publications

  91. Ursin, E., 1960. A quantitative investigation of the echinoderm fauna of the central North Sea. Meddelelser fra Danmark Fiskeri-og-Havundersogelser, 2 (24), pp. 204.

  92. Veale, L.O., Hill, A.S., Hawkins, S.J. & Brand, A.R., 2000. Effects of long term physical disturbance by scallop fishing on subtidal epifaunal assemblages and habitats. Marine Biology, 137, 325-337.

  93. Warner, G.F. & Woodley, J.D., 1975. Suspension feeding in the brittle star Ophiothrix fragilis. Journal of the Marine Biological Association of the United Kingdom, 55, 199-210.

  94. Warner, G.F., 1971. On the ecology of a dense bed of the brittle star Ophiothrix fragilis. Journal of the Marine Biological Association of the United Kingdom, 51, 267-282.

  95. Wiborg, F.K., 1946. Undersøkelser over oskellet (Modiolus modiolus (L.)). Fiskeridirektoratets Skrifter (ser. Havundsrsøkelser), 8, 85.

  96. Widdows, J., Donkin, P., Brinsley, M.D., Evans, S.V., Salkeld, P.N., Franklin, A., Law, R.J. & Waldock, M.J., 1995. Scope for growth and contaminant levels in North Sea mussels Mytilus edulis. Marine Ecology Progress Series, 127, 131-148.

  97. Wildish, D.J. & Fader, G.B.J., 1998. Pelagic-benthic coupling in the Bay of Fundy. Hydrobiologia, 375/376, 369-380.

  98. Wildish, D.J. & Kristmanson, D.D., 1984. Importance of mussels of the benthic boundary layer. Canadian Journal of Fisheries and Aquatic Sciences, 41, 1618-1625.

  99. Wildish, D.J. & Kristmanson, D.D., 1985. Control of suspension feeding bivalve production by current speed. Helgolander Meeresuntersuchungen, 39, 237-243.

  100. Wildish, D.J., Akage, H.M. & Hamilton, N., 2000. Effects of velocity on horse mussel initial feeding behaviour. Canadian Technical Report of Fisheries and Aquatic Sciences, no. 2325, 34pp.

  101. Wildish, D.J., Fader, G.B.J., Lawton, P. & MacDonald, A.J., 1998. The acoustic detection and characteristics of sublittoral bivalve reefs in the Bay of Fundy. Continental Shelf Research, 18, 105-113.

  102. Witman, J.D., 1984. Ecology of rocky subtidal communities: the role of Modiolus modiolus (L.) and the influence of disturbance, competition and mutalism. , Ph.D. thesis. University of New Hampshire, Durham, USA.

  103. Witman, J.D., 1985. Refuges, biological disturbance and rocky subtidal community structure in New England. Ecological Monographs, 55, 421-445.

  104. Young, G.A., 1985. Byssus thread formation by the mussel Mytilus edulis: effects of environmental factors. Marine Ecology Progress Series, 24, 261-271.

Citation

This review can be cited as:

Tillin, H.M. 2016. [Modiolus modiolus] beds on open coast circalittoral mixed sediment. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/342

Last Updated: 04/01/2016