Virgularia mirabilis and Ophiura spp. with Pecten maximus on circalittoral sandy or shelly mud

10-11-2004
Researched byJacqueline Hill & Dr Harvey Tyler-Walters Refereed byDr David Hughes
EUNIS CodeA5.354 EUNIS NameVirgularia mirabilis and Ophiura spp. with Pecten maximus on circalittoral sandy or shelly mud

Summary

UK and Ireland classification

EUNIS 2008A5.354Virgularia mirabilis and Ophiura spp. with Pecten maximus on circalittoral sandy or shelly mud
EUNIS 2006A5.354Virgularia mirabilis and Ophiura spp. with Pecten maximus on circalittoral sandy or shelly mud
JNCC 2004SS.SMu.CSaMu.VirOphPmaxVirgularia mirabilis and Ophiura spp. with Pecten maximus on circalittoral sandy or shelly mud
1997 BiotopeSS.CMS._.VirOphVirgularia mirabilis and Ophiura spp. on circalittoral sandy or shelly mud

Description

Circalittoral fine sandy mud may contain Virgularia mirabilis and Ophiura spp. A variety of species may occur, and species composition at a particular site may relate, to some extent, to the proportions of the major sediment size fractions. Several species are common to most sites including Virgularia mirabilis which is present in moderate numbers,Ophiura albida, and Ophiura ophiura which are often quite common, and Pecten maximus which is usually only present in low numbers. Virgularia mirabilis is usually accompanied by occasional Cerianthus lloydii, Liocarcinus depurator, and Pagurus bernhardus. Amphiura chiajei and Amphiura filiformis may occur in some examples of this biotope. Polychaetes and bivalves are generally the main components of the infauna, although the nemerteans, Edwardsia claparedii, Phoronis muelleri and Labidoplax buski may also be widespread. Of the polychaetes Goniada maculata, Nephtys incisa, Minuspio cirrifera, Chaetozone setosa, Notomastus latericeus and Owenia fusiformis are often the most widespread species whilst Myrtea spinifera, Lucinoma borealis, Mysella bidentata, Abra alba and Corbula gibba are typical bivalves in this biotope. This biotope is primarily identified on the basis of its epifauna and may be an epibiotic overlay over other closely related biotopes such as AfilMysAnit and AfilNten. The biotope is particularly common in sea lochs. (Information from Connor et al., 2004).

Recorded distribution in Britain and Ireland

In Britain occurrence of this biotope is mainly restricted to sealochs on the west coast of Scotland. Also recorded from Orkney and Galway Bay, west Ireland.

Depth range

0-5 m, 20-30 m, 5-10 m

Additional information

This review represents the sensitivity of the CSaMu.VirOphPmax and its sub-biotope CSaMu.VirOphPmax.HAs. Any differences in the response to individual pressures between the biotope and its sub-biotope are highlighted in the text. 

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JNCC

Habitat review

Ecology

Ecological and functional relationships

  • The characterizing and other species in this biotope occupy space in the habitat but their presence is most likely primarily determined by the occurrence of a suitable substratum rather by interspecific interactions. Virgularia mirabilis and brittlestars are functionally dissimilar and are not necessarily associated with each other but occur in the same muddy sediment habitats. There is no information regarding possible interactions between these species. In addition to Virgularia mirabilis and brittlestars the biotope supports a fauna of smaller less conspicuous species, such as polychaetes and bivalves, living within the sediment.
  • Virgularia mirabilis might be adversely affected by high levels of megafaunal bioturbation, perhaps by preventing the survival of newly settled colonies. Seapens and various species of burrowing megafauna certainly coexist but no investigation of the interaction between them has been found. Burrowing species create tunnels in the sediment which themselves provide a habitat for other burrowing or inquilinistic species.
  • Many of the species living in deep mud biotopes are generally cryptic in nature and not usually subject to predation. Evidence of predation on Virgularia mirabilis by fish seems limited to a report by Marshall & Marshall (1882 in Hoare & Wilson, 1977) where the species was found in the stomach of haddock. Many specimens of Virgularia mirabilis lack the uppermost part of the colony which has been attributed to nibbling by fish. Observations by Hoare & Wilson (1977) suggest however, that predation pressure on this species is low. The sea slug Armina loveni is a specialist predator of Virgularia mirabilis. If present in high abundance, the arms of Amphiura filiformis are an important food source for demersal fish providing significant energy transfer to higher trophic levels. Brittlestars of the genus Ophiura are known to be a common prey for flatfish such as plaice (Downie, 1990 cited in Hughes, 1998b). There are also epibenthic predators/scavengers, such as Liocarcinus depurator and Pagurus prideaux, in the biotope. An increase in the numbers of predators can have an influence on the abundance and diversity of species in benthic habitats (Ambrose, 1993; Wilson, 1991). For example, enclosure experiments in a sea loch in Ireland have shown that high densities of swimming crabs such as Liocarcinus depurator, that feed on benthic polychaetes, molluscs, ophiuroids and small crustaceans, led to a significant decline in infaunal organisms (Thrush, 1986).
  • The majority of the species are suspension feeders so competition for food may occur.
  • When present in high abundance the burrowing and feeding activities of Amphiura filiformis can modify the fabric and increase the mean particle size of the upper layers of the substrata by aggregation of fine particles into faecal pellets. Such actions create a more open fabric with a higher water content which affects the rigidity of the seabed (Rowden et al., 1998). Such destabilisation of the seabed can affect rates of particle resuspension.
  • The hydrodynamic regime, which in turn controls sediment type, is the primary physical environmental factor structuring benthic communities such as CMS.VirOph. The hydrography also affects the water characteristics in terms of salinity, temperature and dissolved oxygen. It is also widely accepted that food availability (see Rosenberg, 1995) and disturbance, such as that created by storms, (see Hall, 1994) are also important factors determining the distribution of species in benthic habitats.

Seasonal and longer term change

  • Species such as the sea pen Virgularia mirabilis and Amphiura filiformis appear to be long-lived and are unlikely to show any significant seasonal changes in abundance or biomass. Seapen faunal communities appear to persist over long periods at the same location. Movement of the sea pen Virgularia mirabilis in and out of the sediment may be influenced by tidal conditions (Hoare & Wilson, 1977).
  • The numbers of some of the other species in the biotope may show peak abundances at certain times of the year due to seasonality of breeding and larval recruitment. Immature individuals of Liorcarcinus depurator, for example, are more frequent in the periods May - September.

Habitat structure and complexity

The biotope has very little structural complexity with most species living in or on the sediment. Several species, such as the sea pen Virgularia mirabilis and the anemone Cerianthus lloydii, extend above the sediment surface. However, apart from a couple of species of nudibranch living on the sea pens and the tubiculous amphipod Photis longicaudata associated with Cerianthus lloydii (Moore & Cameron, 1999) these species do not provide significant habitat for other fauna. Excavation of sediment by infaunal organisms, such as errant polychaetes, ensures that sediment is oxygenated to a greater depth allowing the development of a much richer and/or higher biomass community of species within the sediment.

Productivity

Productivity in subtidal sediments is often quite low. Macroalgae are absent from CMS.VirOph and so productivity is mostly secondary, derived from detritus and organic material. Allochthonous organic material is derived from anthropogenic activity (e.g. sewerage) and natural sources (e.g. plankton, detritus). Autochthonous organic material is formed by benthic microalgae (microphytobenthos e.g. diatoms and euglenoids) and heterotrophic micro-organism production. Organic material is degraded by micro-organisms and the nutrients are recycled. The high surface area of fine particles provides surface for microflora. If present in high abundance the arms of Amphiura filiformis can be an important food source for demersal fish and Nephrops norvegicus providing significant energy transfer to higher trophic levels.

Recruitment processes

  • Virgularia mirabilis and the other major component species in this biotopes appear to have a plankton stage within their life cycle, so colonization is likely to occur from distant sources.
  • The reproductive biology of British sea pens has not been studied, but in other species, for instance Ptilosarcus guerneyi from Washington State in the USA, the eggs and sperm are released from the polyps and fertilization takes place externally. The free-swimming larvae do not feed and settle within seven days if a suitable substratum is available (Chia & Crawford, 1973). The limited data available from other species would suggest a similar pattern of patchy recruitment, slow growth and long life-span for Virgularia mirabilis.
  • Tyler (1977) found that populations of Ophiura albida in the Bristol Channel had a well-marked annual reproductive cycle, with spawning taking place in May and early June. Spent adults and planktonic larvae were observed up to early October. In contrast the larger Ophiura ophiura had a more protracted breeding season.
  • Studies of Amphiura filiformis suggest autumn recruitment (Buchanan, 1964) and spring and autumn (Glémarec, 1979). Using a 265µm mesh size Muus (1981) identified a peak settlement period in the autumn with a maximum of 6800 recruits per m2. Muus (1981) shows the mortality of these settlers to be extremely high with less than 5% contributing to the adult population in any given year. In Galway Bay populations, small individuals make up ca. 5% of the population in any given month, which also suggests the actual level of input into the adult population is extremely low (O'Connor et al., 1983). The species is thought to have a long pelagic life so recruitment can come from distant sources.
  • The scallop Pecten maximus appears to have a long breeding period with peaks in spring and autumn (Fish & Fish, 1996). The veliger larvae are planktonic for about three to four weeks and settle on a wide range of algae, bryozoans and hydroids.

Time for community to reach maturity

No evidence on community development was found. Almost nothing is known about the life cycle and population dynamics of British sea pens, but data from other species suggest that they are likely to be long-lived and slow growing with patchy and intermittent recruitment. The other key species, Amphiura filiformis and Pecten maximus are also long lived and take a relatively long time to reach reproductive maturity. It takes approximately 5-6 years for Amphiura filiformis to grow to maturity so population structure will probably not reach maturity for at least this length of time. In addition, Muus (1981) shows the mortality of new settling Amphiura filiformis to be extremely high with less than 5% contributing to the adult population in any given year. Pecten maximus reaches sexual maturity within the first two to three years and has a life span of 10-20 years. The suggested life span for Ophiura ophiura in the west of Scotland was 5-6 years (Gage, 1990). Many of the other species in the biotope, such as polychaetes and bivalves, are likely to reproduce annually, be shorter lived and reach maturity much more rapidly. However, because the key species in the biotope, Virgularia mirabilis and Amphiura filiformis are long lived and take several years to reach maturity the time for the overall community to reach maturity is also likely to be several years, possibly in the region of 5-10 years.

Additional information

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Preferences & Distribution

Recorded distribution in Britain and Ireland

In Britain occurrence of this biotope is mainly restricted to sealochs on the west coast of Scotland. Also recorded from Orkney and Galway Bay, west Ireland.

Habitat preferences

Depth Range 0-5 m, 20-30 m, 5-10 m
Water clarity preferences
Limiting Nutrients Nitrogen (nitrates), Phosphorus (phosphates)
Salinity Full (30-40 psu)
Physiographic Enclosed coast / Embayment, Sea loch / Sea lough
Biological Zone Circalittoral
Substratum Gravelly mud, Sandy gravelly mud, Sandy mud
Tidal Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave Moderately exposed, Sheltered, Very sheltered
Other preferences

Additional Information

Seapen biotopes occur in wave sheltered sealochs and much deeper open sea suggesting that water movement, particularly being sheltered from wave action, is more important to their existence than light.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

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Additional information

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Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

Virgularia mirabilis and Ophiura spp. are the main important characterizing species, giving the name to the biotope (SS.SMu.CSaMu.VirOphPmax). Cerianthus lloydii is another characteristic member of the epifauna found in the majority of records. Pecten maximus can occur in small numbers but is found in the majority of records of the biotope. Connor et al. (2004) suggested that this biotope represented an epifaunal overlay of other similar sedimentary biotopes such as (e.g. CSaMU.AfilMysAnit or CSaMu.AfilNten, so that members of the infauna are probably found in a range of other biotopes in similar sediments. Amphiura spp. may be present but reaches higher abundance in SMU.CFiMu.SpnMeg or CSaMU.AfilMysAnit. The other characterizing species are mobile (e.g. crabs and hermit crabs) and are not restricted to this biotope.

The sub-biotope CSaMu.VirOphPmax.HAs includes a diverse epifauna of hydroids and ascidians due to the presence of small stones, pebbles, and shell on the surface of the sediment.

Therefore, the assessment of sensitivity is based on the dominant epifauna, sandy or gravelly mud habitat, the important characterizing species Virgularia mirabilis, Ophiura spp., and the characteristic Cerianthus lloydii and Pecten maximus where relevant. The sensitivity of other species is also discussed where relevant.

Resilience and recovery rates of habitat

Little information on the reproduction and life history of Virgularia mirabilis was found.  Edwards & Moore (2009) noted that many sea pens exhibited similar characteristics.  Recent studies of oogenesis in Funiculina. quadrangularis and Pennatula phosphorea in Loch Linnhe, Scotland, demonstrated that they were dioecious, with 1:1 sex ratios, highly fecund, with continuous prolonged oocyte development and annual spawning (Edwards & Moore 2008; Edwards & Moore 2009).  In Pennatula phosphorea, oogenesis exceeded 12 months in duration, with many small oocytes of typically 50 per polyp giving an overall fecundity of ca 40,000 in medium to large specimens, depending on size.  However, <30% matured (synchronously) and were spawned in summer (July-August).  Mature oocytes were large (>500µm) which suggested a lecithotrophic larval development (Edwards & Moore, 2008).  In Funiculina. quadrangularis fecundity was again high, expressed as 500-2000 per 1 cm midsection, but not correlated with size, and again, only a small proportion of the oocytes (<10%) matured.  Unlike Pennatula phosphorea, annual spawning occurred in autumn or winter (between October and January).  In addition, the mature oocytes were very large (>800µm), which suggested a lecithotrophic larval development (Edwards & Moore, 2009).  In a study of the intertidal Virgularia juncea fecundity varied with length (46,000 at 50 cm and 87,000 at 70 cm), reached a maximum size of 200-300 µm in May and were presumed to be spawned between August and September (Soong, 2005). Birkland (1974) found the life span of Ptilosarcus gurneyi to be 15 years, reaching sexual maturity between the ages of 5 and 6 years; while Wilson et al. (2002) noted that larger specimens of a tall sea pen (Halipteris willemoesi) in the Bering Sea were 44 years old, with a growth rate of 3.6 - 6.1cm/year.

Hughes (1998a) suggested that patchy recruitment, slow growth, and long life-span were typical of sea pens.  Larval settlement is likely to be patchy in space and highly episodic in time with no recruitment to the population taking place for some years.  Greathead et al. (2007) noted that patchy distribution is typical for sea pen populations.  In Holyhead harbour, for example, animals show a patchy distribution, probably related to larval settlement (Hoare & Wilson, 1977). 

Virgularia mirabilis was found to withdraw into its burrow rapidly (ca 30 seconds) and could not be uprooted by dragged creels (Hoare & Wilson 1977; Eno et al., 2001; Ambroso et al. 2013).  In summary, British sea pen species have been found to recover rapidly from the effects of dragging, uprooting and smothering (Eno et al. 2001). Recovery from effects that remove a proportion of the sea pen population (e.g. bottom gears, hydrographic changes) will depend on recruitment processes and little is known about the life history and population dynamics of sea pens (Hughes 1998a).

Little evidence was found to support this resilience assessment for Cerianthus lloydii. MES (2010) suggested that the genus Cerianthus would be likely to have a low recovery rate following physical disturbance based on its long-life span and slow growth rate. The MES (2010) review also highlighted that there were gaps in information for this species and that age at sexual maturity and fecundity is unknown although the larvae are pelagic (MES 2010). No empirical evidence was found for recovery rates following perturbations for Cerianthus lloydii. This species has limited horizontal mobility and re-colonization via adults is unlikely (Tillin & Tyler-Walters, 2014).

Ophiura spp. are found in sandy, high-energy environments where the sediment is subject to natural disturbance.  These species have life history traits associated with opportunistic species with short generation times, rapid reproduction, and high dispersal potential. Tyler (1977a) found that populations of Ophiura albida in the Bristol Channel had a well-marked annual reproductive cycle, with spawning taking place in May and early June.  Spent adults and planktonic larvae were found up to early October.  This short annual reproductive period led to the occurrence of distinct size cohorts in the adult population. Dahm (1993) determined a maximum age of 9 years at a disk diameter of 9 mm for specimens from German Bight while Künitzer (cited in Dahm, 1993) suggested a life span of up to 10 years in the North Sea.  In contrast, the larger Ophiura ophiura had a more protracted breeding season, and adult size classes were less distinct (Tyler, 1977a).  Ophiura ophiura is reproductively dormant during summer, with oocytes carried overwinter (Tyler, 1977a). Ophiopluteus larvae occur between March and October but year round spawning is unlikely and, like other brittlestar species, oocytes are laid down at the end of the spawning period,lay dormant over winter and develop in the following year (Wood et al., 2010).  Gage (1990) suggested a life span of 5 -6 years for Ophiura ophiura from the west of Scotland, which agreed with Mortensen’s (1927) estimate for the British Isles. However, analysis of growth rings in specimens from the German Bight suggested a maximum age of 9 yr at a disk diameter of 15.2 mm (Dahm, 1993). Dahm (1993) noted that growth rates and life span may vary regionally but that prior studies probably underestimated age and overestimated growth rate. Boos & Franke (2006) found that Ophuira sp. were amongst the six most common species of brittlestar in the German Bight (North Sea) and were part of a stable community of brittlestars present for ca 130 years.

Recovery of Pecten maximus populations may occur through adult migration over small scales or through recolonisation by larvae.  Pecten maximus can swim for short periods by clapping the valves together.  Swimming is limited in terms of distance and endurance and is primarily reserved for escape reactions given the high energy expenditure involved.  Tagging experiments in Loch Creran, western Scotland, found that the vast majority of tagged Pecten maximus adults were within 30 m of the release point after 18 months (Howell & Fraser, 1984).

Adult scallops, therefore, rely on larval dispersal to ensure geographic distribution of the species (Brand, 1991) and recovery following a decline of the population will rely on larval recruitment.  The timing of spawning may be influenced by both internal and external factors such as genetic adaptation (Ansell et al. 1991) age and temperature respectively (Barber & Blake, 1991).  In general, mature scallops spawn over the summer months from April or May to September.  Dispersal potential in Pecten maximus is high given that the length of the pelagic larval stage exceeds one month (Marshall & Wilson, 2009). The generation time for this species is between two and a half and three years.  

However, factors including hydrographic features and the survival of larvae will determine the extent to which the larvae are dispersed and, consequently, the scallops have an aggregated distribution within their geographic range. The major fishing grounds for scallops are generally so widely separated that respective environmental conditions produce marked differences in population parameters (Brand, 1991). In addition, Sinclair et al. (1985) hypothesized that, by using vertical migrations in the water column, Pecten maximus larvae may be able to maintain their location within the confines of the scallop bed. Darby & Durance (1989) considered the Pecten maximus populations of Eddystone Bay, Wolf Rock, and Cardigan Bay to be self-recruiting and suggested this to be the reason why the Cardigan Bay population has never fully recovered after being fished out in one year. It is also likely that the population of Pecten maximus at Mulroy Bay is self-recruiting (Beaumont, 2005).

Self-recruiting populations are dependent on successful recruitment from within the parent bed.  In St Brieuc, France, entire populations of scallops have been shown to spawn within just a few days (Paulet et al. 1988).  Anything that has the potential to disrupt the success of this mass spawning will adversely affect recruitment to the stock.  In addition, Pecten maximus are generally thought to have a low population turnover (Rees & Dare, 1993) and scallop stock recruitment is highly variable (Beukers-Stewart et al., 2003). Sinclair et al. (1985) stated that if all the scallops are fished out of an area, future recruitment should not be expected from contiguous areas within the time frame of interest to fisheries management and, therefore, some minimum spawning stock must remain in each area to ensure long-term harvesting potential. In the Isle of Man, the larval supply rate is low but constant and the comparatively high and constant recruitment rate of juveniles indicates a very high survival rate when there is a low density of spat present at the end of the settlement season (Beukers-Stewart et al., 2003).

Therefore, providing a certain proportion of the population remains after exploitation, a good spawning episode occurs and suitable environmental conditions prevail after exploitation for the larval, veliger and juvenile stages including a suitable substratum and temperature regime, there is the potential for a strong recruitment and recovery.  Under certain environmental conditions, however, recovery could take significantly longer.  If none of the population remained and the population was thought to be self-recruiting, the population may never fully recover.  Overall, Pecten maximus populations have the potential to recover within ca 2-10 years depending on local recruitment.

Hydroids are often the first organisms to colonize available space in settlement experiments (Gili & Hughes, 1995). Few species of hydroids have specific substrata requirements and many are generalists capable of growing on a variety of substrata.  Hydroids are also capable of asexual reproduction and many species produce dormant, resting stages that are very resistant of environmental perturbation (Gili & Hughes, 1995). Nemertesia antennina releases planulae on mucus threads, that increase potential dispersal to 5 -50m, depending on currents and turbulence (Hughes, 1977). Hughes (1977) noted that only a small percentage of the population of Nemertesia antennina in Torbay developed from dormant, regressed hydrorhizae, the majority of the population developing from planulae as three successive generations. Rapid growth, budding and the formation of stolons allow hydroids to colonize space rapidly. Fragmentation may also provide another route for short distance dispersal. Rafting on floating debris (or hitch hiking on ships hulls or in ship ballast water) as dormant stages or reproductive adults, together with their potentially long life span, may have allowed hydroids to disperse over a wide area in the long term and explain the near cosmopolitan distributions of many hydroid species (Cornelius, 1992; Gili & Hughes, 1995).

Ascidia mentula is a larger (up to 18 cm long) and long-lived (up to 7 years). Recruitment was reported to occur year round in Sweden at depths greater than 20 m, with seasonal spawning occurring at 15 m (where sea temperature variability is much greater). Long-term data from populations of the ascidian Ascidia mentula on subtidal vertical rock indicated that recruitment of Ascidia mentula larvae was positively correlated with adult population density, and then by subsequent active larval choice at smaller scales. Factors influencing larval settlement have been listed as light, substratum inclination and texture (Havenhand & Svane, 1989). On a larger scale, hydrodynamics probably determine the distribution (Olson, 1985; Young, 1986).  Although the ascidian tadpole larva has a short life in the plankton, recruitment, and recovery in ascidians is rapid. For example, Sebens (1985; 1986) described the recolonization of epifauna on vertical rock walls.  Rapid colonizers such as encrusting corallines, encrusting bryozoans, amphipods, and tubeworms recolonized within 1-4 months. Ascidians such as Dendrodoa carnea, Molgula manhattensis and Aplidium spp. achieved significant cover in less than a year.

Resilience assessment. The above evidence suggests that Ophiura spp are opportunistic species, widely distributed around the coasts of the British Isles and North East Atlantic, that can reach high abundances in suitable substrata. Their recovery is likely to be rapid (<2 yr., ‘High’ resilience). Where Virgularia mirabilis survives impact undamaged, that is resistance is ‘High’, recovery is likely to be rapid; a resilience of ‘High’ (<2 years).  However, where a proportion of the population is removed or killed then, although the species has a high dispersal potential and long-lived benthic larvae, larval recruitment is probably sporadic and patchy and growth is slow, suggesting that recovery may take many years; a resilience of ‘Low’ (>10 years). There was little evidence regarding the resilience of Cerianthus lloydii. Therefore, a resilience of ‘Medium’ (2 – 10 years) is suggested for all resistance levels (‘None’, ‘Low’, ‘Medium’ or ‘High’) based on expert judgement.  The resilience of Pecten maximus populations is likely to be variable, depending on local hydrography and larval supply, so that they could recover with a couple of years or take many years so that a resilience of ‘Medium’ (2-10 years) is suggested. However, recovery may be prolonged in self-recruiting populations in isolated areas.

Therefore, the resilience of the biotope is likely to be Low (>10 years) as Virgularia mirabilis is the dominant important characterizing species.  Pecten maximus and Cerianthus lloydii may also take many years to recover from a reduction in abundance or extent (e.g., resistance is Medium to None).   The assessment is based on the reproduction and life history characteristics of the important characteristic species, or similar species rather than direct evidence, except in the case of Pecten maximus. Therefore, while confidence in the quality of the evidence and its concordance is Medium, confidence its application in Low. 

The sub-biotope CSaMu.VirOphPmax.Has is distinguished by the presence of hydroid and ascidian epifauna on small stones and pebbles. Recruitment and recovery in hydroids and most ascidians are likely to be rapid (with 2 years) so that the overall resilience assessment of ‘Low’, (based on Virgularia mirabilis) remains unaffected.

Hydrological Pressures

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

In shallow sea lochs, sedimentary biotopes typically experience seasonal changes in temperature between 5°C and 15°C (10°C) (Hughes, 1998a). Although, unusually warm summers or cold winters may change the temperatures outside this range, benthic burrowing species will be buffered from extremes by their presence in the sediment.

Sea pens can withdraw into their burrows for protection. No information was found on the upper limit of sea pens tolerance to temperature. Virgularia mirabilis is recorded from western Europe, the Mediterranean, from Norway and Iceland to Africa in the North Atlantic, and to the Gulf of Mexico in North America (Hughes, 1998a; OBIS 2015). Jones et al. (2000) suggested that Virgularia mirabilis was probably more tolerant of temperature change than other British sea pen species due to its abundance in shallow waters.

Ophiura albida is distributed from northern Norway to the Azores and the Mediterranean while Ophiura ophiura is distributed from northern Norway to Madeira and the Mediterranean (Hayward & Ryland, 1990). Little evidence on temperature tolerance was found. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40 day experiment.

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean. 

Pecten maximus occurs along the European Atlantic coast from northern Norway, south to the Iberian Peninsula and has been reported off West Africa, the Azores, Canary Islands and Madeira (Marshall & Wilson, 2009).  Temperature is considered by many to be the primary trigger in spawning among Pectinidae (Marshall & Wilson, 2009) and there is some evidence to suggest that there may be a critical range (Barber & Blake, 1991).  In the Bay of Brest and the Bay of St Brieuc in France, for instance, the critical temperature range for spawning is thought to be between 15.5 -16°C (Paulet et al., 1988). No information was available on an upper threshold of temperature tolerance for adult Pecten maximus although Gruffydd & Beaumont (1972) observed high larval mortality above 20°C. 

The distribution of the important characterizing species (Virgularia mirabilis and Ophiura spp.), Cerianthus lloydii and Pecten maximus suggest that they are probably resistant of 2°C change in temperature for a year.  Exposure to short-term acute increase of 5°C may interfere with reproduction may cause Virgularia mirabilis and Cerianthus lloydii to withdraw into their burrows temporarily, have a limited effect on Ophiura ophiura, but potentially interfere with spawning in Pecten maximus.  However, there is no evidence to suggest that mortality would result.  Therefore, a resistance of High is suggested but with Low confidence. Therefore, resilience is High, so that the biotope is probably Not sensitive at the benchmark level.

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

In shallow sea lochs, sedimentary biotopes typically experience seasonal changes in temperature between 5°C and 15°C (10°C) (Hughes, 1998a). Although, unusually warm summers or cold winters may change the temperatures outside this range, benthic burrowing species will be buffered from extremes by their presence in the sediment.

Sea pens can withdraw into their burrows for protection. No information was found on the upper limit of sea pens tolerance to temperature. Virgularia mirabilis is recorded from western Europe, the Mediterranean, from Norway and Iceland to Africa in the North Atlantic, and to the Gulf of Mexico in North America (Hughes, 1998a; OBIS 2015). Jones et al. (2000) suggested that Virgularia mirabilis was probably more tolerant of temperature change than other British sea pen species due to its abundance in shallow waters.

Ophiura albida is distributed from northern Norway to the Azores and the Mediterranean while Ophiura ophiura is distributed from northern Norway to Madeira and the Mediterranean (Hayward & Ryland, 1995). Little evidence on temperature tolerance was found. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40 day experiment.

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean.  Crisp (1964) reported that Cerianthus lloydii in North Wales were apparently unaffected by the severe winter of 1962/63. However, no further information on the temperature tolerance of Cerianthus lloydii was found.

Pecten maximus occurs along the European Atlantic coast from northern Norway, south to the Iberian Peninsula and has been reported off West Africa, the Azores, Canary Islands and Madeira (Marshall & Wilson, 2009).  Temperature is considered by many to be the primary trigger in spawning among Pectinidae (Marshall & Wilson, 2009) and there is some evidence to suggest that there may be a critical range (Barber & Blake, 1991).  In the Bay of Brest and the Bay of St Brieuc in France, for instance, the critical temperature range for spawning is thought to be between 15.5 -16°C (Paulet et al., 1988).

No information was available on an upper threshold of temperature tolerance for adult Pecten maximus although Gruffydd & Beaumont (1972) observed high larval mortality above 20°C.  However, Crisp (1964) reported mortalities approaching 100% of Pecten maximus from several areas around the British coast in the severe winter of 1962-1963 where the average sea temperature fell by approximately 4°C.

Sensitivity assessment. The distribution of the important characterizing species (Virgularia mirabilis and Ophiura spp.), Cerianthus lloydii and Pecten maximus suggest that they are probably resistant of 2°C change in temperature for a year.  Exposure to short-term acute decrease of 5°C may interfere with reproduction may cause Virgularia mirabilis and Cerianthus lloydii to withdraw into their burrows temporarily, have a limited effect on Ophiura ophiuraHowever, Pecten maximus may suffer some mortality, especially in the shallower examples of the biotope Therefore, a resistance of Medium is suggested with Low confidence to represent to the loss of Pecten maximus while the other species in the biotope remain. Resilience is probably High, so that the biotope is assessed with a Low sensitivity at the benchmark level.

Medium Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

No information on the salinity tolerance of the important characterizing species was found.  Cerianthus lloydii may be recorded from the intertidal at LWST, but is probably protected from changes in salinity due to its infaunal habitat, buffered by the salinity of the interstitial water of the sediment. Greathead et al. (2007) demonstrated that Virgularia mirabilis was the most ubiquitous of all three of the sea pens in Scotland, found in habitats nearer coastal areas and inner sea lochs. Jones et al. (2000) suggested that Virgularia mirabilis was more tolerant of reduced salinity than other British sea pens due to its distribution in shallower waters. No information on the salinity preferences of Philine aperta was found.

For Pecten maximus, Christophersen & Strand (2003) found that, in the laboratory, the shells of spat held in water with a low salinity (20 ppt) became thin and easily damaged, which ultimately led to a negative shell growth rate.  The scallops made fewer foot movements and retracted the mantle from the shell margin.  Laing (2002) found that between 13-21°C the growth rate was significantly lower at 26 psu than at 28-30 psu.

The MNCR database indicates biotopes where Ophiura albida and Ophiura ophiura are characterizing species occur in full (30-40 units) as well as variable salinity (18-40 units).  Echinoderms 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).  Ophiura albida from Loch Etive, Scotland tolerated 20.7‰ (Pagett, 1980; Russell, 2013) and only a single individual died at this salinity. The LT50 for 40% seawater (ca 14‰) varied between ca 80 hours ca 400 hours depending on the origin of the specimens. Pagett (1980) noted that salinity tolerance was greatest in those specimens taken from waters at 70% seawater at the head of Loch Etive when compared to those at full salinity near the mouth of the Loch.  Wolff (1968) reported that adult Ophiura albida were not seen at salinities below 16.5‰ Cl. Russell (2013) noted that Ophiura ophiura tolerated 27‰.  

An increase in salinity at the benchmark level would result in a salinity of >40 psu, and as hypersaline water is likely to sink to the seabed, the biotope may be affected by hypersaline effluents. Ruso et al. (2007) reported that changes in the community structure of soft sediment communities due to desalinisation plant effluent in Alicante, Spain. In particular, in close vicinity to the effluent, where the salinity reached 39 psu, the community of polychaetes, crustaceans and molluscs was lost and replaced by one dominated by nematodes. Roberts et al. (2010b) suggested that hypersaline effluent dispersed quickly but was more of a concern at the seabed and in areas of low energy where widespread alternations in the community of soft sediments were observed. In several studies, echinoderms and ascidians were amongst the most sensitive groups examined (Roberts et al., 2010b).

Sensitivity assessment. This biotope (CSaMu.VirOphPmax) is recorded from full and variable salinity regimes. However, although the biotope might occur in sea lochs subject to variable salinity, the benthos may not experience variable salinity at depth, and infauna are protected from short-term changes in salinity due to the salinity of the interstitial waters. However, hypersaline effluent is likely to sink to the seabed and may affect the community. Based on the evidence from Ruso et al. (2006) and Roberts et al. (2010) it is likely that the community will be degraded and, especially, Ophiura and Pecten maximus will leave the affected area or be killed.  The effect on sea pens and anemones is unknown. Therefore, a resistance of Medium is suggested with Low confidence. Resilience is probably Medium so that the sensitivity is assessed as Medium.

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

No information on the salinity tolerance of the important characterizing species was found.  Cerianthus lloydii may be recorded from the intertidal at LWST, but is probably protected from changes in salinity due to its infaunal habitat, buffered by the salinity of the interstitial water of the sediment. Greathead et al. (2007) demonstrated that Virgularia mirabilis was the most ubiquitous of all three of the sea pens in Scotland, found in habitats nearer coastal areas and inner sea lochs. Jones et al. (2000) suggested that Virgularia mirabilis was more tolerant of reduced salinity than other British sea pens due to its distribution in shallower waters. No information on the salinity preferences of Philine aperta was found.

For Pecten maximus, Christophersen & Strand (2003) found that, in the laboratory, the shells of spat held in water with a low salinity (20 ppt) became thin and easily damaged, which ultimately led to a negative shell growth rate.  The scallops made fewer foot movements and retracted the mantle from the shell margin.  Laing (2002) found that between 13-21°C the growth rate was significantly lower at 26 psu than at 28-30 psu.

The MNCR database indicates biotopes where Ophiura albida and Ophiura ophiura are characterizing species occur in full (30-40 units) as well as variable salinity (18-40 units).  Echinoderms 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).  Ophiura albida from Loch Etive, Scotland tolerated 20.7‰ (Pagett, 1980; Russell, 2013) and only a single individual died at this salinity. The LT50 for 40% seawater (ca 14‰) varied between ca 80 hours ca 400 hours depending on the origin of the specimens. Pagett (1980) noted that salinity tolerance was greatest in those specimens taken from waters at 70% seawater at the head of Loch Etive when compared to those at full salinity near the mouth of the Loch.  Wolff, 1968 reported that adult Ophiura albida were not seen at salinities below 16.5‰ Cl. Russell (2013) noted that Ophiura ophiura tolerated 27‰.  

Sensitivity assessment. This biotope (CSaMu.VirOphPmax) is recorded from full and variable salinity regimes. However, although the biotope might occur in sea lochs subject to variable salinity, the benthos may not experience variable salinity at depth, and infauna are protected from short-term changes in salinity due to the salinity of the interstitial waters. A decrease in salinity at the benchmark level would result in a reduced salinity regime. The majority of the important characterizing species are only found in full salinity conditions, except Ophiura albida.  Therefore, such a reduction in salinity probably results in mobile species leaving the biotope, the death of species that could not relocate, and a marked reduction in species richness.  Therefore, a resistance of Low is recorded based on expert judgement. Resilience is probably also Low so that sensitivity is assessed as High.

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

The biotope (CSaMu.VirOphPmax) occurs in low energy environments with weak (<0.5 m/sec.) to very weak tidal streams (Connor et al. 2004), which are a prerequisite for the fine mud sediments characteristic of the biotope.  However, CSaMu.VirophPmax.Has occurs in moderately strong to very weak tidal streams and has a higher coarse sediment content (sand, gravel or shell), although it probably occurs at greater depths in areas of moderately strong tidal flow. Virgularia mirabilis coarser sandier muds with small stones and shell fragments (Hughes, 1998a; Greathead et al., 2007), and is probably more tolerant of current or wave induced flow than other British sea pens. Hiscock (1983) examined the effects of water flow on Virgularia mirabilis.  As water flow rates increase, Virgularia mirabilis first responds by swinging polyps around the axial rod to face away from the current (at 0.12 m/s), then polyps face downstream.  With further increase in flow, the stalk bends over and the pinnae are pushed together to an increasing amount with increasing velocity of flow (at 0.33 m/s).  Finally, tentacles retract and at water speeds greater than 0.5 m/s (i.e. 1 knot) the stalk retracts into the mud (Hiscock, 1983).  If water speeds remain at this level or above the sea-pen will be unable to extend above the sediment, unable to feed and could die (Hill & Wilson, 2000).

Cerianthus lloydii is recorded from biotopes with a wide range of water flow regimes, from very weak to strong flow and in muddy to mixed or coarse sediments (Connor et al., 1997b).Therefore, it is likely to have a high tolerance to changes in water flow regimes.

Pecten maximus lives embedded in recesses in the seabed usually with the upper valve flush with the sediment surface.  This position can facilitate feeding by bringing the inhalant current near to the seabed therefore increasing the intake of detritus (Mason, 1983).  It can also reduce the vulnerability of the scallop to dislodgment through increased water flow rate and wave action.  Growth rates of scallops are generally faster in areas of relatively strong currents and reduced growth rates can occur in areas of low current speeds due to food limitation.  However, excessive particle enrichment, commonly associated with areas of high water flow rate, may reduce the effectiveness of the feeding apparatus and reduce ingestion rates (Gibson, 1956).  A reduction in water flow rate may reduce the availability of food particles but it is not likely that this reduction would adversely affect the growth and general condition of the scallop.  Bricelj & Shumway (1991) suggested that scallops can compensate for short-term changes in the availability of food by adjusting the clearance rate of food particles.  Pecten maximus is recorded from biotopes in moderately strong to very weak tidal flow (Connor et al., 1997b).

Ophiura albida and Ophiura ophiura are both recorded in biotopes from very weak to moderately strong (negligible - 1.5m/s) tidal flow (Connor et al., 1997b). Both species are reported to occur on a range of soft sediments (Hayward & Ryland, 1990) including muds, gravel, sand and shell (Boos et al., 2010). Ophiura albida showed a preference for fine sediments due to its habit of burrowing to escape predators, and its preference for surface deposit feeding and scavenging or predating on fine grained sediments (Boos et al., 2010). Ophiura ophiura is larger and demonstrated a little preference of sediment type due to its habit of escaping predators by rapidly moving across the surface of the sediment, together its with relatively unselective predation and scavenging habit (Boos et al., 2010).

Sensitivity assessment. CSaMu.VirOphPmax and CSaMu.VirOphPmax.Has are recorded in weak or very weak flow (Connor et al., 2004) so that a further decrease in flow is not relevant. Increased flow has the potential to modify the sediment, especially at the surface. A significant increase in water flow may winnow away the mud surface or even remove the mud habitat and hence the biotope if prolonged. An increase of 0.2 m/s may begin to erode the mud surface where the site is already subject to flow (e.g. weak flow at the seabed), based on sediment erosion deposition curves (Wright, 2001).  However, given the depth of mud that characterizes the biotope only the surface of the mud may be removed within a year so that it becomes similar to that of CSaMu.VirOphPmax.HAs. Cerianthus lloydii is unlikely to be impacted by a change in the sediment and is a passive predator. Ophiura spp. and Pecten maximus are unlikely to be affected adversely. However, Virgularia mirabilis may be directly affected by an increase in flow, especially if it exceeds 0.5 m/s.  Therefore, a potential reduction in the Virgularia mirabilis abundance may result in the loss this biotope as described by the classification.  Therefore, a resistance of Low is recorded. Resilience is probably also Low so that sensitivity is assessed as High.

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 pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

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

CSaMu.VirOphPmax and CSaMu.VirOphPmax.Has occur in moderately wave exposed to very wave sheltered areas (Connor et al. 2004). As the biotope is dominated by fine muddy sediments it probably occurs are greater depth in the wave exposed rather than weave sheltered areas. Virgularia mirabilis occurs in coastal areas and inner sea lochs but these areas are still sheltered from wave action, and in sandier muds (Hughes, 1998a; Greathead et al. 2007). Cerianthus lloydii is recorded from biotopes from wave exposed to extremely sheltered muddy and in mixed or coarse sediments (Connor et al., 1997b). Therefore, it is likely to tolerate changes in wave action. Ophiura albida is recorded from extremely sheltered to very exposed biotope and Ophiura ophiura from very sheltered to extremely exposed biotopes (Connor et al., 1997b). Pecten maximus is recorded from extremely wave sheltered to wave exposed biotopes.

Sensitivity assessment.  A decrease in wave exposure is unlikely in the sheltered habitats typical of this biotope.  An increase in wave exposure is likely to affect Virgularia mirabilis species adversely, limiting or removing the shallower proportion of the population, and potentially modifying sediment and therefore habitat preferences in the longer-term.  However, a 3-5% increase in significant wave height (the benchmark) is unlikely to be significant. The benchmark level of change may be no more than expected during winter storms even in the sheltered examples of this biotope. Therefore, resistance is recorded as High at the benchmark level. Hence, resilience is High and the biotope is assessed as Not sensitive at the benchmark level.

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 was found

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.

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

Virgularia mirabilis is often found in sea lochs so may be able to tolerate some reduction in oxygenation. However, Jones et al. (2000) reported that sea pen communities were absent from areas which are deoxygenated and characterized by a distinctive bacterial community and Hoare & Wilson (1977) reported that Virgularia mirabilis was absent from sewage related anoxic areas of Holyhead harbour.

Diaz & Rosenberg (1995) noted that anemones include species that were reported to be particularly tolerant of hypoxia (e.g. Cerianthus sp and Epizoanthus erinaceus). A major hypoxic event due a pycnocline in the Gulf of Trieste resulted in a mass mortality of benthos between 12 and 26th September 1983 (Stachowitsch, 1992b), during which the oxygen levels fell below 4.2 mg/l, became anoxic, and hydrogen sulphide and ammonia were released (Faganeli et al., 1985). Amongst the epifauna, the even hypoxia resistant polychaetes and bivalves died after 4-5 days and the only organism to survive after one week were the anemones Cerianthus sp and Epizoanthus erinaceus, the gastropods Aporrhais pespelecani and Trunculariopsis trunculus and the sphinuculid Sipunculus nudis (Stachowitsch, 1992b).

Ophiura albida showed a definite resistance to low oxygen levels with 50% of individuals still surviving after 32 hours in seawater with an oxygen concentration of 0.21 mg/l (Theede et al., 1969). Rosenberg et al. (1991) suggest that some part of the benthic community, including Amphiura filiformis, can withstand oxygen concentrations of around 1 mg/l for several weeks. However, Vistisen & Vismann (1997) noted that the epibenthic Ophiura albida was less tolerant of deoxygenation than Amphiura filiformis. Ophiura albida survived at 10% oxygen saturation for a month but experienced 50% mortality (LT50) after 2.5 days at <1%(anoxia)  No information Ophiura ophiura was found.

Scallops, are incapable of sustaining prolonged valve closure, are relatively intolerant of anoxia (Bricelj & Shumway, 1991). Brand & Roberts (1973) found that scallops transferred to de-oxygenated water (13 mmHg; 0.76 mg O2/l) for three hours experienced rapid bradycardia (reduced heart rate). However, the length of exposure time set in the benchmark is one week which is significantly longer than the length of Brand & Roberts (1973) experimental work. It is likely that scallops will experience some respiratory stress at the benchmark level. It is possible that feeding will be reduced and the animal may become lethargic thus making it more susceptible to predation due to a weakened escape response. This will reduce the viability of the population However, Brand & Roberts (1973) found that the scallops that had been exposed to the deoxygenated water recovered well upon return to well-oxygenated water (135 mmHg; 7.9 mg O2/l).

Sensitivity assessment. The evidence suggests that severe hypoxic or anoxic conditions are likely to be detrimental to sea pens while Cerianthus lloydii may survive even anoxic conditions for a week.   Pecten maximus can survive short-term changes in oxygen levels and aerial exposure but prolonged exposure may be detrimental as it cannot close its valves tightly. It may flee affected areas. Similarly, Ophiura albida may experience some mortality at the benchmark level or significant mortality in anoxic conditions. Therefore, a resistance of Low is suggested to represent the loss of a proportion of the sea pen population, Pecten maximus, and Ophiura  population.  Resilience is probably Low due to the time required for the sea pen population to recover. Therefore, sensitivity is assessed as High.

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

Hoare & Wilson (1977) noted that Virgularia mirabilis was absent from part of the Holyhead Harbour heavily affected by sewage pollution.  However, the species was abundant near the head of Loch Harport, Skye, close to a distillery outfall discharging water enriched in malt and yeast residues and other soluble organic compounds (Nickell & Anderson, 1977; cited in Hughes, 1998a), where the organic content of the sediment was up to 5%.  Virgularia mirabilis was also present in Loch Sween in Scotland in sites where organic content was as high as 4.5% (Atkinson, 1989).

A study in the Bay of Brest (Chauvaud et al., 1998) found that, regardless of the specific phytoplankton composition, high concentrations of chlorophyll-a reduced the daily growth rate of juvenile Pecten maximus. High concentrations of chlorophyll-a following diatom blooms have also been implicated in causing negative effects on the ingestion and respiration of Pecten maximus juveniles either by clogging their gills or by depleting the oxygen at the water-sediment interface during the degradation of organic matter (Lorrain et al., 2000). High levels of nutrient enrichment may lead to eutrophication and the possibility of subsequent increases in turbidity and suspended material and decreases in the amount of available oxygen, depending on other environmental conditions. A decrease in Pecten maximus growth rate and reproduction has been observed in the presence of certain toxic algal blooms (Chauvaud et al., 1998). For instance Gymnodinium cf. nagasakiense can lead to the death of post-larval and juvenile Pecten maximus in the wild (Erard-Le Denn et al., 1990, cited in Chauvaud et al., 1998) and in 1995, three major blooms of Gymnodinium cf. nagasakiense in the Bay of Brest inhibited the settlement of spat, although a rapid return to normal shell growth rates was reported once the numbers of Gymnodinium sp. had decreased (Chauvaud et al., 1998).  In contrast, Reitan et al. (2002) experimentally enhanced the nutrient supply in a landlocked bay in Norway and found that the resulting increase in the phytoplankton biomass had a significant positive effect on growth rates of Pecten maximus.

Borja et al. (2000) and Gittenberger & van Loon (2011) assigned Cerianthus lloydii to their Ecological Group I, ‘species very sensitive to organic enrichment and present under unpolluted conditions (initial state)’. But Amphiura filiformis, Ophiura albida and Ophiura ophiura were assigned to their Ecological Group II (Species indifferent to enrichment, always present in low densities with non-significant variations with time) (from initial state, to slight unbalance) (Gittenberger & van Loon, 2011).  The basis for their assessment and relation to the pressure benchmark is not clear.  Both Ophiura spp. are capable of surface deposit feeding and may benefit from some organic enrichment at the benchmark level.

Sensitivity assessment. Sublittoral muds may be expected to be high in organic nutrients, and the presence of Virgularia mirabilis in areas of up to 4.5% organic carbon (Atkinson, 1989) suggest a resistance to organic enrichment or nutrient enrichment.  Ophiura spp. may benefit from nutrient enrichment. However, algal blooms may be detrimental to Pecten maximus, depending on local conditions. Nevertheless, the biotope is assessed as Not sensitive at the pressure benchmark of compliance with all relevant environmental protection standards.

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

Hoare & Wilson (1977) noted that Virgularia mirabilis was absent from part of the Holyhead Harbour heavily affected by sewage pollution.  However, the species was abundant near the head of Loch Harport, Skye, close to a distillery outfall discharging water enriched in malt and yeast residues and other soluble organic compounds (Nickell & Anderson, 1977; cited in Hughes, 1998a), where the organic content of the sediment was up to 5%.  Virgularia mirabilis was also present in Loch Sween in Scotland in sites where organic content was as high as 4.5% (Atkinson, 1989).  Wilding (2011) noted that the abundance of Pennatula phosphorea was inversely correlated with predicted Infaunal Trophic Index (a predicted estimate of organic waste build-up) around salmon farms in Scotland, but that the effect only extended for 50m from the cages.

Borja et al. (2000) and Gittenberger & van Loon (2011) assigned Cerianthus lloydii to their Ecological Group I, ‘species very sensitive to organic enrichment and present under unpolluted conditions (initial state)’. But Amphiura filiformis, Ophiura albida and Ophiura ophiura were assigned to their Ecological Group II (Species indifferent to enrichment, always present in low densities with non-significant variations with time) (from initial state, to slight unbalance) (Gittenberger & van Loon, 2011).  The basis for their assessment and relation to the pressure benchmark is not clear.  Both Ophiura spp. are capable of surface deposit feeding and may benefit from some organic enrichment at the benchmark level.

No evidence on the effects of organic enrichment on Pecten maximus was found. Although Pecten maximus occurs in this biotope, the areas with the highest abundance and the fastest growth rates of scallops are usually in areas with little mud (Brand, 1991). Gruffydd (1974) found that the maximum shell size of Pecten maximus from the north Irish Sea was significantly negatively correlated with increasing mud content in the sediment. 

An increasing gradient of organic enrichment (e.g. in the vicinity of point sources of organic-rich effluent or sewage sludge dump sites) 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). The effects of organic enrichment on burrowing megafauna and other infauna depended on the degree of enrichment and any resultant hypoxia, which depend on the sediment type and local hydrology.

Sensitivity assessment. Sublittoral muds may be expected to be high in organic nutrients, and the presence of Virgularia mirabilis in areas of up to 4.5% organic carbon (Atkinson, 1989) suggest a resistance to organic enrichment at the benchmark level.  Ophiura spp. may benefit from organic enrichment at the benchmark level but Cerianthus may be lost.  It is unclear what effect organic enrichment may have on Pecten maximus within the biotope. Therefore, a precautionary resistance of Medium is suggested, and as resilience is probably Low, a sensitivity of Medium is recorded.    

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

If sedimentary substrata were replaced with rock substrata the biotope would be lost, as it would not longer be a sedimentary habitat and would no longer support sea pens, burrowing anemones, epibenthic brittlestars or infauna.

Sensitivity assessment. Resistance to the pressure is considered ’None‘, and resilience ’Very low‘ or ‘None’ (as the pressure represents a permanent change) and the sensitivity of this biotope is assessed as ’High’.

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

Virgularia mirabilis occurs in a number of biotopes, on substrata ranging from mud, sandy mud, and gravelly mud, with or with shell fragments or stones (Connor et al., 2004).  Greathead et al. (2007) suggested that the muscular peduncle of Virgularia mirabilis allowed it to occupy coarser muds than the other sea pens, and explained its presence in the Moray Firth and Firth of Forth, and its wider distribution in Scotland. In addition, a 'mud' substratum was the most important factor in a habitat suitability index model for sea pens developed by Greathead et al. (2015). In their model, habitat suitability for Funiculina quadrangularis increased with mud content up to a maximum at 90-100% mud. Pennatula phosphorea and Virgularia mirabilis also had their maximum habitat suitability at 100% mud.  All three species had zero habitat suitability at 0% mud. However, gravel content was also important. Virgularia mirabilis was the most tolerant of gravel content and was still recorded at 50% gravel while the were no records of Pennatula phosporea and Funiculina quadrangularis above 40% and 30% gravel respectively (Greathead et al., 2015).

Cerianthus lloydii is recorded from biotopes in muddy to mixed or coarse sediments (Connor et al., 1997b). Therefore, it is likely to tolerate changes in sediment type. Similarly, Pecten maximus is recorded from gravel, coarse and fine clean sand, muddy sand and sandy muds.

Ophiura albida and Ophiura ophiura are both reported to occur on a range of soft sediments (Hayward & Ryland, 1990) including muds, gravel, sand and shell (Boos et al., 2010). Ophiura albida showed a preference for fine sediments due to its habit of burrowing to escape predators, and its preference for surface deposit feeding and scavenging or predating on fine grained sediments (Boos et al., 2010). Ophiura ophiura is larger and demonstrated a little preference of sediment type due to its habit of escaping predators by rapidly moving across the surface of the sediment, together its with relatively unselective predation and scavenging habit (Boos et al., 2010).

Sensitivity assessment. While the important characteristic species are recorded from a range of sediment types, CSaMu.VirOphPmax is defined by its occurrence in sandy mud or as CSaMu.VirOphPmax.HAs in sandy gravelly mud (Connor et al., 2004).  Therefore, a change in sediment type by one Folk class (see Long, 2006), e.g. from ‘sandy mud’ to ‘sand’ or from ‘sandy or gravelly mud’ to ‘muddy gravel’ would result in loss of the biotope.  Therefore, a resistance of None is recorded.  As the change is permanent, resilience is Very low and sensitivity is assessed as High.

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

Benthic trawls (e.g. rock hopper ground gear, otter trawls) will remove and capture sea pens (Tuck et al., 1998; Kenchington et al., 2011), albeit with limited efficiency. Nevertheless, dredging and suction dredging penetrates to greater depth and are likely to remove sea pens. Virgularia mirabilis will not be able to avoid activities that penetrate into the sediment. Assuming their burrows are only deep enough to hold the entire animal (see Greathead et al., 2007 for sizes) then Virgularia mirabilis burrows are up to 40 cm deep.

Cerianthus lloydii can also withdraw into the sediment, and its burrow is up to 40 cm deep. However, Ophiura spp. only burrow into the surface of the sediment while Pecten maximus lives embedded in recesses in the seabed usually with the upper valve flush with the sediment surface.

Sensitivity assessment. Extraction of sediment to 30 cm (the benchmark) could remove most of the resident sea pens present, the burrowing sea anemones, and epifauna, from the affected area.  Hence, the resistance is probably None. Resilience is probably Low, resulting in a sensitivity of High.

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

Stable sedimentary habitats, such as mud were amongst the most vulnerable to fishing activities, e.g. otter trawling (Ball et al., 2000; Collie et al., 2000). Tracks left by otter boards were visible 18 months after experimental trawls in Gareloch (Ball et al., 2000). Ball et al., (2000) concluded that trawling modified the benthic community due to an increase in opportunistic polychaetes. However, Kaiser et al. (2006) concluded that otter boards had a significant initial effect on muddy sands and muds, but that the effects were short-lived in mud habitats.

In experimental studies (Kinnear et al. 1996; Eno et al. 2001), sea pens were found to be largely resilient to smothering, dragging, or uprooting by creels or pots.  Virgularia mirabilis withdrew very quickly into the sediment when exposed to pots or creels so that it was difficult to determine their response.  However, all sea pens recovered from being dragged over by pots or creels within 24-72 h, with the exception of one individual Funiculina quadrangularis

In Virgularia mirabilis withdrawal from physical stimulus is rapid (ca 30 seconds) (Hoare & Wilson, 1977; Ambroso et al., 2013).  Birkland (1974) maintained that the only way to capture all of the sea pens in an area (quadrat) was to remove them slowly by hand until no more emerged.  But several studies note that their ability to withdraw into the sediment in response to bottom towed or dropped gear (e.g. creels, pots, camera/video mounted towed sleds, experimental grab, trawl, or dredge) means that sea pen  abundance can be difficult to estimate (Birkeland, 1974; Eno et al., 2001; Greathead et al., 2007; Greathead et al., 2011).  The ability to withdraw also suggests that sea pens can avoid approaching demersal trawls and fishing gear.  This was suggested as the explanation for the similarity in the densities of Virgularia mirabilis in trawled and untrawled sites in Loch Fyne, and the lack of change in sea pen density observed after experimental trawling (using modified rock hopper ground gear) over a 18 month period in Loch Gareloch (Howson & Davies 1991; Hughes 1998a; Tuck et al. 1998).  Kenchington et al. (2011) estimated the gear efficiency of otter trawls for sea pens (Anthoptilum and Pennatula) to be in the range of 3.7 – 8.2%, based on estimates of sea pen biomass from (non-destructive) towed camera surveys.  However, species obtained by dredges were invariably damaged (Hoare & Wilson, 1977).  Hoare & Wilson (1977) noted that Virgularia was absent for areas of Holyhead Harbour disturbed by dragging or boat mooring, although no causal evidence was given (Hughes, 1998a).  Sea pens are potentially vulnerable to long lining.  Munoz et al. (2011) noted that small numbers of Pennatulids (inc. Pennatula sp.) were retrieved from experimental long-lining around the Hatton Bank in the north east Atlantic, presumably either attached to hooks or wrapped in line as it passed across the sediment.  Hixon & Tissot (2007) noted that sea pens (Stylatula sp.) were four times more abundant in untrawled areas relative to trawled areas in the Coquille Bank, Oregon, although no causal relationship was shown. 

No information on the effects of abrasion or penetrative gear on Cerianthus lloydii was found. Greathead et al. (2011) were not able to conclude if the variation in Cerianthus abundance in the Fladden Grounds was due to miscounting, its patchy distribution, or fishing activity. 

Pecten maximus is the target of commercial fisheries and hence, gears have been developed to capture this species.  By-catch studies suggest that due to their robust shells captured Pecten maximus suffer low rates of damage.  Jenkins et al. (2001) found that less than 10% of scallops encountering dredges showed any signs of external physical damage on a scallop fishing ground in the north Irish Sea.  Undamaged Pecten maximus captured using dredges, show low levels (5%). of mortality in the laboratory (Jenkins et al., 2001).  Similarly (Bergmann et al., 2001) found that most (98%) of queen scallops Aequipecten opercularis were undamaged when retained in otter trawl hauls in the Clyde Seas Nephrops fishery.  Damage was restricted to chipping of the outer shell.  Ansell et al. (1991) however, stated that up to 19% of the scallops left behind by a dredge are affected to some extent.  Individuals with damaged shells are more prone to predation.  However, Jenkins et al. (2001) reported that, during dredging, more than 90% of Pecten maximus that came into contact with a dredge (including those landed, discarded and left behind by the dredge) were in good condition overall and showed little or no shell damage.  The differences between reported rates of effect may be due to different classification systems used to score impacts. 

Blyth et al. (2004) compared sites that were trawled for scallops to those that were untrawled or previously trawled but not in the 18-24 months prior to the study. They found that significantly fewer scallops were caught in the trawled sites.  They suggested that at least a two year period was necessary for the benthic community to recover to a state that was indistinguishable from non-trawled areas.

Ophiura ophiura is a common by-catch in Nephrops otter trawl fishery in the Clyde Sea.  Bergmann et al. (2001) reported that 100% of the Ophiura ophiura catch as by-catch were damaged. Damage ranged from broken arms to broken discs, and damage increased with animal size. However, Bergmann & Moore (2001b) noted that post-trawling mortality of discarded Ophiura ophiura was 100% within 14 days and that even immediate re-emersion in seawater only reduced mortality to 91%.  In contrast, Bradshaw et al. (2000, 2002) noted that Ophiura albida was consistently more abundant in gravelly sediments dredged by scallop dredges around the Isle of Man, presumably due to their good powers of regeneration and small size. Ophiura ophiura and Ophiura albida were recorded regularly in baited traps, sometimes in relatively high numbers, indicating that these species are mobile and exhibit scavenging behaviour (Groenewold & Fonds, 2000). Ophiura ophiura has been observed scavenging in trawl tracks after the passage of a scallop dredge although divers noted that many were damaged (Ramsay et al., 1998).

Bradshaw et al. (2002) also noted that small tunicates (e.g. Ascidiella) and hydroids (e.g. Nemertesia) were also more abundant in scallop dredged areas, presumably due to their ability to recover rapidly.

Sensitivity assessment. The reviews by Ball et al. (2000), Collie et al. (2000) and Kasier et al. (2006) suggest that stable sediments, e.g. muds and sandy muds are likely to be vulnerable to fishing activities. Cerianthus lloydii will probably withdraw into the sediment to avoid surface abrasion by trawls or pots. While Ophiura ophiura is common by-catch and probably suffers high mortality as a result, it can probably recover quickly and the smaller Ophiura albida may increase in abundance. The evidence for Virgularia mirabilis suggests that its ability to withdraw into the sediment quickly would avoid surface abrasion from creels and pots but that dragging and mooring lines may be damaging, and individuals may be caught and removed by fishing lines (e.g. long-lines). Pecten maximus may be directly targeted and a proportion of the population removed although scallop dredge efficiency is relatively low (Dare et al. 1993).   Therefore, a resistance of Medium is recorded due to the potential disturbance to the biotope as a whole.  As the impact may be limited (see Kenchington et al., 2011), a resilience of Medium is suggested and sensitivity is assessed as Medium.

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

Sensitivity assessment. The reviews by Ball et al. (2000), Collie et al. (2000) and Kasier et al. (2006) suggest that stable sediments, e.g. muds and sandy muds are likely to be vulnerable to fishing activities. Based on the evidence presented under abrasion, Cerianthus lloydii will probably withdraw into the sediment to avoid surface abrasion by trawls or pots. While Ophiura ophiura is common by-catch and probably suffers high mortality as a result, it can probably recover quickly and the smaller Ophiura albida may increase in abundance. The evidence for Virgularia mirabilis suggests that its ability to withdraw into the sediment quickly would avoid surface abrasion from creels and pots but that dragging and mooring lines may be damaging, and individuals may be caught and removed by fishing lines (e.g. long-lines). Pecten maximus may be directly targeted and a proportion of the population removed although scallop dredge efficiency is relatively low (Dare et al. 1993).   Therefore, a resistance of Medium is recorded due to the potential disturbance to the biotope as a whole.  Resilience of is probably Low so that sensitivity is assessed as Medium.

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

The sea pens live in sheltered areas, in fine sediments, subject to high suspended sediment loads.  The effect of increased deposition of fine silt is uncertain but it is possible that feeding structures may become clogged.  When tested, Virgularia mirabilis quickly seized and rejected inert particles (Hoare & Wilson, 1977).  Hiscock (1983) observed Virgularia mirabilis secretes copious amounts of mucus that could keep the polyps clear of silt.  Kinnear et al. (1996) noted that another species of sea pen, Funiculina quadrangularis, was quick to remove any adhering mud particles by the production of copious quantities of mucus.  Virgularia mirabilis is also likely to be able to self-clean (Hiscock, 1983).  No indication of the suspended sediment load was given in any evidence found. 

Growth rates of adult Pecten maximus are adversely affected by increases in suspended sediments concentrations (Bricelj & Shumway, 1991) and excessive particle bombardment may threaten the viability of the feeding apparatus (Gibson, 1956), thereby potentially decreasing ingestion rates. Szostek et al. (2013) examined the effects of increased SPM and burial on juvenile Pecten maximus.  The scallops were exposed to low (50-100 mg/l SPM) and high (200-700 mg/l SPM) for 18 days in pVORT systems.  Shell claps and movements were significantly higher under high rather than low SPM or control (no SPM) but growth rates (over the 18 days) were significantly lower under both low and high SPM than under control conditionsThe energetic cost resulted in lower growth rates (Szostek et al., 2013).  Szostek et al. (2013) noted that while the short term survival (over the 18 day experiment) of Pecten maximus was not affected by SPM levels but that longer term survival required further investigation.

An increase in suspended sediment is unlikely to interfere with feeding in Cerianthus lloydii, which is a passive predator.  Ophiura ophiura and Ophiura albida are both found in a range of sediments, although Ophiura albida has a preference for fine sediments. Both species are omnivorous but Ophiura albida is preferentially a deposit feeders while Ophiura ophiura is mainly a predator or scavenger (Boos et al., 2010), and therefore unlikely to be affected by changes in suspended sediment.  Other members of the infaunal community are deposit feeders, predators or omnivores and unlikely to be affected. 

Sensitivity assessment.  If sea pen feeding is reduced by increases in suspended sediment the viability of the population will be reduced.  Once siltation levels return to normal, feeding will be resumed therefore recovery will be rapid. However, an increase in turbidity, from clear to turbid over the course of a year, (similar to the ‘high SPM’ studied by Szostek et al., 2013) could result in some mortality of the Pecten maximus population due to an increase is energy expenditure and reduced feeding.  Therefore, resistance is assessed as ‘Medium’.  Resilience is probably Medium so that the biotope is assessed as Medium sensitivity at the benchmark level.

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

Natural accretion rates are potentially high in sheltered muddy habitats. Hiscock (1983) observed Virgularia mirabilis secretes copious amounts of mucus, which could keep the polyps clear of silt and is also likely to be able to self-clean. Kinnear et al. (1996) noted that Funiculina quadrangularis was quick to remove any adhering mud particles by the production of copious quantities of mucus, once the source of smothering (in this case potting) was removed.  Virgularia mirabilis can burrow and move into and out of their own burrows.  It is probable therefore that deposition of 5 cm of fine sediment will have little effect other than to temporarily suspend feeding and the energetic cost of burrowing.  

In normal accretion, Cerianthus lloydii keeps pace with the accretion and, as a result, develops burrows much larger than the animal itself (Schafer, 1962, cited in Bromley, 2012). Bromley (2012) reported that an increase in depositional rate led to an avoidance behaviour in Cerianthus lloydii.  The organism ceases tube building activity and instead the animal bunches its tentacles and intrudes its way up to the new surface, where it establishes a new burrow. However, no information on the depth of material through which is can burrow was given.

Direct evidence for the effects of siltation on this ecological group is limited to the experiments undertaken by Last et al. (2011).  Last et al. (2011) buried Ophiura ophiura individuals under three different depths of sediment; shallow (2 cm), medium (5 cm) and deep (7 cm).  The results indicated that Ophiura ophiura is highly tolerant of short term (32 days) burial events, with less than 10% mortality of all buried specimens.  This is largely a reflection of the ability of the species to re-emerge from all depths across all sediment fractions tested.  Survival of specimens that remained buried was low, with 100% mortality of individuals that remained buried after 32 days.  Percentage mortality increased with both depth and duration of burial.  The experiments utilised three different fractions of kiln dried, commercially obtained marine sediment: coarse (1.2-2.0 mm diameter), medium fine (0.25-0.95 mm diameter) and fine (0.1-0.25 mm diameter).

Ophiura ophiura are found in sandier habitats that are subject to high rates of natural disturbance, these species are therefore likely to experience burial through natural sediment movements and be adapted to this, as suggested by the results of experimental smothering (Last et al., 2011).  No evidence for re-emergence thresholds was found. No direct evidence was found on Ophiura albida. However, it is smaller and less mobile than Ophiura ophiura (Boos et al., 2010) and may therefore be more vulnerable to smothering.

Szostek et al. (2013) examined a variety of burial duration (1-8 days), depth of burial (0 to 5cm) and size fraction of the sediment (fine: 0.1-0.3mm, medium fine: 0.4-0.8mm and coarse: 1.2-2mm diameter) on juvenile Pecten maximus.  Emergence was higher at shallow depth and in coarse to medium sediment.  At shallow depths scallops emerged almost immediately or within 1 day except for fine sediments where no scallops emerged from under 3 or 5 cm of burial.  Mortality was low under coarse and medium sediment and was unrelated to depth as only 4 of the 27 that remained buried died.  But mortality was under fine sediment increased with depth, as 15 out of 27 scallops that remained buried died, and with increased duration 100% mortality was observed after 4 and 8 days of burial.

Sensitivity assessment. Both Virgularia and Cerianthus can withdraw into their tube and can probably re-emerge through 5 cm of fines. However, experimental studies have demonstrated juvenile Pecten maximus are killed under 5 cm of fine sediment and that Ophiura ophiura suffered some mortality. Therefore, a resistance of Medium is suggested due to the potential loss of a characterizing species. The resilience of Pecten maximus is probably Medium, so that the biotope is probably of Medium sensitivity to siltation and smothering at the benchmark level. 

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

Sensitivity assessment. Based on the evidence presented above (siltation, 5 cm deposition), the deposition of 30 cm of fine sediment is may affect the community adversely. Virgularia mirabilis and Cerianthus lloydii can burrow and move into and out of their own burrows, which can be up to 40 cm deep. It is probable, therefore, that deposition of 30 cm of fine sediment will have little effect other than to suspend feeding temporarily and the energetic cost of burrowing. However, experimental studies have demonstrated Pecten maximus is killed under 5 cm of fine sediment and that Ophiura ophiura suffered some mortality so that 30 cm of fines is likely to result in further mortality in Pecten maximus and Ophiura spp. Therefore, a resistance of Low is suggested due to the potential loss of a characterizing species.  The resilience is probably Medium based on the recovery of Pecten maximus population, so that sensitivity of the biotope is probably Medium at the benchmark level. 

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 was found.

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 was found

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

Some of the characterizing species associated with this biotope, in particular, the sea pens and scallops, may respond to sound vibrations and can withdraw into the sediment. Feeding will resume once the disturbing factor has passed. However, most of the species are infaunal and unlikely respond to noise disturbance at the benchmark level. Therefore, this pressure is probably Not relevant in this biotope.

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

This biotope is dominated by suspension feeders, deposit feeders and predators, so that the majority of the productivity is secondary. Therefore, the biotope is probably Not sensitive (resistance and resilience are High).

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

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. 

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

Most species within the biotope are burrowing and have no or poor visual perception and are unlikely to be affected by visual disturbance such as shading. Epifauna such as crabs and scallops have well developed visual acuity and are likely to respond to movement in order to avoid predators. However, it is unlikely that the species will be affected by visual disturbance at the benchmark level.

Biological Pressures

 ResistanceResilienceSensitivity
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

The important characterizing species in this biotope are unlikely to be translocated or genetically modified.  However, Pecten maximus has been the subject of intense genetic research to examine population structure, stock, fisheries and aquaculture (Beaumont & Zouros, 1991; Beaumont, 2011). In recent years, the potential for GMO and the development of commercial strains are under investigation (Beaumont, 2011). Brenner et al., 2014) reported that bivalve aquaculture transfers have been responsible for the inadvertent transfer of diseases, pests, non-natives. There is also the potential to affect the genetic integrity of local stocks. Pecten maximus was reported to carry the infectious pancreatic necrosis virus (of fin-fish) but although the virus persisted for a long period of time in the scallops, no viral propagation occurred. However, Brenner et al. (2014) note that scallops should be considered as a potential fish pathogen vector.  Beaumont (2000) noted that the loss of genetic diversity is difficult to avoid in hatchery conditions but suggested that the potential risks and consequences of hybridization should be assessed experimentally before introductions were carried out.  Beaumont (2000) suggested that sterile triploid scallops could be used but noted that reversion to diploidy may occur (Beaumont, 2000; Brenner et al., 2014).

Overall, the translocation of scallop stocks may pose a risk of disease transfer but no direct evidence was found. Similarly, genetically modified scallops may pose a risk to the genetic integrity of wild scallop population but no evidence was found.  Therefore, no assessment was made until further evidence becomes available.

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

Crepidula fornicata and Codium fragile tomentosoides have been reported to foul scallop beds (DAISIE, 2009) but no information on adverse effects was found. Sternapsis scutata is a non-native polychaete that has extended its range in inshore muddy sediments in the south west of the UK (Shelley et al., 2008). However, in mesocosm experiments, little effect on biological functioning was detected after the introduction of the polychaete and a doubling of its biomass (Shelley et al., 2008). No direct evidence on the effect of non-native species on mud communities was found. However, this assessment should be revisited in the light of new evidence.

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

Bivalves, such as scallops, are the host for numerous viruses, bacteria, and parasites, some of which cause disease in the shellfish themselves. For example, Pecten maximus has been reported to host infectious pancreatic necrosis virus (a fin fish virus), several species of Vibrio, rickettsales-like organisms (a bacterium), Pseudoklossia pectinis (a coccidia protist), Polydora spp. ( a burrowing polychaete), Modiolicola spp. (a copepod) (McGladdery et al., 2006). In most cases the virus, bacteria or parasite had no reported effect on the population studied. In France, the mass mortality of Pecten maximus larvae in scallop hatcheries was caused by Vibrio infection and mass mortalities of wild, cultured and captive scallops may have been associated with Rickettsial-like bacterial infections (McGladdery et al., 2006). Polydora spp. also associated with shell damage in wild and cultured scallops.

Sensitivity assessment. No information on diseases in any of the important characterizing species was found. Therefore, a resistance of Medium is suggested to represent the loss of condition of the resident Pecten maximus population, and possible loss of recruitment (larvae) and some mortality. A resilience of High is suggested as the majority of the Pecten population may remain. Therefore, the sensitivity is assessed as Low recorded but with Low confidence.

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

Pecten maximus is the subject of commercial fishing activity and may be targeted via scallop dredging or hand collection. The physical effects of fishing activities are discussed under 'abrasion' and 'penetration' pressure above.While Pecten maximus occurs in low numbers in this biotope, it is an epibenthic suspension feeder and is unlikely to be dependent on any other member of the community for its survival. Similarly, no other member of the community is dependent on the scallop for its survival.  Therefore,a resistance of High is recorded. As resilience is hence High, the biotope is assessed as Not sensitive to this pressure. 

Medium Low Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

The physical effects of fisheries or dredging activities are addressed under abrasion, penetration and extraction pressures above. No clear biological relationships between the important characteristic species were found. Therefore, removal of any one species may not affect other members of the community adversely.  However, if the important characterizing species were removed as by-catch, the character of the biotope would change. A significant decline in the abundance of Virgularia mirabilis or Pecten maximus would result in loss of the biotope as recognised by the habitat classification. Therefore, a resistance of Medium is suggested.  Resilience is probably Low so that sensitivity is assessed as Medium.

Importance review

Policy/Legislation

Habitats of Principal ImportanceMud habitats in deep water
Habitats of Conservation ImportanceMud habitats in deep water
UK Biodiversity Action Plan PriorityMud habitats in deep water

Exploitation

  • Although scallops are exploited commercially, it is unlikely that they are collected from this biotope. However, if dredging for scallops did take place it would probably result in the destruction of sea pens and the loss of the biotope.
  • Due to the circalittoral nature of this biotope they are unlikely to be subject to coastal alteration, construction of tidal barrages or other large-scale environmental modifications. The fine sediments on which this biotope typically exists is not targeted for seabed extraction. Divers generally are not attracted to sedimentary habitats and so there is no likelihood of environmental damage by this means.

Additional information

-

Bibliography

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Citation

This review can be cited as:

Hill, J.M. & Tyler-Walters, H. 2016. Virgularia mirabilis and Ophiura spp. with Pecten maximus on circalittoral sandy or shelly mud. 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/66

Last Updated: 27/05/2016