Sabellaria alveolata reefs on sand-abraded eulittoral rock

24-02-2005
Researched byDr Heidi Tillin & Angus Jackson Refereed byAdmin
EUNIS CodeA2.711 EUNIS NameSabellaria alveolata reefs on sand-abraded eulittoral rock

Summary

UK and Ireland classification

EUNIS 2008A2.711Sabellaria alveolata reefs on sand-abraded eulittoral rock
EUNIS 2006A2.711Sabellaria alveolata reefs on sand-abraded eulittoral rock
JNCC 2004LS.LBR.Sab.SalvSabellaria alveolata reefs on sand-abraded eulittoral rock
1997 BiotopeLR.MLR.Sab.SalvSabellaria alveolata reefs on sand-abraded eulittoral rock

Description

Many wave-exposed boulder scar grounds in the eastern basin of the Irish Sea (and as far south as Cornwall), are characterized by reefs of Sabellaria alveolata which build tubes from the mobile sand surrounding the boulders and cobbles. The tubes formed by Sabellaria alveolata form large reef-like hummocks, which serve to further stabilize the boulders. Other species in this biotope include the barnacles Semibalanus balanoides, Balanus crenatus and Elminius modestus and the molluscs Patella vulgata, Littorina littorea, Nucella lapillus and Mytilus edulis. Low abundances of algae tend to occur in areas of eroded reef. The main algal species include Porphyra spp., Mastocarpus stellatus, Ceramium spp., Fucus vesiculosus, Fucus serratus, Ulva spp. and Ulva spp. On exposed surf beaches in the south-west Sabellaria forms a crust on the rocks, rather than the classic honeycomb reef, and may be accompanied by the barnacle Balanus perforatus (typically common to abundant). On wave-exposed shores in Ireland, the brown alga Himanthalia elongata can also occur. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

In Britain, Sabellaria alveolata distribution is restricted to south and west coasts with the eastern limit in Lyme Bay. The northern limit is the outer Solway Firth. It is also found on south, west and north coasts of Ireland. To date, MLR.Salv has only been recorded in the Solway Firth and along the Cumbrian coast, western Wales, and the Severn Estuary. In Northern Ireland reefs have been recorded from the Down coast (Rossglass and Glassdrummand) although surveys are incomplete. It has also been recorded at two sites in Ireland, Ballycotton Bay (south) and Killala Bay, (north-west).

Depth range

Lower shore, Mid shore

Additional information

Sabellaria alveolata can perform important stabilization of habitat, particularly when forming raised structures and reefs (see Ecology).

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Habitat review

Ecology

Ecological and functional relationships

  • Ecological relationships within MLR.Salv are not especially complex. Nevertheless, diversity of associated fauna may be high. Collins (2001) found 59 faunal taxa and 18 floral taxa associated with Sabellaria alveolata reefs at Criccieth in North Wales, dominated by annelids, molluscs, nematodes and hexapods. Dias & Paula (2001) recorded a total of 137 taxa in Sabellaria alveolata colonies on two shores on the central coast of Portugal. Sheets of Sabellaria alveolata can form ridges on flat shores which can trap water and create small pools (Cunningham et al., 1984) (see Habitat Complexity). This may also result in an increased species diversity, as might the stabilization of mobile sand, shingles, pebbles and cobbles (Holt et al., 1998) often attributed to the presence of extensive Sabellaria alveolata sheets.
  • Algae use older reefs as substratum. Some of these are perennials such as Fucus serratus and others annual ephemerals such as Ulva sp. The attached community may themselves have epifaunal species (Collins, 2001). In addition, the space between the epiphytic algae and the reef provide shelter for mobile organisms.
  • Several grazing molluscs, including Patella vulgata and Littorina littorea, feed directly on these algae as well as on epiphytic microalgae.

Seasonal and longer term change

Some temporal changes may be apparent in Sabellaria alveolata reefs with a cycle of decay and settlement over several years. Recruitment is very sporadic so cycles are not very predictable. Decay is primarily through the effects of storms and wave action. There will also be changes with season in the amount of algae growing in the biotope. Annual species will come and go and perennial species such as Fucus serratus exhibit changes in the level of surface cover they provide. Epiflora such as Fucus serratus, particularly if dense, may act as nursery grounds for various species including Nucella lapillus.

Habitat structure and complexity

Habitat complexity varies temporally with the cycles of development and break up of the reefs. When growing actively as sheets or hummocks the entire sea shore can be covered. Ridges can be formed on flat shores which may trap water leading to the formation of pools (Cunningham et al., 1984). These extensive sheets ('placages'), can stabilize otherwise mobile sand, shingle, cobbles and pebbles (Holt et al., 1998). However, increased habitat diversity, and therefore increased species diversity, are found as the reef begins to break up, cracks, crevices and a greater variety of available surfaces develops, creating a more diverse and complex habitat. Collins (2001) found that reefs in poor condition had a significantly higher diversity of associated infauna than intermediate condition reefs at Criccieth in North Wales. Porras et al. (1996) reported similar findings, in addition to the observation that eroded reefs have higher structural complexity. Collins (2001) also reported that, within reefs in poor condition, the sediment size was significantly larger than in other reefs. In contrast, the levels of organic content were found to be significantly higher in reefs in condition. Sabellaria alveolata reefs, due to their structure, maintain a high level of relative humidity during low tide, thereby protecting some associated flora and fauna from desiccation, which may permit some species to occur at higher levels on the shore than normal.

Productivity

Sabellaria alveolata reefs can support diverse communities (see Ecological Relationships). For example, colonies may support several species of annual and perennial algae, particularly if the reefs are older and beginning to break up. This algal growth can support several species of grazing mollusc (including Littorina littorea and Patella vulgata). Where hummocks or reefs form, the density of Sabellaria alveolata can be very high, causing high secondary productivity.

Recruitment processes

Sabellaria alveolata recruits from pelagic larvae that spend from 6 weeks to 6 months in the plankton. Although reproduction occurs each year, recruitment is very sporadic and unpredictable. Larval settlement appears to favour areas with existing Sabellaria alveolata colonies, or their dead remains (e.g. Wilson, 1971; Cunningham et al., 1984). Fucus serratus also recruits from tiny pelagic plants.

Time for community to reach maturity

Sabellaria alveolata has been recorded as living for up to 9 years but most worms survive for four years or so. The growth of Sabellaria alveolata appears to slow after its first year after settle. Wilson (1971) reported that the growth in the second and third years after settlement in some colonies was about half that of growth in the first year. Such active growth effectively prevents any other species from colonizing the reef. When growth is less active then algae can begin to colonize, as the reef begins to break up the available substratum becomes more heterogeneous permitting establishment of more species. If further recruitment does not then occur, allowing new growth, the reef will disintegrate. There is no real 'mature stage' as such, rather a cycle of growth and decay. Although settlement of Sabellaria alveolata is sporadic, areas that are good for Sabellaria alveolata tend to remain so because larval settlement appears to favour areas with existing Sabellaria alveolata colonies, or their dead remains (e.g. Wilson, 1971; Cunningham et al., 1984).

Additional information

Cunningham et al. (1994) noted the presence of large numbers of Mytilus edulis on the remains of Sabellaria alveolata colonies in several locations including Llwyngwril in Wales and at Dubmill Point in West Cumbria. In some circumstances therefore, the mussels could potentially interrupt the usual cycle of growth and decay of the reef.

Preferences & Distribution

Recorded distribution in Britain and IrelandIn Britain, Sabellaria alveolata distribution is restricted to south and west coasts with the eastern limit in Lyme Bay. The northern limit is the outer Solway Firth. It is also found on south, west and north coasts of Ireland. To date, MLR.Salv has only been recorded in the Solway Firth and along the Cumbrian coast, western Wales, and the Severn Estuary. In Northern Ireland reefs have been recorded from the Down coast (Rossglass and Glassdrummand) although surveys are incomplete. It has also been recorded at two sites in Ireland, Ballycotton Bay (south) and Killala Bay, (north-west).

Habitat preferences

Depth Range Lower shore, Mid shore
Water clarity preferences
Limiting Nutrients No information found
Salinity Full (30-40 psu)
Physiographic Open coast
Biological Zone Lower eulittoral, Eulittoral
Substratum Large to very large boulders, Small boulders, Cobbles, Pebbles, Sand
Tidal
Wave Exposed, Moderately exposed
Other preferences Availability of sand grains.

Additional Information

Although identified in the Severn Estuary, the habitat is rather different and the assemblage present is not likely to be the same as in occurrences of the biotope more typically found on open coasts. At Glasdrummand (Northern Ireland), the Sabellaria alveolata reefs extend into the subtidal. Optimal temperatures are probably higher than those typically found in the waters of the British Isles. There needs to be an adequate supply of suspended coarse sand grains in order for Sabellaria alveolata to be able to build their tubes.

Temperature preferences
The growth of Sabellaria alveolata is severely restricted below 5 °C (Gruet, 1982, cited in Holt et al., 1998). Cunningham et al. (1984) reported increasing growth rates with temperatures up to 20 °C.

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

    -

    Additional information

    Sensitivity reviewHow is sensitivity assessed?

    Sensitivity characteristics of the habitat and relevant characteristic species

    As Sabellaria alveolata is the species that creates the reef habitat the sensitivity assessments are based on Sabellaria alveolata alone and do not consider the sensitivity of associated species that may be free-living or attached to the reef.  Although a wide range of species are associated with reef biotopes which provide habitat and food resources, these characterising species occur in a range of other biotopes and are therefore not considered to be species characterising this biotope group.  The reef and individual Sabellaria alveolata worms are not dependent on associated species to create or modify habitat, provide food or other resources.  

    Resilience and recovery rates of habitat

    Empirical evidence to assess the likely recovery rate of Sabellaria alveolata reefs from impacts is limited and significant information gaps regarding recovery rates, stability and persistence of Sabellaria alveolata reefs were identified. It should also be noted that the recovery rates are only indicative of the recovery potential.  Recovery of impacted populations will always be mediated by stochastic events and processes acting over different scales including, but not limited to, local habitat conditions, further impacts and processes such as larval-supply and recruitment between populations. 

    Studies carried out on reefs of Sabellaria alveolata within the low inter-tidal suggest that areas of small, surficial damage within reefs may be rapidly repaired by the tube building activities of adult worms.  Vorberg (2000) found that trawl impressions made by a light trawl in Sabellaria alveolata reefs disappeared four to five days later due to the rapid rebuilding of tubes by the worms. The daily growth rate of the worms during the restoration phase was significantly higher than undisturbed growth (undisturbed: 0.7 mm, after removal of 2 cm of surface: 4.4 mm) and indicates that as long as the reef is not completely destroyed recovery can occur rapidly.  Although it should be noted that these recovery rates are as a result of short-term effects following once-only disturbance.  Similarly, studies of inter tidal reefs of Sabellaria alveolata by Cunningham et al. (1984) found that minor damage to the worm tubes as a result of trampling, (i.e. treading, walking or stamping on the reef structures) was repaired within 23 days . However, severe damage caused by kicking and jumping on the reef structure, resulted in large cracks between the tubes, and removal of sections (ca 15x15x10 cm) of the structure (Cunningham et al., 1984).  Subsequent wave action enlarged the holes or cracks.  However, after 23 days, at one site, one side of the hole had begun to repair, and tubes had begun to extend into the eroded area. 

    Where reefs are extensively removed, recovery will rely on recolonization of the site  by larvae. Sabellaria alveolata are gonochoristic (sexes separate), reproductive maturity is reached within the first year of life and the species reproduces by external fertilisation of shed gametes. The larvae are free-living within the plankton where they are transported by water movements. Some control over dispersal may be exerted through vertical migration in the water column allowing exposure to different current speeds during daily tidal cycles.  Sabellaria alveolata larvae can be stimulated to settle by the presence of adult tubes, tube remnants or the mucoid tubes of juveniles (Quian, 1999). The presence of living Sabellaria alveolata or tubes therefore will promote the recovery of reefs and their absence may delay recovery of otherwise suitable habitats.  Although larvae may be present every year the degree of settlement varies annually. In 14 years of observations (1961 to 1975), Wilson (1976) observed only three heavy settlements, North Cornwall in 1966, 1970 and 1975 and all were in the period from September to November or December. Observations from other populations concur that intensity of settlement is extremely variable from year to year and place to place (Cunningham et al., 1984; Gruet, 1982). Settlement occurs mainly on existing colonies or their dead remains; chemical stimulation seems to be involved, and this can come from Sabellaria spinulosa tubes as well as Sabellaria alveolata (Cunningham et al., 1984; Gruet, 1982; Wilson, 1971).

    The spawning season and duration of the planktonic phase appear to be variable with authors reporting conflicting results from different populations. Dubois et al., (2007) found larvae in the plankton at Bay of Mont-Saint-Saint Michel (France) from the end of April to October, with peak spawning occurring in May, followed by a smaller spawning peak in September.  Mean planktonic lifetime was calculated between 4 and 10 weeks from samples taken within the bay (Dubois et al. 2007).  These observations fit broadly with those of Gruet and Lassus (1983, cited from Dubois et al. 2007) who  indicated two long spawning periods for a population along the French Atlantic coast (Noirmoutier Island): March to April and June to September. In the Bassin d’Arcachon (French Atlantic coast), Sabellaria alveolata larvae with a larval lifespan estimated to be about 12 weeks were reported in plankton samples mainly from October to March (Cazaux 1970, cited from Dubois et al. 2007). Wilson (1971), however reported a short, single spawning period in July in North Cornwall and suggested that larvae spent between 6 weeks and 6 months in the plankton (Wilson, 1968; Wilson, 1971) so that dispersal could potentially be widespread. Similarly Culloty et al. (2010) observed one main spawning period by populations in south-west Ireland that was, however, more protracted (June to September) than that observed in North Cornwall by Wilson. Differences between spawning regimes may be due to different water temperatures, where conditions for more northern population are less favourable to this southern species (Culloty et al. (2010).

    Growth is rapid, and is promoted by high levels of suspended sand and by higher water temperatures up to 20°C. A mean increase in tube length of up to 12 cm per year has been reported for northern France (Gruet, 1982).  Cunningham et al. (1984) stated that growth is probably lower than this in Britain due to the lower water temperatures, although Wilson (1971) reported growth rates (tube length) of 10-15 cm per year in several colonies at Duckpool, North Cornwall for first year colonies, and around 6 cm in second year worms. Wilson (1971) reported that in good situations the worms mature within the first year, spawning in the July following settlement.

    A typical life span for worms in colonies forming reefs on bedrock and large boulders in Duckpool was 4-5 years (Wilson, 1971), with a likely maximum of around 9 years (Gruet, 1982; Wilson, 1971). Intertidal reefs are dynamic, Dubois et al., (2002 and 2006) described tthree reef forms, where ball-shaped structures created by newly-settled juveniles later merge to form larger reef platforms which then decline to become fissured degraded reefs.   Wilson (1976) observed one small reef from its inception as three small individual colonies in 1961, through a period between 1966 and 1975 where it existed as a reef rather greater than 1 metre in extent and up to 60 cm thick, with major settlement of worms occurring in 1966 and 1970.   In the long term, areas with good Sabellaria reef development tend to remain so. In Ireland, Simkanin et al. (2005) reported no significant change in the intertidal abundance of this species from 1958 to 2003, on the 28 shores compared around the coast. 

    Resilience assessment. The evidence for recovery rates of Sabellaria alveolata reefs from different levels of impact is very limited, for most pressures there are no examples of rates at which reefs recover from different levels of impact.  Recovery rates are likely to be determined by a range of factors such as degree of impact, season of impact, larval supply and local environmental factors including hydrodynamics.

    Observations by Vorberg (2000) and Cunningham et al., (1984) suggest that areas of limited damage on a Sabellaria alveolata reef can be repaired rapidly (within weeks) through the tube-building activities of adults).  The assessment of resilience in this instance as ‘High’ indicating that recovery would be likely to occur within 2 years is relatively precautionary. 

    Predicting the rate of recovery following extensive removal of existing Sabellaria alveolata reef is more problematic. Some thin crusts may be relatively ephemeral and disappear following natural disturbance such as storms but recover the following year (Holt et al. 1998), suggesting that recovery is ‘High’ (within 2 years). In other instances, recolonisation has been observed within 16-18 months but full recovery to a state similar to the pre-impact condition of high adult density and adult biomass is suggested to require three to five years where recruitment is annual (Pearce et al., 2007). Where resistance is assessed as ‘Medium’, resilience is considered to be ‘High’, based on repair and rapid recoloisation facilitated by adults. Recovery from significant impacts (where resistance is assessed as ‘None’ or 'Low') is therefore predicted to be ‘Medium’ (2-10 years).

    Hydrological Pressures

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

    Sabellaria alveolata are a southern species reaching their northern limit in Britain and Ireland and whose global distribution extends south to Morocco (Gruet, 1982). Studies at Hinkley Point, Somerset, found that growth of the tubes in the winter was considerably greater in the cooling water outfall, where the water temperature was raised by around 8-10 °C, than at a control site, although the size of the individual worms themselves seemed to be unaffected (Bamber & Irving, 1997). Dubois et al. (2007) observed that in autumn where water temperatures are 8 °C higher than in spring, a shorter period was required for larvae to metamorphose. 

     Differences between spawning regimes which may be due  to different water temperatures have been observed, where conditions for more northern population are less favourable and lead to single annual spawning events of shorter duration (Culloty et al., 2010). Intertidal populations of Sabellaria alveolata are susceptible to low temperatures in winter.

    Sensitivity assessment. Based on distribution and temperature enhancement of duration and frequency of spawning, metamorphosis and growth rates, Sabellaria alveolata is considered to be ‘Not sensitive’ to an increase in temperature at the pressure benchmark (resistance and resilience are therefore both considered to be 'High').

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

    Sabellaria alveolata are a southern species reaching their northern limit in Britain and Ireland. Studies at Hinkley Point, Somerset, found that growth of the tubes in the winter was considerably greater in the cooling water outfall, where the water temperature was raised by around 8-10 °C, than at a control site, although the size of the individual worms themselves seemed to be unaffected (Bamber & Irving, 1997). 

    Dubois et al. (2007) observed that in autumn where water temperatures are 8 °C higher than in spring, a shorter period was required for larvae to metamorphose. Differences between spawning regimes which may be due  to different water temperatures have been observed, where conditions for more northern population are less favourable and lead to single annual spawning events of shorter duration (Culloty et al., 2010). Intertidal populations of Sabellaria alveolata are susceptible to low temperatures in winter (Crisp, 1964).

    Sensitivity assessment. Based on distribution and  reported temperature effects on duration and frequency of spawning, metamorphosis and growth rates. The effects of acute decreases in temperature at the benchmark will depend on the seasonality of occurrence. Decreases in winter are likely to stress populations more than decreases in summer (although there may be effects on larval supply).  At the centre of their UK range, adult Sabellaria alveolata are considered to have 'High' resistance to both an acute and chronic change at the pressure benchmark in summer, but to have 'Medium' resistance in winter. Resilience is assessed as 'Medium' and sensitivity is therefore assessed as 'Medium'.  Adult Sabellaria alveolata are considered to be ‘Not sensitive’ to a chronic decrease in temperature at the pressure benchmark (resistance and resilience are therefore both considered to be 'High'). The more precautionary sensitivity to acute decreases in winter is presented in the table. 

    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

    No empirical evidence was found to assess the impact of increases in salinity on adult, reef-forming populations. This biotope appears to be restricted to areas of full salinity, defined as 30-35 ppt (Connor et al., 2004). The pressure benchmark of an increase in salinity is, therefore, 'Not relevant' to this biotope. However, it should be noted that reefs could be sensitive to hypersaline conditions above this benchmark. Quintino et al. (2008) examined through laboratory experiments the sub-lethal endpoints of brine exposure on Sabellaria alveolata larvae. Natural seawater where salinities had been increased using commercial salts used to prepare artificial seawater were used as the control. At a salinity of 36 (natural seawater artificially concentrated) 20% of Sabellaria alveolata developed abnormally, at a salinity of 40, this increased to about 70% of the larvae developed abnormally, clearly indicating the effect of increasing salinity on larvae. Although not directly relevant to the pressure benchmark the experiments do suggest that increasing salinity would lead to sub-lethal effects on larvae. It is not clear how these supply effects would ramify at the population level. Recruitment success varies between years (see resilience information) and a shortfall in one year may be compensated in another year when salinity returns to normal, providing the source population is unaffected.

    Sensitivity assessment. This biotope has only been recorded from areas of full salinity (Connor et al., 2004) and, therefore, this pressure is considered ‘Not relevant’ to this biotope at the pressure benchmark. 

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

    It is likely that Sabellaria alveolata can tolerate small declines in salinity as it occurs intertidally where freshwater inputs may lower salinity, either on a semi-permanent basis where rivers discharge into estuaries and bays, or where rainfall and land run-off cause an acute lowering of salinity. In the Bay of Mont-Saint-Michel , for example, where large reefs are found salinities are lower (at <34.8) than in the open sea. (Dubois et al., 2007). Although this biotope is reported to only occur areas of full salinity (30-25ppt) by Connor et al., (2004), sublittoral reefs of Sabellaria alveolata are recorded in the Severn Estuary in areas of variable salinity (Connor et al., 2004).  Lancaster (1993, cited from Holt et al., 1998) also found extensive, healthy hummocks of Sabellaria at Drigg, Cumbria, where there is a large freshwater input from the Drigg BNFL plant.

    Sensitivity assessment. The evidence to assess this pressure is limited. Based on distribution with only occasional records within estuaries, this biotope is considered likely to be sensitive at the lower limits of the pressure benchmark (a change to variable salinity; 18-35ppt) . Resistance is therefore assessed as ‘Low', as a reduction in salinity at the pressure benchmark is considered to result in the loss of most of the reef. Resilience (following habitat recovery) is assessed as ‘Medium’. Sensitivity is, therefore, ‘Medium’. The observed distribution of this biotope may be based on other factors than salinity, such as availability of suitable sediments, and confidence in this assessment is low. 

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

    Holt et al. (1998) suggest that for Sabellaria alveolata reefs the importance of currents vs waves in terms of sediment re-suspension and transport for tube-building varies regionally. In many British localities such as the south west of England, much of Wales and the Cumbrian coast waves seem more important, but in other areas such as parts of the Severn Estuary tidal suspension is probably the key factor. Water flow in some areas will be a key driver of habitat suitability for Sabellaria alveolata, due to the requirement for suspended sand for tube building and the supply or organic particles for food.

    Tests on the mechanical strength and properties of Sabellaria alveolata tubes were performed by Le Cam et al. (2011).  These found that the biomineralised cement the worms produce to cement sand grains to form tubes confer wave resistance. Although thresholds of resistance are not known, the visco-elastic behaviour of the cement enables tubes to dissipate the mechanical energy of breaking waves and presumably also confers resistance to increased water flow rates (Le Cam et al. 2011).

    Tillin (2010) used logistic regression to develop statistical models that indicate how the probability of occurrence of Sabellaria alveolata changes over environmental gradients within the Severn Estuary.  The model predicted response surfaces were derived for each biotope for each of the selected habitat variables, using logistic regression.  From these response surfaces the optimum habitat range for each biotope could be defined based on the range of each environmental variable where the probability of occurrence, divided by the maximum probability of occurrence, is 0.75 or higher.  These results identify the range for each significant variable where the habitat is most likely to occur.  The modelled ranges should be interpreted with caution and apply to the Severn Estuary alone (which experiences large tidal ranges, high currents and extremely high suspended sediment loads and is, therefore, distinct from many other estuarine systems).  However, these ranges do provide some useful information on environmental tolerances.  The models indicate that for subtidal Sabellaria alveolata the maximum optimal current speed (the range in which it is most likely to occur) ranges from 1.26-2.46 m/s and the optimal mean current speed ranges from 0.5-1.22 m/s.  Although the results should be interpreted with caution, the modelled habitat suitability for Sabellaria alveolata indicates that the range of water flow tolerances is relatively broad.

    In general sediment re-suspension and transport models indicate that sands are suspended by currents around 0.20-0.25 m/s and will stay in suspension until flow drops below 0.15-0.18 m/s (ref). Sabellaria alveolata may be relatively insensitive to changes above these flow rates (although the upper tolerance limit is not clear). In sheltered habitats where the water flow rates are approaching the lower limits of water flow tolerance a further reduction at the pressure, benchmark may have negative impacts. Desroy et al., (2011) suggested that modifications to hydrodynamics (where current speed decreased downstream of new mussel farming infrastructure installations facing the reef) indirectly impacted sedimentary patterns and led to increased silt deposition resulting in the deterioration of Sabellaria alveolata reefs in the Bay of Mont-Saint Michel, France.

    Changes in water flow potentially have implications for larval transport and recruitment. Sabellaria alveolata is generally absent from very exposed peninsulas such as the Lleyn, Pembrokeshire and the extreme south west of Cornwall, which probably relates to the effect of water movement on recruitment (Cunningham et al., 1984, cited from Holt et al. 1998). However, behavioural responses by larvae to different flow rates may result in some control over movement.  Dubois et al. (2007) observed the vertical migration of Sabellaria alveolata larvae during the tidal cycle, where larvae migrate upwards in the water column to faster near-surface currents and migrate down the water column on the ebb flow to where currents are weaker. This migration enhances landward transport of larvae to more suitable habitats and prevents seaward loss.

    Sensitivity assessment. A long-term decrease in water flow may reduce the viability of populations by limiting growth and tube building. No evidence was found for threshold levels relating to impacts although Tillin (2010) modelled optimal flow speeds of 0.5-1.22 m/s.  The worms may retract into tubes to withstand periods of high flows at spring tides and some non-lethal reduction in feeding efficiency and growth rate may occur at the edge of the optimal range.  Similarly, a reduction in flow may reduce the supply of tube-building materials and food but again, given the range of reported tolerances a change at the pressure benchmark, mid-range is not considered to result in mortality.  Resistance is therefore assessed as ‘High’ and resilience as ‘High’ (no impact to recover from).  All the biotopes within this biotope group are therefore considered to be ‘Not sensitive’.

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

    A reduction in the amount of time spent under water could cause a proportion of exposed individual Sabellaria alveolata to die, as the worms can only feed when submerged. Sabellaria alveolata reefs also occur subtidally, a decrease in emergence time may have no physiological effect but may lead to increased predation on the reef.

    Sensitivity assessment. This biotope is considered sensitive to changes in emergence. No direct evidence was found relating to this pressure and resistance is therefore assessed as ‘Medium’ and recovery as ‘Medium’ (following habitat recovery). Sensitivity is therefore assessed as ‘Medium’. 

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

    In some areas wave action is an important driver of habitat quality for Sabellaria alveolata, supporting reef development by resuspending and transporting suitable sediment particles (Cunningham et al. 1984).  High densities of Sabellaria alveolata are found on shores exposed to wave action (Anad὚n, 1981; Dias & Paula, 2001), although reefs are generally absent from very exposed peninsulas such as the Lleyn, Pembrokeshire and the extreme south west of Cornwall, which probably relates to the effect of water movement on recruitment (Cunningham et al., 1984, cited from Holt et al. 1998).

    Tests on the mechanical strength and properties of Sabellaria alveolata tubes were performed by Le Cam et al. (2011).  These found that the biomineralised cement the worms produce to cement sand grains to form tubes confer wave resistance. Although thresholds of resistance are not known the visco-elastic behaviour of the cement enables tubes to dissipate the mechanical energy of breaking waves (Le Cam et al. 2011). 

    Sensitivity assessment.  At the pressure benchmark, Sabellaria alveolata are considered to be able to mechanically withstand an increase in wave exposure and to be unaffected by a decrease. The biotope group is therefore considered to be ‘Not Sensitive’ at the pressure benchmark (resistance and resilience are assessed as ‘High’ by default).

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

    Mauchline et al. (1964) examined concentration of radioactive isotopes by organisms on Windscale beach. Sabellaria alveolata built reefs with the smaller particles on the beach which adsorb the greatest amount of radioactivity per weight (due to surface-area effects). Thus Sabellaria reefs could concentrate radioactivity. However the study by Mauchline et al. (1964) did not look for or identify any potential negative effects on the worms such as changes in reproductive success or mortality rates.

    Sensitivity assessment. No evidence.

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

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

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

    No direct evidence was found to assess this pressure. As Sabellaria alveolata are primarily intertidal, respiration could occur during periods of emmersion so that this species is not exposed permanently to hypoxia/anoxia. This feature also occurs in relatively exposed areas on coarse substrates where water mixing is considered sufficient to prevent deoxygenation.

    Sensitivity assessment. Based on habitat parameters mitigating this pressure, resistance is assessed as ‘Medium’ and recovery as ‘High’. Sensitivity is therefore assessed as ‘Low’.

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

    Eutrophication (at levels greater than the pressure benchmark) may support the growth of green algae such as Ulva spp. Dubois et al. (2006) report that algal epibionts reduce recruitment of Sabellaria alveolata, with potential but unknown impacts on long-term maintenance of reefs. At the pressure benchmark the biotope group is considered to be ‘Not Sensitive’.

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

    No evidence was found to support this sensitivity assessment.  Habitat preferences for areas of high water movement suggest that organic matter would not accumulate on reefs, limiting exposure to this pressure.  Sabellaria alveolata would be able to consume re-suspended particulate organic matter.  This conclusion is supported by the enhanced growth rates observed in the congener Sabellaria spinulosa that have been recorded on the vicinity of sewage disposal areas (Walker & Rees, 1980).  Resistance is therefore assessed as ‘High’ to this pressure and recovery is assessed as ‘High’ (no impact to recover from).  

    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 ‘No Resistance’ to this pressure and to be unable to recover from a permanent loss of habitat.  Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’.  Although no specific evidence is described confidence in the resistance assessment is ‘High’, due to the incontrovertible nature of this pressure.  Adjacent habitats and species populations may be indirectly affected where meta-population dynamics and trophic networks are disrupted and where the flow of resources e.g. sediments, prey items, loss of nursery habitat etc. is altered. No recovery is predicted to occur and the rate and confidence in resilience are not assessed.

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

    Sabellaria alveolata generally requires hard substrata on which to form reefs, but these must be in areas with a good supply of suspended coarse sediment. Reefs therefore commonly form on areas of rock or boulders surrounded by sand: the basis for this biotope group. Sabellaria alveolata reefs may also form on stable sediments.  Larsonneur et al., (1984), working in the Bay of St Michel in Normandy, noted that the sand mason Lanice conchilega can stabilise sand well enough to allow subsequent colonisation by Sabellaria alveolata. Settlement is also enhanced by the presence of existing colonies or their dead remains (Holt et al. 1998). Colonies on sand or other sediment may, however, be more short-lived as sediment mobility will disrupt reef formation (Holt et al., 1998).

    Sensitivity assessment. The biotope classification refers specifically to rock habitats and therefore a change in sediment type from a rock substratum to a sedimentary substratum would significantly alter the biotope type. Due to the reduction in habitat suitability for reefs following permanent or prolonged substratum type changes, Sabellaria alveolata are judged to have ‘Low’ resistance to this pressure, resilience is Very low (the pressure is a permanent change) and 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

    Sabellaria alveolata generally requires hard substrata on which to form reefs, but these must be in areas with a good supply of suspended coarse sediment. Reefs therefore commonly form on areas of rock or boulders surrounded by sand: the basis for this biotope group. Sabellaria alveolata reefs may also form on stable sediments.  Larsonneur et al., (1984), working in the Bay of St Michel in Normandy, noted that the sand mason Lanice conchilega can stabilise sand well enough to allow subsequent colonisation by Sabellaria alveolata. Settlement is also enhanced by the presence of existing colonies or their dead remains (Holt et al. 1998).

    There is some evidence that newly constructed groynes off Morecambe have resulted in a coarser sediment regime which has allowed Sabellaria alveolata to colonise boulder and cobble grounds in place of Mytilus edulis  which was previously dominant (Lumb, pers. comm.; Andrews, pers. comm., cited from Holt et al. 1998). Increases in coarse fractions are therefore considered to be beneficial for this species, particularly where these are stable. However, an increase in finer sediment has the potential to restrict development and high levels of silt in sediments will not provide a suitable substratum for colonisation.

    Sensitivity assessment. As this biotope specifically occurs on hard substratum, the pressure benchmark (a change in sediment type) is not considered relevant to the biotope group. 

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

    The removal of substratum down to 30 cm depth is likely to remove the whole Sabellaria alveolata reef within the extraction footprint.  At an expert workshop convened to assess the sensitivity of marine features to support MCZ planning Sabellaria alveolata reefs were assessed as having no resistance to extraction of the feature (benchmark was removal of feature/substrate to 50 cm depth) (Tillin et al. 2010).

    Sensitivity assessment. As Sabellaria alveolata reefs are surface features they will be directly removed by extraction of the reef to 30 cm depth.  Resistance to this pressure is therefore assessed as ‘None’.  Resilience is considered to be ‘Medium’ to allow for estsblishment of reef structure and the potential for variable recruitment and this biotope is therefore considered to have ‘Medium’ sensitivity to this pressure. Confidence in this assessment is assessed as 'High' due to the incontrovertible nature of the pressure. 

     

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

    Impacts of surface abrasion from fishing trawls and trampling have been investigated.  To address concerns regarding damage from fishing activities in the Wadden Sea, Vorberg (2000) used video cameras to study the effect of shrimp fisheries on Sabellaria alveolata reefs.  The imagery showed that the 3 m beam trawl easily ran over a reef that rose to 30 to 40 cm, although the beam was occasionally caught and misshaped on the higher sections of the reef.  At low tide there were no signs of the reef being destroyed although the trawl had left impressions but all traces had disappeared four to five days later due to the rapid rebuilding of tubes by the worms.  The daily growth rate of the worms during the restoration phase was significantly higher than undisturbed growth (undisturbed: 0.7 mm, after removal of 2 cm of surface: 4.4 mm) and indicates that as long as the reef is not completely destroyed recovery can occur rapidly.  These recovery rates are as a result of short-term effects following once-only disturbance.  Cunningham et al. (1984) examined the effects of trampling on Sabellaria alveolata reefs. The reef recovered within 23 days from the effects of trampling, (i.e. treading, walking or stamping on the reef structures) repairing minor damage to the worm tube porches. However, severe damage, estimated by kicking and jumping on the reef structure, resulted in large cracks between the tubes, and removal of sections (ca 15x15x10 cm) of the structure (Cunningham et al., 1984). Subsequent wave action enlarged the holes or cracks. However, after 23 days, at one site, one side of the hole had begun to repair, and tubes had begun to extend into the eroded area. At another site, a smaller section (10x10x10 cm) was lost but after 23 days the space was already smaller due to rapid growth.

    Sensitivity assessment. Based on the evidence above resistance to trampling was assessed as ‘Medium’ as the tubes are able to withstand some damage and be rebuilt, recovery to a single event was considered to take place through tube repair by adults so recovery was assessed as ‘High’ and sensitivity was categorised as ‘Low’. The scale and intensity of impacts would influence the level of resistance and the mechanism of recovery. Where reefs suffer extensive spatial damage requiring larval settlement to return to pre-impact conditions then recovery would be prolonged (years).

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

    This pressure will result in the surface disturbance effects outlined above but effects will be compounded by the penetration and sub-surface damage aspect of this pressure. No empirical evidence was found to assess impacts however it is considered that the deeper and more significant the damage, the higher the risk of removing complete tubes and limiting recovery of the reefs.

    Sensitivity assessment. Based on the evidence cited above for abrasion, resistance was assessed as ’Low’ (taking into account deeper penetration of the disturbance), recovery was assessed as ‘Medium’ (2-10 years) to take into account that larval recruitment may be necessary for the reef structure to recover although small, localised areas of repair would take place within months.  Sensitivity is therefore assessed as ‘Medium’. 

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

    Sabellaria alveolata do not rely on light penetration for photosynthesis and their visual perception is believed to be limited.  Changes in light penetration or attenuationassociated with this pressure are, therefore, not relevant to the Sabellaria alveolata reef biotope, however alterations in the availability of suspended organic matter that can be used as food and the availability of suspended sediment for tube building  could either increase or decrease habitat suitability for Sabellaria alveolata reefs.

    The effect of increased seston concentration on Sabellaria alveolata clearance rates was investigated by Dubois et al. (2009). The range of experimental suspended particulate matter (SPM) concentrations (65-153.8 mg/l) correspond to clear to medium turbidity at the pressure benchmark scale. The number of polychaetes actively feeding increased between  SPM 6.5-12.3 mg/l and no change was observed  between SPM 12.3 and 55.5 mg/l.  At higher levels of SPM clearance rates were reduced, the decline in filter feeding efficiency (measured as a clearance rate) declined at around SPM 45 mg/l and thereafter remained relatively stable.

    Tillin (2010) used logistic regression to develop statistical models that indicate how the probability of occurrence of Sabellaria alveolata changes over environmental gradients within the Severn Estuary.  The model predicted response surfaces were derived for each biotope for each of the selected habitat variables, using logistic regression.  From these response surfaces the optimum habitat range for each biotope could be defined based on the range of each environmental variable where the probability of occurrence, divided by the maximum probability of occurrence, is 0.75 or higher.  These results identify the range for each significant variable where the habitat is most likely to occur.  The modelled ranges should be interpreted with caution and apply to the Severn Estuary alone (which experiences large tidal ranges, high currents and extremely high suspended sediment loads and is therefore distinct from many other estuarine systems).  However, these ranges do provide some useful information on environmental tolerances.  The models indicate that for subtidal Sabellaria alveolata the optimal mean neap sediment concentrations range from 515.7-906 mg/l and optimal mean spring sediment concentrations range from 855.3-1631 mg/l.  The upper levels of these modelled optima broadly correspond with observations by Cayocca et al. (2008, cited in Dubois et al. 2009) who recorded SPM peaks ranging between 200 and 1000 mg/l depending on the flow and ebb conditions, in the vicinity of the largest Sabellaria alveolata reef in the Bay of Mont-Saint-Michel. Outside of these peaks the SPM remained around 50 mg/l the level at which Dubois et al. (2009) recorded changes in clearance rate.

    Sensitivity assessment. Sabellaria alveolata is adapted to turbid systems and can maintain its filtering activity under high seston loads (Dubois et al., 2009).   A supply of suspended sediment is a requirement for the development of reefs (Cunningham et al. 1984). Based on Cayocca et al. (2008, cited in Dubois et al., 2009) the normal range of SPM in which Sabellaria alveolata reefs occur is probably in the intermediate range (based on UKTAG, 2014 ranks) with increases in SPM at the beginning of ebb and flow periods.  It is therefore considered that Sabellaria alveolata reef biotoes are ‘not sensitive’ to increases in peak suspended sediment concentration to the medium turbidity level (100-300 mg/l)  at the pressure benchmark . However, if the increase was constant then reductions in filtration efficiency may negatively affect a proportion of the population , resistance was therefore assessed as ‘Medium’ and recovery as ‘High’ following habitat recovery. Sensitivity is therefore considered to be ‘Low’.  A reduction from intermediate levels to clear (<10 mg/l) where the reduction is due to a reduced supply of organic matter and particulate matter suitable for tube building and food may restrict reef development and reduce the food supply to this species. Resistance was assessed as ‘Low’ and recovery as ‘Medium’ so that sensitivity is considered to be ‘Medium’. 

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

    Sabellaria alveolata was reported to survive short-term burial for days and even weeks in the south west of England as a result of storms that altered sand levels up to two meters, they were, however killed by longer-term burial (Earll & Erwin 1983). In Brittany intensive mussel cultivation on ropes wound around intertidal oak stakes affected nearby Sabellaria alveolata reefs by smothering with faeces and pseudofaeces, though it was not clear if this resulted in any harm, (cited from Holt et al. 1998, no reference given).

     It should be noted that if siltation is associated with altered water flows to allow accumulation, then long term habitat suitability for this species would be unfavourably altered .

    Sensitivity assessment. Sabellaria alveolata reefs occur in littoral wave exposed or moderately exposed locations. Where siltation does occur, wave action is likely to rapidly remove silty deposits. As reefs have some resistance to periodic smothering and burial, resistance to siltation is assessed as ‘High’ and recovery as ‘High’, so that this biotope is considered to be ‘Not Sensitive’.

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

    Sabellaria alveolata was reported to survive short-term burial for days and even weeks in the south west of England as a result of storms that altered sand levels up to two meters, they were, however killed by longer-term burial (Earll & Erwin 1983). Sabellaria alveolata has been identified as sensitive to changes in sediment regime in the Mediterranean Gulf of Valencia, Spain, where Sabellaria alveolata populations were lost as a result of sand level rise resulting from the construction of seawalls, marinas/harbours, and beach nourishment projects (Porras et al., 1996). It is likely that the length of survival  while dependent on length of burial may be influenced by temperatures and oxygen levels so that seasonality and the depth and character of overburden partially determine sensitivity.

    Sensitivity assessment.  Natural events such as storms may lead to episodic burial by coarse sediments with subsequent removal by water action and the degree of mortality will depend on a number of factors including the length of burial. As fine sediments may be relatively cohesive and as water and air penetration is limited the addition of an overburden of 30cm is considered to potentially lead to some mortality if large areas are impacted. Resistance is therefore assessed as ‘Low’ and recovery is assessed as ‘Medium’, and sensitivity to this pressure is categorised as ‘Medium’.

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

    Not assessed.

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

    No evidence.

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

    No evidence.

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

    No evidence.

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

    Barriers that reduce the degree of tidal excursion may reduce the supply of Sabellaria alveolata larvae moving landwards to suitable habitats from source populations. However the presence of barriers may enhance local population supply by preventing the seaward loss of larvae. The residual tidal currents in Bay of Mont-Saint-Saint Michel (France) naturally prevent the loss of larvae from the bay and are believed to enhance settlement locally (Dubois et al., 2007). This species is therefore potentially sensitive to barriers that restrict water movements, whether this will lead to beneficial or negative effects will depend on whether enclosed populations are sources of larvae or are ‘sink’ populations that depend on outside supply of larvae to sustain the local population.

    Sensitivity assessment. As this habitat is potentially sensitive to changes in tidal excursion and exchange, resistance is assessed as ‘Medium’ and resilience as ‘High’, sensitivity is therefore ‘Low’.

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

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

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

    Not relevant.

    Biological Pressures

     ResistanceResilienceSensitivity
    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

    Sabellaria alveolata is not farmed or translocated, therefore this pressure is 'Not relevant'.

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

    In the Bay of Mont Saint-Michel, France, Dubois et al. (2006) found that the non-native oyster Crassostrea gigas had escaped from adjacent aquaculture facilities and were growing on Sabellaria alveolata reefs. Diversity of associated species was highest on the reefs with oysters. There were also some differences in the age structure of these reefs suggesting that there may have been negative effects on Sabellaria alveolata recruitment. Studies have suggested that Crassostrea gigas could increase the probability of interception of Sabellaria alveolata larvae sinking or swimming down to the water column, as demonstrated by  flume settlement experiments and models (Soniat et al., 2004); a potential beneficial effect. However, Green & Crowe (2013) conducted manipulative experiments in the intertidal where live and dead Crassostrea gigas were attached to boulders and observed that the presence of living and dead shells reduced settlement of Sabellaria alveolata in comparison with control boulders.Crassostrea gigas may smother Sabellaria alveolata by growing over the tube ends and could outcompete the larvae, juveniles, and adults for space. In addition, Crassostrea gigas  and Sabellaria alveolata are both suspension feeders, and they ingest food particles in the same size range (Dubois et al., 2003). Oysters have high filtration rates, suggesting that they may outcompete Sabellaria alveolata for food (Dubois et al. 2006).

    Sensitivity assessment. This assessment is based on smothering by Crassostrea gigas as no evidence was found for impacts arising from other non-indigenous species. Little specific evidence was found on impacts, and resistance is assessed as ‘Medium’. Resilience is likely to be 'Very low' as a bed of Crassostrea gigas would need to be removed (by human intervention) before recovery could begin. Therefore, sensitivity is considered to be ‘Medium’.

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

    No evidence found for pathogens or diseases impacting Sabellaria alveolata.

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

    Sabellaria alveolata biotopes may be removed or damaged by people harvesting species such as mussels within the biotope or by contact with static or mobile gears that are targeting other species. These direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures.  Extraction of Sabellaria alveolata by bait digging is a possibility. Damage to colonies by people opening tubes with knives and removing the worms for use as fishing bait has been observed, though nowhere has this been seen on any intensive scale (references in Holt et al., 1998). No evidence was found for trophic or other ecological interactions between commercially targeted species and Sabellaria alveolata.

    Sensitivity assessment. As hand gathering and occurs at a low intensity and Sabellaria alveolata is not commercially targeted the habitat is assessed as ‘Not Sensitive’. Resistance is therefore assessed as ‘High’ and resilience as ‘High’.

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

    Sabellaria alveolata biotopes may be removed or damaged by static or mobile gears that are targeting other species. These direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures.  Sabellaria alveolata creates the biogenic reefs that characterise this biotope, removal of this species as by-catch would therefore remove the biotope.  No evidence was found for key trophic or other ecological interactions between other species within the biotope and Sabellaria alveolata.

    Sensitivity assessment. Removal of the worms and tubes as by-catch would remove the biotope and hence this group is considered to have ‘No’ resistance to this pressure and to have ‘Medium’ recovery. Sensitivity is therefore ‘Medium’. 

    Importance review

    Policy/Legislation

    Habitats of Principal ImportanceSabellaria alveolata reefs
    Habitats of Conservation ImportanceHoneycomb worm reefs
    Habitats Directive Annex 1Reefs
    UK Biodiversity Action Plan PrioritySabellaria alveolata reefs

    Exploitation

    Sabellaria alveolata reefs are sometimes exploited by fishermen as a source of bait although this is only carried out on a very small scale.

    Additional information

    -

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    Citation

    This review can be cited as:

    Tillin, H.M & Jackson, A., 2015. Sabellaria alveolata reefs on sand-abraded eulittoral rock. 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/351

    Last Updated: 03/11/2015