The Marine Life Information Network

Global warming (extreme)

Extreme emission scenario (by the end of this century 2081-2100) benchmark of:

• A 5°C rise in SST and NBT (coastal to the shelf seas),

• A 6°C rise in surface air temperature (in eulittoral and supralittoral habitats).

• A 1°C rise in Deep-sea habitats (>200 m) off the continental shelf, and

• A 5°C rise in surface air temperature in intertidal habitats exclusive to Scotland. Further detail.

Evidence

The honeycomb worm, Sabellaria alveolata, is a warm-temperate species and is distributed from Scotland to Morocco, (Gruet, 1986, Firth et al., 2015) including extensive reefs in the Mediterranean (La Porta & Nicoletti, 2009). This suggests that this species will be tolerant of increases in temperature.

This appears to be backed up by in situ observations of this species. 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. 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. Long-term data for the coast of northern England and Wales shows that Sabellaria alveolata has colonized new locations, recolonizing areas from where it disappeared after the cold winter of 1962/63, and increased its abundance at many locations (Firth et al., 2015). This is possibly in response to recent warming (Firth et al., 2015).

Different spawning regimes, which may be due to different water temperatures, have been observed where conditions for a more northern population are less favourable and led to single annual spawning events of shorter duration (Culloty et al., 2010). Populations of Sabellaria alveolata in Morocco and the Mediterranean may be close to their upper thermal limit, as Muir et al., 2016 found that when individuals were exposed to 25°C, changes in lipid composition appeared to show a stress response.

Sensitivity assessment. Under the middle and high emission and extreme scenarios, seawater temperatures are expected to rise by 3-5°C to potential southern summer temperatures of 22-24°C and northern summer temperatures of 17-19°C. As this species is intertidal, it would also be affected by an increase in air temperature. Currently, summer temperatures can reach up to an average of 25°C, although the highest temperature recorded in 1961-2010 was 38.5°C (Perry & Golding, 2011). If air temperatures were to rise by 3, 4, or 6°C by the end of the century (middle, high and extreme emission scenarios, respectively), this could lead to temperatures reaching average summer high temperatures of between 28 - 32°C.

There is no experimental evidence of the impact of ocean warming on this species but biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). Sabellaria alveolata is known to form extensive reefs in the Tyrrhenian Sea where summer water temperatures reach 27°C (www.seatemperature.org), although in the Mediterranean this species often occurs in the shallow subtidal (La Porta & Nicoletti, 2009).  This species also occurs in Morocco, where air temperatures can regularly reach 28°C in the summer months (www.weather-and-climate.com). In Scotland, this species is at the northern-most edge of its distribution and increases in seawater temperature are likely to be beneficial. This preference for warmer waters is backed up by observations of increased growth at of this species in the cooling waters of the power station at Hinkley Point in Somerset (Bamber & Irving, 1997). Therefore, this biotope is assessed as having a ’High’ resistance to ocean warming.  Resilience is assessed as ‘High, as no recovery is necessary. This biotope is assessed as ‘Not sensitive’ under the middle and high emission and extreme scenarios.

Global warming (high)

High emission scenario (by the end of this century 2081-2100) benchmark of:

• A 4°C rise in SST, NBT (coastal to the shelf seas) and surface air temperature (in eulittoral and supralittoral habitats).

• A 1°C rise in Deep-sea habitats (>200 m) off the continental shelf, and

• A 3°C rise in surface air temperature in intertidal habitats exclusive to Scotland. Further detail.

Evidence

The honeycomb worm, Sabellaria alveolata, is a warm-temperate species and is distributed from Scotland to Morocco, (Gruet, 1986, Firth et al., 2015) including extensive reefs in the Mediterranean (La Porta & Nicoletti, 2009). This suggests that this species will be tolerant of increases in temperature.

This appears to be backed up by in situ observations of this species. 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. 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. Long-term data for the coast of northern England and Wales shows that Sabellaria alveolata has colonized new locations, recolonizing areas from where it disappeared after the cold winter of 1962/63, and increased its abundance at many locations (Firth et al., 2015). This is possibly in response to recent warming (Firth et al., 2015).

Different spawning regimes, which may be due to different water temperatures, have been observed where conditions for a more northern population are less favourable and led to single annual spawning events of shorter duration (Culloty et al., 2010). Populations of Sabellaria alveolata in Morocco and the Mediterranean may be close to their upper thermal limit, as Muir et al., 2016 found that when individuals were exposed to 25°C, changes in lipid composition appeared to show a stress response.

Sensitivity assessment. Under the middle and high emission and extreme scenarios, seawater temperatures are expected to rise by 3-5°C to potential southern summer temperatures of 22-24°C and northern summer temperatures of 17-19°C. As this species is intertidal, it would also be affected by an increase in air temperature. Currently, summer temperatures can reach up to an average of 25°C, although the highest temperature recorded in 1961-2010 was 38.5°C (Perry & Golding, 2011). If air temperatures were to rise by 3, 4, or 6°C by the end of the century (middle, high and extreme emission scenarios, respectively), this could lead to temperatures reaching average summer high temperatures of between 28 - 32°C.

There is no experimental evidence of the impact of ocean warming on this species but biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). Sabellaria alveolata is known to form extensive reefs in the Tyrrhenian Sea where summer water temperatures reach 27°C (www.seatemperature.org), although in the Mediterranean this species often occurs in the shallow subtidal (La Porta & Nicoletti, 2009).  This species also occurs in Morocco, where air temperatures can regularly reach 28°C in the summer months (www.weather-and-climate.com). In Scotland, this species is at the northern-most edge of its distribution and increases in seawater temperature are likely to be beneficial. This preference for warmer waters is backed up by observations of increased growth at of this species in the cooling waters of the power station at Hinkley Point in Somerset (Bamber & Irving, 1997). Therefore, this biotope is assessed as having a ’High’ resistance to ocean warming.  Resilience is assessed as ‘High, as no recovery is necessary. This biotope is assessed as ‘Not sensitive’ under the middle and high emission and extreme scenarios.

Global warming (middle)

Middle emission scenario (by the end of this century 2081-2100) benchmark of:

• A 3°C rise in SST, NBT (coastal to the shelf seas) and surface air temperature (in eulittoral and supralittoral habitats).

• A 1°C rise in Deep-sea habitats (>200 m) off the continental shelf.

• A 2°C rise in surface air temperature in intertidal habitats exclusive to Scotland. Further detail.

Evidence

The honeycomb worm, Sabellaria alveolata, is a warm-temperate species and is distributed from Scotland to Morocco, (Gruet, 1986, Firth et al., 2015) including extensive reefs in the Mediterranean (La Porta & Nicoletti, 2009). This suggests that this species will be tolerant of increases in temperature.

This appears to be backed up by in situ observations of this species. 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. 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. Long-term data for the coast of northern England and Wales shows that Sabellaria alveolata has colonized new locations, recolonizing areas from where it disappeared after the cold winter of 1962/63, and increased its abundance at many locations (Firth et al., 2015). This is possibly in response to recent warming (Firth et al., 2015).

Different spawning regimes, which may be due to different water temperatures, have been observed where conditions for a more northern population are less favourable and led to single annual spawning events of shorter duration (Culloty et al., 2010). Populations of Sabellaria alveolata in Morocco and the Mediterranean may be close to their upper thermal limit, as Muir et al., 2016 found that when individuals were exposed to 25°C, changes in lipid composition appeared to show a stress response.

Sensitivity assessment. Under the middle and high emission and extreme scenarios, seawater temperatures are expected to rise by 3-5°C to potential southern summer temperatures of 22-24°C and northern summer temperatures of 17-19°C. As this species is intertidal, it would also be affected by an increase in air temperature. Currently, summer temperatures can reach up to an average of 25°C, although the highest temperature recorded in 1961-2010 was 38.5°C (Perry & Golding, 2011). If air temperatures were to rise by 3, 4, or 6°C by the end of the century (middle, high and extreme emission scenarios, respectively), this could lead to temperatures reaching average summer high temperatures of between 28 - 32°C.

There is no experimental evidence of the impact of ocean warming on this species but biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). Sabellaria alveolata is known to form extensive reefs in the Tyrrhenian Sea where summer water temperatures reach 27°C (www.seatemperature.org), although in the Mediterranean this species often occurs in the shallow subtidal (La Porta & Nicoletti, 2009).  This species also occurs in Morocco, where air temperatures can regularly reach 28°C in the summer months (www.weather-and-climate.com). In Scotland, this species is at the northern-most edge of its distribution and increases in seawater temperature are likely to be beneficial. This preference for warmer waters is backed up by observations of increased growth at of this species in the cooling waters of the power station at Hinkley Point in Somerset (Bamber & Irving, 1997). Therefore, this biotope is assessed as having a ’High’ resistance to ocean warming.  Resilience is assessed as ‘High, as no recovery is necessary. This biotope is assessed as ‘Not sensitive’ under the middle and high emission and extreme scenarios.

Marine heatwaves (high)

High emission scenario benchmark: A marine heatwave occurring every two years, with a mean duration of 120 days, and a maximum intensity of 3.5°C. Further detail.

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Whilst there are no laboratory studies on the upper thermal limit of Sabellaria alveolata, this species appears to be tolerant to a wide range of temperatures. Muir et al. (2016) found that Sabellaria alveolata was able to adapt to a step-change increase in temperature from 15°C to 25°C. However, over the long term (60 days), changes in lipid composition potentially suggested a stress response. Whilst high temperatures may cause stress, there is no evidence of mortality at seawater temperatures of 25°C. For example, when summer temperatures were increased from 18°C to 23°C for Scottish populations of Sabellaria alveolata, mortality remained the same as controls, except when coupled with high levels of chlorine (Last et al., 2016). Similarly, when the density of tube occupancy was used as a proxy for mortality by Muir et al. (2016), an increase in temperatures from 15°C to 25°C in populations from Scotland to North Africa did not lead to a decrease in occupancy in four out of the five populations tested, with a decrease in occupancy only observed for the Bay of Biscay population, which the authors attributed to the poor state of the reef.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C, and air temperatures exceeding 30°C across much of the UK.

Sabellaria alveolata is known to form extensive reefs in the Tyrrhenian Sea (La Porta & Nicoletti, 2009), where summer water temperatures reach 27°C (www.seatemperature.org) (see Global Warming). As this biotope occurs in the intertidal, this species will not only experience increased sea surface temperatures but will experience extreme air temperature increases also. In the Mediterranean, it can occur in the shallow subtidal (La Porta & Nicoletti, 2009) which may protect it from excessive air temperature increases, although this species also occurs in Morocco, where air temperatures can regularly reach 28°C in the summer months (www.weather-and-climate.com). As Sabellaria alveolata occurs on wave exposed coastlines on the mid and lower shore, wave splash may play an important role in preventing desiccation during emersion. Therefore, this species is likely to be able to cope with future marine heatwaves expected for the end of this century, and under both the middle and high emission scenarios, resistance has been assessed as ‘High’. As no recovery is likely necessary, recovery has been assessed as ‘High’, leading to an assessment of ‘Not sensitive’ for this biotope. 

Marine heatwaves (middle)

Middle emission scenario benchmark:  A marine heatwave occurring every three years, with a mean duration of 80 days, with a maximum intensity of 2°C. Further detail.

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Whilst there are no laboratory studies on the upper thermal limit of Sabellaria alveolata, this species appears to be tolerant to a wide range of temperatures. Muir et al. (2016) found that Sabellaria alveolata was able to adapt to a step-change increase in temperature from 15°C to 25°C. However, over the long term (60 days), changes in lipid composition potentially suggested a stress response. Whilst high temperatures may cause stress, there is no evidence of mortality at seawater temperatures of 25°C. For example, when summer temperatures were increased from 18°C to 23°C for Scottish populations of Sabellaria alveolata, mortality remained the same as controls, except when coupled with high levels of chlorine (Last et al., 2016). Similarly, when the density of tube occupancy was used as a proxy for mortality by Muir et al. (2016), an increase in temperatures from 15°C to 25°C in populations from Scotland to North Africa did not lead to a decrease in occupancy in four out of the five populations tested, with a decrease in occupancy only observed for the Bay of Biscay population, which the authors attributed to the poor state of the reef.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C, and air temperatures exceeding 30°C across much of the UK.

Sabellaria alveolata is known to form extensive reefs in the Tyrrhenian Sea (La Porta & Nicoletti, 2009), where summer water temperatures reach 27°C (www.seatemperature.org) (see Global Warming). As this biotope occurs in the intertidal, this species will not only experience increased sea surface temperatures but will experience extreme air temperature increases also. In the Mediterranean, it can occur in the shallow subtidal (La Porta & Nicoletti, 2009) which may protect it from excessive air temperature increases, although this species also occurs in Morocco, where air temperatures can regularly reach 28°C in the summer months (www.weather-and-climate.com). As Sabellaria alveolata occurs on wave exposed coastlines on the mid and lower shore, wave splash may play an important role in preventing desiccation during emersion. Therefore, this species is likely to be able to cope with future marine heatwaves expected for the end of this century, and under both the middle and high emission scenarios, resistance has been assessed as ‘High’. As no recovery is likely necessary, recovery has been assessed as ‘High’, leading to an assessment of ‘Not sensitive’ for this biotope. 

Ocean acidification (high)

High emission scenario benchmark: a further decrease in pH of 0.35 (annual mean) and corresponding 120% increase in H+ ions , seasonal aragonite saturation of 20% of UK coastal waters and North Sea bottom waters, and the aragonite saturation horizon in the NE Atlantic, off the continental shelf, occurring at a depth of 400 m by the end of this century 2081-2100. Further detail 

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005). There is no direct evidence of the impact of ocean acidification on Sabellaria alveolata or any species from the family Sabellariidae. Unlike the tube-dwelling, calcifying polychaetes from the family Serpulidae, Sabellaria alveolata does not form its tubes by calcification. Tubes are formed from coarse sand and shell grains cemented together with an adhesive protein cement secreted by the worm (Becker et al., 2012).

Non-calcifying polychaetes are thought to be less sensitive than many other taxa to ocean acidification.  When non-calcifying polychaetes were transplanted from control to low pH areas, they showed evidence of either adaptation or acclimation to their conditions (Calosi et al., 2013). There is some evidence that sperm may be affected by ocean acidification at levels expected in the high emission scenario, with percentage sperm motility (Schlegel et al., 2014) and sperm velocity (Campbell et al., 2014) decreasing in the polychaetes Galeolaria caespitosa and Arenicola marina, leading to a decrease in sperm fertility success (Campbell et al., 2014). Reduced sperm fertility and hence recruitment, may lead to some population level effects. However, at natural CO₂ vents, the abundance of polychaetes either remained the same (Kroeker et al., 2011) or increased (Garrard et al., 2014, Vizzini et al., 2017). Most species of polychaetes generally exhibit high fecundity and are free spawning (Ramirez-Llodra, 2002), which may help them maintain population levels, even with a decrease in fertilization success. Fecundity is variable among seasons and between females, but Sabellaria alveolata exhibits high fecundity, releasing an average of 100,000 eggs/individuals into the water column during a spawning cycle (Dubois, 2003).

Sensitivity Assessment. Direct evidence of the impact of ocean acidification on Sabellaria alveolata is lacking. However, non-calcifying polychaetes appear to be tolerant of changes in pH. Therefore, it is likely that the characterizing species of this biotope will show a ‘High’ resistance to a decrease in pH, even though ocean acidification has been shown to lead to negative impacts on polychaete fertilization success under experimental conditions (Campbell et al., 2014, Schlegel et al., 2014). Hence, based on the evidence available, under both the middle and high emission scenarios the biotope is assessed as ‘High’ resistance to ocean acidification, and ‘High’ resilience, leading to an assessment of ‘Not sensitive’ at the benchmark level.

Ocean acidification (middle)

Middle emission scenario benchmark: a further decrease in pH of 0.15 (annual mean) and corresponding 35% increase in H+ ions with no coastal aragonite undersaturation and the aragonite saturation horizon in the NE Atlantic, off the continental shelf, at a depth of 800 m by the end of this century 2081-2100. Further detail.

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005). There is no direct evidence of the impact of ocean acidification on Sabellaria alveolata or any species from the family Sabellariidae. Unlike the tube-dwelling, calcifying polychaetes from the family Serpulidae, Sabellaria alveolata does not form its tubes by calcification. Tubes are formed from coarse sand and shell grains cemented together with an adhesive protein cement secreted by the worm (Becker et al., 2012).

Non-calcifying polychaetes are thought to be less sensitive than many other taxa to ocean acidification.  When non-calcifying polychaetes were transplanted from control to low pH areas, they showed evidence of either adaptation or acclimation to their conditions (Calosi et al., 2013). There is some evidence that sperm may be affected by ocean acidification at levels expected in the high emission scenario, with percentage sperm motility (Schlegel et al., 2014) and sperm velocity (Campbell et al., 2014) decreasing in the polychaetes Galeolaria caespitosa and Arenicola marina, leading to a decrease in sperm fertility success (Campbell et al., 2014). Reduced sperm fertility and hence recruitment, may lead to some population level effects. However, at natural CO₂ vents, the abundance of polychaetes either remained the same (Kroeker et al., 2011) or increased (Garrard et al., 2014, Vizzini et al., 2017). Most species of polychaetes generally exhibit high fecundity and are free spawning (Ramirez-Llodra, 2002), which may help them maintain population levels, even with a decrease in fertilization success. Fecundity is variable among seasons and between females, but Sabellaria alveolata exhibits high fecundity, releasing an average of 100,000 eggs/individuals into the water column during a spawning cycle (Dubois, 2003).

Sensitivity Assessment. Direct evidence of the impact of ocean acidification on Sabellaria alveolata is lacking. However, non-calcifying polychaetes appear to be tolerant of changes in pH. Therefore, it is likely that the characterizing species of this biotope will show a ‘High’ resistance to a decrease in pH, even though ocean acidification has been shown to lead to negative impacts on polychaete fertilization success under experimental conditions (Campbell et al., 2014, Schlegel et al., 2014). Hence, based on the evidence available, under both the middle and high emission scenarios the biotope is assessed as ‘High’ resistance to ocean acidification, and ‘High’ resilience, leading to an assessment of ‘Not sensitive’ at the benchmark level.

Sea level rise (extreme)

Extreme scenario benchmark: a 107 cm rise in average UK by the end of this century (2018-2100). Further detail.

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

Jackson & McIlvenny (2011) predicted that under a 30 cm sea-level rise, between 10 - 27% of the extent of intertidal rocky shores in Scotland would be lost, whilst under a 190 cm of sea-level rise, between 26 -50% would be lost. Using a modelling-based approach, Kaplanis et al. (2019) found that in San Diego County, loss of intertidal habitat would be most extreme within the first metre of sea-level rise, with 29.9% of intertidal rocky shore lost as a result of 20 cm sea-level rise, and 77.7% as a result of 100 cm of sea-level rise.

In the UK, Sabellaria alveolata beds occur on the mid and lower shore of exposed rocky coastlines. 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 (Anadόn, 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).

Understanding of how sea-level rise will affect exposure or tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. The effects of sea-level rise and increased wave action may be increased further due to storms and storms surges.  IPCC (2019) note that the frequency of extreme sea-level events (e.g. due to storms) are predicted to increase as sea-level rises, however, there is no consensus on the future storm and, hence, wave climate around UK coasts (Mossman et al., 2015; Lowe et al., 2018; Palmer et al., 2018).

Sensitivity assessment. It is difficult to assess the effect of sea-level rise scenarios on wave exposure or tidal energy as evidence predicts that any changes will be site-specific, therefore this aspect cannot be assessed. As this biotope occurs on the lower and mid-shore of the intertidal zone in the UK and is not in the subtidal, it is likely that an increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope. Beds may be able to expand their range and migrate upwards to compensate for sea-level rise, if not constrained by lack of suitable habitat (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of Sabellaria alveolata beds on littoral sediment will shrink in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery. In this assessment we have assessed on a worst-case-scenario basis, assuming that landward migration is not possible.

The mean tidal range in the UK varies from 127 cm in the Shetland Islands to 972 cm at Avonmouth, in the Bristol Channel (Woodworth et al., 1991). This large difference in tidal amplitudes suggests that this biotope will be more affected in some parts of the UK than others. In Scotland and Ireland, where mean tidal range is generally less than 3 m (Woodworth et al., 1991), more than half of this biotope may be lost under the extreme scenario, whereas in the Bristol Channel, where mean tidal range exceeds 9 m (Woodworth et al., 1991), only a small portion of this biotope may be lost. Under the medium emission scenario, resistance has been assessed as ‘Medium’, as it is likely that less than 25% of this biotope will be lost. Resilience has been assessed as ‘Very low’, due to the long term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘Medium’.  Under the high emission and extreme scenarios, resistance has been assessed as ‘Low’, as more than 25% of this biotope could be lost. Resilience has been assessed as ‘Very low’, due to the long term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘High’.

Sea level rise (high)

High emission scenario benchmark: a 70 cm rise in average UK by the end of this century (2018-2100). Further detail.

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

Jackson & McIlvenny (2011) predicted that under a 30 cm sea-level rise, between 10 - 27% of the extent of intertidal rocky shores in Scotland would be lost, whilst under a 190 cm of sea-level rise, between 26 -50% would be lost. Using a modelling-based approach, Kaplanis et al. (2019) found that in San Diego County, loss of intertidal habitat would be most extreme within the first metre of sea-level rise, with 29.9% of intertidal rocky shore lost as a result of 20 cm sea-level rise, and 77.7% as a result of 100 cm of sea-level rise.

In the UK, Sabellaria alveolata beds occur on the mid and lower shore of exposed rocky coastlines. 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 (Anadόn, 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).

Understanding of how sea-level rise will affect exposure or tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. The effects of sea-level rise and increased wave action may be increased further due to storms and storms surges.  IPCC (2019) note that the frequency of extreme sea-level events (e.g. due to storms) are predicted to increase as sea-level rises, however, there is no consensus on the future storm and, hence, wave climate around UK coasts (Mossman et al., 2015; Lowe et al., 2018; Palmer et al., 2018).

Sensitivity assessment. It is difficult to assess the effect of sea-level rise scenarios on wave exposure or tidal energy as evidence predicts that any changes will be site-specific, therefore this aspect cannot be assessed. As this biotope occurs on the lower and mid-shore of the intertidal zone in the UK and is not in the subtidal, it is likely that an increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope. Beds may be able to expand their range and migrate upwards to compensate for sea-level rise, if not constrained by lack of suitable habitat (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of Sabellaria alveolata beds on littoral sediment will shrink in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery. In this assessment we have assessed on a worst-case-scenario basis, assuming that landward migration is not possible.

The mean tidal range in the UK varies from 127 cm in the Shetland Islands to 972 cm at Avonmouth, in the Bristol Channel (Woodworth et al., 1991). This large difference in tidal amplitudes suggests that this biotope will be more affected in some parts of the UK than others. In Scotland and Ireland, where mean tidal range is generally less than 3 m (Woodworth et al., 1991), more than half of this biotope may be lost under the extreme scenario, whereas in the Bristol Channel, where mean tidal range exceeds 9 m (Woodworth et al., 1991), only a small portion of this biotope may be lost. Under the medium emission scenario, resistance has been assessed as ‘Medium’, as it is likely that less than 25% of this biotope will be lost. Resilience has been assessed as ‘Very low’, due to the long term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘Medium’.  Under the high emission and extreme scenarios, resistance has been assessed as ‘Low’, as more than 25% of this biotope could be lost. Resilience has been assessed as ‘Very low’, due to the long term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘High’.

Sea level rise (middle)

Middle emission scenario benchmark: a 50 cm rise in average UK sea-level rise by the end of this century (2081-2100). Further detail.

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

Jackson & McIlvenny (2011) predicted that under a 30 cm sea-level rise, between 10 - 27% of the extent of intertidal rocky shores in Scotland would be lost, whilst under a 190 cm of sea-level rise, between 26 -50% would be lost. Using a modelling-based approach, Kaplanis et al. (2019) found that in San Diego County, loss of intertidal habitat would be most extreme within the first metre of sea-level rise, with 29.9% of intertidal rocky shore lost as a result of 20 cm sea-level rise, and 77.7% as a result of 100 cm of sea-level rise.

In the UK, Sabellaria alveolata beds occur on the mid and lower shore of exposed rocky coastlines. 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 (Anadόn, 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).

Understanding of how sea-level rise will affect exposure or tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. The effects of sea-level rise and increased wave action may be increased further due to storms and storms surges.  IPCC (2019) note that the frequency of extreme sea-level events (e.g. due to storms) are predicted to increase as sea-level rises, however, there is no consensus on the future storm and, hence, wave climate around UK coasts (Mossman et al., 2015; Lowe et al., 2018; Palmer et al., 2018).

Sensitivity assessment. It is difficult to assess the effect of sea-level rise scenarios on wave exposure or tidal energy as evidence predicts that any changes will be site-specific, therefore this aspect cannot be assessed. As this biotope occurs on the lower and mid-shore of the intertidal zone in the UK and is not in the subtidal, it is likely that an increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope. Beds may be able to expand their range and migrate upwards to compensate for sea-level rise, if not constrained by lack of suitable habitat (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of Sabellaria alveolata beds on littoral sediment will shrink in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery. In this assessment we have assessed on a worst-case-scenario basis, assuming that landward migration is not possible.

The mean tidal range in the UK varies from 127 cm in the Shetland Islands to 972 cm at Avonmouth, in the Bristol Channel (Woodworth et al., 1991). This large difference in tidal amplitudes suggests that this biotope will be more affected in some parts of the UK than others. In Scotland and Ireland, where mean tidal range is generally less than 3 m (Woodworth et al., 1991), more than half of this biotope may be lost under the extreme scenario, whereas in the Bristol Channel, where mean tidal range exceeds 9 m (Woodworth et al., 1991), only a small portion of this biotope may be lost. Under the medium emission scenario, resistance has been assessed as ‘Medium’, as it is likely that less than 25% of this biotope will be lost. Resilience has been assessed as ‘Very low’, due to the long term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘Medium’.  Under the high emission and extreme scenarios, resistance has been assessed as ‘Low’, as more than 25% of this biotope could be lost. Resilience has been assessed as ‘Very low’, due to the long term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘High’.

Temperature increase (local)

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

Evidence

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 a 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').

Temperature decrease (local)

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

Evidence

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 a 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. 

Salinity increase (local)

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

Evidence

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. 

Salinity decrease (local)

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

Evidence

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 (30-25 ppt) 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; 18-35 ppt). 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. 

Water flow (tidal current) changes (local)

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

Evidence

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 (Wright et al., 2001). 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’.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

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’. 

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

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 (Anadόn, 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).

Transition elements & organo-metal contamination

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

Evidence

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

Hydrocarbon & PAH contamination

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

Evidence

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

Synthetic compound contamination

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

Evidence

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

Radionuclide contamination

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

Evidence

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.

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

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

Evidence

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’.

Nutrient enrichment

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

Evidence

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.Therefore, the biotope is considered to be ‘Not Sensitive’ at the pressure benchmark.

Organic enrichment

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

Evidence

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 in 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).  Hence, sensitivity is recorded as 'Not sensitive'.

Physical loss (to land or freshwater habitat)

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

Evidence

All marine habitats and benthic species are considered to have ‘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.

Physical change (to another seabed type)

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

Evidence

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.

Physical change (to another sediment type)

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

Evidence

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 colonization.

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. 

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

The 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 the 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 the establishment 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. 

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

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 and, although the trawl had left impressions, 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).

Penetration or disturbance of the substratum subsurface

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

Evidence

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’. 

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

Sabellaria alveolata do not rely on light penetration for photosynthesis and their visual perception is believed to be limited.  Changes in light penetration or attenuation associated 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) corresponds 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 biotopes 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’. 

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

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 was 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’.

Smothering and siltation rate changes (heavy)

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

Evidence

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 the 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 are limited, the addition of an overburden of 30 cm 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’.

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

No evidence.

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

No evidence.

Introduction of light or shading

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

Evidence

No evidence.

Barrier to species movement

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

Evidence

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’.

Death or injury by collision

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

Evidence

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

Visual disturbance

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

Evidence

Not relevant.

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

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

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

The Pacific oyster, Magallana (syn. Crassostrea) gigas, is native to warm temperate regions from the northwest Pacific to Japan and northeast Asia, including Cape Mariya (Russia) to Hong Kong (China) (Carrasco & Baron, 2010; GBNNSS, 2011, 2012). It is a fast-growing and tolerant species that has become a successful invader in the coastal waters of all continents, aside from Antarctica (Wrange et al., 2010; Carrasco & Baron, 2010; Padilla, 2010). Magallana gigas is recognised as a beneficial and important species in aquaculture worldwide (Padilla, 2010). It was initially introduced for aquaculture in Europe and the UK in the 1960s due to a decline in the Portuguese oyster (Crassostrea angulata) and the European flat oyster (Ostrea edulis) (Spencer et al., 1994; GBNNSS, 2011, 2012; Humphreys et al., 2014 cited in Alves et al., 2021; Hansen et al., 2023).

Since introduction, the species has invaded and established self-sustaining natural populations throughout Europe from the North Sea, Wadden Sea and Scandinavian coastlines to the Atlantic coastlines of Spain and Portugal, as well as the Mediterranean and Adriatic Sea (Wrange et al., 2010; GBNNSS, 2011, 2012; Ezgeta-Balic et al., 2019; Spagnolo et al., 2019; Bergstrom et al., 2021; Hansen et al., 2023). In the UK, the species predominantly occurs around the southern and western coastlines (OBIS, 2024; NBN, 2024). Shipping activity has also been associated with the introduction of Magallana gigas in the northeastern Adriatic Sea, where it was not introduced for aquaculture (Ezgeta-Balic et al., 2019). It was also suggested that some Magallana gigas populations were established in southwest England from France possibly via fouling on ships (GBNNSS, 2011, 2012; Padilla, 2010; Ezgeta-Balic et al., 2019).

Magallana gigas has a high fecundity, a long-lived pelagic larval phase (2 to 4 weeks) and can produce up to 200 million eggs during spawning (Herbert et al., 2012, 2016; Alves et al., 2021; Wood et al., 2021; Hansen et al., 2023). Hence, as a broadcast spawner, it has a high dispersal potential of more than 1000 km (Padilla, 2010; Wood et al., 2021). Larval mortality can be as large as 99%, as larvae are sensitive to environmental conditions (Alves et al., 2021). However, adults are long-lived so populations can survive with infrequent recruitment (Padilla, 2010). Larval dispersal and mass spawning events have facilitated the settlement and establishment of Pacific oysters, as seen in the Oosterschelde estuary, Netherlands (Hansen et al., 2023). It has been suggested that the spread of the Pacific oyster in Scandinavia is due to northward larval drift on tidal and wind-driven currents (Hansen et al., 2023). Wood et al. (2021) suggested that larval dispersal of the Pacific oyster from populations within and outside the UK was possible via unaided (passive) transport by currents, but that aquaculture and offshore structures (e.g. windfarms) increased the risk of the invasive species spreading and the geographical extent of spread.

Magallana gigas is an ecosystem engineer and can dramatically change habitat structure when it invades. Once successfully settled, groups of Pacific oysters may form dense aggregations, potentially forming a reef, which in some regions can reach densities of 700 individuals m² (Herbert et al., 2012, 2016). Once, the density of live or dead Pacific oysters reaches or exceeds 200 ind./m² little of the underlying substratum remains visible (Herbert et al., 2016). These reefs can stabilize the sediment surface locally (Troost, 2010). When such reefs are formed or, particularly when the species colonizes soft sediments such as mud or sand, it can change and affect local communities, by creating hard substrata for mobile species, which might not otherwise be present before the invasion (Padilla, 2010). However, Hansen et al. (2023) suggested that where the Pacific oyster occurs sporadically, no immediate ecosystem risk is observed.

Magallana gigas also colonizes littoral intertidal biogenic reefs formed by the blue mussel Mytilus edulis or honeycomb worm Sabellaria alveolata (GBNNSS, 2011, 2012; Kochmann, 2012; Kochmann et al., 2013; Herbert et al., 2016; Tillin et al., 2020). The colonization and overgrowth of Magallana gigas may have impacts on Sabellaria alveolata and its habitat formation (Herbert et al., 2012, 2016). Pacific oysters may smother Sabellaria alveolata because it grows over tube ends and could outcompete it for space (Dubois et al., 2006; Desroy et al., 2011). Colonization by the Pacific oyster has been linked to the degradation and deterioration of Sabellaria reef health (Desroy et al., 2011). Desroy et al. (2011) reported several contributing factors, including an increase in silt deposits and fine particles in the sediment from pseudo-faeces produced by the oysters, which can cause increased sedimentation and nutrient enrichment (Green & Crowe, 2013). It has been suggested the increased sediment from oysters might explain why some species normally found in muddy-sand environments were present, further creating new species associations (Dubois et al., 2006).

Dubois et al. (2006) found that Magallana gigas had invaded some Sabellaria alveolata reefs in the Bay of Mont-Saint Michel, France, resulting in densities of more than 100 oysters /m² on some of them. In this area, Sabellaria alveolata reefs were the only available hard substratum for settlement by the Pacific oyster. The study found that an intermediate covering of the Pacific oyster introduced greater species richness and heterogeneity of diversity on the Sabellaria reefs by creating hard substrata habitats and refuges for sessile or mobile species not usually present (Dubois et al., 2006). Green & Crowe (2013) found a lower percentage cover of Sabellaria alveolata on boulders colonized by Magallana gigas in Ireland. 

The presence of other filter feeders such as Magallana gigas increases trophic competition (Desroy et al., 2011, Green & Crowe, 2013). However, high densities of filter-feeding species alter the settlement of particulate matter and larvae as turbulence in the water column is increased (Green & Crowe, 2013). The physical structure of the oyster beds changes the hydrography and provides refuge from predators for oyster larvae, which increases their recruitment (Soniat et al., 2004). Pacific oysters might improve the recruitment of Sabellaria alveolata by increasing the probability of Sabellaria larvae swimming or sinking down the water column (Tillin et al., 2020). However, Dubois et al. (2006) reported that the abundance of smaller class sizes of Sabellaria alveolata was reduced in Sabellaria reefs with epibionts (Pacific oyster or Ulva spp.) indicating negative impacts of Pacific oysters on recruitment, although not as marked as in the presence of algae (Padilla, 2010; Tillin et al., 2020). Secondary impacts have also been reported, including increased recreational harvesting of the oysters on Sabellaria reefs, which led to reef trampling, physical damage and fragmentation (Dubois et al., 2006; Desroy et al., 2011). In the northern part of Bourgneuf Bay, France Magallana gigas was observed in rocky areas usually occupied by Sabellaria alveolata (Cognie et al., 2006; Herbert et al., 2012, 2016). Cognie et al. (2006) suggested that Magallana gigas could compete with Sabellaria alveolata for food and space, leading Herbert et al. (2012) to suggest that the Pacific oyster may prevent new colonization by Sabellaria alveolata.

The slipper limpet Crepidula fornicata was recorded on intertidal Sabellaria alveolata reefs in Champeaux, west Cotentin coast, northern France, at a low density of ca 0.75+/-2 /m² (Schlund et al., 2016). Powell-Jennings & Calloway (2018) reported that Crepidula had a preference for hard grounds colonized by Sabellaria alveolata in Swansea Bay, south Wales, with over 80% of the records of Crepidula associated with the Sabellaria alveolata reef. However, no evidence of their relationship was available and they may be in competition or facilitate each other's presence (Powell-Jennings & Calloway, 2018). 

Sensitivity assessment. The evidence above suggests that both Crepidula and Magallana have the potential to colonize intertidal Sabellaria alveolata reefs. There is no evidence to suggest that Crepidula has a detrimental effect on the reefs. The presence of sand combined with wave exposure and storm-related scour may limit the ability of Crepidula to colonize the habitat and its density. Therefore, the resistance to colonization by Crepidula fornicata is assessed as ‘Medium’. Resilience is likely to be 'Very low' as a bed of Crepidula fornicata would need to be removed (by human intervention) before recovery could begin. Therefore, sensitivity is considered to be ‘Medium’. However, the confidence in this assessment is 'Low' due to the lack of evidence of deleterious effects. 

The presence of Magallana gigas at low densities can increase the species richness and diversity on Sabellaria alveolata reefs, but higher densities of the Pacific oyster may smother Sabellaria alveolata, and outcompete it for space and food (Cognie et al., 2006; Dubois et al., 2006; Desroy et al., 2011). Magallana gigas may prevent the colonization of Sabellaria alveolata in some areas (Herbert et al., 2012). Therefore, the resistance to colonization by Magallana gigas is assessed as 'Low' as a precaution. Resilience is likely to be ‘Very low’ as the Magallana gigas population would need to be removed for recovery to occur. Therefore, the sensitivity of Sabellaria alveolata reef biotopes is assessed as ‘High’. 

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

No evidence found for pathogens or diseases impacting Sabellaria alveolata.

Removal of target species

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

Evidence

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’.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

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’.