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

Caryophyllia smithii is a temperate cup coral that has a wide distribution from Norway to the Mediterranean and South Africa in the Atlantic, found in both shallow and deep water, with records of this species between temperatures of 5-30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982).

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Moreno, 2020). Pentapora foliacea generally occurs in seawater temperatures between 10-20°C (www.obis.org). Multiple studies have shown Pentapora fascialis to display seasonal variation in the deposition of its calcareous skeleton, reflected by the difference in growth bands (Lombardi et al., 2008). Cocito et al. (2006) observed that colonies of Pentapora fascialis grew primarily during the colder months of the year, with slower growth recorded in the warmer months between May and September. Similarly, Lombardi et al. (2006) observed seasonal variation in the zooid size and growth banding, with longer zooid production during the colder months. Also, Lombardi et al. (2008) found the greatest weight percentage of calcite in the winter growth band of Pentapora. Therefore, the formation of Pentapora skeletons appears to be related to seawater temperatures.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea for over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m ) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm²) at 11 m deep survived after the first disturbance. 

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the North West Atlantic coasts, at sea surface temperatures between 5 and 20°C but mostly between 10 and 15°C (www.obis.org).  Across this latitudinal gradient species are likely to experience a range of temperatures from approx. 5 and 18°C (Sea temperature, 2015). 

Alcyonium digitatum spawns during the winter months (Hartnoll, 1975). Gametes are fertilized while in the water column and the embryos give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within one or two further days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975). However, laboratory experiments have observed settlement failure to occur in unsuitable conditions (Hartnoll, 1975). As spawning occurs when sea temperatures are low there is the probability that spawning and settlement could be correlated to climatic conditions, therefore global warming could impact the reproduction and recruitment of Alcyonium digitatum. However, the combination of spawning in winter and the long pelagic lifespan may allow a considerable length of time for the planulae to disperse, settle and metamorphose ahead of the spring plankton bloom (Hartnoll, 1975).

The duration, dispersal and survival of planktonic larvae are dependent on several factors including temperature (O’Connor et al., 2007). O’Connor et al. (2007) reported planktonic larval duration to increase with temperature, therefore cold-water species could see an increase in planktonic larval duration under global warming trends. Larval survival has been reported to decrease exponentially with time (planktonic larval duration) (O’Connor et al., 2007). Elevated temperatures may increase the occurrence of octocoral diseases caused by pathogens that act opportunistically to attack hosts that are under stressful conditions. For example, Cerrano et al. (2000) reported that ecosystems in the Mediterranean are rapidly declining from extensive attacks by microorganisms correlating to elevated seawater temperatures. 

The sponge Cliona celata is widespread from Norway, Iceland and the western Baltic Sea, to the Mediterranean. Elevated temperatures have been found to positively correlate with the growth of clionid sponges and provide opportunities for rapid territory expansion (Ruzler, 2002; Prezeslawski et al., 2008). Carver et al. (2010) observed the maximum growth rates of Cliona celata from June to August when seawater temperatures were >15°C. Duckworth & Peterson (2013) found high water temperatures of 31 °C to have limited negative effects on the growth, survival or boring rates of Cliona celata. 

The bryozoan Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, however, there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature, as acclimation to elevated temperatures appears possible. Menon (1972), for example, reported that the upper lethal temperature and median lethal temperature of Electra pilosa varied significantly with acclimation temperature, e.g. 24 hr upper lethal temperature was ca 25°C in colonies acclimated to 5°C but ca 29°C when acclimated to 22 °C (Menon, 1972).  An acute temperature change may affect growth, feeding and hence reproduction in bryozoans. The bryozoan Porella compressa is primarily recorded between temperatures of 0-15°C (www.obis.org). Therefore, Porella compressa is likely to be influenced by the elevation of seawater temperatures.  

Echinus esculentus is a sea urchin distributed across the N.E. Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Echinus esculentus is common on most coasts of the British Isles but absent from most of the east coast of England, the eastern English Channel and some parts of north Wales. Echinus esculentus has been recorded most commonly at sea temperatures of 5-15°C (www.obis.org).

Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark (Ursin 1960). Temperature, photoperiod and food availability are considered to be factors that control the reproduction of echinoids (Kelly, 2001). Bishop (1985) noted that gametogenesis proceeded at temperatures between 11 - 19 °C although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after up to 24hr at 15°C (Tyler & Young 1998) but normally at the other temperatures tested (4, 7 and 11 °C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Therefore, Echinus esculentus is likely to be intolerant of chronic long term temperature change but would probably be more intolerant of sudden or short term acute change (e.g. 5 °C for one week) in temperature. 

Sensitivity assessment.  Under the middle, high and extreme emission scenarios seawater temperatures are expected to rise by 3-5°C, with potential southern summer temperatures of 22-24°C. The distribution of Alcyonium digitatum suggests that the species may be impacted by ocean warming, as populations of this species have been reported where seawater temperatures range up to 20°C (www.obis.org). Caryophyllia smithii and Parasmittina trispinosa are found in geographical locations with higher temperatures than in the UK, therefore these species are unlikely to be affected by an increase in seawater temperature, as these species are likely to adjust to gradual ocean warming. Elevated temperatures have shown to be advantageous to clionid sponges, with increased growth rates and rapid territorial expansion. The sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods and loss of grazing may change the community. While no evidence on the thermal tolerance of Pentapora foliacea and Porella compressa was found, evidence on the impacts on bryozoan species including Pentapora foliacea (Cocito & Sgorbini, 2014) and Porella compressa could be adversely affected by increased seawater temperatures. Therefore, resistance is assessed as ‘Low’ and resilience as ‘Very low’ so that sensitivity is, therefore, assessed as 'High' at levels predicted for the end of this century.

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

Caryophyllia smithii is a temperate cup coral that has a wide distribution from Norway to the Mediterranean and South Africa in the Atlantic, found in both shallow and deep water, with records of this species between temperatures of 5-30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982).

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Moreno, 2020). Pentapora foliacea generally occurs in seawater temperatures between 10-20°C (www.obis.org). Multiple studies have shown Pentapora fascialis to display seasonal variation in the deposition of its calcareous skeleton, reflected by the difference in growth bands (Lombardi et al., 2008). Cocito et al. (2006) observed that colonies of Pentapora fascialis grew primarily during the colder months of the year, with slower growth recorded in the warmer months between May and September. Similarly, Lombardi et al. (2006) observed seasonal variation in the zooid size and growth banding, with longer zooid production during the colder months. Also, Lombardi et al. (2008) found the greatest weight percentage of calcite in the winter growth band of Pentapora. Therefore, the formation of Pentapora skeletons appears to be related to seawater temperatures.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea for over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m ) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm²) at 11 m deep survived after the first disturbance. 

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the North West Atlantic coasts, at sea surface temperatures between 5 and 20°C but mostly between 10 and 15°C (www.obis.org).  Across this latitudinal gradient species are likely to experience a range of temperatures from approx. 5 and 18°C (Sea temperature, 2015). 

Alcyonium digitatum spawns during the winter months (Hartnoll, 1975). Gametes are fertilized while in the water column and the embryos give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within one or two further days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975). However, laboratory experiments have observed settlement failure to occur in unsuitable conditions (Hartnoll, 1975). As spawning occurs when sea temperatures are low there is the probability that spawning and settlement could be correlated to climatic conditions, therefore global warming could impact the reproduction and recruitment of Alcyonium digitatum. However, the combination of spawning in winter and the long pelagic lifespan may allow a considerable length of time for the planulae to disperse, settle and metamorphose ahead of the spring plankton bloom (Hartnoll, 1975).

The duration, dispersal and survival of planktonic larvae are dependent on several factors including temperature (O’Connor et al., 2007). O’Connor et al. (2007) reported planktonic larval duration to increase with temperature, therefore cold-water species could see an increase in planktonic larval duration under global warming trends. Larval survival has been reported to decrease exponentially with time (planktonic larval duration) (O’Connor et al., 2007). Elevated temperatures may increase the occurrence of octocoral diseases caused by pathogens that act opportunistically to attack hosts that are under stressful conditions. For example, Cerrano et al. (2000) reported that ecosystems in the Mediterranean are rapidly declining from extensive attacks by microorganisms correlating to elevated seawater temperatures. 

The sponge Cliona celata is widespread from Norway, Iceland and the western Baltic Sea, to the Mediterranean. Elevated temperatures have been found to positively correlate with the growth of clionid sponges and provide opportunities for rapid territory expansion (Ruzler, 2002; Prezeslawski et al., 2008). Carver et al. (2010) observed the maximum growth rates of Cliona celata from June to August when seawater temperatures were >15°C. Duckworth & Peterson (2013) found high water temperatures of 31 °C to have limited negative effects on the growth, survival or boring rates of Cliona celata. 

The bryozoan Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, however, there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature, as acclimation to elevated temperatures appears possible. Menon (1972), for example, reported that the upper lethal temperature and median lethal temperature of Electra pilosa varied significantly with acclimation temperature, e.g. 24 hr upper lethal temperature was ca 25°C in colonies acclimated to 5°C but ca 29°C when acclimated to 22 °C (Menon, 1972).  An acute temperature change may affect growth, feeding and hence reproduction in bryozoans. The bryozoan Porella compressa is primarily recorded between temperatures of 0-15°C (www.obis.org). Therefore, Porella compressa is likely to be influenced by the elevation of seawater temperatures.  

Echinus esculentus is a sea urchin distributed across the N.E. Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Echinus esculentus is common on most coasts of the British Isles but absent from most of the east coast of England, the eastern English Channel and some parts of north Wales. Echinus esculentus has been recorded most commonly at sea temperatures of 5-15°C (www.obis.org).

Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark (Ursin 1960). Temperature, photoperiod and food availability are considered to be factors that control the reproduction of echinoids (Kelly, 2001). Bishop (1985) noted that gametogenesis proceeded at temperatures between 11 - 19 °C although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after up to 24hr at 15°C (Tyler & Young 1998) but normally at the other temperatures tested (4, 7 and 11 °C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Therefore, Echinus esculentus is likely to be intolerant of chronic long term temperature change but would probably be more intolerant of sudden or short term acute change (e.g. 5 °C for one week) in temperature. 

Sensitivity assessment.  Under the middle, high and extreme emission scenarios seawater temperatures are expected to rise by 3-5°C, with potential southern summer temperatures of 22-24°C. The distribution of Alcyonium digitatum suggests that the species may be impacted by ocean warming, as populations of this species have been reported where seawater temperatures range up to 20°C (www.obis.org). Caryophyllia smithii and Parasmittina trispinosa are found in geographical locations with higher temperatures than in the UK, therefore these species are unlikely to be affected by an increase in seawater temperature, as these species are likely to adjust to gradual ocean warming. Elevated temperatures have shown to be advantageous to clionid sponges, with increased growth rates and rapid territorial expansion. The sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods and loss of grazing may change the community. While no evidence on the thermal tolerance of Pentapora foliacea and Porella compressa was found, evidence on the impacts on bryozoan species including Pentapora foliacea (Cocito & Sgorbini, 2014) and Porella compressa could be adversely affected by increased seawater temperatures. Therefore, resistance is assessed as ‘Low’ and resilience as ‘Very low’ so that sensitivity is, therefore, assessed as 'High' at levels predicted for the end of this century.

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

Caryophyllia smithii is a temperate cup coral that has a wide distribution from Norway to the Mediterranean and South Africa in the Atlantic, found in both shallow and deep water, with records of this species between temperatures of 5-30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982).

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Moreno, 2020). Pentapora foliacea generally occurs in seawater temperatures between 10-20°C (www.obis.org). Multiple studies have shown Pentapora fascialis to display seasonal variation in the deposition of its calcareous skeleton, reflected by the difference in growth bands (Lombardi et al., 2008). Cocito et al. (2006) observed that colonies of Pentapora fascialis grew primarily during the colder months of the year, with slower growth recorded in the warmer months between May and September. Similarly, Lombardi et al. (2006) observed seasonal variation in the zooid size and growth banding, with longer zooid production during the colder months. Also, Lombardi et al. (2008) found the greatest weight percentage of calcite in the winter growth band of Pentapora. Therefore, the formation of Pentapora skeletons appears to be related to seawater temperatures.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea for over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m ) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm²) at 11 m deep survived after the first disturbance. 

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the North West Atlantic coasts, at sea surface temperatures between 5 and 20°C but mostly between 10 and 15°C (www.obis.org).  Across this latitudinal gradient species are likely to experience a range of temperatures from approx. 5 and 18°C (Sea temperature, 2015). 

Alcyonium digitatum spawns during the winter months (Hartnoll, 1975). Gametes are fertilized while in the water column and the embryos give rise to actively swimming lecithotrophic planulae that may have an extended pelagic life before they eventually settle (usually within one or two further days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975). However, laboratory experiments have observed settlement failure to occur in unsuitable conditions (Hartnoll, 1975). As spawning occurs when sea temperatures are low there is the probability that spawning and settlement could be correlated to climatic conditions, therefore global warming could impact the reproduction and recruitment of Alcyonium digitatum. However, the combination of spawning in winter and the long pelagic lifespan may allow a considerable length of time for the planulae to disperse, settle and metamorphose ahead of the spring plankton bloom (Hartnoll, 1975).

The duration, dispersal and survival of planktonic larvae are dependent on several factors including temperature (O’Connor et al., 2007). O’Connor et al. (2007) reported planktonic larval duration to increase with temperature, therefore cold-water species could see an increase in planktonic larval duration under global warming trends. Larval survival has been reported to decrease exponentially with time (planktonic larval duration) (O’Connor et al., 2007). Elevated temperatures may increase the occurrence of octocoral diseases caused by pathogens that act opportunistically to attack hosts that are under stressful conditions. For example, Cerrano et al. (2000) reported that ecosystems in the Mediterranean are rapidly declining from extensive attacks by microorganisms correlating to elevated seawater temperatures. 

The sponge Cliona celata is widespread from Norway, Iceland and the western Baltic Sea, to the Mediterranean. Elevated temperatures have been found to positively correlate with the growth of clionid sponges and provide opportunities for rapid territory expansion (Ruzler, 2002; Prezeslawski et al., 2008). Carver et al. (2010) observed the maximum growth rates of Cliona celata from June to August when seawater temperatures were >15°C. Duckworth & Peterson (2013) found high water temperatures of 31 °C to have limited negative effects on the growth, survival or boring rates of Cliona celata. 

The bryozoan Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, however, there are records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature, as acclimation to elevated temperatures appears possible. Menon (1972), for example, reported that the upper lethal temperature and median lethal temperature of Electra pilosa varied significantly with acclimation temperature, e.g. 24 hr upper lethal temperature was ca 25°C in colonies acclimated to 5°C but ca 29°C when acclimated to 22 °C (Menon, 1972).  An acute temperature change may affect growth, feeding and hence reproduction in bryozoans. The bryozoan Porella compressa is primarily recorded between temperatures of 0-15°C (www.obis.org). Therefore, Porella compressa is likely to be influenced by the elevation of seawater temperatures.  

Echinus esculentus is a sea urchin distributed across the N.E. Atlantic from Iceland, north to Finmark, Norway and south to Portugal. Echinus esculentus is common on most coasts of the British Isles but absent from most of the east coast of England, the eastern English Channel and some parts of north Wales. Echinus esculentus has been recorded most commonly at sea temperatures of 5-15°C (www.obis.org).

Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark (Ursin 1960). Temperature, photoperiod and food availability are considered to be factors that control the reproduction of echinoids (Kelly, 2001). Bishop (1985) noted that gametogenesis proceeded at temperatures between 11 - 19 °C although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after up to 24hr at 15°C (Tyler & Young 1998) but normally at the other temperatures tested (4, 7 and 11 °C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Therefore, Echinus esculentus is likely to be intolerant of chronic long term temperature change but would probably be more intolerant of sudden or short term acute change (e.g. 5 °C for one week) in temperature. 

Sensitivity assessment.  Under the middle, high and extreme emission scenarios seawater temperatures are expected to rise by 3-5°C, with potential southern summer temperatures of 22-24°C. The distribution of Alcyonium digitatum suggests that the species may be impacted by ocean warming, as populations of this species have been reported where seawater temperatures range up to 20°C (www.obis.org). Caryophyllia smithii and Parasmittina trispinosa are found in geographical locations with higher temperatures than in the UK, therefore these species are unlikely to be affected by an increase in seawater temperature, as these species are likely to adjust to gradual ocean warming. Elevated temperatures have shown to be advantageous to clionid sponges, with increased growth rates and rapid territorial expansion. The sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods and loss of grazing may change the community. While no evidence on the thermal tolerance of Pentapora foliacea and Porella compressa was found, evidence on the impacts on bryozoan species including Pentapora foliacea (Cocito & Sgorbini, 2014) and Porella compressa could be adversely affected by increased seawater temperatures. Therefore, resistance is assessed as ‘Low’ and resilience as ‘Very low’ so that sensitivity is, therefore, assessed as 'High' at levels predicted for the end of this century.

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 are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves 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).

Caryophyllia smithii is a temperate cup coral that has a wide distribution and is found in both shallow and deep waters, with records of this species between temperatures of 5-30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982). Therefore, marine heatwaves could impact the reproduction and recruitment of Caryophyllia smithii. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Leveroni, 2020). Pentapora foliacea generally occurs in seawater temperatures between 10-20°C (www.obis.org). Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea for over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m ) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm²) at 11 m deep survived after the first disturbance. 

The sponge Cliona celata is widespread from Norway, Iceland and the western Baltic Sea, to the Mediterranean. Elevated temperatures have been found to positively correlate with the growth of clionid sponges and provide opportunities for rapid territory expansion (Ruzler, 2002; Prezeslawski et al., 2008). Carver et al, (2010) observed the maximum growth rates of Cliona celata from June to August when seawater temperatures were >15°C. Duckworth & Peterson (2013) found high water temperatures of 31 °C to have limited negative effects on the growth, survival or boring rates of Cliona celata. Therefore, marine heatwaves are unlikely to impact the survival of Cliona celata. 

Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate resulting in metabolic stress (Bishop 1985). Bishop (1985) observed gametogenesis to occur between 11-19°C however, continued exposure to 19°C disrupted gametogenesis. In addition, embryos and larvae developed abnormally after 24hr exposure to 15°C (Bishop, 1985). Therefore, marine heatwaves have the potential to impact the reproduction, recruitment and survival of Echinus esculentus.  No evidence on the impacts of marine heatwaves on Alcyonium digitatum was found, this species appears to be restricted to colder waters. With Alcyonium digitatum occurring in seawater temperatures between 5- 20°C(www.obis.org).  Therefore, Alcyonium digitatum is likely to be impacted by heatwaves under both emission scenarios. 

No evidence on the impacts of marine heatwaves was found for Parasmittina trispinosa was found. Though Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, there are also records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature in the UK, as Parasmittina trispinosa is likely to acclimate to temperatures with time. However, the occurrence of marine heatwaves could cause mass mortality to populations that have not been acclimated to warmer temperatures. The bryozoan Porella compressa is primarily recorded between temperatures of 0-15°C (www.obis.org). Therefore, Porella compressa is likely to be influenced by heatwave events. 

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 occurred 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. There is no experimental evidence of the impact of marine heatwaves on Alcyonium digitatum, however, the species is unknown to tolerate seawater temperatures >20°C. Caryophyllia smithii occurs in seawater temperatures higher than marine heatwave predictions, however, reproduction is cued by changes in temperature therefore marine heatwaves could disrupt natural reproductive processes. Elevated temperatures have shown to be advantageous to clionid sponges, with increased growth rates and rapid territory expansion, therefore Cliona celata is unlikely to be impacted by heatwaves. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods and loss of grazing may alter the community.  Bryozoans are extremely sensitive to elevated temperatures; therefore, marine heatwaves could affect the calcification and survival of the characteristic bryozoan species Pentapora foliacea. Therefore, resistance is assessed as ‘Low’ and resilience as ‘Very low' so that sensitivity is, therefore, assessed as  'High' at levels predicted for the end of this century.

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 are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves 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).

Caryophyllia smithii is a temperate cup coral that has a wide distribution and is found in both shallow and deep waters, with records of this species between temperatures of 5-30°C. Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore, unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns given that gamete release is most likely triggered by seasonal temperature increases (Tranter et al., 1982). Therefore, marine heatwaves could impact the reproduction and recruitment of Caryophyllia smithii. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Leveroni, 2020). Pentapora foliacea generally occurs in seawater temperatures between 10-20°C (www.obis.org). Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea for over nine years. The warming event (a temperature of 23.87 ± 1.4°C at 11 m and of 22.27 ± 1.2°C at 22 m ) in the eastern Ligurian Sea (NW Mediterranean) in 1999 caused rapid declines in the abundance of the bryozoan Pentapora between 11 and 22 m depth with an 86% reduction in colony cover (Cocito & Sgorbini, 2014). Recovery was gradual, with communities at 22 m deep recovering to pre-disturbance levels within four years, however, none of the larger colonies (>1,000 cm²) at 11 m deep survived after the first disturbance. 

The sponge Cliona celata is widespread from Norway, Iceland and the western Baltic Sea, to the Mediterranean. Elevated temperatures have been found to positively correlate with the growth of clionid sponges and provide opportunities for rapid territory expansion (Ruzler, 2002; Prezeslawski et al., 2008). Carver et al, (2010) observed the maximum growth rates of Cliona celata from June to August when seawater temperatures were >15°C. Duckworth & Peterson (2013) found high water temperatures of 31 °C to have limited negative effects on the growth, survival or boring rates of Cliona celata. Therefore, marine heatwaves are unlikely to impact the survival of Cliona celata. 

Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate resulting in metabolic stress (Bishop 1985). Bishop (1985) observed gametogenesis to occur between 11-19°C however, continued exposure to 19°C disrupted gametogenesis. In addition, embryos and larvae developed abnormally after 24hr exposure to 15°C (Bishop, 1985). Therefore, marine heatwaves have the potential to impact the reproduction, recruitment and survival of Echinus esculentus.  No evidence on the impacts of marine heatwaves on Alcyonium digitatum was found, this species appears to be restricted to colder waters. With Alcyonium digitatum occurring in seawater temperatures between 5- 20°C(www.obis.org).  Therefore, Alcyonium digitatum is likely to be impacted by heatwaves under both emission scenarios. 

No evidence on the impacts of marine heatwaves was found for Parasmittina trispinosa was found. Though Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, there are also records of this species between 25 and 30°C (www.obis.org). Therefore, Parasmittina trispinosa is considered unlikely to be affected by long-term changes in temperature in the UK, as Parasmittina trispinosa is likely to acclimate to temperatures with time. However, the occurrence of marine heatwaves could cause mass mortality to populations that have not been acclimated to warmer temperatures. The bryozoan Porella compressa is primarily recorded between temperatures of 0-15°C (www.obis.org). Therefore, Porella compressa is likely to be influenced by heatwave events. 

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 occurred 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. There is no experimental evidence of the impact of marine heatwaves on Alcyonium digitatum, however, the species is unknown to tolerate seawater temperatures >20°C. Caryophyllia smithii occurs in seawater temperatures higher than marine heatwave predictions, however, reproduction is cued by changes in temperature therefore marine heatwaves could disrupt natural reproductive processes. Elevated temperatures have shown to be advantageous to clionid sponges, with increased growth rates and rapid territory expansion, therefore Cliona celata is unlikely to be impacted by heatwaves. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods and loss of grazing may alter the community.  Bryozoans are extremely sensitive to elevated temperatures; therefore, marine heatwaves could affect the calcification and survival of the characteristic bryozoan species Pentapora foliacea. Therefore, resistance is assessed as ‘Low’ and resilience as ‘Very low' so that sensitivity is, therefore, assessed as  'High' at levels predicted for the end of this century.

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). In general, it is thought that calcifying invertebrates will be more sensitive to ocean acidification than non-calcifying invertebrates, which appear to have a more mixed response (Hofmann et al., 2010). It must be noted that many species show variation in their response to pCO₂ independent of their taxonomic group or habitat preferences (Widdicombe & Spicer, 2008; Kroeker et al., 2013).

Ocean acidification has negative impacts on numerous species of coral; however, laboratory evidence has shown that the temperate cup coral Caryophyllia smithii might have some resistance to ocean acidification. Rodolfo-Metalpa et al. (2015) exposed Caryophyllia smithii samples to elevated CO₂ conditions expected for the end of this century for several months. All of the corals survived the treatment and no significant differences in respiration or gross and net calcification rates were observed under high seawater pCO₂. 

Bryozoans are invertebrate calcifiers, therefore they are potentially highly sensitive to ocean acidification (Smith, 2009). The decrease in water pH from global climate change could cause corrosion, changes in mineralogy and decrease the survival of Bryozoans (Smith, 2014). No evidence on the impacts of ocean acidification on the characterizing bryozoan species Parasmittina trispinosa, Pentapora foliacea and Porella compressa were found. However, Swezey et al. (2017) observed that populations of bryozoans raised under high CO₂ conditions grew faster, invested less in reproduction and produced lighter skeletons when compared to genetically identical clones raised under current surface atmospheric CO₂values. In addition, the bryozoans under high CO₂ altered Mg/Ca ratio of skeletal calcite, which could be a protective mechanism against acidification (Swezey et al., 2017). 

Lombardi et al. (2011) investigated the impacts of ocean acidification on the growth, organic tissue and protein profile of bryozoan Myriapora truncata along a gradient of different pH levels in a natural volcanic CO₂ vent site. At sites with normal pH levels (mean pH 8.10),  Myriapora truncata produced new and complete zooids. However, at the intermediate (pH 7.83) and low pH (pH 7.32) sites neither partial nor complete zooids were produced. At the intermediate pH sites, Myriapora truncata increased its skeleton thickness suggesting a protective defence against dissolution, but at the low pH sites, there was a decrease in skeletal weights and corrosion of skeletal structures. Additionally, at intermediate and low pH sites Myriapora truncata upregulated protein production to potentially overcome the low pH conditions, however, the upregulation came at a cost, and fitness was reduced resulting in mortality particularly in the lower pH sites. 

No evidence of the impacts of ocean acidification on Alcyonium digitatum was found. However, studies on the impacts of ocean acidification on octocorals reported various responses (Conci et al., 2021). Gomez et al. (2014) found a significant negative correlation between calcification and CO₂ concentrations for Eunicea flexuosa at a pH range of 8.1–7.1. But another study on Eunicea flexuosa observed no significant differences in branch extension and sclerite structure at pH 7.75 and suggested that Eunicea flexuosa had a degree of resilience to ocean acidification (Enochs et al., 2016). Similarly, ocean acidification did not significantly impact the octocorals Ovabunda macrospiculata, Heteroxenia fuscescens and Sarcophyton sp. with no effects on polyp weight and protein concentration, nor any significant differences in chlorophyll abundance or density of zooxanthellae at pH 7.6 and 7.3 when compared to controls at pH 8.2. The findings suggested that the octocoral’s tissue may provide a protective role against acidification (Gabay et al., 2013; Gabay et al., 2014).

The planktonic larval stage is often thought to be the most sensitive stage to ocean acidification in benthic organisms (Kurihara, 2008, Chan et al., 2015).  The embryos of Alcyonium digitatum are neutrally buoyant and float freely for several days before they give rise to actively swimming lecithotrophic planulae which may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). In laboratory experiments, larvae of Alcyonium digitatum failed to settle within ten days, presumably finding the conditions unsuitable (Hartnoll, 1975), however, the water conditions were not recorded. 

The sponge Cliona celata is a boring species that have been observed to have reduced survival when exposed to lowered pH levels. Duckworth & Peterson (2013) observed that the lowered pH of 7.8 reduced the survival of the sponges with 20% mortality in the lowered pH treatment, while all sponges in the control survived. Additionally, the reduced pH conditions caused Cliona celata to bore more holes and bore two times the amount of shell weight than at pH 8.1.  

Dupont et al. (2010) analysed the literature and suggested that echinoderms were generally robust to ocean acidification, although different life stages and species were affected differently. Limited evidence on the impacts of ocean acidification on Echinus esculentus was found. However, near future CO2-driven ocean acidification (-0.4 units for the end of this century) had negative impacts on survival and developmental dynamics of Echinus esculentus (Dupont and Thorndyke, personal communication, 2009).  Evidence on the reproduction or early life stages of Echinus esculentus was not found, however, studies have found a variety of responses to ocean acidification depending on the species of sea urchin. Dworjanyn & Byrne (2018) found acidification to decrease the gonad index of Tripneustes gratilla, with almost no gonads in urchins at pH 7.6 regardless of temperature. Clark et al, (2009) observed the effects of lowered pH on larvae from tropical (Tripneustes gratilla), temperate (Pseudechinus huttoni, Evechinus chloroticus), and a polar species (Sterechinus neumayeri) of sea urchin. The results indicated that the survival of larvae may not be directly affected by the pH levels predicted for 2100, but the low pH may cause reduced growth and calcification, which could compromise survival. Lee et al. (2019) observed metabolic rates of Strongylocentrotus purpuratus larvae to increase with decreasing pH and reach a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Therefore, ocean acidification could have detrimental effects on the survival, reproduction and recruitment of Echinus esculentus. 

Nevertheless, Suckling et al. (2014) emphasized that studies that presented stressors in a shock-type exposure (as above) may reflect stress response outcomes rather than the results of gradual change in the climate. Cross generation echinoderm studies observed a variety of responses to the progeny produced by adults that have been exposed to low pH. The evidence indicated that the effect on progeny depended on the level of acidification and the conditioning duration of the parents (Byrne et al., 2019). Suckling et al. (2014) found that when Psammechinus miliaris larvae were raised from parents pre-exposed to low pH conditions (pH 7.7 compared to control pH of 7.98), settlement rates were similar to control larvae, and the test (i.e. the urchin shell) diameter was larger, which suggested that this species can acclimate and possibly adapt to low pH conditions. Similarly, Clark et al. (2019) observed that gene expression profiles associated with transgenerational plasticity contributed to Psammechinus miliaris larval resilience when the adults were conditioned to low pH.

From observations at natural vent sites, Connell et al. (2018) observed that increased CO₂ enrichment reduced the abundance and feeding rates of primary grazers (the urchin Evechinus chloroticus), allowing turf algae to increase in abundance. Therefore, ocean acidification could cause changes to community structure. 

Sensitivity Assessment. While limited evidence of the impacts of ocean acidification on Echinus esculentus was found, the effects of ocean acidification on other echinoderms species have shown species dependent sensitivity. No evidence of the effect of ocean acidification on Alcyonium digitatum was found, although the effects of ocean acidification on other species of octocoral have indicated some resilience to low pH. Though Alcyonium digitatum larvae settlement has been reported to be sensitive to environmental conditions, however, the conditions were not verified. Bryozoans appear to be highly sensitive to ocean acidification, with impacts on health, survival and reproduction.  Laboratory evidence has shown that Caryophyllia smithii has some resistance to ocean acidification, therefore the evidence suggests that Caryophyllia smithii may be able to tolerate future pH predictions, however, impacts on reproduction and recruitment were not reviewed. At present, there are no studies to determine whether Echinus esculentus can adapt or acclimate to future pH conditions, but on the evidence available, Echinus esculentus could be lost from this biotope under the predicted emissions scenarios. Loss of this important grazer may change the abundance and diversity of the faunal turf, and result in a different biotope. Similarly, the characteristic bryozoans, especially Pentapora foliacea may be lost. Therefore, resistance is assessed as ‘Low’ under both the middle and high emission scenarios (0.15 and 0.35 pH unit decrease, respectively). Resilience is assessed as ‘Very low’ because of the long-term nature of ocean acidification so that sensitivity is assessed as ‘High’  albeit with ‘Low’ confidence.

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). In general, it is thought that calcifying invertebrates will be more sensitive to ocean acidification than non-calcifying invertebrates, which appear to have a more mixed response (Hofmann et al., 2010). It must be noted that many species show variation in their response to pCO₂ independent of their taxonomic group or habitat preferences (Widdicombe & Spicer, 2008; Kroeker et al., 2013).

Ocean acidification has negative impacts on numerous species of coral; however, laboratory evidence has shown that the temperate cup coral Caryophyllia smithii might have some resistance to ocean acidification. Rodolfo-Metalpa et al. (2015) exposed Caryophyllia smithii samples to elevated CO₂ conditions expected for the end of this century for several months. All of the corals survived the treatment and no significant differences in respiration or gross and net calcification rates were observed under high seawater pCO₂. 

Bryozoans are invertebrate calcifiers, therefore they are potentially highly sensitive to ocean acidification (Smith, 2009). The decrease in water pH from global climate change could cause corrosion, changes in mineralogy and decrease the survival of Bryozoans (Smith, 2014). No evidence on the impacts of ocean acidification on the characterizing bryozoan species Parasmittina trispinosa, Pentapora foliacea and Porella compressa were found. However, Swezey et al. (2017) observed that populations of bryozoans raised under high CO₂ conditions grew faster, invested less in reproduction and produced lighter skeletons when compared to genetically identical clones raised under current surface atmospheric CO₂values. In addition, the bryozoans under high CO₂ altered Mg/Ca ratio of skeletal calcite, which could be a protective mechanism against acidification (Swezey et al., 2017). 

Lombardi et al. (2011) investigated the impacts of ocean acidification on the growth, organic tissue and protein profile of bryozoan Myriapora truncata along a gradient of different pH levels in a natural volcanic CO₂ vent site. At sites with normal pH levels (mean pH 8.10),  Myriapora truncata produced new and complete zooids. However, at the intermediate (pH 7.83) and low pH (pH 7.32) sites neither partial nor complete zooids were produced. At the intermediate pH sites, Myriapora truncata increased its skeleton thickness suggesting a protective defence against dissolution, but at the low pH sites, there was a decrease in skeletal weights and corrosion of skeletal structures. Additionally, at intermediate and low pH sites Myriapora truncata upregulated protein production to potentially overcome the low pH conditions, however, the upregulation came at a cost, and fitness was reduced resulting in mortality particularly in the lower pH sites. 

No evidence of the impacts of ocean acidification on Alcyonium digitatum was found. However, studies on the impacts of ocean acidification on octocorals reported various responses (Conci et al., 2021). Gomez et al. (2014) found a significant negative correlation between calcification and CO₂ concentrations for Eunicea flexuosa at a pH range of 8.1–7.1. But another study on Eunicea flexuosa observed no significant differences in branch extension and sclerite structure at pH 7.75 and suggested that Eunicea flexuosa had a degree of resilience to ocean acidification (Enochs et al., 2016). Similarly, ocean acidification did not significantly impact the octocorals Ovabunda macrospiculata, Heteroxenia fuscescens and Sarcophyton sp. with no effects on polyp weight and protein concentration, nor any significant differences in chlorophyll abundance or density of zooxanthellae at pH 7.6 and 7.3 when compared to controls at pH 8.2. The findings suggested that the octocoral’s tissue may provide a protective role against acidification (Gabay et al., 2013; Gabay et al., 2014).

The planktonic larval stage is often thought to be the most sensitive stage to ocean acidification in benthic organisms (Kurihara, 2008, Chan et al., 2015).  The embryos of Alcyonium digitatum are neutrally buoyant and float freely for several days before they give rise to actively swimming lecithotrophic planulae which may have an extended pelagic life before they eventually settle (usually within one or two additional days) and metamorphose to polyps (Matthews, 1917; Hartnoll, 1975; Budd, 2008). In laboratory experiments, larvae of Alcyonium digitatum failed to settle within ten days, presumably finding the conditions unsuitable (Hartnoll, 1975), however, the water conditions were not recorded. 

The sponge Cliona celata is a boring species that have been observed to have reduced survival when exposed to lowered pH levels. Duckworth & Peterson (2013) observed that the lowered pH of 7.8 reduced the survival of the sponges with 20% mortality in the lowered pH treatment, while all sponges in the control survived. Additionally, the reduced pH conditions caused Cliona celata to bore more holes and bore two times the amount of shell weight than at pH 8.1.  

Dupont et al. (2010) analysed the literature and suggested that echinoderms were generally robust to ocean acidification, although different life stages and species were affected differently. Limited evidence on the impacts of ocean acidification on Echinus esculentus was found. However, near future CO2-driven ocean acidification (-0.4 units for the end of this century) had negative impacts on survival and developmental dynamics of Echinus esculentus (Dupont and Thorndyke, personal communication, 2009).  Evidence on the reproduction or early life stages of Echinus esculentus was not found, however, studies have found a variety of responses to ocean acidification depending on the species of sea urchin. Dworjanyn & Byrne (2018) found acidification to decrease the gonad index of Tripneustes gratilla, with almost no gonads in urchins at pH 7.6 regardless of temperature. Clark et al, (2009) observed the effects of lowered pH on larvae from tropical (Tripneustes gratilla), temperate (Pseudechinus huttoni, Evechinus chloroticus), and a polar species (Sterechinus neumayeri) of sea urchin. The results indicated that the survival of larvae may not be directly affected by the pH levels predicted for 2100, but the low pH may cause reduced growth and calcification, which could compromise survival. Lee et al. (2019) observed metabolic rates of Strongylocentrotus purpuratus larvae to increase with decreasing pH and reach a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Therefore, ocean acidification could have detrimental effects on the survival, reproduction and recruitment of Echinus esculentus. 

Nevertheless, Suckling et al. (2014) emphasized that studies that presented stressors in a shock-type exposure (as above) may reflect stress response outcomes rather than the results of gradual change in the climate. Cross generation echinoderm studies observed a variety of responses to the progeny produced by adults that have been exposed to low pH. The evidence indicated that the effect on progeny depended on the level of acidification and the conditioning duration of the parents (Byrne et al., 2019). Suckling et al. (2014) found that when Psammechinus miliaris larvae were raised from parents pre-exposed to low pH conditions (pH 7.7 compared to control pH of 7.98), settlement rates were similar to control larvae, and the test (i.e. the urchin shell) diameter was larger, which suggested that this species can acclimate and possibly adapt to low pH conditions. Similarly, Clark et al. (2019) observed that gene expression profiles associated with transgenerational plasticity contributed to Psammechinus miliaris larval resilience when the adults were conditioned to low pH.

From observations at natural vent sites, Connell et al. (2018) observed that increased CO₂ enrichment reduced the abundance and feeding rates of primary grazers (the urchin Evechinus chloroticus), allowing turf algae to increase in abundance. Therefore, ocean acidification could cause changes to community structure. 

Sensitivity Assessment. While limited evidence of the impacts of ocean acidification on Echinus esculentus was found, the effects of ocean acidification on other echinoderms species have shown species dependent sensitivity. No evidence of the effect of ocean acidification on Alcyonium digitatum was found, although the effects of ocean acidification on other species of octocoral have indicated some resilience to low pH. Though Alcyonium digitatum larvae settlement has been reported to be sensitive to environmental conditions, however, the conditions were not verified. Bryozoans appear to be highly sensitive to ocean acidification, with impacts on health, survival and reproduction.  Laboratory evidence has shown that Caryophyllia smithii has some resistance to ocean acidification, therefore the evidence suggests that Caryophyllia smithii may be able to tolerate future pH predictions, however, impacts on reproduction and recruitment were not reviewed. At present, there are no studies to determine whether Echinus esculentus can adapt or acclimate to future pH conditions, but on the evidence available, Echinus esculentus could be lost from this biotope under the predicted emissions scenarios. Loss of this important grazer may change the abundance and diversity of the faunal turf, and result in a different biotope. Similarly, the characteristic bryozoans, especially Pentapora foliacea may be lost. Therefore, resistance is assessed as ‘Low’ under both the middle and high emission scenarios (0.15 and 0.35 pH unit decrease, respectively). Resilience is assessed as ‘Very low’ because of the long-term nature of ocean acidification so that sensitivity is assessed as ‘High’  albeit with ‘Low’ confidence.

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). Evidence appears to suggest that impacts of sea-level rise on exposure or tidal energy will be non-linear and site-specific (Pickering et al., 2012, Li et al., 2016).  This biotope occurs on mixed sediment, in moderately exposed to sheltered areas, subject to strong to weak tidal streams and, therefore, should be reasonably robust to any changes which occur. Furthermore, this biotope occurs at depths of 10-50 m around the UK, and sea-level rises predicted for the end of this century should have limited impacts on this biotope.

Sensitivity assessment. As this biotope CR.MCR.EcCr.CarSp.PenPcom can occur from 10-50 m depth, in a range of different energy environments, it is assumed that a sea-level rise of 50 cm, 70 cm or 107 cm (middle and high emission, and extreme scenarios) would have limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. 

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). Evidence appears to suggest that impacts of sea-level rise on exposure or tidal energy will be non-linear and site-specific (Pickering et al., 2012, Li et al., 2016).  This biotope occurs on mixed sediment, in moderately exposed to sheltered areas, subject to strong to weak tidal streams and, therefore, should be reasonably robust to any changes which occur. Furthermore, this biotope occurs at depths of 10-50 m around the UK, and sea-level rises predicted for the end of this century should have limited impacts on this biotope.

Sensitivity assessment. As this biotope CR.MCR.EcCr.CarSp.PenPcom can occur from 10-50 m depth, in a range of different energy environments, it is assumed that a sea-level rise of 50 cm, 70 cm or 107 cm (middle and high emission, and extreme scenarios) would have limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. 

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). Evidence appears to suggest that impacts of sea-level rise on exposure or tidal energy will be non-linear and site-specific (Pickering et al., 2012, Li et al., 2016).  This biotope occurs on mixed sediment, in moderately exposed to sheltered areas, subject to strong to weak tidal streams and, therefore, should be reasonably robust to any changes which occur. Furthermore, this biotope occurs at depths of 10-50 m around the UK, and sea-level rises predicted for the end of this century should have limited impacts on this biotope.

Sensitivity assessment. As this biotope CR.MCR.EcCr.CarSp.PenPcom can occur from 10-50 m depth, in a range of different energy environments, it is assumed that a sea-level rise of 50 cm, 70 cm or 107 cm (middle and high emission, and extreme scenarios) would have limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. 

Temperature increase (local)

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

Evidence

Caryophyllia smithii is found across the British Isles (NBN, 2015) and has been recorded in Greece (Koukouras, 2010).  It is therefore unlikely to be significantly affected by an increase at the benchmark level. However, Tranter et al. (1982) suggested Caryophyllia smithii reproduction was cued by seasonal increases in seawater temperature. Therefore unseasonal increases in temperature may disrupt natural reproductive processes and negatively influence recruitment patterns.

Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Ursin (1960) reported Echinus esculentus occurred at temperatures between 0-18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11-19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24 hr exposure to 15°C but normally at 4, 7 and 11°C (Tyler & Young 1998).  High temperature (up to 31 °C) had little effect on the growth, survival and boring rate of the sponge Cliona celata Alcyonium digitatum is described as a northern species by Hiscock et al. (2004), but is distributed from northern Norway (70°N) to Portugal (41°N) (Hartnoll, 1975; Budd, 2008) and is commonly found across the British Isles (Fish  & Fish, 1992).  Bishop (1985) suggested that Echinus esculentus cannot tolerate high temperatures for prolonged periods due to increased respiration rate and resultant metabolic stress. Ursin (1960) reported Echinus esculentus occurred at temperatures between 0-18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11-19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24 hr exposure to 15°C but normally at 4, 7 and 11°C (Tyler & Young 1998).  Parasmittina trispinosa is commonly found across the whole of the British Isles (NBN, 2015) and is distributed from the Northern coast of Norway to the Mediterranean (Hayward & Ryland, 1990). 

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years.  High temperature events causied mass mortality among a number of species.  The decline in Pentapora fascialis colony cover between 11 and 22 m depth followed the unusually warm summer in 1999 (temperature at 11 m of 23.87 ± 1.4 °C)  with a 86% reduction in live colony portion and the larger colonies were most affected.  Gradual recovery took place, with deeper communities recovering to pre-disturbance levels within four years.  Whilst Hayward & Ryland (1999) conflated Pentapora foliacea and Pentapora fascialis, Lombardi et al. (2010) concluded that Pentapora foliacea and Pentpora fascialis were distinct species and that P. foliacea was the resident species in the North East Atlantic while P.fascialis was included in the Mediterranean clade (Duckworth & Bradley, 2012).  

Sensitivity assessment. Whilst Caryophyllia smithii, Alcyonium digitatum and the bryozoans are likely to tolerate an increase in temperature at the benchmark level, evidence suggests that Echinus esculentus may be affected. Resistance has been assessed as ‘Medium’, resilience has been assessed as ‘High’ and sensitivity has been assessed as ‘Low’.

Temperature decrease (local)

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

Evidence

Alcyonium digitatum is described as a northern species by Hiscock et al. (2004), but is distributed from Northern Norway (70°N) to Portugal (41°N) (Hartnoll, 1975; Budd, 2008).   Alcyonium digitatum was also reported to be apparently unaffected by the severe winter of 1962-1963 where air temperature reached -5.8°C (Crisp, 1964a). Parasmittina trispinosa is commonly found across the whole of the British Isles (NBN, 2015) and is distributed from the northern coast of Norway to the Mediterranean (Hayward& Ryland, 1990).

Ursin (1960) reported Echinus esculentus occurred at temperatures between 0-18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11-19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24 hr exposure to 15°C but normally at 4, 7 and 11°C (Tyler & Young 1998).  Echinus esculentus has been recorded from the Murmansk Coast, Russia. Due to the high latitude at which Echinus esculentus can occur, it is unlikely to be affected by a decrease in temperature at the pressure benchmark.

Pentapora foliacea is found as far north the Minch off western Scotland (Lombardi et al., 2010). Patzold et al. (1987) recorded the formation of a growth bands in Pentapora foliacea during times of reduced reproduction, which appeared during periods of colder water temperatures.  Once established, colonies are most likely able to withstand occasional lower or higher than normal temperatures, but long-term decreases in temperature may cause distribution range to shrink. Caryophyllia smithii is a southern species (Fish & Fish, 1992) with a northern range limit in the Shetland isles (NBN, 2015).  Therefore, it is likely to be negatively affected by cold temperatures in northern examples of this biotope.

Sensitivity assessment. Alcyonium digitatum, Echinus esculentus have northern/boreal distributions and are unlikely to be affected at the benchmark level. Spirobranchus triqueter is unable to build calcareous tubes at low temperatures, however, during winter, this is unlikely to have any significant effects on recruitment. In addition, the depth of the biotope probably protects it from short-term acute decreases in temperature. The important characterizing Caryophyllia smithii and Pentapora foliacea are close to their northern distribution limit within the British Isles and a decrease at the benchmark level may result in some mortality in northern examples of the biotope.  Therefore, resistance is therefore ‘Medium’, resilience is ‘High’ and sensitivity is ‘Low’.

Salinity increase (local)

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

Evidence

Echinoderms are generally stenohaline and possess no osmoregulatory organ (Boolootian, 1966) and lack the ability to osmo- and ion-regulate (Stickle & Diehl, 1987). The inability of echinoderms to osmoregulate extracellularly causes body fluid volume to decrease when individuals experience higher external salinity.  Protracted hypersalinity is likely to result in the decline of echinoderm populations. Echinoderm larvae have a narrow range of salinity tolerance and will develop abnormally and die if exposed to increased salinity (Tyler-Walters, 2008).   Alcyonium digitatum distribution and the depth at which it occurs also suggest it would not likely experience regular salinity fluctuations and therefore not resists significant increases in salinity.  CR.MCR.EcCr.CarSp.PenPcom occurs in full salinity (Connor et al., 2004), it is therefore possible that an increase in salinity may cause a decline in the abundance of Alcyonium digitatum, Echinus esculentus and the faunal crust.

Sensitivity assessment. It is likely that Echinus esculentus is stenohaline and hypersaline conditions would probably affect the species.  Resistance has been assessed as ‘Low’, resilience as ‘Medium’, and sensitivity has been assessed as ‘Medium’.  Due to the lack of information regarding salinity effects on the characterizing species, confidence in this assessment has been assessed as low.

Salinity decrease (local)

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

Evidence

Alcyonium digitatum is found at the entrances to sea lochs (Budd, 2008) and estuaries (Braber & Borghouts, 1977) where salinity may vary occasionally. Furthermore, Alcyonium digitatum is found within a number of variable salinity biotopes, e.g. MCR.BYH.Flu.Hocu (Connor et al., 2004).  However, its distribution and the depth, at which it occurs suggest that Alcyonium digitatum would not likely often experience salinity fluctuations and is, therefore, unlikely to survive significant reductions in salinity (Budd, 2008).

Caryophyllia smithii has been recorded in biotopes from Full to Low salinity (Connor et al., 2004) and would probably tolerate a change at the benchmark level.

Echinoderms are generally unable to tolerate low salinity (stenohaline) and possess no osmoregulatory organ (Boolootian, 1966). At low salinity urchins gain weight, and the epidermis loses its pigment as patches are destroyed; prolonged exposure is fatal. However, within Echinus esculentus there is some evidence to suggest intracellular regulation of osmotic pressure due to increased amino acid concentrations. Echinus esculentus is found within a number of variable and reduced salinity biotopes, e.g. IR.LIR.KVS.SlatPsaVS (Connor et al., 2004).

Novosel et al. (2004) described large colonies of Pentapora fascialis growing inside the plumes of marine freshwater springs (3 psu lower than water outside of the channel).

Sensitivity assessment. CR.MCR.EcCr.CarSp.PenPcom is recorded exclusively in full marine conditions (30-35 ppt) (Connor et al., 2004). Records from the MNCR suggest Alcyonium digitatum and Echinus esculentus can occur in reduced salinity habitats, however the evidence suggests that these species would decrease in abundance.  In addition, a reduction in salinity may result in a reduction in species richness of the biotope. Therefore, resistance has been assessed as ‘Low’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

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

The biotope (EcCr.CarSp.PenPcom) occurs in extremely to moderately wave exposed conditions in areas of moderately strong to negligible water flow at 10-50m depth (Connor et al., 2004).  The biotope is structured by grazing, especially by Echinus esculentus.  The biotope probably occurs at a critical range of water movement that allows the Echinus esculentus population to remain in high enough abundance to structure the biotope.  Deep examples probably depend on water flow or extreme wave action, while shallow examples depend on wave action or water flow.

Alcyonium digitatum and the bryozoans are suspension feeders relying on water currents to supply food. These taxa, therefore, thrive in conditions of vigorous water flow e.g. around Orkney and St Abbs, Scotland, where the community may experience tidal currents of 3 and 4 knots (1.5 and 2 m/s) during spring tides (De Kluijver, 1993).

Echinus esculentus occurred in kelp beds on the west coast of Scotland in currents of about 0.5 m/sec. Outside the beds, specimens were occasionally seen being rolled by the current (Comely & Ansell, 1988), which may have been up to 1.4 m/sec. Echinus esculentus are also displaced by storm action. After disturbance Echinus esculentus migrates up the shore, an adaptation to being washed to deeper water by wave action (Lewis & Nichols, 1979a). Therefore, increased water flow may remove the population from the affected area, probably to deeper water, however individuals would probably not be killed in the process and could recolonize the area quickly.

Sensitivity assessment. This biotope occurs in negligible water flow, so a reduction in water flow would therefore not affect the biotope.  All characterizing species are likely to be tolerant of an increase at the benchmark level (0.1-0.2 m/s), being present in biotopes with stronger water flow.

Resistance is therefore ‘High’, resilience is ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Emergence regime changes

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

Evidence

Changes in emergence are ‘Not relevant’ to this biotope as it is restricted to fully subtidal/circalittoral conditions - the pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

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

The biotope (EcCr.CarSp.PenPCom) occurs in extremely to moderately wave exposed conditions in areas of moderately strong to negligible water flow at 10-50m depth (Connor et al., 2004).  The biotope is structured by grazing, especially by Echinus esculentus.  The biotope probably occurs at a critical range of water movement that allows the Echinus population to remain in high enough abundance to structure the biotope.  Deep examples probably depend on water flow or extreme wave action, while shallow examples depend on wave action or water flow.

Alcyonium digitatum are suspension feeders relying on water currents to supply food. These taxa therefore thrive in conditions of vigorous water flow. As a circalittoral biotope (recorded from 5 - 50 m), the depth at which these biotopes occur may therefore also reduce the direct physical effects of a localised change in wave height; wave attenuation is directly related to water depth (Hiscock, 1983).

Caryophyllia smithii was recorded in very sheltered to extremely exposed biotopes (Connor et al., 2004).

Pentapora foliacea was recorded as occurring in biotopes experiencing moderate to extreme wave exposure (Connor et al., 2004). However, extreme wave action (storms) has been noted to cause widespread destruction of colonies (Cocito et al. (1998a). Significant increases in wave exposure may therefore cause damage to colonies.

Echinus esculentus occurred in kelp beds on the west coast of Scotland in currents of about 0.5 m/sec. Outside the beds, specimens were occasionally seen being rolled by the current (Comely & Ansell, 1988), which may have been up to 1.4 m/sec. Urchins are removed from the stipe of kelps by wave and current action. Echinus esculentus are also displaced by storm action. After disturbance, Echinus esculentus migrates up the shore, an adaptation to being washed to deeper water by wave action (Lewis & Nichols, 1979a). Keith Hiscock (pers. comm.) reported Echinus esculentus occurred in significant numbers as shallow as 15 m below low water at the extremely wave exposed site of Rockall, Scotland.

Sensitivity assessment. Whilst storm events may have an impact on the biotope, a change at the benchmark level is not likely to have a significant effect on the characterizing species. Resistance has been assessed as ‘High’, resilience has been assessed as ‘High’ and the biotope is assessed as ‘Not sensitive’ at the benchmark level.

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

Little is known about the effects of heavy metals on echinoderms. Bryan (1984) reported that early work had shown that echinoderm larvae were sensitive to heavy metals contamination, for example Migliaccio et al. (2014) reported exposure of Paracentrotus lividis larvae to increased levels of cadmium and manganese caused abnormal larval development and skeletal malformations. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu).

No information was found on the direct biological effects of heavy metal contamination on Alcyonium digitatum. Possible sub-lethal effects of exposure to heavy metals, may result in a change in morphology, growth rate or disruption of reproductive cycle. The vulnerability of this species to concentrations of pollutants may also depend on variations in other factors e.g. temperature and salinity conditions outside the normal range.

Bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1979; Holt et al., 1995). Bryozoans were shown to bioaccumulate heavy metals to a certain extent (Holt et al., 1995). For example, Bowerbankia gracialis and Nolella pusilla accumulated Cd, exhibiting sublethal effects (reduced sexual reproduction and inhibited resting spore formation) between 10-100 µg Cd /l and fatality above 500 µg Cd/l (Kayser, 1990).

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.

Echinus esculentus was reported absent after the oil spill however returned after 2-5 years. Large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m in the vicinity of Sennen cove, presumably due to a combination of wave exposure and heavy spraying of dispersants following the Torrey Canyon oil spill (Smith, 1968). Smith (1968) also demonstrated that 0.5 -1ppm of the detergent BP1002 resulted in developmental abnormalities in its echinopluteus larvae. Echinus esculentus populations in the vicinity of an oil terminal in La Coruna Bay, Spain, showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gommez & Miguez-Rodriguez, 1999).

Oil pollution is mainly a surface phenomenon, so its impact upon circalittoral turf communities is likely to be limited. However, as in the case of the Prestige oil spill off the coast of France, high swell and winds can cause oil pollutants to mix with the seawater and potentially negatively affect sub-littoral habitats (Castège et al., 2014). Smith (1968) reported dead colonies of Alcyonium digitatum at a depth of 16m in the locality of Sennen Cove, Cornwall which was likely a result of toxic detergents sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill (Budd, 2008). Little information on the effects of hydrocarbons on bryozoans could be found. Ryland & De Putron (1998) did not detect adverse effects of oil contamination on the bryozoan Alcyonidium spp. in Milford Haven or St. Catherine's Island, south Pembrokeshire although it did alter the breeding period. Echinus esculentus is subtidal and unlikely to be directly exposed to oil spills. However, as with the ‘Prestige’ oil spill rough seas can cause mixing with the oil and the seawater, and therefore sub-tidal habitats can be affected by the oil spill. Castège et al., (2014) recorded the recovery of rocky shore communities following the Prestige oil spill which impacted the French Atlantic coast. Rough weather at the time of the spill increased mixing between the oil and seawater, causing sub-tidal communities/habitats to be affected.

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.

Smith (1968) reported dead colonies of Alcyonium digitatum at a depth of 16 m in the locality of Sennen Cove, Cornwall resulting from the offshore spread and toxic effect of detergents (a mixture of a surfactant and an organic solvent). Possible sub-lethal effects of exposure to synthetic chemicals may result in a change in morphology, growth rate or disruption of reproductive cycle. The vulnerability of this species to concentrations of pollutants may also depend on variations in other factors e.g. temperature and salinity conditions outside the normal range (Budd, 2008).

Hoare & Hiscock (1974) suggested that polyzoa (bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay, Anglesey and reported that Flustra foliacea did not occur less than 165m from the effluent source. The evidence therefore suggests that Parasmittina trispinosa would be sensitive to synthetic compounds.

Radionuclide contamination

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

Evidence

'No evidence' was found.

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

Mass mortality of species including Echinus esculentus was observed due to a stratified hypoxic event below 8 m caused by a phytotplankton bloom ( Griffiths et al., 1979).  Hiscock & Hoare (1975) reported an oxycline forming in the summer months (Jun-Sep) in a quarry lake (Abereiddy, Pembrokeshire) from close to full oxygen saturation at the surface to <5% saturation below ca 10 m.  During these summer events, no echinoderms were recorded at depths below 10 - 11 m.  At the time of writing there was insufficient evidence on which to assess this pressure. There is anecdotal evidence to suggest that Alcyonium digitatum is sensitive to hypoxic events. However, because the degree of de-oxygenation wasn’t quantified the evidence cannot be compared to the pressure benchmark.  In general, respiration in most marine invertebrates does not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates this concentration is about 2 ml/l, or even less (Herreid, 1980; Rosenberg et al., 1991; Diaz & Rosenberg, 1995).  Alcyonium digitatum mainly inhabits environments in which the oxygen concentration usually exceeds 5 ml/l and respiration is aerobic (Budd, 2008). In August 1978 a dense bloom of a dinoflagellate, Gyrodinium aureolum occurred surrounding Geer Reef in Penzance Bay, Cornwall and persisted until September that year. Observations by local divers indicated a decrease in underwater visibility (<1 m) from below 8 m. It was also noted that many of the faunal species appeared to be affected, e.g. no live Echinus esculentus were observed whereas on surveys prior to August were abundant, Alcyonium sp. and bryozoans were also in an impoverished state. During follow up surveys conducted in early September Alcyonium sp. were noted to be much healthier and feeding. It was suggested the decay of Gyrodinium aureolum either reduced oxygen levels or physically clogged faunal feeding mechanisms. Adjacent reefs where also surveyed during the same time period and the effects of the Gyrodinium aureolum bloom were less apparent. It was suggested that higher water agitation in shallow water on reefs more exposed to wave action were less effected by the phytoplankton bloom (Griffiths et al., 1979).   CR.MCR.EcCr.CarSp.PenPcom is recorded from very weak to moderately strong tidal streams (negligible to 1.5 m/sec) (Connor et al., 2004). Whilst mixing with surrounding oxygenated water is likely to occur in examples of this biotope that experience moderate water movement (Dennis, 1979), de-oxygenation is likely to become a chronic factor in examples where there is negligible water movement. 

Whilst little information on Pentapora spp. was found, O’Dea & Okamura (2000) found that annual growth of the bryozoan Flustra foliacea in western Europe has substantially increased since 1970.  They suggest that this could be due to eutrophication in coastal regions due to organic pollution, leading to increased phytoplankton biomass (see Allen et al., 1998).    Echavarri-Erasun et al. (2007) described the effects of deep water sewage discharge on the relative abundance of rocky reef communities.  Species typical of hard substrata (including Caryophyllia smithii and bryozoans) increased in total richness and abundance near the outfall. 

Sensitivity assessment

The characterizing species are likely to suffer significant mortality in a hypoxic event at the benchmark level, especially in examples of the biotope that occur with negligible water flow in which it may take longer for the oxygen levels to recover.  Whilst the majority of assessed species are sessile, Echinus esculentus is mobile and may escape the hypoxic event (depending on extent and conditions). Resistance is assessed as ‘Low’, Resilience as ‘Medium’ (assuming recovery to normal oxygen conditions) and sensitivity as ‘Medium’.

Nutrient enrichment

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

Evidence

t was suggested by Comely & Ansell (1988) that Echinus esculentus could absorb dissolved organic material for the purposes of nutrition. Nutrient enrichment may encourage the growth of ephemeral and epiphytic algae and therefore increase sea-urchin food availability. Lawrence (1975) reported that sea urchins had persisted over 13 years on barren grounds near sewage outfalls, presumably feeding on dissolved organic material, detritus, plankton and microalgae, although individuals died at an early age.  Alcyonium digitatum is a suspension feeders of phytoplankton and zooplankton. Nutrient enrichment of coastal waters that enhances the population of phytoplankton may be beneficial to these species in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). High primary productivity in the water column combined with high summer temperature and the development of thermal stratification (which prevents mixing of the water column) can lead to hypoxia (see de-oxygenation).  Nutrient enrichment could also lead to algal blooms.

Whilst little information on Pentapora spp. was found, O’Dea & Okamura (2000) found that annual growth of the bryozoan Flustra foliacea in western Europe has substantially increased since 1970.  They suggest that this could be due to eutrophication in coastal regions due to organic pollution, leading to increased phytoplankton biomass (see Allen et al., 1998).

This biotope is considered to be 'Not sensitive' at the pressure benchmark that assumes compliance with good status as defined by the WFD.

Organic enrichment

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

Evidence

It was suggested by Comely & Ansell (1988) that Echinus esculentus could absorb dissolved organic material for the purposes of nutrition. Organic enrichment may encourage the growth of ephemeral and epiphytic algae and therefore increase sea-urchin food availability. Lawrence (1975) reported that sea urchins had persisted over 13 years on barren grounds near sewage outfalls, presumably feeding on dissolved organic material, detritus, plankton and microalgae, although individuals died at an early age. Alcyonium digitatum is a suspension feeders of phytoplankton and zooplankton. Organic enrichment of coastal waters that enhances the population of phytoplankton may be beneficial to these species in terms of an increased food supply but the effects are uncertain (Hartnoll, 1998). High primary productivity in the water column combined with high summer temperature and the development of thermal stratification (which prevents mixing of the water column) can lead to hypoxia, (see de-oxygenation)

Sensitivity assessment.  ‘No evidence’ of the effects of organic enrichment in circalittoral faunal crusts was found.

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

If rock were replaced with sediment, this would represent a fundamental change to the physical character of the biotope and the species would be unlikely to recover. The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very low’. Sensitivity has been assessed as ‘High’.

Physical change (to another sediment type)

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

Evidence

‘Not relevant’ to biotopes occurring on bedrock.

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 species characterizing this biotope are epifauna or epiflora occurring on rock and would be sensitive to the removal of the habitat. However, extraction of rock substratum is considered unlikely and this pressure is considered to be ‘Not relevant’ to hard substratum habitats.

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

Alcyonium digitatum, Echinus esculentus and Parasmittina trispinosa are sessile or slow moving species that might be expected to suffer from the effects of abrasion. Boulcott & Howell (2011) conducted experimental Newhaven scallop dredging over a circalittoral rock habitat in the sound of Jura, Scotland and recorded the damage to the resident community. Only 13% of photographic samples showed visible damage to Alcyonium digitatum. Where Alcyonium digitatum damage was evident it tended to be small colonies that were ripped off the rock. The authors highlight physical damage to faunal turfs (erect bryozoans and hydroids) was difficult to quantify in the study. However, the faunal turf communities did not show large signs of damage and were only damaged by the scallop dredge teeth, which was often limited in extent (approximately 2 cm wide tracts). The authors indicated that species such as Alcyonium digitatum and faunal turf communities were not as vulnerable to damage through trawling as sedimentary fauna and whilst damage to circalittoral rock fauna did occur it was of an incremental nature, with loss of species such as Alcyonium digitatum and faunal turf communities increasing with repeated trawls.  Species with fragile tests, such as Echinus esculentus were reported to suffer badly as a result of scallop or queen scallop dredging (Bradshaw et al., 2000; Hall-Spencer & Moore, 2000a). Kaiser et al. (2000) reported that Echinus esculentus were less abundant in areas subject to high trawling disturbance in the Irish Sea. Jenkins et al. (2001) conducted experimental scallop trawling in the North Irish sea and recorded the damage caused to several conspicuous megafauna species.  The authors used simultaneous assessment of both bycatch and organisms left on the seabed to estimate capture efficiency for both target and non-target organisms. This found 16.4% of Echinus esculentus were crushed or dead, 29.3% had >50% spine loss/minor cracks, 1.1% had  <50% spine loss and the remaining 53.3% were in good condition. Sea urchins can rapidly regenerate spines, e.g. Psammechinus miliaris were found to re-grow all spines within a period of 2 months (Hobson, 1930).  The trawling examples mentioned above were conducted on sedimentary habitats and thus the evidence is not directly relevant to rock based, however it does indicate the likely effects of abrasion on Echinus esculentus.

Some large Pentapora foliacea individuals were observed to be badly smashed by potting (Eno et al., 2001).

Van Dolah et al. (1987) studied the effects on sponges and corals of one trawl event over a low-relief hard bottom habitat off Georgia, US.  The densities of individuals taller than 10 cm of three species of sponges in the trawl path and in adjacent control area were assessed by divers, and were compared before, immediately after and 12 months after trawling.  Of the total number of sponges remaining in in the trawled area, 32% were damaged.  Most of the affected sponges were the barrel sponges Cliona spp. However the abundance of sponges had increased to pre-trawl densities, or greater12 months after trawling.

Sensitivity assessment. Whilst abrasion pressures tend to heavily impact sessile or slow moving marine species, the evidence suggests that mortality amongst the characterizing species is ‘Medium’ (<25% loss) for the characterizing  Alcyonium digitatum and Echinus esculentus.  It should be noted that this is dependent on the abrasion activity and heavier gears may well cause more damage. 

Based on the evidence for the characterizing species, resistance is ‘Medium’, resilience as ‘High’ and sensitivity as ‘Low’.

Please note Boulcott & Howell (2011) did not mention the abrasion caused by fully loaded collection bags on the new haven dredges. A fully loaded Newhaven dredge may cause higher damage to community than indicated in their study.

Penetration or disturbance of the substratum subsurface

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

Evidence

The species characterizing this biotope group are epifauna or epiflora occurring on rock which is resistant to subsurface penetration.  The assessment for abrasion at the surface only is therefore considered to equally represent sensitivity to this pressure. This pressure is considered to be ‘Not Relevant’ to hard rock biotopes.

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

Alcyonium digitatum and Parasmittina trispinosa are not thought to be highly susceptible to changes in water clarity due to the fact they are suspension feeding organisms and are not directly dependent on sunlight for nutrition. Alcyonium digitatum has been shown to be tolerant of high levels of suspended sediment. Hill et al. (1997) demonstrated that Alcyonium digitatum sloughed off settled particles with a large amount of mucous. Alcyonium digitatum is also known to inhabit the entrances to sea lochs (Budd, 2008) or the entrances to estuaries (Braber & Borghouts, 1977) where water clarity is likely to be highly variable.  Also, Moore (1977a) suggested that Echinus esculentus was unaffected by turbid conditions. Echinus esculentus is an important grazer in CR.MCR.EcCr.CarSp.PenPcom but also feeds on detritus or dissolved organic material (Lawrence, 1975, Comely & Ansell, 1988). 

Populations of Caryophyllia smithii were studied at three sites of differing sedimentation regime in Lough Hyne, Ireland. (Bell & Turner, 2000)The height, length, width and density of individuals were measured along with the depth of accumulated sediment on the rock substratum at each site. Calyx size was largest at the site of least sedimentation and smallest at the site of most sedimentation. In contrast, height of individuals was greatest at the site of most sedimentation and smallest at the site of least sedimentation. The height of individuals correlated with the level of surrounding sediment. Caryophyllia smithii was more abundant in areas with higher sedimentation (Bell & Turner, 2000).

Bryozoans are suspension feeders that may be adversely affected by increases in suspended sediment, due to clogging of their feeding apparatus. 

Colonies of Pentapora fascialis can reach a height of 30 cm in the British Isles (Hayward & Ryland, 1979).  Partial mortality due to siltation has been recorded in the Mediterranean (Cocito et al., 1998) although recovery was observed in in all but one colony (which fragmented into two smaller colonies).

Sensitivity assessment. The biotope is faunally dominated and circalittoral and is therefore not dependent on light, so a change in suspended sediment is unlikely to affect the characterizing species and resistance is therefore assessed as ‘High’, Resilience as ‘High’ and the biotope is ‘Not sensitive’.

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

CR.MCR.EcCr.CarSp.PenPcom occurs on vertical faces and overhangs which would afford the characterizing species protection in the event of sediment deposition.  Alcyonium digitatum is sessile and thus would be unable to avoid the deposition of a smothering layer of sediment, however, colonies can attain a height of up to 20 cm (; Budd, 2008; Edwards, 2008), so would still be able to feed in the event of sediment deposition. Parasmittina trispinosa is an encrusting species and would thus likely be smothered, and depending on sediment retention, could block larval settlement.

Colonies of Pentapora fascialis can reach a height of 30 cm in the British Isles (Hayward & Ryland, 1979).  Partial mortality due to siltation has been recorded in the Mediterranean (Cocito et al., 1998) although recovery was observed in in all but one colony (which fragmented into two smaller colonies).

Echinus esculentus are mobile, large globular urchins which can reach a diameter of 17 cm (Tyler-Walters, 2000).  Comely & Ansell (1988) recorded large Echinus esculentus from kelp beds on the west coast of Scotland in which the substratum was seasonally covered with "high levels" of silt. This suggests that Echinus esculentus is unlikely to be killed by smothering, however, smaller specimens and juveniles may be less resistant. A layer of sediment may interfere with larval settlement.  If retained within the host biotope for extended periods a layer of 5 cm of the sediment may negatively affect successive recruitment events, however this is unlikely given the typically vertical nature of the biotope.

Caryophyllia smithii is small (approx. <3 cm height from the seabed) and would therefore likely be inundated in a “light” sedimentation event. However Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of “moderate” sedimentation (7mm ± 0.5mm) in Lough Hyne. It is therefore likely that Caryophyllia smithii would be resistant to periodic sedimentation. If 5cm of sediment were removed rapidly, via tidal currents, Caryophyllia smithii would likely remain within the biotope.  Burton et al. (2005) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover.

Sensitivity assessment. CR.MCR.EcCr.CarSp.PenPcom typically occurs on vertical sides of rock and sedimentation would be unlikely, with removal likely to be rapid.  Areas at the base of the rock could be affected, but overall, resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Smothering and siltation rate changes (heavy)

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

Evidence

CR.MCR.EcCr.CarSp.PenPcom typically occurs on vertical sides of rock  which would afford the characterizing species some protection in the event of sediment deposition. 

Colonies of Pentapora fascialis can reach a height of 30 cm in the British Isles (Hayward & Ryland, 1979).  Partial mortality due to siltation has been recorded in the Mediterranean (Cocito et al., 1998) although recovery was observed in in all but one colony (which fragmented into two smaller colonies).

Caryophyllia smithii is small (approx. <3 cm height from the seabed) and would therefore likely be inundated in a “heavy” sedimentation event. Whilst Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of “moderate” sedimentation (7mm ± 0.5mm) in Lough Hyne, it is unlikely that Caryophyllia smithii would survive.  Burton et al. (2005) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover.

Alcyonium digitatum is sessile and thus would be unable to avoid the deposition of a smothering layer of sediment.  However Alcyonium digitatum colonies can attain a height of up to 20 cm (; Budd, 2008; Edwards, 2008), so would still be able to feed in the event of sediment deposition. However, Parasmittina trispinosa is an encrusting species and would thus likely be smothered, and depending on sediment retention, could block larval settlement. Echinus esculentus are mobile, large globular urchins which can reach a diameter of 17 cm (Tyler-Walters, 2000).  Comely & Ansell (1988) recorded large Echinus esculentus from kelp beds on the west coast of Scotland in which the substratum was seasonally covered with "high levels" of silt. This suggests that Echinus esculentus is unlikely to be killed by smothering, however, smaller specimens and juveniles may be less resistant. A layer of sediment could interfere with larval settlement.  If sediment is retained within the host biotope for extended periods a layer sediment may negatively affect successive recruitment events, however given that the biotope tends to occur on vertical faces and overhangs, this is unlikely.

Sensitivity assessment. CR.MCR.EcCr.CarSp.PenPcom occurs typically on vertical sides of rock and sedimentation would be unlikely, with removal likely to be rapid.  Smothering at the base of rocks could result in burial of the encrusting bryozoans and would affect Alcyonium digitatum which grows to 20 cm tall (Budd, 2008; Edwards, 2008). A cautious assessment of ‘Medium’ resistance is applied. Resilience is ‘High’ and sensitivity is ‘Low’.

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

'No evidence' was found.

Underwater noise changes

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

Evidence

Echinus esculentus, Alcyonium digitatum and Parasmittina trispinosa have no hearing perception but vibrations may cause an impact, however there is ‘No evidence’ to support an assessment.   

Introduction of light or shading

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

Evidence

There is some evidence that the basiepithelial nerve plexus below the entire outer skins of echinoderms is sensitive to light (Hill, 2008).

There is no evidence to suggest that algal species would benefit if exposed to anthropogenic light sources. CR.MCR.EcCr.CarSp.PenPcom is a circalittoral biotope and therefore defined as occurring at low light levels due to depth. Increased shading (e.g. by construction of a pontoon, pier etc) could be beneficial to the characterizing species within this biotope.

Sensitivity assessment. Resistance is assessed as 'High', with 'High' resilience and the biotope is 'Not Sensitive'.

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 and changes in tidal excursion are 'Not relevant' to biotopes restricted to open waters.

Death or injury by collision

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

Evidence

'Not relevant' to seabed habitats.  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

Echinus esculentus was identified by Kelly & Pantazis (2001) as a species suitable for culture for the urchin roe industry. However, at present no evidence could be found to suggest that significant Echinus esculentus mariculture was present in the UK. If industrially cultivated it is feasible that Echinus esculentus individuals could be translocated. ‘No evidence’ of cultivation or translocation of other characterizing species was found.

Introduction or spread of invasive non-indigenous species

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

Evidence

Crepidula fornicata larvae require hard substrata for settlement. It prefers muddy gravelly, shell-rich, substrata that include gravel, or shells of other Crepidula, or other species e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. But it also recorded from rock, artificial substrata, and Sabellaria alveolata reefs (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Helmer et al., 2019; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Tillin et al., 2020). Close examination of the literature (2023) shows that evidence of its colonization and density on bedrock in the infralittoral or circalittoral was lacking. Tillin et al. (2020) suggested that Crepidula could colonize circalittoral rock due to its presence on tide-swept rough grounds in the English Channel (Hinz et al., 2011). However, Hinz et al. (2011) reported that Crepidula fornicata only dominated one assemblage (with an average of 181 individuals per trawl) on gravel substratum with boulders. Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas dominated by boulders, and Bohn et al. (2013a, 2013b, 2015) and Preston et al. (2020) showed that while Crepidula could settle on slate panels or ‘stone’ it preferred shell, especially that of conspecifics. In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats. It was only recorded at low density (0.1-0.9/m²) in one faunal turf biotope (CR.MCR.CFaVS.CuSpH.As) (JNCC, 2015). Faunal turfs are dominated by suspension feeders so larval predation is probably high, which may prevent colonization by Crepidula. Also, faunal turf species actively compete for space and many are fast growing and opportunistic, so may out-compete Crepidula for space even if it gained a foothold in the community. 

Styela clava was first recorded in the UK at Plymouth in 1952 (Eno et al., 1997). Where Styela clava and Ciona intestinalis co-occur they may compete for space and food (Jackson, 2008).

Didemnum vexillum is an invasive colonial sea squirt native to Asia which was first recorded in the UK in Darthaven Marina, Dartmouth in 2005. Didemnum vexillum can form extensive mats over the substrata it colonizes; binding boulders, cobbles and altering the host habitat (Griffith et al., 2009). Didemnum vexillum can also grow over and smother the resident biological community. Recent surveys within Holyhead Marina, North Wales have found Didemnum vexillum growing on and smothering native tunicate communities, including Ciona intestinalis (Griffith et al., 2009). Due to the rapid-re-colonization of Didemnum vexillum eradication attempts have to date failed.  Presently, Didemnum vexillum is isolated to several sheltered locations in the UK (NBN, 2015). However Didemnum vexillum has successfully colonized the offshore location of the Georges Bank, USA (Lengyel et al., 2009) which is more exposed than the locations which Didemnum vexillum have colonized in the UK. It is therefore possible that Didemnum vexillum could colonize more exposed locations within the UK and could therefore pose a threat to these biotopes.

Several invasive bryozoans are of concern including Schizoporella japonica (Ryland et al., 2014) and Tricellaria inopinata (Dyrynda et al., 2000; Cook et al., 2013b).

Sensitivity assessment. The circalittoral rock characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata due to the extremely wave exposed to moderately wave exposed conditions, in which wave action and storms may mitigate or prevent the colonization by Crepidula at high densities, although Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). Crepidula has been recorded from the lower intertidal to ca 160 m in depth but is most common in the shallow subtidal above 50 m (Blanchard, 1997; Thieltges et al., 2003; Bohn et al., 2012, 2015; Hinz et al., 2011; OBIS, 2023; Tillin et al., 2020), therefore, colonization of Crepidula would be limited to low densities in deeper examples of the biotope. In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats or infralittoral or circalittoral rock habitats. At present, there is 'Insufficient evidence' to suggest that the circalittoral rock biotopes are sensitive to colonization by Crepidula fornicata or other invasive species; further evidence is required. 

Introduction of microbial pathogens

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

Evidence

Echinus esculentus is susceptible to 'Bald-sea-urchin disease', which causes lesions, loss of spines, tube feet, pedicellariae, destruction of the upper layer of skeletal tissue and death. It is thought to be caused by the bacteria Vibrio anguillarum and Aeromonas salmonicida. Bald sea-urchin disease was recorded from Echinus esculentus on the Brittany Coast. Although associated with mass mortalities of Strongylocentrotus franciscanus in California and Paracentrotus lividus in the French Mediterranean it is not known if the disease induces mass mortality (Bower, 1996).

Alcyonium digitatum acts as the host for the endoparasitic species Enalcyonium forbesi and Enalcyonium rubicundum (Stock, 1988). Parasitisation may reduce the viability of a colony but not to the extent of causing mortality.  No further evidence was found to substantiate this suggestion. Specimens of Cliona spp. exhibited blackened damage since 2013 in Skomer. Preliminary results have shown that clean, fouled and blackened Cliona all have very different bacterial communities. The blackened Cliona are effectively dead and have a bacterial community similar to marine sediments. The fouled Cliona have a very distinct bacterial community that may suggest a specific pathogen caused the effect (Burton, pers comm; Preston & Burton, 2015).  Stebbing (1971b) reported that encrusting epizoites reduced the growth rate of Flustra foliacea by ca 50%. The bryozoan Bugula flabellata produces stolons that grow in and through the zooids of Flustra foliacea, causing "irreversible degeneration of the enclosed polypide" (Stebbing, 1971b). No evidence of Parasmittina trispinosa disease could be found.

Sensitivity assessment. Whilst evidence of disease in the characterizing species could be found, ‘No evidence’ of mass-mortality through disease could be found.

Removal of target species

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

Evidence

Despite historic extraction as a curio (Jangoux, 1980; Nichols, 1984), Echinus esculentus is not thought to be currently targeted.  'No evidence' for the targeted removal of Alcyonium digitatum or bryozoans could be found.

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

The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of non-target species on this biotope. Alcyonium digitatum goes through an annual cycle, from February to July all Alcyonium digitatum colonies are feeding, from July to November an increasing number of colonies stop feeding. During this period a large number of polyps can retract and a variety of filamentous algae, hydroids and amphipods can colonize the surface of colonies epiphytically. From December-February the epiphytic community is however sloughed off (Hartnoll, 1975). If Alcyonium digitatum were removed the epiphytic species would likely colonize rock surfaces and are therefore not dependent on Alcyonium digitatum.

While recovery of the characterizing species should be possible within 2-10 years following non-targeted removal (e.g. from static or mobile gears), loss of Echinus esculentus from the biotope subsequent loss of grazing pressure would result in increasing competition from algae and increased competition for space, which could lead to a change in biotope classification e.g. to XFa biotopes with a more .  Alcyonium digitatum and faunal turf communities (which include bryozoans such as Parasmittina trispinosa) are probably resistant to abrasion through bottom fishing (see abrasion pressure).

Sensitivity assessment. A decrease in Caryophyllia smithii or Alcyonium digitatum would result in a decline in the biotope richness.  However, removal of Echinus esculentus could result in restructuring of the biotope.  If all are lost, reclassification would be necessary.  Resistance has therefore been assessed as ‘None’, resilience as ’Medium’ and sensitivity as ‘Medium’.