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 (Global warming pressure definitions).

Evidence

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the northwest 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). Jenkins & Stevens (2022) examined the possible impact of climate change on Alcyonium digitatum distribution. They noted there will likely be a shift north as more suitable habitat becomes available in higher latitudes. However, suitability predictions in the southern portion of their study area decreased.

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. 

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 primarily between sea temperatures of 5 and 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 and 19°C, although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after up to 24 hr 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. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Moreno, 2020). The bryozoan Parasmittina trispinosa has been recorded from Britain, north to western Norway, the Faroe Isles, northwestern Atlantic coasts, the Californian coast and the Gulf of Mexico. 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.

Coralline crusts, including Lithophyllum incrustans, are found further south than the UK and are considered to tolerate increased temperatures, although they may be more sensitive to drying rather than higher temperatures. Edyvean & Ford (1984b) suggest that populations of Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning, but no information on thresholds was provided (Edyvean & Ford, 1984b). Populations of Lithophyllum incrustans were less stable in tide pools with a smaller volume of water, which were more exposed to temperature and salinity changes due to lower buffering capacity. Sexual plants (or the spores that give rise to them) were suggested to be more susceptible than asexual plants to extremes of local environmental variables (temperature, salinity, etc.) as they occur with greater frequency at sites where temperature and salinity were more stable (Edyvean & Ford, 1984b). Lithophyllum incrustans is close to the northern edge of its range and is likely to tolerate increased temperatures.

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 and 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).

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. While no evidence on the impacts of ocean warming on the characterizing species Alcyonium digitatum was found, biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). The distribution of Alcyonium digitatum suggests that the species is likely to be impacted by ocean warming, as populations of this species only occur where seawater temperatures range up to 20°C (www.obis.org).  Parasmittina trispinosa, Caryophyllia smithii and the coralline crusts are found in geographical locations with higher temperatures than in the UK, so that these species are unlikely to be affected by an increase in seawater temperature under these scenarios. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods. A reduction in grazing due to loss of Echinus esculentus may result in loss of the biotope if it is replaced by a more abundant and diverse faunal turf, eg, FaT.CTub.Adig.  As CR.MCR.EcCr.AdigVt is a grazed biotope, and the main characterizing species, Alcyonium digitatum, is unknown to tolerate high temperatures. 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. 

Evidence

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the northwest 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). Jenkins & Stevens (2022) examined the possible impact of climate change on Alcyonium digitatum distribution. They noted there will likely be a shift north as more suitable habitat becomes available in higher latitudes. However, suitability predictions in the southern portion of their study area decreased.

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. 

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 primarily between sea temperatures of 5 and 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 and 19°C, although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after up to 24 hr 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. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Moreno, 2020). The bryozoan Parasmittina trispinosa has been recorded from Britain, north to western Norway, the Faroe Isles, northwestern Atlantic coasts, the Californian coast and the Gulf of Mexico. 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.

Coralline crusts, including Lithophyllum incrustans, are found further south than the UK and are considered to tolerate increased temperatures, although they may be more sensitive to drying rather than higher temperatures. Edyvean & Ford (1984b) suggest that populations of Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning, but no information on thresholds was provided (Edyvean & Ford, 1984b). Populations of Lithophyllum incrustans were less stable in tide pools with a smaller volume of water, which were more exposed to temperature and salinity changes due to lower buffering capacity. Sexual plants (or the spores that give rise to them) were suggested to be more susceptible than asexual plants to extremes of local environmental variables (temperature, salinity, etc.) as they occur with greater frequency at sites where temperature and salinity were more stable (Edyvean & Ford, 1984b). Lithophyllum incrustans is close to the northern edge of its range and is likely to tolerate increased temperatures.

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 and 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).

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. While no evidence on the impacts of ocean warming on the characterizing species Alcyonium digitatum was found, biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). The distribution of Alcyonium digitatum suggests that the species is likely to be impacted by ocean warming, as populations of this species only occur where seawater temperatures range up to 20°C (www.obis.org).  Parasmittina trispinosa, Caryophyllia smithii and the coralline crusts are found in geographical locations with higher temperatures than in the UK, so that these species are unlikely to be affected by an increase in seawater temperature under these scenarios. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods. A reduction in grazing due to loss of Echinus esculentus may result in loss of the biotope if it is replaced by a more abundant and diverse faunal turf, eg, FaT.CTub.Adig.  As CR.MCR.EcCr.AdigVt is a grazed biotope, and the main characterizing species, Alcyonium digitatum, is unknown to tolerate high temperatures. 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. 

Evidence

Alcyonium digitatum is a boreal species of octocoral recorded along the Atlantic Coasts of Europe from Portugal to Norway and Iceland, and along the northwest 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). Jenkins & Stevens (2022) examined the possible impact of climate change on Alcyonium digitatum distribution. They noted there will likely be a shift north as more suitable habitat becomes available in higher latitudes. However, suitability predictions in the southern portion of their study area decreased.

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. 

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 primarily between sea temperatures of 5 and 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 and 19°C, although continued exposure to 19°C destroyed synchronicity of gametogenesis between individuals. Embryos and larvae developed abnormally after up to 24 hr 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. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and are expected to affect calcification (Smith, 2014; Moreno, 2020). The bryozoan Parasmittina trispinosa has been recorded from Britain, north to western Norway, the Faroe Isles, northwestern Atlantic coasts, the Californian coast and the Gulf of Mexico. 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.

Coralline crusts, including Lithophyllum incrustans, are found further south than the UK and are considered to tolerate increased temperatures, although they may be more sensitive to drying rather than higher temperatures. Edyvean & Ford (1984b) suggest that populations of Lithophyllum incrustans are affected by temperature changes and salinity and that temperature and salinity ‘shocks’ induce spawning, but no information on thresholds was provided (Edyvean & Ford, 1984b). Populations of Lithophyllum incrustans were less stable in tide pools with a smaller volume of water, which were more exposed to temperature and salinity changes due to lower buffering capacity. Sexual plants (or the spores that give rise to them) were suggested to be more susceptible than asexual plants to extremes of local environmental variables (temperature, salinity, etc.) as they occur with greater frequency at sites where temperature and salinity were more stable (Edyvean & Ford, 1984b). Lithophyllum incrustans is close to the northern edge of its range and is likely to tolerate increased temperatures.

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 and 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).

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. While no evidence on the impacts of ocean warming on the characterizing species Alcyonium digitatum was found, biogeographic distribution is often a good predictor of temperature tolerance (Jeffree & Jeffree, 1994). The distribution of Alcyonium digitatum suggests that the species is likely to be impacted by ocean warming, as populations of this species only occur where seawater temperatures range up to 20°C (www.obis.org).  Parasmittina trispinosa, Caryophyllia smithii and the coralline crusts are found in geographical locations with higher temperatures than in the UK, so that these species are unlikely to be affected by an increase in seawater temperature under these scenarios. However, the sea urchin Echinus esculentus cannot tolerate high temperatures for prolonged periods. A reduction in grazing due to loss of Echinus esculentus may result in loss of the biotope if it is replaced by a more abundant and diverse faunal turf, eg, FaT.CTub.Adig.  As CR.MCR.EcCr.AdigVt is a grazed biotope, and the main characterizing species, Alcyonium digitatum, is unknown to tolerate high temperatures. 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 (Marine heatwave pressure definitions).

Evidence

Marine heatwaves are extreme weather events defined as periods of extreme sea surface temperature that persist 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).

No studies on the impacts of marine heatwaves on Alcyonium digitatum were found. However, this species appears to be restricted to colder waters and occurs in seawater temperatures between 5 and 20°C (www.obis.org).  Therefore, Alcyonium digitatum is likely to be impacted by heatwaves under both scenarios. 

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 and 19°C however, continued exposure to 19°C disrupted gametogenesis. In addition, embryos and larvae developed abnormally after 24 hr exposure to 15°C (Bishop, 1985). Therefore, marine heatwaves have the potential to impact the reproduction, recruitment and survival of Echinus esculentus. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and is expected to affect calcification (Smith, 2014; Leveroni, 2020). However, although Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, 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 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.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years, during those years, marine heatwave events caused mass mortality among a number of species. A 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. 

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 and 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. 

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 the characteristic species of this biotope, however as Alcyonium digitatum is not known to tolerant seawater temperatures >20°C and the sea urchin Echinus esculentus cannot tolerate high temperatures, resistance is assessed as “Low”, under the middle and high emissions scenario, and resilience is assessed as “Low”, so the biotope is assessed as “High” sensitivity.

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. 

Evidence

Marine heatwaves are extreme weather events defined as periods of extreme sea surface temperature that persist 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).

No studies on the impacts of marine heatwaves on Alcyonium digitatum were found. However, this species appears to be restricted to colder waters and occurs in seawater temperatures between 5 and 20°C (www.obis.org).  Therefore, Alcyonium digitatum is likely to be impacted by heatwaves under both scenarios. 

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 and 19°C however, continued exposure to 19°C disrupted gametogenesis. In addition, embryos and larvae developed abnormally after 24 hr exposure to 15°C (Bishop, 1985). Therefore, marine heatwaves have the potential to impact the reproduction, recruitment and survival of Echinus esculentus. 

Elevated seawater temperatures generally increase the metabolic rate of bryozoans and is expected to affect calcification (Smith, 2014; Leveroni, 2020). However, although Parasmittina trispinosa generally occurs in temperatures between 5 and 15°C, 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 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.

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years, during those years, marine heatwave events caused mass mortality among a number of species. A 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. 

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 and 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. 

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 the characteristic species of this biotope, however as Alcyonium digitatum is not known to tolerant seawater temperatures >20°C and the sea urchin Echinus esculentus cannot tolerate high temperatures, resistance is assessed as “Low”, under the middle and high emissions scenario, and resilience is assessed as “Low”, so the biotope is assessed as “High” sensitivity.

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 (Ocean acidification pressure definitions).

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).

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. 

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. 

Duvane & Dupont (2024) studied the biological response of Echinus esculentus larvae to stable (pH 8.13, 7.82, 7.53) and fluctuating pH treatments (12 hours at pH 8.13 and 12 hours at pH 7.53) following natural or inverted diurnal cycles. They observed that under constant conditions, low pH deviating from the present range of natural variability had a negative effect on larval growth rate and calcification, and under fluctuating conditions, a desynchronization of the pH variation with the photoperiod led to decreased larval growth rate and calcification. Duvane & Dupont (2024) concluded that overall larval fitness (survival, growth and calcification) was higher under fluctuating conditions compared to constant ones, and that there was evidence of adaptation to variability in Echinus esculentus with an associated cost of plasticity (the ability of a single genotype to produce more than one alternative phenotype in response to environmental conditions) but not a cost of canalization (the constancy of phenotypes in the face of environmental perturbations). For example, an organism might maintain its growth rate in different pHs through plasticity in metabolic processes supporting growth (Sunday et al., 2014 cited in Duvane & Dupont, 2024).

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 the 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 (urchins, Evechinus chloroticus), allowing turf algae to increase in abundance. Therefore, ocean acidification could cause changes to community structure. 

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 was found. However, Swezey et al. (2017) observed that populations of bryozoans raised under high CO₂ (1254 μatm; pH 7.60) conditions grew faster, invested less in reproduction and produced lighter skeletons when compared to genetically identical clones raised under current surface atmospheric CO₂ values (400 μatm; pH 8.04). In addition, the bryozoans under high CO₂ altered the 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. 

Brodie et al. (2014) reported that Corallina species were more resilient to ocean acidification than other calcified algae species, although competition from flesh algal species that benefit from high CO₂ may indirectly cause the loss of calcified species from biotopes. Similarly, observations have indicated Corallinales to be adversely affected at locations where CO₂ gradients occur naturally, with evidence of Corallinales being outcompeted by heterokont algae at Mediterranean CO₂ seeps (Martin and Hall-Spencer, 2017).  

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. 

Sensitivity Assessment

While no evidence of the effect of ocean acidification on Alcyonium digitatum was found, the effects of ocean acidification on other species of octocoral show some resilience to low pH. Alcyonium digitatum larvae settlement has been reported to be sensitive to environmental conditions, but the conditions were not stated. Ocean acidification studies have shown negative impacts on the health and reproduction of sea urchins. In addition, bryozoans appear to be highly sensitive to ocean acidification, with impacts on health, survival and reproduction.  Unfortunately, at present, there are no studies to determine whether Alcyonium digitatum, Echinus esculentus and Parasmittina trispinosa can adapt or acclimate to future pH conditions, but, on the evidence available, Parasmittina trispinosa and Echinus esculentus could be lost from this biotope. Therefore, as CR.MCR.EcCr.AdigVt is a grazed biotope, under both the middle and high emission scenarios (0.15 and 0.35 pH unit decrease, respectively), the biotope is assessed as having a resistance level of 'low', and a resilience level of ‘Very low’ because of the long-term nature of ocean acidification.  Therefore, sensitivity is assessed as ‘High’ under both scenarios, albeit with ‘Low’ confidence.

Ocean acidification (middle)

Middle emission scenario benchmark: a further decrease in pH of 0.15 (annual mean) and a 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. 

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).

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. 

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. 

Duvane & Dupont (2024) studied the biological response of Echinus esculentus larvae to stable (pH 8.13, 7.82, 7.53) and fluctuating pH treatments (12 hours at pH 8.13 and 12 hours at pH 7.53) following natural or inverted diurnal cycles. They observed that under constant conditions, low pH deviating from the present range of natural variability had a negative effect on larval growth rate and calcification, and under fluctuating conditions, a desynchronization of the pH variation with the photoperiod led to decreased larval growth rate and calcification. Duvane & Dupont (2024) concluded that overall larval fitness (survival, growth and calcification) was higher under fluctuating conditions compared to constant ones, and that there was evidence of adaptation to variability in Echinus esculentus with an associated cost of plasticity (the ability of a single genotype to produce more than one alternative phenotype in response to environmental conditions) but not a cost of canalization (the constancy of phenotypes in the face of environmental perturbations). For example, an organism might maintain its growth rate in different pHs through plasticity in metabolic processes supporting growth (Sunday et al., 2014 cited in Duvane & Dupont, 2024).

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 the 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 (urchins, Evechinus chloroticus), allowing turf algae to increase in abundance. Therefore, ocean acidification could cause changes to community structure. 

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 was found. However, Swezey et al. (2017) observed that populations of bryozoans raised under high CO₂ (1254 μatm; pH 7.60) conditions grew faster, invested less in reproduction and produced lighter skeletons when compared to genetically identical clones raised under current surface atmospheric CO₂ values (400 μatm; pH 8.04). In addition, the bryozoans under high CO₂ altered the 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. 

Brodie et al. (2014) reported that Corallina species were more resilient to ocean acidification than other calcified algae species, although competition from flesh algal species that benefit from high CO₂ may indirectly cause the loss of calcified species from biotopes. Similarly, observations have indicated Corallinales to be adversely affected at locations where CO₂ gradients occur naturally, with evidence of Corallinales being outcompeted by heterokont algae at Mediterranean CO₂ seeps (Martin and Hall-Spencer, 2017).  

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. 

Sensitivity Assessment

While no evidence of the effect of ocean acidification on Alcyonium digitatum was found, the effects of ocean acidification on other species of octocoral show some resilience to low pH. Alcyonium digitatum larvae settlement has been reported to be sensitive to environmental conditions, but the conditions were not stated. Ocean acidification studies have shown negative impacts on the health and reproduction of sea urchins. In addition, bryozoans appear to be highly sensitive to ocean acidification, with impacts on health, survival and reproduction.  Unfortunately, at present, there are no studies to determine whether Alcyonium digitatum, Echinus esculentus and Parasmittina trispinosa can adapt or acclimate to future pH conditions, but, on the evidence available, Parasmittina trispinosa and Echinus esculentus could be lost from this biotope. Therefore, as CR.MCR.EcCr.AdigVt is a grazed biotope, under both the middle and high emission scenarios (0.15 and 0.35 pH unit decrease, respectively), the biotope is assessed as having a resistance level of 'low', and a resilience level of ‘Very low’ because of the long-term nature of ocean acidification.  Therefore, sensitivity is assessed as ‘High’ under both scenarios, albeit with ‘Low’ confidence.

Sea level rise (extreme)

Extreme scenario benchmark: a 107 cm rise in average UK sea-level by the end of this century (2018-2100) (Sea-level rise pressure definitions).

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1 to 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 5-50 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.AdigVt can occur from 5 to 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, high and extreme emission scenarios) would have a limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity is assessed as ‘Not sensitive’. 

Sea level rise (high)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1 to 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 5-50 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.AdigVt can occur from 5 to 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, high and extreme emission scenarios) would have a limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity is assessed as ‘Not sensitive’. 

Sea level rise (middle)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1 to 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 5-50 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.AdigVt can occur from 5 to 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, high and extreme emission scenarios) would have a limited effect. Therefore, resistance is assessed as ‘High’ under all three scenarios, so that resilience is ‘High’ and sensitivity is assessed as ‘Not sensitive’. 

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year (Temperature change pressure definition).

Evidence

Alcyonium digitatum is described as a northern species by Hiscock et al. (2004) Itis distributed from northern Norway (70°N) to Portugal (41°N) (Hartnoll, 1975; Budd, 2008) and is commonly found across the British Isles (Fish & Fish, 1996). Temperature at the seafloor is an important predictor of Alcyonium digitatum, yet there are no published studies that explore the thermal minima or maxima for the species, so the only current evidence that gives insight into the thermal niches of this species is the sea temperatures at the locations where they are observed (Jenkins & Stevens, 2022). Currently, Alcyonium digitatum is commonly found in inshore and offshore areas of northwest and northern France, the Channel Islands, most of the British Isles, including the Shetland Islands, parts of the southern North Sea, parts of southern Norway, and along the Atlantic slope (Jenkins & Stevens, 2022). Alcyonium digitatum can be found alongside Eunicella verrucosa, and in Britain and Ireland, Eunicella verrucosa has been observed in waters where 9.2°C was the lowest average seafloor temperature, the median temperature was 10.5°C, and the highest temperature was 11.4°C (Jenkins & Stevens, 2022). Jenkins & Stevens (2022) noted there will likely be a shift north as more suitable habitat becomes available in higher latitudes; however, suitability predictions in the southern portion of their study area decreased.

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 that Echinus esculentus occurred at temperatures between 0 and 18°C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11 to 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). In addition, maximum spawning occurs in spring although individuals may spawn over a protracted period throughout the year. Gonad weight is at its maximum in February/March in the English Channel (Comely & Ansell, 1988; Hamed et al., 2024) but decreases during spawning in spring and then increases again through summer and winter until the next spawning season.

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). 

Caryophyllia smithii is found across the British Isles (NBN, 2015; Coolen et al., 2015) and has been recorded in Greece (Koukouras, 2010). In the Mediterranean, Caryophyllia smithii has been recorded in seawater between 13 and 14°C (Rodolfo‐Metalpa et al., 2015). 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. Holt (pers. comm.) also suggested that long-term increases in temperature due to climate change may allow the parasitic barnacle Adna anglica to extend its range northwards and overlap the range of this biotope. Adna anglica is a southern species, limited to the southwest of Britain, where it parasitizes Caryophillia and has probably contributed to the decrease in abundance of Leptopsammia (Holt pers. comm.). It may impact the abundance of Caryophyllia if climate change allows it to extend its range northwards (Holt pers. comm.).

Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over nine years. High temperature events were recorded, the first causing mass mortality among a number of species. Gradual recovery took place, with deeper communities recovering to pre-disturbance levels within four years.

Sensitivity assessment

Whilst Alcyonium digitatum and Parasmittina trispinosa are likely to tolerate an increase in temperature at the benchmark level, the 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 (Temperature change pressure definition).

Evidence

Alcyonium digitatum is described as a northern species by Hiscock et al. (2004). It 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, 1996). 

Temperature at the seafloor is an important predictor of Alcyonium digitatum distribution, yet there are no published studies that explore the thermal minima or maxima for the species. The only current evidence that gives insight into the thermal niches of this species is the sea temperatures at the locations where they are observed (Jenkins & Stevens, 2022). Currently, Alcyonium digitatum is commonly found in inshore and offshore areas of northwest and northern France, the Channel Islands, most of the British Isles, including the Shetland Islands, parts of the southern North Sea, parts of southern Norway, and along the Atlantic slope (Jenkins & Stevens, 2022). Alcyonium digitatum can be found alongside Eunicella verrucosa, and in Britain and Ireland, Eunicella verrucosa has been observed in waters where 9.2°C was the lowest average seafloor temperature, the median temperature was 10.5°C, and the highest temperature was 11.4°C (Jenkins & Stevens, 2022). Alcyonium digitatum was also reported to be apparently unaffected by the severe winter of 1962 to 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). Caryophyllia smithii is a southern species (Fish & Fish, 1996) with a northern range limit in the Shetland Isles (NBN, 2015). It is therefore likely to be close to its northerly range limit and, therefore, likely to be negatively affected by a decrease in temperature at the benchmark level. 

Ursin (1960) reported that Echinus esculentus occurred at temperatures between 0 and 18 °C in Limfjord, Denmark. Bishop (1985) noted that gametogenesis occurred at 11 to 19°C, however, continued exposure to 19°C disrupted gametogenesis. Embryos and larvae developed abnormally after 24-hour 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. In addition, maximum spawning occurs in spring, although individuals may spawn over a protracted period throughout the year. Gonad weight is at its maximum in February/March in the English Channel (Comely & Ansell, 1988; Hamed et al., 2024) but decreases during spawning in spring and then increases again through summer and winter until the next spawning season.

Sensitivity assessment

None of the characterizing species are at their southern distribution limit and are unlikely to suffer mortality by a decrease in temperature at the benchmark level.  Resistance is therefore recorded as ‘High’, resilience as ‘High’, and the biotope is ‘Not Sensitive’ at the benchmark level.

Salinity increase (local)

Benchmark. An increase in one MNCR salinity category above the usual range of the biotope or habitat (Salinity regime change pressure definition).

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 would not resist significant increases in salinity. CR.MCR.EcCr.AdigVt occurs in full salinity (Connor et al., 2004), and 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 (Salinity regime change pressure definition 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).

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 (18 to 40) and reduced (18 to 30) salinity biotopes, e.g. IR.LIR.KVS.SlatPsaVS (Connor et al., 2004).

Barrett et al. (2024) studied the effect of low salinity on Echinus esculentus. Experiments were conducted on populations of Echinus esculentus originally collected from Loch Linnhe, Scotland, and were exposed to low salinity over the short term (11‰, 16, 21, 26 and 31‰ for 24 hours) and long term (21, 26 and 31‰ for 25 days). Over the short term, oxygen consumption, activity coefficient and coelomic fluid osmolality were directly correlated with reduced salinity, with 100% survival at ≥21‰ and 0% mortality at ≤16‰ (Barrett et al., 2024). Over the long term at 21‰ (25 days), oxygen consumption was significantly higher, feeding was significantly reduced, and activity coefficient values were significantly lower than at control salinity (31‰) (Barrett et al., 2024). Furthermore, beneficial functional resistance (righting ability and metabolic capacity) to acute low salinity was observed at 26‰. Barrett et al. (2024) concluded that Echinus esculentus demonstrated phenotypic plasticity that enabled acclimation to reduced salinity around 26‰. However, 21‰ represented a lower acclimation threshold, potentially limiting its distribution in coastal areas prone to high freshwater input.

Sensitivity assessment

CR.MCR.EcCr.AdigVt is recorded exclusively in full marine conditions (30 to 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’, and resilience as ‘Medium’. Hence, 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 and 0.2 m/s for more than one year (Water flow pressure definition). 

Evidence

The biotope (EcCr.AdigVT) occurs on the vertical faces and overhangs of exposed to moderately exposed lower infralittoral and upper circalittoral bedrock subject to moderately strong to weak tidal streams at 5 to 50 m depth (Connor et al., 2004; JNCC, 2022). 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 for water movement

Alcyonium digitatum, Caryophyllia smithii, and bryozoans are suspension feeders, relying on water currents to supply food (Hiscock, 1983; O’Reilly et al., 2022). These taxa, therefore, thrive in conditions of vigorous water flow, e.g. around Orkney and St Abbs, Scotland, where Alcyonium digitatum-dominated biotopes may experience tidal currents of 3 and 4 knots (approximately 1.5 m/s) during spring tides (De Kluijver, 1993; Coolen et al., 2015).

In flume experiments, Hiscock (1983) noted that the tentacles of Caryophyllia smithii were displaced by currents over ca 0.5 m/s but withdrawn at 0.75 m/s and took several hours to re-emerge after cessation of strong flow. Hiscock (1983) noted that Caryophyllia smithii was most abundant in semi-exposed and sheltered habitats. The other cup corals (Balanophyllia regia, Hoplangia durotrix and Leptopsammia pruvoti) were recorded from weak and very weak tidal streams in cave and overhang biotopes (Connor et al., 2004). 

The life cycle of Caryophyllia smithii includes a larval planktotrophic stage with a duration of 8 to 10 weeks, during which the released larvae float freely in the water column and are transported in the direction of net water movement, which is driven by tidal currents and wind. These residual currents in the North Sea, UK, range between 0.02 and 0.08 cm/s (Coolen et al., 2015). Caryophyllia smithii, in particular, is described as favouring sites with a high tidal flow (Bell & Turner, 2000; Wood, 2005; Coolen et al., 2015). However, Caryophyllia smithii has been recorded in biotopes from negligible to strong water flow (0 to 6 knots; 0 to > 3 m/s) (Connor et al., 2004). Rodolfo‐Metalpa et al. (2015) noted that Caryophyllia smithii was recorded in waters with a tidal current of 24 cm/s (± 15) off the coast of Italy. This biotope consists mainly of species firmly attached to the substratum, which would be unlikely to be displaced by an increase in the strength of tidal streams at the benchmark level.

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, but individuals would probably not be killed in the process and could recolonize the area quickly.

Sensitivity assessment

This biotope occurs from moderately strong to 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 to 0.2 m/s), because the biotope occurs in stronger water flow (>0.5 m/s). 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. (Emergence regime change pressure definition).

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 (Wave action pressure definition). 

Evidence

The biotope (EcCr.AdigVT) occurs on the vertical faces and overhangs of exposed to moderately exposed lower infralittoral and upper circalittoral bedrock subject to moderately strong to weak tidal streams at 5 to 50 m depth (Connor et al., 2004; JNCC, 2022).  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 to 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). Jenkins & Stevens (2022) noted that seabed slope, temperature at the seafloor, and wave orbital velocity were important predictors of distribution in Alcyonium digitatum, and that specifically, wave orbital velocity was more important than tidal velocity for bringing in fresh nutrients and oxygen, both for polyps to feed on and for exporting waste products.

Caryophyllia smithii has been recorded in very sheltered to extremely exposed biotopes (Connor et al., 2004; JNCC, 2015). Bell (2002) reported that Caryophyllia smithii near Lough Hyne (Ireland) exposed to strong wave action on open coasts were relatively small, possibly due to juvenile morphological variability, as Caryophyllia smithii found deeper and in sediment were thinner and taller.

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. Therefore, 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 Transitional metal or organometal (e.g. TBT) contaminants via uncontrolled releases or incidental spills (Transitional metals and organometals pressure definition).

Evidence

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

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 that 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 the 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).

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant hydrocarbon or polyaromatic hydrocarbon (PAH) contaminants via uncontrolled releases or incidental spills (Hydrocarbon & PAH pressure definition).

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 synthetic compound contaminants via uncontrolled releases or incidental spills (Synthetic compound contamination pressure definition).

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 the 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 (Radionuclides contamination pressure definition).

Evidence

'No evidence' was found.

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant "other" substances (solid, liquid or gas) contaminants via uncontrolled releases or incidental spills (Introduction of other substances pressure definition). 

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) (deoxygenation pressure definition).

Evidence

Mass mortality of species, including Echinus esculentus, was observed due to a stratified hypoxic event below 8 m caused by a phytoplankton 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 to 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 that the decay of Gyrodinium aureolum either reduced oxygen levels or physically clogged faunal feeding mechanisms. Adjacent reefs were 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 affected by the phytoplankton bloom (Griffiths et al., 1979).   CR.MCR.EcCr.AdigVt 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.

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 the extent and conditions). Resistance is assessed as ‘Low’, Resilience as ‘Medium’ (assuming recovery to normal oxygen conditions) and sensitivity as ‘Medium’.

Nutrient enrichment

Benchmark. Increased levels of the elements nitrogen, phosphorus, silicon, and iron in the marine environment compared to background concentrations (Nutrient enrichment pressure definition).

Evidence

It 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 feeder 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.

Sensitivity assessment

Limited evidence on the effects of nutrient enrichment on the characteristic species was found. The evidence suggests that the characteristic species vary in their response to nutrients. Therefore, the evidence is ‘insufficient’ to form the basis of an assessment.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr (Organic enrichment pressure definition).

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 (Physical loss pressure definition). 

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 (Physical change in subtratum type pressure definition).

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. Alcyonium digitatum is also capable of settling on other substrata, including artificial structures, shells, cobble and other (unstable) coarse substrata (Rouse et al., 2019; Jenkins & Stevens, 2022). High terrain ruggedness index (TRI) values are often associated with hard substrata, which may explain the positive relationship between the density of records and TRI. Areas with a high TRI would indicate a more complex seabed with local topographic highs, which coral species have been found to prefer (Langton, Stirling & Boulcott, 2023). A study by Becker et al. (2020) noted how Alcyonium digitatum had a significant positive correlation with hard ground greater than 22%. In addition, the probability of occurrence of Echinus esculentus was highest in areas with hard ground greater than 19%, and shell >2 mm more than 0.04 weight% (by percentage weight) (Becker et al., 2020). While observing an undersea pipeline in the North Sea, Rouse et al. (2019) saw that Alcyonium digitatum was present in the highest densities on pipelines located on mud, while Echinus esculentus were more common on pipelines in sand. 

Sensitivity assessment

Resistance to the pressure is considered ‘None’, and resilience is ‘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) (Physical change in sediment type pressure definition). 

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) (Removal of substratum pressure definition). 

Evidence

The species characterizing this biotope are epifauna or epiflora occurring on rock and would be sensitive to the removal of the habitat. However, the 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) (Surface abrasion/disturbance pressure definition).

Evidence

Alcyonium digitatum, Echinus esculentus and Parasmittina trispinosa are sessile or slow-moving species. Faunal crust and turf species create biogenic habitats, often form complex ecological associations, and tend to be long-lived, slow-growing, and fragile, sensitive to abrasion disturbance and vulnerable to damage (Kaiser et al. 2018; Graves et al., 2023). Fishing disturbance is one of the largest abrasion pressures for these characterizing species (Kaiser et al. 2018; Kazanidis et al., 2019; Graves et al., 2023); however, they are also vulnerable to other anthropogenic physical disturbances, such as from oil and gas exploration, deep-sea mining, and recreational SCUBA diving (Vad et al., 2018; Betti et al., 2019; Graves et al., 2023).

Alcyonium digitatum is not a protected species in British waters and has been documented as locally depleted (reductions in colony numbers and size) in some areas due to benthic trawling, such as Lyme Bay, before the trawling ban (Holland, Jenkins, & Stevens, 2017). Magorrian & Service (1998) reported that trawling for queen scallops resulted in the removal of emergent epifauna and damage to horse mussel beds in Strangford Lough. They suggested that the emergent epifauna, such as Alcyonium digitatum, were less resistant than the horse mussels themselves and reflected early signs of damage (Service & Magorrian, 1997; Magorrian & Service, 1998; Service, 1998). Veale et al. (2000) reported that the abundance, biomass and production of epifaunal assemblages, including Alcyonium digitatum, decreased with increasing fishing effort. However, the fact that Alcyonium digitatum is more abundant on high fishing effort grounds suggests that this seemingly fragile species is more sensitive to abrasive disturbance than might be assumed (Bradshaw et al., 2000), presumably owing to the ability for the replacement of senescent cells and regeneration of damaged tissue, in addition to the early larval colonization of available substrata.

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 that 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 were 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 because 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 two months (Hobson, 1930). The trawling examples mentioned above were conducted on sedimentary habitats and thus the evidence is not directly relevant to rocky habitats, however it does indicate the likely effects of abrasion on Echinus esculentus.

The characterizing species are likely to be affected by physical disturbances. Physical disturbance by fishing gear has been shown to adversely affect sessile benthic and emergent epifaunal communities, with hydroid and bryozoan matrices reported to be greatly reduced in fished areas and increase when fishing activity is removed (Jennings & Kaiser, 1998; Sheehan et al., 2017; Kaiser et al., 2018; Long et al., 2021; Langton, Stirling & Boulcott, 2023). Also, heavy mobile gears could also result in the movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998).

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. In addition, the vertical nature of this biotope also likely provides protection from most or harsh fishing activities. Based on the evidence for the characterizing species, resistance is ‘Medium’, resilience is ‘High’, and sensitivity is ‘Low’. Please note that Boulcott & Howell (2011) did not mention the abrasion caused by fully loaded collection bags on the Newhaven dredges. A fully loaded Newhaven dredge may cause higher damage to communities 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) (Sub-surface penetration pressure definition).

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 (Suspended sediment pressure definition).

Evidence

Alcyonium digitatum and Parasmittina trispinosa are not thought to be highly susceptible to changes in water clarity due to the fact that 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. 

Bell & Turner (2000) studied populations of Caryophyllia smithii at three sites of differing sedimentation regimes in Lough Hyne, Ireland. Calyx size was largest at the site of least sedimentation and smallest at the site of most sedimentation. In contrast, the 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. High density was correlated with high sedimentation and depth (Bell & Turner, 2000). 

Moore (1977a) suggested that Echinus esculentus was unaffected by turbid conditions. Echinus esculentus is an important grazer in CR.MCR.EcCr.AdigVt but also feeds on detritus or dissolved organic material (Lawrence, 1975, Comely & Ansell, 1988). 

Sensitivity assessment

The above evidence suggests that a change in suspended sediment is unlikely to affect the characterizing species. Hence, 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 (Smothering pressure definition).

Evidence

CR.MCR.EcCr.AdigVt 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. 

Caryophyllia smithii is a small (approx. <3 cm height from the seabed) species and would therefore likely be inundated in a ‘light’ sedimentation event. Coolen et al. (2015) noted how a low abundance of Caryophyllia smithii is typically observed at locations with low tidal current strength and high sedimentation. For example, in the Skomer Island, UK, Marine Conservation Zone, higher numbers of Caryophyllia smithii were observed on vertical walls, likely due to less surface sediment accumulating there (Lock et al., 2025). However, Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of “moderate” sedimentation (7 mm ± 0.5 mm) in Lough Hyne. It is therefore likely that Caryophyllia smithii would be resistant to periodic sedimentation. If 5 cm of sediment were removed rapidly, via tidal currents, Caryophyllia smithii would likely remain within the biotope. Lock et al. (2006) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover. Bell (2002) reported that juvenile Caryophyllia smithii are morphologically variable and initially undergo rapid growth with tall and thin forms in deeper, sheltered, relatively sedimented conditions near Lough Hyne, Ireland. It was concluded that this was to escape the thin layer of sediment present.  

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.

Sensitivity assessment

CR.MCR.EcCr.AdigVt occurs on vertical faces and overhangs, 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 (Smothering pressure definition).

Evidence

CR.MCR.EcCr.AdigVt typically occurs on vertical faces and overhangs, which would afford the characterizing species some 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, Alcyonium digitatum colonies can attain a height of up to 20 cm (Budd, 2008; Edwards, 2008), so they 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. 

Caryophyllia smithii is a small (approx. <3 cm height from the seabed) species and would therefore likely be inundated in a “light” sedimentation event. Coolen et al. (2015) noted how a low abundance of Caryophyllia smithii is typically observed at locations with low tidal current strength and high sedimentation. For example, in the Skomer Island, UK, Marine Conservation Zone, higher numbers of Caryophyllia smithii were observed on vertical walls, likely due to less surface sediment accumulating there (Lock et al., 2025). However, Bell & Turner (2000) reported Caryophyllia smithii was abundant at sites of “moderate” sedimentation (7 mm ± 0.5 mm) in Lough Hyne. It is therefore likely that Caryophyllia smithii would be resistant to periodic sedimentation. If 5 cm of sediment were removed rapidly, via tidal currents, Caryophyllia smithii would likely remain within the biotope. Lock et al. (2006) partly attributed fluctuations in Caryophyllia smithii abundance at Skomer Island to surface sediment cover. Bell (2002) reported that juvenile Caryophyllia smithii are morphologically variable and initially undergo rapid growth with tall and thin forms in deeper, sheltered, relatively sedimented conditions near Lough Hyne, Ireland. It was concluded that this was to escape the thin layer of sediment present. Whilst the majority of the characterizing species are likely to be buried in 30 cm of sediment deposition, the biotope occurs on vertical rock in high-energy conditions, and burial is unlikely.

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 of 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.AdigVt occurs on vertical faces and overhangs, and sedimentation would be unlikely, with removal likely to be rapid.  Smothering at the base of rocks could result in the 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) (Litter pressure definition). 

Evidence

All characterizing species for this biotope are sessile or slow-moving epifauna, being either encrusting, branching or cup-like. The species that create biogenic habitats, such as corals, often form complex ecological associations and tend to be long-lived, slow-growing and fragile, sensitive to disturbance and vulnerable to damage (Kaiser et al. 2018; Graves et al., 2023). Physical disturbance by fishing gear has been shown to adversely affect sessile benthic and emergent epifaunal communities, with hydroid and bryozoan matrices reported to be greatly reduced in fished areas and increased when fishing activity is removed (Jennings & Kaiser, 1998; Sheehan et al., 2017; Kaiser et al., 2018). Both Sheehan et al. (2017) and Giusti et al. (2019) highlight how, in addition to the direct damage from fishing, ghost fishing may also be responsible for some coral mortality, Eunicella verrucosa in this case, either through direct damage or making them more vulnerable to removal from their anchorage to the sea floor, particularly during storms.

There are no records of ghost fishing affecting the characterizing species for this biotope. However, epifaunal communities are vulnerable to damage from fishing gear, and are likely vulnerable to being dislodged or damaged through lost fishing gear, and possibly certain types of marine litter.

Sensitivity assessment

Ghost fishing by discarded fishing gear, lines and pots could cause severe damage to the community, especially the tall erect epifauna, where discarded lines may catch the upright epifauna and increase drag, especially in stormy weather (Sheehan et al., 2017; Giusti et al., 2019). However, this biotope occurs on vertical rock, which will likely limit interactions with larger marine debris. Fishing lines can also cause lesions to gorgonian coenenchyme, leading to greater aggregates of epibionts, which can eventually cause the branch to rupture (Bo et al., 2014; Canessa et al., 2022). Taking all the evidence from ghost fishing and discarded lines into account, resistance is assessed as ‘Medium’, resilience as ‘High’ and sensitivity as ‘Low’, albeit with Low confidence due to the lack of direct evidence

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT (Electromagnetic pressure definition).

Evidence

Evidence on the effect of electromagnetic fields (EMFs) on benthic organisms is still severely lacking. Some studies have investigated the effect of anthropogenically induced EMFs on benthic invertebrates at intensities ranging between 2 nT and 40 mT, which is often much higher than in-situ measurements from subsea cables. While some report changes to behaviour, physiology, reproduction, development, immunology, cytotoxicity and orientation, others demonstrate no effect from exposure to the EMF (Albert et al., 2020; Hutchison et al., 2020), depending on the study species and duration and intensity of exposure. There have been no studies investigating the effect of EMFs at the population or community level for benthic organisms. 

One study exists on the effect of EMFs on Echinus esculentus. Chapman et al. (2023) simulated an EMF of 500 μT, as modelled for an export cable over a rocky shore, where the industry standard cable burial would not be possible; however, no significant differences were found in either behavioural or physiological responses on Echinus esculentus. A similar study was performed on the reef-forming annelid, Ficopomatus enigmaticus (Oliva et al., 2023). Sperm cells from this species were exposed to 0.5 and 1.0 mT of static magnetic field. After only three hours of exposure, sperm fertilization rate was reduced, and significant increases in DNA damage and mitochondrial activity, indicative of a stress response, were reported. However, there is ‘Insufficient evidence’ on which to base an assessment of the likely sensitivity of this biotope to EMFs.

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 (Introduced light or shade pressure definition).

Evidence

Although there is some evidence that the basiepithelial nerve plexus below the entire outer skin of echinoderms is sensitive to light (Hill, 2008), there is no evidence to suggest the impact of light on echinoderms. No evidence was found for the effect of light on Alcyonium digitatum or Parasmittina trispinosa, however, it is well understood that light influences the spawning of tropical corals, along with other environmental cues such as solar insolation, day length, and temperature (Davies et al., 2023; Egger et al., 2025). However, for temperate and intermediate-water species, some of these cues may be absent or differ significantly. Many cold-water corals live beyond the reach of moonlight, but the species in this biotope can be found within the first 200 m of depth where light, both natural and artificial, would reach (Holland, Jenkins, & Stevens, 2017; Egger et al., 2025). In addition, shading of light or the introduction of light within the first 50 m could influence marine organisms, such as triggering early coral spawning or affecting the opening and reproduction rhythm of bivalves (Charifi et al., 2023; Davies et al., 2023; Smyth et al.,2021). Below 200 m, it is unlikely that these species would be impacted, as the light level that reaches beyond this point is very low and unsuitable for photosynthesis.

Sensitivity assessment

CR.MCR.EcCr.AdigVt 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 these biotopes. Given the rapid expansion of the evidence base but the continuing lack of data at the level of individual biotopes, resistance and resilience cannot be robustly assessed. Sensitivity is therefore recorded as ‘Insufficient evidence’.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion (Barrier to species movement pressure definition).

Evidence

‘Not relevant’ as 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 (Death for collision pressure definition).

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 (Visual disturbance pressure definition). 

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 may result in changes in the genetic structure of local populations, hybridization, or a change in community structure (Translocation pressure definition).

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 Alcyonium digitatum and Parasmittina trispinosa was found.

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) (pathogen or disease pressure definition).

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.

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

However, 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 (targeted removal pressure definition).

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 (non-targeted removed pressure definition).

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

Decrease in Alcyonium digitatum would result in a decline in the biotope richness.  However, removal of Echinus esculentus could result in restructuring of the biotope.  If both are lost, reclassification would be necessary.  Resistance has therefore been assessed as ‘None’, resilience as ’Medium’ and sensitivity as ‘Medium’.

The American slipper limpet, Crepidula fornicata

Evidence

Crepidula fornicata larvae require hard substrata for settlement. It prefers muddy, gravelly, shell-rich substrata that include gravel, the 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 at 60 metres 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 a gravel substratum with boulders. Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas dominated by boulders. 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 they may out-compete Crepidula for space even if it gained a foothold in the community. 

Sensitivity assessment

The circalittoral rock characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata, although a lack of wave action might allow limited colonization than more exposed sites. Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). and has been recorded from the lower intertidal to ca 160 m in depth, but it 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. However, 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.

The carpet sea squirt, Didemnum vexillum

Evidence

The carpet sea squirt Didemnum vexillum (syn. Didemnum vestitum; Didemnum vestum) is a colonial ascidian with rapidly expanding populations that have invaded most temperate coastal regions around the world (Kleeman, 2009; Stefaniak et al., 2012; Tillin et al., 2020). It is an ‘ecosystem engineer’ that can change or modify invaded habitats and alter biodiversity (Griffith et al., 2009; Mercer et al., 2009). Didemnum vexillum has colonized and established populations in the northeast Pacific, Canadian and USA coast; New Zealand; France, Spain, and the Wadden Sea, Netherlands; the Mediterranean Sea and Adriatic Sea (Bullard et al., 2007; Coutts & Forrest, 2007; Dijkstra et al., 2007; Valentine et al., 2007a; Valentine et al., 2007b; Lambert, 2009; Hitchin, 2012; Tagliapietra et al., 2012; Gittenberger et al., 2015; Vercaemer et al., 2015; Mckenzie et al., 2017; Cinar & Ozgul, 2023; Holt, 2024). In the UK, Didemnum vexillum has colonized Holyhead marina and Milford Haven, Wales; the west coast of Scotland (marinas around Largs, Clyde, Loch Creran and Loch Fyne), South Devon (Plymouth, Yealm, and Dartmouth estuaries), the Solent, northern Kent, Essex, and Suffolk coasts (Griffith et al., 2009; Lambert, 2009; Hitchin, 2012; Minchin & Nunn, 2013; Bishop et al., 2015; Mckenzie et al., 2017; Tillin et al., 2020, Holt, 2024; NBN, 2024).

Although a widespread invader, Didemnum vexillum has a limited ability for natural dispersal since the pelagic larvae remain in the water column for a short time (up to 36 hours). Therefore, it has a short dispersal phase that can allow the species to build localized populations (Herborg et al., 2009; Vercaemer et al., 2015; Holt, 2024). However, Bullard et al. (2007) suggested that Didemnum vexillum can form new colonies asexually by fragmentation. Colonies can produce long tendrils from an encrusting colony, which can fragment, disperse and settle, attaching to suitable hard substrata elsewhere (Bullard et al., 2007; Lambert, 2009; Stefaniak & Whitlatch, 2014). A fragmented colony can spread naturally for up to three weeks, transported by ocean currents, attached to floating seaweed, seagrass or other floating biota, or as free-floating spherical colonies (Bullard et al., 2007; Lengyel et al., 2009; Stefaniak & Whitlatch, 2014; Holt, 2024). Fragments can reattach to suitable substrata within six hours of contact. Fragments have the potential to disperse around 20 km before reattachment (Lengyel et al., 2009). Valentine et al. (2007a) reported that colonies of Didemnum vexillum enlarged by 6 to 11 times by asexual budding after 15 days and enlarged 11 to 19 times after 30 days. Valentine et al. (2007a) concluded fragments could successfully grow, survive, and help to spread Didemnum vexillum.

While natural fragmentation of tendrils is thought to allow Didemnum vexillum to invade longer distances and increase its dispersal potential, Stefaniak & Whitlatch (2014) found that only one tendril out of 80 reattached to the flat, bare substrata used in their study, because tendrils required an extensive (at least eight-hour) period of contact to reattach. Stefaniak & Whitlatch (2014) suggested that once fragmented from a colony, the success of tendril reattachment was limited, and reattachment was not a major contributor to the invasive success of Didemnum vexillum. However, Stefaniak & Whitlatch (2014) also found that larvae-packed tendril fragments may increase natural dispersal distance, reproduction, and invasive success of Didemnum vexillum, and increase the distance larvae can travel. Not all colonies produce tendrils at all locations.

Human-mediated transport via aquaculture facilities, boat hulls, commercial fishing vessels, and ballast water is probably the most important vector that has aided the long-distance dispersal of Didemnum vexillum and explains its prevalence in harbours and marinas (Bullard et al., 2007; Dijkstra et al., 2007; Griffith et al., 2009; Herborg et al., 2009). Fragmentation of colonies during transport or human disturbance (such as trawling or dredging) could indirectly disperse the species and enable it to find suitable conditions for establishment (Herborg et al., 2009). For example, in oyster farms in British Columbia, large fragments of Didemnum sp. come off oyster strings when they are pulled out of water, and other fragments can be pulled off oysters and mussels and thrown back into the water, which is likely to aid dispersal of the invasive species (Bullard et al., 2007). Dijkstra et al. (2007) hypothesised that Didemnum sp. was introduced to the Gulf of Maine with oyster aquaculture in the Damariscotta River and transported via Pacific oysters.

Didemnum vexillum was likely introduced into the UK from northern Europe or Ireland via poorly maintained or not antifouled vessels, movement of contaminated shellfish stock and aquaculture equipment, or via marine industries such as oil, gas, renewables, and dredging (Holt, 2024). Recent evidence from genetic material suggests that human-mediated dispersal, between marinas and shellfish culture sites, is the most likely pathway for connectivity of Didemnum vexillum populations throughout Ireland and Britain (Prentice et al., 2021; Holt, 2024). Didemnum vexillum can disperse away from artificial substrata, invading and colonizing natural substrata in surrounding areas (Tillin et al., 2020). Holt (2024) noted that Didemnum vexillum had not spread as far as feared in the UK since it was first recorded. The current evidence of Didemnum vexillum’s ability to spread on natural habitats in this area is sparse and often conflicting, complicated by genetics, its apparent variable habitat preferences and tolerances and its variable ability to adapt to ‘new’ conditions (Holt 2024).

Didemnum vexillum has a seasonal growth cycle that is influenced by temperature (Valentine et al., 2007a). In warmer months (June and July), colonies may be large and well-developed encrusting mats. Populations experience more rapid growth from July to September, sometimes continuing into December. Colonies begin to decline in health and ‘die-off’ when temperatures drop below 5°C during winter months from around October to April (Gittenberger, 2007; Valentine et al., 2007a; Herborg et al., 2009). Cold water months cause colonies to regress and reduce in size, yet they often regenerate as temperatures warm (Griffith et al., 2009; Kleeman, 2009; Mercer et al., 2009), although some populations may not survive winter at all (Dijkstra et al., 2007). The early growth phase, from May to July, is initiated by smaller colonies developing from remnants of colonies that survived the cold water (Valentine et al., 2007a). The seasonal growth cycle is also likely influenced by location. For example, the Didemnum sp. growth cycle for colonies in Sandwich tide pool (temperature range from -1 °C to 24 °C, with daily fluctuations), probably does not occur in deep offshore subtidal habitats in Georges Bank (annual temperature range from 4 °C to 15°C, and daily fluctuations are minimal) (Valentine et al., 2007a).  Larval release and recruitment typically occur between 14 and 20°C and slow or cease below 9 to 11°C as summer ends (Griffith et al., 2009; McKenzie et al., 2017). In New Zealand, recruitment occurs from November to July, where the highest average temperatures were recorded in February (18 to 22°C), and the lowest average temperatures were recorded in July (9 to 10°C) (Fletcher et al., 2013a). In this New Zealand study, higher water temperatures were associated with a higher level of recruitment (Fletcher et al., 2013a).

Didemnum vexillum requires suitable hard substrata for successful settlement and the establishment of colonies. It can grow quickly and establish large colonies of dense encrusting mats on a variety of hard substrata (Valentine et al., 2007a; Griffith et al., 2009; Lambert, 2009; Groner et al., 2011; Cinar & Ozgul, 2023). Gittenberger (2007) stated that invasive Didemnum sp. was a threat to native ecosystems because of its ability to overgrow virtually all hard substrata present. Suitable hard substrata can include rocky substrata such as bedrock, gravel, pebble, cobble, or boulders or artificial substrata such as a variety of maritime structures, such as pontoons, docks, wood and metal pilings, chains, ropes and moorings, plastic and ship hulls and at aquaculture facilities (Valentine et al., 2007a&b; Bullard et al., 2007; Griffith et al., 2009; Lambert, 2009; Tagliapietra et al., 2012; Tillin et al., 2020). Didemnum vexillum has been reported colonizing these types of hard substrata in the USA, Canada, northern Kent, and the Solent (Bullard et al., 2007; Valentine et al., 2007a; Valentine et al., 2007b; Hitchin, 2012; Vercaemer et al., 2015; Tillin et al., 2020).

Didemnum vexillum has the ability to rapidly overgrow and displace on other sessile organisms such as other colonial ascidians (Ciona intestinalis, Styela clava, Ascidiella aspera, Botrylloides violaceus, Botryllus schlosseri, Diplosoma listerianium and Aplidium spp.), bryozoan, hydroids, sponges (Clione celata and Halichrondria sp.), anemone (Diadumene cincta), calcareous tube worms, eelgrass (Zostera marina), kelp (Laminaria spp. and Agarum sp.), green algae (Codium fragile subsp. fragile), red algae (Plocamium, Chondrus crispus and bush weed Agardhiella subulata), brown algae (Ascophyllum nodosum, Sargassum, Halidrys, Fucus evanescens and Fucus serratus), calcareous algae (Corallina officinalis), mussels (Mytilus galloprovincialis, Perna canaliculus  and Mytilus edulis), barnacles, oysters (Magallana gigas, Ostrea edulis and Crassostrea virginica), sea scallops (Placopecten magellanicus), or dead shells (Dijkstra et al., 2007; Gittenberger, 2007; Valentine et al., 2007a; Valentine et al., 2007b; Griffith et al., 2009; Carman & Grunden, 2010; Dijkstra & Nolan, 2011; Groner et al., 2011; Hitchin, 2012; Tagliapietra et al., 2012; Minchin & Nunn, 2013; Gittenberger et al., 2015; Long & Groholz, 2015; Vercaemer et al., 2015).

In contrast, Didemnum vexillum’s preference for sheltered conditions, established colonies observed in Georges Bank and Long Island Sound were exposed to moderately strong tidal currents (1 to 2 knots; ca 0.5 to 1 m/s recorded at both sites) that may mobilise sediment (Valentine et al., 2007b; Mercer et al., 2009; Tillin et al., 2020). However, Valentine et al. (2007b) describe the substratum as immobile, presumably consolidated, gravel, cobbles, and pebbles. Kleeman (2009) stated that the presence of a consistent mild wave action or ‘swash zone’ appears to favour Didemnum sp. establishment in the intertidal. Although some evidence suggests that waves and currents can facilitate the fragmentation and spread of Didemnum vexillum (Mckenzie et al., 2017), the tidal current velocities at some sites where Didemnum vexillum has been reported (for example, New England, where current velocities reach up to around 3 m/s) is lower than the current velocity required for the dislodgement of Didemnum vexillum fragments (around 7.6 m/s) (Reinhardt et al., 2012). This suggests that not all tidal currents are likely to dislodge Didemnum vexillum fragments. When on boat hulls, the species can experience higher current velocities, which are enough to cause dislodgement (Reinhardt et al., 2012).  

Sensitivity assessment

Didemnum vexillum has been recorded in the sublittoral to depths of 81 m in Georges Bank and 30 m in Long Island, USA (Bullard et al., 2007; Valentine et al., 2007b; Mercer et al., 2009). This biotope occurs on bedrock, which could provide a suitable hard substratum for colonization by Didemnum sp. Didemnum vexillum is reported to prefer sheltered conditions but has also been recorded in moderately strong currents (Valentine et al., 2007b; Mercer et al., 2009; Tillin et al., 2020) and is predicted to survive stronger currents, as the current velocity which will dislodge Didemnum vexillum is around 7.6 m/s (Reinhardt et al., 2012). This biotope experiences weak to moderately strong water flow (<0.5 to 1.5 m/s) and extreme to moderately exposed wave exposure. However, the effect of wave action reduces with depth, so it is possible that only the most wave-exposed examples of the biotope could be unsuitable for Didemnum. Didemnum vexillum regresses as temperatures decline in winter, so shallow examples may be able to recover their condition in winter (Gittenberger, 2007; Valentine et al., 2007a; Herborg et al., 2009). However, deeper examples may not experience enough temperature change to trigger the decline in Didemnum vexillum (Valentine et al., 2007a). If Didemnum sp. could gain a 'foothold', it might overgrow, smother or cause mortality of faunal turf species and other epifauna. Holt (2024) noted that Didemnum vexillum had not spread as far as feared in the UK since it was first recorded. Therefore, a resistance of 'Medium' (some, <25% mortality) is suggested as a precaution in case Didemnum vexillum could colonize the biotope, but with 'Low' confidence due to the lack of direct evidence. Resilience is assessed as 'Very low' as recovery would require the physical removal of Didemnum sp., so sensitivity is assessed as 'Medium'. 

The Pacific oyster, Magallana gigas

Evidence

The majority of the evidence indicates that infralittoral rock and other habitats that occur at depths more than 10 m are unlikely to be suitable for Magallana gigas because it is considered an intertidal and shallow subtidal species rarely recorded below extreme low water (Herbert et al., 2012, 2016; Tillin et al., 2020). Therefore, this biotope is probably 'Not sensitive to this INIS.

Wireweed, Sargassum muticum

Evidence

The depth and sedimentation probably exclude macroalgae from this biotope. Hence, it is unlikely to be colonized by Sargassum. Therefore, this biotope is probably 'Not sensitive to this INIS.

Wakame, Undaria pinnatifida

Evidence

The depth and sedimentation probably exclude macroalgae from this biotope. Hence, it is unlikely to be colonized by Undaria. Therefore, this biotope is probably 'Not sensitive to this INIS.

Other INIS

Evidence

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). At present, there is 'Insufficient evidence' to suggest that the circalittoral rock biotopes are sensitive to colonization by other invasive species; further evidence is required.