The Marine Life Information Network

Global warming (extreme)

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

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

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

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

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

Evidence

The three main species of seapen occurring around the UK are Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis. Virgularia mirabilis is the most abundant of the sea pens, and is common to all coasts of the UK, although less common in the south (Greathead et al., 2007). This species is abundant across the northwest European Shelf and in the Mediterranean, and occurs throughout the North Atlantic possibly as far as North America (Hughes, 1998a).

Ophiura spp. are opportunistic species with short generation times, rapid reproduction, and high dispersal potential. Ophiura ophiura and Ophiura albida are widespread and highly abundant species, recorded from North Norway and Iceland, south to the Azores, Madeira and into the Mediterranean and the Black Sea, frequent in the North Sea and Scandinavian waters and into the transitional area between the North Sea and the Baltic (Mortensen, 1927; Ursin, 1960; Tyler, 1977a; Feder, 1981; Southward & Campbell, 2006; OBIS, 2022). Therefore, the species is likely to experience a wide range of temperature regimes. OBIS (2023) lists records of Ophiura ophiura and Ophiura albida from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C.

Temperature is a common spawning trigger in Ophiuroids but while Ophiura ophiura spawned at 12.5°C in 1974 but in 1973 larvae were found at 7.25°C in the coldest month of the year, so Tyler (1977a) suggested another environmental factor was involved. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven-fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40-day experiment. In addition, Wood et al. (2010) suggested that the increase in metabolic rate could result in a reduction in arm regeneration and growth, despite the high temperatures increasing the regeneration rate, the regenerated arms had lower muscle density and impacted the survivorship of individuals in the long term (Wood et al., 2010). Therefore, elevated temperatures result in increased metabolic rate and regeneration rate but this may increase predation risk and mortality amongst Ophiuroids (Wood et al., 2010, Christensen et al., 2023, Lang et al., 2023).  

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean (De Kluijver et al., 2024). There is no further information available on the temperature tolerance of Cerianthus lloydii. Cerianthids can occur across wide temperature range (8.36 – 11.51°C) and depth ranges from shallow waters to deep-sea environments (238 – 1,070 m). Hydrozoans have been recorded in depths ranging to 8,400 m, indicating adaptations to varied thermal niches throughout the water column (Davies et al., 2014; Stepanjants & Chernyshev, 2015). However, large knowledge gaps limit current understanding of the ecological feedbacks that may occur to cerianthids as a result of climate change driven temperature increase.

Pecten maximus occurs along the European Atlantic coast from northern Norway, south to the Iberian peninsula and has also been reported off West Africa, the Azores, Canary Islands and Madeira (Marshall & Wilson, 2008). Temperature is considered by many to be the primary trigger in spawning among Pectinidae (Marshall & Wilson, 2008) and there is some evidence to suggest that there may be a critical range (Barber & Blake, 1991). In the Bay of Brest and the Bay of St Brieuc in France, for instance, the critical temperature range for spawning is thought to be between 15.5 -16°C (Paulet et al., 1988). Gruffydd & Beaumont (1972) observed high larval mortality above 20°C. Recent evidence has suggested that prolonged exposure to 25°C, extends Pecten maximus beyond its optimal thermal window and thermal limit. This increased temperature generates heat stress, which has been shown to impact metabolic pathways, reduce respiration rates, induce chronic cell stress, and negatively impact Pecten maximus survival (Artiguard et al., 2014, Artiguard et al., 2015a, Artiguard et al., 2015b, Götze et al., 2020). OBIS (2023) lists records of Pecten maximus from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C.

Sensitivity assessment. The distribution of the important characterizing species Virgularia mirabilis and Ophiura spp., Cerianthus lloydii and Pecten maximus suggest that they are probably resistant of chronic change in temperature for a year. No empirical evidence was found for the temperature tolerance of seapens, although the fact that Virgularia mirabilis is widespread in the Mediterranean and the most common seapen recorded in the Adriatic Sea, at shallow depths of 10 m (Bastari et al., 2018), suggests that they will have some tolerance to increases in temperature. In deeper waters, Mediterranean bottom water temperatures are much cooler than sea surface temperatures in the summer time, and whilst sea surface temperatures in the Adriatic Sea can often reach 28°C (www.seatemperature.org), at 40 m depth, temperatures can be > 8°C cooler (Giorgetti, 1999). The distribution of Ophiura albida suggests that the species is likely to be tolerant of ocean warming. The distribution of Ophiura ophiura suggests that it is probably resistant to a 2°C change in temperature for a year. Exposure to a short-term acute increase in temperature may have an effect on the metabolism of Ophiura ophiura but there is no evidence to suggest that mortality would result and it is highly mobile, and able to avoid areas with unsuitable temperatures Cerianthids have been recorded across a broad temperature range and depth, suggesting that species within Cerianthidae can adapt to a diversity of thermal niches (Davies et al., 2014). However, exposure to an increase of 5°C may interfere with reproduction and spawning of Pecten maximus and the evidence above suggests increasing temperature negatively impacts survivorship. 

Under the middle and high emission and extreme scenarios seawater temperatures are expected to temperatures rise by 3-5°C to potential southern summer temperatures of 23-24°C and northern summer temperatures of 17-19°C. Virgularia is likely to be able to tolerate temperature increases predicted for Scotland. However, some genotypes may fail to adapt to increasing temperatures in the south of the UK, so some mortality from the increased temperature cannot be ruled out. Similarly, Pecten maximus may be lost from the more southerly or shallow examples of the biotope. Therefore, for all three scenarios (middle and high emission and extreme scenarios) resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as loss is likely to be a long-term decline, due to the long-term nature of ocean warming. This biotope is assessed as ‘Medium’ sensitivity to ocean warming under all three scenarios, albeit with ‘Low’ confidence.

Global warming (high)

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

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

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

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

Evidence

The three main species of seapen occurring around the UK are Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis. Virgularia mirabilis is the most abundant of the sea pens, and is common to all coasts of the UK, although less common in the south (Greathead et al., 2007). This species is abundant across the northwest European Shelf and in the Mediterranean, and occurs throughout the North Atlantic possibly as far as North America (Hughes, 1998a).

Ophiura spp. are opportunistic species with short generation times, rapid reproduction, and high dispersal potential. Ophiura ophiura and Ophiura albida are widespread and highly abundant species, recorded from North Norway and Iceland, south to the Azores, Madeira and into the Mediterranean and the Black Sea, frequent in the North Sea and Scandinavian waters and into the transitional area between the North Sea and the Baltic (Mortensen, 1927; Ursin, 1960; Tyler, 1977a; Feder, 1981; Southward & Campbell, 2006; OBIS, 2022). Therefore, the species is likely to experience a wide range of temperature regimes. OBIS (2023) lists records of Ophiura ophiura and Ophiura albida from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C.

Temperature is a common spawning trigger in Ophiuroids but while Ophiura ophiura spawned at 12.5°C in 1974 but in 1973 larvae were found at 7.25°C in the coldest month of the year, so Tyler (1977a) suggested another environmental factor was involved. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven-fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40-day experiment. In addition, Wood et al. (2010) suggested that the increase in metabolic rate could result in a reduction in arm regeneration and growth, despite the high temperatures increasing the regeneration rate, the regenerated arms had lower muscle density and impacted the survivorship of individuals in the long term (Wood et al., 2010). Therefore, elevated temperatures result in increased metabolic rate and regeneration rate but this may increase predation risk and mortality amongst Ophiuroids (Wood et al., 2010, Christensen et al., 2023, Lang et al., 2023).  

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean (De Kluijver et al., 2024). There is no further information available on the temperature tolerance of Cerianthus lloydii. Cerianthids can occur across wide temperature range (8.36 – 11.51°C) and depth ranges from shallow waters to deep-sea environments (238 – 1,070 m). Hydrozoans have been recorded in depths ranging to 8,400 m, indicating adaptations to varied thermal niches throughout the water column (Davies et al., 2014; Stepanjants & Chernyshev, 2015). However, large knowledge gaps limit current understanding of the ecological feedbacks that may occur to cerianthids as a result of climate change driven temperature increase.

Pecten maximus occurs along the European Atlantic coast from northern Norway, south to the Iberian peninsula and has also been reported off West Africa, the Azores, Canary Islands and Madeira (Marshall & Wilson, 2008). Temperature is considered by many to be the primary trigger in spawning among Pectinidae (Marshall & Wilson, 2008) and there is some evidence to suggest that there may be a critical range (Barber & Blake, 1991). In the Bay of Brest and the Bay of St Brieuc in France, for instance, the critical temperature range for spawning is thought to be between 15.5 -16°C (Paulet et al., 1988). Gruffydd & Beaumont (1972) observed high larval mortality above 20°C. Recent evidence has suggested that prolonged exposure to 25°C, extends Pecten maximus beyond its optimal thermal window and thermal limit. This increased temperature generates heat stress, which has been shown to impact metabolic pathways, reduce respiration rates, induce chronic cell stress, and negatively impact Pecten maximus survival (Artiguard et al., 2014, Artiguard et al., 2015a, Artiguard et al., 2015b, Götze et al., 2020). OBIS (2023) lists records of Pecten maximus from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C.

Sensitivity assessment. The distribution of the important characterizing species Virgularia mirabilis and Ophiura spp., Cerianthus lloydii and Pecten maximus suggest that they are probably resistant of chronic change in temperature for a year. No empirical evidence was found for the temperature tolerance of seapens, although the fact that Virgularia mirabilis is widespread in the Mediterranean and the most common seapen recorded in the Adriatic Sea, at shallow depths of 10 m (Bastari et al., 2018), suggests that they will have some tolerance to increases in temperature. In deeper waters, Mediterranean bottom water temperatures are much cooler than sea surface temperatures in the summer time, and whilst sea surface temperatures in the Adriatic Sea can often reach 28°C (www.seatemperature.org), at 40 m depth, temperatures can be > 8°C cooler (Giorgetti, 1999). The distribution of Ophiura albida suggests that the species is likely to be tolerant of ocean warming. The distribution of Ophiura ophiura suggests that it is probably resistant to a 2°C change in temperature for a year. Exposure to a short-term acute increase in temperature may have an effect on the metabolism of Ophiura ophiura but there is no evidence to suggest that mortality would result and it is highly mobile, and able to avoid areas with unsuitable temperatures Cerianthids have been recorded across a broad temperature range and depth, suggesting that species within Cerianthidae can adapt to a diversity of thermal niches (Davies et al., 2014). However, exposure to an increase of 5°C may interfere with reproduction and spawning of Pecten maximus and the evidence above suggests increasing temperature negatively impacts survivorship. 

Under the middle and high emission and extreme scenarios seawater temperatures are expected to temperatures rise by 3-5°C to potential southern summer temperatures of 23-24°C and northern summer temperatures of 17-19°C. Virgularia is likely to be able to tolerate temperature increases predicted for Scotland. However, some genotypes may fail to adapt to increasing temperatures in the south of the UK, so some mortality from the increased temperature cannot be ruled out. Similarly, Pecten maximus may be lost from the more southerly or shallow examples of the biotope. Therefore, for all three scenarios (middle and high emission and extreme scenarios) resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as loss is likely to be a long-term decline, due to the long-term nature of ocean warming. This biotope is assessed as ‘Medium’ sensitivity to ocean warming under all three scenarios, albeit with ‘Low’ confidence.

Global warming (middle)

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

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

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

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

Evidence

The three main species of seapen occurring around the UK are Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis. Virgularia mirabilis is the most abundant of the sea pens, and is common to all coasts of the UK, although less common in the south (Greathead et al., 2007). This species is abundant across the northwest European Shelf and in the Mediterranean, and occurs throughout the North Atlantic possibly as far as North America (Hughes, 1998a).

Ophiura spp. are opportunistic species with short generation times, rapid reproduction, and high dispersal potential. Ophiura ophiura and Ophiura albida are widespread and highly abundant species, recorded from North Norway and Iceland, south to the Azores, Madeira and into the Mediterranean and the Black Sea, frequent in the North Sea and Scandinavian waters and into the transitional area between the North Sea and the Baltic (Mortensen, 1927; Ursin, 1960; Tyler, 1977a; Feder, 1981; Southward & Campbell, 2006; OBIS, 2022). Therefore, the species is likely to experience a wide range of temperature regimes. OBIS (2023) lists records of Ophiura ophiura and Ophiura albida from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C.

Temperature is a common spawning trigger in Ophiuroids but while Ophiura ophiura spawned at 12.5°C in 1974 but in 1973 larvae were found at 7.25°C in the coldest month of the year, so Tyler (1977a) suggested another environmental factor was involved. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven-fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40-day experiment. In addition, Wood et al. (2010) suggested that the increase in metabolic rate could result in a reduction in arm regeneration and growth, despite the high temperatures increasing the regeneration rate, the regenerated arms had lower muscle density and impacted the survivorship of individuals in the long term (Wood et al., 2010). Therefore, elevated temperatures result in increased metabolic rate and regeneration rate but this may increase predation risk and mortality amongst Ophiuroids (Wood et al., 2010, Christensen et al., 2023, Lang et al., 2023).  

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean (De Kluijver et al., 2024). There is no further information available on the temperature tolerance of Cerianthus lloydii. Cerianthids can occur across wide temperature range (8.36 – 11.51°C) and depth ranges from shallow waters to deep-sea environments (238 – 1,070 m). Hydrozoans have been recorded in depths ranging to 8,400 m, indicating adaptations to varied thermal niches throughout the water column (Davies et al., 2014; Stepanjants & Chernyshev, 2015). However, large knowledge gaps limit current understanding of the ecological feedbacks that may occur to cerianthids as a result of climate change driven temperature increase.

Pecten maximus occurs along the European Atlantic coast from northern Norway, south to the Iberian peninsula and has also been reported off West Africa, the Azores, Canary Islands and Madeira (Marshall & Wilson, 2008). Temperature is considered by many to be the primary trigger in spawning among Pectinidae (Marshall & Wilson, 2008) and there is some evidence to suggest that there may be a critical range (Barber & Blake, 1991). In the Bay of Brest and the Bay of St Brieuc in France, for instance, the critical temperature range for spawning is thought to be between 15.5 -16°C (Paulet et al., 1988). Gruffydd & Beaumont (1972) observed high larval mortality above 20°C. Recent evidence has suggested that prolonged exposure to 25°C, extends Pecten maximus beyond its optimal thermal window and thermal limit. This increased temperature generates heat stress, which has been shown to impact metabolic pathways, reduce respiration rates, induce chronic cell stress, and negatively impact Pecten maximus survival (Artiguard et al., 2014, Artiguard et al., 2015a, Artiguard et al., 2015b, Götze et al., 2020). OBIS (2023) lists records of Pecten maximus from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C.

Sensitivity assessment. The distribution of the important characterizing species Virgularia mirabilis and Ophiura spp., Cerianthus lloydii and Pecten maximus suggest that they are probably resistant of chronic change in temperature for a year. No empirical evidence was found for the temperature tolerance of seapens, although the fact that Virgularia mirabilis is widespread in the Mediterranean and the most common seapen recorded in the Adriatic Sea, at shallow depths of 10 m (Bastari et al., 2018), suggests that they will have some tolerance to increases in temperature. In deeper waters, Mediterranean bottom water temperatures are much cooler than sea surface temperatures in the summer time, and whilst sea surface temperatures in the Adriatic Sea can often reach 28°C (www.seatemperature.org), at 40 m depth, temperatures can be > 8°C cooler (Giorgetti, 1999). The distribution of Ophiura albida suggests that the species is likely to be tolerant of ocean warming. The distribution of Ophiura ophiura suggests that it is probably resistant to a 2°C change in temperature for a year. Exposure to a short-term acute increase in temperature may have an effect on the metabolism of Ophiura ophiura but there is no evidence to suggest that mortality would result and it is highly mobile, and able to avoid areas with unsuitable temperatures Cerianthids have been recorded across a broad temperature range and depth, suggesting that species within Cerianthidae can adapt to a diversity of thermal niches (Davies et al., 2014). However, exposure to an increase of 5°C may interfere with reproduction and spawning of Pecten maximus and the evidence above suggests increasing temperature negatively impacts survivorship. 

Under the middle and high emission and extreme scenarios seawater temperatures are expected to temperatures rise by 3-5°C to potential southern summer temperatures of 23-24°C and northern summer temperatures of 17-19°C. Virgularia is likely to be able to tolerate temperature increases predicted for Scotland. However, some genotypes may fail to adapt to increasing temperatures in the south of the UK, so some mortality from the increased temperature cannot be ruled out. Similarly, Pecten maximus may be lost from the more southerly or shallow examples of the biotope. Therefore, for all three scenarios (middle and high emission and extreme scenarios) resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as loss is likely to be a long-term decline, due to the long-term nature of ocean warming. This biotope is assessed as ‘Medium’ sensitivity to ocean warming under all three scenarios, albeit with ‘Low’ confidence.

Marine heatwaves (high)

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

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Whilst there are no laboratory studies on the upper thermal limit of UK species of seapen, their biogeographical distribution suggests that they may be tolerant to a wide range of temperatures, although their preference for deeper waters (generally found at depths of >50 m in the Adriatic Sea; Bastari et al., 2018) suggests that they may not be tolerant of extremes in temperature. For example Virgularia mirabilis and Pennatula phosphorea occur at shallow depths of 10 and 16 m respectively, whilst Funiculina quadrangularis is a deeper water species, occurring at depths of >40 m (Bastari et al., 2018), suggesting that Virgularia mirabilis and Pennatula phosphorea may be more tolerant of fluctuations in temperature.

No evidence on the upper thermal limit of Ophiura albida or Ophiura ophiura was found but these species appear to be tolerant of a wide range of temperatures (see global warming above), suggesting they may be more tolerant to fluctuations in temperature. For example, Ophiura albida are widely distributed across the Mediterranean Sea, (Koukouras et al., 2007; www.obis.org), where sea temperatures can reach 28°C in summer months (www.seatemperature.org). Exposure to a short-term acute increase of 5°C may have an effect on the metabolism of Ophiura ophiura but there is no evidence to suggest that mortality would result. However, recent evidence found an increase in respiration and arm regeneration in the brittle star Ophionereis schayeri in response to a stimulated winter heatwave (3°C increase for 10 weeks), which lead to increased mortality (Christensen et al., 2023). An increase in metabolic rate as a result of increased temperatures has also been seen in Ophiura ophiura but no mortality was recorded in the 40-day experiment (Wood et al., 2010). Therefore, prolonged exposure to elevated temperatures results in increased metabolic rate, increased regeneration rate and mortality, suggesting Ophiuroids may be vulnerable to marine heatwaves (Wood et al., 2010, Christensen et al., 2023, Lang et al., 2023).

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore.  This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay.  Larvae, but not adults, have been recorded from the Mediterranean (De Kluijver et al., 2024). There is no further information available on the temperature tolerance of Cerianthus lloydii.

Evidence has suggested that prolonged exposure to 25°C, extends Pecten maximus beyond its optimal thermal window and thermal limit. This increased temperature generates heat stress which has been shown to impact metabolic pathways, reduce respiration rates, induce chronic cell stress and negatively impact Pecten maximus survival (Artiguard et al., 2014, Artiguard et al., 2015a, Artiguard et al., 2015b, Götze et al., 2020). Hence, heatwaves may pose a threat to Pecten maximus as it creates condition at the upper limit of its environmental tolerance.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C. As a precautionary approach, this biotope has been assessed as having ‘Medium’ sensitivity to marine heatwaves. The recovery of Virgularia populations is likely to be ‘Low’, hence, recovery may be interrupted by the occurrence of a further heatwave before the habitat can recover.  Therefore, resilience has been assessed as ‘Very low’, leading to a sensitivity assessment of ‘Medium’ for this biotope, but with ‘Low’ confidence.

Marine heatwaves (middle)

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

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Whilst there are no laboratory studies on the upper thermal limit of UK species of seapen, their biogeographical distribution suggests that they may be tolerant to a wide range of temperatures, although their preference for deeper waters (generally found at depths of >50 m in the Adriatic Sea; Bastari et al., 2018) suggests that they may not be tolerant of extremes in temperature. For example Virgularia mirabilis and Pennatula phosphorea occur at shallow depths of 10 and 16 m respectively, whilst Funiculina quadrangularis is a deeper water species, occurring at depths of >40 m (Bastari et al., 2018), suggesting that Virgularia mirabilis and Pennatula phosphorea may be more tolerant of fluctuations in temperature.

No evidence on the upper thermal limit of Ophiura albida or Ophiura ophiura was found but these species appear to be tolerant of a wide range of temperatures (see global warming above), suggesting they may be more tolerant to fluctuations in temperature. For example, Ophiura albida are widely distributed across the Mediterranean Sea, (Koukouras et al., 2007; www.obis.org), where sea temperatures can reach 28°C in summer months (www.seatemperature.org). Exposure to a short-term acute increase of 5°C may have an effect on the metabolism of Ophiura ophiura but there is no evidence to suggest that mortality would result. However, recent evidence found an increase in respiration and arm regeneration in the brittle star Ophionereis schayeri in response to a stimulated winter heatwave (3°C increase for 10 weeks), which lead to increased mortality (Christensen et al., 2023). An increase in metabolic rate as a result of increased temperatures has also been seen in Ophiura ophiura but no mortality was recorded in the 40-day experiment (Wood et al., 2010). Therefore, prolonged exposure to elevated temperatures results in increased metabolic rate, increased regeneration rate and mortality, suggesting Ophiuroids may be vulnerable to marine heatwaves (Wood et al., 2010, Christensen et al., 2023, Lang et al., 2023).

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore.  This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay.  Larvae, but not adults, have been recorded from the Mediterranean (De Kluijver et al., 2024). There is no further information available on the temperature tolerance of Cerianthus lloydii.

Evidence has suggested that prolonged exposure to 25°C, extends Pecten maximus beyond its optimal thermal window and thermal limit. This increased temperature generates heat stress which has been shown to impact metabolic pathways, reduce respiration rates, induce chronic cell stress and negatively impact Pecten maximus survival (Artiguard et al., 2014, Artiguard et al., 2015a, Artiguard et al., 2015b, Götze et al., 2020). Hence, heatwaves may pose a threat to Pecten maximus as it creates condition at the upper limit of its environmental tolerance.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C. As a precautionary approach, this biotope has been assessed as having ‘Medium’ sensitivity to marine heatwaves. The recovery of Virgularia populations is likely to be ‘Low’, hence, recovery may be interrupted by the occurrence of a further heatwave before the habitat can recover.  Therefore, resilience has been assessed as ‘Very low’, leading to a sensitivity assessment of ‘Medium’ for this biotope, but with ‘Low’ confidence.

Ocean acidification (high)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005).

Seapens are colonial octocorals from the order Pennutulacea. Research on octocorals, suggests that most species of octocoral will be tolerant of ocean acidification at levels expected for the end of this century under both the middle emission and high emission scenario (Gabay et al., 2013, Gabay et al., 2014, Enochs et al., 2015, Gomez et al., 2018). Whilst seapens generally have a calcareous rod, formed from sclerites, the ability of octocorals to tolerate low pH may be because their fleshy tissue may act as a barrier, protecting the organism from low external pH (Gabay et al., 2013, Gabay et al., 2014). An exception to this is the octocoral, Corallium rubrum. The octocoral Corallium rubrum is unusual in that it is highly calcified compared to other species of octocoral. In response to experimental acidification, this species has been shown to exhibit a decrease in feeding activity and calcification (Cerrano et al., 2013).

Echinoderms skeleton is made from magnesium calcite and their ability to regenerate involves altering calcification rates, which may make them vulnerable to acidification (Wood et al., 2010). Ophiura ophiura is a particularly heavily calcified brittlestar (Wood et al., 2010). However, evidence has suggested that early life stages may be more sensitive to ocean acidification. 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), and brittlestar larvae seem to be more sensitive to ocean acidification than sea urchins (Dupont & Thorndyke, 2008, Chan et al., 2015). The larvae of Ophiothrix fragilis, Ophiura albida and Ophiocomina nigra have been shown to be sensitive to a small (0.2 unit) experimental pH decrease, leading to a decrease in survival and changes to developmental dynamics (Dupont & Thorndyke, 2008). A 0.2 unit pH decrease led to almost 100% mortality in Ophiothrix fragilis larvae after one week's exposure (Dupont & Thorndyke, 2009). Under low pH conditions, surviving larvae of Ophiothrix fragilis show skeletal malformations (Dupont & Thorndyke, 2008).

There is limited evidence on the effects of ocean acidification on adult stages of Ophiura spp. species. Brittlestars have been shown to increase their biological processes metabolism and calcification under stress which helps their tolerance but this has caused muscle wastage in regenerated arms and is not sustainable in the long term (Wood et al., 2008, Wood et al. 2010). In Wood et al.‘s study (2010) there was no impact on mortality and no change to the calcium carbonate of its skeleton in response to low pH levels. However, the study assumed that metabolism needs to be increased further to facilitate increased rates of calcification, if the metabolism cannot do this may cause dissolution (Wood et al. 2010). This suggests that adult Ophiura spp. may be able to tolerate a decrease in pH levels, but the observation that a small decrease in pH (0.2 units) had a dramatic effect on the survival and normal growth of these species’ larvae suggests that ocean acidification could adversely affect recruitment and, hence, the survival of the brittlestar beds. In addition, it was also recognized that there may be a negative combined effect of temperature and pH on Ophiura ophiura (Wood et al. 2010).

Evidence has suggested that Pecten maximus embryos and larvae are vulnerable to an increase in pCO₂ levels, which causes an increase in shell deformities, reduced growth rates and increased mortality (Andersen et al., 2013, Andersen et al., 2017). Shell deformities observed in the shells hinges provides particularly negative effects on larval survival, as the hinge is crucial for feeding and excretion (Andersen et al., 2013). It is suggested that a decrease of 0.06 – 0.32 units in pH will negatively impact Pecten maximus in early life stages (Andersen et al., 2017).

However, juvenile Pecten maximus may be able to tolerate changes in pH as evidence found an increase in pCO₂ levels did not significantly affect metabolic functions, shell growth or mortality (Sanders et al., 2013). Cameron et al., (2019) examined the effect of different pH on calcification rate and condition index in scallops (Pecten maximus) at a range of seasonal temperatures. They concluded that king scallops were relatively resilient to CO₂ induced ocean acidification but that their allocation of resources to tissue or shell growth in response to CO₂ stress varied seasonally. In addition, Harney et al. (2023) examined the effects of increased pCO₂ and temperature on the physiology of French and Norwegian scallop spat. In French spat, 7 out of 12 proteomic markers responded to temperature rather than pCO₂. Oxygen uptake increase in French spat in response to pCO₂ alone but to both temperature and pCO₂ in Norwegian spat. French spat showed higher metabolic plasticity than Norwegian spat but at a cost to survivability. On the other hand, Schalkhausser et al.’s study (2013) found that elevated CO₂ levels impacts the escape response of scallops. To escape predators, scallops ‘clap’ the valves of shell together to propel and swim away and the study found in high CO₂ environments the response still occurred but the clapping muscle force was reduced. This makes Pecten maximus vulnerable to predators in predicted ocean acidification conditions.

Sensitivity Assessment. Direct evidence of the impact of ocean acidification on seapens is lacking. However, in general, lightly calcified octocorals appear to be tolerant, therefore it is likely that Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis will be tolerant of levels of ocean acidification expected for the end of this century. However, the Ophiura and Pecten populations may be adversely affected by ocean acidification. Therefore, based on the evidence available, under both the middle and high emission scenarios the biotope is assessed as having ‘Medium’ resistance to ocean acidification to represent the possible loss of component species rather than seapens, Resilience is assessed as ‘Very low’, and sensitivity as of ‘Medium. at the benchmark level.

Ocean acidification (middle)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005).

Seapens are colonial octocorals from the order Pennutulacea. Research on octocorals, suggests that most species of octocoral will be tolerant of ocean acidification at levels expected for the end of this century under both the middle emission and high emission scenario (Gabay et al., 2013, Gabay et al., 2014, Enochs et al., 2015, Gomez et al., 2018). Whilst seapens generally have a calcareous rod, formed from sclerites, the ability of octocorals to tolerate low pH may be because their fleshy tissue may act as a barrier, protecting the organism from low external pH (Gabay et al., 2013, Gabay et al., 2014). An exception to this is the octocoral, Corallium rubrum. The octocoral Corallium rubrum is unusual in that it is highly calcified compared to other species of octocoral. In response to experimental acidification, this species has been shown to exhibit a decrease in feeding activity and calcification (Cerrano et al., 2013).

Echinoderms skeleton is made from magnesium calcite and their ability to regenerate involves altering calcification rates, which may make them vulnerable to acidification (Wood et al., 2010). Ophiura ophiura is a particularly heavily calcified brittlestar (Wood et al., 2010). However, evidence has suggested that early life stages may be more sensitive to ocean acidification. 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), and brittlestar larvae seem to be more sensitive to ocean acidification than sea urchins (Dupont & Thorndyke, 2008, Chan et al., 2015). The larvae of Ophiothrix fragilis, Ophiura albida and Ophiocomina nigra have been shown to be sensitive to a small (0.2 unit) experimental pH decrease, leading to a decrease in survival and changes to developmental dynamics (Dupont & Thorndyke, 2008). A 0.2 unit pH decrease led to almost 100% mortality in Ophiothrix fragilis larvae after one week's exposure (Dupont & Thorndyke, 2009). Under low pH conditions, surviving larvae of Ophiothrix fragilis show skeletal malformations (Dupont & Thorndyke, 2008).

There is limited evidence on the effects of ocean acidification on adult stages of Ophiura spp. species. Brittlestars have been shown to increase their biological processes metabolism and calcification under stress which helps their tolerance but this has caused muscle wastage in regenerated arms and is not sustainable in the long term (Wood et al., 2008, Wood et al. 2010). In Wood et al.‘s study (2010) there was no impact on mortality and no change to the calcium carbonate of its skeleton in response to low pH levels. However, the study assumed that metabolism needs to be increased further to facilitate increased rates of calcification, if the metabolism cannot do this may cause dissolution (Wood et al. 2010). This suggests that adult Ophiura spp. may be able to tolerate a decrease in pH levels, but the observation that a small decrease in pH (0.2 units) had a dramatic effect on the survival and normal growth of these species’ larvae suggests that ocean acidification could adversely affect recruitment and, hence, the survival of the brittlestar beds. In addition, it was also recognized that there may be a negative combined effect of temperature and pH on Ophiura ophiura (Wood et al. 2010).

Evidence has suggested that Pecten maximus embryos and larvae are vulnerable to an increase in pCO₂ levels, which causes an increase in shell deformities, reduced growth rates and increased mortality (Andersen et al., 2013, Andersen et al., 2017). Shell deformities observed in the shells hinges provides particularly negative effects on larval survival, as the hinge is crucial for feeding and excretion (Andersen et al., 2013). It is suggested that a decrease of 0.06 – 0.32 units in pH will negatively impact Pecten maximus in early life stages (Andersen et al., 2017).

However, juvenile Pecten maximus may be able to tolerate changes in pH as evidence found an increase in pCO₂ levels did not significantly affect metabolic functions, shell growth or mortality (Sanders et al., 2013). Cameron et al., (2019) examined the effect of different pH on calcification rate and condition index in scallops (Pecten maximus) at a range of seasonal temperatures. They concluded that king scallops were relatively resilient to CO₂ induced ocean acidification but that their allocation of resources to tissue or shell growth in response to CO₂ stress varied seasonally. In addition, Harney et al. (2023) examined the effects of increased pCO₂ and temperature on the physiology of French and Norwegian scallop spat. In French spat, 7 out of 12 proteomic markers responded to temperature rather than pCO₂. Oxygen uptake increase in French spat in response to pCO₂ alone but to both temperature and pCO₂ in Norwegian spat. French spat showed higher metabolic plasticity than Norwegian spat but at a cost to survivability. On the other hand, Schalkhausser et al.’s study (2013) found that elevated CO₂ levels impacts the escape response of scallops. To escape predators, scallops ‘clap’ the valves of shell together to propel and swim away and the study found in high CO₂ environments the response still occurred but the clapping muscle force was reduced. This makes Pecten maximus vulnerable to predators in predicted ocean acidification conditions.

Sensitivity Assessment. Direct evidence of the impact of ocean acidification on seapens is lacking. However, in general, lightly calcified octocorals appear to be tolerant, therefore it is likely that Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis will be tolerant of levels of ocean acidification expected for the end of this century. However, the Ophiura and Pecten populations may be adversely affected by ocean acidification. Therefore, based on the evidence available, under both the middle and high emission scenarios the biotope is assessed as having ‘Medium’ resistance to ocean acidification to represent the possible loss of component species rather than seapens, Resilience is assessed as ‘Very low’, and sensitivity as of ‘Medium. at the benchmark level.

Sea level rise (extreme)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt. Sea levels have risen 1 - 3 mm yr^-1 in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). The most recent projections on sea-level rise suggest a rise of 50 cm under the middle emission scenario, 70 cm under the high emission scenario, and 107 cm under the extreme scenario.

All three UK species of seapen (Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis) are known to reside at depths of up to 800 m (Bastari et al., 2018) suggesting that, as long as the substratum (fine mud) remains the same these species will be tolerant of future sea-level rise for all three scenarios (middle emission 50 cm, high emission 70 cm, and extreme scenario 107 cm). However, Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis are shallow water species (0 - 50 m) (Kushida et al., 2022).

The other characterizing species also have a broad depth range, which may allow them to tolerate sea-level rise. Ophiuroids can be found across from low shore to the deep sea, but species of Ophiura spp. are often found dominating coastal zones and shallower waters (Stohr et al., 2012). Ophiura ophiura is commonly found from lower shore to 850 m. It is also a highly mobile species capable of moving to more suitable habitats. Pecten maximus is common at depths from 5 – 200 m (Lawler & Naeri, 2021). Cerianthids can occur across depths 238 – 1,070 m in UK deep-sea environments and the Cerianthid anemones in Atlantic mid bathyal mud are deep-sea biotopes, relevant to the Atlantic mid bathyal zone, at depths of 600 – 1300 m. Cerianthus lloydii has been recorded at depths ranging from 0 – 900 m (OBIS, 2024).

This biotope occurs in areas sheltered from wave action and subject to weak or negligible tidal streams (Hughes, 1998a). Understanding of how sea-level rise will affect tidal energy, and the tide-swept nature of a habitat, is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. The effects of sea-level rise and increased wave action may be increased further due to storms and storms surges. IPCC (2019) note that the frequency of extreme sea-level events (e.g. due to storms) are predicted to increase as sea-level rises, however there is no consensus on the future storm and, hence, wave climate around UK coasts (Mossman et al., 2015; Lowe et al., 2018; Palmer et al., 2018).

Sensitivity assessment. This habitat occurs from 5 - 50 m, although seapens, Ophiuroids, Cerianthids and Pecten maximus can be found at deeper depths. Therefore, an increase in sea-level rise is unlikely to have a large impact on this biotope and therefore resistance to sea-level rise has been assessed as ‘High’ for the middle (50 cm), and high (70 cm) emission scenario, and for the extreme scenario (107 cm). As no recovery is deemed necessary, resilience has been assessed as ‘High’, and therefore this species has been classified as ‘Not sensitive’ to sea-level rise at each of the benchmarks.

Sea level rise (high)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt. Sea levels have risen 1 - 3 mm yr^-1 in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). The most recent projections on sea-level rise suggest a rise of 50 cm under the middle emission scenario, 70 cm under the high emission scenario, and 107 cm under the extreme scenario.

All three UK species of seapen (Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis) are known to reside at depths of up to 800 m (Bastari et al., 2018) suggesting that, as long as the substratum (fine mud) remains the same these species will be tolerant of future sea-level rise for all three scenarios (middle emission 50 cm, high emission 70 cm, and extreme scenario 107 cm). However, Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis are shallow water species (0 - 50 m) (Kushida et al., 2022).

The other characterizing species also have a broad depth range, which may allow them to tolerate sea-level rise. Ophiuroids can be found across from low shore to the deep sea, but species of Ophiura spp. are often found dominating coastal zones and shallower waters (Stohr et al., 2012). Ophiura ophiura is commonly found from lower shore to 850 m. It is also a highly mobile species capable of moving to more suitable habitats. Pecten maximus is common at depths from 5 – 200 m (Lawler & Naeri, 2021). Cerianthids can occur across depths 238 – 1,070 m in UK deep-sea environments and the Cerianthid anemones in Atlantic mid bathyal mud are deep-sea biotopes, relevant to the Atlantic mid bathyal zone, at depths of 600 – 1300 m. Cerianthus lloydii has been recorded at depths ranging from 0 – 900 m (OBIS, 2024).

This biotope occurs in areas sheltered from wave action and subject to weak or negligible tidal streams (Hughes, 1998a). Understanding of how sea-level rise will affect tidal energy, and the tide-swept nature of a habitat, is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. The effects of sea-level rise and increased wave action may be increased further due to storms and storms surges. IPCC (2019) note that the frequency of extreme sea-level events (e.g. due to storms) are predicted to increase as sea-level rises, however there is no consensus on the future storm and, hence, wave climate around UK coasts (Mossman et al., 2015; Lowe et al., 2018; Palmer et al., 2018).

Sensitivity assessment. This habitat occurs from 5 - 50 m, although seapens, Ophiuroids, Cerianthids and Pecten maximus can be found at deeper depths. Therefore, an increase in sea-level rise is unlikely to have a large impact on this biotope and therefore resistance to sea-level rise has been assessed as ‘High’ for the middle (50 cm), and high (70 cm) emission scenario, and for the extreme scenario (107 cm). As no recovery is deemed necessary, resilience has been assessed as ‘High’, and therefore this species has been classified as ‘Not sensitive’ to sea-level rise at each of the benchmarks.

Sea level rise (middle)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt. Sea levels have risen 1 - 3 mm yr^-1 in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). The most recent projections on sea-level rise suggest a rise of 50 cm under the middle emission scenario, 70 cm under the high emission scenario, and 107 cm under the extreme scenario.

All three UK species of seapen (Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis) are known to reside at depths of up to 800 m (Bastari et al., 2018) suggesting that, as long as the substratum (fine mud) remains the same these species will be tolerant of future sea-level rise for all three scenarios (middle emission 50 cm, high emission 70 cm, and extreme scenario 107 cm). However, Virgularia mirabilis, Pennatula phosphorea, and Funiculina quadrangularis are shallow water species (0 - 50 m) (Kushida et al., 2022).

The other characterizing species also have a broad depth range, which may allow them to tolerate sea-level rise. Ophiuroids can be found across from low shore to the deep sea, but species of Ophiura spp. are often found dominating coastal zones and shallower waters (Stohr et al., 2012). Ophiura ophiura is commonly found from lower shore to 850 m. It is also a highly mobile species capable of moving to more suitable habitats. Pecten maximus is common at depths from 5 – 200 m (Lawler & Naeri, 2021). Cerianthids can occur across depths 238 – 1,070 m in UK deep-sea environments and the Cerianthid anemones in Atlantic mid bathyal mud are deep-sea biotopes, relevant to the Atlantic mid bathyal zone, at depths of 600 – 1300 m. Cerianthus lloydii has been recorded at depths ranging from 0 – 900 m (OBIS, 2024).

This biotope occurs in areas sheltered from wave action and subject to weak or negligible tidal streams (Hughes, 1998a). Understanding of how sea-level rise will affect tidal energy, and the tide-swept nature of a habitat, is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. The effects of sea-level rise and increased wave action may be increased further due to storms and storms surges. IPCC (2019) note that the frequency of extreme sea-level events (e.g. due to storms) are predicted to increase as sea-level rises, however there is no consensus on the future storm and, hence, wave climate around UK coasts (Mossman et al., 2015; Lowe et al., 2018; Palmer et al., 2018).

Sensitivity assessment. This habitat occurs from 5 - 50 m, although seapens, Ophiuroids, Cerianthids and Pecten maximus can be found at deeper depths. Therefore, an increase in sea-level rise is unlikely to have a large impact on this biotope and therefore resistance to sea-level rise has been assessed as ‘High’ for the middle (50 cm), and high (70 cm) emission scenario, and for the extreme scenario (107 cm). As no recovery is deemed necessary, resilience has been assessed as ‘High’, and therefore this species has been classified as ‘Not sensitive’ to sea-level rise at each of the benchmarks.

Temperature increase (local)

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

Evidence

In shallow sea lochs, sedimentary biotopes typically experience seasonal changes in temperature between 5°C and 15°C (10°C) (Hughes, 1998a). Although unusually warm summers or cold winters may change the temperatures outside this range, benthic burrowing species will be buffered from extremes by their presence in the sediment. Sea pens can withdraw into their burrows for protection. No information was found on the upper limit of sea pens tolerance to temperature. Virgularia mirabilis is recorded from western Europe, the Mediterranean, from Norway and Iceland to Africa in the North Atlantic, and to the Gulf of Mexico in North America (Hughes, 1998a; OBIS 2015). Jones et al. (2000) suggested that Virgularia mirabilis was probably more tolerant of temperature change than other British sea pen species due to its abundance in shallow waters.

Ophiura albida is distributed from northern Norway to the Azores and the Mediterranean while Ophiura ophiura is distributed from northern Norway to Madeira and the Mediterranean (Hayward & Ryland, 1990). Little evidence on temperature tolerance was found. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven-fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40 day experiment.  Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean. 

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

Gili & Hughes (1995) reported that temperature was a critical factor stimulating or preventing reproduction and that most species have an optimal temperature for reproduction.  However, limited evidence for thermal thresholds and thermal ranges were available for the characterizing species recorded in this biotope.  Cantero et al. (2002) describe the presence and year-round fertility of Obelia dichotoma, Kirchenpaureria pinnata, Nemertesia ramosa and Halecium spp.in the Mediterranean, indicating probable tolerance to temperature increases at the benchmark level. Ascidia mentula and Corella parallelogramma are recorded from north of Norway, throughout the British Isles and south into the Mediterranean (OBIS, 2018). 

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

Temperature decrease (local)

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

Evidence

In shallow sea lochs, sedimentary biotopes typically experience seasonal changes in temperature between 5°C and 15°C (10°C) (Hughes, 1998a). Although unusually warm summers or cold winters may change the temperatures outside this range, benthic burrowing species will be buffered from extremes by their presence in the sediment. Sea pens can withdraw into their burrows for protection. No information was found on the upper limit of sea pens tolerance to temperature. Virgularia mirabilis is recorded from western Europe, the Mediterranean, from Norway and Iceland to Africa in the North Atlantic, and to the Gulf of Mexico in North America (Hughes, 1998a; OBIS, 2015). Jones et al. (2000) suggested that Virgularia mirabilis was probably more tolerant of temperature change than other British sea pen species due to its abundance in shallow waters.

Ophiura albida is distributed from northern Norway to the Azores and the Mediterranean while Ophiura ophiura is distributed from northern Norway to Madeira and the Mediterranean (Hayward & Ryland, 1995). Little evidence on temperature tolerance was found. Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven-fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40 day experiment. Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay. Larvae, but not adults, have been recorded from the Mediterranean.  Crisp (1964) reported that Cerianthus lloydii in North Wales were apparently unaffected by the severe winter of 1962/63. However, no further information on the temperature tolerance of Cerianthus lloydii was found.

Pecten maximus occurs along the European Atlantic coast from northern Norway, south to the Iberian Peninsula and has been reported off West Africa, the Azores, Canary Islands and Madeira (Marshall & Wilson, 2009).  Temperature is considered by many to be the primary trigger in spawning among Pectinidae (Marshall & Wilson, 2009) and there is some evidence to suggest that there may be a critical range (Barber & Blake, 1991).  In the Bay of Brest and the Bay of St Brieuc in France, for instance, the critical temperature range for spawning is thought to be between 15.5 -16°C (Paulet et al., 1988). No information was available on an upper threshold of temperature tolerance for adult Pecten maximus although Gruffydd & Beaumont (1972) observed high larval mortality above 20°C.  However, Crisp (1964) reported mortalities approaching 100% of Pecten maximus from several areas around the British coast in the severe winter of 1962-1963 where the average sea temperature fell by approximately 4°C.

Gili & Hughes (1995) reported that temperature was a critical factor stimulating or preventing reproduction and that most species have an optimal temperature for reproduction.  However, limited evidence for thermal thresholds and thermal ranges were available for the characterizing species recorded in this biotope.  Palerud et al. (2004) described the presence of the characterizing hydroids Halecium halecinum and Nemertesia sp. in Svalbard, suggesting that these hydroids are probably tolerant of the lowest temperatures they are likely to encounter in Britain and Ireland of ca 4°C (Beszczynska-Möller & Dye, 2013). Ascidia mentula and Corella parallelogramma are recorded from north of Norway, throughout the British Isles and south into the Mediterranean (OBIS, 2018). 

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

Salinity increase (local)

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

Evidence

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

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

The MNCR database indicates biotopes where Ophiura albida and Ophiura ophiura are characterizing species occur in full (30-40 units) as well as variable salinity (18-40 units).  Echinoderms are stenohaline species owing to the lack of an excretory organ and a poor ability to osmo- and ion-regulate (Stickle & Diehl, 1987; Russell, 2013).  Ophiura albida from Loch Etive, Scotland tolerated 20.7‰ (Pagett, 1980; Russell, 2013) and only a single individual died at this salinity. The LT50 for 40% seawater (ca 14‰) varied between ca 80 hours ca 400 hours depending on the origin of the specimens. Pagett (1980) noted that salinity tolerance was greatest in those specimens taken from waters at 70% seawater at the head of Loch Etive when compared to those at full salinity near the mouth of the Loch.  Wolff (1968) reported that adult Ophiura albida were not seen at salinities below 16.5‰ Cl. Russell (2013) noted that Ophiura ophiura tolerated 27‰.  

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

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

Salinity decrease (local)

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

Evidence

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

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

The MNCR database indicates biotopes where Ophiura albida and Ophiura ophiura are characterizing species occur in full (30-40 units) as well as variable salinity (18-40 units).  Echinoderms are stenohaline species owing to the lack of an excretory organ and a poor ability to osmo- and ion-regulate (Stickle & Diehl, 1987; Russell, 2013).  Ophiura albida from Loch Etive, Scotland tolerated 20.7‰ (Pagett, 1980; Russell, 2013) and only a single individual died at this salinity. The LT50 for 40% seawater (ca 14‰) varied between ca 80 hours ca 400 hours depending on the origin of the specimens. Pagett (1980) noted that salinity tolerance was greatest in those specimens taken from waters at 70% seawater at the head of Loch Etive when compared to those at full salinity near the mouth of the Loch.  Wolff, 1968 reported that adult Ophiura albida were not seen at salinities below 16.5‰ Cl. Russell (2013) noted that Ophiura ophiura tolerated 27‰.  Similarly, Kirchenpaureria pinnata and the Nemertesia spp. were recorded from biotopes at full and variable salinity, while ascidians Ascidia mentula and Corella parallelogramma were recorded from biotopes at full, variable and reduced salinities (Connor et al., 2004). 

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

Water flow (tidal current) changes (local)

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

Evidence

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

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

Ophiura albida and Ophiura ophiura are both recorded in biotopes from very weak to moderately strong (negligible - 1.5m/s) tidal flow (Connor et al., 1997b). Both species are reported to occur on a range of soft sediments (Hayward & Ryland, 1990) including muds, gravel, sand and shell (Boos et al., 2010). Ophiura albida showed a preference for fine sediments due to its habit of burrowing to escape predators, and its preference for surface deposit feeding and scavenging or predating on fine grained sediments (Boos et al., 2010). Ophiura ophiura is larger and demonstrated a little preference of sediment type due to its habit of escaping predators by rapidly moving across the surface of the sediment, together with its relatively unselective predation and scavenging habit (Boos et al., 2010).  Kirchenpaureria pinnata and the ascidians Ascidia mentula and Corella parallelogramma were recorded from biotopes at moderately strong to very weak flow, while Nemertesia spp. were also recorded in strong or very strong flow (Connor et al., 2004).

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

Emergence regime changes

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

Evidence

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

Wave exposure changes (local)

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

Evidence

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

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

Transition elements & organo-metal contamination

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

Evidence

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

Hydrocarbon & PAH contamination

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

Evidence

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

Synthetic compound contamination

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

Evidence

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

Radionuclide contamination

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

Evidence

No evidence was found

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

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

Evidence

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

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

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

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

Hydroids mainly inhabit environments in which the oxygen concentration exceeds 5 ml/l (ca 7 mg/l) (Gili & Hughes, 1995). Although no information was found on oxygen consumption for the characterizing hydroids, Sagasti et al. (2000) reported that epifaunal species, including several hydroids and Obelia bidentata (as bicuspidata) in the York River, Chesapeake Bay, tolerated summer hypoxic episodes of between 0.5 and 2 mg O₂/l (0.36 and 1.4 ml/l) for 5-7 days at a time, with few changes in abundance or species composition.  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  (ca 0.5 mg/l) below ca 10 m.  Despite the presence of Kirchenpaueria pinnata, and Ascidia mentula in shallower water, no sponges or ascidians were recorded at depths below the oxycline at 10 -11 m.  The ability of solitary ascidians to withstand decreasing oxygen levels has not been well documented. Mazouni et al. (2001) noted that whilst oysters (Magallana gigas) can survive short-term exposure to periods of anoxia (Thau Lagoon, France), the associated biofouling community dominated by Ciona intestinalis suffered heavy mortality.  It should be noted, however, that Ciona intestinalis is frequently found in areas with restricted water renewal where oxygen concentrations may drop (Carver et al., 2006).  In addition, in a systematic review of the effects of hypoxia cnidarians were amongst the most tolerant groups studied (Vaquer-Sunyer & Duarte, 2008).

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

Nutrient enrichment

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

Evidence

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

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

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

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

Organic enrichment

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

Evidence

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

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

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

Witt et al. (2004) found that the hydroid Obelia spp. was more abundant in a sewage disposal area in the Weser estuary (Germany), which experienced sedimentation of 1 cm for more than 25 days.  However, another hydroid (Sertularia cupressina) was reduced in abundance when compared with unimpacted reference areas.   As suspension feeders, an increase in organic content at the benchmark is likely to be of benefit to the characterizing hydroids. There is some suggestion that there are possible benefits to the ascidians from the increased organic content of water; Ascidian ‘richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996).  Kocak & Kucuksezgin (2000) noted that Ciona intestinalis was one of the rapid breeding opportunistic species that tended to be dominant in Turkish harbours enriched by organic pollutants and was frequently found in polluted environments (Carver et al., 2006).  Ascidia mentula has been reported in Iberian bays subject to both nutrient-rich upwelling events and anthropogenic organic pollution (Aneiros et al., 2015).

An increasing gradient of organic enrichment (e.g. in the vicinity of point sources of organic-rich effluent or sewage sludge dump sites) results in a decline in the suspension feeding fauna and an increase in the number of deposit feeders, in particular, polychaete worms (Pearson & Rosenberg, 1978). The effects of organic enrichment on burrowing megafauna and other infauna depended on the degree of enrichment and any resultant hypoxia, which depend on the sediment type and local hydrology.

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

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

If sedimentary substrata were replaced with rock substrata the biotope would be lost, as it would no longer be a sedimentary habitat and would no longer support sea pens, burrowing anemones, epibenthic brittlestars or infauna.

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

Physical change (to another sediment type)

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

Evidence

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

Cerianthus lloydii is recorded from biotopes in muddy to mixed or coarse sediments (Connor et al., 1997b). Therefore, it is likely to tolerate changes in sediment type. Similarly, Pecten maximus is recorded from gravel, coarse and fine clean sand, muddy sand and sandy muds. Ophiura albida and Ophiura ophiura are both reported to occur on a range of soft sediments (Hayward & Ryland, 1990) including muds, gravel, sand and shell (Boos et al., 2010). Ophiura albida showed a preference for fine sediments due to its habit of burrowing to escape predators, and its preference for surface deposit feeding and scavenging or predating on fine grained sediments (Boos et al., 2010). Ophiura ophiura is larger and demonstrated a little preference of sediment type due to its habit of escaping predators by rapidly moving across the surface of the sediment, together with its relatively unselective predation and scavenging habit (Boos et al., 2010).

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

Habitat structure changes - removal of substratum (extraction)

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

Evidence

Benthic trawls (e.g. rock hopper ground gear, otter trawls) will remove and capture sea pens (Tuck et al., 1998; Kenchington et al., 2011), albeit with limited efficiency. Nevertheless, dredging and suction dredging penetrates to greater depth and are likely to remove sea pens. Virgularia mirabilis will not be able to avoid activities that penetrate into the sediment. Assuming their burrows are only deep enough to hold the entire animal (see Greathead et al., 2007 for sizes) then Virgularia mirabilis burrows are up to 40 cm deep. Cerianthus lloydii can also withdraw into the sediment, and its burrow is up to 40 cm deep. However, Ophiura spp. only burrow into the surface of the sediment while Pecten maximus lives embedded in recesses in the seabed usually with the upper valve flush with the sediment surface.

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

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

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

In experimental studies (Kinnear et al. 1996; Eno et al. 2001), sea pens were found to be largely resilient to smothering, dragging, or uprooting by creels or pots.  Virgularia mirabilis withdrew very quickly into the sediment when exposed to pots or creels so that it was difficult to determine their response.  In Virgularia mirabilis withdrawal from a physical stimulus is rapid (ca 30 seconds) (Hoare & Wilson, 1977; Ambroso et al., 2013).  Birkland (1974) maintained that the only way to capture all of the sea pens in an area (quadrat) was to remove them slowly by hand until no more emerged.  But several studies note that their ability to withdraw into the sediment in response to bottom towed or dropped gear (e.g. creels, pots, camera/video mounted towed sleds, experimental grab, trawl, or dredge) means that sea pen abundance can be difficult to estimate (Birkeland, 1974; Eno et al., 2001; Greathead et al., 2007; Greathead et al., 2011).  The ability to withdraw also suggests that sea pens can avoid approaching demersal trawls and fishing gear.  This was suggested as the explanation for the similarity in the densities of Virgularia mirabilis in trawled and untrawled sites in Loch Fyne, and the lack of change in sea pen density observed after experimental trawling (using modified rock hopper ground gear) over an 18 month period in Loch Gareloch (Howson & Davies 1991; Hughes 1998a; Tuck et al. 1998).  Kenchington et al. (2011) estimated the gear efficiency of otter trawls for sea pens (Anthoptilum and Pennatula) to be in the range of 3.7 – 8.2%, based on estimates of sea pen biomass from (non-destructive) towed camera surveys.  However, species obtained by dredges were invariably damaged (Hoare & Wilson, 1977).  Hoare & Wilson (1977) noted that Virgularia was absent for areas of Holyhead Harbour disturbed by dragging or boat mooring, although no causal evidence was given (Hughes, 1998a).  Sea pens are potentially vulnerable to long lining.  Munoz et al. (2011) noted that small numbers of Pennatulids (inc. Pennatula sp.) were retrieved from experimental long-lining around the Hatton Bank in the North East Atlantic, presumably either attached to hooks or wrapped in line as it passed across the sediment.  Hixon & Tissot (2007) noted that sea pens (Stylatula sp.) were four times more abundant in untrawled areas relative to trawled areas in the Coquille Bank, Oregon, although no causal relationship was shown. 

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

Pecten maximus is the target of commercial fisheries and hence, gears have been developed to capture this species.  By-catch studies suggest that due to their robust shells captured Pecten maximus suffer low rates of damage.  Jenkins et al. (2001) found that less than 10% of scallops encountering dredges showed any signs of external physical damage on a scallop fishing ground in the north Irish Sea.  Undamaged Pecten maximus captured using dredges, show low levels (5%). of mortality in the laboratory (Jenkins et al., 2001).  Similarly (Bergmann et al., 2001) found that most (98%) of queen scallops Aequipecten opercularis were undamaged when retained in otter trawl hauls in the Clyde Seas Nephrops fishery.  Damage was restricted to chipping of the outer shell.  Ansell et al. (1991) however, stated that up to 19% of the scallops left behind by a dredge are affected to some extent.  Individuals with damaged shells are more prone to predation.  However, Jenkins et al. (2001) reported that, during dredging, more than 90% of Pecten maximus that came into contact with a dredge (including those landed, discarded and left behind by the dredge) were in good condition overall and showed little or no shell damage.  The differences between reported rates of effect may be due to different classification systems used to score impacts.  Blyth et al. (2004) compared sites that were trawled for scallops to those that were untrawled or previously trawled but not in the 18-24 months prior to the study. They found that significantly fewer scallops were caught in the trawled sites.  They suggested that at least a two year period was necessary for the benthic community to recover to a state that was indistinguishable from non-trawled areas.

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

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

Penetration or disturbance of the substratum subsurface

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

Evidence

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

Changes in suspended solids (water clarity)

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

Evidence

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

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

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

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

Smothering and siltation rate changes (light)

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

Evidence

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

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

Direct evidence for the effects of siltation on this ecological group is limited to the experiments undertaken by Last et al. (2011).  Last et al. (2011) buried Ophiura ophiura individuals under three different depths of sediment; shallow (2 cm), medium (5 cm) and deep (7 cm).  The results indicated that Ophiura ophiura is highly tolerant of short-term (32 days) burial events, with less than 10% mortality of all buried specimens.  This is largely a reflection of the ability of the species to re-emerge from all depths across all sediment fractions tested.  Survival of specimens that remained buried was low, with 100% mortality of individuals that remained buried after 32 days.  Percentage mortality increased with both depth and duration of burial.  The experiments utilised three different fractions of kiln dried, commercially obtained marine sediment: coarse (1.2-2.0 mm diameter), medium fine (0.25-0.95 mm diameter) and fine (0.1-0.25 mm diameter). Ophiura ophiura are found in sandier habitats that are subject to high rates of natural disturbance, these species are therefore likely to experience burial through natural sediment movements and be adapted to this, as suggested by the results of experimental smothering (Last et al., 2011).  No evidence for re-emergence thresholds was found. No direct evidence was found on Ophiura albida. However, it is smaller and less mobile than Ophiura ophiura (Boos et al., 2010) and may, therefore, be more vulnerable to smothering.

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

In general, it appears that hydroids are sensitive to silting (Boero, 1984; Gili & Hughes, 1995) and the decline of beds in the Wadden Sea have been linked to environmental changes including siltation.  Round et al. (1961) reported that the hydroid Sertularia (now Amphisbetia) operculata died when covered with a layer of silt after being transplanted to sheltered conditions.  Boero (1984) suggested that deepwater hydroid species develop upright, thin colonies that accumulate little sediment, while species in turbulent water movement were adequately cleaned of silt by water movement.  Hughes (1977) found that maturing hydroids that had been smothered with detritus and silt lost most of the hydrocladia and hydranths. After one month, the hydroids were seen to have recovered but although neither the growth rate nor the reproductive potential appeared to have been affected, the viability of the planulae may have been affected.  Nemertesia ramosa is an upright hydroid with a height of up to 15 cm and Nemertesia antennina grows up to 25 cm and Kirchenpaueria pinnata grows up to 10 cm in height (Hayward & Ryland, 1994). The structure of Nemertesia spp. is fairly tough and flexible, and Nemertesia spp. are recorded from sediment scoured methane-derived authigenic carbonates in the mid-Irish Sea (Whomersley et al., 2010b; O'Reilly et al., 2014).  Smothering with 5 cm of sediment may cover over some individuals; others may just have the lower section of the main stem covered.

The solitary ascidians are attached permanently to the substratum and are active suspension feeder.  Ascidia mentula is a large solitary sea squirt that can be over 18 cm in length but is attached on its left side and does not protrude above the substratum and Corella parrallelogramma is up to 5 cm in height. The complete disappearance of the sea squirt Ascidiella aspersa biocoenosis and ‘associated sponges’ in the Black Sea near the Kerch Strait was attributed to siltation (Terent'ev, 2008 cited in Tillin & Tyler-Walters, 2014). 

Sensitivity assessment. Both Virgularia and Cerianthus can withdraw into their tube and can probably re-emerge through 5 cm of fines. However, experimental studies have demonstrated juvenile Pecten maximus are killed under 5 cm of fine sediment and that Ophiura ophiura suffered some mortality. Smothering by 5 cm of sediment is may also result in mortality amongst the characteristic ascidians and smaller specimens of hydroids. Therefore, a resistance of 'Medium' is suggested due to the potential loss in abundance of one or more of the characterizing species. The resilience of Pecten maximus is probably 'Medium' so that the biotope is probably of 'Medium' sensitivity to siltation and smothering at the benchmark level. 

Smothering and siltation rate changes (heavy)

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

Evidence

Sensitivity assessment. Based on the evidence presented above (siltation, 5 cm deposition), the deposition of 30 cm of fine sediment is may affect the community adversely. Virgularia mirabilis and Cerianthus lloydii can burrow and move into and out of their own burrows, which can be up to 40 cm deep. It is probable, therefore, that deposition of 30 cm of fine sediment will have little effect other than to suspend feeding temporarily and the energetic cost of burrowing. However, experimental studies have demonstrated Pecten maximus is killed under 5 cm of fine sediment and that Ophiura ophiura suffered some mortality so that 30 cm of fines is likely to result in further mortality in Pecten maximus and Ophiura spp. In addition, the epifaunal community of hydroids and ascidians is likely to be completely smothered and may be lost. Therefore, technically the biotope VirOphPmax.HAs would be lost and the biotope replaced by VirOphPmax so resistance is assessed as 'None'. Once the deposited sediment is removed or redistributed and shell and small stones reappear, the hydroids and ascidians would recolonize quickly. However, resilience is probably 'Medium' based on the recovery of Pecten maximus population, so that sensitivity of the biotope is probably 'Medium' at the benchmark level. 

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

No evidence was found

Underwater noise changes

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

Evidence

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

Introduction of light or shading

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

Evidence

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

Barrier to species movement

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

Evidence

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

Death or injury by collision

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

Evidence

Not relevant to seabed habitats. 

Visual disturbance

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

Evidence

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

Genetic modification & translocation of indigenous species

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

Evidence

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

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

Introduction or spread of invasive non-indigenous species

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

Evidence

The American slipper limpet Crepidula fornicata was introduced to the UK and Europe in the 1870s from the Atlantic coasts of North America with imports of the eastern oyster Crassostrea virginica. It was recorded in Liverpool in 1870 and the Essex coast in 1887-1890. It has spread through expansion and introductions along the full extent of the English Channel and into the European mainland (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Helmer et al., 2019; Hinz et al., 2011; McNeill et al., 2010; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015).

Crepidula fornicata is recorded from shallow, sheltered bays, lagoons and estuaries or the sheltered sides of islands, in variable salinity (18 to 40) although it prefers ca 30 (Tillin et al., 2020). Larvae require hard substrata for settlement. It prefers muddy gravelly, shell-rich, substrata that include gravel, or shells of other Crepidula, or other species e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. But it also recorded in a wide variety of habitats including clean sands, artificial substrata, Sabellaria alveolata reefs and areas subject to moderately strong tidal streams (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015; Tillin et al., 2020). 

High densities of Crepidula fornicata cause ecological impacts on sedimentary habitats. The species can form dense carpets that can smother the seabed in shallow bays, changing and modifying the habitat structure. At high densities, the species physically smothers the sediment, and the resultant build-up of silt, pseudofaeces, and faeces is deposited and trapped within the bed (Tillin et al., 2020, Fitzgerald, 2007, Blanchard, 2009, Stiger-Pouvreau & Thouzeau, 2015). The biodeposition rates of Crepidula are extremely high and once deposited, form an anoxic mud, making the environment suitable for other species, including most infauna (Stiger-Pouvreau & Thouzeau, 2015, Blanchard, 2009). For example, in fine sands, the community is replaced by a reef of slipper limpets, that provide hard substrata for sessile suspension-feeders (e.g., sea squirts, tube worms and fixed shellfish), while mobile carnivorous microfauna occupy species between or within shells, resulting in a homogeneous Crepidula dominated habitat (Blanchard, 2009). Blanchard (2009) suggested the transition occurred and became irreversible at 50% cover of the limpet. De Montaudouin et al. (2018) suggested that homogenization occurred above a threshold of 20-50 Crepidula /m². 

Impacts on the structure of benthic communities will depend on the type of habitat that Crepidula colonizes. De Montaudouin & Sauriau (1999) reported that in muddy sediment dominated by deposit-feeders, species richness, abundance and biomass increased in the presence of high densities of Crepidula (ca 562 to 4772 ind./m²), in the Bay of Marennes-Oléron, presumably because the Crepidula bed provided hard substrata in an otherwise sedimentary habitat. In medium sands, Crepidula density was moderate (330-1300 ind./m²) but there was no significant difference between communities in the presence of Crepidula. Intertidal coarse sediment was less suitable for Crepidula with only moderate or low abundances (11 ind./m²) and its presence did not affect the abundance or diversity of macrofauna. However, there was a higher abundance of suspension–feeders and mobile Crustacea in the absence of Crepidula (De Montaudouin & Sauriau, 1999). The presence of Crepidula as an ecosystem engineer has created a range of new niche habitats, reducing biodiversity as it modifies habitats (Fitzgerald, 2007). De Montaudouin et al. (1999) concluded that Crepidula did not influence macroinvertebrate diversity or density significantly under experimental conditions, on fine sands in Arcachon Bay, France. De Montaudouin et al. (2018) noted that the limpet reef increased the species diversity in the bed, but homogenised diversity compared to areas where the limpets were absent. In the Milford Haven Waterway (MHW), the highest densities of Crepidula were found in areas of sediment with hard substrata, e.g., mixed fine sediment with shell or gravel or both (grain sizes 16-256 mm) but, while Crepidula density increased as gravel cover increased in the subtidal, the reverse was found in the intertidal (Bohn et al., 2015). Bohn et al. (2015) suggested that high densities of Crepidula in high-energy environments were possible in the subtidal but not the intertidal, suggesting the availability of this substratum type is beneficial for its establishment. Hinz et al. (2011) reported a substantial increase in the occurrence of Crepidula off the Isle of Wight, between 1958 and 2006, at a depth of ca 60 m, on hard substrata (gravel, cobbles, and boulders), swept by strong tidal streams. Presumably, Crepidula is more tolerant of tidal flow than the oscillatory flow caused by wave action which may be less suitable (Tillin et al., 2020). 

The availability of hard substrata (e.g., gravel) may only restrict initial colonization as higher densities of Crepidula function as substrata for subsequent colonization (Thieltges et al., 2004; Blanchard, 2009). However, Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas of homogenous fine sediment and areas dominated by boulders. Bohn et al. (2015) suggested that wave action (exposure) probably prevented the establishment of large numbers of Crepidula in high-energy areas. Blanchard (2009) noted that sandy areas in the Bay of Saint-Mont Michel were not colonized by Crepidula because of surface sand mobility. Thieltges et al. (2003) also noted that storm events removed some clumps of mussels and presumably Crepidula onto tidal flats where they disappeared, which caused their abundance to fluctuate. Similarly, Crepidula was absent from sandy substrata in Swansea Bay but was most abundant in the shelter of the breakwater at the Swansea east site (Powell-Jennings & Calloway, 2018).

King scallop (Pecten maximus and Queen scallop (Aequipecten opercularis) in the Bay of Brest, have been reported to decrease in the presence of Crepidula, largely due to silting and biodeposition that changes the habitat (Stiger Pouvreau & Thouzeau, 2015; Thouzeau et al., 2000). The scallop post larvae are unable to settle and survive on muddy Crepidula substrata. Crepidula could potentially be the main competitor for Pecten maximus, especially creating competition for space (Menesguen & Gregoris, 2018; Ragueneau et al., 2018). However, no direct competition for food was observed between Crepidula and the scallops (Thouzeau et al., 2000, Chauvaud et al. 2000) and scallop shell growth rates did not decrease with increasing Crepidula populations. Therefore, although Crepidula populations will likely impact scallop post-larvae settlement, it does not affect shell growth rates or adult survivorship (Thouzeau et al., 2000). Models show that competition for space between the species does not impact the abundance of Crepidula, but does lower the abundance of Pecten sp. (Menesguen & Gregoris, 2018). 

Codium fragile tomentosoides have been reported to foul scallop beds (DAISIE, 2009) but no information on adverse effects was found. Sternapsis scutata is a non-native polychaete that has extended its range in inshore muddy sediments in the southwest of the UK (Shelley et al., 2008). However, in mesocosm experiments, little effect on biological functioning was detected after the introduction of the polychaete and a doubling of its biomass (Shelley et al., 2008).

Sensitivity assessment. The sediments characterizing this biotope are likely to be too mobile and unsuitable for most of the invasive non-indigenous species currently recorded in the UK. The above evidence suggests that Crepidula fornicata could colonize sandy mud habitats in the subtidal, typical of this biotope, due to the presence of gravel, shells or any other hard substrata that can be used for larvae settlement (Tillin et al., 2020). In addition, this habitat is moderately exposed to very sheltered, so storms may mobilise the sediment (JNCC, 2022), which may also mitigate or prevent colonization by Crepidula at high densities in shallow wave exposed examples, although it has been recorded from areas of strong tidal streams (Hinz et al., 2011). Therefore, the habitat may be more suitable for Crepidula in wave sheltered areas of the biotope and where water movement is mediated by tidal flow rather than wave action, e.g., the deeper examples of the biotope.

Therefore, resistance is assessed as 'Medium' in examples where wave action is high and subject to storms but 'Low' in wave sheltered areas dominated by tidal flow. Resilience is assessed as 'Very low' as it would require the removal of Crepidula, probably by artificial means. Hence, sensitivity is assessed as 'High' based on the worst-case scenario. Crepidula has not yet been reported to occur in this biotope so the confidence in the assessment is 'Low'. No direct evidence of the effect of other non-native species on mud communities was found. However, this assessment should be revisited in the light of new evidence.

Introduction of microbial pathogens

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

Evidence

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

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

Removal of target species

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

Evidence

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

Removal of non-target species

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

Evidence

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