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 distribution of seaweeds is climatically defined (Breeman, 1990). Northern boundaries are set by winter temperatures that are lethal or summer temperatures too low for growth and/or reproduction, whilst southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic, is found as far south as New York State, USA. In the UK, sea surface temperatures are between 6-19°C (Huthnance, 2010), and Saccharina latissima is in the middle of its biogeographic range. At its southern distribution in New York, temperatures can regularly reach ≥ 20°C for six weeks or more during summer months (Gerard & Du Bois, 1988).

Temperature is a major environmental factor controlling the development of the microscopic stages of Saccharina latissima, with major changes in survival, growth, and gametogenesis occurring within a few degrees of upper thermal limits (Redmond, 2013). The temperature isotherm of 19-20°C was reported as limiting Saccharina latissima growth (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013), and the maximum temperature for gametophytes survival is 23°C. Bolton & Lüning (1982) report an experimental optimal temperature of 10-15°C for growth of the Saccharina latissima sporophyte, with growth reduced by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C.

In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima that were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations, which rarely experience ≥17°C, showed 100% mortality after three weeks of exposure to 20°C.

Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway. In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. However, there was annual variation. High mortality occurred from August-November each year. In 2008, only six of the original 17 transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration at which temperatures remain above 20°C. High sea temperatures have been linked to slow growth of Saccharina latissima which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011). 

Assis et al. (2018) predicted that under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from the coast of Portugal, France and from the southwest coast of the UK. The authors projected that under RCP 2.6, 13% of suitable Laminaria hyperborea habitat would be lost from the Western English Channel, whilst under the RCP 8.5 emission, 87% of suitable habitat was expected to be lost.

Modiolus modiolus is a Boreal species that is distributed from the White Sea and Norway, off the Faroes and Iceland, south to the Bay of Biscay and occasionally North Africa. Also from Labrador to North Carolina in the Atlantic and from the Bering Sea south to Japan and California in the Pacific. Although this species is widespread, Modiolus modiolus beds are more limited in their distribution. In the UK, Modiolus modiolus is not known to form beds beyond the North Sea and the southern Irish Sea. The reproductive cycle of Modiolus modiolus varies considerably over its geographic range, with spawning appearing to commence over a reasonably small range of temperatures (7-10°C; Brown, 1984), which might explain the limited distribution of these beds. The depth range of Modiolus modiolus increases at higher latitudes with intertidal specimens more common on northern Norwegian shores where air temperatures are lower (Davenport & Kjørsvik, 1982).

Observations on Modiolus modiolus exposed to high temperatures suggest that this species is restricted by upper seawater temperatures of 23°C (Read & Cumming, 1967), although individuals may survive short-term exposure to higher temperatures. Read (1967) found that in intertidal pools most submerged Modiolus modiolus survived following exposure to temperatures that rose from 19 to 32.5°C over 5.5 hours. Modiolus barbatus, which has a more southerly distribution in the North East Atlantic and the Mediterranean, has been shown to experience metabolic depression and switch to anaerobic metabolism at temperatures exceeding 24°C, with some mortality (Anestis et al., 2008).

Psammechinus miliaris is distributed from the Shetland Islands to the Bay of Biscay, with some scattered observations further south (www.obis.org). This species generally occurs in water temperatures of 4 – 17°C. Kelly (2001) suggests that experiencing cold water over winter is important for the completion of gametogenesis in female Psammechinus miliaris, as significantly fewer females in the temperature-controlled treatment (with seawater maintained at 9°C) produced mature eggs.

Sensitivity Assessment. This biotope only occurs in Scotland, often in sealochs. UK populations of Saccharina latissima are found in the middle of their distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise.

Sea surface temperatures around Scotland range between 6-16°C (www.seatemperature.org). Under the middle and high emission scenarios sea temperatures are predicted to rise by between 3-4°C by the end of this century, leading to Scottish winter seawater temperatures of 9 - 10°C and summer highs of 19 - 20°C. Populations of Saccharina latissima may be able to adapt to cope with a gradual rise in ocean temperatures of this magnitude although Psammechinus miliaris and Modiolus modiolus may be negatively impacted. In particular, an increase in winter seawater temperatures is likely to reduce the window for reproduction in both species. Therefore, resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as the loss is likely to be a long-term decline, due to the long-term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ sensitivity to ocean warming in middle and high emission scenario benchmark levels.

Under the extreme scenario, whereby sea temperatures rise by 5°C to potential southern summer temperatures of 20°C and winter low temperatures of 11°C (www.seatemperature.org), all three characterizing species for this biotope are likely to suffer negative impacts. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. Therefore, this biotope is assessed as ‘High’ sensitivity to ocean warming under the extreme scenario.  

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 distribution of seaweeds is climatically defined (Breeman, 1990). Northern boundaries are set by winter temperatures that are lethal or summer temperatures too low for growth and/or reproduction, whilst southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic, is found as far south as New York State, USA. In the UK, sea surface temperatures are between 6-19°C (Huthnance, 2010), and Saccharina latissima is in the middle of its biogeographic range. At its southern distribution in New York, temperatures can regularly reach ≥ 20°C for six weeks or more during summer months (Gerard & Du Bois, 1988).

Temperature is a major environmental factor controlling the development of the microscopic stages of Saccharina latissima, with major changes in survival, growth, and gametogenesis occurring within a few degrees of upper thermal limits (Redmond, 2013). The temperature isotherm of 19-20°C was reported as limiting Saccharina latissima growth (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013), and the maximum temperature for gametophytes survival is 23°C. Bolton & Lüning (1982) report an experimental optimal temperature of 10-15°C for growth of the Saccharina latissima sporophyte, with growth reduced by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C.

In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima that were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations, which rarely experience ≥17°C, showed 100% mortality after three weeks of exposure to 20°C.

Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway. In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. However, there was annual variation. High mortality occurred from August-November each year. In 2008, only six of the original 17 transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration at which temperatures remain above 20°C. High sea temperatures have been linked to slow growth of Saccharina latissima which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011). 

Assis et al. (2018) predicted that under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from the coast of Portugal, France and from the southwest coast of the UK. The authors projected that under RCP 2.6, 13% of suitable Laminaria hyperborea habitat would be lost from the Western English Channel, whilst under the RCP 8.5 emission, 87% of suitable habitat was expected to be lost.

Modiolus modiolus is a Boreal species that is distributed from the White Sea and Norway, off the Faroes and Iceland, south to the Bay of Biscay and occasionally North Africa. Also from Labrador to North Carolina in the Atlantic and from the Bering Sea south to Japan and California in the Pacific. Although this species is widespread, Modiolus modiolus beds are more limited in their distribution. In the UK, Modiolus modiolus is not known to form beds beyond the North Sea and the southern Irish Sea. The reproductive cycle of Modiolus modiolus varies considerably over its geographic range, with spawning appearing to commence over a reasonably small range of temperatures (7-10°C; Brown, 1984), which might explain the limited distribution of these beds. The depth range of Modiolus modiolus increases at higher latitudes with intertidal specimens more common on northern Norwegian shores where air temperatures are lower (Davenport & Kjørsvik, 1982).

Observations on Modiolus modiolus exposed to high temperatures suggest that this species is restricted by upper seawater temperatures of 23°C (Read & Cumming, 1967), although individuals may survive short-term exposure to higher temperatures. Read (1967) found that in intertidal pools most submerged Modiolus modiolus survived following exposure to temperatures that rose from 19 to 32.5°C over 5.5 hours. Modiolus barbatus, which has a more southerly distribution in the North East Atlantic and the Mediterranean, has been shown to experience metabolic depression and switch to anaerobic metabolism at temperatures exceeding 24°C, with some mortality (Anestis et al., 2008).

Psammechinus miliaris is distributed from the Shetland Islands to the Bay of Biscay, with some scattered observations further south (www.obis.org). This species generally occurs in water temperatures of 4 – 17°C. Kelly (2001) suggests that experiencing cold water over winter is important for the completion of gametogenesis in female Psammechinus miliaris, as significantly fewer females in the temperature-controlled treatment (with seawater maintained at 9°C) produced mature eggs.

Sensitivity Assessment. This biotope only occurs in Scotland, often in sealochs. UK populations of Saccharina latissima are found in the middle of their distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise.

Sea surface temperatures around Scotland range between 6-16°C (www.seatemperature.org). Under the middle and high emission scenarios sea temperatures are predicted to rise by between 3-4°C by the end of this century, leading to Scottish winter seawater temperatures of 9 - 10°C and summer highs of 19 - 20°C. Populations of Saccharina latissima may be able to adapt to cope with a gradual rise in ocean temperatures of this magnitude although Psammechinus miliaris and Modiolus modiolus may be negatively impacted. In particular, an increase in winter seawater temperatures is likely to reduce the window for reproduction in both species. Therefore, resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as the loss is likely to be a long-term decline, due to the long-term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ sensitivity to ocean warming in middle and high emission scenario benchmark levels.

Under the extreme scenario, whereby sea temperatures rise by 5°C to potential southern summer temperatures of 20°C and winter low temperatures of 11°C (www.seatemperature.org), all three characterizing species for this biotope are likely to suffer negative impacts. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. Therefore, this biotope is assessed as ‘High’ sensitivity to ocean warming under the extreme scenario.  

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 distribution of seaweeds is climatically defined (Breeman, 1990). Northern boundaries are set by winter temperatures that are lethal or summer temperatures too low for growth and/or reproduction, whilst southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic, is found as far south as New York State, USA. In the UK, sea surface temperatures are between 6-19°C (Huthnance, 2010), and Saccharina latissima is in the middle of its biogeographic range. At its southern distribution in New York, temperatures can regularly reach ≥ 20°C for six weeks or more during summer months (Gerard & Du Bois, 1988).

Temperature is a major environmental factor controlling the development of the microscopic stages of Saccharina latissima, with major changes in survival, growth, and gametogenesis occurring within a few degrees of upper thermal limits (Redmond, 2013). The temperature isotherm of 19-20°C was reported as limiting Saccharina latissima growth (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013), and the maximum temperature for gametophytes survival is 23°C. Bolton & Lüning (1982) report an experimental optimal temperature of 10-15°C for growth of the Saccharina latissima sporophyte, with growth reduced by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C.

In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima that were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations, which rarely experience ≥17°C, showed 100% mortality after three weeks of exposure to 20°C.

Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway. In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. However, there was annual variation. High mortality occurred from August-November each year. In 2008, only six of the original 17 transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration at which temperatures remain above 20°C. High sea temperatures have been linked to slow growth of Saccharina latissima which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011). 

Assis et al. (2018) predicted that under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from the coast of Portugal, France and from the southwest coast of the UK. The authors projected that under RCP 2.6, 13% of suitable Laminaria hyperborea habitat would be lost from the Western English Channel, whilst under the RCP 8.5 emission, 87% of suitable habitat was expected to be lost.

Modiolus modiolus is a Boreal species that is distributed from the White Sea and Norway, off the Faroes and Iceland, south to the Bay of Biscay and occasionally North Africa. Also from Labrador to North Carolina in the Atlantic and from the Bering Sea south to Japan and California in the Pacific. Although this species is widespread, Modiolus modiolus beds are more limited in their distribution. In the UK, Modiolus modiolus is not known to form beds beyond the North Sea and the southern Irish Sea. The reproductive cycle of Modiolus modiolus varies considerably over its geographic range, with spawning appearing to commence over a reasonably small range of temperatures (7-10°C; Brown, 1984), which might explain the limited distribution of these beds. The depth range of Modiolus modiolus increases at higher latitudes with intertidal specimens more common on northern Norwegian shores where air temperatures are lower (Davenport & Kjørsvik, 1982).

Observations on Modiolus modiolus exposed to high temperatures suggest that this species is restricted by upper seawater temperatures of 23°C (Read & Cumming, 1967), although individuals may survive short-term exposure to higher temperatures. Read (1967) found that in intertidal pools most submerged Modiolus modiolus survived following exposure to temperatures that rose from 19 to 32.5°C over 5.5 hours. Modiolus barbatus, which has a more southerly distribution in the North East Atlantic and the Mediterranean, has been shown to experience metabolic depression and switch to anaerobic metabolism at temperatures exceeding 24°C, with some mortality (Anestis et al., 2008).

Psammechinus miliaris is distributed from the Shetland Islands to the Bay of Biscay, with some scattered observations further south (www.obis.org). This species generally occurs in water temperatures of 4 – 17°C. Kelly (2001) suggests that experiencing cold water over winter is important for the completion of gametogenesis in female Psammechinus miliaris, as significantly fewer females in the temperature-controlled treatment (with seawater maintained at 9°C) produced mature eggs.

Sensitivity Assessment. This biotope only occurs in Scotland, often in sealochs. UK populations of Saccharina latissima are found in the middle of their distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise.

Sea surface temperatures around Scotland range between 6-16°C (www.seatemperature.org). Under the middle and high emission scenarios sea temperatures are predicted to rise by between 3-4°C by the end of this century, leading to Scottish winter seawater temperatures of 9 - 10°C and summer highs of 19 - 20°C. Populations of Saccharina latissima may be able to adapt to cope with a gradual rise in ocean temperatures of this magnitude although Psammechinus miliaris and Modiolus modiolus may be negatively impacted. In particular, an increase in winter seawater temperatures is likely to reduce the window for reproduction in both species. Therefore, resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as the loss is likely to be a long-term decline, due to the long-term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ sensitivity to ocean warming in middle and high emission scenario benchmark levels.

Under the extreme scenario, whereby sea temperatures rise by 5°C to potential southern summer temperatures of 20°C and winter low temperatures of 11°C (www.seatemperature.org), all three characterizing species for this biotope are likely to suffer negative impacts. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. Therefore, this biotope is assessed as ‘High’ sensitivity to ocean warming under the extreme scenario.  

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). Saccharina latissima has disappeared almost completely from the Danish estuary Limfjorden, where maximum surface temperatures in summer have increased by 0.7°C per decade over the last 40 years while the number of days with temperatures above 20°C has increased dramatically from 1-2 days year to >25 days year (Pedersen, 2015). Similarly, Saccharina latissima has been lost from the Skagerrak coast of Norway, which is thought to be due to an increase in summer temperatures, coupled with eutrophication (Moy & Christie, 2012).

Under experimental conditions, Nepper-Davidson et al. (2019) exposed a northern (Denmark) population of Saccharina latissima to a simulated three-week heatwave of three different intensities; 18, 21 and 24°C. When exposed to heatwaves of 18 and 21°C there was a decrease in photosynthesis and growth. When a 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, and the experiment was terminated (Nepper-Davidsen et al., 2019). These results suggest that this species is unlikely to survive heatwaves of the length and magnitude predicted by the end of this century for both the middle and high emission scenarios.

Modiolus modiolus is a Boreal species, which is thought to have an upper thermal limit of 23°C (Read & Cumming, 1967), although individuals are known to be able to survive short-term exposure to higher temperatures. For example, in intertidal pools, the majority of submerged Modiolus modiolus survived following exposure to temperatures that rose from 19 to 32.5°C over the course of 5.5 hours. Reproduction occurs in this species across a relatively small window (7-10°C; Brown, 1984), and if marine heatwaves occur in winter, this could lead to inhibition of reproduction that has already been limited by ocean warming.

Both Psammechinus miliaris and Modiolus modiolus occur in intertidal rockpools, where temperature can be > 10°C warmer than seawater during summer, with large diurnal and seasonal fluctuations (Daniel & Boyden, 1975), suggesting these species have some temperature 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 21°C in Scotland. These temperatures may limit Saccharina latissima growth, although is unlikely to cause mortality. If a heatwave occurred in winter, this could lead to winter temperatures rising to 11°C, which could potentially lead to suppression of sexual reproduction in Psammechinus miliaris and Modiolus modiolus during the heatwave, although this is not expected to have large population-level effects, and Modiolus modiolus is known to spawn throughout most of the year in Ireland (Read & Cumming, 1967). Under the middle emission scenario, resistance is assessed as ‘High’ and resilience is assessed as ‘High’, as no recovery is deemed necessary. Therefore, this biotope has been assessed as having ‘Medium’ sensitivity to the middle emission scenario.

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 23°C in the summer in Scotland or 13°C in the winter. Under this scenario, if a heatwave occurs in the summer, it is likely to cause widespread mortality of Saccharina latissima. Therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ Therefore, this biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the high emission scenario.

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). Saccharina latissima has disappeared almost completely from the Danish estuary Limfjorden, where maximum surface temperatures in summer have increased by 0.7°C per decade over the last 40 years while the number of days with temperatures above 20°C has increased dramatically from 1-2 days year to >25 days year (Pedersen, 2015). Similarly, Saccharina latissima has been lost from the Skagerrak coast of Norway, which is thought to be due to an increase in summer temperatures, coupled with eutrophication (Moy & Christie, 2012).

Under experimental conditions, Nepper-Davidson et al. (2019) exposed a northern (Denmark) population of Saccharina latissima to a simulated three-week heatwave of three different intensities; 18, 21 and 24°C. When exposed to heatwaves of 18 and 21°C there was a decrease in photosynthesis and growth. When a 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, and the experiment was terminated (Nepper-Davidsen et al., 2019). These results suggest that this species is unlikely to survive heatwaves of the length and magnitude predicted by the end of this century for both the middle and high emission scenarios.

Modiolus modiolus is a Boreal species, which is thought to have an upper thermal limit of 23°C (Read & Cumming, 1967), although individuals are known to be able to survive short-term exposure to higher temperatures. For example, in intertidal pools, the majority of submerged Modiolus modiolus survived following exposure to temperatures that rose from 19 to 32.5°C over the course of 5.5 hours. Reproduction occurs in this species across a relatively small window (7-10°C; Brown, 1984), and if marine heatwaves occur in winter, this could lead to inhibition of reproduction that has already been limited by ocean warming.

Both Psammechinus miliaris and Modiolus modiolus occur in intertidal rockpools, where temperature can be > 10°C warmer than seawater during summer, with large diurnal and seasonal fluctuations (Daniel & Boyden, 1975), suggesting these species have some temperature 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 21°C in Scotland. These temperatures may limit Saccharina latissima growth, although is unlikely to cause mortality. If a heatwave occurred in winter, this could lead to winter temperatures rising to 11°C, which could potentially lead to suppression of sexual reproduction in Psammechinus miliaris and Modiolus modiolus during the heatwave, although this is not expected to have large population-level effects, and Modiolus modiolus is known to spawn throughout most of the year in Ireland (Read & Cumming, 1967). Under the middle emission scenario, resistance is assessed as ‘High’ and resilience is assessed as ‘High’, as no recovery is deemed necessary. Therefore, this biotope has been assessed as having ‘Medium’ sensitivity to the middle emission scenario.

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 23°C in the summer in Scotland or 13°C in the winter. Under this scenario, if a heatwave occurs in the summer, it is likely to cause widespread mortality of Saccharina latissima. Therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ Therefore, this biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the high emission scenario.

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), with it expected to drop by a further 0.35 units by the end of this century, dependent on emission scenario.  Marine autotrophs will generally benefit from ocean acidification, through an increase in the availability of aqueous CO₂ for photosynthesis (Koch et al., 2013). Most species of kelp appear to be undersaturated in respect to carbon dioxide, although they can generally utilise HCO₃ and have external carbonic anhydrase for extracellular dehydration of HCO₃ to CO₂ (Koch et al., 2013).

Under experimental CO₂ enrichment led at levels expected by the end of this century germination rates in Saccharina latissima were the same as control samples but gametophyte size increased, suggesting a benefit to juvenile stages of this species (Roleda et al., 2012). Nunes et al. (2015) found that experimental exposure of adult Saccharina latissima to enhanced CO₂ led to an increase in net primary production, whilst Gordillo et al. (2015) found that enhanced CO₂ led to increased photosynthesis and growth. In contrast, Iñiguez et al. (2016) found no increase in carbon fixation under elevated CO₂ conditions. Whilst contrasting in findings, these studies show that ocean acidification is unlikely to negatively impact Saccharina latissima.

Dupont et al. (2010) analysed the literature and found that echinoderms are generally robust to ocean acidification, although different life stages and species are affected differently. Miles et al. (2007) suggested that Psammechinus miliaris would be sensitive to a pH drop of 0.5 units, as specimens were unable to regulate internal pH when exposed to a short-term (8 days) experimental decrease in pH, plus there was evidence of dissolution of the skeleton. These impacts were much more pronounced at lower pH (< 7). Suckling et al. (2014) found that when Psammechinus miliaris larvae were raised from parents pre-exposed to low pH conditions (pH 7.7 compared to control pH of 7.98), settlements rates were similar to control larvae, and test diameter was larger, which suggested that this species can acclimate and possibly adapt to low pH conditions.

There is no empirical evidence on the impact of ocean acidification on the horse mussel Modiolus modiolus. Bivalves generally appear quite tolerant to decreases in pH, and are abundant at acidified CO₂ vents (Garrard et al., 2014, Kroeker et al., 2011), although it may be the larval stages which are most susceptible to ocean acidification (Kurihara, 2008). Under experimental conditions, it was found that normal shell development and growth of the D-veliger larvae of Mytilus galloprovincialis and Crassostrea gigas were related to aragonite saturation state rather than pH, with larvae growing well at a pH of 7.6 when aragonite saturation state was high, but decreasing as aragonite saturation fell below 2, regardless of pH (Waldbusser et al., 2015). Both Psammechinus miliaris and Modiolus modiolus occur in intertidal rockpools, where pH can vary by 3 units throughout the year, with large diurnal and seasonal variation (Morris & Taylor, 1983), which suggests some tolerance to changes in pH.

Sensitivity assessment. Under the middle emission scenario, a pH decrease of 1.5 units is expected to occur by the end of this century. Neither Saccharina latissima, Psammechinus miliaris nor Modiolus modiolus are expected to suffer significant negative impacts. Therefore, resistance to ocean acidification under the middle emission scenario has been assessed as ‘High’, whilst resilience is assessed as ‘High’, and this biotope is assessed as ‘Not sensitive’ to ocean acidification at this benchmark level. Under the high emission scenario, 20% of coastal areas are predicted to suffer from seasonal aragonite undersaturation (Ostle et al., 2016). Aragonite undersaturation will primarily occur in Scotland, where this biotope primarily occurs. It is expected that under this scenario, some negative impacts may be experienced by Psammechinus miliaris or Modiolus modiolus, therefore some loss is likely to occur. Therefore, resistance has been assessed as ‘Medium’, whilst resilience is assessed as ‘Very Low’ due to the long term nature of ocean acidification. Under the high emission scenario, sensitivity to ocean acidification is assessed as ‘Medium’.

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), with it expected to drop by a further 0.35 units by the end of this century, dependent on emission scenario.  Marine autotrophs will generally benefit from ocean acidification, through an increase in the availability of aqueous CO₂ for photosynthesis (Koch et al., 2013). Most species of kelp appear to be undersaturated in respect to carbon dioxide, although they can generally utilise HCO₃ and have external carbonic anhydrase for extracellular dehydration of HCO₃ to CO₂ (Koch et al., 2013).

Under experimental CO₂ enrichment led at levels expected by the end of this century germination rates in Saccharina latissima were the same as control samples but gametophyte size increased, suggesting a benefit to juvenile stages of this species (Roleda et al., 2012). Nunes et al. (2015) found that experimental exposure of adult Saccharina latissima to enhanced CO₂ led to an increase in net primary production, whilst Gordillo et al. (2015) found that enhanced CO₂ led to increased photosynthesis and growth. In contrast, Iñiguez et al. (2016) found no increase in carbon fixation under elevated CO₂ conditions. Whilst contrasting in findings, these studies show that ocean acidification is unlikely to negatively impact Saccharina latissima.

Dupont et al. (2010) analysed the literature and found that echinoderms are generally robust to ocean acidification, although different life stages and species are affected differently. Miles et al. (2007) suggested that Psammechinus miliaris would be sensitive to a pH drop of 0.5 units, as specimens were unable to regulate internal pH when exposed to a short-term (8 days) experimental decrease in pH, plus there was evidence of dissolution of the skeleton. These impacts were much more pronounced at lower pH (< 7). Suckling et al. (2014) found that when Psammechinus miliaris larvae were raised from parents pre-exposed to low pH conditions (pH 7.7 compared to control pH of 7.98), settlements rates were similar to control larvae, and test diameter was larger, which suggested that this species can acclimate and possibly adapt to low pH conditions.

There is no empirical evidence on the impact of ocean acidification on the horse mussel Modiolus modiolus. Bivalves generally appear quite tolerant to decreases in pH, and are abundant at acidified CO₂ vents (Garrard et al., 2014, Kroeker et al., 2011), although it may be the larval stages which are most susceptible to ocean acidification (Kurihara, 2008). Under experimental conditions, it was found that normal shell development and growth of the D-veliger larvae of Mytilus galloprovincialis and Crassostrea gigas were related to aragonite saturation state rather than pH, with larvae growing well at a pH of 7.6 when aragonite saturation state was high, but decreasing as aragonite saturation fell below 2, regardless of pH (Waldbusser et al., 2015). Both Psammechinus miliaris and Modiolus modiolus occur in intertidal rockpools, where pH can vary by 3 units throughout the year, with large diurnal and seasonal variation (Morris & Taylor, 1983), which suggests some tolerance to changes in pH.

Sensitivity assessment. Under the middle emission scenario, a pH decrease of 1.5 units is expected to occur by the end of this century. Neither Saccharina latissima, Psammechinus miliaris nor Modiolus modiolus are expected to suffer significant negative impacts. Therefore, resistance to ocean acidification under the middle emission scenario has been assessed as ‘High’, whilst resilience is assessed as ‘High’, and this biotope is assessed as ‘Not sensitive’ to ocean acidification at this benchmark level. Under the high emission scenario, 20% of coastal areas are predicted to suffer from seasonal aragonite undersaturation (Ostle et al., 2016). Aragonite undersaturation will primarily occur in Scotland, where this biotope primarily occurs. It is expected that under this scenario, some negative impacts may be experienced by Psammechinus miliaris or Modiolus modiolus, therefore some loss is likely to occur. Therefore, resistance has been assessed as ‘Medium’, whilst resilience is assessed as ‘Very Low’ due to the long term nature of ocean acidification. Under the high emission scenario, sensitivity to ocean acidification is assessed as ‘Medium’.

Sea level rise (extreme)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). This biotope occurs on stony mixed sediment, at 0 – 10 m depth, in full or variable salinity, in sheltered or moderately exposed conditions, with weak or very weak tidal currents (JNCC, 2015), and is common in sea lochs in Scotland.

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

Sensitivity assessment. It is difficult to assess the effect of sea-level rise scenarios on exposure or tidal energy, as evidence predicts that any changes will be site-specific. This biotope occurs from the sublittoral fringe down to 10 m, although all three characteristic species (Saccharina latissima, Psammechinus miliaris and Modiolus modiolus) are known to have a more extensive depth range, and as long as tidal currents or exposure did not become unfavourable as a result of sea-level rise, it is likely that a sea-level rise of 50 cm or 70 cm (middle to high emission scenarios) would have limited effect but that a 107 cm rise (the extreme scenario) might result in loss of part of the deeper extent of the biotope in some sites. This may be counteracted by landward migration of the biotope if suitable habitat is available. Therefore, resistance is assessed as ‘High’ under the middle and high emission scenarios so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’.  But resistance is possibly ‘Medium’ under the extreme scenario so that resilience is ‘Very low’ and sensitivity assessed as ‘Medium’, albeit with ‘Low’ confidence.

Sea level rise (high)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). This biotope occurs on stony mixed sediment, at 0 – 10 m depth, in full or variable salinity, in sheltered or moderately exposed conditions, with weak or very weak tidal currents (JNCC, 2015), and is common in sea lochs in Scotland.

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

Sensitivity assessment. It is difficult to assess the effect of sea-level rise scenarios on exposure or tidal energy, as evidence predicts that any changes will be site-specific. This biotope occurs from the sublittoral fringe down to 10 m, although all three characteristic species (Saccharina latissima, Psammechinus miliaris and Modiolus modiolus) are known to have a more extensive depth range, and as long as tidal currents or exposure did not become unfavourable as a result of sea-level rise, it is likely that a sea-level rise of 50 cm or 70 cm (middle to high emission scenarios) would have limited effect but that a 107 cm rise (the extreme scenario) might result in loss of part of the deeper extent of the biotope in some sites. This may be counteracted by landward migration of the biotope if suitable habitat is available. Therefore, resistance is assessed as ‘High’ under the middle and high emission scenarios so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’.  But resistance is possibly ‘Medium’ under the extreme scenario so that resilience is ‘Very low’ and sensitivity assessed as ‘Medium’, albeit with ‘Low’ confidence.

Sea level rise (middle)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). This biotope occurs on stony mixed sediment, at 0 – 10 m depth, in full or variable salinity, in sheltered or moderately exposed conditions, with weak or very weak tidal currents (JNCC, 2015), and is common in sea lochs in Scotland.

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

Sensitivity assessment. It is difficult to assess the effect of sea-level rise scenarios on exposure or tidal energy, as evidence predicts that any changes will be site-specific. This biotope occurs from the sublittoral fringe down to 10 m, although all three characteristic species (Saccharina latissima, Psammechinus miliaris and Modiolus modiolus) are known to have a more extensive depth range, and as long as tidal currents or exposure did not become unfavourable as a result of sea-level rise, it is likely that a sea-level rise of 50 cm or 70 cm (middle to high emission scenarios) would have limited effect but that a 107 cm rise (the extreme scenario) might result in loss of part of the deeper extent of the biotope in some sites. This may be counteracted by landward migration of the biotope if suitable habitat is available. Therefore, resistance is assessed as ‘High’ under the middle and high emission scenarios so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’.  But resistance is possibly ‘Medium’ under the extreme scenario so that resilience is ‘Very low’ and sensitivity assessed as ‘Medium’, albeit with ‘Low’ confidence.

Temperature increase (local)

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

Evidence

The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima geographic distribution (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990) however, the optimal temperature range for sporophyte growth is 10-15°C (Bolton & Lüning, 1982). Bolton & Lüning (1982) observed that sporophyte growth was inhibited by 50-70% at 20°C and following 7 days at 23°C all specimens completely disintegrated. In the field Saccharina latissima has shown significant regional variation in its acclimation to temperature changes, for example Gerard & Dubois (1988) observed sporophytes of Saccharina latissima which were regularly exposed to ≥20°C could tolerate these temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. Therefore the response of Saccharina latissima to a change in temperatures is likely to be locally variable.

Andersen et al. (2011) transplanted Saccharina latissima in the Skagerrak region, Norway and from 2006-2009. There was annual variation however high mortality occurred from August-November within each year of the experiment. In 2008 of the original 17 sporophytes 6 survived from March-September (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration which temperatures remain above 20°C. High sea temperature has been linked to slow growth of Saccharina latissima which is likely to decrease the photosynthetic ability of, and increase the vulnerability of Saccharina latissima to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011). These factors combined with establishment of annual filamentous algae in Skagerrak, Norway are likely to prevent the establishment of self sustaining populations in the area (Anderson et al., 2011; Moy & Christie, 2012).

Mortensen (1927) reported Psammechinus miliaris was found in Limfjorden, Denmark where winter temperatures are regularly just above 0°C (Ursin, 1960). At Psammechinus miliaris southern range edge, Morocco and the Azores (Mortensen, 1927), winter-summer seawater temperatures range from17-21 °C (Sea temperature, 2015). Furthermore Psammechinus miliaris reproduces in waters around the Faeroes where the summer temperatures seldom exceed 11°C (Ursin, 1960). The optimal temperature tolerance is therefore likely to be between 0-21°C.

Modiolus modiolus is a boreal species that reaches its southern limit in UK waters and forms beds of large individuals only in the north of Britain and Ireland (Hiscock et al., 2004). The depth range of Modiolus modiolus increases at higher latitudes with intertidal specimens more common on northern Norwegian shores where air temperatures are lower (Davenport & Kjørsvik, 1982). Little direct information on temperature tolerance in Modiolus modiolus was found, however, its upper lethal temperature is lower than that for Mytilus edulis (Bayne, 1976) by about 4°C (Henderson, 1929, cited in Davenport & Kjørsvik, 1982). Subtidal populations are protected from major, short-term changes in temperature by their depth. However, Holt et al. (1998) suggested that because Modiolus modiolus reaches its southern limit in British waters it may be susceptible to long-term increases in summer water temperatures. Hiscock et al. (2004) suggest that warmer seas may prevent recovery of damaged beds and recruitment to undamaged beds so that decline in occurrence of beds can be expected at least in the south of their range. Declines of horse mussel beds in Strangford Lough (Magorrian, 1995) may be linked to increased water temperatures but other factors such as trawling have also contributed to changes.

SS.SMp.KSwSS.SlatMxVS is distributed from the west coast of Scotland to Shetland (Connor et al., 2004). At this latitude sea surface temperature ranges from 14.5-16.9°C in summer and 4-10°C in winter (Beszczynska-Möller & Dye, 2013).

Sensitivity assessment. A 5°C increase for one month combined with high UK summer temperatures may cause mortality in Saccharina latissima populations that are not acclimated to >20°C. Modiolus modiolus is a boreal species, and the fact that dense aggregations seem to reach their southerly limit around British shores suggests this species would be sensitive to acute and chronic increases in temperature. Resistance has been assessed as Low and resilience as Medium. Sensitivity has been assessed as Medium.

Temperature decrease (local)

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

Evidence

Saccharina lattissima has a lower temperature threshold for sporophyte growth at 0°C (Lüning, 1990). Mortensen (1927) reported Psammechinus miliaris was found in Limfjorden, Denmark where winter temperatures are regularly just above 0°C. Modiolus modiolus is a boreal species that reaches its southern limit in UK waters and forms beds of large individuals only in the north of Britain and Ireland (Hiscock et al., 2004). Davenport & Kjørsvik (1982) suggested that its inability to tolerate temperature change was a factor preventing Modiolus modiolus from colonizing the intertidal in the UK. Intertidal specimens were more common on northern Norwegian shores (Davenport & Kjørsvik, 1982). Subtidal populations are protected from major, short-term changes in temperature by their depth. Subtidal red algae can survive at temperatures between -2°C and 18-23°C (Lüning, 1990; Kain & Norton, 1990).

Sensitivity assessment. None of the characterizing species are likely to be adversely affected by a temperature decrease at the benchmark level. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not sensitive’.

Salinity increase (local)

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

Evidence

Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu. Saccharina latissima showed high photosynthetic ability at >80% of the control levels between 25-55 psu. The affect of long-term salinity changes (>5 days) or salinity >60 PSU on Saccharina latissima’ photosynthetic ability was not tested.

Gezelius (1963) reported mature individuals of the littoral growth form of Psammechinus miliaris had an optimal salinity range of 20-32ppt but could tolerate 40ppt, and the sub-littoral growth form had an optimal salinity tolerance of 26-38 ppt but could tolerate as high as 40 ppt.

Modiolus modiolus are osmoconfers, in short-term fluctuating salinities valve closure limits exposure to salinity changes in the surrounding waters, although slow diffusion through the byssal aperture means that the osmolarity of fluids will eventually increase (Shumway, 1977; Davenport & Kjørsvik,1982). Experimental evidence for short-term tolerances of Modiolus modious to increased salinities is provided by Pierce (1970). Modiolus modious was exposed to a range of salinities between 1.5 and 54 psu and survived for 21 days (the duration of the experiment) at salinities between 27 and 41‰ However above 41‰ was considered lethal, and 50% of the individuals within the hypersaline? experiments died(Pierce, 1970)..

Sensitivity assessment. SS.SMp.KSwSS.SlatMxVS is found in both full and variable salinity, this assessment assumes an increase to greater than full salinity (>40‰). The evidence suggests Saccharina latissima can tolerate exposure to hypersaline conditions of 55‰ for short periods however the effects of long-term salinity increases are unknown. >40‰ would be outside Psammechinus miliaris optimal salinity range and may cause minor declines in growth. Modiolus modiolus abundance may also decline. Resistance has been assessed as ‘Low’, resilience as ‘Medium’. The sensitivity of this biotope to an increase in salinity has been 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

Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu. Saccharina latissima showed high photosynthetic ability at >80% of the control levels between 25-55 psu. Hyposaline treatment of 10-20 psu led to a gradual decline of photosynthetic ability. After 2 days at 5 psu Saccharina latissima showed a significant decline in photosynthetic ability at approx. 30% of control. After 5 days at 5 psu Saccharina latissima specimens became bleached and showed signs of severe damage. The affect of long-term salinity changes (>5 days) or salinity >60 PSU on Saccharina latissima’ photosynthetic ability was not tested. The experiment was conducted on Saccharina latissima from the Arctic, and at extremely low water temperatures (1-5°C) macroalgae acclimation to rapid salinity changes could be slower than at temperate latitudes. It is therefore possible that resident Saccharina latissima of the UK maybe be able to acclimate to salinity changes more effectively.

Lindahl & Runnström (1929) showed that Psammechinus miliaris from the littoral (Z form) and sublittoral (S form) had different salinity optima. Gezelius (1963) reported the littoral growth form had an optimal salinity range of 20-32 ppt, whereas the sub-littoral growth form 26-38 ppt. Mature examples of the littoral growth form tolerated 15 ppt for a period of 27 days however were not able to produce gametes at this salinity.

Davenport & Kjørsvik (1982) reported the presence of large horse mussels in rock pools at 16 psu in Norway, subject to freshwater inflow, and noted that they were probably exposed to lower salinities. By keeping the shell valves closed the fluid in the mantle cavity of two individuals was found to be at a salinity of 28–29 despite some hours of exposure (Davenport & Kjørsvik, 1982). Short-term tolerances to a salinity of 15 were similarly identified for Modiolus modiolus from the White Sea, north west Russia (where salinity is typically 25), whereas salinity levels of between 30 and 35 appeared optimal. However, after a winter and spring of extremely high rainfall, populations of Modiolus modiolus at the entrance to Loch Leven (near Fort William) were found dead, almost certainly due to low salinity outflow (K. Hiscock, pers. comm). Holt et al. (1998) reported that dense populations of very young Modiolus modiolus do occasionally seem to occur sub tidally in estuaries, but the species is more poorly adapted to fluctuating salinity than many other mussel species (Bayne, 1976) and dense populations of adults are not found in low salinity areas.

Laboratory experiments exposing Modiolus modiolus to reduced salinity water have demonstrated short-term effects. Pierce (1970) exposed Modiolus spp. to a range of salinities between 1.5 and 54 psu and reported that Modiolus modiolus survived for 21 days (the duration of the experiment) between 27 and 41 psu. Shumway (1977) exposed individual Modiolus modiolus to simulated tidal, (sinusoidal) fluctuations between full seawater (salinity 32‰) and 50% freshwater and to more abrupt changes in salinity in laboratory experiments. Individual Modiolus modiolus that were able to close their valves survived 10 days exposure to salinity changes compared with individuals which had their shells wedged open that survived for 3 days of the experiment only. Exposure to reduced salinities has been observed to lead to reduced ctenidial ciliary stroke, (after 3 days at a salinity of 15 and 10°C, Schlieper et al., 1958) and increased intracellular liquid/water (Gainey, 1994).

Sensitivity assessment. SS.SMp.KSwSS.SlatMxVS is found in both full and variable salinity, this assessment assumes a decrease to reduced salinity (18-30‰). Such a decrease in salinity may cause a decline in Saccharina latissima sporophyte growth and negatively affect Psammechinus miliaris reproduction. The available evidence indicates that Modiolus modiolus is an osmoconformer able to tolerate decreases in salinity for a short period. However, a decrease in salinity at the pressure benchmark from full salinity or variable to reduced (18-30 ppt) would be considered to result in the mortality of the characterizing species within the biotope over the course of a year. Resistance has been assessed ’Low‘. Resilience has been assessed as ’Medium‘. Sensitivity has been assessed as ’Medium’.

Water flow (tidal current) changes (local)

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

Evidence

SS.SMp.KSwSS.SlatMxVS is found from strong (1.5-3 m/sec) -very weak (negligible) tidal streams (Connor et al., 2004). Indicating the characterizing species are tolerant of tidal streams within this range.

Peteiro & Freire (2013) measured Saccharina latissima growth from 2 sites, the first had maximal water velocities of 0.3m/sec and the second 0.1m/sec. At site 1 Saccharina latissima had significantly larger biomass than at site 2 (16 kg/m to 12 kg/m respectively). Peteiro & Freire (2013) suggested that faster water velocities were beneficial to Saccharina latissima growth. However, Gerard & Mann (1979) found Saccharina latissima productivity is reduced in moderately strong tidal streams (≤1 m/sec) when compared to weak tidal streams (<0.5 m/sec). Despite the results published in Gerard & Mann (1979) Saccharina latissima can characterize or be a dominant in the tide swept biotopes IR.MIR.KT.XKTX & IR.MIR.KT.SlatT, which have been recorded from very strong (>3 m/sec) to moderately strong tidal streams (≤1 m/sec) (Connor et al., 2004), indicating Saccharina latissima can tolerate greater tidal streams than <1 m/sec.

Holt et al. (1998) suggested water movement was important in the development of dense reefs and beds of Modiolus modiolus. It is likely therefore that there is an optimum range of water flows, currently unknown, which are strong enough to disperse larvae and provide food but are not so strong that the current removes the bed, prevents settlement of larvae within beds (which is key for self-recruiting populations) or prevents the extension of feeding siphons. Conversely, decreased flow rates may inhibit larval settlement and the supply of suspended food and allow greater siltation on beds.

Adult Modiolus modiolus occur commonly in areas with moderate to high water exchange in Nova Scotia (Wildish & Peer, 1983; Wildish & Kristmanson, 1985, 1994; Wildish & Fader, 1998; Wildish et al., 1998), and low field densities have been correlated with low current regimes and reduced food availability. Densities of up to 220 individuals/m2 have been recorded from the Faroese shelf (Dinesen, 1999) where maximal tidal current speed has been estimated to be between 79 and 98 cm/s at two Modiolus modiolus sites (Nørrevang et al., 1994: BIOFAR Stn. 661 & 662, cited from Dinesen & Morton, 2014). Mair et al. (2000) also observed that in Scottish sites with Modiolus modiolus beds, densities were greater where there were high tidal currents.

Sensitivity assessment. Large scale changes tidal velocities (>1m/sec) may influence biotope structure. However, the available evidence suggests that a change in flow velocities of between 0.1-0.2m/sec would not have a significant effect. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’ at the benchmark level.

Emergence regime changes

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

Evidence

SS.SMp.KSwSS.SlatMxVS is recorded from the low shore to 20 m BCD An increase in emergence will result in an increased risk of desiccation and mortality of Saccharina latissima and Modiolus modiolus. Removal of canopy forming kelps, through desiccation, has also been shown to increase desiccation and mortality of understorey macro-algae (Hawkins & Harkin, 1985). Providing that suitable substrata are present, the biotope is likely to re-establish further down the shore within a similar emergence regime to that which existed previously.

Sensitivity assessment. Resilience has been assessed as ‘Low’. Resistance as ‘Medium’. The sensitivity of this biotope to a change in emergence is considered as ‘Medium’.

Wave exposure changes (local)

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

Evidence

At the time of writing there is limited direct evidence for the effect of increases in wave exposure on Saccharina latissima or Psammechinus miliaris other than they are predominantly recorded in wave sheltered locations (Birkett et al., 1998; Kelly, 2000). Similarly there was no direct evidence for the effect of increased wave exposure on Modiolus modiolus. However, Modiolus modiolus is recorded from moderately exposed-very sheltered locations (MNCR data see below). Due to their size (adults: 10-22 cm (Tyler-Walters, 2007) may become dislodged if wave action increases above this range within shallow examples of SS.SMp.KSwSS.SlatMxVS. Furthermore an increase in wave action may also remove smaller sediment fractions and therefore affect the biological community.

SS.SMp.KSwSS.SlatMxVS is recorded from sheltered-ultra wave sheltered sites (Connor et al., 2004). Therefore, a large increase in wave exposure to e.g. moderate wave exposure is likely to have a fundamental effect on local sediment and characterizing species. However a change in nearshore significant wave height >3% but <5%is not likely to have a significant effect.

Sensitivity assessment. Wave exposure is one of the principal defining features biotope structures, and large changes in wave exposure are likely to alter the relative abundance of the dominant macro-algae, grazing and understorey community, alter the sedimentary substratum and hence, the biotope. However a change in near shore significant wave height of 3-5% is unlikely to have any significant effect on SS.SMp.KSwSS.SlatMxVS. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not Sensitive’ at the benchmark level.

Please note the latest version of the JNCC National Biodiversity Database was used as the source of the MNCR data. However, it should be noted that a) not all biotopes were recorded with full habitat/site information, and b) the extraction only recorded the habitat conditions where the biotope was recorded and not the relevant species presence, abundance or biomass within each site. Therefore, this information represents the range of habitat conditions in which the biotopes can be found rather than identifying optimum habitats for species. This caveat applies to all assessments made using this data.

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.

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al,. (1999) reported that Hg was very toxic to macrophytes. The effects of copper, zinc and mercury on Saccharina latissima have been investigated by Thompson & Burrows (1984). They observed that the growth of sporophytes was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l.

At the time of writing, little is known about the effects of heavy metals on echinoderms. Bryan (1984) reported that early work had shown that echinoderm larvae were intolerant of heavy metals, e.g. the intolerance of larvae of Paracentrotus lividus to copper (Cu) had been used to develop a water quality assessment. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu). Sea-urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Taken together with the findings of Gomez & Miguez-Rodriguez (1999) above it is likely that echinoderms are intolerant of heavy metal contamination.

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.

Saccharina latissima fronds, being predominantly subtidal, would not come into contact with freshly released oil but only to sinking emulsified oil and oil adsorbed onto particles (Birkett et al., 1998). The mucilaginous slime layer coating of laminarians may protect them from smothering by oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. However, Holt et al. (1995) reported that oil spills in the USA and from the 'Torrey Canyon' had little effect on kelp forests. Similarly, surveys of subtidal communities at a number sites between 1-22.5m below chart datum showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997). An assessment of holdfast fauna in Laminaria showed that although species richness and diversity decreased with increasing proximity to the Sea Empress oil spill, overall the holdfasts contained a reasonably rich and diverse fauna, even though oil was present in most samples (Sommerfield & Warwick, 1999).

Echinoderms seem especially sensitive to the toxic effects of oil, likely because of the large amount of exposed epidermis (Suchanek, 1993). Schäfer & Köhler (2009) found 20 day exposure to sub-lethal concentrations of phenanthrene resulted in severe ovarian lesions of Psammechinus miliaris limiting the production of gametes.

Following the Torrey Canyon incident, large numbers of dead Psammechinus miliaris were found in the vicinity of Sennen, UK possibly due to exposure to the oil spill and the heavy spraying of hydrocarbon based dispersants in that area (Smith, 1968). Other significant effects have been observed in other species of urchins. For example, mass mortality of the echinoderm Echinocardium cordatum was observed shortly after the Amoco Cadiz oil spill (Cabioch et al., 1978) and reduced abundance of the species was detectable up to >1000m away one year after the discharge of oil-contaminated drill cuttings in the North Sea (Daan & Mulder, 1996). In the Mediterranean around Naples, urchins were absent from areas which has visible signs of massive pollution of both sewage and oil. Echinus esculentus populations in the vicinity of an oil terminal in A Coruna Bay, Spain, showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gomez & Miguez-Rodriguez 1999). But the observed effects may have been due to a single contaminant or synergistic effects of all present.

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.

Johansson (2009) exposed samples of Saccharina latissima to several antifouing compounds, observing chlorothalonil, DCOIT, dichlofluanid and tolylfluanid inhibited photosynthesis. Exposure to Chlorothalonil and tolylfluanid, was also found to continue inhibiting oxygen evolution after exposure had finished, and may cause irreversible damage.

Smith (1968) noted that epiphytic and benthic red algae were intolerant of dispersant or oil contamination due to the Torrey Canyon oil spill; only the epiphytes Crytopleura ramosa and Spermothamnion repens and some tufts of Jania rubens survived together with Osmundea pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe.

Considerable observations and work, mainly on Echinus esculentus but also on Psammechinus miliaris (Smith, 1968; Gomez & Miguez-Rodriguez, 1999; Dinnel et al., 1988) indicate high intolerance to synthetic contaminants. Newton & McKenzie (1995) state that echinoderms tend to be very intolerant of various types of marine pollution, but there is little more detailed information than this. Following the Torrey Canyon incident, large numbers of dead Psammechinus miliaris in the vicinity of Sennen, UK presumably due to the heavy spraying of dispersants in that area and exposure to the oil spill (Smith, 1968).

Radionuclide contamination

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

Evidence

No evidence

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

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

Evidence

Reduced oxygen concentrations can inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012). A rapid recovery from a state of low oxygen is expected if the environmental conditions are transient. If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2mg/l (Cole et al., 1999).

Theede et al. (1969) examined the relative tolerance of gill tissue from several species of bivalve to exposure to 0.21 mg/l O₂ with or without 6.67 mg of sulphide (at 10 °C and 30 psu). Modiolus modiolus tissue was found to be the most resistant of the species studied, retaining some ciliary activity after 120 hrs compared with 48 hrs for Mytilus edulis.

Under hypoxic conditions echinoderms become less mobile and stop feeding. Death of a bloom of the phytoplankton Gyrodinium aureolum in Mounts Bay, Penzance in 1978 produced a layer of brown slime on the sea bottom. This resulted in the death of fish and invertebrates, including Echinus esculentus, presumably due to anoxia caused by the decay of the dead dinoflagellates (Griffiths et al., 1979). Spicer (1995) investigated the effects of environmental hypoxia on the oxygen and acid-base status of Psammechinus miliaris. Oxygen uptake is not regulated by this species during progressive hypoxia. The habitat of this species includes rock pools on the shore that can experience quite severe hypoxia or even anoxia. Psammechinus miliaris must be able to tolerate low oxygen conditions provided the event is brief. In prolonged events, subtidal Psammechinus miliaris would presumably react in a similar fashion to the Echinus esculentus above.

Sensitivity Assessment. Reduced oxygen levels are likely to inhibit macroalgal photosynthesis and respiration but not cause a loss of the macroalgae population directly. Resistance has been assessed as ‘Medium’, Resilience as ‘High’. Sensitivity has been assessed as ‘Low’ at the benchmark level.

Nutrient enrichment

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

Evidence

Johnston & Roberts (2009) conducted a meta analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relative tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein).

Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, UK when compared to other sites along the east coast of Scotland. At St Andrews nitrate levels were 20.22µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Norwegian Salmon farms, where elevated ammonium can be readily absorbed. Read et al. (1983) reported after the installation of a new sewage treatment works which reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent.

Navarro & Thompson (1996) suggested that Modiolus modiolus was adapted to an intermittent and often inadequate food supply. The persistence of a Modiolus modiolus population in the vicinity of a sewage sludge dumping site, North Norfolk (Richardson et al., 2001) suggests that the species is tolerant of high nutrient levels. Moderate nutrient enrichment may, therefore, be beneficial by increasing phytoplankton productivity and organic particulates, and hence food availability.

Sensitivity assessment. The evidence suggests that enrichment would not directly affect Saccharina latissima and may benefit Modiolus modiolus. Nutrient enrichment may increase turbidity which may decrease water clarity (see above) and therefore macroalgae photosynthesis. But This biotope has been assessed as 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

Organic enrichment

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

Evidence

Johnston & Roberts (2009) conducted a meta analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relative tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein).

The persistence of a Modiolus modiolus population in the vicinity of a sewage sludge dumping site, North Norfolk (Richardson et al., 2001) suggests that the species is tolerant of high levels of organic matter. At the pressure benchmark which refers to enrichment rather than gross organic pollution (Tillin & Tyler-Walters, 2014) the extra rate of organic matter accumulation may not far exceed the natural background level, particularly in sheltered areas.

Sensitivity assessment. The evidence suggests that enrichment would not directly affect the characterizing species but that the community may suffer an overall reduction in species richness (Johnston & Roberts, 2009). In addition, organic enrichment may increase turbidity which may decrease water clarity and therefore macro-algae photosynthesis (see water clarity above). Resistance has therefore been assessed as ‘Medium’, resilience as ‘High’, and sensitivity has been assessed as ’Low’.

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 sediment were replaced with rock or artificial substrata, this would represent a fundamental change to the biotope (Macleod et al., 2014). All the characterizing species within this biotope can grow in rock biotopes (Birkett et al., 1998; Connor et al., 2004), however SS.SMp.KSwSS is by definition a sediment biotope and introduction of rock would change it to a rock based biotope.

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

Physical change (to another sediment type)

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

Evidence

The benchmark for this pressure refers to a change in one Folk class. The pressure benchmark originally developed by Tillin et al., (2010) used the modified Folk triangle developed by Long (2006) which simplified sediment types into four categories: mud and sandy mud, sand and muddy sand, mixed sediments and coarse sediments. The change referred to is therefore a change in sediment classification rather than a change in the finer-scale original Folk categories (Folk, 1954). The change in one Folk class is considered to relate to a change in classification to adjacent categories in the modified Folk triangle. For mixed sediments and sand and muddy sand habitats a change in one Folk class may refer to a change to any of the sediment categories. Dredging and dumping of sediment, and infrastructure developments, can lead to changes in sediment character.

SS.SMp.KSwSS.SlatMxVS occurs on mixed substrata, therefore within this pressure a change in one folk class relates to a change to either “Coarse sediment”, “Mud and sandy Mud” and “Sand and sandy mud”. Macro-algae are likely to successfully recruit onto the larger sediment/small rock fractions within these biotopes (e.g. gravel, pebbles, cobbles).Therefore, if the proportion of stabilised large sediment/small rock fractions increased this may benefit these biotopes. Conversely if the proportion of smaller sediment fractions increased within these biotopes (as with “Mud and sandy Mud” and “Sand and sandy mud”) then macro-algal recruitment would likely be significantly reduced.

Sensitivity assessment. Resistance has been assessed as ‘None’, resilience as Very low (the pressure is a permanent change), and sensitivity 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

SS.SMp.KSwSS.SlatMxVS is a sediment biotope, found on a varied mixture of sediment and rock fractions. Extraction of substratum to 30 cm is likely to remove small sediment fractions (e.g. gravel) and may mobilize the remaining larger rock fractions (e.g. cobbles) causing high mortality within the resident community.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

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

Abrasion of the substratum e.g. from bottom or pot fishing gear, cable laying etc. may cause localised mobility of the substrata and mortality of the resident community. The effect would be situation dependent however if bottom fishing gear were towed over a site it may mobilise a high proportion of the rock substrata and cause high mortality in the resident community e.g. overturning cobbles and causing mortality in the attached algal canopies.

No specific examples of anthropogenic abrasion could be found for this biotope. However, bottom fishing gear (e.g. scallop dredging) are known to cause high mortality in bycatch species by overturning sediment and physically crushing fragile species (Bradshaw et al., 2001), which includes urchins.

The test of Psammechinus miliaris is brittle and easily damaged by impact or abrasion. Spines and podia may be damaged or broken off. The spines may provide some degree of cushioning for the test. Beam trawling was reported to remove ca 20 to 50% of this species (Kaiser & Spencer, 1994), and the impact of scallop dredging is likely to be similar. Damage to the test will generally be lethal, if not outright because internal organs become exposed to predators and possible infection.

Sensitivity assessment. Resistance has been assessed as ‘Low’, Resilience as ‘Medium’. Sensitivity has been 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

Penetration and/or disturbance of the substrate below the surface of the seabed, may cause localised mobility of the substrata and mortality of the resident community. No specific examples of anthropogenic penetration could be found for this biotope. However, bottom fishing gear (e.g. scallop dredging) are known to cause high mortality in bycatch species by overturning sediment and physically crushing fragile species (Bradshaw et al., 2001), and may also cause high mortality in in-fauna species such as Cerianthus lloydii.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

Changes in suspended solids (water clarity)

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

Evidence

Suspended Particle Matter (SPM) concentration has a linear relationship with sub surface light attenuation (Kd) (Devlin et al., 1998). Light penetration influences the maximum depth at which kelp species can grow and it has been reported that laminarians grow at depths at which the light levels are reduced to 1 percent of incident light at the surface. Maximal depth distribution of laminarians therefore varies from 100 m in the Mediterranean to only 6-7 m in the silt laden German Bight. In Atlantic European waters, the depth limit is typically 35 m. In very turbid waters the depth at which kelp is found may be reduced, or in some cases excluded completely (e.g. Severn Estuary), because of the alteration in light attenuation by suspended sediment (Lüning, 1990; Birkett et al. 1998b).​ Laminaria spp. show a decrease of 50% photosynthetic activity when turbidity increases by 0.1/m (light attenuation coefficient =0.1-0.2/m; Staehr & Wernberg, 2009). An increase in water turbidity will likely affect the photosynthetic ability of kelp, decrease abundance and density. 

Psammechinus miliaris is omnivorous, feeding directly on live and dead algae but also on an array of attached fauna (Kelly, 2000). The feeding plasticity of Psammechinus miliaris is likely to ameliorate some of the effects of diminished kelp growth as a result of decreased light availability.

Changes in light penetration or attenuation associated with this pressure are not relevant to Modiolus modiolus. However alterations in the availability of food or the energetic costs in obtaining food or changes in scour could either increase or decrease habitat suitability for Modiolus modiolus. Modiolus modiolus is found in a variety of turbid and clear water conditions (Holt et al., 1998). Decreases in turbidity may increase phytoplankton productivity and potentially increase food availability. Therefore, Modiolus modiolus may benefit from reduced turbidity.

Sensitivity Assessment. A decrease in turbidity is likely to support enhanced growth (and possible habitat expansion) and is therefore not considered in this assessment. Psammechinus miliaris and Modiolus modiolus are resilient to changes in water clarity. An increase in water clarity from clear to intermediate (10-100 mg/l) represent a change in light attenuation of ca 0.67-6.7 Kd/m, and is likely to result in a greater than 50% reduction in photosynthesis of Laminariales. Therefore, the dominant kelp species will probably suffer a severe decline and resistance to this pressure is assessed as ‘None’. Resilience to this pressure is defined as ‘High’ at the benchmark level due to the scale of the impact. Hence, this biotope is regarded as having a sensitivity of ‘Medium‘.

Smothering and siltation rate changes (light)

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

Evidence

Smothering by sediment e.g. 5 cm material during a discrete event, is unlikely to damage Saccharina latissima sporophytes but may affect holdfast fauna, gametophyte survival, interfere with zoospore settlement and therefore recruitment processes (Moy & Christie, 2012). Given the short life expectancy of Saccharina latissima (2-4 years (Parke, 1948)), SS.SMp.KSwSS.SlatMxVS is likely to be dependent on annual Saccharina latissima recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 5 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that kelp gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

Psammechinus miliaris is quite small (typically up to 4 cm) and is likely to be inundated by 5 cm of sediment (Jackson, 2008). If unable to 'dig out' of the sediment, deposited sediment may cause mortality. Mature individuals of Modiolus modiolus can reach 10-25 cm and are unlikely to completely inundated by light deposition of up to 5 cm during a discrete event.

SS.SMp.KSwSS.SlatMxVS is recorded from strong (1.5-3 m/sec) to very weak (negligible) tidal streams. Within tide swept examples of SS.SMp.KSwSS.SlatMxVS sediment are likely to be removed within a few tidal cycles. In tidally sheltered examples of SS.SMp.KSwSS.SlatMxVS sediments could remain and recovery rate would be related to sediment retention but will probably be dissipated within a year.

Sensitivity assessment. To reflect the potential effect that deposited sediment could have on Psammechinus miliaris. Resistance has been assessed as ‘Low’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

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

Smothering by sediment e.g. 30 cm material during a discrete event, is unlikely to damage Saccharina latissima sporophytes but will likely affect holdfast fauna, gametophyte survival, interfere with zoospore settlement and therefore recruitment processes (Moy & Christie, 2012). Given the short life expectancy of Saccharina latissima (2-4 years (Parke, 1948), SS.SMp.KSwSS.SlatMxVS is likely to be dependent on annual Saccharina latissima recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 5 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that kelp gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

Psammechinus miliaris is quite small (typically up to 4 cm) and is likely to be inundated by 30 cm of sediment (Jackson, 2008). If unable to 'dig out' of the sediment, deposited sediment may cause mortality. Mature individuals of Modiolus modiolus can reach 10-25 cm and may also become inundated/smothered by heavy deposition of up to 30 cm during a discrete event.

SS.SMp.KSwSS.SlatMxVS is recorded from strong (1.5-3 m/sec) to very weak (Negligible) tidal streams. Within tide swept examples of SS.SMp.KSwSS.SlatMxVS sediment are likely to be removed within a few tidal cycles. In tidally sheltered examples of SS.SMp.KSwSS.SlatMxVS sediments could remain and recovery rate would be related to sediment retention but will probably be dissipated within a year.

Sensitivity assessment. To reflect the potential effect that deposited sediment could have on Psammechinus miliaris and Modiolus modiolus. Resistance has been assessed as ‘None’, resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

Litter

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

Evidence

Not assessed. There is no evidence to suggest that litter would significantly affect kelp.

Electromagnetic changes

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

Evidence

No evidence

Underwater noise changes

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

Evidence

Not relevant

Introduction of light or shading

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

Evidence

There is no evidence to suggest that anthropogenic light sources would affect macroalgae. Shading (e.g. by construction of a pontoon, pier etc) could adversely affect SS.SMp.KSwSS.SlatMxVS in areas where the water clarity is also low, and tip the balance to shade tolerant species, resulting in the loss of Saccharina latissima from areas of the biotope directly within the shaded area, or a reduction in seaweed abundance.

Sensitivity assessment. Resistance is probably 'Low', with a 'High' resilience and a sensitivity of 'Low', albeit with 'low' confidence due to the lack of direct evidence.

Barrier to species movement

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

Evidence

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 spores, but spore 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. Collision from grounding vessels is addressed under abrasion above.

Visual disturbance

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

Evidence

Not relevant

Genetic modification & translocation of indigenous species

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

Evidence

Saccharina latissima has shown significant regional acclimation to environmental conditions. Gerard & Dubois (1988) found Saccharina latissima sporophytes which were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. It is therefore possible that transplanted eco-types of Saccharina latissima may react differently to environmental conditions that differ from those of their origin.

Modiolus modiolus bed restoration projects may translocate stock to re-populate areas of suitable habitat (Elsasser et al., 2013). However, no evidence was found for detrimental effects arising from this practice, although there is potential for the movement of pathogens and non-indigenous, invasive species.

However, at the time of writing there is No evidence for translocation of any other characzerising species over significant geographic distances. Nor is there any evidence regarding the genetic modification or effects of translocation.

Introduction or spread of invasive non-indigenous species

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

Evidence

Competition with invasive macroalgae may be a potential threat to this biotope (de Bettignies et al., 2021). Potential invasives include Undaria pinnatifida and Sargassum muticum.  Sargassum muticum is a circumglobal invasive species (Engelen et al., 2015).  It is recorded (2015) from Norway to Morocco and into the Mediterranean in the eastern Atlantic and from Alaska to Baja California in the eastern Pacific and from southern Russia to southern China in the western Pacific (Engelen et al., 2015).  It colonizes a variety of habitats and can tolerate -1°C to 30°C and survive salinities below 10 ppt.  Although fertilization does not occur below 15 ppt and growth of germlings is limited below 10°C it can complete its life cycle as long as temperatures are over 8°C for at least four months of the year (Engelen et al., 2015).  However, its distribution is limited by the availability of hard substratum (e.g. stones >10 cm) and light (Staeher et al., 2000; Strong & Dring 2011; Engelen et al., 2015).  It is most abundant between 1 and 3 m below mean water.  But it has been recorded at 18 m or 30 m in the clear waters of California.  However, it is a poor competitor under low light and only develops dense canopies in shallow areas (Engelen et al., 2015).

Sargassum muticum was shown to replace and out-compete leathery, canopy-forming macroalgae such as Saccharina latissima, Halidrys siliquosa, and Fucus spp. and, to a lesser degree, understorey species such as Codium fragile, Chondrus crispus and Dictyota dichotoma in Limfjorden, Denmark between 1984 and 1997 (Staehr et al., 2000; Engelen et al., 2015; de Bettignies et al., 2021).  The invasion in Limfjorden had stabilized by 2005 although many of the native macroalgal species continued to decline (Engelen et al., 2015).  In Limfjorden, the distribution of Sargassum muticum was limited to areas with hard substratum, in particular stones > 10 cm in diameter, while smaller stones, gravel and sand were unsuitable.  It was most abundant between 1 and 4 m in depth but had low cover at 0-0.5 m or 4-6 m, in the turbid waters of the Limfjorden.  Limfjorden is wave sheltered although wave exposure has been reported to restrict the growth and survival of Sargassum muticum (Staehr et al., 2000).  Viejo et al. (1995) reported that Sargassum muticum transplanted to wave exposed shores in Spain experienced >80% breakages within a month and that the growth of undamaged plants was significantly lower than that of plants on sheltered shores.  Similarly, Andrew & Viejo (1998) noted that Sargassum muticum was restricted to intertidal rockpools in wave exposed sites in the Bay of Biscay.

Strong & Dring (2011) used canopy removal experiments to investigate inter- and intra-species competition between Sargassum muticum and Saccharina latissima in the Dorn, Strangford Lough, N. Ireland.  The Dorn consists of tidal pools, very sheltered from wave action but with moderately strong tidal streams (1-2 knots).  Sargassum muticum grew better in mixed stands with Saccharina latissima than in the highest density monospecific stands examined.  However, the growth of Saccharina was not affected by the proportion of Sargassum in mixed stands.  They concluded that Saccharina was not impacted significantly by the alien species while Sargassum benefited from growth in mixed stands.  Experimental manipulation of subtidal algal canopies in San Juan Islands, Washington State, USA, showed that Sargassum muticum reduced the abundance of native macroalgae, including the kelp Laminaria bongardiana due to shading.  However, experimental removal of Sargassum resulted in the recovery of native species within about one year (Britton-Simmons, 2004; Engelen et al., 2015).  The negative effects of Sargassum muticum on native macroalgae are mainly due to competition for light, rather than changes in nutrient availability, sedimentation or water flow (Britton-Simmons, 2004; Engelen et al., 2015).  

Undaria pinnatifida (Wakame or Asian kelp) is a large brown seaweed and an Invasive Non-Indigenous Species (INIS) that could out-compete native UK kelp species (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012; Brodie et al., 2014; Hieser et al., 2014; Arnold et al., 2016; Epstein & Smale, 2017; Epstein & Smale, 2018; Kraan, 2017; Epstein et al., 2019a,b; Tidbury, 2020).  Undaria pinnatifida originates from Japan but is established currently on the coastlines of New Zealand, Australia, Northern France, Spain, Italy, the UK, Portugal, Belgium, Holland, Argentina, Mexico, and the USA (De Leij et al., 2017).  Undaria pinnatifida was first recorded in the UK in the Hamble Estuary in 1994 (Macleod et al., 2016).  It has since proliferated along UK coastlines.  One year after its discovery at the Queen Anne Battery marina, Plymouth, it had become a major fouling plant on pontoons (Minchin & Nunn, 2014).  Although initially restricted to artificial habitats, such as marinas and ports, it is now widespread in natural habitats in several areas, including Plymouth Sound.

Undaria pinnatifida seems to settle better on artificial substrata (e.g. floats, marinas, or piers) than on natural rocky shores among local kelps (Vaz-Pinto et al., 2014).  It is found predominantly in low intertidal to shallow subtidal habitats (Epstein et al., 2019b) and is significantly more abundant on artificial substrata compared to natural rocky substrata (Heiser et al., 2014; Epstein & Smale, 2018).  James (2017) suggested that Undaria pinnatifida could out-compete native species on artificial substrata (such as marinas and wharf structures).  In Plymouth, UK, De Leij et al. (2017) found that natural habitats with dense native macroalgal canopies, such as Laminaria hyperborea, Laminaria ochroleuca, Laminaria digitata, and Saccharina latissima had more resistance to Undaria pinnatifida invasion than disturbed or sparse canopies, due to limited space and light availability for Undaria pinnatifida recruits.  However, the dense canopies did not always prevent the invasion of Undaria pinnatifida as sporophytes were still recorded within dense Laminaria canopies, so canopy disturbance was not always required (De Leij et al., 2017; Epstein & Smale, 2018).

Undaria pinnatifida species behaves as a winter annual and recruitment occurs in winter followed by rapid growth through spring, maturity, and then senescence through summer, with only the microscopic life stages persisting through autumn.  It exhibits multiple dispersal strategies, such as short-range spore dispersal, and long-range dispersal as whole drift plants or fragments.  Undaria pinnatifida has spread rapidly across the UK and Europe, resulting in community-wide responses and impacts (Vaz-Pinto et al., 2014; Epstein & Smale, 2017).  Its impacts are complex and context-specific, depending on space, time, and taxa present in the introduced location (Epstein & Smale, 2017; Teagle et al., 2017; Tidbury, 2020).

Undaria pinnatifida has a wide physiological niche meaning it can occur in both coastal and estuarine environments showing tolerance for varying salinities, turbidity, and siltation (Heiser et al., 2014; Epstein & Smale, 2018). Undaria pinnatifida can inhibit a broad range of habitats including – reefs; coastal brackish/saline lagoons; large shallow inlets and bays; estuaries; estuarine rocky habitats; natural or near-natural estuary; coastal lagoons; and tidal rivers, estuaries, mudflats, sandflats and lagoons (James, 2017).   Undaria pinnatifida prefers sites sheltered with low wave exposure and weak tidal streams (Heiser et al., 2014; Epstein & Smale, 2018).  In natural habitats, Undaria pinnatifida was not recorded if the wave fetch was greater than 642 km but increased in abundance and cover in very sheltered sites (Epstein & Smale, 2018).

In Plymouth Sound (UK), Epstein et al. (2019b) found that within its depth range (+1 to –4 m), Undaria pinnatifida co-existed with seven species of canopy-forming brown macroalgae, including Saccharina latissima.  However, they reported that Undaria pinnatifida biomass was negatively related to Saccharina latissima in both intertidal and subtidal habitats. This was only statistically significant in subtidal habitats, which suggested that there was some competition between the two species (Epstein et al., 2019b). Heiser et al. (2014) surveyed 17 sites within Plymouth Sound, UK and found that Saccharina latissima was significantly more abundant at sites with Undaria pinnatifida with ca 5 Saccharina latissima individuals present per m², compared to ca 0.5 Saccharina latissima individuals per m² present at sites without Undaria pinnatifida.

Undaria pinnatifida has been reported to both co-exist with and out-compete Saccharina latissima (Farrell & Fletcher, 2006; Heiser et al., 2014; Epstein et al., 2019b). For example, in Torquay Marina, UK, Farrell & Fletcher (2006) completed a canopy removal experiment between 1996-2002. They reported that Saccharina latissima decreased in both control and treatment plots from ca 3 plants per 0.45 m² in 1996 to ca 1 plant per 0.45 m² in 1997 and had disappeared completely from pontoons by 2002. This coincided with a significant increase in Undaria pinnatifida from zero plants per 0.45 m² in 1996 to ca 6 plants per 0.45 m² in 1997.  However, there was a slight decrease in Undaria pinnatifida in both control and treatment plots between 1997 and 1998.  By 2002, Undaria pinnatifida had recovered at control and treatment plots to ca 4-6 plants per 0.45 m² whereas Saccharina latissima had not.

Undaria pinnatifida was successfully eradicated on a sunken ship in Clatham Islands, New Zealand, by applying a heat treatment of 70°C (Wotton et al., 2004).  However, numerous other eradication attempts have failed and, as noted by Fletcher & Farrell (1998), once established Undaria pinnatifida resists most attempts at long-term removal.

The proliferation of Undaria pinnatifida and competition with native species may cause a reduction in local biodiversity (Valentine & Johnson, 2003; Vaz-Pinto et al., 2014; Arnold et al., 2016; Teagle, 2017; Tidbury, 2020).  A shift towards Undaria pinnatifida dominated beds could result in diminished epibiotic assemblages and lower local biodiversity compared with assemblages associated with native perennial kelp species, such as Laminaria spp. and Saccharina latissima (Arnold et al., 2016; Teagle et al., 2017).  In Plymouth, UK, Arnold et al. (2016) found that Undaria pinnatifida supported less than half the number of taxa and had no unique epibionts compared to Laminaria ochroleuca and Saccharina latissima (Arnold et al., 2016).

Sensitivity assessment. The above evidence suggests that both Sargassum muticum and Undaria pinnatifida can both compete with and co-exist with Saccharina latissima, depending on local conditions.  For example, Undaria pinnatifida can out-compete Saccharina latissima in artificial habitats, such as in Torquay Marina, but within natural habitats, it can co-exist with native kelp species within its depth range (-1 to 4 m), as shown in Plymouth Sound, UK.  Similarly, Sargassum muticum out-competed Saccharina latissima in theLimfjorden but coexisted in the Dorn in Strangford Lough.

This Saccharina latissima dominated biotope (SS.SMp.KSwSS.SlatMxVS) is found at variable depth (0-20 m JNCC, 2015) and variable salinity with moderately strong to weak tidal streams and wave exposed to very sheltered conditions.  The evidence above suggests that Undaria prefers sheltered conditions, with low tidal flow, in the shallow subtidal and sublittoral fringe (ca +1 to 4 m in depth), while Sargassum also prefers wave sheltered conditions and shallow water (ca 1 to 4 m depth).  Therefore, Undaria pinnatifida and Sargassum muticum are only likely to threaten the most shallow (e.g. 0-5 m) and wave sheltered examples of this biotope, where suitable had substrata are available.  They may either co-exist with or out-compete Saccharina latissima, resulting in a potentially significant (25-75%) reduction in the abundance or extent of the native kelp and a possible decrease in the diversity of other macroalgae.  Therefore, resistance is assessed as ‘Low’ for shallow, wave sheltered examples of the biotope, i.e. above 5 m in depth, while it is probably ‘Not relevant’ to examples below 5 m.  Recovery after invasion by Sargassum or Undaria, although rapid, would require direct intervention (removal) so that resilience is assessed as ‘Very low’.  Hence, the sensitivity of shallow, sheltered, examples of the biotope is assessed as ‘High’.  Overall, confidence is assessed as ‘Low’ due to evidence of variation and site-specific nature of competition between native kelps, Sargassum muticum, and Undaria pinnatifida.

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

Saccharina latissima may be infected by the microscopic brown alga Streblonema aecidioides. Infected algae show symptoms of Streblonema disease, i.e. alterations of the blade and stipe ranging from dark spots to heavy deformations and completely crippled thalli (Peters & Scaffelke, 1996). Infection can reduce growth rates of host algae.

Psammechinus miliaris is susceptible to 'Bald-sea-urchin disease', which causes lesions, loss of spines, tube feet, pedicellariae, destruction of the upper layer of skeletal tissue and death (Maes et al., 1986). It is thought to be caused by the bacteria Vibrio anguillarum and Aeromonas salmonicida. This disease has been recorded from Psammechinus miliaris from the French Atlantic coast. Although associated with mass mortalities of Strongylocentrotus franciscanus in California and Paracentrotus lividus in the French Mediterranean there is no evidence of mass mortalities of Psammechinus miliaris associated with this disease around Britain and Ireland.

Brown & Seed (1977) reported a low level of infestation (ca 2%) of Modiolus modiolus with pea crabs Pinnotheres sp. in Port Erin, Isle of Man and Strangford Lough. Comely (1978) reported that ca 20% of older specimens, in an ageing population, were damaged or shells malformed by the boring sponge Cliona celata. Infestation by the boring sponge reduces the strength of the shell and may render the population more intolerant of physical disturbance (see above). However, little other information concerning the effects of parasites or disease on the condition of horse mussels was found.

Shumway (1990) reviewed the effects of algal blooms on shellfish and reported that a bloom of Gonyaulax tamarensis (Protogonyaulax) was highly toxic to Modiolus modiolus. Shumway (1990) also noted that both Mytilus spp. and Modiolus spp. accumulated paralytic shellfish poisoning (PSP) toxins faster than most other species of shellfish, e.g. horse mussels retained Gonyaulax tamarensis toxins for up to 60 days (depending on the initial level of contamination). Landsberg (1996) also suggested that there was a correlation between the incidence of neoplasia or tumours in bivalves and out-breaks of paralytic shellfish poisoning in which bivalves accumulate toxins from algal blooms, although a direct causal effect required further research.

The parasites Martelia refringens or other Marteilia sp. can cause significant bivalve infections. Although these have been reported to infect Modiolus modiolus (Bower et al., 2004) no evidence was available to assess the scale of impact and therefore there is not enough evidence to assess sensitivity of Modiolus modiolus to this pressure

Sensitivity assessment. Evidence suggests that a number of characterizing species are susceptible to a number of disease or parasites that could result in loss of condition and possibly a proportion of the individual species populations. Therefore, resistance to the pressure is considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to introduction of microbial pathogens is assessed as ‘Low’.

Removal of target species

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

Evidence

Targeted removal of characterizing species SS.SMp.KSwSS.SlatMxVS would likely have a fundamental effect on the ecology. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al 2013) and not directly extracted from the seabed, as is the case with Laminaria hyperborea (see Christie et al., 1998). As a consequence related literature on which to assess the “resistance” of Saccharina latissima to targeted harvesting is sparse. Psammechinus miliaris is targeted as a potential aquaculture species. When fed a nutritious diet in culture, the gonad biomass rapidly proliferates which can then be marketed as urchin “roe” (Kelly et al., 1998; 2000). However, a study of a littoral and sublittoral population, Kelly (2000) concluded that a wild fishery was not commercially viable because of the low gonad content of wild populations. While some extraction of Psammechinus miliaris may conceivably develop for roe-enhancement through feeding artificial or nutrient enriched diets (Dr Maeve Kelly pers comm.), this is currently not in practice within the UK.

Artisanal fisheries have targeted Modiolus modiolus as bait for the long-ling fishery (Jeffreys 1863; Wiborg 1946) and, more locally, for human consumption around the British Isles (Jeffreys 1863; Holt et al. 1998) and the Faroe Islands (Dinesen & Ockelmann 2005). However at the time of writing Modiolus modiolus is not directly targeted in the UK.

Sensitivity assessment. At the time of writing none of the characterizing species are commercially extracted from the seabed. If extracted in the future resistance would need to be re-assessed. This pressure has been assessed as ‘Not Relevant.

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

Incidental removal of characterizing species from this biotope would likely have a fundamental effect on the ecology. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al 2013) and not directly extracted from the seabed, as is the case with Laminaria hyperborea (see Christie et al., 1998). As a consequence related literature on which to assess the “resistance” of Saccharina latissima to incidental harvesting is sparse.

Psammechinus miliaris may suffer as a result of trawling or dredging for other benthic species. Species with fragile tests such as urchins have been reported to be particularly sensitive to damage from mobile fishing gear (see Jennings & Kaiser, 1998; Bergman & van Santbrink, 2000). Kaiser & Spencer (1994) reported a ca20 - 50% mortality in Psammechinus miliaris as a result of a single pass of an experimental 4m beam trawl. Similarly, sparse Modiolus modiolus may be removed by a passing mobile gear, or crushed by mobilized cobbles and pebbles.

Sensitivity assessment. For this assessment it has been assumed that incidental removal could result in removal of the characterizing species, depending on the footprint of the activity. i. Resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’.