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 (Kain, 1979, Van Den Hoek, 1982, Breeman, 1990, Lüning, 1990). Northern boundaries are set by lethal winter temperatures 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, and found as far south as New York State, USA. In the UK, sea surface temperatures are range 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 has been 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 reducing by 50-70% at 20°C, and all experimental specimens disintegrating after 7 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 tolerated these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 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 6 of the 17 original 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 had regularly exceeded 20°C and so had 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 will move northwards, retreating from the coast of Portugal, France and the southwest coast of the UK. The authors projected that, under RCP 2.6, 13% 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.

Dendrodoa grossularia gamete release occurs from spring-autumn, with peaks in early spring and another in late summer. Gamete release is reduced at temperatures above 15°C and totally suppressed above ca 20°C (Millar, 1954). Currently, no information could be found on the upper temperature threshold of mature Dendrodoa grossularia. However, Dendrodoa grossularia is at its southern range edge within the UK and, therefore, an increase in temperature that is outside the normal range for the UK is likely to cause mortality.

Many of the red algae species associated with the understory turf can tolerate warm water temperatures. Hypoglossum hypoglossoides is distributed from the northern islands of Scotland to the Caribbean, whilst Nitophyllum punctatum is distributed from Scotland to the Mediterranean (www.obis.org). The optimal temperature for Gracilaria gracilis growth was found to be 18°C, but high growth was recorded up to 25.5°C (Rebello et al., 1996).

Sensitivity Assessment. UK populations of Saccharina latissima are found in the middle of the species 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.

With sea surface temperature around the UK of between 6-19°C (Huthnance, 2010), populations of Saccharina latissima and its understory turf may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C (middle emission scenario) by the end of this century, leading to maximum summer high temperatures in the south of the UK of 22°C.  However, increasing temperatures are likely to lead to a decrease in growth and some mortality. The ascidian Dendrodoa grossularia is likely to be lost from this biotope as a result of rising temperatures under all three scenarios. 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 the middle emission scenario.

For the high emission scenario and extreme scenario, whereby sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century both Dendrodoa grossularia and Sacharina latissima is likely to be lost from southern England, as gametophytes are not thought to be able to survive at temperatures ≥23°C. This assessment corresponds with the results of ecological niche modelling by Assis et al. (2018), who predicted that Saccharina latissima would be lost from the southwest coast of the UK, as a result of climate change.  As this biotope primarily occurs in the southwest of the UK, this means that much of this biotope will be lost. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. This biotope is assessed as having ‘High’ sensitivity to ocean warming in the high emission and extreme scenarios.  

Global warming (high)

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

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

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

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

Evidence

The distribution of seaweeds is climatically defined (Kain, 1979, Van Den Hoek, 1982, Breeman, 1990, Lüning, 1990). Northern boundaries are set by lethal winter temperatures 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, and found as far south as New York State, USA. In the UK, sea surface temperatures are range 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 has been 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 reducing by 50-70% at 20°C, and all experimental specimens disintegrating after 7 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 tolerated these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 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 6 of the 17 original 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 had regularly exceeded 20°C and so had 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 will move northwards, retreating from the coast of Portugal, France and the southwest coast of the UK. The authors projected that, under RCP 2.6, 13% 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.

Dendrodoa grossularia gamete release occurs from spring-autumn, with peaks in early spring and another in late summer. Gamete release is reduced at temperatures above 15°C and totally suppressed above ca 20°C (Millar, 1954). Currently, no information could be found on the upper temperature threshold of mature Dendrodoa grossularia. However, Dendrodoa grossularia is at its southern range edge within the UK and, therefore, an increase in temperature that is outside the normal range for the UK is likely to cause mortality.

Many of the red algae species associated with the understory turf can tolerate warm water temperatures. Hypoglossum hypoglossoides is distributed from the northern islands of Scotland to the Caribbean, whilst Nitophyllum punctatum is distributed from Scotland to the Mediterranean (www.obis.org). The optimal temperature for Gracilaria gracilis growth was found to be 18°C, but high growth was recorded up to 25.5°C (Rebello et al., 1996).

Sensitivity Assessment. UK populations of Saccharina latissima are found in the middle of the species 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.

With sea surface temperature around the UK of between 6-19°C (Huthnance, 2010), populations of Saccharina latissima and its understory turf may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C (middle emission scenario) by the end of this century, leading to maximum summer high temperatures in the south of the UK of 22°C.  However, increasing temperatures are likely to lead to a decrease in growth and some mortality. The ascidian Dendrodoa grossularia is likely to be lost from this biotope as a result of rising temperatures under all three scenarios. 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 the middle emission scenario.

For the high emission scenario and extreme scenario, whereby sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century both Dendrodoa grossularia and Sacharina latissima is likely to be lost from southern England, as gametophytes are not thought to be able to survive at temperatures ≥23°C. This assessment corresponds with the results of ecological niche modelling by Assis et al. (2018), who predicted that Saccharina latissima would be lost from the southwest coast of the UK, as a result of climate change.  As this biotope primarily occurs in the southwest of the UK, this means that much of this biotope will be lost. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. This biotope is assessed as having ‘High’ sensitivity to ocean warming in the high emission and extreme scenarios.  

Global warming (middle)

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

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

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

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

Evidence

The distribution of seaweeds is climatically defined (Kain, 1979, Van Den Hoek, 1982, Breeman, 1990, Lüning, 1990). Northern boundaries are set by lethal winter temperatures 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, and found as far south as New York State, USA. In the UK, sea surface temperatures are range 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 has been 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 reducing by 50-70% at 20°C, and all experimental specimens disintegrating after 7 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 tolerated these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 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 6 of the 17 original 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 had regularly exceeded 20°C and so had 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 will move northwards, retreating from the coast of Portugal, France and the southwest coast of the UK. The authors projected that, under RCP 2.6, 13% 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.

Dendrodoa grossularia gamete release occurs from spring-autumn, with peaks in early spring and another in late summer. Gamete release is reduced at temperatures above 15°C and totally suppressed above ca 20°C (Millar, 1954). Currently, no information could be found on the upper temperature threshold of mature Dendrodoa grossularia. However, Dendrodoa grossularia is at its southern range edge within the UK and, therefore, an increase in temperature that is outside the normal range for the UK is likely to cause mortality.

Many of the red algae species associated with the understory turf can tolerate warm water temperatures. Hypoglossum hypoglossoides is distributed from the northern islands of Scotland to the Caribbean, whilst Nitophyllum punctatum is distributed from Scotland to the Mediterranean (www.obis.org). The optimal temperature for Gracilaria gracilis growth was found to be 18°C, but high growth was recorded up to 25.5°C (Rebello et al., 1996).

Sensitivity Assessment. UK populations of Saccharina latissima are found in the middle of the species 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.

With sea surface temperature around the UK of between 6-19°C (Huthnance, 2010), populations of Saccharina latissima and its understory turf may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C (middle emission scenario) by the end of this century, leading to maximum summer high temperatures in the south of the UK of 22°C.  However, increasing temperatures are likely to lead to a decrease in growth and some mortality. The ascidian Dendrodoa grossularia is likely to be lost from this biotope as a result of rising temperatures under all three scenarios. 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 the middle emission scenario.

For the high emission scenario and extreme scenario, whereby sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century both Dendrodoa grossularia and Sacharina latissima is likely to be lost from southern England, as gametophytes are not thought to be able to survive at temperatures ≥23°C. This assessment corresponds with the results of ecological niche modelling by Assis et al. (2018), who predicted that Saccharina latissima would be lost from the southwest coast of the UK, as a result of climate change.  As this biotope primarily occurs in the southwest of the UK, this means that much of this biotope will be lost. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. This biotope is assessed as having ‘High’ sensitivity to ocean warming in the high emission and extreme scenarios.  

Marine heatwaves (high)

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

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). 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 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, so 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.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Dendrodoa grossularia is likely to be lost from this biotope as a result of rising temperatures and Saccharina latissima is likely to be impacted (see Global warming). A heatwave of this magnitude is likely to cause mass 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.’ This biotope is assessed as having ‘High’ sensitivity to marine heatwaves under 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 26.5°C. Under this scenario, both Dendrodoa grossularia and Saccharina latissima are likely to be already lost from this biotope as a result of rising temperatures (see Global warming) although mortality of any surviving specimens would occur as a result of this projected heatwave. 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 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, so 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.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. Dendrodoa grossularia is likely to be lost from this biotope as a result of rising temperatures and Saccharina latissima is likely to be impacted (see Global warming). A heatwave of this magnitude is likely to cause mass 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.’ This biotope is assessed as having ‘High’ sensitivity to marine heatwaves under 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 26.5°C. Under this scenario, both Dendrodoa grossularia and Saccharina latissima are likely to be already lost from this biotope as a result of rising temperatures (see Global warming) although mortality of any surviving specimens would occur as a result of this projected heatwave. 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 will not negatively impact Saccharina latissima.

The impact of ocean acidification on Dendrodoa grossularia is not known, although ocean acidification is thought to generally be positive for tunicates, which have been classified as one of the winners of ocean acidification (Dupont & Thorndyke, 2009).

Sensitivity Assessment. Kelp forests live in a naturally variable pH habitat, with diel fluctuations of 0.3 - 0.45 pH units (Krause-Jensen et al., 2015, Britton et al., 2016), and boundary layer pH fluctuation of up to 0.8 units (Krause-Jensen et al., 2015). Neither the macroalga Saccharina latissima nor the tunicate Dendrodoa grossularia are expected to exhibit negative effects of ocean acidification at levels expected for the end of this century. Therefore, under both the middle and high emission scenario resistance is assessed as ‘High’, and resilience is assessed as ‘High’ leading to a score of ‘Not sensitive’.

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 will not negatively impact Saccharina latissima.

The impact of ocean acidification on Dendrodoa grossularia is not known, although ocean acidification is thought to generally be positive for tunicates, which have been classified as one of the winners of ocean acidification (Dupont & Thorndyke, 2009).

Sensitivity Assessment. Kelp forests live in a naturally variable pH habitat, with diel fluctuations of 0.3 - 0.45 pH units (Krause-Jensen et al., 2015, Britton et al., 2016), and boundary layer pH fluctuation of up to 0.8 units (Krause-Jensen et al., 2015). Neither the macroalga Saccharina latissima nor the tunicate Dendrodoa grossularia are expected to exhibit negative effects of ocean acidification at levels expected for the end of this century. Therefore, under both the middle and high emission scenario resistance is assessed as ‘High’, and resilience is assessed as ‘High’ leading to a score of ‘Not sensitive’.

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 in sheltered, infralittoral rock in estuaries primarily in the south-west of England, and is generally only found at shallow depths, due to the highly turbid nature of the water (JNCC, 2015).

Light availability and water turbidity are principle factors in determining kelp depth range (Birkett et al. 1998b), with laminarians being reported to be able to withstand light levels of up to 1% surface irradiance. In Maine, USA, Saccharina latissima is abundant at both turbid and deep sites where surface irradiance averages 2.5% surface irradiance, and have adapted to low-light conditions (Gerard, 1990).

This biotope occurs on tide-swept infralittoral rock. Understanding how sea-level rise will affect 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.

Sensitivity assessment. An increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope, which is already constrained to shallow waters through limits to light availability. This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. It is unknown how tidal energy will change, or what alterations this may lead to for this biotope. For the middle and high emission scenarios (50 and 70 cm rise) the resistance has been assessed as ‘Medium’ while resilience is assessed as ‘Very low’.  Therefore, sensitivity is assessed as ‘Medium’ sensitivity to sea-level rise predicted for the end of this century in these scenarios.

Under the extreme sea-level rise scenario of 107 cm, there is potential that more than 25% of the bed could be lost, dependent on depth distribution.  Therefore, resistance has been assessed as ‘Low’, and resilience as ‘Very low’, albeit with ‘Low’ confidence.  This biotope is assessed as having ‘High’ sensitivity under the extreme sea-level rise scenario predicted for the end of this century. 

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 in sheltered, infralittoral rock in estuaries primarily in the south-west of England, and is generally only found at shallow depths, due to the highly turbid nature of the water (JNCC, 2015).

Light availability and water turbidity are principle factors in determining kelp depth range (Birkett et al. 1998b), with laminarians being reported to be able to withstand light levels of up to 1% surface irradiance. In Maine, USA, Saccharina latissima is abundant at both turbid and deep sites where surface irradiance averages 2.5% surface irradiance, and have adapted to low-light conditions (Gerard, 1990).

This biotope occurs on tide-swept infralittoral rock. Understanding how sea-level rise will affect 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.

Sensitivity assessment. An increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope, which is already constrained to shallow waters through limits to light availability. This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. It is unknown how tidal energy will change, or what alterations this may lead to for this biotope. For the middle and high emission scenarios (50 and 70 cm rise) the resistance has been assessed as ‘Medium’ while resilience is assessed as ‘Very low’.  Therefore, sensitivity is assessed as ‘Medium’ sensitivity to sea-level rise predicted for the end of this century in these scenarios.

Under the extreme sea-level rise scenario of 107 cm, there is potential that more than 25% of the bed could be lost, dependent on depth distribution.  Therefore, resistance has been assessed as ‘Low’, and resilience as ‘Very low’, albeit with ‘Low’ confidence.  This biotope is assessed as having ‘High’ sensitivity under the extreme sea-level rise scenario predicted for the end of this century. 

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 in sheltered, infralittoral rock in estuaries primarily in the south-west of England, and is generally only found at shallow depths, due to the highly turbid nature of the water (JNCC, 2015).

Light availability and water turbidity are principle factors in determining kelp depth range (Birkett et al. 1998b), with laminarians being reported to be able to withstand light levels of up to 1% surface irradiance. In Maine, USA, Saccharina latissima is abundant at both turbid and deep sites where surface irradiance averages 2.5% surface irradiance, and have adapted to low-light conditions (Gerard, 1990).

This biotope occurs on tide-swept infralittoral rock. Understanding how sea-level rise will affect 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.

Sensitivity assessment. An increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope, which is already constrained to shallow waters through limits to light availability. This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. It is unknown how tidal energy will change, or what alterations this may lead to for this biotope. For the middle and high emission scenarios (50 and 70 cm rise) the resistance has been assessed as ‘Medium’ while resilience is assessed as ‘Very low’.  Therefore, sensitivity is assessed as ‘Medium’ sensitivity to sea-level rise predicted for the end of this century in these scenarios.

Under the extreme sea-level rise scenario of 107 cm, there is potential that more than 25% of the bed could be lost, dependent on depth distribution.  Therefore, resistance has been assessed as ‘Low’, and resilience as ‘Very low’, albeit with ‘Low’ confidence.  This biotope is assessed as having ‘High’ sensitivity under the extreme sea-level rise scenario predicted for the end of this century. 

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 lattisma growth (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990). Optimal temperature for Saccharina latissima sporophyte growth was 10-15°C (Bolton & Lüning, 1982), while  reported  growth was inhibited by 50-70% at 20°C and all experimental specimens completely disintegrated after 7 days at 23°C.  In the field, Saccharina latissima has however shown significant regional variation in its acclimation response to changing environmental conditions.  For example 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.  Therefore, the response 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 and 2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration which temperatures remain above 20°C. High sea temperatures 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).

Dendrodoa grossularia gamete release occurs from spring-autumn, with peaks in early spring and another in late summer. Gamete release is reduced at temperatures above 15°C and totally suppressed above ca 20°C (Miller, 1954). At the time of writing no information could be found on the upper temperature threshold of mature Dendrodoa grossularia. However, Dendrodoa grossularia is at its southern range edge within the UK and therefore a dramatic increase in temperature that is outside the normal range for the UK may cause mortality.

IR.MIR.KT.SlatT is recorded exclusively within the south west UK (Connor et al., 2004), where temperature ranges from 8-16°C (Beszczynska-Möller & Dye, 2013).

Sensitivity assessment. A 2°C increase for one year may impair Saccharina latissima sporophyte growth but otherwise not affect the characterizing species. Saccharina latissima populations that are not acclimated to >20°C may incur mass mortality within 3 weeks of exposure. Therefore, an increase of 5°C combined with high summer temperatures may cause mass Saccharina latissima mortality. Resistance has been assessed as ‘None’, and resilience as ‘High’. 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). Subtidal red algae can survive at temperatures between -2 °C and 18-23 °C (Lüning, 1990; Kain & Norton, 1990). Dendrodoa grossularia is has been recorded from Nottinghambukta, Svalbard where annual temperature can range from 3-5°C.

Sensitivity assessment. An acute or long-term decrease in temperature within the UK, at the benchmark level, is not likely to have a significant effect on IR.MIR.KT.SlatT. 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 and5 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. The hypersaline tolerance of Dendrodoa grossularia is unknown.

Sensitivity assessment. The evidence suggests that Saccharina latissima can tolerate short-term (<5 days) exposure to hypersaline conditions of ≥40‰. Resistance has been assessed as ‘High’, resilience as ‘High’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Not Sensitive’.

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 the authors suggest that 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 and quicker.

Dendrodoa grossularia has been recorded as an abundant component of benthic fauna in Nottinghambukta, Svalbard where salinity can range from 6 and 20‰ (Różycki & Gruszczyński, 1991).

Sensitivity assessment. A decrease in one MNCR salinity scale from ‘Variable Salinity’ (30-40psu) to ‘Reduced Salinity’ (18-30 psu) may cause a decline in the photosynthetic ability of Saccharina latissima and hence growth. Dendrodoa grossularia abundance in Nottinghambukta, Svalbard where salinity is extremely low indicates it would be unaffected. Resistance has been assessed as ‘Low’ and resilience as ‘High’. Therefore, sensitivity of this biotope to a decrease in salinity has been assessed as ‘Low’.

Water flow (tidal current) changes (local)

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

Evidence

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 (≤1m/sec) when compared to weak tidal streams (<0.5m/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 (>3m/sec) to moderately strong tidal streams (≤1m/sec) (Connor et al., 2004), indicating Saccharina latissima can tolerate greater tidal streams than 1m/sec.

Sensitivity assessment. IR.MIR.KT.SlatT is recorded predominantly from strong-moderately strong (0.5-3m/sec) tidal streams. Large scale changes tidal velocities (>1m/sec) may increase the predominance of tide swept biotopes (e.g. IR.MIR.KR.LhypT/X, IR.MIR.KT.XKTX or IR.MIR.KT.SlatT) and replace IR.MIR.KT.SlatT. However, the available evidence suggests that a change in flow velocities of between 0.1-0.2m/sec would have no significant effect on IR.MIR.KT.SlatT. 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

IR.MIR.KT.SlatT core records occur exclusively from 0-5m (Connor et al., 2004). An increase in emergence will result in an increased risk of desiccation and mortality of Saccharina latissima in shallow examples of the biotope. Removal of canopy forming kelps has also been shown to increase desiccation and mortality of the understorey macro-algae (Hawkins & Harkin, 1985). Several mobile species such as sea urchins and brittle stars are likely to move away. However, 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 ‘High’. The sensitivity of this biotope to a change in emergence is considered as ‘Low’.

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

Wave exposure is one of the principal defining features of kelp biotopes, and changes in wave exposure are likely to alter the relative abundance of the kelp species, grazing and understorey community, and hence, the biotope (Birkett et al., 2004). Saccharina latissima is rarely dominant at wave exposed sites, however if present, develops a short thick stipe and a short, narrow and tightly wrinkled blade (Birkett et al., 1998). Furthermore, IR.MIR.KT.SlatT is recorded from sheltered to extremely sheltered sites (Connor et al., 2004).

Sensitivity assessment. However a change in near shore significant wave height of 3-5% is unlikely to have any significant effect on IR.MIR.KT.SlatT. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not Sensitive’ at the benchmark level.

Transition elements & organo-metal contamination

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

Evidence

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

Saccharina latissima sporophytes have a low intolerance to heavy metals, but the early life stages are more intolerant. 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. 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.

Dendrodoa grossularia does grow in the intertidal (Miller, 1954) and may therefore become smothered in the event of an oil spill, however at the time of writing there no evidence to support this.

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.

O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Saccharina latissima has also been found to be sensitive to antifouling compounds. 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.

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).

Sensitivity Assessment. Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. In addition, in tide swept conditions, deoxygenation is likely to highly localised and short lived.  Resistance has been assessed as ‘High’, Resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Nutrient enrichment

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

Evidence

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 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. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment however could also be time dependant.

Johnston & Roberts (2009) conducted a meta analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected six 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 macro-algal 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).

Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore organic enrichment may denude the associated community. However, the biotope is probably ‘Not sensitive’ at the benchmark levels (i.e. compliance with WFD criteria).

Organic enrichment

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

Evidence

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 20.22 µM, 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. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment however could also be time dependant.

Johnston & Roberts (2009) conducted a meta analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected six 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 macro-algal 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).

Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore organic enrichment may denude the associated community. Resistance has therefore been assessed as ‘Medium’, resilience as ‘High’. 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 rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which kelp species would not be able to tolerate (Birkett et al., 1998). The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very low’ or ‘None’. The sensitivity of this biotope to change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa is assessed as ‘High’

Physical change (to another sediment type)

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

Evidence

Not relevant

Habitat structure changes - removal of substratum (extraction)

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

Evidence

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

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

Low level disturbances (e.g. solitary anchors) are unlikely to cause harm to the biotope as a whole, due to the impact’s small footprint. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al. 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to in/direct harvesting or abrasion is limited.

Sensitivity assessment. Abrasion by passing trawls or harvesting of macroalgae is likely remove a large proportion of the kelp biomass.  For example in kelp harvesting is likely to remove all the large canopy forming plants (Svendsen, 1972; Christie et al., 1998).  However, Saccharina latissima has been shown to be an early colonizer with the potential to recover rapidly (Kain, 1967; Leinaas & Christie, 1996). Therefore, resistance has been assessed as ‘None’, resilience as ‘High’, and sensitivity as ‘Low’.

Penetration or disturbance of the substratum subsurface

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

Evidence

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

Changes in suspended solids (water clarity)

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

Evidence

Suspended Particle Matter (SPM) concentration has a linear relationship with sub surface light attenuation (Kd) (Devlin et al., 2008). An increase in SPM results in a decrease in sub-surface light attenuation. Light availability and water turbidity are principal factors in determining kelp depth range (Birkett 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 (Birkett et al. 1998b; Lüning, 1990). 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.

Sensitivity Assessment. An increase in water clarity from clear to intermediate (10-100mg/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 Laminaria spp. Therefore the dominant kelp species will probably suffer a severe decline and resistance to this pressure is assessed as ‘None’.  Resilience is probably to this pressure is defined as ‘High’ at the benchmark. Hence, this biotope is regarded as having a sensitivity of ‘Medium ‘to this pressure.

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)), IR.MIR.KT.SlatT 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.

Dendrodoa grossularia is a small ascidian, capable of reaching a size of approx 8.5 mm (Miller, 1954) and is therefore likely to be inundated by deposition of 5 cm of sediment. If inundation is long lasting then the understorey community may be adversely affected. However, IR.MIR.KT.SlatT is found within strong-moderately strong (0.5-3 m/sec) and therefore deposited sediments are unlikely to remain for more than a few tidal cycles.

Sensitivity assessment. Resistance has been assessed as ‘Medium’, 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 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)), IR.MIR.KT.SlatT is likely to be dependent on annual recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 30cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that 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.

Dendrodoa grossularia is a small ascidian, capable of reaching a size of approx 8.5mm (Miller, 1954) and is therefore likely to be inundated by deposition of 30 cm of sediment. If inundation is long lasting then the understorey community may be adversely affected. However, IR.MIR.KT.SlatT is found within strong-moderately strong (0.5-3m/sec) and therefore deposited sediments are likely to be cleared rapidly, but inundation is likely to cause mortality in the understorey community.

Sensitivity assessment. Resistance has been assessed as ‘Low’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Litter

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

Evidence

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

Saccharina lattissima has no hearing perception but vibrations may cause an impact, however no studies exist to support an assessment (where 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 IR.MIR.KT.SlatT. Shading (e.g. by construction of a pontoon, pier etc) could adversely affect IR.MIR.KT.SlatT in areas where the water clarity is also low, and tip the balance to shade tolerant species, resulting in the loss of the biotope directly within the shaded area. IR.MIR.KT.SlatT is already affected by high water turbidity (Connor et al., 2004), and Saccharina lattissima is therefore relatively sparse.

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 to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

Visual disturbance

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

Evidence

Not relevant

Genetic modification & translocation of indigenous species

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

Evidence

No evidence

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.  Potential invasives include Undaria pinnatifida, Sargassum muticum and Codium fragile spp. tormentosoides. In Nova Scotia, Codium fragile spp. tormentosoides competes successfully with native kelps for space including Laminaria digitata, exploiting gaps within the kelp beds.  Once established, the algal mat created by Codium fragile spp. tormentosoides prevents re-colonization by other macroalgae (Scheibling & Gagnon, 2006).

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 is 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 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.

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).

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.

Sensitivity assessment.  The above evidence suggests that 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.  However, this Saccharina latissima dominated biotope (IR.MIR.KT.SlatT) biotope is found in the shallow infralittoral (0-5 m, JNCC, 2015) sheltered from wave action but structured by strong tidal streams in turbid and variable salinity waters.  The evidence above suggests that Undaria prefers sheltered conditions, with a low tidal flow, and is less likely to out-compete Saccharina latissima under the conditions that define this biotope. 

However, Sargassum muticum prefers wave sheltered shallow sites in the sublittoral fringe and shallow infralittoral. Sargassum muticum was reported to out-compete and replace Saccharina latissima, and achieve maximum abundance at 1-4 m, in the turbid waters of the Limfjorden (Staehr et al., 2000; Engelen et al., 2015). But Strong & Dring (2011) concluded that Sargassum was not a threat to Saccharina latissima in the Dorn, Strangford Lough where it coexisted and grew better in mixed stands.  Hence, competition with Sargassum is probably site-specific and dependent on local conditions.

Therefore, resistance is assessed as ‘Low’ to represent colonization by Sargassum and the possible loss of Saccharina latissima, especially as the turbid conditions mirror those found in Limfjorden.  Even if the two species co-exist, the invasion may result in a change in the classification of the biotope and the structure of the understorey macroalgae (Staehr et al., 2000).  Recovery after invasion by Sargassum, although rapid, would require direct intervention (removal).  Hence, resilience is probably ‘Very low’ so sensitivity is assessed as ‘High’.  Overall, confidence is assessed as ‘Low’ due to evidence of variation and site-specific nature of competition between native kelps and both Undaria pinnatifida and Sargassum muticum.

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.

Sensitivity assessment. 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

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. Similarly, at the time of writing, no evidence could be found to suggest that Dendrodoa grossularia is commercially exploited.

Sensitivity assessment. At the time of writing none of the characterising 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. Laminaria digitata is commercially extracted 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). Similarly Dendrodoa grossularia is not currently a commercially exploited species. As a consequence relevant literature on which to assess the “resistance” of IR.MIR.KT.SlatT to incidental harvesting is sparse. If removed the characterizing species are likely to recover within 2 years.

Sensitivity assessment. Resistance has been assessed as ‘None’, resilience as ‘High’ and sensitivity as ‘Medium’.