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 kelp is strongly influenced by climatic conditions; therefore, kelp species are extremely sensitive to the ongoing ocean warming (Kain, 1979; Van Den Hoek, 1982; Breeman, 1990; Lüning, 1990; Assis et al., 2016; Smale, 2020). Northern distribution 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). Kelps have a high dependence on ocean temperatures, which make them highly vulnerable to ocean warming (Assis et al., 2014). Laminaria hyperborea is a cold- temperate kelp species, distributed from the Barents Sea down to the coast of Portugal (Schoschina, 1997). 

Laminaria hyperborea has an optimum temperature for growth of 15°C, and an upper temperature limit of 21°C (Bolton & Lüning, 1982). At 17°C gamete survival is reduced (Steinhoff et al., 2008) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is therefore likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. However, sporophytes can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998b).

There is evidence that climate change is already having an impact on Laminaria hyperborea populations in the English Channel. Poleward range expansion of the warm temperate Laminaria ochroleuca as a result of ocean warming has led to competition with Laminaria hyperborea in UK waters (Smale et al., 2015). Laminaria ochroleucawas not found in the UK last century.  But Laminaria ochroleuca has now increased its range to include the southwest of England (Smale et al., 2015) and the west coast of Ireland (Schoenrock et al., 2019). While, since 1970 Laminaria hyperborea has undergone a range constriction of ~250 km at its warm leading-edge (Frontier et al., 2021). 

During the 2013-2014 Northeast Atlantic storm season, the UK was subjected to some of the most intense storms recorded within the past five years. A study by Smale & Vance. (2015) investigated the impacts of the storms on kelp canopies along the south coast of the UK, findings indicated monospecific canopies of Laminaria hyperborea were unaffected by the storms. However, the storms significantly altered a mixed canopy study site, composed of Laminaria ochroleuca, Saccharina latissima and Laminaria hyperborea. Therefore, if climate change continues to change species composition within kelp forests resistance to storm disturbance could be altered.

Smale et al. (2015) found that Laminaria hyperborea suffered from much higher epiphytic loadings and lower productivity than its competitor Laminaria ochroleuca during the summer months, which reduced its competitive ability. The decreased competitive ability because of ocean warming corresponds to findings by Pessarrodona et al. (2018), who found a decrease in the size of Laminaria hyperborea plants along a north-south gradient in Scotland, with average maximum stipe lengths of over 150 cm, whereas in southern England they were less than 100 cm. Similarly, Smale et al. (2020b) observed clear differences between net primary productivity (NNP) and carbon standing stock of Laminaria hyperborea between the colder northern and warmer southern test sites in the UK, with NNP and standing stock being 1.5 and 2.5 times greater in the northern sites. Identifying ocean temperatures as a lively driver of productivity, with reduced NNP and standing stock observed in warmer waters (Smale et al., 2020b). 

The decrease in productivity in southern England suggests that Laminaria hyperborea is already growing at suboptimal temperatures. Assis et al. (2018) predicted that under the highest emission scenario (RCP 8.5) the biogeographic range of Laminaria hyperborea will move northwards, and this retreat would lead to this species being lost from approximately 30% of the UK coastline.

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23°C (Lüning 1990; Kain & Norton, 1990). Temperature increases may affect growth, recruitment, or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13°C.  Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), and maintenance of sea temperatures above 13°C may affect recruitment success.

Sensitivity assessment. Laminaria hyperborea is already growing at suboptimal temperatures in the southern UK, based on evidence of its decreased productivity comparative to Scotland (Pessarrodona et al., 2018; Smale et al., 2020b), and predictions have estimated Laminaria hyperborea to be lost from the UK by 2100 as a result of warming (Brodie et al., 2014). Sea surface temperatures around the UK currently ranging from 6-19°C (Huthnance, 2010).  Under the middle emission scenario, a rise of 3°C could lead to maximum summer high temperatures in the south of the UK of 22°C. This is above the upper thermal limit of 21°C for Laminaria hyperborea (Bolton & Lüning, 1982), and is likely to lead to loss of this species from the south of England. Furthermore, biomass and plant size are expected to decrease as waters warm, with Scottish Laminaria hyperborea stipe lengths decreasing to lengths observed in southern England, leading to a decline in carbon assimilation, productivity and habitat quality. 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 under this scenario.

For the high emission scenario and extreme scenario, this northward retreat of the distribution of Laminaria hyperborea is expected to increase. Under the high emission scenario it is expected to be lost from 30% of the coastline around the UK (Assis et al., 2018), and under the extreme scenario more is projected to be lost. Populations that remain around the UK will become less productive. Therefore, under these scenarios, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very Low’. Therefore, this biotope IR.HIR.KFaR.LhypFa is assessed as ‘High’ sensitivity to ocean warming under this 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 kelp is strongly influenced by climatic conditions; therefore, kelp species are extremely sensitive to the ongoing ocean warming (Kain, 1979; Van Den Hoek, 1982; Breeman, 1990; Lüning, 1990; Assis et al., 2016; Smale, 2020). Northern distribution 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). Kelps have a high dependence on ocean temperatures, which make them highly vulnerable to ocean warming (Assis et al., 2014). Laminaria hyperborea is a cold- temperate kelp species, distributed from the Barents Sea down to the coast of Portugal (Schoschina, 1997). 

Laminaria hyperborea has an optimum temperature for growth of 15°C, and an upper temperature limit of 21°C (Bolton & Lüning, 1982). At 17°C gamete survival is reduced (Steinhoff et al., 2008) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is therefore likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. However, sporophytes can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998b).

There is evidence that climate change is already having an impact on Laminaria hyperborea populations in the English Channel. Poleward range expansion of the warm temperate Laminaria ochroleuca as a result of ocean warming has led to competition with Laminaria hyperborea in UK waters (Smale et al., 2015). Laminaria ochroleucawas not found in the UK last century.  But Laminaria ochroleuca has now increased its range to include the southwest of England (Smale et al., 2015) and the west coast of Ireland (Schoenrock et al., 2019). While, since 1970 Laminaria hyperborea has undergone a range constriction of ~250 km at its warm leading-edge (Frontier et al., 2021). 

During the 2013-2014 Northeast Atlantic storm season, the UK was subjected to some of the most intense storms recorded within the past five years. A study by Smale & Vance. (2015) investigated the impacts of the storms on kelp canopies along the south coast of the UK, findings indicated monospecific canopies of Laminaria hyperborea were unaffected by the storms. However, the storms significantly altered a mixed canopy study site, composed of Laminaria ochroleuca, Saccharina latissima and Laminaria hyperborea. Therefore, if climate change continues to change species composition within kelp forests resistance to storm disturbance could be altered.

Smale et al. (2015) found that Laminaria hyperborea suffered from much higher epiphytic loadings and lower productivity than its competitor Laminaria ochroleuca during the summer months, which reduced its competitive ability. The decreased competitive ability because of ocean warming corresponds to findings by Pessarrodona et al. (2018), who found a decrease in the size of Laminaria hyperborea plants along a north-south gradient in Scotland, with average maximum stipe lengths of over 150 cm, whereas in southern England they were less than 100 cm. Similarly, Smale et al. (2020b) observed clear differences between net primary productivity (NNP) and carbon standing stock of Laminaria hyperborea between the colder northern and warmer southern test sites in the UK, with NNP and standing stock being 1.5 and 2.5 times greater in the northern sites. Identifying ocean temperatures as a lively driver of productivity, with reduced NNP and standing stock observed in warmer waters (Smale et al., 2020b). 

The decrease in productivity in southern England suggests that Laminaria hyperborea is already growing at suboptimal temperatures. Assis et al. (2018) predicted that under the highest emission scenario (RCP 8.5) the biogeographic range of Laminaria hyperborea will move northwards, and this retreat would lead to this species being lost from approximately 30% of the UK coastline.

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23°C (Lüning 1990; Kain & Norton, 1990). Temperature increases may affect growth, recruitment, or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13°C.  Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), and maintenance of sea temperatures above 13°C may affect recruitment success.

Sensitivity assessment. Laminaria hyperborea is already growing at suboptimal temperatures in the southern UK, based on evidence of its decreased productivity comparative to Scotland (Pessarrodona et al., 2018; Smale et al., 2020b), and predictions have estimated Laminaria hyperborea to be lost from the UK by 2100 as a result of warming (Brodie et al., 2014). Sea surface temperatures around the UK currently ranging from 6-19°C (Huthnance, 2010).  Under the middle emission scenario, a rise of 3°C could lead to maximum summer high temperatures in the south of the UK of 22°C. This is above the upper thermal limit of 21°C for Laminaria hyperborea (Bolton & Lüning, 1982), and is likely to lead to loss of this species from the south of England. Furthermore, biomass and plant size are expected to decrease as waters warm, with Scottish Laminaria hyperborea stipe lengths decreasing to lengths observed in southern England, leading to a decline in carbon assimilation, productivity and habitat quality. 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 under this scenario.

For the high emission scenario and extreme scenario, this northward retreat of the distribution of Laminaria hyperborea is expected to increase. Under the high emission scenario it is expected to be lost from 30% of the coastline around the UK (Assis et al., 2018), and under the extreme scenario more is projected to be lost. Populations that remain around the UK will become less productive. Therefore, under these scenarios, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very Low’. Therefore, this biotope IR.HIR.KFaR.LhypFa is assessed as ‘High’ sensitivity to ocean warming under this 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 kelp is strongly influenced by climatic conditions; therefore, kelp species are extremely sensitive to the ongoing ocean warming (Kain, 1979; Van Den Hoek, 1982; Breeman, 1990; Lüning, 1990; Assis et al., 2016; Smale, 2020). Northern distribution 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). Kelps have a high dependence on ocean temperatures, which make them highly vulnerable to ocean warming (Assis et al., 2014). Laminaria hyperborea is a cold- temperate kelp species, distributed from the Barents Sea down to the coast of Portugal (Schoschina, 1997). 

Laminaria hyperborea has an optimum temperature for growth of 15°C, and an upper temperature limit of 21°C (Bolton & Lüning, 1982). At 17°C gamete survival is reduced (Steinhoff et al., 2008) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is therefore likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. However, sporophytes can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998b).

There is evidence that climate change is already having an impact on Laminaria hyperborea populations in the English Channel. Poleward range expansion of the warm temperate Laminaria ochroleuca as a result of ocean warming has led to competition with Laminaria hyperborea in UK waters (Smale et al., 2015). Laminaria ochroleucawas not found in the UK last century.  But Laminaria ochroleuca has now increased its range to include the southwest of England (Smale et al., 2015) and the west coast of Ireland (Schoenrock et al., 2019). While, since 1970 Laminaria hyperborea has undergone a range constriction of ~250 km at its warm leading-edge (Frontier et al., 2021). 

During the 2013-2014 Northeast Atlantic storm season, the UK was subjected to some of the most intense storms recorded within the past five years. A study by Smale & Vance. (2015) investigated the impacts of the storms on kelp canopies along the south coast of the UK, findings indicated monospecific canopies of Laminaria hyperborea were unaffected by the storms. However, the storms significantly altered a mixed canopy study site, composed of Laminaria ochroleuca, Saccharina latissima and Laminaria hyperborea. Therefore, if climate change continues to change species composition within kelp forests resistance to storm disturbance could be altered.

Smale et al. (2015) found that Laminaria hyperborea suffered from much higher epiphytic loadings and lower productivity than its competitor Laminaria ochroleuca during the summer months, which reduced its competitive ability. The decreased competitive ability because of ocean warming corresponds to findings by Pessarrodona et al. (2018), who found a decrease in the size of Laminaria hyperborea plants along a north-south gradient in Scotland, with average maximum stipe lengths of over 150 cm, whereas in southern England they were less than 100 cm. Similarly, Smale et al. (2020b) observed clear differences between net primary productivity (NNP) and carbon standing stock of Laminaria hyperborea between the colder northern and warmer southern test sites in the UK, with NNP and standing stock being 1.5 and 2.5 times greater in the northern sites. Identifying ocean temperatures as a lively driver of productivity, with reduced NNP and standing stock observed in warmer waters (Smale et al., 2020b). 

The decrease in productivity in southern England suggests that Laminaria hyperborea is already growing at suboptimal temperatures. Assis et al. (2018) predicted that under the highest emission scenario (RCP 8.5) the biogeographic range of Laminaria hyperborea will move northwards, and this retreat would lead to this species being lost from approximately 30% of the UK coastline.

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23°C (Lüning 1990; Kain & Norton, 1990). Temperature increases may affect growth, recruitment, or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13°C.  Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), and maintenance of sea temperatures above 13°C may affect recruitment success.

Sensitivity assessment. Laminaria hyperborea is already growing at suboptimal temperatures in the southern UK, based on evidence of its decreased productivity comparative to Scotland (Pessarrodona et al., 2018; Smale et al., 2020b), and predictions have estimated Laminaria hyperborea to be lost from the UK by 2100 as a result of warming (Brodie et al., 2014). Sea surface temperatures around the UK currently ranging from 6-19°C (Huthnance, 2010).  Under the middle emission scenario, a rise of 3°C could lead to maximum summer high temperatures in the south of the UK of 22°C. This is above the upper thermal limit of 21°C for Laminaria hyperborea (Bolton & Lüning, 1982), and is likely to lead to loss of this species from the south of England. Furthermore, biomass and plant size are expected to decrease as waters warm, with Scottish Laminaria hyperborea stipe lengths decreasing to lengths observed in southern England, leading to a decline in carbon assimilation, productivity and habitat quality. 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 under this scenario.

For the high emission scenario and extreme scenario, this northward retreat of the distribution of Laminaria hyperborea is expected to increase. Under the high emission scenario it is expected to be lost from 30% of the coastline around the UK (Assis et al., 2018), and under the extreme scenario more is projected to be lost. Populations that remain around the UK will become less productive. Therefore, under these scenarios, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very Low’. Therefore, this biotope IR.HIR.KFaR.LhypFa is assessed as ‘High’ sensitivity to ocean warming under this 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 are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Marine heatwaves are known to cause significant impacts to kelp forests, particularly if a population is found towards the edge of its southern limit (Smale et al., 2019). 

In Baja California, Mexico, an extreme heat even between 2014– 2016, led to both a decrease in density of Macrocystis pyrifera and a decrease in the number of fronds per individual in Baja California, Mexico (Arafeh-Dalmau et al., 2019). Additionally, there was a significant change to the understory algal composition, and half of the fish and invertebrates associated with this habitat disappeared. The same heatwave, coupled with a loss of starfish through disease and an increase in urchin grazing, led to the loss of > 90% of Macrocystis pyrifera from 350 km of coastline in northern California (Rogers-Bennett & Catton, 2019).

Under experimental conditions, Nepper-Davidson et al. (2019) exposed a northern (Denmark) population of Saccharina lattisima to a simulated three week heatwaves 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, so the experiment was terminated (Nepper-Davidsen et al., 2019). 

Laminaria hyperborea is a cold-temperate species of kelp with an optimum temperature for growth of 15°C, and an upper temperature limit of 21°C (Bolton & Lüning, 1982). Germination success can decrease by almost two thirds at temperatures as low as 17°C. Therefore it is expected that similar to other kelp species, Laminaria hyperborea will be highly sensitive to marine heatwaves.

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. Laminaria hyperborea is unlikely to survive a heatwave of this magnitude and is, therefore, likely to suffer severe mortality in the south. In Scotland, where a significant portion of Laminaria hyperborea populations occur, temperatures are not predicted to rise above 20°C, and are, therefore,  Laminaria hyperborea is likely to survive a heatwave of this magnitude.  Therefore, resistance has been assessed as ‘Medium’. As a further heatwave (as defined by the pressure benchmark) is likely to affect this habitat before full recovery, resilience has been assessed as ‘Low.’ Therefore, this biotope IR.HIR.KFaR.LhypFa is assessed as having ‘Medium’ 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 in southern England. Laminaria hyperborea is unlikely to survive a heatwave of this magnitude, and as temperatures are likely to reach >21°C in Scotland under this scenario, there is likely to be mortality throughout this species’ UK biogeographic distribution. Therefore, resistance has been assessed as ‘Low’. As a further heatwave is likely to affect this habitat before full recovery (under the pressure benchmark definition), resilience has been assessed as ‘Low.’ Therefore, this biotope IR.HIR.KFaR.LhypFa 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 are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Marine heatwaves are known to cause significant impacts to kelp forests, particularly if a population is found towards the edge of its southern limit (Smale et al., 2019). 

In Baja California, Mexico, an extreme heat even between 2014– 2016, led to both a decrease in density of Macrocystis pyrifera and a decrease in the number of fronds per individual in Baja California, Mexico (Arafeh-Dalmau et al., 2019). Additionally, there was a significant change to the understory algal composition, and half of the fish and invertebrates associated with this habitat disappeared. The same heatwave, coupled with a loss of starfish through disease and an increase in urchin grazing, led to the loss of > 90% of Macrocystis pyrifera from 350 km of coastline in northern California (Rogers-Bennett & Catton, 2019).

Under experimental conditions, Nepper-Davidson et al. (2019) exposed a northern (Denmark) population of Saccharina lattisima to a simulated three week heatwaves 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, so the experiment was terminated (Nepper-Davidsen et al., 2019). 

Laminaria hyperborea is a cold-temperate species of kelp with an optimum temperature for growth of 15°C, and an upper temperature limit of 21°C (Bolton & Lüning, 1982). Germination success can decrease by almost two thirds at temperatures as low as 17°C. Therefore it is expected that similar to other kelp species, Laminaria hyperborea will be highly sensitive to marine heatwaves.

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. Laminaria hyperborea is unlikely to survive a heatwave of this magnitude and is, therefore, likely to suffer severe mortality in the south. In Scotland, where a significant portion of Laminaria hyperborea populations occur, temperatures are not predicted to rise above 20°C, and are, therefore,  Laminaria hyperborea is likely to survive a heatwave of this magnitude.  Therefore, resistance has been assessed as ‘Medium’. As a further heatwave (as defined by the pressure benchmark) is likely to affect this habitat before full recovery, resilience has been assessed as ‘Low.’ Therefore, this biotope IR.HIR.KFaR.LhypFa is assessed as having ‘Medium’ 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 in southern England. Laminaria hyperborea is unlikely to survive a heatwave of this magnitude, and as temperatures are likely to reach >21°C in Scotland under this scenario, there is likely to be mortality throughout this species’ UK biogeographic distribution. Therefore, resistance has been assessed as ‘Low’. As a further heatwave is likely to affect this habitat before full recovery (under the pressure benchmark definition), resilience has been assessed as ‘Low.’ Therefore, this biotope IR.HIR.KFaR.LhypFa 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 up to 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, including Laminaria hyperborea, 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). This was confirmed for Laminaria hyperborea by Olischläger et al. (2012) who found that ocean acidification at levels expected for the end of this century (700 µatm CO₂; a value between the middle and high emission scenario) led to an increase in female gametogenesis and increasing net photosynthesis and growth of sporophytes.

Research on other kelp species has revealed a positive or neutral effect of ocean acidification (Roleda et al., 2012, Fernández et al., 2015, Nunes et al., 2015, Iñiguez et al., 2016b, a), except for one study, which found that ocean acidification negatively impacted photosynthesis and growth in the southern hemisphere species, Ecklonia radiata (Britton et al., 2016).

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). Laminaria hyperborea is not expected to be impacted by 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 up to 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, including Laminaria hyperborea, 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). This was confirmed for Laminaria hyperborea by Olischläger et al. (2012) who found that ocean acidification at levels expected for the end of this century (700 µatm CO₂; a value between the middle and high emission scenario) led to an increase in female gametogenesis and increasing net photosynthesis and growth of sporophytes.

Research on other kelp species has revealed a positive or neutral effect of ocean acidification (Roleda et al., 2012, Fernández et al., 2015, Nunes et al., 2015, Iñiguez et al., 2016b, a), except for one study, which found that ocean acidification negatively impacted photosynthesis and growth in the southern hemisphere species, Ecklonia radiata (Britton et al., 2016).

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). Laminaria hyperborea is not expected to be impacted by 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 on very exposed and exposed, but wave surged, upper infralittoral bedrock and massive boulders. Wave surge is reduced with increasing depth; therefore, sea-level rise may reduce the effect of wave surge in the deeper examples or deeper reaches of this biotope.

The distribution of Laminaria hyperborea is positivity related to wave exposure, and as wave exposure increases, so does biomass and abundance (Pedersen et al., 2012). Total plant biomass and production per unit area double along an exposure gradient, due to larger leaf lengths and increased density at high wave energy sites (Pedersen et al., 2012). Understanding how sea-level rise will affect exposure and 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.

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. An increase in depth due to sea-level rise is likely to impact both Laminaria hyperborea and any understory algae, negatively impacting this biotope. The most important factors explaining the distribution of Laminaria hyperborea along the Norwegian coast were depth, wave exposure, light exposure and topography (Bekkby et al., 2009). This species requires rocky substratum for attachment.

Sensitivity assessment. This biotope IR.HIR.KFaR.LhypFa is recorded from 0-20 m in depth.  As wave surge diminishes with increased depth, sea-level rise is likely to lead to the density of faunal turf reducing at the deeper reaches of this biotope and transitioning into a biotope characterised by kelp and dense red seaweeds (IR.HIR.KFaR.LhypR.Ft or IR.HIR.KFaR.LhypR.Pk) or dense foliose red algae (IR.HIR.KFaR.FoR.Dic). This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of suitable substrate or human-modified shorelines.

There is likely to be considerable variation between sites, the relative contribution of wave surge and exposure to habitat suitability, and the depth range occupied by the biotope. Hence, it is difficult to assess the effect of the different sea-level rise scenarios. However, as the biotope can occur from 0-20 m in depth, it is assumed at 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 emission scenario) might result in loss of some of the deeper extent of the biotope in some sites. 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 emission 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 very exposed and exposed, but wave surged, upper infralittoral bedrock and massive boulders. Wave surge is reduced with increasing depth; therefore, sea-level rise may reduce the effect of wave surge in the deeper examples or deeper reaches of this biotope.

The distribution of Laminaria hyperborea is positivity related to wave exposure, and as wave exposure increases, so does biomass and abundance (Pedersen et al., 2012). Total plant biomass and production per unit area double along an exposure gradient, due to larger leaf lengths and increased density at high wave energy sites (Pedersen et al., 2012). Understanding how sea-level rise will affect exposure and 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.

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. An increase in depth due to sea-level rise is likely to impact both Laminaria hyperborea and any understory algae, negatively impacting this biotope. The most important factors explaining the distribution of Laminaria hyperborea along the Norwegian coast were depth, wave exposure, light exposure and topography (Bekkby et al., 2009). This species requires rocky substratum for attachment.

Sensitivity assessment. This biotope IR.HIR.KFaR.LhypFa is recorded from 0-20 m in depth.  As wave surge diminishes with increased depth, sea-level rise is likely to lead to the density of faunal turf reducing at the deeper reaches of this biotope and transitioning into a biotope characterised by kelp and dense red seaweeds (IR.HIR.KFaR.LhypR.Ft or IR.HIR.KFaR.LhypR.Pk) or dense foliose red algae (IR.HIR.KFaR.FoR.Dic). This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of suitable substrate or human-modified shorelines.

There is likely to be considerable variation between sites, the relative contribution of wave surge and exposure to habitat suitability, and the depth range occupied by the biotope. Hence, it is difficult to assess the effect of the different sea-level rise scenarios. However, as the biotope can occur from 0-20 m in depth, it is assumed at 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 emission scenario) might result in loss of some of the deeper extent of the biotope in some sites. 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 emission 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 very exposed and exposed, but wave surged, upper infralittoral bedrock and massive boulders. Wave surge is reduced with increasing depth; therefore, sea-level rise may reduce the effect of wave surge in the deeper examples or deeper reaches of this biotope.

The distribution of Laminaria hyperborea is positivity related to wave exposure, and as wave exposure increases, so does biomass and abundance (Pedersen et al., 2012). Total plant biomass and production per unit area double along an exposure gradient, due to larger leaf lengths and increased density at high wave energy sites (Pedersen et al., 2012). Understanding how sea-level rise will affect exposure and 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.

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. An increase in depth due to sea-level rise is likely to impact both Laminaria hyperborea and any understory algae, negatively impacting this biotope. The most important factors explaining the distribution of Laminaria hyperborea along the Norwegian coast were depth, wave exposure, light exposure and topography (Bekkby et al., 2009). This species requires rocky substratum for attachment.

Sensitivity assessment. This biotope IR.HIR.KFaR.LhypFa is recorded from 0-20 m in depth.  As wave surge diminishes with increased depth, sea-level rise is likely to lead to the density of faunal turf reducing at the deeper reaches of this biotope and transitioning into a biotope characterised by kelp and dense red seaweeds (IR.HIR.KFaR.LhypR.Ft or IR.HIR.KFaR.LhypR.Pk) or dense foliose red algae (IR.HIR.KFaR.FoR.Dic). This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of suitable substrate or human-modified shorelines.

There is likely to be considerable variation between sites, the relative contribution of wave surge and exposure to habitat suitability, and the depth range occupied by the biotope. Hence, it is difficult to assess the effect of the different sea-level rise scenarios. However, as the biotope can occur from 0-20 m in depth, it is assumed at 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 emission scenario) might result in loss of some of the deeper extent of the biotope in some sites. 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 emission 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

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0 - 20°C. Upper and lower lethal temperatures have been estimated at between 1-2°C above or below the extremes of this range (Birkett et al., 1988). Above 17°C gamete survival is reduced (Kain, 1964 & 1971) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is therefore likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. Sporophytes however can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998).

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23°C (Lüning 1990; Kain & Norton, 1990).  Temperature increase may affect growth, recruitment or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13°C. Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), and maintenance of sea temperatures above 13°C may affect recruitment success.

Sensitivity assessment. This biotope is distributed throughout the UK (Connor et al., 2004). Northern to southern Sea Surface Temperature (SST) ranges from 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013). Overall, a chronic change (2°C for a year) outside normal range for a year may reduce recruitment and growth, resulting in a minor loss in the population of kelp, especially in winter months or in southern examples of the biotope. However, an acute change (5°C for a month; e.g. from thermal effluent) may result in loss of abundance of kelp or extent of the bed, especially in winter. Therefore, resistance to the pressure is considered 'Medium', and resilience 'Medium'. The sensitivity of this biotope to increases in temperature 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

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0 - 20°C. Upper and lower lethal temperatures have been estimated at between 1-2 °C above or below the extremes of this range (Birkett et al., 1988). Subtidal red algae can survive at temperatures between -2 °C and 18-23 °C (Lüning, 1990; Kain & Norton, 1990).

Laminaria hyperborea is a boreal northern species with a geographic range from mid Portugal to Northern Norway (Birket et al., 1998), and a mid range within southern Norway (60°-65° North)(Kain, 1971). The average seawater temperature for southern Norway in October is 12-13°C (Miller et al., 2009), and average annual sea temperature, from 1970-2014, is 8°C (Beszczynska-Möller & Dye, 2013). The available information suggests that Laminaria hyperborea and biotope structure would not be affected by a change in sea temperature at the benchmark level.

Sensitivity assessment. Resistance to the pressure is considered ‘High’, and resilience ‘High’. The sensitivity of this biotope to decreases in temperature has been assessed 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

Lüning (1990) suggest that “kelps” are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu (MNCR category- 'Full' salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al, (1998) suggested that long-term increases in salinity may affect Laminaria hyperborea growth and may result in loss of affected kelp, and therefore loss of the biotope.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘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

Lüning (1990) suggest that “kelps” are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu (MNCR category-Full Salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al,. (1998) suggest that long-term changes in salinity may result in loss of affected kelp and, therefore loss of this biotope.

Hopkin & Kain (1978) tested Laminaria hyperborea sporophyte growth at various low salinity treatments. The results showed that Laminaria hyperborea sporophytes could grow “normally” at 19 psu, growth was reduced at 16 psu and did not grow at 7 psu. A decrease in one MNCR salinity scale from 'Full' salinity (30-40psu) to 'Reduced' salinity (18-30 psu) would result in a decrease of Laminaria hyperborea sporophyte growth. Laminaria hyperborea may also be out-competed by low salinity tolerant species e.g. Saccharina latissma (Karsten, 2007), or the Invasive Non Indigenous Species Undaria pinnatifida (Burrows et al., 2014).

If salinity was returned to 'Full' salinity (30-40 psu) Laminaria hyperborea could out-compete Saccharina latissma and re-establish community dominance in 2-4 years (Kain, 1975; Leinaas & Christie, 1996), however full habitat structure may take over 10 years to recover (Birkett et al., 1998; Cristie et al., 1998). The ability of Laminaria hyperborea to out-compete Undaria pinnatifida within the UK is however unknown (Heiser et al., 2014), and as such interspecific interaction between Laminaria hyperborea and Undaria pinnatifida is not included within this sensitivity assessment.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’.  The sensitivity of this biotope to decreases in salinity 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

Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Ireland, from March 2009-April 2010. Maximal significant wave height (Hm0) was 3.67 & 2m at the exposed and sheltered sites, and maximal water velocity (Velrms) was 0.6 & 0.3m/s at the exposed and sheltered sites respectively. Despite the differences in wave exposure and water velocity there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered sites. Therefore water flow was found to have no significant effect on Laminaria hyperborea growth at the observed range of water velocities.

Biotope structure is however different between wave exposed and sheltered sites. Pedersen et al. (2012) observed Laminaria hyperborea biomass, productivity and density increased with an increase in wave exposure. At low wave exposure Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates than at exposed sites. At low wave exposure Pedersen et al. (2012) suggested that high epiphytic loading on Laminaria hyperborea impaired light conditions, nutrient uptake, and increased the drag on the host Laminaria hyperborea during extreme storm events.

The morphology of the stipe and blade of kelps vary with water flow.  In wave exposed areas, for example, Laminaria hyperborea develops a long and flexible stipe and this is probably a functional adaptation to strong water movement (Sjøtun, 1998). In addition, the lamina becomes narrower and thinner in strong currents (Sjøtun & Fredriksen, 1995). However, the stipe of Laminaria hyperborea is relatively stiff and can snap in strong currents. Laminaria hyperborea is usually absent from areas of high wave action or strong currents, although it is found  in the Menai Strait, Wales, where tidal velocities can exceed 4 m/s (NBN, 2015) and in tidal rapids in Norway (J. Jones, pers. comm.)  Laminaria hyperborea growth can persist in very strong tidal streams (>3 m/s).

Increase water flow rate may also remove or inhibit grazers including Patella pellucida and Echinus esculentus and remove epiphytic algae growth (Pedersen et al., 2012). The associated algal flora and suspension feeding faunal populations change significantly with different water flow regimes. Increased water flow rates may reduce the understorey epiflora, to be replaced by an epifauna dominated community (e.g. sponges, anemones and polyclinid ascidians) as in the biotope IR.HIR.KFaR.LhypFa. The composition of the holdfast fauna may also change, e.g. energetic or sheltered water movements favour different species of amphipods (Moore, 1985).

IR.HIR.KFaR.LhypR, IR.HIR.KFaR.LhypFa, IR.MIR.KR.Lhyp, and their associated sub-biotopes are found within strong (1.5-3 m/s)-moderate (0.5-1.5 m/s) tidal streams. A change in peak mean spring bed flow velocity which does not result in a change in tidal streams above or below 0.5-3 m/s is not likely to affect the dominance of Laminaria hyperborea within the community, but may cause changes in the understorey community. The prominent understorey filter feeding community within IR.HIR.KFaR.LhypFa is reliant on high water movement. A decrease in tidal streams may result in a decline of filter feeding fauna and an increase in red seaweeds within the understorey community or vice versa with an increase in tidal streams A decrease in tidal flow within this range may also decrease urchin dislodgment and increase urchin grazing. An increase in urchin grazing may cause a decline in the understorey community abundance and diversity (as in IR.MIR.KR.Lhyp.GzFt/Pk and IR.MIR.KR.LhypPar).

Sensitivity assessment. A change in peak mean spring bed flow velocity of between 0.1m/s to 0.2m/s for more than 1 year is not likely to affect the dominance of Laminaria hyperborea, however subtle differences in tidal regime may influence the understorey community. Resistance to the pressure is considered ‘High’, and resilience ‘High’. Hence, the sensitivity of this biotope to changes in peak mean spring bed velocity has been assessed as ‘Not Sensitive’.

However, if peak mean spring bed flow velocity changes but remains within 0.5-3 m/s Laminaria hyperborea is likely to remain the dominant habitat but the understorey community may be affected; directly by a change in water velocity or through increased grazing pressure.

Emergence regime changes

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

Evidence

The upper limit of the Laminaria hyperborea bed is determined by wave action and water flow, desiccation, and competition from the more emergence resistant Laminaria digitata. Laminaria hyperborea exposed at extreme low water are very intolerant of desiccation, the most noticeable effect being bleaching of the frond and subsequent death of the meristem and loss of the plant. An increase in wave exposure (see below- water flow), as a result of increased emergence, has been found to exclude Laminaria hyperborea from shallow waters due to dislodgement of the sporophyte or snapping of the stipe (Birket et al., 1998). Hence, an increase in emergence is likely to lead to mortality of exposed Laminaria hyperborea and the associated habitat.

An increase in water depth/decreased emergence (at the benchmark level) may increase the upper depth restriction of Laminaria hyperborea forest biotope variants. However, limited light availability at depth will decrease the lower extent of Laminaria hyperborea, and may therefore result in a shift from forest to park biotope variants at depth. Further increases in depth will cause a community shift to that characterized by circalittoral faunal species, however this is beyond the scope of the benchmark.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to changes in tidal emergence has been assessed 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

Kregting et al., (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Ireland from March 2009-April 2010. Wave exposure was found to be between 1.1. to 1.6 times greater between the exposed and sheltered sites. Maximal significant wave height (Hm0) was 3.67 & 2m at the exposed and sheltered sites. Maximal water velocity (Velrms) was 0.6 & 0.3m/s at the exposed and sheltered sites. Despite the differences in wave exposure and water velocity there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered site.

Biotope structure is however different between wave exposed and sheltered sites. Pedersen et al., (2012) observed Laminaria hyperborea biomass, productivity and density increased with an increase in wave exposure. At low wave exposure Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates than at exposed sites. At low wave exposure high epiphytic loading on Laminaria hyperborea was theorised to impair light conditions, nutrient uptake, and increase the drag of the host Laminaria hyperborea during extreme storm events.

The morphology of the stipe and blade of kelps vary with water flow. In wave exposed areas, for example, Laminaria hyperborea develops a long and flexible stipe and this is probably a functional adaptation to strong water movement (Sjøtun, 1998). In addition, the lamina becomes narrower and thinner in strong currents (Sjøtun & Fredriksen, 1995). However, the stipe of Laminaria hyperborea is relatively stiff and can snap in strong currents. Lamiaria hyperborea is usually absent from areas of extreme wave action and can be replaced by Alaria esculenta. In extreme wave exposures Alaria esculenta can dominate the shallow sub-littoral to a depth of 15m (Birket et al., 1998).

Increase water flow rate may also remove or inhibit grazers including Patella pellucida and Echinus esculentus and remove epiphytic algae growth (Pedersen et al., 2012). The associated algal flora and suspension feeding faunal populations change significantly with different water flow regimes. Increased water flow rates may reduce the understorey epiflora, to be replaced by an epifauna dominated community (e.g. sponges, anemones and polyclinid ascidians) as in the biotope IR.HIR.KFaR.LhypFa. The composition of the holdfast fauna may also change, e.g. energetic or sheltered water movements favour different species of amphipods (Moore, 1985).

IR.HIR.KFaR.LhypR, IR.HIR.KFaR.LhypFa, IR.MIR.KR.Lhyp, and their associated sub-biotopes are found between extremely exposed to moderate wave exposure. Changes in local wave height above or below that experienced in extremely exposed to moderately exposed sites will affect the dominance of Laminaria hyperborea. Smaller changes in local wave height have the potential to cause changes to the understorey community. The prominent understorey filter feeding community within IR.HIR.KFaR.LhypFa is reliant on wave surge currents. A decrease in wave surge may result in a decline of filter feeding fauna and an increase in red seaweeds within the understorey community or vice versa. A decrease in local wave height may also decrease the chance of urchins being dislodged (removed) from biotopes found at sites with traditionally high wave exposure and may therefore increase urchin grazing. An increase in urchin grazing may cause a decline in the understorey community abundance and diversity (as in IR.MIR.KR.Lhyp.GzFt/Pk and IR.MIR.KR.LhypPar).

Sensitivity assessment. A change in nearshore significant wave height >3% but <5% is however unlikely to have a significant effect. Resistance to the pressure is considered ‘High’, and resilience ‘High’. Hence, the sensitivity of this biotope to changes in local wave height has been assessed as ‘Not Sensitive’.

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 a,. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on Laminaria hyperborea gametophytes and sporophytes, including reduced growth and respiration. Sheppard et al., (1980) noted that increasing levels of heavy metal contamination along the west coast of Britain reduced species number and richness in holdfast fauna, except for suspension feeders which became increasingly dominant. Gastropods may be relatively tolerant of heavy metal pollution (Bryan, 1984). Echinus esculentus recruitment is likely to be impaired by heavy metal contamination due to the intolerance of its larvae. Echinus esculentus are long-lived and poor recruitment may not reduce grazing pressure in the short-term. Although macroalgae species may not be killed, except by high levels of contamination, reduced growth rates may impair the ability of the biotope to recover from other environmental disturbances.

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.

Laminaria hyperborea fronds, being almost exclusively sub tidal, would not come into contact with freshly released oil, but only to sinking emulsified oil and oil adsorbed onto particles (Birket 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, including Laminaria hyperbora communities, 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). Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy 1984; cited in Holt et al., 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. Holt et al., (1995) concluded that Delesseria sanguinea is probably generally sensitive of chemical contamination. Overall the red algae are likely to be highly intolerant to hydrocarbon contamination. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

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). Although Laminaria hyperborea sporelings and gametophytes are intolerant of atrazine (and probably other herbicides) overall they may be relatively tolerant of synthetic chemicals (Holt et al., 1995). Laminaria hyperborea survived within >55m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater than 5 years of age, suggesting that spores and/or early stages were more intolerant (Hoare & Hiscock, 1974). Patella pellucida was excluded from Amlwch Bay by the pollution and the species richness of the holdfast fauna decreased with proximity to the effluent discharge; amphipods were particularly intolerant although polychaetes were the least affected (Hoare & Hiscock, 1974). The richness of epifauna/flora decreased near the source of the effluent and epiphytes were absent from Laminaria hyperborea stipes within Amlwch Bay. The red alga Phyllophora membranifolia was also tolerant of the effluent in Amlwch Bay. Smith (1968) also 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. Delesseria sanguinea was probably to most intolerant since it was damaged at depths of 6m (Smith, 1968). Holt et al., (1995) suggested that Delesseria sanguinea is probably generally sensitive of chemical contamination. Although Laminaria hyperborea may be relatively insensitive to synthetic chemical pollution, evidence suggests that grazing gastropods, amphipods and red algae are sensitive. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

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 have been shown to inhibiting 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.  However, small invertebrate epifauna may be lost, causing a reduction in species richness. Therefore a resistance of ‘High’ is recorded.  Resilience is likely to be ‘High’, and the biotopes is probably ‘Not sensitive’ at the benchmark level.

Nutrient enrichment

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

Evidence

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of nutrient enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996).

Increased nutrients may result in phytoplankton blooms that increase turbidity (see above). Increased nutrients may favour sea urchins, e.g. Echinus esculentus, due their ability to absorb dissolved organics, and result in increased grazing pressure leading to loss of understorey epiflora/fauna, decreased kelp recruitment and possibly 'urchin barrens'. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity, siltation and competition may significantly affect the structure of the biotope.

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

Organic enrichment

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

Evidence

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic enrichment since healthy populations are found at ends of sub littoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increase in ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect the structure of Laminaria hyperborea biotopes.

Sensitivity assessment. Resistance to the pressure is considered 'Medium', and resilience 'High'. The sensitivity of this biotope to organic enrichment is 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 Laminaria hyperborea would not be able to tolerate (Birket 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

Not relevant to rock substrata.

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

Christie et al., (1998) observed Laminaria hyperborea habitat regeneration following commercial Laminaria hyperborea trawling in south Norway. Within the study area, trawling removed all large canopy-forming adult Laminaria hyperborea, however sub-canopy recruits were largely unaffected. In 2-6 years of harvesting a new canopy had formed 1m off the seabed. The associated holdfast communities recovered in 6 years, however the epiphytic stipe community did not fully recover within the same time period. Christie et al., (1998) suggested that kelp habitats were relatively resistant to direct disturbance/removal of Laminaria hyperborea canopy.

Recurrent disturbance occurring at a smaller time scale than the recovery period of 2-6 years (stated above) could extend recovery time. Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of “urchin barrens”, following removal of urchins. The substratum was initially colonized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.

Penetration or disturbance of the substratum subsurface

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

Evidence

Not relevant, please refer to pressure “Abrasion/disturbance of the substrata on the surface of the seabed”.

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 down to 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 Laminaria hyperborea 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 Laminaria hyperborea and Laminaria ochroleuca and decrease Laminaria hyperborea abundance and density (see sub-biotope- IR.MIR.KR.Lhyp.Pk). Kain (1964) suggested that early Laminaria hyperborea gametophyte development could occur in the absence of light. Furthermore, observations from south Norway found that a pool of Laminaria hyperborea recruits could persist growing beneath Laminaria hyperborea canopies for several years, indicating that sporophyte growth can occur in light-limited environments (Christe et al., 1998). However in habitats exposed to high levels of suspended silts Laminaria hyperborea is out-competed by Saccharina latissima, a silt tolerant species, and thus, a decrease in water clarity is likely to decrease the abundance of Laminaria hyperborea in the affected area (Norton, 1978).

Sensitivity Assessment. Changes in water clarity are likely to affect photosynthetic rates and enable Saccharina latissima to compete more successfully with Laminaria hyperborea.  A decrease in turbidity is likely to support enhanced growth (and possible habitat expansion) and is therefore not considered in this assessment.  An increase in water clarity from clear to intermediate (10-100 mg/l) represents 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 significant decline and resistance to this pressure is assessed as ‘Low’. Resilience to this pressure is probably ‘Medium’ at the benchmark.  Hence, this biotope is assessed 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 Laminaria hyperborea sporophytes but is likely to affect gametophyte survival as well as holdfast fauna, and interfere with zoospore settlement.  Given the microscopic size of the gametophyte, 5 cm 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 one month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

If inundation is long lasting then the understorey epifauna/flora may be adversely affected, e.g. suspension or filter feeding fauna and/or algal species.  This biotope occurs in high wave exposures and therefore deposited sediments are unlikely to remain for more than a few tidal cycles, except in the deepest of rock-pools. Therefore the effects of depositing 5 cm of fine sediment in a discrete event are likely to be transient.

Sensitivity assessment. Resistance to the pressure is considered ‘High’, and resilience ‘High’. The sensitivity of this biotope to light deposition of up to 5 cm of fine material added to the seabed in a single discreet event is assessed as ‘Not sensitive’.

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 Laminaria hyperborea plants but is likely to affect gametophyte survival, holdfast communities, epiphytic community at the base of the stype, and interfere with zoospore settlement. Given the microscopic size of the gametophyte, 30 cm 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 within a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within one month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

If clearance of deposited sediment occurs rapidly then understorey communities are expected to recover quickly. If inundation is long lasting then the understorey epifauna/flora may be adversely affected, e.g. suspension or filter feeding fauna and/or algal species.  While this  biotope occurs in high to moderate energy habitats (due to water flow or wave action) deposition of 30cm of sediment represents a large volume of material that would likely remain for a number of tidal cycles and is expected to damage understorey flora/fauna as well as juvenile Laminaria hyperborea.

Sensitivity assessment. Resistance to the pressure is considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to heavy deposition of up to 30cm of fine material added to the seabed in a single discreet event is 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.

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

Shading of the biotope (e.g. by construction of a pontoon, pier etc) could adversely affect the biotope 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, or a reduction in laminarian abundance from forest to park type biotopes.

Sensitivity assessment. Resistance is probably 'Low', with a 'Medium' resilience and a sensitivity of 'Medium', 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

At the time of writing no evidence regarding the genetic modification or effects of translocation of native kelp populations was found.

Introduction or spread of invasive non-indigenous species

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

Evidence

Competition with invasive macroalgae may be a potential threat to this biotope. 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 to 0.5 m and 4 to 6 m, in the turbid waters of the Limfjorden. Limfjorden is wave sheltered but 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 the 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, the 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) and has since proliferated along UK coastlines. One year after its discovery at the Queen Anne Battery marina, Plymouth, it became 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 that canopy disturbance was not always required (De Leij et al., 2017; Epstein & Smale, 2018).  

Undaria 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 has a greater preference for 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 St Malo, France, there was evidence that Undaria pinnatifida co-existed with Laminaria hyperborea under certain conditions (Castric-Fey et al., 1993). Epstein & Smale (2018) also observed that Undaria pinnatifida was relatively common (abundance of >70 individuals per 25 m transect) at three sites in Devon, UK (Jennycliff, Bovisand and Beacon Cove) where Laminaria spp. were abundant (40 - 79%) or superabundant (>80%), which suggested that Undaria pinnatifida could co-exist within refugia amongst areas with dense Laminaria spp.. 

In Plymouth Sound, UK, Heiser et al. (2014) observed that Laminaria hyperborea was significantly less abundant at sites with the presence of Undaria pinnatifida, with only ca 0.5 Laminaria hyperborea individuals per m² present compared to ca 8 individuals per m² at sites without the presence of Undaria pinnatifida. However, the results from their correlation study only showed that the species were not found together (pers. comm., Epstein 2021). Whereas exclusion and succession experiments on reefs tell us that Laminaria spp. exclude Undaria pinnatifida, not the other way around. Epstein & Smale (2018) reported that in Devon, UK, persistent, dense, and intact Laminaria spp. canopies in rocky reef habitats exerted a strong influence over the presence/absence, abundance, and percentage cover of Undaria pinnatifida. A dense canopy of native kelp restricts the proliferation of Undaria pinnatifida and disturbance of the canopy is often the key to the recruitment of Undaria pinnatifida. Epstein et al. (2019b) reported that Undaria pinnatifida density and biomass were significantly negatively correlated with the sum of all Laminaria spp. in Plymouth, UK. The evidence indicated that native Laminaria spp. canopies in the UK inhibited Undaria pinnatifida and implied that Undaria pinnatifida was opportunistic but competitively inferior (Farrell & Fletcher, 2006; Heiser et al., 2014; Minchin & Nunn, 2014; De Leij et al., 2017; Epstein & Smale, 2018; Epstein et al., 2019b). However, Epstein et al. (2019b) also noted that Laminaria hyperborea had a non-significant positive relationship with Undaria pinnatifida due to low densities of Laminaria hyperborea across the study area, resulting in insufficient data. 

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 Laminaria hyperborea. De Leij et al. (2017) found that natural habitats with dense native macroalgal canopies, such as Laminaria hyperborea had more resistance to Undaria pinnatifida invasion than disturbed or sparse canopies, due to limited space and light availability for Undaria recruits. However, the dense canopies will not prevent the invasion of Undaria, as sporophytes were still recorded within dense Laminaria canopies, and this suggests that canopy disturbance is not always required. 

Undaria pinnatifida was successfully eradicated on a sunken ship in Chatham 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 co-exist with Laminaria hyperborea where sites are suitable e.g., Laminaria hyperborea in Plymouth Sound, UK. A dense kelp canopy may restrict or slow the proliferation of Undaria pinnatifida, however, there is mixed evidence of its colonization with Laminaria hyperborea beds and in some areas, a lower abundance of Laminaria hyperborea may result in increased Undaria pinnatifida growth. 

This Laminaria hyperborea dominated biotope (IR.HIR.KFaR.LhypFa) is found within the upper infralittoral zone with extreme wave exposure and moderately strong to very weak tidal streams. The evidence above suggests that Sargassum muticum prefers sheltered, shallow sites in the sublittoral fringe. It was reported to out-compete and replace Saccharina latissima in the Limfjorden and achieve maximum abundance between 1 and 4 m (Staehr et al., 2000; Engelen et al., 2015). However, no evidence of the effects of Sargassum on Laminaria hyperborea beds was found. Therefore, competition with Sargassum is probably site-specific and dependent on local conditions, so it is unlikely to survive even in the shallow depths due to the wave exposed conditions that characterize this biotope. 

Similarly, Undaria pinnatifida prefers sheltered conditions that are within its depth range (+1 to –4 m) and a low tidal flow, so like Sargassum it is unlikely that even in the shallow depths Undaria will out-compete or replace Laminaria hyperborea in this biotope due high degree of wave exposure. Therefore, resistance to Undaria or Sargassum is assessed as ‘High’, resilience as ‘High’, so sensitivity is ‘Not sensitive’. Overall, confidence is assessed as ‘Low’ due to evidence of variation and the site-specific nature of competition between native kelps 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

Galls on the blade of Laminaria hyperborea and spot disease are associated with the endophyte Streblonema sp. although the causal agent is unknown (bacteria, virus or endophyte). Resultant damage to the blade and stipe may increase losses in storms. The endophyte inhibits spore production and therefore recruitment and recoverability (Lein et al., 1991).

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

Christie et al. (1998) observed Laminaria hyperborea habitat regeneration following commercial Laminaria hyperborea trawling in south Norway. Within the study area trawling removed all large canopy-forming adult Laminaria hyperborea, however sub-canopy recruits were unaffected. Within 2-3 years of harvesting a new canopy had formed 1 m off the seabed. The associated holdfast communities recovered in 6 years however the epiphytic stipe community did not fully recover within the same time period. Christie et al., (1998) suggested that kelp habitats were relatively resistant to direct disturbance of Laminaria hyperborea canopy.

Recurrent disturbance occurring at a smaller time scale than the recovery period of 2-6 years (stated above) could extend recovery time. Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of “urchin barrens”, following removal of urchins. The substratum was initially colinized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community.

Following disturbance or in areas were recurrent rapid disturbance occurs Laminaria hyperborea recruitment could also be affected by interspecifc competitive interactions with Invasive Non Indigenous Species or ephemeral algal species (Brodie et al., 2014; Smale et al., 2013), however evidence for this is limited and thus not included within this assessment.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.

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/accidental removal of Laminaria hyperborea from extraction of other marine resources, e.g. fisheries or aggregates, is likely to cause similar effects to that of direct harvesting of Laminaria hyperborea; hence the same evidence has been used for both pressure assessments.

Christie et al. (1998) observed Laminaria hyperborea habitat regeneration following commercial Laminaria hyperborea trawling in south Norway. Within the study area trawling removed all large canopy-forming adult Laminaria hyperborea, however sub-canopy recruits were unaffected. Within 2-6years of harvesting a new canopy had formed 1m off the seabed. The associated holdfast communities recovered in 6 years however the epiphytic stipe community did not fully recover within the same time period. Christie et al., (1998) suggested that kelp habitats were relatively resistant to direct disturbance of Laminaria hyperborea canopy.

Recurrent disturbance occurring at a smaller time scale than the recovery period of 2-6 years (stated above) could extend recovery time. Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of “urchin barrens”, following removal of urchins. The substratum was initially colinized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community.

Following disturbance or in areas were recurrent rapid disturbance occurs Laminaria hyperborea recruitment could also be affected by interspecifc competitive interactions with Invasive Non Indigenous Species or ephemeral algal species (Brodie et al., 2014; Smale et al., 2013), however evidence for this is limited and thus not included within this assessment.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.