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). As temperatures increase, populations found towards the upper limit of their temperature range may be adversely affected by warming as physiological thresholds are exceeded (Wiens, 2016). Thermal stress can lead to mortality and consequent population-level effects, such as decreased abundance, altered size structure, local extinction and range contractions (Smale, 2020). 

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). Therefore, Laminaria hyperborea recruitment could be impaired at a sustained temperature increase 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 ochroleuca was 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).

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 the species being lost from approximately 30% of the coastline of the UK.

Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic, is found as far south as New York State, USA. At its southern distribution in New York, temperatures can regularly reach ≥20°C for six weeks or more during summer months (Gerard & Du Bois, 1988).

Saccharina latissima has an optimal growth temperature between 10- 15°C, with growth reducing by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C (Bolton & Lüning, 1982). The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima growth (Müller et al., 2009). Temperature is an environmental factor controlling the development of the microscopic stages of Saccharina latissima, with crucial changes in survival, growth, and gametogenesis occurring within a few degrees of its upper thermal limits (Redmond, 2013). The optimal germination temperature for Saccharina latissima is between 2°C and 12°C, with gametophyte survival between 23-25°C (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013). Park et al. (2017) observed reductions in the percentage of sporophytes produced at 15°C when compared to values produced at 5°C and 10°C. 

In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed that sporophytes of Saccharina latissima that were regularly exposed to ≥20°C tolerated these high temperatures, whereas sporophytes from other populations that rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C.

Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway, where community structure has shifted from Saccharina latissima forests to communities dominated by filamentous macroalgae (Moy & Christie, 2012). In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. High mortality occurred from August-November each year. In 2008, only six of the seventeen original transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region had regularly exceeded 20°C and so had the duration at which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

Assis et al. (2018) predicted that, under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from their southern-most locations, with a predicted loss of Saccharina latissima from the southwest coast of the UK. 

Chorda filum is a cold boreal species, with a wide geographical distribution along the Arctic, Atlantic and Pacific coasts (www.obis.org).  Chorda filum has been reported to have relatively good growth between the temperatures of 5-15°C. However, a temperature of 20°C reduced or inhibited growth (Kawai et al., 2000). Chorda filum has an upper temperature tolerance of 26-28°C (Dieck, 1993). Although, Lüning (1980) observed that Chorda filum could not reproduce between the temperatures of 15-20°C but found that sporophytes could tolerate ≤26 °C. In addition, Lüning (1990) reported that gametogenesis occurred at temperatures between 5°C and 10°C in the autumn months. 

Many of the red algae species associated with the understorey turf can tolerate warm water temperatures. Corallina officinalis may tolerate between -4 and 28°C (Lüning, 1990), although when Colthart & Johansen (1973) exposed this species to a number of different temperatures, they found that growth was maintained at 18°C and ceased at 25°C. Abrupt temperature changes (10°C in California, Seapy & Littler 1984; 4.8 to 8.5°C, Hawkins & Hartnoll, 1985) resulted in dramatic declines. However, in both cases recovery was rapid, suggesting that the crustose bases survived. 

Ulva sp. are distributed globally (Guiry & Guiry, 2015) and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva sp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days.  Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA.  Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30°C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).

Spirobranchus triqueter occurs as far south as the Mediterranean. Therefore, it will be subject to a wider range of temperatures than experienced in the British Isles (www.obis.org). Castric-Fey (1983) found that animals settling during spring showed the best growth rate and the best larval settlement occurred in the summer months. Therefore, it is assumed that Spirobranchus triqueter has some tolerance to increased temperatures. 

Sensitivity assessment. UK populations of Saccharina latissima are found in the middle of the species distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise. However, Laminaria hyperborea is already growing at suboptimal temperatures in the southern UK, based on evidence of decreased productivity comparative to Scotland (Pessarrodona et al., 2018; Smale et al., 2020b), and predictions have estimated Laminaria hyperborean to be lost from the UK by 2100 as a result of warming (Brodie et al., 2014). 

Under the middle emission scenario, a rise of 3°C could lead to maximum summer high temperatures of 22°C in the south of the UK. Populations of Saccharina latissima and the understorey community of mixed red seaweeds may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C. However, 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 sizes 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 and extreme emission scenario where sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century Saccharina latissima and Laminaria hyperborea is likely to be lost from southern England. The 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 even more is projected to be lost. Populations of Laminaria hyperborea that remain around the UK are predicted to become less productive. Therefore, under these scenarios, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very Low’. Therefore, this biotope 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). As temperatures increase, populations found towards the upper limit of their temperature range may be adversely affected by warming as physiological thresholds are exceeded (Wiens, 2016). Thermal stress can lead to mortality and consequent population-level effects, such as decreased abundance, altered size structure, local extinction and range contractions (Smale, 2020). 

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). Therefore, Laminaria hyperborea recruitment could be impaired at a sustained temperature increase 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 ochroleuca was 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).

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 the species being lost from approximately 30% of the coastline of the UK.

Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic, is found as far south as New York State, USA. At its southern distribution in New York, temperatures can regularly reach ≥20°C for six weeks or more during summer months (Gerard & Du Bois, 1988).

Saccharina latissima has an optimal growth temperature between 10- 15°C, with growth reducing by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C (Bolton & Lüning, 1982). The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima growth (Müller et al., 2009). Temperature is an environmental factor controlling the development of the microscopic stages of Saccharina latissima, with crucial changes in survival, growth, and gametogenesis occurring within a few degrees of its upper thermal limits (Redmond, 2013). The optimal germination temperature for Saccharina latissima is between 2°C and 12°C, with gametophyte survival between 23-25°C (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013). Park et al. (2017) observed reductions in the percentage of sporophytes produced at 15°C when compared to values produced at 5°C and 10°C. 

In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed that sporophytes of Saccharina latissima that were regularly exposed to ≥20°C tolerated these high temperatures, whereas sporophytes from other populations that rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C.

Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway, where community structure has shifted from Saccharina latissima forests to communities dominated by filamentous macroalgae (Moy & Christie, 2012). In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. High mortality occurred from August-November each year. In 2008, only six of the seventeen original transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region had regularly exceeded 20°C and so had the duration at which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

Assis et al. (2018) predicted that, under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from their southern-most locations, with a predicted loss of Saccharina latissima from the southwest coast of the UK. 

Chorda filum is a cold boreal species, with a wide geographical distribution along the Arctic, Atlantic and Pacific coasts (www.obis.org).  Chorda filum has been reported to have relatively good growth between the temperatures of 5-15°C. However, a temperature of 20°C reduced or inhibited growth (Kawai et al., 2000). Chorda filum has an upper temperature tolerance of 26-28°C (Dieck, 1993). Although, Lüning (1980) observed that Chorda filum could not reproduce between the temperatures of 15-20°C but found that sporophytes could tolerate ≤26 °C. In addition, Lüning (1990) reported that gametogenesis occurred at temperatures between 5°C and 10°C in the autumn months. 

Many of the red algae species associated with the understorey turf can tolerate warm water temperatures. Corallina officinalis may tolerate between -4 and 28°C (Lüning, 1990), although when Colthart & Johansen (1973) exposed this species to a number of different temperatures, they found that growth was maintained at 18°C and ceased at 25°C. Abrupt temperature changes (10°C in California, Seapy & Littler 1984; 4.8 to 8.5°C, Hawkins & Hartnoll, 1985) resulted in dramatic declines. However, in both cases recovery was rapid, suggesting that the crustose bases survived. 

Ulva sp. are distributed globally (Guiry & Guiry, 2015) and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva sp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days.  Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA.  Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30°C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).

Spirobranchus triqueter occurs as far south as the Mediterranean. Therefore, it will be subject to a wider range of temperatures than experienced in the British Isles (www.obis.org). Castric-Fey (1983) found that animals settling during spring showed the best growth rate and the best larval settlement occurred in the summer months. Therefore, it is assumed that Spirobranchus triqueter has some tolerance to increased temperatures. 

Sensitivity assessment. UK populations of Saccharina latissima are found in the middle of the species distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise. However, Laminaria hyperborea is already growing at suboptimal temperatures in the southern UK, based on evidence of decreased productivity comparative to Scotland (Pessarrodona et al., 2018; Smale et al., 2020b), and predictions have estimated Laminaria hyperborean to be lost from the UK by 2100 as a result of warming (Brodie et al., 2014). 

Under the middle emission scenario, a rise of 3°C could lead to maximum summer high temperatures of 22°C in the south of the UK. Populations of Saccharina latissima and the understorey community of mixed red seaweeds may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C. However, 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 sizes 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 and extreme emission scenario where sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century Saccharina latissima and Laminaria hyperborea is likely to be lost from southern England. The 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 even more is projected to be lost. Populations of Laminaria hyperborea that remain around the UK are predicted to become less productive. Therefore, under these scenarios, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very Low’. Therefore, this biotope 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). As temperatures increase, populations found towards the upper limit of their temperature range may be adversely affected by warming as physiological thresholds are exceeded (Wiens, 2016). Thermal stress can lead to mortality and consequent population-level effects, such as decreased abundance, altered size structure, local extinction and range contractions (Smale, 2020). 

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). Therefore, Laminaria hyperborea recruitment could be impaired at a sustained temperature increase 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 ochroleuca was 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).

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 the species being lost from approximately 30% of the coastline of the UK.

Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic, is found as far south as New York State, USA. At its southern distribution in New York, temperatures can regularly reach ≥20°C for six weeks or more during summer months (Gerard & Du Bois, 1988).

Saccharina latissima has an optimal growth temperature between 10- 15°C, with growth reducing by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C (Bolton & Lüning, 1982). The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima growth (Müller et al., 2009). Temperature is an environmental factor controlling the development of the microscopic stages of Saccharina latissima, with crucial changes in survival, growth, and gametogenesis occurring within a few degrees of its upper thermal limits (Redmond, 2013). The optimal germination temperature for Saccharina latissima is between 2°C and 12°C, with gametophyte survival between 23-25°C (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013). Park et al. (2017) observed reductions in the percentage of sporophytes produced at 15°C when compared to values produced at 5°C and 10°C. 

In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed that sporophytes of Saccharina latissima that were regularly exposed to ≥20°C tolerated these high temperatures, whereas sporophytes from other populations that rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C.

Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway, where community structure has shifted from Saccharina latissima forests to communities dominated by filamentous macroalgae (Moy & Christie, 2012). In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. High mortality occurred from August-November each year. In 2008, only six of the seventeen original transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region had regularly exceeded 20°C and so had the duration at which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

Assis et al. (2018) predicted that, under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from their southern-most locations, with a predicted loss of Saccharina latissima from the southwest coast of the UK. 

Chorda filum is a cold boreal species, with a wide geographical distribution along the Arctic, Atlantic and Pacific coasts (www.obis.org).  Chorda filum has been reported to have relatively good growth between the temperatures of 5-15°C. However, a temperature of 20°C reduced or inhibited growth (Kawai et al., 2000). Chorda filum has an upper temperature tolerance of 26-28°C (Dieck, 1993). Although, Lüning (1980) observed that Chorda filum could not reproduce between the temperatures of 15-20°C but found that sporophytes could tolerate ≤26 °C. In addition, Lüning (1990) reported that gametogenesis occurred at temperatures between 5°C and 10°C in the autumn months. 

Many of the red algae species associated with the understorey turf can tolerate warm water temperatures. Corallina officinalis may tolerate between -4 and 28°C (Lüning, 1990), although when Colthart & Johansen (1973) exposed this species to a number of different temperatures, they found that growth was maintained at 18°C and ceased at 25°C. Abrupt temperature changes (10°C in California, Seapy & Littler 1984; 4.8 to 8.5°C, Hawkins & Hartnoll, 1985) resulted in dramatic declines. However, in both cases recovery was rapid, suggesting that the crustose bases survived. 

Ulva sp. are distributed globally (Guiry & Guiry, 2015) and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva sp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days.  Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA.  Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30°C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).

Spirobranchus triqueter occurs as far south as the Mediterranean. Therefore, it will be subject to a wider range of temperatures than experienced in the British Isles (www.obis.org). Castric-Fey (1983) found that animals settling during spring showed the best growth rate and the best larval settlement occurred in the summer months. Therefore, it is assumed that Spirobranchus triqueter has some tolerance to increased temperatures. 

Sensitivity assessment. UK populations of Saccharina latissima are found in the middle of the species distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise. However, Laminaria hyperborea is already growing at suboptimal temperatures in the southern UK, based on evidence of decreased productivity comparative to Scotland (Pessarrodona et al., 2018; Smale et al., 2020b), and predictions have estimated Laminaria hyperborean to be lost from the UK by 2100 as a result of warming (Brodie et al., 2014). 

Under the middle emission scenario, a rise of 3°C could lead to maximum summer high temperatures of 22°C in the south of the UK. Populations of Saccharina latissima and the understorey community of mixed red seaweeds may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C. However, 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 sizes 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 and extreme emission scenario where sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century Saccharina latissima and Laminaria hyperborea is likely to be lost from southern England. The 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 even more is projected to be lost. Populations of Laminaria hyperborea that remain around the UK are predicted to become less productive. Therefore, under these scenarios, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very Low’. Therefore, this biotope 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).

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

Under experimental conditions, Nepper-Davidson et al. (2019) exposed a northern (Denmark) population of Saccharina latissima to a simulated three-week heatwave of three different intensities; 18, 21 and 24°C. When exposed to heatwaves of 18 and 21°C there was a decrease in photosynthesis and growth. When a 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, so the experiment was terminated (Nepper-Davidsen et al., 2019). 

Simonson et al. (2015) investigated the impacts of four temperature treatments (11°C, 14°C, 18°C & 21°C) on Saccharina latissima tissue over three weeks. Histological analysis showed temperature mediated tissue damage, including holes, splitting of the medulla, damage to the meristoderm and loss of differentiation between tissue layers at temperatures between 14-21°C. 

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.

Chorda filum has been reported to have an upper temperature tolerance of 26-28°C (Dieck, 1993), however, temperatures of >20°C can reduce or inhibited growth (Kawai et al., 2000), and temperatures of >15°C can inhibit reproduction (Lüning, 1980). Therefore, marine heatwaves could potentially have an impact on the growth and survival of Chorda filum. In addition, marine heatwaves are highly likely to inhibit reproduction and reduce recruitment of the species, depending on the timing of the heatwave. However, no evidence of the effects of marine heatwaves on Chorda filum was found. 

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 and Saccharina latissima are unlikely to survive a heatwave of this magnitude and likely to suffer severe mortality in the south. Although, In Scotland, where a significant portion of these biotopes occur, temperatures are not predicted to rise above 20°C, and therefore, Laminaria hyperborea and Saccharina latissima are likely to survive a heatwave of this magnitude.  However, the southern assemblages are likely to be impacted therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ This biotope IR.MIR.KT.XKT is assessed as having ‘High’ sensitivity to marine heatwaves under the middle emission scenario. 

Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C in southern England. Laminaria hyperborea and Saccharina latissima are 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 ‘None’. As a further heatwave is likely to affect this habitat before full recovery (under the pressure benchmark definition), resilience has been assessed as ‘Very low.’ Therefore, this biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the high emission scenario.

Marine heatwaves (middle)

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

Evidence

Marine heatwaves 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).

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

Under experimental conditions, Nepper-Davidson et al. (2019) exposed a northern (Denmark) population of Saccharina latissima to a simulated three-week heatwave of three different intensities; 18, 21 and 24°C. When exposed to heatwaves of 18 and 21°C there was a decrease in photosynthesis and growth. When a 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, so the experiment was terminated (Nepper-Davidsen et al., 2019). 

Simonson et al. (2015) investigated the impacts of four temperature treatments (11°C, 14°C, 18°C & 21°C) on Saccharina latissima tissue over three weeks. Histological analysis showed temperature mediated tissue damage, including holes, splitting of the medulla, damage to the meristoderm and loss of differentiation between tissue layers at temperatures between 14-21°C. 

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.

Chorda filum has been reported to have an upper temperature tolerance of 26-28°C (Dieck, 1993), however, temperatures of >20°C can reduce or inhibited growth (Kawai et al., 2000), and temperatures of >15°C can inhibit reproduction (Lüning, 1980). Therefore, marine heatwaves could potentially have an impact on the growth and survival of Chorda filum. In addition, marine heatwaves are highly likely to inhibit reproduction and reduce recruitment of the species, depending on the timing of the heatwave. However, no evidence of the effects of marine heatwaves on Chorda filum was found. 

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 and Saccharina latissima are unlikely to survive a heatwave of this magnitude and likely to suffer severe mortality in the south. Although, In Scotland, where a significant portion of these biotopes occur, temperatures are not predicted to rise above 20°C, and therefore, Laminaria hyperborea and Saccharina latissima are likely to survive a heatwave of this magnitude.  However, the southern assemblages are likely to be impacted therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ This biotope IR.MIR.KT.XKT is assessed as having ‘High’ sensitivity to marine heatwaves under the middle emission scenario. 

Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C in southern England. Laminaria hyperborea and Saccharina latissima are 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 ‘None’. As a further heatwave is likely to affect this habitat before full recovery (under the pressure benchmark definition), resilience has been assessed as ‘Very low.’ Therefore, this biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the high emission scenario.

Ocean acidification (high)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005), with it expected to drop 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 HCO₃to 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).

Under experimental CO₂ enrichment at levels expected by the end of this century, germination rates in Saccharina latissima were the same as control samples but gametophyte size increased, suggesting a benefit for juvenile stages of this species (Roleda et al., 2012). Nunes et al. (2015) found that experimental exposure of adult Saccharina latissima to enhanced CO₂ led to an increase in net primary production, while Gordillo et al. (2015) found that enhanced CO₂ led to increased photosynthesis and growth. In contrast, Iñiguez et al. (2016) found no increase in carbon fixation under elevated CO₂ conditions. Although contrasting in findings, these studies show that ocean acidification will not negatively impact Saccharina latissima.

Corallina officinalis is a highly calcified, erect, red algae. Results of experimental CO₂ enrichment suggest that this species could be significantly negatively affected by future ocean acidification. Hofmann et al. (2012) found that growth and photosynthesis decreased as a result of a 0.3 unit decrease in pH. Further investigation showed that skeletal CaCO₃ decreased with increasing CO₂ at levels expected for both the middle emission and high emission scenarios, although this decrease was small (< 2%) (Hofmann et al., 2013). Yildiz et al. (2013) showed that although CaCO₃ decreased in Corallina officinalis as a result of ocean acidification, photosynthesis increased. When ocean acidification was combined with an increase in UV radiation, which led to an increase in growth rate. They summarised that a decrease in CaCO₃ content may not be negative but may lead to this species absorbing and using light differently. Brodie et al. (2014) reported that Corallina species were more resilient to ocean acidification than other calcified algae species, although competition from flesh algal species that benefit from high CO₂ may indirectly cause the loss of calcified species from biotopes. Similarly, observations have indicated Corallinales to be adversely affected at locations where CO₂ gradients occur naturally, with evidence of Corallinales being outcompeted by heterokont algae at Mediterranean CO₂ seeps (Martin & Hall-Spencer, 2017).  

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 and Saccharina latissima are 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 HCO₃to 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).

Under experimental CO₂ enrichment at levels expected by the end of this century, germination rates in Saccharina latissima were the same as control samples but gametophyte size increased, suggesting a benefit for juvenile stages of this species (Roleda et al., 2012). Nunes et al. (2015) found that experimental exposure of adult Saccharina latissima to enhanced CO₂ led to an increase in net primary production, while Gordillo et al. (2015) found that enhanced CO₂ led to increased photosynthesis and growth. In contrast, Iñiguez et al. (2016) found no increase in carbon fixation under elevated CO₂ conditions. Although contrasting in findings, these studies show that ocean acidification will not negatively impact Saccharina latissima.

Corallina officinalis is a highly calcified, erect, red algae. Results of experimental CO₂ enrichment suggest that this species could be significantly negatively affected by future ocean acidification. Hofmann et al. (2012) found that growth and photosynthesis decreased as a result of a 0.3 unit decrease in pH. Further investigation showed that skeletal CaCO₃ decreased with increasing CO₂ at levels expected for both the middle emission and high emission scenarios, although this decrease was small (< 2%) (Hofmann et al., 2013). Yildiz et al. (2013) showed that although CaCO₃ decreased in Corallina officinalis as a result of ocean acidification, photosynthesis increased. When ocean acidification was combined with an increase in UV radiation, which led to an increase in growth rate. They summarised that a decrease in CaCO₃ content may not be negative but may lead to this species absorbing and using light differently. Brodie et al. (2014) reported that Corallina species were more resilient to ocean acidification than other calcified algae species, although competition from flesh algal species that benefit from high CO₂ may indirectly cause the loss of calcified species from biotopes. Similarly, observations have indicated Corallinales to be adversely affected at locations where CO₂ gradients occur naturally, with evidence of Corallinales being outcompeted by heterokont algae at Mediterranean CO₂ seeps (Martin & Hall-Spencer, 2017).  

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 and Saccharina latissima are 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). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

This biotope (IR.MIR.KT.XKTX) occurs on sheltered, very sheltered and extremely sheltered infralittoral bedrock, boulders and cobbles (JNCC, 2015). Light availability and water turbidity are principal 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. 

Understanding how sea-level rise will affect tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. 

Although the distribution of Laminaria hyperborea is positivity related to wave exposure (Pedersen et al., 2012), and Saccharina latissima is abundant at both turbid and deep sites (Gerard, 1990), this biotope (IR.MIR.KT.XKTX) occurs at wave sheltered sites, so that an increase in wave exposure (e.g. to moderate or higher) is likely to result in modification of the community and loss of the biotope. 

Spirobranchus triqueter has been noted to occur in areas with very sheltered to exposed water flow rates (Price et al., 1980). Wood (1988) observed Spirobranchus sp. in strong tidal streams and Hiscock (1983) found that in strong tidal streams or strong wave action where abrasion occurs, fast-growing species such as Spirobranchus triqueter occur.

Corallina officinalis is an understorey, shade-tolerant algae. Reduced light attenuation is unlikely to affect Corallina officinalis except at the deepest extent of its distribution in subtidal populations. However, reduced light will probably reduce growth rates. Corallina officinalis thrives in exposed conditions where it may replace fucoids, although it is also found in sheltered conditions. In exposed conditions, it may grow as a cushion-like or compact turf (Irvine & Chamberlain 1994; Dommasnes 1968).

Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum on which Chorda filum grows, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. 

Sensitivity assessment. An increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope, which is already constrained to shallow waters through limits to light availability. The biotope is recorded from 0 to 10 m in depth (JNCC, 2015). 

This biotope (IR.MIR.KT.XKTX) may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. 

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 (IR.MIR.KT.XKTX) can occur from 0-10 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 may be ‘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). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

This biotope (IR.MIR.KT.XKTX) occurs on sheltered, very sheltered and extremely sheltered infralittoral bedrock, boulders and cobbles (JNCC, 2015). Light availability and water turbidity are principal 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. 

Understanding how sea-level rise will affect tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. 

Although the distribution of Laminaria hyperborea is positivity related to wave exposure (Pedersen et al., 2012), and Saccharina latissima is abundant at both turbid and deep sites (Gerard, 1990), this biotope (IR.MIR.KT.XKTX) occurs at wave sheltered sites, so that an increase in wave exposure (e.g. to moderate or higher) is likely to result in modification of the community and loss of the biotope. 

Spirobranchus triqueter has been noted to occur in areas with very sheltered to exposed water flow rates (Price et al., 1980). Wood (1988) observed Spirobranchus sp. in strong tidal streams and Hiscock (1983) found that in strong tidal streams or strong wave action where abrasion occurs, fast-growing species such as Spirobranchus triqueter occur.

Corallina officinalis is an understorey, shade-tolerant algae. Reduced light attenuation is unlikely to affect Corallina officinalis except at the deepest extent of its distribution in subtidal populations. However, reduced light will probably reduce growth rates. Corallina officinalis thrives in exposed conditions where it may replace fucoids, although it is also found in sheltered conditions. In exposed conditions, it may grow as a cushion-like or compact turf (Irvine & Chamberlain 1994; Dommasnes 1968).

Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum on which Chorda filum grows, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. 

Sensitivity assessment. An increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope, which is already constrained to shallow waters through limits to light availability. The biotope is recorded from 0 to 10 m in depth (JNCC, 2015). 

This biotope (IR.MIR.KT.XKTX) may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. 

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 (IR.MIR.KT.XKTX) can occur from 0-10 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 may be ‘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). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

This biotope (IR.MIR.KT.XKTX) occurs on sheltered, very sheltered and extremely sheltered infralittoral bedrock, boulders and cobbles (JNCC, 2015). Light availability and water turbidity are principal 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. 

Understanding how sea-level rise will affect tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. 

Although the distribution of Laminaria hyperborea is positivity related to wave exposure (Pedersen et al., 2012), and Saccharina latissima is abundant at both turbid and deep sites (Gerard, 1990), this biotope (IR.MIR.KT.XKTX) occurs at wave sheltered sites, so that an increase in wave exposure (e.g. to moderate or higher) is likely to result in modification of the community and loss of the biotope. 

Spirobranchus triqueter has been noted to occur in areas with very sheltered to exposed water flow rates (Price et al., 1980). Wood (1988) observed Spirobranchus sp. in strong tidal streams and Hiscock (1983) found that in strong tidal streams or strong wave action where abrasion occurs, fast-growing species such as Spirobranchus triqueter occur.

Corallina officinalis is an understorey, shade-tolerant algae. Reduced light attenuation is unlikely to affect Corallina officinalis except at the deepest extent of its distribution in subtidal populations. However, reduced light will probably reduce growth rates. Corallina officinalis thrives in exposed conditions where it may replace fucoids, although it is also found in sheltered conditions. In exposed conditions, it may grow as a cushion-like or compact turf (Irvine & Chamberlain 1994; Dommasnes 1968).

Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum on which Chorda filum grows, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. 

Sensitivity assessment. An increase in sea level height of 50, 70 and 107 cm could have severe repercussions for the extent of this biotope, which is already constrained to shallow waters through limits to light availability. The biotope is recorded from 0 to 10 m in depth (JNCC, 2015). 

This biotope (IR.MIR.KT.XKTX) may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. 

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 (IR.MIR.KT.XKTX) can occur from 0-10 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 may be ‘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., 1988b).  Above 17°C Laminaria hyperborea 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., 1998b).

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

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

IR.MIR.KT.XKT & IR.MIR.KT.XKTX 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).

Sensitivity assessment. A 2°C increase for one year may impair Laminaria hyperborea recruitment processes and Saccharina latissima sporophyte growth but otherwise not affect the characterizing species.  A 5°C increase for one month combined with high UK summer temperatures is likely to affect Laminaria hyperborea sporophyte growth. Saccharina latissima populations that are not acclimated to >20°C may incur mass mortality within 3 weeks of exposure. Resistance has been assessed as ‘Low’, to reflect the potential mass mortality effect of sudden temperature increases on Saccharina latissima, and resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. 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 these ranges (Birkett et al., 1988b). Saccharina lattissima has a lower temperature threshold for sporophyte growth at 0°C (Lüning, 1990). Subtidal red algae can survive at temperatures between -2 °C and 18-23 °C (Lüning, 1990; Kain & Norton, 1990).

Sensitivity assessment. Both Laminaria hyperborea and Saccharina latissima have northern distributions (Birkett et al., 1998b). An acute or long-term decrease in temperature within the UK, at the benchmark level, is not likely to have any dramatic effect on biotope structure. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not sensitive’.

Salinity increase (local)

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

Evidence

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 and growth rates are likely to be affected by periodic salinity stress. Birkett et al. (1998b) 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.

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

Sensitivity assessment. The evidence suggests that Saccharina latissima can tolerate exposure to hypersaline conditions of ≥40‰. However, optimal salinities for Laminaria hyperborea growth are assumed to be 30-35 psu. Hence, increases in salinity to >40‰ may cause mortality for Laminaria hyperborea. Resistance has been assessed as ‘Low’, resilience as ‘Medium’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Medium’.

Salinity decrease (local)

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

Evidence

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 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. 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.

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

Sensitivity assessment. IR.MIR.KT.XKT & IR.MIR.KT.XKTX are recorded in both full and variable salinity (18-40) A decrease in one MNCR salinity scale to ‘Reduced' salinity (18-30 psu) may result in a decrease of Laminaria hyperborea sporophyte growth and Saccharina latissima. Resistance has been assessed as ‘Low’ and resilience as ‘Medium’. Therefore, the sensitivity of this biotope to a decrease 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

Peteiro & Freire (2013) measured Saccharina latissima growth from 2 sites, the first had maximal water velocities of 0.3 m/sec and the second 0.1 m/sec. At site 1 Saccharina latissima had significantly larger biomass than at site 2 (16 kg/m to 12 kg/m respectively). Peteiro & Freire (2013) suggested that faster water velocities were beneficial to Saccharina latissima growth. However, Gerard & Mann (1979) found Saccharina latissima productivity is reduced in moderately strong tidal streams (≤1m/sec) when compared to weak tidal streams (<0.5 m/sec). Despite these results where the substratum is unstable Saccharina lattissima can become the dominant canopy-forming kelp within tide swept conditions, as in IR.MIR.KT.XKTX (Connor et al., 2004).

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 & 0.3 m/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.

Sensitivity assessment. IR.MIR.KT.XKT & IR.MIR.KT.XKTX are predominantly recorded from “Moderately strong” tidal streams (0.5-1.5 m/sec). Due to the range of tidal velocities that these biotopes are recorded within a change in the flow of between 0.1-0.2 m/sec would likely have no significant effect on Laminaria hyperborea or Saccharina latissima growth or productivity. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’ at the benchmark level.

Emergence regime changes

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

Evidence

IR.MIR.KT.XKT & IR.MIR.KT.XKTX are shallow water biotopes, recorded predominantly from 0-5 m BCD.  An increase in emergence will result in an increased risk of desiccation and mortality of the dominant kelp species (Laminaria hyperborea & Saccharina latissima). Removal of canopy-forming kelps has also been shown to increase desiccation and mortality of the understorey macroalgae (Hawkins & Harkin, 1985). Several mobile species such as sea urchins, brittle stars and feather stars are likely to move away. However, providing that suitable substrata are present, the biotope is likely to re-establish further down the shore within a similar emergence regime to that which existed previously.

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

Wave exposure changes (local)

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

Evidence

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 to 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 & 2 m at the exposed and sheltered sites. Maximal water velocity (Velrms) was 0.6 & 0.3 m/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.

However, Pedersen et al. (2012) observed Laminaria hyperborea biomass, productivity and density increased with greater wave exposure.  At low wave exposure, Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates. At low wave exposure, high epiphytic loading on Laminaria hyperborea was suggested to impair photosynthesis, nutrient uptake, and increase the drag of the host Laminaria hyperborea during extreme storm events. The morphology of kelp stipe and blades vary in different water flows and wave exposures 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 et al., 1998). In addition, the lamina becomes narrower and thinner in strong currents (Sjøtun & Fredriksen, 1995).

Saccharina latissima is rarely found at wave exposed sites (Birkett et al., 1998b). Saccharina latissima, if present, develops a short thick stipe and a short, narrow and tightly wrinkled blade (Birkett et al., 1998b).

Sensitivity assessment. Wave exposure is one of the principal defining features of kelp biotopes, and changes in wave exposure are likely to alter the relative abundance of the kelp species, understorey community and hence the biotope. IR.MIR.KT.XKT & IR.MIR.KT.XKTX are recorded from wave sheltered sites so that an increase in wave exposure (e.g. to moderate or higher) is likely to result in modification of the community and loss of the biotope. However, a change in near shore significant wave height of 3-5% is unlikely to have any significant effect on IR.MIR.KT.XKT & IR.MIR.KT.XKTX. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not Sensitive’ at the benchmark level.

Transition elements & organo-metal contamination

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

Evidence

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. 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.

Sporophytes of Saccharina latissima have a low intolerance to heavy metals, but the early life stages are more intolerant. The effects of copper, zinc and mercury on Saccharina latissima have been investigated by Thompson & Burrows (1984). They observed that the growth of sporophytes was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l. Little is known about the effects of heavy metals on echinoderms. Bryan (1984) reported that early work had shown that echinoderm larvae were intolerant of heavy metals, e.g. the intolerance of larvae of Paracentrotus lividus to copper (Cu) had been used to develop a water quality assessment. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu). Sea-urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Taken together with the findings of Gomez & Miguez-Rodriguez (1999) above it is likely that echinoderms are intolerant of heavy metal contamination.

However, this pressure is Not assessed.

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 and Saccharina latissima fronds, being predominantly subtidal, would not come into contact with freshly released oil but only to sinking emulsified oil and oil adsorbed onto particles (Birkett et al., 1998b). 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 hyperborea 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 to chemical contamination.

Synthetic compound contamination

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

Evidence

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

O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Saccharina latissima has also been found to be sensitive to antifouling compounds. Johansson (2009) exposed samples of Saccharina latissima to several antifouling compounds, observing chlorothalonil, DCOIT, dichlofluanid and tolylfluanid inhibited photosynthesis. Exposure to Chlorothalonil and tolylfluanid was also found to continue inhibiting oxygen evolution after exposure had finished, and may cause irreversible damage.

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; Johansson, 2009). Laminaria hyperborea survived within >55 m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater than five 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 to 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 was found

Introduction of other substances

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

Evidence

This pressure is Not assessed.

De-oxygenation

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

Evidence

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

Sensitivity Assessment. Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. In addition, IR.MIR.KT.XKT & IR.MIR.KT.XKTX are tide swept so that any deoxygenation would be highly localised and transient. Resistance has been assessed as ‘High’, Resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Nutrient enrichment

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

Evidence

Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, UK when compared to other sites along the east coast of Scotland. At St Andrews, nitrate levels were 20.22µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Salmon farms, where elevated ammonium can be readily absorbed.  Read et al. (1983) reported after the installation of a new sewage treatment  works that reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however, 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment, however, could also be time dependent.

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

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic 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). Increases 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.

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

Organic enrichment

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

Evidence

Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, UK when compared to other sites along the east coast of Scotland. At St Andrews, nitrate levels were 20.22 µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Norwegian Salmon farms, where elevated ammonium can be readily absorbed.  Read et al. (1983) reported after the installation of a new sewage treatment  works that reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. Within 3 years of the experiment no significant effect was observed in the communities, however, 4-5 years into the experiment a shift occurred from perennials to ephemeral algae occurred. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment, however, could also be time dependent.

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

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic 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).  Increases 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.

Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore, organic enrichment may denude the associated community. Resistance has therefore been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ’Low’.

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

If rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which kelp species would not be able to tolerate (Birkett et al., 1998b). 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

Low-level disturbances (e.g. solitary anchors) are unlikely to cause harm to the biotope as a whole, due to the impact’s small footprint.  Commercial Laminaria hyperborea trawling occurs in Norway (see resilience). Trawling typically removes all large canopy-forming sporophytes (Svendsen, 1972; Christie et al., 1998). Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al., 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to in/direct harvesting or abrasion is limited.

Sensitivity assessment. Abrasion by passing trawls or harvesting of macroalgae is likely to remove a large proportion of the kelp biomass.  However, Saccharina latissima has been shown to be an early colonizer (Kain, 1967; Leinaas & Christie, 1996) with the potential to recover rapidly, whereas Laminaria hyperborea may take 2-6 and the associated community 7->10 years to recover (Birkett et al., 1998b). Therefore, resistance has been assessed as ‘None’, resilience as ‘Medium’, and sensitivity 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 substratum 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., 1998b). 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 or Saccharina latissima sporophytes but may affect holdfast fauna, gametophyte survival, interfere with zoospore settlement and therefore recruitment processes (Moy & Christie, 2012). Given the short life expectancy of Saccharina latissima (2-4 years-(Parke, 1948)), IR.MIR.KT.XKT & IR.MIR.KT.XKTX is likely to be dependent on annual Saccharina latissima recruitment (Moy & Christie, 2012). Given the microscopic size of the gametophyte, 5 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that kelp gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation and/or spore settlement.

IR.MIR.KT.XKT & IR.MIR.KT.XKTX are predominantly recorded in more than moderate tidal streams (>0.5 m/s), and deposited sediment is, therefore, likely to be removed within a few tidal cycles and effects likely to be transient.

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

Smothering and siltation rate changes (heavy)

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

Evidence

Smothering by sediment e.g. 30 cm material during a discrete event is unlikely to damage Laminaria hyperborea or Saccharina latissima sporophytes but may affect holdfast fauna, gametophyte survival, interfere with zoospore settlement and therefore recruitment processes (Moy & Christie, 2012). Given the short life expectancy of Saccharina latissima (2-4 years-(Parke, 1948)), IR.LIR.K.LhypSlat is likely to be dependent on annual recruitment (Moy & Christie, 2012). 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 by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within one month (Dieck, 1993). Resistance to this factor is likely to be lower during the peak periods of sporulation and/or spore settlement.

Within the heavy sediment deposition, pressure sediment retention within the host habitat is likely to be longer than that of the light deposition pressure, however, IR.MIR.KT.XKT & IR.MIR.KT.XKTX are predominantly recorded in more than moderate tidal streams (>0.5 m/s), and deposited sediment is, therefore, likely to be removed within a few tidal cycles and effects likely to be transient.

Sensitivity assessment. To reflect the increase in time the sediment may be retained during a heavy deposition of sediment resistance has been assessed as ‘Medium’, resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.

Litter

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

Evidence

Not assessed

Electromagnetic changes

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

Evidence

No evidence

Underwater noise changes

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

Evidence

Not relevant

Introduction of light or shading

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

Evidence

There is no evidence to suggest that anthropogenic light sources would affect Laminaria hyperborea or habitats. 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

No evidence

Introduction or spread of invasive non-indigenous species

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

Evidence

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

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

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

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

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

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

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

Undaria pinnatifida has a wide physiological niche meaning it can occur in both coastal and estuarine environments showing tolerance for varying salinities, turbidity, and siltation (Heiser et al., 2014; Epstein & Smale, 2018).  Undaria pinnatifida prefers sites sheltered with low wave exposure and weak tidal streams (Heiser et al., 2014; Epstein & Smale, 2018).  In natural habitats, Undaria pinnatifida was not recorded if the wave fetch was greater than 642 km but increased in abundance and cover in very sheltered sites (Epstein & Smale, 2018). In 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 Undaria pinnatifida. However, the results from their correlation study only showed that the species were not found together (pers. comm., Epstien 2021). Whereas, exclusion and succession experiments on reefs tell us that Laminaria spp. exclude Undaria pinnatifida, not the other way round. 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 restricted 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.

Epstein et al. (2019b) reported that Undaria pinnatifida biomass was negatively related to Saccharina latissima in both intertidal and subtidal habitats.  This was only statistically significant in subtidal habitats, which suggested that there was some competition between the two species (Epstein et al., 2019b).  Heiser et al. (2014) surveyed 17 sites within Plymouth Sound, UK, and found that Saccharina latissima was significantly more abundant at sites with Undaria pinnatifida with ca 5 Saccharina latissima individuals present per m², compared to ca 0.5 Saccharina latissima individuals per m² present at sites without Undaria pinnatifida.

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

In Plymouth Sound (UK), Epstein et al. (2019b) found that within its depth range (+1 to –4 m), Undaria pinnatifida co-existed with seven species of canopy-forming brown macroalgae, including Saccharina latissima and Laminaria hyperborea.  De Leij et al. (2017) found that natural habitats with dense native macroalgal canopies, such as Laminaria hyperborea 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 will not prevent invasion of Undaria pinnatifida as sporophytes were still recorded within dense Laminaria canopies, suggesting that canopy disturbance is not always required.

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

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

Sensitivity assessment.  The above evidence suggests that Undaria pinnatifida can co-exist with Saccharina latissima and Laminaria hyperborea.  For example, within natural habitats, it can co-exist with native kelp species within its depth range (-1 to 4 m), as shown in Plymouth Sound, UK.  A dense native kelp canopy may restrict or slow the proliferation of Undaria pinnatifida.  However, there has been 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 Saccharina latissima dominated biotope (IR.MIR.KT.LdigT) is found in the shallow sublittoral (0-10 m, JNCC, 2015) sheltered from wave action but structured by strong tidal streams. The evidence above suggests that Undaria prefers sheltered conditions, with low tidal flow.  It is unlikely to out-compete or replace Saccharina latissima under the physical conditions that characterize this biotope. 

However, Sargassum muticum prefers wave sheltered shallow sites in the sublittoral fringe and shallow infralittoral.  It was reported to out-compete and replace Saccharina latissima in the Limfjorden, and achieve maximum abundance at 1-4 m (Staehr et al., 2000; Engelen et al., 2015).  But Strong & Dring (2011) concluded that Sargassum was not a threat to Saccharina latissima in the Dorn, Strangford Lough where it coexisted and grew better in mixed stands.  Hence, competition with Sargassum is probably site-specific and dependent on local conditions. No evidence of the effects of Sargassum on Laminaria hyperborea beds was found.

Therefore, resistance is assessed as ‘Low’ to represent colonization by Sargassum of the shallow (0-5 m) examples of the biotope and the possible loss of Saccharina latissima.  Even if the two species co-exist, the invasion may result in a change in the classification of the biotope and the structure of the understorey macroalgae (Staehr et al., 2000).  Recovery after invasion by Sargassum, although rapid, would require direct intervention (removal).  Hence, resilience is probably ‘Very low’ so sensitivity is assessed as ‘High’.  Overall, confidence is assessed as ‘Low’ due to evidence of variation and site-specific nature of competition between native kelps and both Undaria pinnatifida and Sargassum muticum.

Introduction of microbial pathogens

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

Evidence

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

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

There has been recent commercial interest in Saccharina lattisima as a consumable called ‘sea vegetables’ (Birkett et al., 1998b). Laminaria hyperborea is also extracted on a commercial scale in southern Norway, primarily for alginate (Werner & Kraan, 2004).

Commercial Laminaria hyperborea trawling occurs in Norway, during which Christie et al. (1998) report all large canopy-forming sporophytes are removed, sub-canopy sporophytes and understorey community, however, remain intact. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al., 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to direct harvesting is limited.

Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘Medium’. Sensitivity has been 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 and Saccharina latissima is likely to cause similar effects to that of direct harvesting; as such the same evidence has been used for both pressure assessments. There has been recent commercial interest in Saccharina latissima as a consumable called ‘sea vegetable’’ (Birkett et al., 1998b). Laminaria hyperborea is also extracted on a commercial scale in southern Norway, primarily for alginates (Werner & Kraan, 2004).

Commercial Laminaria hyperborea trawling occurs in Norway, during which Christie et al. (1998) report all large canopy-forming sporophytes are removed, sub-canopy sporophytes and understorey community, however, remain intact. Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al., 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to direct harvesting is limited.

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