The Marine Life Information Network

Global warming (extreme)

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

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

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

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

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

Evidence

The distribution of seaweeds is defined climatically (Kain, 1979, Van Den Hoek, 1982, Breeman, 1990, Lüning, 1990). Northern boundaries are set by lethal winter temperatures or summer temperatures too low for growth and/or reproduction, whilst southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Pelvetia canaliculata is a cold-temperate species that occurs in the North-East Atlantic from Russia to Northern Portugal (Neiva et al., 2014). Pelvetia canaliculata is a high intertidal species and its distribution is set by both marine and terrestrial climatic conditions (Neiva et al., 2014). Upper limits on the shore are set by extreme physical stress, whilst its lower limit on the shore is controlled by species competition (Hawkins & Harkin, 1985).

Pelvetia canaliculata appears better adapted to withstand high temperatures than many other fucoids, which may be why this species can withstand life on the higher shore (Pfetzing et al., 2000). When exposed experimentally to a range of temperatures for 24 hours, the growth rate of Pelvetia canaliculata increases up to 20°C at all times of the year, with warm- adapted autumn specimens increasing their growth at higher temperatures, although growth sharply decreases at temperatures greater than 30°C. However, growth is still greater than other species of fucoid tested (Strömgren, 1977). After three weeks, temperatures greater than 30°C became lethal (Strömgren, 1977). Maximum photosynthesis in Pelvetia canaliculata occurs across a wide range of temperatures (15 - 27°C; Pfetzing et al., 2000).

In 1983, an extremely hot July led to damage and mortality in Pelvetia canaliculata (Hawkins & Harkin, 1985). An assessment of the distribution of Pelvetia canaliculata at its southern limit in Portugal, suggests that this species has already shifted its southern range northwards, as it is no longer found in the Berlengas Island, and its most southerly point is now the Cabo do Mundo, 245 km further north (Lima et al., 2007). 

Semibalanus balanoides is pre-eminently a boreal species, adapted to cool environments. Ocean warming is likely to affect this species. Increased temperature is likely to favour chthamalid barnacles rather than Semibalanus balanoides (Southward et al. 1995). Reproduction in Semibalanus balanoides is inhibited by temperatures greater than 10°C (Barnes, 1989). Cirral beating rate reaches a maximum at 18°C in the UK (Southward, 1955) and 21°C at Woods Hole, USA, where summers are warmer (unpublished data, Crisp & Southward). This rate declines until all spontaneous activity ceases at 31°C and coma is induced at a temperature of 37°C (Southward, 1955). It has also been noted that high internal temperatures of approximately 44°C can cause 50% mortality if experienced for more than 45 minutes (Southward, 1958).

Sensitivity assessment. Sea surface temperatures around the UK are currently between 6-19°C (Huthnance, 2010). Under the three scenarios (middle and high emission and extreme), summer sea temperatures in the south of the UK may rise to temperatures of 22, 23, and 24°C respectively. In the south of the UK, summer air temperatures generally reach a mean maximum of 22°C, and under the three scenarios (middle and high emission and extreme) this temperature is projected to increase to temperatures of 25, 26, and 27°C respectively.

Pelvetia canaliculata is able to withstand short-term high increases in temperature, although prolonged increases in temperature lead to damage and mortality. At the southern tip of its range in Portugal, sea temperatures generally reach a maximum of 20°C during the summer months (www.seatemperature.org), whilst air temperatures reach 26°C (www.weather-atlas.com). It is unknown whether its southern limit is controlled by sea or air temperatures, although as it occurs on the high shore, it can spend up to 90% of the time out of the water (Fish & Fish, 1996), therefore air temperatures may be more significant for this species, and have been taken into primary consideration for this sensitivity assessment.

Semibalanus balanoides is likely to contract its range northwards, although where this species of barnacle is lost, it is likely to be replaced by warm-water chthamalid barnacles, which would not impact on the designation of this biotope.

Under the middle and high emission scenario, Pelvetia canaliculata is expected to experience mean maximum air temperatures of 25 -26°C in the south of the UK. As this species is known to tolerate these temperatures at the south of its limit in Portugal, resistance has been assessed as ‘High’, whilst resilience is assessed as ‘High’.  Therefore, this biotope is assessed as ‘Not sensitive’ to ocean warming under the middle and high emission scenarios.

Under the extreme scenario, Pelvetia canaliculata is predicted to experience mean maximum air temperatures of up to 27°C, which is greater than what this species experiences at its southerly limit, and therefore some mortality and potential loss of this species from the south of the UK is expected. Therefore, under this scenario, resistance has been assessed as ‘Medium’, whereas resilience has been assessed as ‘Very low’ due to the long term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ to ocean warming under the extreme scenario.

Global warming (high)

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

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

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

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

Evidence

The distribution of seaweeds is defined climatically (Kain, 1979, Van Den Hoek, 1982, Breeman, 1990, Lüning, 1990). Northern boundaries are set by lethal winter temperatures or summer temperatures too low for growth and/or reproduction, whilst southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Pelvetia canaliculata is a cold-temperate species that occurs in the North-East Atlantic from Russia to Northern Portugal (Neiva et al., 2014). Pelvetia canaliculata is a high intertidal species and its distribution is set by both marine and terrestrial climatic conditions (Neiva et al., 2014). Upper limits on the shore are set by extreme physical stress, whilst its lower limit on the shore is controlled by species competition (Hawkins & Harkin, 1985).

Pelvetia canaliculata appears better adapted to withstand high temperatures than many other fucoids, which may be why this species can withstand life on the higher shore (Pfetzing et al., 2000). When exposed experimentally to a range of temperatures for 24 hours, the growth rate of Pelvetia canaliculata increases up to 20°C at all times of the year, with warm- adapted autumn specimens increasing their growth at higher temperatures, although growth sharply decreases at temperatures greater than 30°C. However, growth is still greater than other species of fucoid tested (Strömgren, 1977). After three weeks, temperatures greater than 30°C became lethal (Strömgren, 1977). Maximum photosynthesis in Pelvetia canaliculata occurs across a wide range of temperatures (15 - 27°C; Pfetzing et al., 2000).

In 1983, an extremely hot July led to damage and mortality in Pelvetia canaliculata (Hawkins & Harkin, 1985). An assessment of the distribution of Pelvetia canaliculata at its southern limit in Portugal, suggests that this species has already shifted its southern range northwards, as it is no longer found in the Berlengas Island, and its most southerly point is now the Cabo do Mundo, 245 km further north (Lima et al., 2007). 

Semibalanus balanoides is pre-eminently a boreal species, adapted to cool environments. Ocean warming is likely to affect this species. Increased temperature is likely to favour chthamalid barnacles rather than Semibalanus balanoides (Southward et al. 1995). Reproduction in Semibalanus balanoides is inhibited by temperatures greater than 10°C (Barnes, 1989). Cirral beating rate reaches a maximum at 18°C in the UK (Southward, 1955) and 21°C at Woods Hole, USA, where summers are warmer (unpublished data, Crisp & Southward). This rate declines until all spontaneous activity ceases at 31°C and coma is induced at a temperature of 37°C (Southward, 1955). It has also been noted that high internal temperatures of approximately 44°C can cause 50% mortality if experienced for more than 45 minutes (Southward, 1958).

Sensitivity assessment. Sea surface temperatures around the UK are currently between 6-19°C (Huthnance, 2010). Under the three scenarios (middle and high emission and extreme), summer sea temperatures in the south of the UK may rise to temperatures of 22, 23, and 24°C respectively. In the south of the UK, summer air temperatures generally reach a mean maximum of 22°C, and under the three scenarios (middle and high emission and extreme) this temperature is projected to increase to temperatures of 25, 26, and 27°C respectively.

Pelvetia canaliculata is able to withstand short-term high increases in temperature, although prolonged increases in temperature lead to damage and mortality. At the southern tip of its range in Portugal, sea temperatures generally reach a maximum of 20°C during the summer months (www.seatemperature.org), whilst air temperatures reach 26°C (www.weather-atlas.com). It is unknown whether its southern limit is controlled by sea or air temperatures, although as it occurs on the high shore, it can spend up to 90% of the time out of the water (Fish & Fish, 1996), therefore air temperatures may be more significant for this species, and have been taken into primary consideration for this sensitivity assessment.

Semibalanus balanoides is likely to contract its range northwards, although where this species of barnacle is lost, it is likely to be replaced by warm-water chthamalid barnacles, which would not impact on the designation of this biotope.

Under the middle and high emission scenario, Pelvetia canaliculata is expected to experience mean maximum air temperatures of 25 -26°C in the south of the UK. As this species is known to tolerate these temperatures at the south of its limit in Portugal, resistance has been assessed as ‘High’, whilst resilience is assessed as ‘High’.  Therefore, this biotope is assessed as ‘Not sensitive’ to ocean warming under the middle and high emission scenarios.

Under the extreme scenario, Pelvetia canaliculata is predicted to experience mean maximum air temperatures of up to 27°C, which is greater than what this species experiences at its southerly limit, and therefore some mortality and potential loss of this species from the south of the UK is expected. Therefore, under this scenario, resistance has been assessed as ‘Medium’, whereas resilience has been assessed as ‘Very low’ due to the long term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ to ocean warming under the extreme scenario.

Global warming (middle)

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

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

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

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

Evidence

The distribution of seaweeds is defined climatically (Kain, 1979, Van Den Hoek, 1982, Breeman, 1990, Lüning, 1990). Northern boundaries are set by lethal winter temperatures or summer temperatures too low for growth and/or reproduction, whilst southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Pelvetia canaliculata is a cold-temperate species that occurs in the North-East Atlantic from Russia to Northern Portugal (Neiva et al., 2014). Pelvetia canaliculata is a high intertidal species and its distribution is set by both marine and terrestrial climatic conditions (Neiva et al., 2014). Upper limits on the shore are set by extreme physical stress, whilst its lower limit on the shore is controlled by species competition (Hawkins & Harkin, 1985).

Pelvetia canaliculata appears better adapted to withstand high temperatures than many other fucoids, which may be why this species can withstand life on the higher shore (Pfetzing et al., 2000). When exposed experimentally to a range of temperatures for 24 hours, the growth rate of Pelvetia canaliculata increases up to 20°C at all times of the year, with warm- adapted autumn specimens increasing their growth at higher temperatures, although growth sharply decreases at temperatures greater than 30°C. However, growth is still greater than other species of fucoid tested (Strömgren, 1977). After three weeks, temperatures greater than 30°C became lethal (Strömgren, 1977). Maximum photosynthesis in Pelvetia canaliculata occurs across a wide range of temperatures (15 - 27°C; Pfetzing et al., 2000).

In 1983, an extremely hot July led to damage and mortality in Pelvetia canaliculata (Hawkins & Harkin, 1985). An assessment of the distribution of Pelvetia canaliculata at its southern limit in Portugal, suggests that this species has already shifted its southern range northwards, as it is no longer found in the Berlengas Island, and its most southerly point is now the Cabo do Mundo, 245 km further north (Lima et al., 2007). 

Semibalanus balanoides is pre-eminently a boreal species, adapted to cool environments. Ocean warming is likely to affect this species. Increased temperature is likely to favour chthamalid barnacles rather than Semibalanus balanoides (Southward et al. 1995). Reproduction in Semibalanus balanoides is inhibited by temperatures greater than 10°C (Barnes, 1989). Cirral beating rate reaches a maximum at 18°C in the UK (Southward, 1955) and 21°C at Woods Hole, USA, where summers are warmer (unpublished data, Crisp & Southward). This rate declines until all spontaneous activity ceases at 31°C and coma is induced at a temperature of 37°C (Southward, 1955). It has also been noted that high internal temperatures of approximately 44°C can cause 50% mortality if experienced for more than 45 minutes (Southward, 1958).

Sensitivity assessment. Sea surface temperatures around the UK are currently between 6-19°C (Huthnance, 2010). Under the three scenarios (middle and high emission and extreme), summer sea temperatures in the south of the UK may rise to temperatures of 22, 23, and 24°C respectively. In the south of the UK, summer air temperatures generally reach a mean maximum of 22°C, and under the three scenarios (middle and high emission and extreme) this temperature is projected to increase to temperatures of 25, 26, and 27°C respectively.

Pelvetia canaliculata is able to withstand short-term high increases in temperature, although prolonged increases in temperature lead to damage and mortality. At the southern tip of its range in Portugal, sea temperatures generally reach a maximum of 20°C during the summer months (www.seatemperature.org), whilst air temperatures reach 26°C (www.weather-atlas.com). It is unknown whether its southern limit is controlled by sea or air temperatures, although as it occurs on the high shore, it can spend up to 90% of the time out of the water (Fish & Fish, 1996), therefore air temperatures may be more significant for this species, and have been taken into primary consideration for this sensitivity assessment.

Semibalanus balanoides is likely to contract its range northwards, although where this species of barnacle is lost, it is likely to be replaced by warm-water chthamalid barnacles, which would not impact on the designation of this biotope.

Under the middle and high emission scenario, Pelvetia canaliculata is expected to experience mean maximum air temperatures of 25 -26°C in the south of the UK. As this species is known to tolerate these temperatures at the south of its limit in Portugal, resistance has been assessed as ‘High’, whilst resilience is assessed as ‘High’.  Therefore, this biotope is assessed as ‘Not sensitive’ to ocean warming under the middle and high emission scenarios.

Under the extreme scenario, Pelvetia canaliculata is predicted to experience mean maximum air temperatures of up to 27°C, which is greater than what this species experiences at its southerly limit, and therefore some mortality and potential loss of this species from the south of the UK is expected. Therefore, under this scenario, resistance has been assessed as ‘Medium’, whereas resilience has been assessed as ‘Very low’ due to the long term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ to ocean warming under the extreme scenario.

Marine heatwaves (high)

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

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018).  Pelvetia canaliculata can withstand short-term increases in temperature but sustained high temperatures lead to damage and mortality (see Global Warming above). Pfetzing et al. (2000) found that maximum photosynthesis in Pelvetia canaliculata can occur across a wide range of temperatures (15-27°C), suggesting a thermal tolerance for this species, although temperatures become greater than 30°C become lethal (Strömgren, 1977). 

In July 1983, there was a heatwave in the UK, with mean daily temperatures averaging 19.5°C, compared to average July temperatures between 1961-1990 of 16.1°C (Parker et al., 1992). Maximum temperatures in England were up to 5°C hotter than average, and the mean maximum temperature in Plymouth was 24°C. During this summer, Pelvetia canaliculata was surveyed at the Isle of Man and Plymouth and showed signs of damage and/ or mortality in both locations (Hawkins & Harkin, 1985). This suggests that this species is likely to show some susceptibility to future heatwaves.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England, whereas mean maximum air temperatures could reach 27°C. This temperature is higher than Pelvetia canaliculata experiences at its southern limit in Portugal (see Global warming), and Pelvetia canaliculata is known to suffer damage from sharp increases in temperatures (e.g. Hawkins & Harkin, 1985); i.e. some mortality is likely. Therefore, resistance has been assessed as ‘Medium’. As some recovery is possible between heatwave events under the middle emissions scenario, recovery has been assessed as ‘Medium’, leading to an assessment of ‘Medium’ for this biotope 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 sea temperatures reaching up to 26.5°C, and mean maximum air temperatures exceeding 30°C across the south of the UK. Under this scenario, it is likely that Pelvetia canaliculata may suffer widespread mortality, through acute physiological stress and, therefore, resistance has been assessed as ‘Low’. Under this scenario, a further heatwave may occur before this biotope has recovered and resilience has been assessed as ‘Very low’, leading to a sensitivity assessment of ‘High’ under the high emission scenario. 

Marine heatwaves (middle)

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

Evidence

Marine heatwaves due to increased air-sea heat flux are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018).  Pelvetia canaliculata can withstand short-term increases in temperature but sustained high temperatures lead to damage and mortality (see Global Warming above). Pfetzing et al. (2000) found that maximum photosynthesis in Pelvetia canaliculata can occur across a wide range of temperatures (15-27°C), suggesting a thermal tolerance for this species, although temperatures become greater than 30°C become lethal (Strömgren, 1977). 

In July 1983, there was a heatwave in the UK, with mean daily temperatures averaging 19.5°C, compared to average July temperatures between 1961-1990 of 16.1°C (Parker et al., 1992). Maximum temperatures in England were up to 5°C hotter than average, and the mean maximum temperature in Plymouth was 24°C. During this summer, Pelvetia canaliculata was surveyed at the Isle of Man and Plymouth and showed signs of damage and/ or mortality in both locations (Hawkins & Harkin, 1985). This suggests that this species is likely to show some susceptibility to future heatwaves.

Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England, whereas mean maximum air temperatures could reach 27°C. This temperature is higher than Pelvetia canaliculata experiences at its southern limit in Portugal (see Global warming), and Pelvetia canaliculata is known to suffer damage from sharp increases in temperatures (e.g. Hawkins & Harkin, 1985); i.e. some mortality is likely. Therefore, resistance has been assessed as ‘Medium’. As some recovery is possible between heatwave events under the middle emissions scenario, recovery has been assessed as ‘Medium’, leading to an assessment of ‘Medium’ for this biotope 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 sea temperatures reaching up to 26.5°C, and mean maximum air temperatures exceeding 30°C across the south of the UK. Under this scenario, it is likely that Pelvetia canaliculata may suffer widespread mortality, through acute physiological stress and, therefore, resistance has been assessed as ‘Low’. Under this scenario, a further heatwave may occur before this biotope has recovered and resilience has been assessed as ‘Very low’, leading to a sensitivity assessment of ‘High’ under the high emission scenario. 

Ocean acidification (high)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005), with it expected to drop by a further 0.35 units by the end of this century, dependent on emission scenario. Marine autotrophs will generally benefit from ocean acidification, through an increase in the availability of aqueous CO₂ for photosynthesis (Koch et al., 2013). Many species of algae, including Pelvetia canaliculata, appear to be under-saturated in respect to carbon dioxide, although they can generally utilise HCO₃ and have external carbonic anhydrase for extracellular dehydration of HCO₃ to CO₂ (Koch et al., 2013).

There is currently no empirical evidence of the impact of ocean acidification on the fucoid seaweed Pelvetia canaliculata, although as this species spends large periods of time emerged, it is less likely to be affected by hypercapnia than species that are fully submerged. Fucus vesiculosus, another fucoid seaweed, appears to be robust to ocean acidification, although not all results are unidirectional. For example, elevated CO₂ levels enhanced the growth of adult Fucus vesiculosus in two studies (Nygård & Dring, 2008, Graiff et al., 2015) but reduced the growth rate in another (Gutow et al., 2014). When the effect of ocean acidification on fertility was tested experimentally, no negative impact on fertility was observed, although there was an increase in the maturation rate, which may lead to unknown ecological effects (Graiff et al., 2017). 

A pH decrease of 0.4 units led to a decrease in embryonic development rate (Findlay et al., 2009), and growth and development of metamorphosing Semibalanus balanoides post-larvae (Findlay et al., 2010b), and is likely to decrease population abundance (Findlay et al., 2010a). The effect of ocean acidification on chthamalid barnacles is currently unknown, although it is likely to be species-specific, and some species appear tolerant to large decreases in pH, such as the barnacle Amphibalanus amphitrite, which maintains growth, tissue mass and egg abundance when exposed to a pH decrease of 0.5 units (Nardone et al., 2018).

Sensitivity assessment. Pelvetia canaliculata is a high intertidal species that spends more time emersed than submerged (Fish & Fish, 1996). Most fucoids have higher photosynthetic rates during emersion, therefore, most of the carbon dioxide acquired by Pelvetia canaliculata will be derived from the atmosphere.  The only experimental evidence of the effect of ocean acidification on fucoids come from studies on Fucus vesiculosus and, although this research suggests that Fucus vesiculosus will be robust to future levels of CO₂, and Pelvetia canaliculata may also be resistant. Semibalanus balanoides is known to be susceptible to a decrease in pH expected under the high emission scenario, although it is unknown whether chthamalid barnacles are susceptible. Pelvetia canaliculata and barnacles are the key characterizing species for this biotope.  There is no evidence that any of the characterising species will be sensitive to ocean acidification at levels expected for the middle emission scenario, therefore resistance is assessed as ‘High’, and resilience is assessed as ‘High’ leading to an assessment of ‘Not sensitive’.

Barnacles, and particularly their larvae, are likely to be sensitive to ocean acidification at levels expected for the high emission scenario, therefore resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very low’ due to the long-term nature of ocean acidification, leading to an assessment of ‘Medium’.

Ocean acidification (middle)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005), with it expected to drop by a further 0.35 units by the end of this century, dependent on emission scenario. Marine autotrophs will generally benefit from ocean acidification, through an increase in the availability of aqueous CO₂ for photosynthesis (Koch et al., 2013). Many species of algae, including Pelvetia canaliculata, appear to be under-saturated in respect to carbon dioxide, although they can generally utilise HCO₃ and have external carbonic anhydrase for extracellular dehydration of HCO₃ to CO₂ (Koch et al., 2013).

There is currently no empirical evidence of the impact of ocean acidification on the fucoid seaweed Pelvetia canaliculata, although as this species spends large periods of time emerged, it is less likely to be affected by hypercapnia than species that are fully submerged. Fucus vesiculosus, another fucoid seaweed, appears to be robust to ocean acidification, although not all results are unidirectional. For example, elevated CO₂ levels enhanced the growth of adult Fucus vesiculosus in two studies (Nygård & Dring, 2008, Graiff et al., 2015) but reduced the growth rate in another (Gutow et al., 2014). When the effect of ocean acidification on fertility was tested experimentally, no negative impact on fertility was observed, although there was an increase in the maturation rate, which may lead to unknown ecological effects (Graiff et al., 2017). 

A pH decrease of 0.4 units led to a decrease in embryonic development rate (Findlay et al., 2009), and growth and development of metamorphosing Semibalanus balanoides post-larvae (Findlay et al., 2010b), and is likely to decrease population abundance (Findlay et al., 2010a). The effect of ocean acidification on chthamalid barnacles is currently unknown, although it is likely to be species-specific, and some species appear tolerant to large decreases in pH, such as the barnacle Amphibalanus amphitrite, which maintains growth, tissue mass and egg abundance when exposed to a pH decrease of 0.5 units (Nardone et al., 2018).

Sensitivity assessment. Pelvetia canaliculata is a high intertidal species that spends more time emersed than submerged (Fish & Fish, 1996). Most fucoids have higher photosynthetic rates during emersion, therefore, most of the carbon dioxide acquired by Pelvetia canaliculata will be derived from the atmosphere.  The only experimental evidence of the effect of ocean acidification on fucoids come from studies on Fucus vesiculosus and, although this research suggests that Fucus vesiculosus will be robust to future levels of CO₂, and Pelvetia canaliculata may also be resistant. Semibalanus balanoides is known to be susceptible to a decrease in pH expected under the high emission scenario, although it is unknown whether chthamalid barnacles are susceptible. Pelvetia canaliculata and barnacles are the key characterizing species for this biotope.  There is no evidence that any of the characterising species will be sensitive to ocean acidification at levels expected for the middle emission scenario, therefore resistance is assessed as ‘High’, and resilience is assessed as ‘High’ leading to an assessment of ‘Not sensitive’.

Barnacles, and particularly their larvae, are likely to be sensitive to ocean acidification at levels expected for the high emission scenario, therefore resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very low’ due to the long-term nature of ocean acidification, leading to an assessment of ‘Medium’.

Sea level rise (extreme)

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

Evidence

Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). 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). Jackson & McIlvenny (2011) predicted that under a 30 cm sea-level rise, between 10-27% of the extent of intertidal rocky shores in Scotland would be lost, whilst under a 190 cm of sea-level rise, between 26 - 50% would be lost. Using a modelling-based approach, Kaplanis et al. (2019) found that in San Diego County loss of intertidal habitat would be most extreme within the first metre of sea-level rise, with 29.9% of intertidal rocky shore lost as a result of 20 cm sea-level rise, and 77.7% as a result of 100 cm of sea-level rise.

Pelvetia canaliculata is an extreme upper shore macroalga that can grow above the high-water mark, in the splash zone. It also requires periods of emersion to survive; immersion for more than 6 hours in 12 can cause mortality (Schonbeck & Norton, 1979b). Pelvetia canaliculata is rapidly out-competed in these areas by faster-growing lower shore species such as Fucus spiralis (Rugg & Norton, 1987).

Sensitivity assessment. This biotope occurs primarily on the west coast, throughout the UK.  The mean tidal range in the UK varies from 127 cm in the Shetland Islands to 972 cm at Avonmouth, in the Bristol Channel (Woodworth et al., 1991). This large difference in tidal amplitudes suggests that this biotope will be more affected in some parts of the UK than others. As this biotope occurs in the littoral fringe, this biotope is not expected to be submerged by sea-level rise under any of these scenarios, although as the sea-rises, Pelvetia canaliculata is likely to be heavily grazed, and may be outcompeted by faster growing fucoids such as Fucus spiralis, it (see Subrahmanyan, 1960).

Pelvetia canaliculata may be able to expand its range and migrate upwards to compensate for sea-level rise, if not constrained by lack of suitable habitat (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of Pelvetia canaliculata will shrink significantly in response to a 50, 70 or 107 cm sea-level rise, particularly in the north, where tidal ranges are smaller. The possibility to migrate inshore will be site-specific, hence, the assessment is based on a worst-case-scenario, i.e. that landward migration is not possible.

In Scotland and Ireland, where mean tidal range is generally less than 3 m (Woodworth et al., 1991), more than half of this biotope may be lost under the extreme scenario, whereas in the Bristol Channel, where mean tidal range exceeds 9 m (Woodworth et al., 1991), only a small portion of this biotope may be lost. Under the medium and high emission scenarios, resistance has been assessed as ‘Medium’, as it is expected less than 25% of this biotope will be lost. Resilience has been assessed as ‘Very low’, due to the long-term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘Medium’. Under the extreme scenario, resistance has been assessed as ‘Low’, as it is likely that more than 25% of this biotope could be lost as other fucoids outcompete it. Resilience has been assessed as ‘Very low’, due to the long-term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘High’.

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). Jackson & McIlvenny (2011) predicted that under a 30 cm sea-level rise, between 10-27% of the extent of intertidal rocky shores in Scotland would be lost, whilst under a 190 cm of sea-level rise, between 26 - 50% would be lost. Using a modelling-based approach, Kaplanis et al. (2019) found that in San Diego County loss of intertidal habitat would be most extreme within the first metre of sea-level rise, with 29.9% of intertidal rocky shore lost as a result of 20 cm sea-level rise, and 77.7% as a result of 100 cm of sea-level rise.

Pelvetia canaliculata is an extreme upper shore macroalga that can grow above the high-water mark, in the splash zone. It also requires periods of emersion to survive; immersion for more than 6 hours in 12 can cause mortality (Schonbeck & Norton, 1979b). Pelvetia canaliculata is rapidly out-competed in these areas by faster-growing lower shore species such as Fucus spiralis (Rugg & Norton, 1987).

Sensitivity assessment. This biotope occurs primarily on the west coast, throughout the UK.  The mean tidal range in the UK varies from 127 cm in the Shetland Islands to 972 cm at Avonmouth, in the Bristol Channel (Woodworth et al., 1991). This large difference in tidal amplitudes suggests that this biotope will be more affected in some parts of the UK than others. As this biotope occurs in the littoral fringe, this biotope is not expected to be submerged by sea-level rise under any of these scenarios, although as the sea-rises, Pelvetia canaliculata is likely to be heavily grazed, and may be outcompeted by faster growing fucoids such as Fucus spiralis, it (see Subrahmanyan, 1960).

Pelvetia canaliculata may be able to expand its range and migrate upwards to compensate for sea-level rise, if not constrained by lack of suitable habitat (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of Pelvetia canaliculata will shrink significantly in response to a 50, 70 or 107 cm sea-level rise, particularly in the north, where tidal ranges are smaller. The possibility to migrate inshore will be site-specific, hence, the assessment is based on a worst-case-scenario, i.e. that landward migration is not possible.

In Scotland and Ireland, where mean tidal range is generally less than 3 m (Woodworth et al., 1991), more than half of this biotope may be lost under the extreme scenario, whereas in the Bristol Channel, where mean tidal range exceeds 9 m (Woodworth et al., 1991), only a small portion of this biotope may be lost. Under the medium and high emission scenarios, resistance has been assessed as ‘Medium’, as it is expected less than 25% of this biotope will be lost. Resilience has been assessed as ‘Very low’, due to the long-term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘Medium’. Under the extreme scenario, resistance has been assessed as ‘Low’, as it is likely that more than 25% of this biotope could be lost as other fucoids outcompete it. Resilience has been assessed as ‘Very low’, due to the long-term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘High’.

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). Jackson & McIlvenny (2011) predicted that under a 30 cm sea-level rise, between 10-27% of the extent of intertidal rocky shores in Scotland would be lost, whilst under a 190 cm of sea-level rise, between 26 - 50% would be lost. Using a modelling-based approach, Kaplanis et al. (2019) found that in San Diego County loss of intertidal habitat would be most extreme within the first metre of sea-level rise, with 29.9% of intertidal rocky shore lost as a result of 20 cm sea-level rise, and 77.7% as a result of 100 cm of sea-level rise.

Pelvetia canaliculata is an extreme upper shore macroalga that can grow above the high-water mark, in the splash zone. It also requires periods of emersion to survive; immersion for more than 6 hours in 12 can cause mortality (Schonbeck & Norton, 1979b). Pelvetia canaliculata is rapidly out-competed in these areas by faster-growing lower shore species such as Fucus spiralis (Rugg & Norton, 1987).

Sensitivity assessment. This biotope occurs primarily on the west coast, throughout the UK.  The mean tidal range in the UK varies from 127 cm in the Shetland Islands to 972 cm at Avonmouth, in the Bristol Channel (Woodworth et al., 1991). This large difference in tidal amplitudes suggests that this biotope will be more affected in some parts of the UK than others. As this biotope occurs in the littoral fringe, this biotope is not expected to be submerged by sea-level rise under any of these scenarios, although as the sea-rises, Pelvetia canaliculata is likely to be heavily grazed, and may be outcompeted by faster growing fucoids such as Fucus spiralis, it (see Subrahmanyan, 1960).

Pelvetia canaliculata may be able to expand its range and migrate upwards to compensate for sea-level rise, if not constrained by lack of suitable habitat (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of Pelvetia canaliculata will shrink significantly in response to a 50, 70 or 107 cm sea-level rise, particularly in the north, where tidal ranges are smaller. The possibility to migrate inshore will be site-specific, hence, the assessment is based on a worst-case-scenario, i.e. that landward migration is not possible.

In Scotland and Ireland, where mean tidal range is generally less than 3 m (Woodworth et al., 1991), more than half of this biotope may be lost under the extreme scenario, whereas in the Bristol Channel, where mean tidal range exceeds 9 m (Woodworth et al., 1991), only a small portion of this biotope may be lost. Under the medium and high emission scenarios, resistance has been assessed as ‘Medium’, as it is expected less than 25% of this biotope will be lost. Resilience has been assessed as ‘Very low’, due to the long-term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘Medium’. Under the extreme scenario, resistance has been assessed as ‘Low’, as it is likely that more than 25% of this biotope could be lost as other fucoids outcompete it. Resilience has been assessed as ‘Very low’, due to the long-term nature of sea-level rise.  Therefore, sensitivity is assessed as ‘High’.

Temperature increase (local)

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

Evidence

Pelvetia canaliculata is common throughout the British Isles.  The distribution of Pelvetia canaliculata extends as far south as Spain and Portugal.  Although species ranges may not accurately describe their ability to withstand localized changes in temperature, they may to some extent display the limits of the species genetic ability to acclimatize to temperatures.  A combination of physiological and biochemical resilience allows Pelvetia canaliculata is able to withstand the extreme environmental conditions found at the top of the shore.  Growth rates in Pelvetia canaliculata have been found to increase up until 20^oC where they plateau up to 25^oC (Pfetzing et al., 2000).  Pelvetia canaliculata can withstand emersion and high temperatures for up to four days before recovery to pre-emersion rates of photosynthesis isn’t possible (Pfetzing et al., 2000). However, Pelvetia canaliculata suffered significantly during the unusually hot summer of 1983 when the average temperature was 8.3°C higher than normal (Hawkins & Hartnoll, 1985).  Schonbeck & Norton (1978) found that Pelvetia canaliculata in the upper part of the Pelvetia zone showed signs of tissue damage 21 – 28 days after neap tides coincided with drying conditions and high air temperatures.

Fucus spiralis is at the upper limit of its temperature tolerance in this biotope.  Any increase in temperature could cause this species to die off, and removed from this biotope.  Fucus spiralis biotopes are very often found below this biotope on rocky shores.  When the temperature pressure is removed, Fucus spiralis could recruit from the zone below this biotope.  Increased temperature may reduce habitat suitability for Semibalanus balanoides, the more cold adapted species.  Changes in temperature may lead to Semibalanus balanoides being replaced with the warm adapted Chthalamus montagui.  As the environmental niche is still being filled by a barnacle species this will not make any important changes in the biotopes to which barnacles are relevant.

Sensitivity assessment.  An increase in temperature at the pressure benchmark is likely to cause Pelvetia canaliculata to die off at the top of the shore due to increased levels of desiccation caused by higher temperatures.  A shift in the area of the shore on which Pelvetia canaliculata can survive would cause some mortality of the species.  However, it will not cause large losses of the characterizing species.  Fucus spiralis is at the top of its temperature tolerance at the bottom of this biotope.  Any increase in temperature is likely to see a decrease in Fucus spiralis if not complete mortality within this biotope.  Within the biotope LR.MLR.BF.PelB, an increase in temperature may create a competitive edge for Chthalamus montagui.  This is unlikely to cause any significant changes in the biotope as the functional niche will still be filled.  Both resistance and resilience have been assessed as ‘Medium’, resulting in a sensitivity of ‘Medium’.

Temperature decrease (local)

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

Evidence

Pelvetia canaliculata is common throughout the British Isles.  The distribution of Pelvetia canaliculata extends as far north as Iceland and Norway.  Although species ranges may not accurately describe their ability to withstand localized changes in temperature.  They may to some extent display the limits of the species genetic ability to acclimatize to temperatures.  The growth rates and photosynthetic capabilities of macroalgae vary due to seasonal acclimation (Davison et al., 1989).  A 5 °C decrease in temperature is likely to lower growth rates in Pelvetia canaliculata, unless the decrease occurs during a summer when temperatures are in excess of 25 °C (Pfetzing et al., 2000).  Acclimation to a decrease in temperature is likely in Pelvetia canaliculata considering its range.  However, if a rapid 5 °C decrease were to occur in the winter the species may not be able to acclimate in time and some permanent damage may occur.  During warmer summer months a decrease in temperature can lead to lowered levels of evaporation and consequently lower levels of desiccation.  This could be beneficial if temperatures are in excess of 25 °C (Pfetzing et al., 2000).

Fucus spiralis is at the top of its temperature tolerance in this biotope.  Any decrease in temperature could allow this species to extend further up the shore.  Fucus spiralis can out-compete Pelvetia canaliculata as it grows faster and overshadows the slower growing Pelvetia canaliculata.  A decrease in temperature may reduce habitat suitability for Chthalamus montagui, the more warm adapted species.  Changes in temperature may lead to Semibalanus balanoides replacing Chthalamus montagui.  As the environmental niche is still being filled by a barnacle species this will not make any important changes in the biotopes to which barnacles are relevant.

Sensitivity assessment.  Direct empirical evidence on the cold tolerance of Pelvetia canaliculata is unavailable. Instead and assessment has been made using the available information on the acclimation and upper temperature tolerance of Pelvetia canaliculata.  This evidence suggests that this species is unlikely to be significantly negatively affected by a change in temperature at the pressure benchmark.  The only case during which some mortality may occur is if a decrease of 5 °C for a month occurred during winter, when Pelvetia canaliculata may not be able to acclimate fast enough.  Fucus spiralis may move further higher on the shore, possibly causing a change in the biotope lower limit.  Within LR.MLR.BF.PelB the dominant barnacle species may change, but the function niche will still be filled.  The resistance and resilience have been assessed as ‘High’, resulting in a ‘Not sensitive’ assessment.

Salinity increase (local)

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

Evidence

Biotopes found in the intertidal will naturally experience fluctuations in salinity where evaporation increases salinity and inputs of rainwater expose individuals to freshwater.  Species found in the intertidal therefore have behavioural or physiological adaptations to changes in salinity.

Fucus spiralis is tolerant of short-term increases in salinity.  Fucus spiralis populations in New Hampshire were reported to survive between 2 – 32psu (Niemeck & Mathieson, 1976).  Littorina saxatilis is a mobile species has the ability to remove itself from unfavourable conditions.  This littorinid is also found occasionally in upper shore rock pool biotopes (such as LR.FLR.Rkp.G).  Its presence in biotopes where salinities are highly variable is evidence for this species ability to cope with short-term fluctuations in salinity.  However, the impact of more long-term increases in salinity is unknown.

Semibalanus balanoides is tolerant of a wide range of salinities, and has the ability to isolate itself from water by closing their opercula valves (Foster, 1971b).  They can also withstand large changes in salinity over moderately long periods of time by falling into a "salt sleep" and can be found on shores (example from Sweden) with large fluctuations in salinity around a mean of 24 psu (Jenkins et al., 2001b).  Barnes & Barnes (1974) found that larvae from both Chthamalus stellatus and Semibalanus (as Balanus) balanoides, completed their development to nauplii larvae at salinities between 20-40%.

Sensitivity assessment.  Pelvetia canaliculata biotopes exist in both full (30 – 40) and variable (18 – 40) salinities (Connor et al., 2004).  LR.MLR.BF.PelB occurs only in fully marine conditions if there was to be an increase in the salinity regime within this biotope the conditions would become hypersaline.  There is no epirical evidence to suggest how the species within this biotope would react to these condtions. LR.LLR.FVS.PelVS occurs only in variable salinity regimes. Here a change in salinity would create a full salinity regime.  The conditions for many of the constiuent species would become more optimal and as such there would not be a decrease in the health of this biotope.  It is not clear how LR.MLR.BF.PelB would change in hypersaline conditions but as conditions for this biotope are no longer optimal there is likely to be a decrease in the characterizing species resulting in the resilience and resistance being 'Medium'.  And an overall sensitivity assessment of 'Medium'.  LR.LLR.FVS.PelVS is assessed to have a 'High' resistance and resilience to this pressure.  Giving an overall sensitivity of 'Not sensitive'. 

Salinity decrease (local)

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

Evidence

Biotopes found in the intertidal will naturally experience fluctuations in salinity where evaporation increases salinity and inputs of rainwater expose individuals to freshwater.  Species found in the intertidal, therefore, have behavioural or physiological adaptations to changes in salinity.  Fucus spiralis is tolerant of decreases in salinity.

Fucus spiralis populations in New Hampshire were reported to survive between 2 – 32 psu (Niemeck & Mathieson, 1976).  Littorina saxatilis is a mobile species has the ability to remove itself from unfavourable conditions.  This littorinid is also found occasionally in upper shore rock pool biotopes (such as LR.FLR.Rkp.G).  Its presence in biotopes where salinities are highly variable is evidence for this species ability to cope with short-term fluctuations in salinity.  A long-term decrease in salinity is unlikely to have an effect on Fucus spiralis in this biotope.

Semibalanus balanoides is tolerant of a wide range of salinities, and has the ability to isolate itself from water by closing their opercula valves (Foster, 1971b).  They can also withstand large changes in salinity over moderately long periods of time by falling into a "salt sleep" and can be found on shores (example from Sweden) with large fluctuations in salinity around a mean of 24 (Jenkins et al., 2001b).  Barnes & Barnes (1974) found that larvae from both Chthamalus stellatus and Semibalanus (as Balanus) balanoides, completed their development to nauplii larvae at salinities between 20-40%.

Sensitivity assessment.  Pelvetia canaliculata biotopes exist in both full (30 – 40) and variable (18 – 40) salinities (Connor et al., 2004).  LR.MLR.BF.PelB occurs only in fully marine conditions so that a decrease in the salinity regime within this biotope would result in 'reduced' (18-30). There are functioning Pelvetia canaliculata biotopes within this salinity regime that shows the characterizing species ability to survive, long-term, within this salinity regime.  LR.LLR.FVS.PelVS occurs only in variable salinity regimes. The conditions for many of the constituent species would no longer be optimal under the 'reduced' salinity regime, as many of the species can only survive short periods at reduced salinity levels. Consequently there would be a decrease in the health of this biotope.  For LR.LLR.FVS.PelVS the resilience and resistance being 'Medium'.  And an overall sensitivity assessment of 'Medium'.  LR.MLR.BF.PelB is assessed to have a 'Medium' resistance and resilience to this pressure.  As although there wouldn’t be mortality of the characterizing species, the shift in salinity regime would cause a change to an alternative biotope.  Therefore, sensitivity is 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

LR.LLR.FVS.PelVS can be found in very weak (negligable) to moderately strong (1 - 3 knots) tidal streams.  LR.LLR.FVS.PelB can be found in very weak to strong (3 – 6 knots) tidal streams (Connor et al., 2004).  Although no empirical data can be found on the effects of water flow on Pelvetia canaliculata, a study into its effects on Fucus spiralis found that plants were torn from their anchorage at 7 – 8 m/sec (Jonsson et al., 2006).  If water flows were to increase above 3 m/sec, plants may not be immediately torn from the substrate but dispersal, fertilization, settlement and recruitment may be affected (Pearson & Brawley, 1996).  Risk of dislodgement will also increase where algae are attached to smaller sediment fractions instead of bedrock.  If sediment type is small and the substratum is less stable, individuals may reach a critical size when the drag force exceeds gravity and the plant is moved together with its substratum (Malm, 1999).  A decrease in water flow is unlikely to have a negative impact on this biotope as it occurs most frequently at very weak water flows (< 0.5 m/sec.) (Connor et al., 2004).

Growth and reproduction of Semibalanus balanoides is influenced by food supply and water velocity (Bertness et al., 1991).  Laboratory experiments demonstrate that barnacle feeding behaviour alters over different flow rates but that barnacles can feed at a variety of flow speeds (Sanford et al., 1994).  Flow tank experiments using velocities of 0.03, 0.07 and 0.2 m/s showed that a higher proportion of barnacles fed at higher flow rates (Sanford et al., 1994).  Feeding was passive, meaning the cirri were held out to the flow to catch particles; although active beating of the cirri to generate feeding currents occurs in still water (Crisp & Southward, 1961).  Field observations at sites in southern New England (USA) found that Semibalanus balanoides from all sites responded quickly to higher flow speeds, with a higher proportion of individuals feeding when current speeds were higher.  Barnacles were present at a range of sites, varying from sheltered sites with lower flow rates (maximum observed flow rates <0.06- 0.1 m/s), a bay site with higher flow rates (maximum observed flows 0.2-0.3 m/s) and open coast sites (maximum observed flows 0.2-0.4 m/s).  Recruitment was higher at the site with flow rates of 0.2-0.3 m/s (although this may be influenced by supply) and at higher flow microhabitats within all sites.  Both laboratory and field observations indicate that flow is an important factor with effects on feeding, growth and recruitment in Semibalanus balanoides (Sanford et al., 1994; Leonard et al., 1998), however, the results suggest that flow is not a limiting factor determining the overall distribution of barnacles, including Chthamalus montagui as they can adapt to a variety of flow speeds.

Patella vulgata inhabits a range of tidal conditions and is therefore, likely to tolerate a change in water flow rate.  The streamlined profile of limpet shells is of importance in increasing their tolerance of water movement, and this is undoubtedly one factor in determining the different shape of limpets at different exposures.  With increasing exposure to wave action the shell develops into a low profile reducing the risk of being swept away.  The strong muscular foot and a thin film of mucus between the foot and the rock enable Patella vulgata to grip very strongly to the substratum (Fretter & Graham, 1994).  The ability of limpets to resist accelerating, as distinct from constant currents, may set a limit to the kind of habitat which they can occupy and limit the size to which they can grow.

Sensitivity assessment:  At the level of the benchmark a change in water flow will not have an impact on the biological communities within these biotopes. Consequently both resistance and resilience have been assessed as ‘High’, resulting in an overall sensitivity of ‘Not Sensitive’.

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

Of the fucoids found in the British Isles, Pelvetia canaliculata is the better adapted to desiccation stresses, therefore, it is often the dominant macroalgae high on intertidal rocky shores.  Pelvetia canaliculata can spend as much as 90% of its time out of water (Fish & Fish, 1996) and has been found to survive up to 8 days emersion (Pfetzing, 2000) and as much as 65% water loss (Schonbeck & Norton, 1978).  Schonbeck & Norton (1980) found that Pelvetia canaliculata can recover well from desiccation, and can also increase desiccation tolerance quickly (Schonbeck & Norton, 1979).  Recovery from desiccation includes the ability to quickly regain nutrient uptake and photosynthesising capability (Hurd & Dring, 1990, 1991).  Field observations of Pelvetia canaliculata on the Isle of Cumbrae by Schonbeck & Norton (1978) found that environmental conditions constantly pruned the higher limits of this species.  Individuals in the upper part of the Pelvetia zone were found to suffer tissue damage 21 – 28 days after neap tides coincided with drying conditions and especially high air temperatures (Schonbeck & Norton, 1978).  Subrahmanyan (1960) observed that on the Isle of Man when neap tides and calm condition coincided, the water did not reach the bottom of the Pelvetia canaliculata habitat.  However, spring high tides cover the entire habitat.  The release of Pelvetia canaliculata reproductive bodies are reported to occur on a two weekly cycle, during spring high tides (Subrahmanyan, 1960).  This ensures that gametes are released into a liquid medium.  The lower limits of Pelvetia are controlled by interspecific competition.  Lower on the shore Fucus spiralis is able to grow faster than Pelvetia canaliculata, and out-competes Pelvetia canaliculata for resources (Subrahmanyan, 1960).  Pelvetia canaliculata is also heavily grazed lower on the shore (Subrahmanyan, 1960).  In addition to interspecific competition, submersion induced decay limits Pelvetia canaliculata’s ability to survive lower on the shore (Rugg & Norton, 1987).  If Pelvetia canaliculata is submerged for six or more hours in every 12, rot begins (Rugg & Norton, 1987; Schonbeck & Norton, 1979).  Visible signs of rot begin roughly four weeks after high levels of immersion begin (Rugg & Norton, 1987).  This rot is fatal to Pelvetia canaliculata if immersion is not decreased.  The occurrence of the rot is definite and has been tested in a range of different environmental conditions; the reason for the occurrence isn’t known and could be infections, or caused by Pelvetia canaliculata's inability to live underwater (Rugg & Norton, 1987).

Increased emergence would reduce the feeding time and increase desiccation for barnacles within the biotope.  Chthamalus montagui are very tolerant of high periods of emersion, yet Patel & Crisp (1960) found that when barnacles which were brooding eggs were kept out of the water, a second batch of eggs was not produced.  Decreased emergence is likely to lead to the habitat the biotope is found in becoming more suitable for the lower shore species generally found below the biotope, leading to replacement.  Competition between Semibalanus balanoides and Chthalamus montagui is likely to play an important role in the changes in species distribution.  Semibalanus balanoides is less tolerant of desiccation stress than Chthamalus montagui but is considered to out-compete Chthamalus montagui in the mid and lower shore.  Mobile species found within these biotopes such as littorinids and Patella vulgata are able to relocate if physiological pressures become too strong.

Sensitivity assessment.  Although Pelvetia canaliculata is highly adapted to long periods of emersion, the upper limit of this species is limited by environmental conditions linked to high air temperatures.  Those Pelvetia canaliculata individuals living at the highest level on the shore are living at the top of their physiological tolerance limits and so would not be likely to tolerate an increase in emersion levels.  Consequently the upper limit of this biotope would be depressed if there was a decrease in immersion.  Decreases in the level of emersion would result in the species being competitively displaced by faster growing species such as Fucus spiralis the fucoid which usually grows below Pelvetia canaliculata.  If there was a lack of Fucus spiralis below the Pelvetia zone then Pelvetia canaliculata would succumb to the rot, bought on by greater levels of immersion.  Similar changes in distributions of other species associated with the relevant biotopes will occur.  The resistance of this biotope to this pressure is ‘Low’, resilience is ‘Medium’ giving a sensitivity of ‘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

An increase in wave exposure generally leads to a decrease in macroalgae abundance and size (Lewis, 1961, Stephenson & Stephenson, 1972, Hawkins et al., 1992, Jonsson et al., 2006).  On the Isle of Man, the density of Pelvetia canaliculata was found to be inversely proportional to the level of wave exposure (Subrahmanyan, 1960).  The greater the wave exposure, the less dense the growths of Pelvetia canaliculata.  In moderately exposed conditions, Pelvetia canaliculata is capable of growing above the high water mark, where is it supplied with water through spray and wave splash.  In more sheltered conditions, Pelvetia canaliculata is found further down the shore where it is immersed by spring tides.

Chthamalus montagui increases in abundance in sheltered locations and towards the high-water neap-tide level on all shores where chthamalid species occur.  The edible periwinkle Littorina littorea may also colonize suitable areas following a decrease in wave exposure.  A decrease in wave exposure may ultimately reduce Patella vulgata abundance because the species does not favour thick algal cover that is often present on very sheltered shores.  Alternatively an increase in significant wave height, linked to increased exposure, may result in population changes with fewer barnacles present and with the limpet Patella ulyssiponensis present, or present in greater numbers, rather than Patella vulgata (Thompson, 1980).

Sensitivity assessment.  At the pressure benchmark this biotope will not be affected.  Therefore, resistance and resilience are both ‘High’, resulting in a sensitivity assessment of ‘Not sensitive’.

Transition elements & organo-metal contamination

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

Evidence

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

Hydrocarbon & PAH contamination

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

Evidence

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

Synthetic compound contamination

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

Evidence

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

Radionuclide contamination

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

Evidence

No evidence.

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

Cole et al. (1999) suggested possible adverse effects on marine species below oxygen levels of 4 mg/l and probable adverse effects below 2 mg/l.  Sustained reduction of dissolved oxygen can lead to hypoxic (reduced dissolved oxygen) and anoxic (extremely low or no dissolved oxygen) conditions.  Continued or repeated episodes of reduced dissolved oxygen have the potential to severely degrade an ecosystem (Cole et al., 1999). Reduced oxygen concentrations have been shown to 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).  If levels do drop below 4 mg/l negative effects on marine organisms can be expected with adverse effects occurring below 2mg/l (Cole et al., 1999).  Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly.  However, small invertebrate epifauna may be lost, causing a reduction in species richness.

In laboratory experiments a reduction in the oxygen tension of seawater from 148 mmHg (air saturated seawater) to 50 mm Hg rapidly resulted in reduced heart rate in limpets of the genus Patella (Marshall & McQuaid, 1993).  Heartbeat rate returned to normal in oxygenated water within two hours.  Limpets can survive for a short time in anoxic seawater; Grenon & Walker, (1981) found that in oxygen-free water limpets could survive up to 36 hours, although Marshall & McQuaid (1989) found a lower tolerance for Patella granularis, which survived up to 11 hours in anoxic water.  Therefore, some individuals may survive for one week at an oxygen concentration of 2 mg/l.  Exposure would be mediated by the position of the biotope in the upper to mid-shore as Patella vulgata is able to respire in the air and would only be exposed to low oxygen in the water column intermittently during periods of tidal immersion. In addition, in areas of wave exposure and moderately strong current flow low oxygen levels in the water are unlikely to persist for very long.

Barnacles, in general, seem to have a high tolerance of anaerobic conditions.  Chthamalus montagui has been shown to be relatively unaffected by smothering by oil.  Monterosso (1930) showed experimentally that the species can survive complete smothering by petroleum jelly for approximately two months.  Complete smothering caused by the Torrey Canyon oil spill yielded similar results; a few Semibalanus balanoides died, yet Chthamalus montagui seemed unaffected (Smith, 1968).  Semibalanus balanoides can respire anaerobically, so they can tolerate some reduction in oxygen concentration (Newell, 1979). When placed in wet nitrogen, where oxygen stress is maximal and desiccation stress is low, Semibalanus balanoides have a mean survival time of 5 days (Barnes et al., 1963).

Sensitivity assessment.  The characterizing species Pelvetia canaliculata and the associated community require oxygen.  However, this macroalga spends extended periods of time emersed due to its location on the upper shore.  LR.MLR.BF.PelB  occurs in the littoral fringe, which is rarely inundated and is often exposed to the air,  and consequently, a large proportion of time will be spent in the air where oxygen is not limited so the metabolic processes of photosynthesis and respiration can take place.  The high shore location of barnacles within the LR.MLR.BF.PelB biotope may be negatively affected by reduced levels of oxygen due to the short time frame in which they are immersed.  Although the evidence does suggest that barnacles are tolerant of reduced oxygen levels.  Even if the water lapping over the littoral fringe was deoxygenated, wave action (in this wave exposed biotope) and turbulent flow over the rock surface would probably aerate the water column. Hence, the biotope is unlikely to be exposed to deoxygenated conditions and the pressure is considered to be 'Not relevant'.

Nutrient enrichment

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

Evidence

The nutrient enrichment of a marine environment leads to organisms no longer being limited by the availability of certain nutrients.  The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta analysis of the effect of contaminants on species richness and evenness in the marine environment.  Of the 47 papers reviewed relating to nutrients as a contaminants, over 75% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect.  Not all of the 47 papers considered the impact of nutrients on intertidal rocky shores.  Yet this finding is still relevant as the meta analysis revealed that the effect of marine pollutants on species diversity were ‘remarkably consistent’ between habitats (Johnston & Roberts, 2009).  It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009).  Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant.  These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls.  However research into the impacts of nutrient enrichment from these sources on intertidal rocky shores often lead to shores lacking species diversity and the domination by algae with fast growth rates (Abou-Aisha et al., 1995, Archambault et al., 2001, Arévalo et al., 2007, Diez et al., 2003, Littler & Murray, 1975).

Nutrient enrichment alters the selective environment by favouring fast growing, ephemeral species such as Ulva lactuca and Ulva intestinalis (Berger et al., 2004, Kraufvelin, 2007).  Rohde et al. (2008) found that both free growing filamentous algae and epiphytic microalgae can increase in abundance with nutrient enrichment.  This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Berger et al., 2003; Kraufvelin et al., 2007).  Nutrient enrichment can also enhance fouling of Fucus fronds by biofilms (Olsenz, 2011).  Nutrient enriched environments can not only increase algae abundance, but the abundance of grazing species (Kraufvelin, 2007).

Changes in community composition on intertidal rocky shores can happen rapidly, and fast growing ephemeral species can become established quickly in the presence of higher concentrations of nutrients.  The establishment and growth of these species are not controlled by wave exposure (Kraufvelin, 2007).  However, even though these fast growing ephemeral species can become well established quickly, healthy communities on intertidal rocky shores can survive long periods of time, and maintain ecological function after these species have become established (Bokn et al., 2002, 2003, Karez et al.,2004, Kraufvelin, 2007, Kraufvelin et al., 2006).

Sensitivity assessment. A slight increase in nutrients may enhance growth rates but high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae and an increase in the number of grazers.  However, if the biotope is well established and in a healthy state the biotope could have the potential to persist.  The effect of an increase in this pressure to the benchmark level should not have a negative impact on the biotope.  Therefore the resistance has been assessed as ‘High’.  As there will be nothing for the biotope to recover from therefore the resilience is also ‘High’. These two rankings give an overall sensitivity of ‘Not Sensitive’.

Organic enrichment

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

Evidence

The organic enrichment of a marine environment at this pressure benchmark leads to organisms no longer being limited by the availability of organic carbon.  The consequent changes in ecosystem functions can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) and decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).

Johnston & Roberts (2009) undertook a review and meta analysis of the effect of contaminants on species richness and evenness in the marine environment.  Of the 49 papers reviewed relating to sewage as a contaminant, over 70% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect.  Not all of the 49 papers considered the impact of sewage on intertidal rocky shores.  Yet this finding is still relevant as the meta analysis revealed that the effect of marine pollutants on species diversity were ‘remarkably consistent’ between habitats (Johnston & Roberts, 2009).  It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009).  Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant.  These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls.  However, research into the impacts of organic enrichment from these sources on intertidal rocky shores often lead to shores lacking species diversity and the domination by algae with fast growth rates (Abou-Aisha et al., 1995, Archambault et al., 2001, Arévalo et al., 2007, Diez et al., 2003, Littler & Murray, 1975).

Organic enrichment alters the selective environment by favouring fast growing, ephemeral species such as Ulva lactuca and Ulva intestinalis (Berger et al., 2004, Kraufvelin, 2007).  Rohde et al. (2008) found that both free growing filamentous algae and epiphytic microalgae can increase in abundance with nutrient enrichment.  This stimulation of annual ephemerals may accentuate the competition for light and space and hinder perennial species development or harm their recruitment (Berger et al., 2003; Kraufvelin et al., 2007).  Nutrient enrichment can also enhance fouling of fucoid fronds by biofilms (Olsenz, 2011).  Nutrient enriched environments can not only increase algae abundance, but the abundance of grazing species (Kraufvelin, 2007).  Bellgrove et al. (2010) found that coralline turfs out-competed fucoids at a site associated with organic enrichment caused by an ocean sewage outfall.

Changes in community composition on intertidal rocky shores can happen rapidly, and fast growing ephemeral species can become established quickly in the presence of higher concentrations of nutrients.  The establishment and growth of these species are not controlled by wave exposure (Kraufvelin, 2007).  However, even though these fast growing ephemeral species can become well established quickly, healthy communities on intertidal rocky shores can survive long periods of time, and maintain ecological function after these species have become established (Bokn et al., 2002, 2003, Karez et al.,2004, Kraufvelin, 2007, Kraufvelin et al., 2006b).

Sensitivity assessment.  Little empirical evidence was found to support an assessment of this biotope at this benchmark.  Due to the potential negative impacts that have been reported to result from the introduction of excess organic carbon, resistance has been assessed as ‘Medium’ and resilience has been assessed as ‘Medium’. This gives an overall sensitivity score of ‘Medium’.

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

This biotope occurs on hard rock bedrock, boulders and cobbles, a change in substratum would significantly alter the character of the biotope and would lead to the development of a biological assemblage more typical of the changed conditions.  A change to an artificial substratum could also impact this biotope as species may have settlement preferences for particular surface textures.  Therefore the replacement of natural surfaces with artificial ones may lead to changes in the biotope through changes in species composition, richness and diversity (Green et al., 2012; Firth et al., 2013).

Sensitivity assessment.  A change in substratum would result in the loss of the characterizing species Pelvetia canaliculata along with other species associated with this biotope.  Resistance is assessed as ‘None’.  As this pressure represents a permanent change, recovery is impossible as the suitable substratum for the biological community of this biotope is lacking. Consequently, resilience is assessed as ‘Very Low’.  The habitat, therefore, scores a ‘High’ sensitivity. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another sediment type)

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

Evidence

Not relevant to biotopes occurring on bedrock.

Habitat structure changes - removal of substratum (extraction)

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

Evidence

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

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

Trampling on the rocky shore has been observed to reduce fucoid cover, decrease the microhabitat available for epiphytic species, increase bare space and increase cover of opportunistic species such as Ulva (Fletcher & Frid, 1996a).  This biotope is found in the upper intertidal shore.  An area easily accessible by humans especially at low tide.  Individual microalgae’s are flexible but not physically robust.  Fucoids are intolerant of abrasion from human trampling, which has been shown to reduce the cover of seaweeds on a shore (Holt et al., 1997; Tyler-Walters & Arnold, 2008).

Brosnan (1993) investigated the effect of trampling on an intertidal rocky shore area dominated by algae and barnacle assemblages in Oregon.  The effects of 250 tramples per plot, once a month for a year were recorded.  Abundances of algae in each plot were reduced from 80% to 35% within a month of the introduction of the pressure and remained low for the remainder of the experiment.  As few as 20 steps / m² on stations on an intertidal rocky shore in the north-east of England were sufficient to reduce the abundance of fucoids (Fletcher & Frid, 1996a).  This reduction in the complexity of the algae community, in turn, reduced the microhabitat available for epiphytic species.  Trampling pressure can thus result in an increase in the area of bare rock on the shore (Hill et al., 1998). Chronic trampling can affect community structure with shores becoming dominated by algal turf or crusts (Tyler-Walters, 2005).  Pinn & Rodgers (2005) compared the biological communities found on two intertidal rocky shore ledges in Dorset. They found that the ledge which had a higher number of visitors had few branching algal species, including fucoids, but had greater abundances of crustose and ephemeral species (Pinn & Rodgers, 2005).  The densities of fucoids were recorded from the intertidal rocky shore at Wembury, Devon in 1930 (Colman, 1933) and 1973 (Boalch et al., 1974).  Boalch et al. (1974) found a reduction in fucoids on the shore at Wembury compared to the abundances recorded by Coleman (1933).

The barnacles and limpets that contribute to LR.MLR.BF.PelB typically occur on the rock surfaces where they will be exposed to abrasion.  Although limpets and barnacles are protected by hard shells or plates, abrasion may damage and kill individuals or detach these. All removed barnacles would be expected to die as there is no mechanism for these to reattach.  Removal of limpets may result in these being displaced to a less favourable habitat and injuries to foot muscles may prevent reattachment.  Evidence for the effects of abrasion is provided by a number of experimental studies on trampling (a source of abrasion) and on abrasion by wave thrown rocks and pebbles.  The effects of trampling on barnacles appear to be variable with some studies not detecting significant differences between trampled and controlled areas (Tyler-Walters & Arnold, 2008).  However, this variability may be related to differences in trampling intensities and abundance of populations studied.  The worst case incidence was reported by Brosnan & Crumrine (1994) who reported that a trampling pressure of 250 steps in a 20 x 20 cm plot one day a month for a period of a year significantly reduced barnacle cover at two study sites.  Barnacle cover reduced from 66% to 7% cover in 4 months at one site and from 21% to 5% within 6 months at the second site.  Overall barnacles were crushed and removed by trampling.  Barnacle cover remained low until recruitment the following spring.  Long et al. (2011) also found that heavy trampling (70 humans / km shoreline) led to reductions in barnacle cover.  Single step experiments provide a clearer, quantitative indication of sensitivity to direct abrasion.  Povey & Keough (1991) in experiments on shores in Mornington peninsula, Victoria, Australia, found that in single step experiments 10 out of 67 barnacles, (Chthamalus antennatus about 3 mm long), were crushed.  However, on the same shore, the authors found that limpets may be relatively more resistant to abrasion from trampling.  Following step and kicking experiments, few individuals of the limpet Cellana tramoserica, (similar size to Patella vulgata) suffered damage (Povey & Keough, 1991).  One kicked limpet (out of 80) was broken and 2 (out of 80) limpets that were stepped on could not be relocated the following day (Povey & Keough, 1991).  Trampling may lead to indirect effects on limpet populations, Bertocci et al. (2011) found that the effects of trampling on Patella sp. increased the temporal and spatial variability of in abundance.  The experimental plots were sited on a wave-sheltered shore dominated by Ascophyllum nodosum.  On these types of shore, trampling in small patches, that removes macroalgae and turfs, will indirectly enhance habitat suitability for limpets by creating patches of exposed rock for grazing.

Sensitivity assessment.  Fucoids are not tolerant of abrasion, and the effect of the pressure at this benchmark will cause a reduction in the abundances of Pelvetia canaliculata.  Both barnacles and limpets are also negatively affected by trampling.  Therefore the resistance is ‘Low’, the resilience is assessed as ‘Medium’.  Consequently, the sensitivity of this biotope has been assessed as ‘Medium’.

Penetration or disturbance of the substratum subsurface

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

Evidence

The species characterizing this biotope group are epifauna or epiflora occurring on rock, which is resistant to subsurface penetration.  Therefore, ‘penetration’ is 'Not relevant'. The assessment for abrasion at the surface only is, therefore, considered to equally represent sensitivity to this pressure’. Please refer to ‘abrasion’ above.

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

In general, increased suspended particles may enhance food supply (where these are organic in origin) or decrease feeding efficiency (where the particles are inorganic and require greater filtration efforts).  Very high levels of silt may clog respiratory and feeding organs of the suspension feeding barnacle species.  In addition, increased turbidity will decrease light penetration reducing photosynthesis by macroalgae within this biotope.  Increased levels of particles may increase scour and deposition in the biotope depending on local hydrodynamic conditions, although changes in substratum are assessed through the physical change (to another seabed type) pressure.  Pelvetia canaliculata is found on the upper zone of intertidal rocky shores.  Water depths within this part of the intertidal will never be great.  So although an increase in turbidity at this pressure benchmark will increase light attenuation it is likely that light will still penetrate to the depth at which the algae are found.  Allowing Pelvetia canaliculata to continue to photosynthesize whilst immersed.  Pelvetia canaliculata spends as much as 90% of the time emersed (Fish & Fish, 1996).  During this time the macroalgae can continue to photosynthesise unless environmental conditions become too severe (Beer & Kautsky, 1992).

A significant decrease in suspended organic particles may reduce food input to the biotope resulting in reduced growth and fecundity of barnacles.  This would be most relevant to the LR.MLR.BF.PelB biotope.  However, local primary productivity may be enhanced where suspended sediments decrease, increasing food supply.

Sensitivity assessment. This biotope is found on the upper intertidal shore and consequently is subject to long periods of emersion during which time macroalgae can continue to photosynthesize as long as plants have a sufficiently high water content.  Therefore, photosynthesis and growth will not be greatly affected.  Hence, the resistance and resilience of this biotope have been assessed as ‘High’, and the sensitivity of this biotope to this pressure, at the benchmark, is ‘Not Sensitive’.

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

A discrete event where sediment inundates this biotope to 5 cm will have different effects on the characterizing species depending on the state of the tide.  During high tide, the characterizing species will be vertical in the water column.  Any deposition at this state of the tide will mean that only a proportion of the stipe and holdfast will be covered.  Fronds of Pelvetia canaliculata can reach up to 15 cm in length.  Consequently, sediment deposition at high tide could leave up to 10 cm of Pelvetia canaliculata fronds sediment free.  In contrast, if the tide is out, then fronds of the characterizing fucoid canopy will be flat on the substratum and will be smothered by the sediment deposit.  The level of water flow caused by tidal movements and wave exposure within this biotope could remove from the shore within a few tidal cycles.  There may be some decay of parts of the plants which are covered by the sediment.  Germlings are likely to be smothered and killed regardless of the state of the tide and are inherently most susceptible to this pressure.  Indeed early life stages are smaller in size than adults and are thus most vulnerable to this pressure as even a small load of added sediment will lead to the complete burial.  Sediment deposition can reduce macroalgal recruitment by (1) reducing the amount of substratum available for attachment of propagules; (2) scour, removing attached juveniles and (3) burial, altering the light and/or the chemical micro-environment (Devinny & Volse, 1978, Eriksson & Johansson, 2003).

In New Hampshire, the lower limits of Semibalanus balanoides (as Balanus balanoides) appear to be set by sand inundation (Daly & Mathieson, 1977).  Field observations and laboratory experiments have highlighted the sensitivity of limpets to sediment deposition.  Airoldi & Hawkins (2007) tested the effects of different grain sizes and deposit thickness in laboratory experiments using Patella vulgata.  Sediments were added as a ‘fine’ rain to achieve deposit thicknesses of approximately 1 mm, 2 mm, and 4 mm in controlled experiments and grazing and mortality observed over 8-12 days.  Limpets were more sensitive to sediments with a higher fraction of fines (67 % silt) than coarse (58 % sand).  Coarse sediments of thicknesses approximately 1, 2 and 4 mm decreased grazing activity by 35, 45 and 50 % respectively.  At 1 and 2 mm thicknesses, fine sediments decreased grazing by 40 and 77 %.  The addition of approximately 4 mm of fine sediment completely inhibited grazing.  Limpets tried to escape the sediment but lost attachment and died after a few days (Airoldi & Hawkins, 2007).

Sensitivity assessment.  There is no empirical evidence for the effects of sediment inundation on Pelvetia canaliculata.  Many fucoids, including Ascophyllum nodosum and Fucus vesiculosus, are intolerant of sediment.  It is likely that Pelvetia canaliculata is also intolerant of sediment inundation for the same reasons, as the physical environment within which it is found does not require it to have a tolerance of this pressure.  Many of the smaller species found within the biotope would be totally smothered by 5 cm.  Experimentation has shown that sedimentation of 4 mm can cause mortality of Patella vulgata (Airoldi & Hawkins, 2007).  The level of water movement within this biotope can be considerable and consequently deposited sediment will be removed within a small number of tides.  This is likely to cause some damage to the characterizing species and the other associated species.  Therefore, resistance and resilience have both been assessed as ‘Medium’. Overall the sensitivity of the biotope is assessed as ‘Medium’ at the level of the benchmark.

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

Several studies found that increasing the vertical sediment burden negatively impact fucoids survival and associated communities.  At the level of the benchmark (30 cm of fine material added to the seabed in a single event) smothering is likely to result in mortalities of the characterizing species Pelvetia canaliculata.  The maximum frond length of this species is 15 cm.  The state of the tide would not change the effect of deposition at this benchmark.  Even if deposition were to occur at high tide the fronds of Pelvetia canaliculata would be entirely covered.  This inundation with sediment would inhibit photosynthesis, and would most likely lead to degradation of the macroalgae.  Water movement within this biotope created by tidal streams and waves will remove sediment but it could take a number of tidal cycles.  Filter feeding species such as the barnacles Semibalanus balanoides and Chthalamus montagui found in LR.MLR.BF.PelB would be entirely smothered, as would Patella vulgata.  In this particular biotope, the level of water flow through tidal movement and wave exposure (exposed) could be high enough to remove the sediment relatively quickly.  The level of sediment deposition would mean that this could take long enough to cause mortality of organisms. 

Sensitivity assessment.  Resistance is ‘Low ‘and resilience is ‘Medium’.  Overall, the biotope has a ‘Medium’ sensitivity to siltation at the pressure benchmark.

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

Species characterizing this habitat do not have hearing perception but vibrations may cause an impact.  However, no studies exist to support an assessment.

Introduction of light or shading

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

Evidence

Increased levels of diffuse irradiation correlate with increased growth in macroalgae (Aguilaria et al., 1999).  Levels of diffuse irradiation increase in summer, and with a decrease in latitude.  As Pelvetia canaliculata is found in the middle its natural range in the British Isles an increase in the level of diffuse irradiation will not cause a negative impact on the species or the biotope.  Pelvetia canaliculata is likely to be affected by a decrease in light availability. 

Semibalanus balanoides sheltered from the sun grew bigger than un-shaded individuals (Hatton, 1938; cited in Wethey, 1984), although the effect may be due to indirect cooling effects rather than shading.  Barnacles are also frequently found under algal canopies suggesting that they are tolerant of shading.  Light levels have also been demonstrated to influence a number of phases of the reproductive cycle in Semibalanus balanoides.  In general, light inhibits aspects of the breeding cycle.  Penis development is inhibited by light (Barnes & Stone, 1972) while Tighe-Ford (1967) showed that constant light inhibited gonad maturation and fertilization.  Davenport & Crisp (unpublished data from Menai Bridge, Wales, cited from Davenport et al., 2005) found that experimental exposure to either constant darkness, or 6 h light: 18 h dark photoperiods induced autumn breeding in Semibalanus.  They also confirmed that very low continuous light intensities (little more than starlight) inhibited breeding.  Latitudinal variations in the timing of the onset of reproductive phases (egg mass hardening) have been linked to the length of darkness (night) experienced by individuals rather than temperature (Davenport et al., 2005).  Changes in light levels associated with climate change (increased cloud cover) were considered to have the potential to alter the timing of reproduction (Davenport et al., 2005) and to shift the range limits of this species southward.  

Sensitivity assessment.  It is not clear how these findings may reflect changes in light levels from artificial sources, and whether observable changes would occur at the population level as a result.  There is, therefore, 'No evidence' on which to base an assessment.

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 propagule dispersal.  But propagule dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

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

Evidence

Not relevant to seabed habitats. NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

Visual disturbance

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

Evidence

Not relevant.

Genetic modification & translocation of indigenous species

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

Evidence

Key characterizing species within this biotope are not cultivated or translocated.  This pressure is therefore considered not relevant to this biotope.

Introduction or spread of invasive non-indigenous species

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

Evidence

There are no known invasive non-indigenous species in the British Isles that invade upper intertidal rocky shores where these biotopes and Pelvetia canaliculata are found.  The Australasian barnacle Austrominius (previously Elminius) modestus was introduced to British waters on ships during the second world war.  However, its overall effect on the dynamics of rocky shores has been small as Austrominius modestus has simply replaced some individuals of a group of co-occurring barnacles (Raffaelli & Hawkins, 1999).  Although present, monitoring indicates it has not outnumbered native barnacles in the Isle of Cumbrae (Gallagher et al., 2015) it may dominate in estuaries where it is more tolerant of lower salinities than Semibalanus balanoides (Gomes-Filho, et al., 2010).  The degree of wave exposure experienced by a biotope will limit colonization by Austrominius modestus which tends to be present in more sheltered biotopes.  The higher wave exposures seen in the LR.MLR.BF.PelB biotope may not be suitable for this species of barnacle and are likely to limit its ability to compete with Chthalamus montagui and Semibalanus balanoides.

Sensitivity assessment.  Fucoid species have been negatively affected by both the direct and indirect consequences of invasive non-indigenous species being present.  However, no evidence can be found on the impacts of invasive non-indigenous species on Pelvetia canaliculata within this biotope.  There is the possibility that For this reason the effect of this pressure has been given as ‘No Evidence’. Literature for this pressure should be revisited.

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

There is insufficient evidence to support a review of the pressure at this benchmark.  Pelvetia canaliculata is known to harbour a large number of micro-organisms on its outer surface (Rugg & Norton, 1987).  A number of fungal species have also been found within the tissues of Pelvetia canaliculata, of which the ascomycetous fungi Mycosphaerella ascophylli is most commonly mentioned in literature (Subrahmanyan, 1960; Rugg & Norton, 1987).  The interactions between this fungi and Pelvetia canaliculata are not fully understood.  The number of microbial pathogens on Pelvetia canaliculata decreases in the summer.  This is thought to be due to higher air temperatures causing mortality of pathogens (Rugg & Norton, 1987).  Any introduction of microbial pathogen may be limited by the extreme physical conditions found within the habitat in which Pelvetia canaliculata is found.

Barnacles and the limpet Patella vulgata are considered subject to persistent, low levels of infection by pathogens and parasites.  Patella vulgata has been reported to be infected by the protozoan Urceolaria patellae (Brouardel, 1948) at sites sheltered from extreme wave action in Orkney.  Baxter (1984) found shells to be infested with two boring organisms, the polychaete Polydora ciliate and a siliceous sponge Cliona celata.

Sensitivity assessment.  Based on the characterizing species and the lack of evidence for widespread, high-levels of mortality due to microbial pathogens it is considered that the sensitivity assessment of this biotope is ‘No evidence’.

Removal of target species

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

Evidence

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of target species on this biotope.  There is no evidence for the intertidal collection of Pelvetia canaliculata.  Many intertidal microalgae’s are harvested from the shore for both commercial and recreational purposes.  The easy intertidal access to this species means that it would be easily collected from a shore.  As the key characterizing and structuring species, extensive removal of Pelvetia canaliculata would alter the character of the biotope.

Patella vulgata is targeted for consumption and is found occasionally within the LR.MLR.BF.PelB biotope.  However, it is not considered a characterizing species within this biotope and removal is unlikely to have an impact on the presence of the other characterizing species Semibalanus balanoides / Chthalamus montagui and Pelvetia canaliculata.

Sensitivity assessment.  As no evidence for the harvesting of the characterizing species within this biotope the sensitivity assessment is considered to be ‘Not relevant’.

Removal of non-target species

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

Evidence

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures.  The characterizing species Pelvetia canaliculata creates a dominant turf within this biotope.  The dominance of this characterizing species means it could easily be incidentally removed from this biotope as by-catch when other species are being targeted.  The loss of this species and other associated species would decrease species richness and negatively impact on the ecosystem function.

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope. The resistance to removal is ‘Low’ due to the easy accessibility of the biotopes location and the inability of these species to evade collection. The resilience is ‘Medium’, with recovery only being able to begin when the harvesting pressure is removed altogether. This gives an overall sensitivity score of ‘Medium’.