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

Deep waters off the continental shelf (200 – 2,500 m) are expected to see a lower temperature rise (≈ 1^oC) than shallow water habitats by the end of this century, regardless of the scenario (FAO (Fisheries and Aquaculture Organisation), 2019).  Lophelia pertusa is typically found in areas where temperatures range from 4 to 12°C (Davies et al., 2008, Lunden et al., 2014),  with UK reefs and colonies generally in water temperatures of 6-10°C (Frederiksen et al., 1992, Duineveld et al., 2007, Roberts et al., 2009). The upper lethal limit for this species is thought to be 15°C (Brooke et al., 2013). Madrepora oculata is found in temperatures varying from approximately 5°C in the NE Atlantic (Wild et al., 2008) to 13.9°C in the Mediterranean (Freiwald et al., 2009).

Whilst temperatures are thought to generally be very stable in Lophelia pertusa environments (Dullo et al., 2008), there are occasions when substantial increases in temperature can be observed. For example on the Tisler Reef, in Norway, in 2006 and 2008 the temperature rose by approximately 4°C in 24 hours, spiked at 12°C and remained above 10°C for approximately 30 days (Guihen et al., 2012). No Lophelia pertusa mortality was observed during this time, although mass mortality of the deepwater sponge, Geodia baretti, occurred (Guihen et al., 2012). Furthermore, over coral mounds off the coast of North Carolina, US, incursion of the Gulf Stream can lead to temperatures fluctuating greatly, reaching 15°C on a regular basis, from a mean bottom water temperature of 9.9°C (Brooke et al., 2013). ). In the Gulf of Mexico, Lophelia pertusa occurred in areas where temperatures were 8.5-10.6°C (Davies et al., 2010). Temperature variations of 0.8°C were observed over 5-11 hr periods, associated with internal waves. Furthermore, high-frequency temperature variability over 20-30-minute periods was also recorded at one of the coral sites (476m depth), where a temperature rise of 0.5°C occurred, followed by a slower temperature decline. These fluctuations exhibit 5- to 11-hour cycles. These observations suggest that this species can tolerate temperature increases.

Results of the effect of short-term (≤6 months) experimental increases in temperature on Lophelia pertusa have been somewhat mixed, with some finding this species sensitive to increased temperatures (Dodds et al., 2007, Lunden et al., 2014), and others showing positive effects of temperature increases (Büscher et al., 2017). Buscher et al. (2017) found an increase in growth rates in Norwegian populations in response to a six-month increase in temperature from 8-12°C. In the study by Lunden et al. (2013) a 2°C increase in temperature (from 8-10°C) saw a 10% decrease in survivorship, although some genotypes were more sensitive than others to the increase in temperature. Naumann et al. (2014) examined the respiration rate and calcification rates of Lophelia pertusa and Madrepora oculata collected from the Mediterranean at 12, 9 and 6°C after acclimation for one month. Lophelia pertusa was found to acclimate to lower temperatures (9 and 6°C) and maintained a constant respiration rate although calcification rates were reduced by 58% at 12°C. On the other hand, Madrepora oculata respiration decreased at the lower temperatures. Madrepora oculata appears to exhibit greater growth at temperatures towards the upper end of its temperature range (Naumann et al., 2014), which may be why this species is more abundant in the Mediterranean (Arnaud-Haond et al., 2017).

Sensitivity assessment. Under all three scenarios (middle and high emission, and extreme scenarios), waters off the continental shelf are expected to increase marginally by approximately 1°C, increasing the temperature at which UK Lopelia pertusa and Madrepora oculata colonies are found to be between 6 and 11°C, which is not outside their current temperature distribution. Whilst an increase of 1°C is not expected to cause catastrophic effects, laboratory experiments suggest an increase in temperature may lead to some stress on Lophelia pertusa, potentially leading to changes in feeding and respiration rates. It must be taken into consideration that any negative impacts observed in laboratory experiments were observed when temperatures were increased suddenly by 2°C or more, and experiments run over relatively short timescales (< 6 months). Under future projections for all scenarios, the temperature increase in deep waters is expected to rise by only 1°C, with this increase occurring over the next 50-80 years, giving NE Atlantic populations of Lophelia pertusa the chance to adapt, as it has to warmer water temperatures in the Gulf of Mexico and the Mediterranean. Madrepora oculata appears to respond positively to an increase in temperature and therefore is not expected to be sensitive to a 1°C increase in temperature. For this reason, the resistance has been assessed as ‘High’, whilst resilience has been assessed as ‘High’. This leads to an overall sensitivity score of ‘Not sensitive’ at this level benchmark.

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

Deep waters off the continental shelf (200 – 2,500 m) are expected to see a lower temperature rise (≈ 1^oC) than shallow water habitats by the end of this century, regardless of the scenario (FAO (Fisheries and Aquaculture Organisation), 2019).  Lophelia pertusa is typically found in areas where temperatures range from 4 to 12°C (Davies et al., 2008, Lunden et al., 2014),  with UK reefs and colonies generally in water temperatures of 6-10°C (Frederiksen et al., 1992, Duineveld et al., 2007, Roberts et al., 2009). The upper lethal limit for this species is thought to be 15°C (Brooke et al., 2013). Madrepora oculata is found in temperatures varying from approximately 5°C in the NE Atlantic (Wild et al., 2008) to 13.9°C in the Mediterranean (Freiwald et al., 2009).

Whilst temperatures are thought to generally be very stable in Lophelia pertusa environments (Dullo et al., 2008), there are occasions when substantial increases in temperature can be observed. For example on the Tisler Reef, in Norway, in 2006 and 2008 the temperature rose by approximately 4°C in 24 hours, spiked at 12°C and remained above 10°C for approximately 30 days (Guihen et al., 2012). No Lophelia pertusa mortality was observed during this time, although mass mortality of the deepwater sponge, Geodia baretti, occurred (Guihen et al., 2012). Furthermore, over coral mounds off the coast of North Carolina, US, incursion of the Gulf Stream can lead to temperatures fluctuating greatly, reaching 15°C on a regular basis, from a mean bottom water temperature of 9.9°C (Brooke et al., 2013). ). In the Gulf of Mexico, Lophelia pertusa occurred in areas where temperatures were 8.5-10.6°C (Davies et al., 2010). Temperature variations of 0.8°C were observed over 5-11 hr periods, associated with internal waves. Furthermore, high-frequency temperature variability over 20-30-minute periods was also recorded at one of the coral sites (476m depth), where a temperature rise of 0.5°C occurred, followed by a slower temperature decline. These fluctuations exhibit 5- to 11-hour cycles. These observations suggest that this species can tolerate temperature increases.

Results of the effect of short-term (≤6 months) experimental increases in temperature on Lophelia pertusa have been somewhat mixed, with some finding this species sensitive to increased temperatures (Dodds et al., 2007, Lunden et al., 2014), and others showing positive effects of temperature increases (Büscher et al., 2017). Buscher et al. (2017) found an increase in growth rates in Norwegian populations in response to a six-month increase in temperature from 8-12°C. In the study by Lunden et al. (2013) a 2°C increase in temperature (from 8-10°C) saw a 10% decrease in survivorship, although some genotypes were more sensitive than others to the increase in temperature. Naumann et al. (2014) examined the respiration rate and calcification rates of Lophelia pertusa and Madrepora oculata collected from the Mediterranean at 12, 9 and 6°C after acclimation for one month. Lophelia pertusa was found to acclimate to lower temperatures (9 and 6°C) and maintained a constant respiration rate although calcification rates were reduced by 58% at 12°C. On the other hand, Madrepora oculata respiration decreased at the lower temperatures. Madrepora oculata appears to exhibit greater growth at temperatures towards the upper end of its temperature range (Naumann et al., 2014), which may be why this species is more abundant in the Mediterranean (Arnaud-Haond et al., 2017).

Sensitivity assessment. Under all three scenarios (middle and high emission, and extreme scenarios), waters off the continental shelf are expected to increase marginally by approximately 1°C, increasing the temperature at which UK Lopelia pertusa and Madrepora oculata colonies are found to be between 6 and 11°C, which is not outside their current temperature distribution. Whilst an increase of 1°C is not expected to cause catastrophic effects, laboratory experiments suggest an increase in temperature may lead to some stress on Lophelia pertusa, potentially leading to changes in feeding and respiration rates. It must be taken into consideration that any negative impacts observed in laboratory experiments were observed when temperatures were increased suddenly by 2°C or more, and experiments run over relatively short timescales (< 6 months). Under future projections for all scenarios, the temperature increase in deep waters is expected to rise by only 1°C, with this increase occurring over the next 50-80 years, giving NE Atlantic populations of Lophelia pertusa the chance to adapt, as it has to warmer water temperatures in the Gulf of Mexico and the Mediterranean. Madrepora oculata appears to respond positively to an increase in temperature and therefore is not expected to be sensitive to a 1°C increase in temperature. For this reason, the resistance has been assessed as ‘High’, whilst resilience has been assessed as ‘High’. This leads to an overall sensitivity score of ‘Not sensitive’ at this level benchmark.

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

Deep waters off the continental shelf (200 – 2,500 m) are expected to see a lower temperature rise (≈ 1^oC) than shallow water habitats by the end of this century, regardless of the scenario (FAO (Fisheries and Aquaculture Organisation), 2019).  Lophelia pertusa is typically found in areas where temperatures range from 4 to 12°C (Davies et al., 2008, Lunden et al., 2014),  with UK reefs and colonies generally in water temperatures of 6-10°C (Frederiksen et al., 1992, Duineveld et al., 2007, Roberts et al., 2009). The upper lethal limit for this species is thought to be 15°C (Brooke et al., 2013). Madrepora oculata is found in temperatures varying from approximately 5°C in the NE Atlantic (Wild et al., 2008) to 13.9°C in the Mediterranean (Freiwald et al., 2009).

Whilst temperatures are thought to generally be very stable in Lophelia pertusa environments (Dullo et al., 2008), there are occasions when substantial increases in temperature can be observed. For example on the Tisler Reef, in Norway, in 2006 and 2008 the temperature rose by approximately 4°C in 24 hours, spiked at 12°C and remained above 10°C for approximately 30 days (Guihen et al., 2012). No Lophelia pertusa mortality was observed during this time, although mass mortality of the deepwater sponge, Geodia baretti, occurred (Guihen et al., 2012). Furthermore, over coral mounds off the coast of North Carolina, US, incursion of the Gulf Stream can lead to temperatures fluctuating greatly, reaching 15°C on a regular basis, from a mean bottom water temperature of 9.9°C (Brooke et al., 2013). ). In the Gulf of Mexico, Lophelia pertusa occurred in areas where temperatures were 8.5-10.6°C (Davies et al., 2010). Temperature variations of 0.8°C were observed over 5-11 hr periods, associated with internal waves. Furthermore, high-frequency temperature variability over 20-30-minute periods was also recorded at one of the coral sites (476m depth), where a temperature rise of 0.5°C occurred, followed by a slower temperature decline. These fluctuations exhibit 5- to 11-hour cycles. These observations suggest that this species can tolerate temperature increases.

Results of the effect of short-term (≤6 months) experimental increases in temperature on Lophelia pertusa have been somewhat mixed, with some finding this species sensitive to increased temperatures (Dodds et al., 2007, Lunden et al., 2014), and others showing positive effects of temperature increases (Büscher et al., 2017). Buscher et al. (2017) found an increase in growth rates in Norwegian populations in response to a six-month increase in temperature from 8-12°C. In the study by Lunden et al. (2013) a 2°C increase in temperature (from 8-10°C) saw a 10% decrease in survivorship, although some genotypes were more sensitive than others to the increase in temperature. Naumann et al. (2014) examined the respiration rate and calcification rates of Lophelia pertusa and Madrepora oculata collected from the Mediterranean at 12, 9 and 6°C after acclimation for one month. Lophelia pertusa was found to acclimate to lower temperatures (9 and 6°C) and maintained a constant respiration rate although calcification rates were reduced by 58% at 12°C. On the other hand, Madrepora oculata respiration decreased at the lower temperatures. Madrepora oculata appears to exhibit greater growth at temperatures towards the upper end of its temperature range (Naumann et al., 2014), which may be why this species is more abundant in the Mediterranean (Arnaud-Haond et al., 2017).

Sensitivity assessment. Under all three scenarios (middle and high emission, and extreme scenarios), waters off the continental shelf are expected to increase marginally by approximately 1°C, increasing the temperature at which UK Lopelia pertusa and Madrepora oculata colonies are found to be between 6 and 11°C, which is not outside their current temperature distribution. Whilst an increase of 1°C is not expected to cause catastrophic effects, laboratory experiments suggest an increase in temperature may lead to some stress on Lophelia pertusa, potentially leading to changes in feeding and respiration rates. It must be taken into consideration that any negative impacts observed in laboratory experiments were observed when temperatures were increased suddenly by 2°C or more, and experiments run over relatively short timescales (< 6 months). Under future projections for all scenarios, the temperature increase in deep waters is expected to rise by only 1°C, with this increase occurring over the next 50-80 years, giving NE Atlantic populations of Lophelia pertusa the chance to adapt, as it has to warmer water temperatures in the Gulf of Mexico and the Mediterranean. Madrepora oculata appears to respond positively to an increase in temperature and therefore is not expected to be sensitive to a 1°C increase in temperature. For this reason, the resistance has been assessed as ‘High’, whilst resilience has been assessed as ‘High’. This leads to an overall sensitivity score of ‘Not sensitive’ at this level benchmark.

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 caused by increased air-sea flux of heat are only expected to penetrate surface waters (≤ 50 m) (Cerrano et al., 2000, Garrabou et al., 2009; Dan Smale, pers. comms.) Therefore, sensitivity to marine heatwaves is probably ‘Not relevant’ in this bathyal habitat.

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 caused by increased air-sea flux of heat are only expected to penetrate surface waters (≤ 50 m) (Cerrano et al., 2000, Garrabou et al., 2009; Dan Smale, pers. comms.) Therefore, sensitivity to marine heatwaves is probably ‘Not relevant’ in this bathyal habitat.

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

Due to their calcified nature, both deep and shallow-water scleractinian corals are generally thought to be highly sensitive to ocean acidification (Hall-Spencer & Harvey, 2019). The deep-water species, Lophelia pertusa, is a plastic species which has a wide bathymetric range (30-3000 m), lives in several different temperate habitats, and can thrive in the Mingulay Reef complex, where tidal downwellings cause daily variations in pH equivalent to a 25 year jump in atmospheric CO₂ (Hennige et al., 2015). This suggests that it may have some tolerance to changes in pH.

Results of the impact of short-term experimental acidification on Lophelia pertusa generally show negative effects such as a decrease in respiration rates (Hennige et al., 2014; 0.3 unit decrease), and calcification rates (Maier et al., 2009; both at 0.15 and 0.3 unit decrease), or no observable effects (Maier et al., 2013b). Georgian et al. (2016), found variability in response between populations. For populations in the Gulf of Mexico, decreasing pH led to a decrease in respiration, prey capture rates and net calcification, whilst populations in Norway responded to a decrease in pH by increasing respiration and prey capture rates, leading to increased calcification (Georgian et al., 2016). Longer term studies (≥ 6 months) show potential for acclimation, with results suggesting that Lophelia pertusa can maintain calcification at levels of ocean acidification expected for the end in both the mid- and high-emission scenario  (Form & Riebesell, 2012, Maier et al., 2013a, Movilla et al., 2014, Hennige et al., 2015). Experimental exposures have similarly shown that calcification rates (Maier et al., 2012, Maier et al., 2013b) and respiration rates (Maier et al., 2013a) are maintained at ocean acidification levels expected for the high emission scenario in Madrepora oculata.

As the oceans absorb carbon dioxide from the atmosphere, leading to a decrease in pH and an increase in acidity, there is a further concern; the shoaling of the aragonite saturation horizon (ASH). The ASH is defined as the depth in the oceans at which aragonite saturation equals 1. Below this depth, aragonite saturation will fall below 1, and dissolution of calcified structures may occur. Currently, the depth of the ASH in the North Atlantic is approximately 2,000 m (Jiang et al., 2015). This depth has already become 80-150 m shallower over the past two centuries (Chung et al., 2003; Feely et al., 2004). By the end of this century, the depth of the ASH is expected to become shallower still, reaching depths of up to 400m under the high emission scenario (RCP 8.5) and 600m for the middle emission scenario (RCP 4.5) (Zheng & Long, 2014).

For both Lophelia pertusa (Form & Riebesell, 2012, Hennige et al., 2015, Büscher et al., 2017, Kurman et al., 2017), and Madrepora oculata (Maier et al., 2016), when the aragonite saturation state fell below 1, net calcification became close to zero, or fell below zero, as rates of dissolution overtook calcification. Experimental evidence suggests that some Lophelia genotypes may be more resilient than others to ocean acidification (Kurman et al., 2017). Whilst it is thought that most Lophelia pertusa populations occur above the aragonite saturation horizon, Lophelia pertusa is known to persist at aragonite saturation states < 1 along the Californian margin (Gomez et al., 2018), and under experimental conditions fragments managed to maintain slight net positive calcification under low pH and an aragonite saturation state of 0.76 (±0.10) during a 12-month duration (Hennige et al., 2015), suggesting some tolerance to future conditions. This said, this is the first observation of Lophelia pertusa below the ASH (Gomez et al., 2018), and Lophelia was not found at an aragonite saturation state < 1.25 in the Gulf of Mexico (Lunden et al., 2013). Lophelia pertusa has been shown to be able to upregulate the internal pH and therefore saturation state at the site of calcification (McCulloch et al., 2012), although upregulation is energetically costly (McCulloch et al., 2012). The persistence of Lophelia pertusa along the California margin may be due to the extremely high productivity of the area (Gomez et al., 2018), whilst maintenance of net calcification under experimental conditions (Hennige et al., 2015) may be due to an abundant food source.

As the aragonite saturation horizon shoals, dissolution of the exposed coral skeleton will occur, although live coral tissue will protect against dissolution. This may be compounded by the fact that under high CO₂ conditions, Lophelia branches grew longer and thinner, and there was a noticeable change in biomineralisation processes, leading to branches becoming 20-30% weaker than those in control conditions (Hennige et al., 2015). Results from the field suggest that Lophelia pertusa branches found in aragonite undersaturated waters have a lower skeletal density than populations found in saturated waters (Gomez et al., 2018). Dissolution of the exposed skeleton and a weakening of the integrity of live coral branches will lead to a loss of structural complexity becoming more susceptible to mechanical damage and bioerosion (Hennige et al., 2015).

Sensitivity Assessment. Whilst there is evidence that some populations of Lophelia pertusa can survive at an aragonite saturation state <1 (Gomez et al., 2018) this is the only record of this species being found in undersaturated waters, in an area of extreme productivity. Whilst this offers some hope for future cold-water coral colonies, evidence suggests that aragonite undersaturation is likely to lead to some mortality of this habitat, and even if net calcification can be maintained, it is likely that there will be some loss of colony integrity, making it more susceptible to mechanical damage or bioerosion. Under the middle emission scenario, the aragonite saturation horizon is expected to rise to approximately 800 m, meaning that ca 50% of the mid-bathyal depth zone (600 to 1,300 m) is expected to become undersaturated in aragonite. Whilst some Lophelia pertusa and Madrepora oculata colonies may be able to maintain calcification, there will likely be some mortality and some dissolution of exposed skeletons. For this scenario resistance has been assessed as ‘Medium’. Cold water corals are slow growing, and the undersaturation of waters will continue into the future, reducing growth even further, therefore their resilience has been assessed as ‘Very low’. This gives a sensitivity assessment of ‘Medium’.

Under the high emission scenario, the aragonite saturation horizon is expected to rise to approximately 400 m, meaning that the mid bathyal depth zone (600 to 1,300 m) is expected to become undersaturated in aragonite. Whilst some Lophelia pertusa and Madrepora oculata colonies may be able to maintain calcification in areas of extreme productivity, there will likely be significant mortality and some dissolution of exposed skeletons. For this scenario resistance has been assessed as ‘None’. Cold water corals are slow growing, and the undersaturation of waters will continue into the future, reducing growth even further, therefore their resilience has been assessed as ‘Very low’. This gives a sensitivity assessment of ‘High’.

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

Due to their calcified nature, both deep and shallow-water scleractinian corals are generally thought to be highly sensitive to ocean acidification (Hall-Spencer & Harvey, 2019). The deep-water species, Lophelia pertusa, is a plastic species which has a wide bathymetric range (30-3000 m), lives in several different temperate habitats, and can thrive in the Mingulay Reef complex, where tidal downwellings cause daily variations in pH equivalent to a 25 year jump in atmospheric CO₂ (Hennige et al., 2015). This suggests that it may have some tolerance to changes in pH.

Results of the impact of short-term experimental acidification on Lophelia pertusa generally show negative effects such as a decrease in respiration rates (Hennige et al., 2014; 0.3 unit decrease), and calcification rates (Maier et al., 2009; both at 0.15 and 0.3 unit decrease), or no observable effects (Maier et al., 2013b). Georgian et al. (2016), found variability in response between populations. For populations in the Gulf of Mexico, decreasing pH led to a decrease in respiration, prey capture rates and net calcification, whilst populations in Norway responded to a decrease in pH by increasing respiration and prey capture rates, leading to increased calcification (Georgian et al., 2016). Longer term studies (≥ 6 months) show potential for acclimation, with results suggesting that Lophelia pertusa can maintain calcification at levels of ocean acidification expected for the end in both the mid- and high-emission scenario  (Form & Riebesell, 2012, Maier et al., 2013a, Movilla et al., 2014, Hennige et al., 2015). Experimental exposures have similarly shown that calcification rates (Maier et al., 2012, Maier et al., 2013b) and respiration rates (Maier et al., 2013a) are maintained at ocean acidification levels expected for the high emission scenario in Madrepora oculata.

As the oceans absorb carbon dioxide from the atmosphere, leading to a decrease in pH and an increase in acidity, there is a further concern; the shoaling of the aragonite saturation horizon (ASH). The ASH is defined as the depth in the oceans at which aragonite saturation equals 1. Below this depth, aragonite saturation will fall below 1, and dissolution of calcified structures may occur. Currently, the depth of the ASH in the North Atlantic is approximately 2,000 m (Jiang et al., 2015). This depth has already become 80-150 m shallower over the past two centuries (Chung et al., 2003; Feely et al., 2004). By the end of this century, the depth of the ASH is expected to become shallower still, reaching depths of up to 400m under the high emission scenario (RCP 8.5) and 600m for the middle emission scenario (RCP 4.5) (Zheng & Long, 2014).

For both Lophelia pertusa (Form & Riebesell, 2012, Hennige et al., 2015, Büscher et al., 2017, Kurman et al., 2017), and Madrepora oculata (Maier et al., 2016), when the aragonite saturation state fell below 1, net calcification became close to zero, or fell below zero, as rates of dissolution overtook calcification. Experimental evidence suggests that some Lophelia genotypes may be more resilient than others to ocean acidification (Kurman et al., 2017). Whilst it is thought that most Lophelia pertusa populations occur above the aragonite saturation horizon, Lophelia pertusa is known to persist at aragonite saturation states < 1 along the Californian margin (Gomez et al., 2018), and under experimental conditions fragments managed to maintain slight net positive calcification under low pH and an aragonite saturation state of 0.76 (±0.10) during a 12-month duration (Hennige et al., 2015), suggesting some tolerance to future conditions. This said, this is the first observation of Lophelia pertusa below the ASH (Gomez et al., 2018), and Lophelia was not found at an aragonite saturation state < 1.25 in the Gulf of Mexico (Lunden et al., 2013). Lophelia pertusa has been shown to be able to upregulate the internal pH and therefore saturation state at the site of calcification (McCulloch et al., 2012), although upregulation is energetically costly (McCulloch et al., 2012). The persistence of Lophelia pertusa along the California margin may be due to the extremely high productivity of the area (Gomez et al., 2018), whilst maintenance of net calcification under experimental conditions (Hennige et al., 2015) may be due to an abundant food source.

As the aragonite saturation horizon shoals, dissolution of the exposed coral skeleton will occur, although live coral tissue will protect against dissolution. This may be compounded by the fact that under high CO₂ conditions, Lophelia branches grew longer and thinner, and there was a noticeable change in biomineralisation processes, leading to branches becoming 20-30% weaker than those in control conditions (Hennige et al., 2015). Results from the field suggest that Lophelia pertusa branches found in aragonite undersaturated waters have a lower skeletal density than populations found in saturated waters (Gomez et al., 2018). Dissolution of the exposed skeleton and a weakening of the integrity of live coral branches will lead to a loss of structural complexity becoming more susceptible to mechanical damage and bioerosion (Hennige et al., 2015).

Sensitivity Assessment. Whilst there is evidence that some populations of Lophelia pertusa can survive at an aragonite saturation state <1 (Gomez et al., 2018) this is the only record of this species being found in undersaturated waters, in an area of extreme productivity. Whilst this offers some hope for future cold-water coral colonies, evidence suggests that aragonite undersaturation is likely to lead to some mortality of this habitat, and even if net calcification can be maintained, it is likely that there will be some loss of colony integrity, making it more susceptible to mechanical damage or bioerosion. Under the middle emission scenario, the aragonite saturation horizon is expected to rise to approximately 800 m, meaning that ca 50% of the mid-bathyal depth zone (600 to 1,300 m) is expected to become undersaturated in aragonite. Whilst some Lophelia pertusa and Madrepora oculata colonies may be able to maintain calcification, there will likely be some mortality and some dissolution of exposed skeletons. For this scenario resistance has been assessed as ‘Medium’. Cold water corals are slow growing, and the undersaturation of waters will continue into the future, reducing growth even further, therefore their resilience has been assessed as ‘Very low’. This gives a sensitivity assessment of ‘Medium’.

Under the high emission scenario, the aragonite saturation horizon is expected to rise to approximately 400 m, meaning that the mid bathyal depth zone (600 to 1,300 m) is expected to become undersaturated in aragonite. Whilst some Lophelia pertusa and Madrepora oculata colonies may be able to maintain calcification in areas of extreme productivity, there will likely be significant mortality and some dissolution of exposed skeletons. For this scenario resistance has been assessed as ‘None’. Cold water corals are slow growing, and the undersaturation of waters will continue into the future, reducing growth even further, therefore their resilience has been assessed as ‘Very low’. This gives a sensitivity assessment of ‘High’.

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

At a depth of 200 to 600 m, these biotopes will not be affected by sea-level rise.  Therefore, sensitivity to this climate change pressure is probably ‘Not relevant’ in this bathyal habitat.

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

At a depth of 200 to 600 m, these biotopes will not be affected by sea-level rise.  Therefore, sensitivity to this climate change pressure is probably ‘Not relevant’ in this bathyal habitat.

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

At a depth of 200 to 600 m, these biotopes will not be affected by sea-level rise.  Therefore, sensitivity to this climate change pressure is probably ‘Not relevant’ in this bathyal habitat.

Temperature increase (local)

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

Evidence

Lophelia pertusa distribution is controlled by several environmental factors, including temperature, oxygen saturation, food supply, currents, availability of suitable substratum, and carbonate chemistry (Davies et al., 2008; Roberts et al., 2009; Georgian et al., 2014; Maier et al., 2023).  Reef-forming cold-water corals occur in cool waters <14°C (Gomez et al., 2022; Maier et al., 2023). The distribution of Lophelia pertusa in the North Atlantic appears to correlate with water masses within certain temperature ranges rather than other environmental factors (Frederiksen et al., 1992; Freiwald,1998).  Lophelia pertusa is typically found in areas where temperatures range from 4 to 12°C (Davies et al., 2008; Robert et al., 2006; Lunden et al., 2014).  Lophelia pertusa around the UK, Ireland, and Norway are found in water temperatures 6 to 8°C (Zibrowius, 1980; Frederiksen et al., 1992; Freiwald et al., 2004), while Tursi et al. (2004) recorded Lophelia pertusa living within areas with sea temperatures between 12.5 to 14°C in the Mediterranean and Gomez et al. (2022) recorded Lophelia reefs with a thermal thermal tolerance between 6 and 12°C off the coast of South Carolina, USA at 650 to 850 m depth. Orejas et al. (2021) noted that Madrepora oculata had a wide thermal envelope and thrived in cold waters (ca 6°C) in northern cold-water coral sites off Norway and Ireland, to sites at ca 12°C off Angola to sites at 13°C in the Mediterranean. 

A single Lophelia pertusa was reported on the Beryl Alpha platform between depths of 75 and 114 m (Roberts, 2002a).  The water column around the platform was stratified; the salinity varied from 34.8 ppt at the surface to just over 35 ppt at 50 m, while the surface temperature remained fairly constant at 11.5°C to a depth of 50 m before dropping rapidly to 8°C between 70 and 110 m (Roberts, 2002a).  Roberts (2002a) noted that the depth of Lophelia pertusa corresponded with 8°C and a salinity of 35 ppt.  He suggested that Lophelia pertusa was restricted to depths of greater than 70 m by the temperature and salinity, competition from other epifauna (e.g. sponges and sea anemones) and possibly by wave action during storms (Roberts, 2002a).

Temperature fluctuations measured within Lophelia pertusa reefs typically range between 1 and 2°C (Schroeder, 2002; Wisshak et al., 2005; Davies et al., 2009; cited by Form & Riebesell, 2012).  Rogers (1999) suggested that the death of coral on the upper reaches of a reef may reflect changes in the depth of the thermocline. But the upper limit of the Lophelia pertusa reefs may be attributed to other factors, e.g. the origin of the water masses, salinity, wave action, or competition with other species e.g. sponges (Frederiksen et al., 1992; Rogers, 1999; Mortensen et al., 2001; Dr Alex Rogers, 2005 pers comm.).

Dodds et al. (2007) found that the metabolic rates of Lophelia pertusa increased dramatically when specimens collected from the Mingulay Reef complex were exposed to temperatures greater than those experienced within the reef.  An increase in temperature from 6.5 to 9°C and 9°C to 11°C (ca 2°C) resulted in a doubling in oxygen consumption (Dodds et al., 2007).  Dodds et al. (2007) suggested that the physiological response observed indicated a sensitivity to even this small temperature change. Naumann et al. (2014) examined the respiration rates and calcification rates of Lophelia pertusa collected from the Mediterranean at 12, 9 and 6°C after acclimation for one month. Lophelia pertusa was found to acclimate to lower temperatures (9 and 6°C) and maintained a constant respiration rate although calcification rates were reduced by 58% at 6°C.  Lunden et al. (2014) found that when Lophelia pertusa, collected from the Gulf of Mexico, were exposed to temperatures of 14°C in the laboratory experienced 47% mortality within seven days and 100% mortality in the subsequent three-week recovery period; at 16°C mortality was 100% after seven days.

Brooke et al. (2013) examined the thermal tolerance of Lophelia pertusa fragments from the Gulf of Mexico to a range of temperatures (5, 8, 15, 20 and 25°C) for 24 hrs and seven days. Survival was ca 60% after 24 hrs at 20°C but only ca 20% after seven days. Survival was relatively high (ca 80%) after seven days at 15°C, although there was variation in survival between replicates. Survival was also high (a mean of ca 90% but a range of 55-100%) after six months in fragments transplanted (on benthic landers to 418 or 450 m) to the waters of North Carolina, which experienced a wider range of temperatures than the Gulf of Mexico. Brooke et al. (2013) noted that deep coral reefs of the southeastern United States experience temperature fluctuations from a mean of ca 8.5°C to a spike of 15°C for hours to days. Guihen et al. (2012) also reported marked temperature fluctuations on the Tisler Reef, Norway in 2006 and 2008 where the temperature rose by ca 4°C in 24 hrs, spiked at 12°C and remained above 10°C for ca 30 days. No mortality of Lophelia was observed, although the periods of warm water coincided with the mass mortality of the resident population of the deep-water sponge Geodia baretti (Guihen et al., 2012). Brooke et al. (2013) concluded that Lophelia pertusa had a high tolerance to temperature fluctuations, as it was exposed to rapid and frequent changes to 15°C (possibly higher) and that these exposures were too brief to affect the survival of the coral colonies adversely.  Cordes et al. (2023) documented a large cold-water coral reef (ca 150 m in length) off Blake Plateau, USA which experienced temperature fluctuations of ca 6.4°C (between 4.3 and 10.7°C) in a matter of hours and currents more than 0.8 m/s during warm events that lasted up to seven days. These temperature spikes affected coral physiology but not survivorship (Gomez et al., 2022 cited in Cordes et al., 2023). 

Naumann et al. (2014) examined the respiration rate and calcification rates of Lophelia pertusa and Madrepora oculata collected from the Mediterranean at 12, 9 and 6°C after acclimation for one month. Lophelia pertusa was found to acclimate to lower temperatures (9 and 6°C) and maintained a constant respiration rate although calcification rates were reduced by 58% at 12°C. On the other hand, Madrepora oculata respiration decreased at the lower temperatures. Madrepora oculata appears to exhibit greater growth at temperatures towards the upper end of its temperature range (Naumann et al., 2014), which may be why this species is more abundant in the Mediterranean (Arnaud-Haond et al., 2017).

Chapron et al. (2021) suggested that Lophelia pertusa and Madrepora oculata occurred close to their upper thermal limit in the Mediterranean. Coral nubbins survived in experimental conditions exposed to 10, 13 and 15°C. But Lophelia experienced 46% mortality at 17°C after one month and 80% mortality after six months, while Madrepora experienced 70% mortality after one month, and 100% after six months. Chapron et al. (2021) noted that a 2°C increase (to 15°C) resulted in lower energy reserves and growth in Lophelia while Madrepora was more resilient. However, a 4°C increase (to 17°C) resulted in reduced physiological activity and death in both species. Büscher et al. (2022) examined the tolerance of Lophelia coral fragments, in both white and orange colour morphs, from Trondheim-Fjord, Norway to changes in temperature and carbon dioxide (pCO₂). White corals exhibited the highest calcification rates at 14°C, while the optimum temperature range for orange corals was between 10 and 12°C. Calcification rates, respiration rates, and polyp mortality were consistently higher in orange coral polyps (a mean of 55% in orange vs 22% in white colour morphs) but mortality increased substantially in both colour morphs at 14 to 15°C (Büscher et al., 2022). Increased temperature (up to 12°C) was reported to increase the recovery time of Lophelia polyps after exposure to the dispersant Corexit 9500 (Weinnig et al., 2020).

Sensitivity assessment.  Lophelia pertusa is an extremely long-lived species found in deep water where short-term temperature fluctuations are typically 1-2°C. It was thought to be stenothermal; adapted to relatively stable thermal conditions in deep water (Rogers, 1999). However, exceptional short-term and rapid temperature changes have been recorded in the Tisler Reef, Norway and may be routine in the Gulf of Mexico or off the coast of North Carolina (Guihen et al., 2012; Brooke et al., 2013). An upper-temperature limit of 14°C is suggested for Lophelia pertusa by the observations of Lunden et al. (2014) while Brook et al. (2003) suggest it may be higher. Local populations can probably adapt to local conditions. Roberts et al. (2009) noted that the downwelling of warmer (by 0.75°C) water within the Mingulay Reef (in response to the tidal cycle) would increase the corals' metabolic rate at the same time as supplying increased food. It is also noted that while Brooke et al. (2013) recorded high survivorship (a mean of ca 90%) in transplanted fragments after six months, the range of mortality was 0-45%. Chapron et al. (2021) reported that a 2°C increase (to 15°C) for up to six months lowered energy reserves and growth but an increase of 4°C (to 17°C) for up to six months resulted in significant mortality in both Lophelia and Madrepora.  The effects of a prolonged chronic increase in temperature (e.g. 2°C for a year, the benchmark) could probably depend on the reef location and other factors such as food supply. The evidence suggests (Guihen et al., 2012; Brooke et al., 2013) that Lophelia reefs in the North East Atlantic could probably survive a localised short-term increase in temperature of 5°C for a month, as long as the temperature did not exceed 14 to 15°C. However, if the temperature exceeded 14 to 15°C Lophelia and Madrepora polyps could experience significant mortality (Chapron et al., 2021; Büscher et al., 2022). Therefore, resistance is assessed as ‘Low’ as a precaution based on possible long-term effects of increased temperature or exposure to localised thermal effluent (albeit unlikely). Hence, resilience is assessed as ‘Very Low’ and sensitivity as ‘High’. 

Temperature decrease (local)

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

Evidence

Lophelia pertusa distribution is controlled by a number of environmental factors, including; temperature, oxygen saturation, food supply, availability of suitable substratum, and carbonate chemistry (Davies et al., 2008; Roberts et al., 2009; Georgian et al., 2014).  The distribution of Lophelia pertusa in the North Atlantic appears to correlate with water masses within certain temperature ranges rather than other environmental factors (Frederiksen et al., 1992; Freiwald,1998).  Lophelia pertusa is typically found in areas where temperatures range from 4 to 12°C (Davies et al., 2008; Robert et al., 2006; Lunden et al., 2014).  Lophelia pertusa around the UK, Ireland, and Norway are found in water temperatures 6 to 8°C (Zibrowius, 1980; Frederiksen et al., 1992; Freiwald et al., 2004), while Tursi et al. (2004) recorded Lophelia pertusa living within areas with sea temperatures between 12.5 to 14°C in the Mediterranean. Orejas et al. (2021) noted that Madrepora oculata had a wide thermal envelope and thrived in cold waters (ca 6°C) in northern cold-water coral sites off Norway and Ireland, to sites at ca 12°C off Angola to sites at 13°C in the Mediterranean. 

A single Lophelia pertusa was reported on the Beryl Alpha platform between depths of 75 and 114 m (Roberts, 2002a).  The water column around the platform was stratified; the salinity varied from 34.8 ppt at the surface to just over 35 ppt at 50 m, while the surface temperature remained fairly constant at 11.5°C to a depth of 50 m before dropping rapidly to 8°C between 70 and 110 m (Roberts, 2002a).  Roberts (2002a) noted that the depth of Lophelia pertusa corresponded with 8°C and a salinity of 35 ppt.  He suggested that Lophelia pertusa was restricted to depths of greater than 70 m by the temperature and salinity, competition from other epifauna (e.g. sponges and sea anemones) and possibly by wave action during storms (Roberts, 2002a).

Temperature fluctuations measured within Lophelia pertusa reefs typically range between 1 and 2°C (Schroeder, 2002; Wisshak et al., 2005; Davies et al., 2009; cited by Form & Riebesell, 2012).  Rogers (1999) suggested that the death of coral on the upper reaches of a reef may reflect changes in the depth of the thermocline.  But the upper limit of the Lophelia pertusa reefs may be attributed to other factors, e.g. the origin of the water masses, salinity, wave action, or competition with other species e.g. sponges (Frederiksen et al., 1992; Rogers, 1999; Mortensen et al., 2001; Dr Alex Rogers, 2005 pers comm.).

Dodds et al. (2007) found that the metabolic rates of Lophelia pertusa increased dramatically when specimens collected from the Mingulay Reef complex were exposed to temperatures greater than those experienced within the reef.  An increase in temperature from 6.5 to 9°C and 9°C to 11°C (ca 2°C) resulted in a doubling in oxygen consumption (Dodds et al., 2007).  Dodds et al. (2007) suggested that the physiological response observed indicated a sensitivity to even this small temperature change. Naumann et al. (2014) examined the respiration rate and calcification rates of Lophelia pertusa collected from the Mediterranean at 12, 9 and 6°C after acclimation for one month. Lophelia pertusa was found to acclimate to lower temperatures (9 and 6°C) and maintained a constant respiration rate although calcification rates were reduced by 58% at 6°C.  Lunden et al. (2014) found that when Lophelia pertusa, collected from the Gulf of Mexico, were exposed to temperatures of 14°C in the laboratory experienced 47% mortality within seven days and 100% mortality in the subsequent three-week recovery period; at 16°C mortality was 100% after seven days.

Brooke et al. (2013) examined the thermal tolerance of Lophelia pertusa fragments from the Gulf of Mexico to a range of temperatures (5, 8, 15, 20 and 25°C) for 24 hrs and seven days. Survival was ca 60% after 24 hrs at 20°C but only ca 20% after seven days. Survival was relatively high (ca 80%) after seven days at 15°C, although there was variation in survival between replicates.  Survival was also high (a mean of ca 90% but a range of 55-100%) after six months in fragments transplanted (on benthic landers to 418 or 450 m) to the waters of North Carolina, which experienced a wider range of temperatures than the Gulf of Mexico. Brooke et al. (2013) noted that deep coral reefs of the southeastern United States experience temperature fluctuations from a mean of ca 8.5°C to a spike of 15°C for hours to days. Guihen et al. (2012)  also reported marked temperature fluctuations on the Tisler Reef, Norway in 2006 and 2008 where the temperature rose by ca 4°C in 24 hrs, spiked at 12°C and remained above 10°C for ca 30 days. No mortality of Lophelia was observed, although the periods of warm water coincided with the mass mortality of the resident population of the deep-water sponge Geodia baretti (Guihen et al., 2012). Brooke et al. (2013) concluded that Lophelia pertusa had a high tolerance to temperature fluctuations, as it was exposed to rapid and frequent changes to 15°C (possibly higher) and that these exposures were too brief to adversely affect the survival of the coral colonies. Cordes et al. (2023) documented a large cold-water coral reef (ca 150 m in length) off Blake Plateau, USA which experienced temperature fluctuations of ca 6.4°C (between 4.3 and 10.7°C) in a matter of hours and currents more than 0.8 m/s during warm events that lasted up to seven days. These temperature spikes affected coral physiology but not survivorship (Gomez et al., 2022 cited in Cordes et al., 2023). 

Chapron et al. (2021) suggested that Lophelia pertusa and Madrepora oculata occurred close to their upper thermal limit in the Mediterranean. Coral nubbins survived in experimental conditions exposed to 10, 13 and 15°C. But Lophelia experienced 46% mortality at 17°C after one month and 80% mortality after six months, while Madrepora experienced 70% mortality after one month, and 100% after six months. Chapron et al. (2021) noted that a 2°C increase (to 15°C) resulted in lower energy reserves and growth in Lophelia while Madrepora was more resilient. However, a 4°C increase (to 17°C) resulted in reduced physiological activity and death in both species. Büscher et al. (2022) examined the tolerance of Lophelia coral fragments, in both white and orange colour morphs, from Trondheim-Fjord, Norway to changes in temperature and carbon dioxide (pCO₂). White corals exhibited the highest calcification rates at 14°C, while the optimum temperature range for orange corals was between 10 and 12°C. Calcification rates, respiration rates, and polyp mortality were consistently higher in orange coral polyps (a mean of 55% in orange vs 22% in white colour morphs) but mortality increased substantially in both colour morphs at 14 to 15°C (Büscher et al., 2022). Increased temperature (up to 12°C) was reported to increase the recovery time of Lophelia polyps after exposure to the dispersant Corexit 9500 (Weinnig et al., 2020).

Sensitivity assessment.  Lophelia pertusa is an extremely long-lived species found in deep water where short-term temperature fluctuations are typically 1 to 2°C. It was thought to be stenothermal; adapted to relatively stable thermal conditions in deep water (Rogers, 1999). However, exceptional short-term and rapid temperature changes have been recorded in the Tisler Reef, Norway and may be routine in the Gulf of Mexico or off the coast of North Carolina (Guihen et al., 2012; Brooke et al., 2013).  Although no evidence of exposure to temperature decreases was found, the ability of Lophelia and Madrepora to survive in variable temperature regimes suggests that cold-water coral reefs are probably more tolerant of temperature change than originally thought. The effects of a prolonged chronic decrease in temperature (e.g. 2°C for a year, the benchmark) would probably depend on the location of the reef and other factors such as food supply. However, there is no empirical evidence of the effect of temperature changes at the level of the benchmark, especially a decrease in temperature. It is also noted that while Brooke et al. (2013) recorded a mean survivorship of ca 90% in transplanted fragments after six months, the range of mortality was 0-45%.  Therefore, resistance is assessed as ‘Medium’ as a precaution based on possible long-term effects of temperature change or exposure to localised thermal effluent (albeit unlikely). Hence, resilience is assessed as ‘Very Low’ and sensitivity as ‘Medium’.  

Salinity increase (local)

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

Evidence

Lophelia pertusa occurs in waters of 35 to 37 psu but in fjords tolerates salinities as low as 32 psu (Rogers, 1999; Mortensen et al., 2001).  However, Rogers (1999) regarded Lophelia pertusa to be stenohaline. Orejas et al. (2021) reported that Madrepora oculata was recorded at salinities between 34.8 and 38. Lophelia pertusa and Madrepora oculata reefs and their associated fauna occur in relatively stable waters, which are not subject to large fluctuations in salinity.  While Lophelia pertusa is probably highly intolerant of changes in salinity at the benchmark level, it is unlikely to experience an increase in salinity except in rare cases such as the unlikely production of hypersaline effluents by offshore installations. 

Sensitivity assessment.  Due to the stable conditions in which Lophelia pertusa and Madrepora oculata usually found a change in salinity is likely to cause mortality of the coral polyps.  Consequently, resistance has been assessed as ‘Low’, resilience as ‘Very low’, and sensitivity assessed as ‘High’.

Salinity decrease (local)

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

Evidence

Lophelia pertusa occurs in waters of 35 to 37 psu but in fjords tolerates salinities as low as 32 psu (Rogers, 1999; Mortensen et al., 2001).  However, Rogers (1999) regarded Lophelia pertusa to be stenohaline.  Orejas et al. (2021) reported that Madrepora oculata was recorded at salinities between 34.8 and 38. Lophelia pertusa and Madrepora oculata reefs and their associated fauna occur in relatively stable waters, which are not subject to fluctuations in salinity.  While Lophelia pertusa is probably highly intolerant of changes in salinity at the benchmark level, it is unlikely to experience a decrease in salinity except in rare cases.  However, in shallow fjordic water, Lophelia pertusa is restricted to the deeper, stable oceanic water below the relatively reduced salinity coastal waters at the surface.  An increase in freshwater runoff may increase the depth of the pycnocline and would probably result in the death of the upper extent of the reef.

Sensitivity assessment.  Resistance has been assessed as ‘Low’ and resistance as ‘Very Low’ so that overall sensitivity is assessed as ‘High’ at the level of the benchmark.

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

Early records of cold-water coral reefs are associated with strong water flows (Roberts et al., 2009).  Further investigation found that Lophelia pertusa reefs occur where the topography causes current acceleration, e.g. on raised seabed features (e.g. seamounts and banks) and where the channel narrows in Norwegian fjords (Rogers, 1999).  In their review, Maier et al. (2023) concluded that above-average surface productivity and currents were important drivers of the distribution of most cold-water coral species. Higher water flow rates are thought to aid the two dominant food supply mechanisms to Lophelia pertusa; the regular rapid downwelling of surface water delivering pulses of warm nutrient-rich surface water, and, the periodic advection of high turbidity bottom waters (Davies et al., 2008; Roberts et al., 2009). Maier et al. (2023) concluded that cold-water coral reefs occur in areas of feast or famine where the local hydrograph produces periodic pulses of food due to internal waves operating on seasonal, multi-year, decadal or millennial cycles, with currents that interact with the deep-sea topography (such as sea mounts, continental shelf margins, fjord sills) or the cold-water reefs themselves to form internal waves, hydraulics jumps and trapped waves. The resultant downwelling can rapidly transport surface productivity (such as plankton or POM) to the reef (Maier et al., 2023). For example, fresh organic matter can be transported from the surface in less than one hour to 140 m on Mingulay Reef (reviewed by Maier et al., 2023). Internal waves also resuspend deposited organic matter into the bottom or intermediate layers (Maier et al., 2023). 

Frederiksen et al. (1992) suggested that Lophelia pertusa reefs around the Lousy and Hatton Banks would typically encounter current speeds of 0.01-0.1 m/s. Water flow rates >0.4 m/s were recorded by moored and landed deployed current meters close to deep-water coral mounds in the Porcupine Seabight (Grehan et al., 2003), while Masson et al. (2003) recorded a maximum residual bottom water flow of 0.35 m/s over 20 days in July 2000 over the Darwin Mounds.  Current speeds of 0.01 -0.1 m/s, 0.35 or 0.4 m/s approximate to between weak and moderately strong water flow.  However, oceanic and tidal currents in the region of the Faroes were reported to be about 0.5 m/s (moderately strong) and in the region of west Shetland 0.5 to 0.7 m/s or more (moderately strong). Meinis et al. (2007) reported current speeds of up to 0.45 m/s, with a residual current of 0.1 m/s, along coral mounds on the southwest Rockall Trough. Similarly, Davies et al. (2008) reviewed the environmental parameters for the occurrence of Lophelia pertusa. They concluded that it occupied a niche where the current speed (ranging from 0.004 to 0.51 m/s, with a mean of 0.07 m/s) and productivity (a mean of 0.9 mg/m³) were higher than average. Maier et al. (2023) concluded that cold-water coral reefs occurred at water flow rates of 0.11 +/- 0.07 m/s based on their global review.

Mortensen (2001) investigated the growth and behaviour of Lophelia pertusa in an aquarium with flowing seawater.  No polyp mortality was observed in the vicinity of his aquaria inlets but high mortality at the opposite end.  Similarly, the death of coral polyps within a coral coppice was thought to be due to reduced water flow within the colony (Wilson, 1979b). Mortensen (2001) also noted that high current flow (greater than ca 0.05 m/s) was detrimental to growth, presumably due to reduced food capture rates.  Purser et al. (2010) collected samples of Lophelia pertusa from the Tisler Reef off Norway.  They then kept them in controlled laboratory aquaria and tested the effect of flow velocity on food capture rates. Flow rates were kept at 0.025 m/s and 0.05 m/s, and the reduction in Artemia salina nauplii concentrations was recorded.  Maximum net capture rates were found at 0.025 m/s (Purser et al., 2010). Orejas et al. (2016) also concluded from flume studies that water flow rates impacted food capture efficiency in Lophelia pertusa. It mostly captured zooplankton at low flow speeds of 0.02 m/s and phytoplankton at 0.05 m/s and polyp expansion was greatest at low flow speeds of 0.005 and 0.67 m/s rather than at 0.15 and 0.27 m/s. Although cold-water coral reefs are associated with areas of high bottom currents velocities (as above), Orejas et al. (2016) noted that strong currents were often short-lived and driven by tidal events and that currents were slow for several hours between tidal cycles, for example in the Mingulay Reef velocity could decrease to less than 0.02 m/s during each tidal cycle. In addition, the structure of the coral matrix also slows the currents locally within the coral matrix itself and the reef colonies probably dissipate higher current velocities with increasing size (Orejas et al., 2016). The coral reef structure slowed local current velocity to optimise food capture rates at 0.05 m/s for phytoplankton (phytodetritus) and 0.02 m/s for zooplankton capture (reviewed by Maier et al., 2023). However, small, discrete colonies probably have less effect on water flow rates. 

Sensitivity assessment.  Cold-water coral reefs rely on constant, mass water flow, and resultant internal waves to create periodic downwelling and upwelling events to supply food and nutrients and prevent the build-up of sediment.  A decrease in water flow across the reef would reduce the availability of food, which may decrease the health of the Lophelia pertusa and Madrepora oculata colonies.  If it were reduced below a certain level, mortality could occur.  Although Lophelia pertusa relies on water flow, Mortensen's data (2001) suggests a sustained water flow over 0.05 m/s may reduce growth under laboratory conditions.  However, areas in which cold-water coral reefs are found experience great changes in water flow rates throughout the tidal cycle (reviewed by Maier et al., 2023). Therefore, both resistance and resilience have been assessed as ‘High’, and sensitivity assessed as ‘Not sensitive’ at the benchmark level.

Emergence regime changes

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

Evidence

Cold-water coral reefs occur in oceanic waters, at depths of over 200 m, except in Norwegian fjords where the upper depth limit may be 50 m, below the influence of coastal waters. Therefore, it is unlikely to be affected by changes in the emergence regime and 'Not relevant' has been recorded. 

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

The discrete Lophelia pertusa colonies (DisLop) biotopes occur below 200 m in depth, at which depth even the wave action generated by storm conditions is unlikely to penetrate.  Therefore, ‘Not relevant’ has been recorded.

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

Weinnig et al. (2020) examined the effects of oil and dispersants on Lophelia pertusa colonies, based on concentrations released from the Deepwater Horizon oil spill. Lophelia pertusa exposed to low concentrations of oil (10 mg/l), dispersants (7.7 mg/l) and oil+dispersant (10 mg/l + 1.5%), did not show signs of a reduction in health, and no signs of stress were shown when only exposed to high concentrations (200 mg/l) of oil. However, Lophelia pertusa that had been exposed to high concentrations (154 mg/l) of dispersants showed a decline in health and those exposed to high oil + high dispersants displayed phenotypic changes after 24 hours of exposure, with tissue between polyps seen to detach from the skeleton. These did not recover when returned to normal seawater. Seawater temperature also affected recovery from dispersant exposure, with increased temperature slowing down recovery. Samples exposed to dispersants, but within normal seawater temperature ranges (8°C), recovered within 24 hours whereas those exposed to increased temperatures (12°C) had not recovered after 24 hours (Weinnig et al., 2020). Weinnig et al. (2020) noted that no visible impacts were observed on Lophelia pertusa colonies after the Deepwater Horizon spill but sublethal effects may have gone unnoticed. 

Bytingsvik et al. (2020) examined the effects of the dispersant Corexti 9500 and single aromatic hydrocarbons (toluene, phenanthrene and 2-methylnaphthalene) on Lophelia pertusa in 96-hour experiments. They measured polyp activity (number of polyps extended) every 24 hours as a sensitive sublethal endpoint. Corexit 9500 (96-hour EC50 = 34.8 mg/l) was less toxic to the coral than aromatic hydrocarbons tested (96-hour EC50s for toluene = 19.6 mg/l, Phenanthrene = 1.08 mg/l, and 2-methylnaphthalene = 0.5 mg/l) of which toluene was the least toxic. After the acute 96-hour tests polyps exposed to 2-methylnaphthalene were transferred to clean water for eight weeks. Mortality was measured after sixty days and 39% mortality was observed in the highest concentration tested (not given). Bytingsvik et al. (2020) estimated an LC50 of 3.93 mg/l for 2-methylnaphthalene. 

Sensitivity assessment. The above evidence suggests that exposure to oil and dispersants reduced health and caused sublethal effects in Lophelia polyps (Weinnig et al., 2020). Exposure to aromatic hydrocarbons induced sublethal effects after 24 hours but also resulted in significant delayed mortality (Bytingsvik et al., 2020). Therefore, resistance is assessed as 'Low' as a worst-case scenario but with 'Low' confidence since it is based on a single hydrocarbon from one study. Hence, resilience is assessed as 'Very low' and sensitivity as 'High' but with 'Low' confidence.

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

Larsson et al. (2013) exposed Lophelia pertusa fragments to fine (<63 µm) natural sediment and drill cuttings at 5 mg/l and 25 mg/l for 12 weeks in the laboratory. After 12 weeks, mortality was low with only 0.3% (1 polyp) dying after exposure to 25 mg/l natural sediment and 2.2% (8 polyps) dying after exposure to 12 weeks but zero in controls. They attributed the mortality to the build-up of sediment on the fragments and potential resultant smothering (Larsson & Purser, 2011; Larsson et al., 2013).  At the low concentration of sediments, the polyps were fully extended but only half extended at the high concentration and there was a trend towards lower growth rates when exposed to drill cuttings rather than natural sediment (Larsson et al., 2013b). In addition, Larsson et al. (2013) reported significant mortality (67%) in planulae exposed to 25 mg/l of drilling cuttings after four days, while mortality at 5 mg/l was low and not significantly different from controls. Gilmour (1999; cited in Larsson et al., 2013) reported larval mortality was an average of 98% after two days of exposure to 50 and 100 mg/l of natural sediment. Nevertheless, Larsson et al. (2013) concluded that Lophelia pertusa polyps coped reasonably well with increased suspended sediment and deposition rates.

Järnegren et al. (2020) examined the effects of drilling wastes on eight and 21-day larvae of Lophelia pertusa in the laboratory. Larvae were exposed to varied concentrations of bentonite, barite and drill cuttings for 24 hours in the laboratory and then transferred to clean water for 24 hours for recovery. The larvae were assessed for non-lethal and lethal effects. The 24-hour EC50s for eight-day and 21-day larvae were 10.1 and 9.6 mg/l respectively for bentonite, 37.7 and 39.8 mg/l for drill cuttings, and 19.9 mg/l in eight-day larvae exposed to barite. The 24-hour LC50s for eight-day and 21-day larvae were 79.5 and 53.0 mg/l respectively for bentonite, 112.4 and 380.0 mg/l for drill cuttings, and 133.4 mg/l in eight-day larvae exposed to barite. The effects of the suspended particles were primarily due to clogging of the larval cilia. Mortality in the experiments was low and the LC50s were modelled based on the experimental data. Bentonite was the most toxic and the only material to result in experimental mortality in 21-day larvae at 53 mg/l. However, the 21-day larvae were more sensitive than the eight-day larvae (Järnegren et al., 2020). Järnegren et al. (2020) noted that the Lophelia larvae tested were ca 23 times more sensitive than in prior studies. However, they also noted that Lophelia reefs within ca 100 m of exploratory drilling in Norwegian water were not exposed to more than 25 mg/l for a few days, and no adverse effects on the reef were observed (Purser, 2011, cited in Järnegren et al., 2020) but also noted that this concentration could adversely affect larvae. 

Aller et al. (2013) exposed Lophelia fragments from Tisler Reef to reef sediment and drill cuttings at concentrations of 66, 198 and 462 mg/cm² under experimental conditions. They noted that the branching structure of the fragments and mucus release prevented the build-up of sediment on the polyps (a mean of 2 mm for drill cuttings and 3 mm for natural sediment) and that the polyps tolerated the reduction in oxygen levels without any visible detrimental effects.  They concluded that exposure to suspended sediment from oil and gas drilling activities would not cause coral death within <12 days even at three or seven times the regulatory levels. 

Baussant et al. (2022) exposed Lophelia nubbins to barite, bentonite and drill cutting particles in realistic exposure concentrations (ca 4 to 60 mg/l) in pulsed exposure experiments (4-hour pulses) for five days followed by two weeks of recovery. Respiration rates and growth were not significantly different between treatments. Mortality (ca 20%) occurred in all treatments including the controls but was only significantly higher in polyps exposed to 19 and 49 mg/l drill cutting particles two to six weeks after exposure. Baussant et al. (2022) concluded that Lophelia polyps were resilient to short, realistic exposure to suspended drill waste particles but suggested a risk of long-term effects if exposed to ca 20 mg/l. 

Sensitivity assessment. The above evidence suggests that exposure to drilling wastes (e.g. bentonite, barite and drill cuttings) could result in some mortality in polyps and larvae but that planulae may be significantly affected under laboratory conditions (Larsson et al., 2013; Järnegren et al., 2020; Baussant et al., 2022). Larval mortality and abnormal development may impact recruitment and recovery, which is slow in Lophelia pertusa, even though their fecundity and dispersal potential are high. Overall, resistance is assessed as 'Medium' based on the potential direct impact. Resilience is assessed as 'Very low' and sensitivity as 'Medium'. 

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

It was suggested that the lower limit of Lophelia pertusa's bathymetric distribution is partially determined by the oxygen minimum zone (Freiwald, 1998; Rogers, 1999). Dodds et al. (2007) investigated the metabolic tolerance of Lophelia pertusa collected from the Mingulay Reef, Scotland to temperature and dissolved oxygen (DO) change in the laboratory. They found that Lophelia pertusa could survive anoxia for one hour, and hypoxia (2-3 kPa; 0.88 to 1.32 mg/l) for 96 hours (four days).  Lophelia pertusa was able to increase its uptake of oxygen by the expansion of the surface area of its polyp in response to low oxygen concentrations (Dodds et al., 2007). Lophelia pertusa was able to regulate its oxygen consumption until the oxygen concentration fell below 98-10 kPA at 9°C. Dodds et al. (2007) suggested that the critical oxygen concentration for this species, below which it would not be able to carry out normal aerobic function was ca 9.5 kPa (ca 3.26 ml/l; ca 4.56 mg/l). Davies et al. (2008) mapped the suitable habitat for Lophelia pertusa and found that Lophelia pertusa records were associated with areas of water with an ambient oxygen concentration between 4.3 to 7.2 ml/l (6.47-10.35 mg/l), with a mean of 6 to 6.2 ml/l (ca 8.4 to 8.6 mg/l) and that the species was not found in areas where the oxygen concentration was less than 2.37 ml/l (3.32 mg/l). Lunden et al. (2014) studied, among other things, the effect of decreasing oxygen concentration of Lophelia pertusa collected from the Gulf of Mexico.  Oxygen concentrations within the Gulf of Mexico are lower than those recorded in the North East Atlantic, with records ranging from 1.5 to 3.2 ml/l (ca 2.1 to 4.48 mg/l) (Lunden et al., 2014).  Laboratory experiments exposed Lophelia pertusa to different oxygen concentrations for seven days. The Lophelia pertusa samples survived (0% mortality) exposure to 5.3 ml/l (ca 7.4 mg/l) and 2.9 ml/l (ca 4 mg/l) but 100% mortality at ca 1.57 ml/l (ca 2.2 mg/l) after seven days. 

However, extensive Lophelia reefs have been discovered off the coast of West Africa in the oxygen minimum zone (OMZ) (Hebbeln et al., 2020; Buhl-Mortensen et al., 2024). Hebbeln et al. (2020) documented 100 m high reefs dominated by Lophelia at 330 to 470 m and dispersed colonies of cold-water corals at 250 to 500 m off the coast of Angola in water at 6.8 to 14.2°C and dissolved oxygen concentration of 0.6 to 1.15 ml/l (ca 0.84 to 1.61 mg/l). Sporadic occurrences of small Lophelia colonies were also observed off Mauritania at 1.1 to 1.4 ml/l oxygen (ca 1.54 to 1.96 mg/l oxygen) (Ramos et al., 2017 cited in Hebbeln et al., 2020). Buhl-Mortensen et al. (2024) reported healthy reefs (with over 20% cover) off Ghana and Mauritania at dissolved oxygen (DO) concentrations of 1.1 to 1.6 ml/l (ca 1.54 to 2.24 mg/l) in corrosive waters (low pH and aragonite) with high nutrient concentrations. However, the North Morrocco reefs had few colonies but were sited in well-oxygenated waters with high aragonite (Buhl-Mortensen et al., 2024). Norwegian reefs occur in waters with a DO concentration of ca 5 ml/l (ca 7 mg/l). Gori et al. (2023) found no significant differences in respiration rates in Lophelia specimens exposed to low oxygen (1.4 ml/l; 1.96 mg/l) or under-saturated oxygen concentrations (6.1 ml/l; 8.54 mg/l) after 10 days in the laboratory. They noted that the respiratory rates they recorded were similar to those reported from normoxic areas. 

In their review, Buhl-Mortensen et al. (2024) concluded that the tolerance range of hypoxia was larger than that for temperature in Lophelia. They noted that the large Ghanian and Mauritanian reefs were much older than the North Atlantic examples (at ca 20,000 years) and were not hindered by low DO, low pH, and low aragonite concentrations. They concluded that Lophelia had a wide tolerance to hypoxia and acidification but that temperature and situation may be more serious threats. However, they noted that local adaptation may affect tolerance to low oxygen and corrosive conditions (Hebbeln et al., 2020; Buhl-Mortensen et al., 2024). Hebbeln et al. (2020) suggested that the global DO tolerance range of Lophelia pertusa was less than 1 ml/l to greater than 6 ml/l (ca <1.4 mg/l to >8.4 mg/l) but that the tolerance range may be smaller at the regional scale.

Orejas et al. (2021) described extensive reefs of Madrepora oculata that reach heights of 1.25 m and densities of ca 0.53 /m2, thriving in the oxygen minimum zone off the coast of Angola, West Africa. They noted that Madrepora oculata showed a wide inter-regional tolerance to DO and occurred in waters of 6.7 ml/l (ca 9.38 mg/l) off Norway to 0.5 m/l/ (ca 0.7 mg/l) off Angola. They suggested that the high food availability in Angolan reefs compensated for the metabolic stress of low DO (Orejas et al., 2021). 

Sensitivity assessment.  The recent (2020 to 2024) evidence suggests that extensive Lophelia reefs can thrive in waters where the DO was less than 1.4 mg/l (Hebbeln et al., 2020; Buhl-Mortensen et al., 2024). Similarly, Madrepora reefs can thrive in waters as low as 0.7 mg/l DO (Orejas et al., 2021). Laboratory tests on Lophelia samples collected from the Mingulay Reef reported they could survive hypoxia for four days but not function below ca 4.56 mg/l DO while Lophelia collected from the Gulf of Mexico died after exposure to ca 2.2 mg/l DO for seven days (Dodds et al., 2007; Lunden et al., 2014). The evidence suggests that Lophelia pertusa and Madrepora oculata can adapt to low oxygen concentrations in the long term but that hypoxia tolerance may vary regionally. Therefore, populations in the North East Atlantic may be more sensitive to hypoxia than populations along the west coast of Africa or the Gulf of Mexico. However, the short-term acute hypoxia, represented by the benchmark, may also be mitigated by the large water masses and strong currents typical of areas dominated by cold-water coral reefs. Therefore, resistance is assessed as ‘Medium’ to represent some mortality under the worst-case scenario. Hence, resilience is assessed as ‘Very low, and sensitivity as 'Medium' but with 'Low' confidence. 

Nutrient enrichment

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

Evidence

The physical structure and position of cold-water coral structures (reefs and mounds) have been shown to induce up-welling and down-welling events, determined by the tidal currents and the tidal cycles, that provide food to the reef and link surface water productivity with deep waters (Roberts et al., 2009; Soetaert et al., 2016; Kazanditis & Witte, 2016). The nutrient levels (e.g. nitrates, phosphates, and ammonia) and inorganic carbon in the vicinity of cold-water coral reefs in the North East Atlantic vary with the tidal cycle and with depth (Findlay et al., 2014). For example, Findlay et al. (2014) reported a range of inorganic carbon of 2088 to 2186 µmol/kg and nitrate (NO₃) or 4.1-18.8 µmol/l in the sites they examined in the North East Atlantic. Davies et al. (2008) also report a range of nitrate levels of 8 - 23.4 µM (mean of 13.8 µM)  for sites where Lophliea pertusa was recorded in the North East Atlantic. Davies et al. (2008) noted a negative correlation between high nutrient concentrations (nitrate, phosphate and silicate) with Lophelia pertusa distribution. They also noted that the species was not found in the lowest nutrient concentrations and that while high nutrient levels limited distribution, the species probably required intermediate levels (Davies et al., 2008).

The evidence suggests that high or low nutrient levels, when compared across the North East Atlantic (Davies et al., 2008) may be detrimental. Nevertheless, no information on the effect of nutrient enrichment on cold-water coral reefs or mounds was found.  Therefore, 'No evidence' is recorded. 

Organic enrichment

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

Evidence

The physical structure and position of cold-water coral structures (reefs and mounds) have been shown to induce up-welling and down-welling events, determined by the tidal currents and the tidal cycles, that provide food to the reef and link surface water productivity with deep waters (Roberts et al., 2009; Duineveld et al., 2012; Soetaert et al., 2016; Kazanidis & Witte, 2016). Kazanidis & Witte (2016) note that the supply of organic matter to the cold-water corals also benefits other suspension feeders in the community. For example, the Mingulay area had a higher biomass of suspension or filter feeders than the Logachev area. Kazanidis & Witte (2016) suggested that this was due to the benthopelagic coupling of highly productive surface waters with the reef and higher velocity of bottom currents in the Migulary area compared to the Logachev area. Madrepora oculata was considered to be a less opportunistic feeder than Lophelia pertusa and more sensitive to fluctuations in food availability (Chapron et al., 2020; reviewed by Maier et al., 2023).  Maier et al. (2023) concluded that Lophelia pertusa was well-adapted to a feast-famine environment due to its ability to exploit phytodetritus and plankton food pulses but switch to other food sources when they are absent, its low growth rate that can be boosted when food is abundant, and its ability to build up tissue food reserves, mainly for reproduction, whose use is synchronised with seasonal changes in food supply (reviewed by Maier et al., 2023). Maier et al. (2023) also noted that above-average surface productivity and currents were drivers of cold-water coral distribution, globally. 

Nevertheless, no information on the effect of organic enrichment (at the level of the benchmark) on cold-water coral reefs or mounds was found.  Therefore, 'No evidence' is recorded.

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

Lophelia pertusa and Madrepora oculata larvae must settle onto hard substrata (Roberts et al., 2009; Maier et al., 2023) to enable them to find a solid anchor point, from which the hard skeleton of the coral can attach. The presence of Lophelia pertusa on oil and gas platforms (Gass & Roberts, 2006) suggests that their larvae are able to settle onto artificial substrata. The discrete Lophelia pertusa colonies (DisLop) biotopes occur on bedrock, boulders, cobbles and isolated drop stones (M.AtUB.Ro.MixCor.DisLop & M.AtMB.Ro.MixCor.DisLop) or coarse sediment and coral rubble (M.AtUB.Co.MixCor.DisLop & M.AtMB.Co.MixCor.DisLop) where the substratum provides adequate hard substratum for colonization by the coral colonies. Therefore, a change from hard to artificial or hard to coarse sediment might be tolerated, in theory, while a change to soft sediment would probably exclude cold-water corals. However, for a change in substrata to occur, the original substratum would need to be removed first, which would result in the removal of living coral and dead coral debris, resulting in the destruction of the reef and loss of the biotope. 

Sensitivity assessment.  Therefore, a resistance of ‘None’ and a resilience of ‘Very low’ have been recorded, resulting in a sensitivity of ‘High’.

Physical change (to another sediment type)

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

Evidence

The discrete Lophelia pertusa colonies (DisLop) biotopes occur on bedrock, boulders, cobbles and isolated drop stones (M.AtUB.Ro.MixCor.DisLop & M.AtMB.Ro.MixCor.DisLop) or coarse sediment and coral rubble (M.AtUB.Co.MixCor.DisLop & M.AtMB.Co.MixCor.DisLop) where the substratum provides adequate hard substratum for colonization by the coral colonies. Therefore, a permanent change from coarse sediment and coral rubble to soft (sand or mud dominated) sediment would probably exclude cold-water corals. 

Sensitivity assessment.  Therefore, a resistance of ‘None’ and a resilience of ‘Very low’ have been recorded, resulting in a sensitivity of ‘High’.

Habitat structure changes - removal of substratum (extraction)

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

Evidence

Extraction of the substratum to 30 cm within this biotope would mean that all reef-forming, characterizing species would be removed within the area of impact. This would destroy the habitat and result in the loss of the biotope. Examples of the DisLop biotopes that were exclusively on bedrock would probably be unaffected but any colonies on boulders, cobbles, coral rubble or coarse sediment would be lost. 

Sensitivity assessment.  Resistance is assessed as ‘None’.  The long-lived nature and slow growth rate of the characterizing species mean that resilience is assessed as  ‘Very low’, and sensitivity assessment as ‘High’.

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

Although cold-water coral reefs occur at great depths, they are likely to be subject to physical disturbance due to anchorage or positioning of offshore structures on the seabed but especially due to deep-sea trawling. Rogers (1999) suggested that trawling gear would break up the structure of the reef, fragment the reefs, and potentially result in the complete disintegration of the coral matrix, and loss of the associated species.

Fosså et al. (2002) documented and photographed the damage caused to west Norwegian Lophelia pertusa reefs by trawling activity (see Fosså, 2003 for photographs).  They reported that four, out of five sites studied, contained damaged corals. In the shallow regions of Sørmannsneset, only fragments of dead Lophelia pertusa were seen, spread around the site with no evidence of living colonies in the surrounding area, and Fosså et al. (2002) concluded that the colonies had been "wiped out".  Overall, they estimated that between 30 and 50% of Lophelia pertusa reefs were either impacted or destroyed by bottom trawling in western Norway.  Mechanical damage by fishing gear would also damage or kill the associated epifaunal species, some of which are slow-growing e.g. sponges, potentially turn over the coral rubble field, and modify the substratum (Rogers, 1999; Fosså et al., 2002).  Fosså et al. (2002) demonstrated that gorgonian (horny) corals were also torn apart by bottom trawling. Fosså (2003) also note that fixed fishing nets, e.g. gill nets, and long-line fisheries and their associated anchors could potentially result in damage to the reefs such as breakage of the coral colonies. However, damage by long-line or gill net fisheries is probably of limited extent compared to bottom trawling (Fosså, 2003). Hall-Spencer et al. (2002) also provided photographic evidence of an area of reef impacted by bottom trawling, with a clearly visible trench (5 -10 cm deep) made by otter boards surrounded by smashed coral fragments in west Norway. Hall-Spencer et al. (2002) also noted that otter trawling with rockhopper gear damaged coral habitats in west Ireland, based on analysis of by-catch but also noted that fishing vessels actively avoided rough ground and that the majority of trawls did not result in Lophelia pertusa by-catch. Koslow et al. (2001) reported that on shallow, heavily fished seamounts off Tasmania, trawling had effectively removed the dominant cold-water coral and its associated fauna. The substratum of heavily fished seamounts was primarily bare rock or coral rubble and sand, features not seen on any lightly fished or un-fished seamount.  The abundance and richness of benthic fauna were also "markedly reduced" on heavily fished seamounts (Koslow et al. (2001).

Sensitivity assessment.  Overall, there is significant evidence of damage to Lophelia pertusa and other cold-water coral reefs due to deep-sea trawling.  Resistance is assessed as ‘None’, and resilience is ‘Very low’, giving the biotope a sensitivity of ‘High’.

Penetration or disturbance of the substratum subsurface

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

Evidence

Penetration and or disturbance of the substratum would result in similar, if not identical results as Abrasion or removal of a Lophelia pertusa reef and its associated community (see abrasion/disturbance).

Sensitivity assessment.   If the substratum is penetrated or disturbed, then the overlying reef would also be affected.  The extremely long-lived and slow-growing nature of Lophelia pertusa, the characterizing species within this biotope, means that damage incurred would take a long time to recover.  Therefore, resistance is assessed as ‘None’ resilience as ‘Very low’ and sensitivity as ‘High’.

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

A change in suspended solids can have two major effects on a biotope. Firstly a change in suspended solids can change the levels of light attenuation, and therefore the amount of light which will reach the biotope. However, this biotope is found below the photic zone within the North East Atlantic so this is not a consideration.  Secondly, a change in suspended solids can alter the food supply to the biotope.  The characterizing species, Lophelia pertusa, is a filter-feeding organism and relies on the supply of suspended organic matter for sustenance. The location of Lophelia pertusa reefs is determined by a multitude of factors, however, a combination of water flow and seafloor relief is important for the supply of food particles and larvae (Flach & Thomsen 1998; Gage et al. 2000; Hughes & Gage, 2004). Reefs are found in areas where the topography works to accelerate near-bed currents, which enhances food supply (Mortensen et al., 2001; Thiem et al., 2006; Kiriakoulakis et al., 2007; Robert et al., 2009; Davies et al., 2009; Soetaert et al., 2016; Kazanditis & Witte, 2016; reviewed by Maier et al., 2023).   

Davies et al. (2009) measured the turbidity of the water along a transect within the Mingulay reef complex off the west coast of Scotland. Turbidity levels varied along the transect. However, on the sections of the transect closer to the top of the reef, lower turbidity levels appeared to be during the onset of an ebb tide (Davies et al., 2009). Increased turbidity was found to correlate with an increase in the speed of water flow, therefore, throughout the space of one tide, there was considerable variation in the levels of suspended solids within the water column. This information suggests that over a short time period Lophelia pertusa and their associated species can tolerate changes in suspended solids. 

Mortensen (2001) found that when both food and sediment were presented to Lophelia pertusa at the same time sediment was ingested. However, the process of feeding and polyp cleaning does not occur at the same time (Brooke et al., 2009). An increase in turbidity within the Lophelia pertusa environment would lead to more settlement of sediment onto the coral polyps. This would increase the time required to remove the sediment from the polyp, which could restrict the time available for feeding.  Brooke et al. (2009) suggested that this could lead to the starvation of the coral polyp even though food may be available.

Brooke et al. (2009) compared the tolerance of two morphotypes of Lophelia pertusa (gracilis, fragile; brachcephala, heavily calcified) to different turbidity levels.  The fragments collected from the Gulf of Mexico were kept in aquaria, at five different turbidity levels, for 14 days. Both morphotypes of Lophelia pertusa found in clear conditions (<10 mg/l) had 100% survival rates. Over 80% of Lophelia pertusa kept at intermediate turbidity conditions (10 to 100 mg/l) survived. Two of the experimental turbidites fell within the medium turbidity water frame directive (WFD) ranking system, these were 103 mg/l and 245 mg/l.  In the former, both morphotypes had a survival rate of >50%, and the latter had a survival rate of >30%.  The more fragile morphotype, gracilis, experienced 100% mortality in the very turbid category (ca 362 mg/l) and brachycephala had an extremely low survival rate (Brooke et al., 2009). From the results of this laboratory experiment, Brooke et al. (2009) summarized that Lophelia pertusa survival decreased in steps, rather than a continuous linear decline; suggesting that the corals have physiological thresholds beyond which they are unable to cope with turbidity levels and mortality can occur.

Aller et al. (2013) exposed Lophelia fragments from Tisler Reef to reef sediment and drill cuttings at concentrations of 66, 198 and 462 mg/cm² under experimental conditions. They noted that the branching structure of the fragments and mucus release prevented the build-up of sediment on the polyps (a mean of 2 mm for drill cuttings and 3 mm for natural sediment) and that the polyps tolerated the reduction in oxygen levels without any visible detrimental effects.  They concluded that exposure to suspended sediment from oil and gas drilling activities would not cause coral death within <12 days even at three or seven times the regulatory levels. 

Larsson et al. (2013b) reported that suspended sediment exposure has no significant effect on respiration or fatty acid composition in Lophelia pertusa and that the amount of additional mucus produced to clean its polyps was low and did not significantly affect energy expenditure. Larsson et al. (2013) exposed Lophelia pertusa fragments to fine (<63 µm) natural sediment and drill cuttings at 5 mg/l and 25 mg/l for 12 weeks in the laboratory. After 12 weeks, mortality was low with only 0.3% (1 polyp) dying after exposure to 25 mg/l natural sediment and 2.2% (8 polyps) dying after exposure to 12 weeks but zero in controls. They attributed the mortality to the build-up of sediment on the fragments and potential resultant smothering (see below) (Larsson & Purser, 2011; Larsson et al., 2013b).  At the low concentration of sediment, the polyps were fully extended but only half extended at the high concentration and there was a trend towards lower growth rates when exposed to drill cuttings rather than natural sediment Larsson et al. (2013b).  In addition, Larsson et al. (2013a) reported significant mortality (67%) in planulae exposed to 25 mg/l of drilling cuttings after four days, while mortality at 5 mg/l was low and not significantly different from controls. Larsson et al. (2013) also reported Gilmour (1999; cited in Larsson et al., 2013a) found that larval mortality was an average of 98% after two days of exposure to 50 and 100 mg/l of natural sediment. Nevertheless, Larsson et al. (2013a) concluded that Lophelia pertusa polyps coped reasonably well with increased suspended sediment and deposition rates. In comparison, information on natural sedimentation rates experienced in reef habitats is limited. Brooke et al. (2009) reported suspended sediment levels of 9-10 mg/l  and sedimentation rates of 31 and 47 g/m²/d at two sites in the Gulf of Mexico. But Larson et al. (2013a) noted that these rates were probably high compared to the typical 0.5 -3.7 g/m²/day reported in the North East Atlantic cold-water coral habitats, which in turn suggested that Lophelia pertusa was capable of tolerating naturally occurring suspended sediment levels. Kutti et al. (2022) noted that Lophelia was thought to be resilient to enhanced turbidity.

Purser (2015) examined the effects on nine Lophelia reefs, in situ, in Norwegian waters, immediately and 13 months after exposure to drill cuttings. The reefs were monitored using ROV and positioned between 100 m and 350 m of drilling waste release. Purser (2015) found no significant difference in Lophelia pertusa polyp behaviour in areas exposed to >25 mg/l of drilling waste material (modelled) and those exposed to negligible concentrations of drilling wastes. There were no observable effects on the associated community and no observable degradation in reef structure. Kutti et al. (2022) examined the physiology of naturally occurring and transplanted coral 250 m and 1 km downstream of an average size Norwegian fish farm after one year. They observed a steady decline in metabolic rates, growth and energy reserves with increasing modelled sedimentation rates of organic wastes from the farm. No mortality was observed. They noted that inorganic particulate did not reduce metabolic rates in prior studies (e.g. Larsson et al., 2013; Purser, 2015) while the organic particles in their study, did reduce metabolic rates. 

Järnegren et al. (2020) examined the effects of drilling wastes on eight and 21-day larvae of Lophelia pertusa in the laboratory. Larvae were exposed to varied concentrations of bentonite, barite and drill cuttings for 24 hours in the laboratory and then transferred to clean water for 24 hours for recovery. The larvae were assessed for non-lethal and lethal effects. The 24-hour EC50s for eight-day and 21-day larvae were 10.1 and 9.6 mg/l respectively for bentonite, 37.7 and 39.8 mg/l for drill cuttings, and 19.9 mg/l in eight-day larvae exposed to barite. The 24-hour LC50s for eight-day and 21-day larvae were 79.5 and 53.0 mg/l respectively for bentonite, 112.4 and 380.0 mg/l for drill cuttings, and 133.4 mg/l in eight-day larvae exposed to barite. The effects of the suspended particles were primarily due to clogging of the larval cilia. Mortality in the experiments was low and the LC50s were modelled based on the experimental data. Bentonite was the most toxic and the only material to result in experimental mortality in 21-day larvae at 53 mg/l. However, the 21-day larvae were more sensitive than the eight-day larvae (Järnegren et al., 2020). Järnegren et al. (2020) noted that the Lophelia larvae tested were ca 23 times more sensitive than in prior studies. However, they also noted that Lophelia reefs within ca 100 m of exploratory drilling in Norwegian water were not exposed to more than 25 mg/l for a few days, and no adverse effects on the reef were observed (Purser, 2015) but also noted that this concentration could adversely affect larvae. 

Baussant et al. (2022) exposed Lophelia nubbins to barite, bentonite and drill cutting particles in realistic exposure concentrations (ca 4 to 60 mg/l) in pulsed exposure experiments (4-hour pulses) for five days followed by two weeks of recovery. Respiration rates and growth were not significantly different between treatments. Mortality (ca 20%) occurred in all treatments including the controls but was only significantly higher in polyps exposed to 19 and 49 mg/l drill cutting particles two to six weeks after exposure. Baussant et al. (2022) concluded that Lophelia polyps were resilient to short, realistic exposure to suspended drill waste particles but suggested a risk of long-term effects if exposed to ca 20 mg/l. 

Bilan et al. (2023) exposed several cold-water coral species from the Blanes Canyon, Meditteranean to pulses of fine sediment (silt and clay) collected from the canyon bed, under experimental conditions. Coral nubbins were exposed to sediment slurry for one hour daily for nine months. The low (6.7 +/- 1.9 mg/l) and high (38.1 +/- 3.8 mg/l) suspended sediment concentrations (SSC) were based on in situ measured trawling-induced turbidity.  Lophelia pertusa experienced a significant increase in mortality (an average of 16 +/- 19% mortality) when exposed to SSC but no difference between the treatments. Madrepora oculata experienced mortality in all treatments (including the control) but significantly higher in SSC treatments (an average of 64 +/- 29% mortality). Both species showed a decrease in respiration by the end of the experiment. Bilan et al. (2023) concluded that Madrepora oculata was more sensitive than Lophelia pertusa but that both colonial corals experienced substantial mortality due to increased SSC and that bottom trawling could indirectly impact cold-water corals in the Mediterranean canyons due to resuspension of sediments. 

A decrease in the levels of suspended material at the benchmark level could lead to a reduction in food availability to Lophelia pertusa, and other filter-feeding organisms within the biotope. However, Larsson et al. (2013b) reported that Lophelia pertusa tolerated living on minimal resources (food) for several months. In their experiments, Lophelia survived (100%) starvation for 28 weeks (Larsson et al., 2013b). Maier et al. (2023) also concluded that cold-water corals were adapted to feast-famine conditions. 

Sensitivity assessment.  The evidence suggests that a change in turbidity from clear to intermediate (<10 mg/l to 10-100 mg/l) for a year could result in limited or some mortality depending on duration and local hydrography. For example, Brooke et al. (2009) demonstrated significant mortality after only 14 days at 103 and 245 mg/l. However, Bilan et al. (2023) reported <25% mortality in Lophelia pertusa exposed to daily pulses of 6.7 or 38.1 mg/l of fine sediment for nine months. In addition, larvae, especially planulae larvae, were reported to experience significant mortality after exposure to drilling cuttings (Larsson et al., 2013), which could adversely affect recruitment. Therefore, resistance is assessed as ‘Medium’, resilience as ‘Very low’, and sensitivity as ‘Medium’ at the benchmark level. However, Bilan et al. (2023)  noted that current studies highlight the variation in response of Lophelia pertusa to suspended sediment exposure. 

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

Rogers (1999) suggested that Lophelia pertusa would be intolerant of increased rates of sedimentation, caused by decreased water flow, or the resuspension and subsequent sedimentation of sediment by marine activities, such as offshore construction or mobile fishing gear (e.g. beam or otter trawls), or the discharge of drill cuttings. An increase in sedimentation is thought to be one of the largest sources of degradation of coral reefs (Norse, 1993) and may suppress the growth rates of Lophelia colonies (Fosså et al., 2002).  Information on natural rates of sedimentation experienced in reef habitats is limited. Rogers (1999) suggested that sedimentation rates of >10 mg/cm²/day in shallow water coral reefs were high. Brooke et al. (2009) reported suspended sediment levels of 9-10 mg/l  and sedimentation rates of 31 and 47 g/m²/day at two sites in the Gulf of Mexico. But Larson et al. (2013a) noted that these rates were probably high compared to the typical 0.5 -3.7 g/m²/d reported in the North East Atlantic cold-water coral habitats, which in turn suggested that Lophelia pertusa was capable of tolerating naturally occurring suspended sediment levels and sedimentation rates. 

Mortensen (2001) reported that 25-100% of polyps died after being starved for three months or more but in some cases, polyps survived starvation for 16 and 20 months. However, Larsson et al. (2013b) reported that Lophelia pertusa tolerated living on minimal resources (food) for several months. In their experiments, Lophelia survived (100%) starvation for 28 weeks (ca six months) (Larsson et al., 2013b). Maier et al. (2023) concluded that cold-water corals were adapted to feast-famine conditions in the deep sea. 

Preliminary results suggested that sand deposition rates of 0.1 mg/cm²/min significantly reduced polyp expansion in Lophelia pertusa (Roberts & Anderson, 2002b), which would reduce feeding and hence growth rates. Mortensen (2001) demonstrated that Lophelia pertusa was able to remove sediment particles <3 mm within 3-5 min and 3-5 mm particles within ca 15 min due to the beating of cilia towards the tips of the tentacles, and reported that the living coenosarc (coral tissue) was always clean of sediment. Earlier studies by Shelton (1980), showed that Lophelia pertusa could remove graphite particles within ca 30 sec.  Similarly, Reigl (1995) demonstrated that scleractinian corals were able to clean sand from their surface actively.  When exposed to 200 mg of sand per cm² in a single application, scleractinian corals cleared 50% of the sand within 1,000 min, and all the species studied survived for six weeks of continuous exposure to 200 mg of sand per cm².  Reigl (1995) concluded that corals could cope with considerable amounts of sand deposition. Nevertheless, Rogers (1999) suggested that an increase in sedimentation was likely to interfere with feeding and hence growth, which would alter the balance between growth and bioerosion, potentially resulting in reef degradation. In addition, smothering could prevent the settlement of larvae and hence recruitment.

In burial experiments, Larsson & Purser (2011) exposed Lophelia fragments to regular depositions of sediment (<63 µm ) over three weeks resulting in a covering of the polyps by 6.5 mm or 19.0 mm of sediment. Mortality was low for the duration of the experiment with only 3.7% (seven polyps) dying under 19 mm and 0.5% (one polyp) dying under 6.5 mm of sediment (Larsson & Purser, 2011). Allers et al. (2013) investigated the resilience of Lophelia pertusa taken from Tisler Reef, Norway to sedimentation in laboratory-based experiments. They found that mucus production and the branching morphology of Lophelia pertusa meant that sediment accumulation was relatively slow. Even high sediment deposition (462 mg/cm²) did not result in complete coverage of the fragment's skeleton by sediment. Short-term (<24 hours) exposure to sedimentation reduced the availability of oxygen to Lophelia pertusa.  However, the organism could tolerate both low-oxygen and anoxic conditions without suffering visible, short-term effects (Allers et al., 2013).  As little as 3 mm of sediment covering a Lophelia pertusa polyp led to complete anoxia within six days, and the thicker the covering of sediment the faster anoxia occurred (Allers et al., 2013). But complete burial for over 24 hours (based on incubation for 24, 48 and 72 hours) caused suffocation and 100% mortality (Allers et al., 2013). 

Brooke et al. (2009) reported different tolerance of Lophelia pertusa to total burial. Samples of Lophelia pertusa were collected from the Gulf of Mexico and tested for their tolerance to complete burial in sediment to a depth of over 1 cm.  It was found that a significant tolerance threshold was reached between two and four days, after which time very low survival rates were recorded and 100% mortality occurred after seven days (Brooke et al., 2009). In burial experiments, Larsson & Purser (2011) exposed Lophelia fragments to regular depositions of sediment (<63 µm) over three weeks resulting in a covering of the polyps by 6.5 mm or 19.0 mm of sediment. Mortality was low for the duration of the experiment with only 3.7% (seven polyps) dying under 19 mm and 0.5% (one polyp) dying under 6.5 mm of sediment (Larsson & Purser, 2011).

Sensitivity assessment.  At the benchmark level (a single deposition of 5 cm of sediment), the majority of the Lophelia pertusa polyps would probably be unaffected due to the size of the colony, which is raised above the seabed.  Purser (2015) noted that the burial of polyps in the natural environment was unlikely as settled material would fall off the coral branches, due to its height above the sea floor and aided by mucus release. The levels of water flow within this environment are recorded as significant, therefore, it is likely that the sediment would be re-suspended, and removed relatively quickly.  But if the sediment were to remain for more than two days then it is possible that any polyps that were buried would suffer mortality. However, only small colonies or fragmented colonies are likely to be affected. Hence, the resistance of this biotope to the pressure at the benchmark is assessed as ‘Medium’ as a worst-case scenario, resilience as ‘Very low’, and sensitivity assessed as ‘Medium’. Lophelia is likely to be more sensitive to prolonged sedimentation (rather than a single event) depending on the local hydrography and the sediment type. 

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

Sensitivity assessment.  Based on the evidence provided for the ‘light’ smothering and siltation pressures above, at the benchmark level (a single deposition of 30 cm of sediment), the majority of the Lophelia pertusa polyps would probably be unaffected due to the size of the colony, which is raised above the seabed. Purser (2015) noted that the burial of polyps in the natural environment was unlikely as settled material would fall off the coral branches, due to its height above the sea floor and aided by mucus release. Small colonies or fragments are likely to be affected depending on their size. However, no information on the size range of colonies without this biotope was available. The levels of water flow within this environment are recorded as significant, therefore, it is likely that the sediment would be re-suspended, and removed relatively quickly. But if the sediment were to remain for more than two days then it is possible that any polyps that were buried would suffer mortality. Hence, the resistance of this biotope to the pressure at the benchmark is assessed as ‘Medium’ as a worst-case scenario, resilience as ‘Very low’, and sensitivity assessed as ‘Medium’. Lophelia is likely to be more sensitive to prolonged sedimentation (rather than a single event) depending on the local hydrography and the sediment type. 

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

Natural light rarely penetrates to the depth this biotope is found in the North East Atlantic. Therefore, an increase in the amount of natural light is ‘Not relevant’ to this biotope.  However, due to the oil and gas platforms and other forms of exploration or removal of resources, it is possible that artificial light could be introduced to this biotope. There is no evidence to support an assessment at this pressure benchmark.

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 larval 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 – this pressure applies to mobile species, e.g. fish and marine mammals rather than seabed habitats.

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

This pressure is 'not relevant' to the characterizing species within 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

No alien or non-native species are known to compete with Lophelia pertusa or other cold-water corals. 

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

Appah et al. (2022) reported the presence of Vibrio spp. and Rickettsiales-like organisms (RLOs) in the tissue of Lophelia pertusa collected from Porcupine Bank. However, no signs of disease were reported. The parasitic foraminiferan Hyrrokkin sarcophaga was reported to grow on polyps of Lophelia pertusa in aquaria (Mortensen, 2001).  The foraminiferan dissolves a hole in the coral skeleton and invades the polyp.  In his aquaria, two Lophelia pertusa polyps became infested but did not seem to be influenced by the infestation (Mortensen, 2001).  Any parasitic infestation is likely to reduce the viability of the host, even if only a few or possibly hundreds of polyps were affected.  However, 'Insufficient evidence' is recorded because of the lack of evidence of disease. 

Removal of target species

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

Evidence

Lophelia pertusa is not directly targeted by a commercial fishery.  However, with the advent of deep-water fisheries, the habitats within which Lophelia pertusa is found have been heavily targeted by deep-water fishing trawlers because of their high biodiversity. None of the species targeted by the commercial fishery have known symbiotic relationships.  The only known species with which Lophelia pertusa has a symbiotic relationship with is the polychaete Eunice norvegica (Mueller et al., 2013).

Sensitivity assessment.  The biological impact of the removal of species associated with Lophelia pertusa is not thought to have a negative impact on this biotope.  Consequently, resistance and resilience are assessed as ‘High’, resulting in a sensitivity assessment of ‘Not sensitive’. The potential physical effects of commercial fisheries are addressed under the 'abrasion' and 'penetration' pressures above. 

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

Extraction of Lophelia pertusa colonies from the reef would result in fragmentation of the coral, and destruction of the reef structure.  The development of larger vessels and more powerful trawls, e.g. rockhopper gear designed to operate on rough stony bottoms, has probably exposed the reefs to increased impacts from fishing (Fosså et al., 2002; Fosså, 2003).  For example, the fishery of the continental break targeted Greenland halibut, redfish, and saithe.  The orange-roughy is another valuable deep-sea species associated with offshore banks, pinnacles and canyons with strong currents, which are favoured by Lophelia pertusa (Rogers, 1999).  In the UK, monkfish is a major fishery in the vicinity of the Lophelia pertusa reefs around Rockall (Dr Jason Hall-Spencer, pers comm.). 

Demersal fishing operations have been shown to have a significant negative impact on Lophelia pertusa reefs within the North-east Atlantic.  Unequivocal evidence for the physical damage of bottom trawling in cold-water habitats has been presented for many areas around the world (Roberts et al., 2009), including areas within the North East Atlantic.  Fosså et al. (2002) used remotely operated vehicles to survey areas of cold-water coral reefs off the west coast of Norway.  They described areas historically known as cold-water coral reefs, containing Lophelia pertusa, to show only scattered coral fragments or crushed and broken coral skeletons.  When their findings were extrapolated it was estimated that between 30 – 50% of Lophelia pertusa reefs from Norway had been damaged by trawling (Fosså et al., 2002).  Hall-Spencer et al. (2002) found that cold-water coral reefs containing Lophelia pertusa off the West Ireland continental shelf break were being damaged by commercial trawls for deep-water fish.  Coral aged to be at least 4500 years old, was being removed from reefs as by-catch.  Grehan et al. (2004) collected imagery data from cold-water coral reefs containing Lophelia pertusa off the West Ireland continental shelf break and West Norway.  They found widespread damage caused by trawling to cold-water coral reefs within these geographical areas.

Trawling can also re-suspend seabed sediments and cause further damage to the habitat through smothering (see smothering pressure).  Trawling experiments in the Mediterranean found that water-column turbidity increased by as much as three times for five days after a trawling event (Palanques et al., 2001; taken from Roberts et al., 2009).  No evidence was available on the impact of re-suspended sediment caused by trawling, the radius of its effects on Lophelia pertusa, or the effects on the associated species. 

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope. The resistance to removal is ‘None’ due to the easy accessibility of the biotope's location and the inability of these species to evade collection. The resilience is ‘Very low’, with recovery only being able to begin when the harvesting pressure is removed altogether. This gives an overall sensitivity score of ‘High’.