The Marine Life Information Network

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; Sigwart et al., 2025). Reef-forming cold-water corals occur in cool waters <14°C (Gomez et al., 2022; Maier et al., 2023). Lophelia pertusa is found from the southwestern Barents Sea to West Africa on the eastern Atlantic margin, and from Nova Scotia down the western Atlantic margin into the Gulf of Mexico. It also occurs off oceanic islands, such as the Azores, Canary Islands, and Madeira, and along the southeastern slope of Brazil (Davies et al., 2008). In the North Atlantic, Lophelia pertusa’s distribution 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; Buhl-Mortensen et al., 2024). Lophelia pertusa populations around the UK, Ireland, and Norway are found in water temperatures of 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. Gomez et al. (2022) recorded Lophelia reefs with a thermal tolerance between 6 and 12°C off the coast of South Carolina, USA, at 650 to 850 m depth. In Norway, Lophelia pertusa is observed in waters between 6.83 and 8.97°C at depths between 170 and 300 m (Büscher et al., 2024), and off the Mauritania/Senegal coast, Lophelia reefs were observed in waters between 8.8 to 11.6°C between 450 to 650 m deep (Moctar et al., 2024).

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.). Weinnig, Herrera & Cordes (2024) studied the response of Lophelia pertusa fragments (collected in the Gulf of Mexico between 392 and 483 m deep, where bottom water temperature is ~ 8°C) to warming in a laboratory setting. An increase from 8 to 12°C led to an upregulation of Lophelia's humoral immune response and bradykinin catabolic process, which are indications of a mild stress response. The response was suspected to be mild due to 12°C being toward the upper limit of Lophelia pertusa thermal tolerance, and a temperature of 12°C has not reportedly induced mortality in previous studies (Weinnig, Herrera & Cordes, 2024). In addition, depending on locality, Lophelia pertusa can live in water at 12°C for much longer than 24 hours, even though the upper range detected in the Gulf of Mexico is ∼12°C (Weinnig, Herrera & Cordes, 2024).

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 hours and seven days. Survival was ca 60% after 24 hours 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 to100%) 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 hours, 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). 

Chapron et al. (2021) and Chemel (2023) 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. Chemel (2023) conducted an aquarium experiment to predict the effect of temperature on North East Atlantic Lophelia pertusa. They found that, on a long-term scale (four months), while a 4°C reduction in temperature did not affect Lophelia physiology and microbiome, a 4°C increase in temperature led to massive mortality. Mortality was associated with a high level of stress in the coral, as attested by the upregulation of the number of genes related to immune, inflammatory and antioxidant responses, cell death and apoptosis, DNA repair and maintenance, but also the shift in coral bacterial community towards pathogens and opportunistic bacteria (Chemel, 2023). Overall, Chemel (2023) concluded that North East Atlantic Lophelia pertusa are as sensitive to warming as other populations, and it appears that all Lophelia, independently of the region they come from, will be strongly impacted by an increase of +3°C.

Chemel et al. (2024) conducted a further study examining the effect of increasing temperature on North East Atlantic Lophelia pertusa and found that, Lophelia exhibits significant mortality related to changes in its microbiome composition at temperature increases of + 3 and + 5°C. The presence of gene markers for bacterial virulence factors in Lophelia suggested that the coral death was due to infection by pathogenic bacteria (Chemel et al., 2024). Specifically, within eight weeks, survival of the North East Atlantic Lophelia (where it experiences temperatures between 8 and 12°C) dropped from 60% at 13°C (+ 3°C) to 33% at 15 °C (+ 5°C) (Chemel et al., 2024). These results suggest that Lophelia pertusa can only survive a long-term temperature increase of <3°C, as a long-term increase of >3°C will limit the capacity of the coral to maintain or regulate its microbiome under elevated temperature, which results in a proliferation of potentially pathogenic bacteria (Chemel et al., 2024). It is not yet known whether Lophelia pertusa in the Atlantic are already living at their thermal optimum, making them highly vulnerable to increases in temperature, or whether they can thrive in waters as warm as their Mediterranean counterparts. However, as Chapron et al. (2021) observed, Mediterranean Lophelia, normally living at 13°C, were strongly affected by water temperatures of 17°C.

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). An increase in temperature, combined with lower oxygen levels, may also negatively affect skeletal linear extension and budding rate of Lophelia polyps (Sanna & Freiwald, 2024), and could lead to an overall reduction in Lophelia reef growth rates.

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 (see 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 to 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. Chemel et al. (2024) observed that an increase of +3°C (to 13°C) and + 5°C (to 15°C) on North East Atlantic Lophelia pertusa led to significant mortality related to changes in its microbiome composition. 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; Chemel et al., 2024) 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, then polyps could experience significant mortality (Chapron et al., 2021; Büscher et al., 2022; Chemel et al., 2024). 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 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; Sigwart et al., 2025). Reef-forming cold-water corals occur in cool waters <14°C (Gomez et al., 2022; Maier et al., 2023). Lophelia pertusa is found from the southwestern Barents Sea to West Africa on the eastern Atlantic margin, and from Nova Scotia down the western Atlantic margin into the Gulf of Mexico. It also occurs off oceanic islands, such as the Azores, Canary Islands, and Madeira, and along the southeastern slope of Brazil (Davies et al., 2008). In the North Atlantic, Lophelia pertusa’s distribution 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; Buhl-Mortensen et al., 2024). Lophelia pertusa populations around the UK, Ireland, and Norway are found in water temperatures of 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. Gomez et al. (2022) recorded Lophelia reefs with a thermal tolerance between 6 and 12°C off the coast of South Carolina, USA, at 650 to 850 m depth. In Norway, Lophelia pertusa is observed in waters between 6.83 and 8.97°C at depths between 170 and 300 m (Büscher et al., 2024), and off the Mauritania/Senegal coast, Lophelia reefs were observed in waters between 8.8 to 11.6°C between 450 to 650 m deep (Moctar et al., 2024).

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 hours and seven days. Survival was ca 60% after 24 hours 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 to 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 hours, 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). 

Chemel (2023) conducted an aquarium experiment to predict the effect of temperature on North East Atlantic Lophelia pertusa. They found that, on a long-term scale (four months), while a 4°C reduction in temperature did not affect Lophelia physiology and microbiome, a 4°C increase in temperature led to massive mortality. Mortality was associated with a high level of stress in the coral, as attested by the upregulation of the number of genes related to immune, inflammatory and antioxidant responses, cell death and apoptosis, DNA repair and maintenance, but also the shift in coral bacterial community towards pathogens and opportunistic bacteria (Chemel, 2023). 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). 

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, its ability to survive in variable temperature regimes suggests that Lophelia, and hence the reef, is 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 little empirical evidence of the effect of temperature changes at the level of the benchmark, especially a decrease in temperature. However, Chemel (2023), noting on a long-term (four months) scale that a 4°C lower temperature did not affect North East Atlantic Lophelia physiology and microbiome. 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 to 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’ but with ‘Low’ confidence.

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; Sanna, Büscher & Freiwald, 2023; Büscher et al., 2024). However, Rogers (1999) regarded Lophelia pertusa to be stenohaline. Orejas et al. (2021) reported that Madrepora oculata was recorded at salinities of between 34.8 and 38. The Lophelia pertusa reef and its 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 an increase in salinity except in rare cases, such as the unlikely production of hypersaline effluents by offshore installations. 

Sensitivity assessment. Due to the highly stable conditions in which Lophelia pertusa is 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 has been 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; Sanna, Büscher & Freiwald, 2023; Büscher et al., 2024). However, Rogers (1999) regarded Lophelia pertusa to be stenohaline. Orejas et al. (2021) reported that Madrepora oculata was recorded at salinities of between 34.8 and 38. The Lophelia pertusa reef and its 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. Yet Mohn et al. (2023) documented currents twice at fast (>0.8 m/s) at Rockall on top of the Oreo mound, which contain dense assemblages of Lophelia, but at the Haas mound, where flows are slower and more in line with the presumed optimal coral feeding range (< 0.07 m/s), there were patchy distributions of Lophelia. Previous studies have also documented the highest colony growth rates for Lophelia pertusa upstream, against dominating currents (Mohn et al., 2023). 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. Sanna, Büscher & Freiwald (2023) and Büscher et al. (2024) studied Lophelia pertusa in Norwegian waters (at offshore and inshore sites between 170 and 300 m deep) and found that although reefs usually experienced low flow speeds (0.08 to 0.2 m/s), both offshore and inshore reefs would experience much greater flow rates between 1 and 1.57 m/s during the late autumn and winter months,. These high flow rates are expected to increase the food encounter rates of corals and prevent the polyps from clogging with sediments. However, in contrast, laboratory experiments have estimated that the efficient prey capture rate of Lophelia pertusa is a relatively low flow, < 0.07 m/s (~ 0.025 cm/s for zooplankton and ~ 0.05 m/s for phytoplankton), as with stronger flow, the prey could escape from the polyps (Büscher et al., 2024).

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 was observed 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 current 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.

However, the structure of the coral matrix 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).

Sensitivity assessment. Lophelia pertusa 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, although the coral matrix itself probably slows water flow within the reef. A decrease in water flow across the reef would reduce the availability of food, which may decrease the health of the Lophelia pertusa colony. 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 Lophelia pertusa reefs are found experience great changes in water flow rates throughout the tidal cycle (reviewed by Maier et al., 2023; Sanna, Büscher & Freiwald, 2023; Büscher et al., 2024). Therefore, both resistance and resilience have been assessed as ‘High’, and sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Emergence regime changes

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

Evidence

Lophelia pertusa and 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

Offshore Lophelia pertusa reefs occur, by definition, in extremely wave exposed conditions, although wave action is ameliorated by depth. Draper (1967) noted that wave periods in offshore areas are generally longer than in enclosed seas and therefore penetrate to greater depths. However, Draper (1967) estimated that as far out as the continental shelf, for one day a year, storm conditions could generate an oscillatory water movement on the seabed of only ca 0.4 m/s at 180 m. In Norwegian fjords where Lophelia pertusa reefs occur as shallow as 50 m, wave action is slight at the surface and most likely does not penetrate more than a few tens of metres. Inner fjords have limited fetch so that wave action is unlikely to penetrate to more than a few tens of metres even in storm conditions (Dr Keith Hiscock pers. comm.).

The oscillatory water movement generated by wave action could potentially result in the fragmentation of branching coral skeletons at the upper limit of their depth distribution, although their skeletons are fairly robust.  Occasional fragmentation may not unduly affect the reef but allow it to spread in the long-term as the fragments continue to grow, or provide a substratum for colonization by Lophelia pertusa larvae.  However, Lophelia pertusa occurs at depths at which 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 was 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 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 Morocco reefs had few colonies but were sited in well-oxygenated waters with high aragonite (Buhl-Mortensen et al., 2024). Similarly, while observing Lophelia reefs off the Mauritania/Senegal coasts, Moctar et al. (2024) measured oxygen concentrations as low as 1 ml/l (ca 1.4 mg/l) and documented that of the 13 colonies, six were large and healthy reefs with between 15 and 50% of live coverage. 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 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). Furthermore, Hanz et al. (2019) cited in Moctar et al. (2024), noted how Lophelia pertusa was tolerant to hypoxia, being recorded in the Angolan margin in DO concentrations of 0.5 to 1.5 ml/L (0.7 to 2.1 mg/l). Finally, an increase in temperature, combined with lower oxygen levels, may also negatively affect skeletal linear extension and budding rate of Lophelia polyps, as observed by Sanna & Freiwald (2024), and could lead to an overall reduction in Lophelia reef growth rates.

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; Moctar 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 2,088 to 2,186 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 Lophlia 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, 'Insufficient 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 larvae must settle onto hard substrata (Roberts et al., 2009) to enable them to find a solid anchor point, from which the hard skeleton of the coral can attach, including both natural (such as rocks and barnacles) and artificial (plastic and concrete) sources, with elevated positions above the seabed appearing to be advantageous towards settlement (Strong et al., 2023). The presence of Lophelia pertusa on oil and gas platforms (Gass & Roberts, 2006; Fortune et al., 2024) suggests that their larvae are able to settle onto metal substrata as well. However, Strong et al. (2023) noticed how mooring anchors were free from Lophelia colonization, possibly due to their occasional burial and/or scouring by mobile sediment as well as the friable nature of the oxidized surface of the anchors. There is no information available on the preference of Lophelia pertusa larvae for certain types of hard substrata. 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

Lophelia pertusa larvae have to settle onto a hard substratum.  The branching nature of this reef-forming species means that their structures can extend out over soft substratum.  However, as this species requires a hard substratum onto which to anchor, a change in soft sediment type is not relevant to this biotope. 

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

Lophelia pertusa larvae have to settle onto hard substrata.  However, a large reef may grow out over soft sediment, from which sediment may be extracted.  The reef structure can also significantly change the water flow rates, which can mean that sediment being carried in suspension, is deposited in the reef.  Extraction of substratum to 30 cm within this biotope would mean that all of the reef forming, characterizing species, Lophelia pertusa, would be removed.  This would entirely destroy the habitat and would result in the loss of the biotope.

Sensitivity assessment.  Lophelia pertusa and the biotope have no resistance the removal of substratum to 30 cm, therefore, the resistance is assessed as ‘None’.  The extremely long lived nature and slow growth rate of the characterizing species Lophelia pertusa means that resilience is ‘Very Low’, giving this biotope an overall sensitivity assessment of ‘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 Lophelia pertusa 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. Multiple studies suggest that Lophelia pertusa has been significantly impacted by trawling, with some indicating up to 50% of reef damage by trawl gear (Sigwart et al., 2025). 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. Secondary effects, such as increased resuspended sediments from trawling and smothering, are also of concern to corals (Strong et al., 2023). In addition, oil and gas drilling is a threat of major concern to Lophelia pertusa in Africa, Brazil, the USA, and the Caribbean, and drilling activities are expanding in the South Atlantic. Sigwart et al. (2025) estimate that, given the level of damage from trawl and drill activities, this indicates the destruction or severe degradation of at least 30% of Lophelia reefs worldwide in the last 30 years (Sigwart et al., 2025).

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 to 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). Le Goff-Vitry et al. (2004) cited in Villafranca-Sánchez, Guijarro-Garcia & Giménez-Casalduero (2025) reported that intense trawling may have led to an increase in asexual reproduction in Lophelia pertusa off the coast of Spain on the Seco de Palos seamount, possibly as a strategy to combat continuous trawling in their habitat

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.  A resistance of ‘None’ has been given.  If the substratum is either 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 biotopes, means that damage incurred would take an extremely long time to recover.  Therefore, resilience has been assessed as ‘Very Low’ resulting in sensitivity being ‘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 that 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 to 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 to 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 from the 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-sized 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, Mediterranean, 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. 

Mobilia et al. (2023) exposed Goniocorella dumosa, a cold-water coral similar to Lophelia pertusa, to four-day pulses of four target sediment concentrations, 0 mg/l (representing control conditions) and 45, 102, and 435 mg/l (targeting concentrations expected from mining and trawling disturbance). All coral fragments survived, and oxygen consumption rates were not affected by treatments and time. Although no visible detrimental effects on coral health were noted after the first pulse of sediment exposure, both a loss of coenosarc (living tissue) and instances of polyp mortality were observed on fragments exposed to suspended sediments during the following sediment pulses (Mobilia et al., 2023). This observed decline in coral health over time indicated that cold-water corals could cope with sediment disturbance from human activities that disturb the seafloor for periods of up to four days, but that repeated or prolonged sediment exposure could cause a deterioration in coral health (Mobilia et al., 2023).

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

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 (Rogers, 1999; Strong et al., 2023). 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).

Fähse et al. (2023) studied the response of cold-water corals in an aquarium experiment to increased sedimentation over a 12-week period to a 100- and 1000-fold higher sediment level compared to the natural level in Comau Fjord, Brazil. They observed 32% (100-fold) and 80% (1000-fold) of the corals experienced a decrease in tissue cover, along with a decrease in respiration rate of 34% and 66%, respectively. Under the highest concentration, corals showed reduced polyp expansion and a significantly reduced growth of approximately 95% compared to corals at natural concentration (Fähse et al., 2023). Murray et al. (2025) examined the effect of sedimentation from drill waste on the cold-water coral Flabellum alabastrum and found that over 10 days of exposure to one of three treatments (barite, bentonite, or barite and bentonite combined), sedimentation to a total depth of 6.3 mm caused observable and non-lethal responses. In addition, behavioural and mucosal responses of waste-exposed individuals had returned to baseline control levels within two days of post-experiment recovery. This is consistent with observed robustness to drilling wastes in Lophelia pertusa, where polyp mortality mainly occurred at higher concentrations of 19 and 40 mg/l (Baussant et al., 2022) or when they were completely covered (Murray et al., 2025).

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 to 10 mg/l and sedimentation rates of 31 and 47 g/m²/day at two sites in the Gulf of Mexico. Yet Larson et al. (2013a) noted that these rates were probably high compared to the typical 0.5 to 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 to100% 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 to 5 min and 3 to 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). 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. Yet, 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 is 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. 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. Yet, 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 is 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

Evidence on the effect of electromagnetic fields (EMFs) on benthic organisms is still severely lacking. Some studies have investigated the effect of anthropogenically induced EMFs on benthic invertebrates at intensities ranging between 2 nT and 40 mT, which is often much higher than in-situ measurements from subsea cables. While some report changes to behaviour, physiology, reproduction, development, immunology, cytotoxicity and orientation, others demonstrate no effect from exposure to the EMF (Albert et al., 2020; Hutchison et al., 2020), depending on the study species and duration and intensity of exposure. There have been no studies investigating the effect of EMFs at the population or community level for benthic organisms. 

No studies have examined the effect of EMFs on Lophelia pertusa. However, one study was performed on the reef-forming annelid, Ficopomatus enigmaticus (Oliva et al., 2023). Sperm cells from this species were exposed to 0.5 and 1.0 mT of static magnetic field. After only three hours of exposure, sperm fertilization rate was reduced, and significant increases in DNA damage and mitochondrial activity indicative of a stress response were reported. However, there is ‘Insufficient evidence’ on which to base an assessment of the likely sensitivity of this biotope to EMFs.

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. Clippele (2023) studied the effect of noise on Lophelia pertusa larvae and found that noise pollution may deter larvae from swimming, thus preventing colonization, of suitable habitats. Larvae exposed to noise pollution (ship’s produced noise for 60 minutes at a frequency range of 100Hz to 20kHz) limited most of their swimming to surface waters, compared to the control group (healthy reef sounds, healthy reef sounds + coral rubble for 60 minutes at a frequency range of 100Hz to 20kHz), which swam more freely in the water column, exploring the bottom waters (Clippele, 2023). However, due to the limited studies that exist, there is ‘Insufficient evidence’ 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 of this biotope, which 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. Since 2016, research on artificial light at night (ALAN) has expanded considerably in the marine and coastal environment. Light was previously assumed to be of low ecological significance in subtidal and intertidal habitats, but there is now evidence that ALAN is widespread in the marine environment, with biologically relevant levels of light penetrating to depths of up to 50m (Davies et al., 2020; Smyth et al., 2021). ALAN can alter biological processes across taxa and at multiple levels of organisation. Documented responses include disruption of diel and circalunar rhythms, changes in activity and foraging, altered predator–prey interactions, shifts in community composition, and impacts on algal growth and phenology (Davies et al., 2014, 2015b; Gaston et al., 2017; Tidau et al., 2021; Lynn et al., 2022; Marangoni et al., 2022; Miller & Rice, 2023; Ferretti et al., 2025). Evidence for benthic habitats and assemblages specifically is beginning to emerge (e.g. Trethewy et al., 2023; Schaefer et al., 2025), but remains limited and fragmented, often focusing on single taxa or short-term experiments. Mortality thresholds, long-term consequences, and responses at the biotope scale are rarely addressed, and there are major gaps around indirect effects such as trophic cascades or habitat modification.

Sensitivity assessment. Given the rapid expansion of the evidence base but the continuing lack of data at the level of individual biotopes, resistance and resilience cannot be robustly assessed. Sensitivity is therefore recorded as 'Insufficient evidence'.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Not relevant – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit 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 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 the 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 their aquaria, two Lophelia pertusa polyps became infested but did not seem to be influenced by the infestation (Mortensen, 2001). Chemel (2023) conducted an aquarium experiment to predict the effect of temperature on North East Atlantic Lophelia pertusa and found that, on a long-term scale (four months), while a 4°C lower temperature did not affect Lophelia physiology and microbiome, a 4°C increase in temperature led to massive mortality. Mortality was associated with a high level of stress in the coral, as attested by the upregulation of the number of genes related to immune, inflammatory and antioxidant responses, cell death and apoptosis, DNA repair and maintenance, but also the shift in coral bacterial community towards pathogens and opportunistic bacteria (Chemel, 2023).

Chemel et al. (2024) conducted a further study examining the effect of increasing temperature on North East Atlantic Lophelia pertusa and found that at temperature increases of +3 and + 5°C, Lophelia exhibited significant mortality related to changes in its microbiome composition. The presence of gene markers for bacterial virulence factors suggested that the coral death was due to infection by pathogenic bacteria (Chemel et al., 2024). Specifically, within eight weeks, survival of the North East Atlantic Lophelia (where it experiences temperatures between 8 and 12°C) dropped from 60% at 13 °C (+ 3 °C) to 33% at 15 °C (+ 5 °C) (Chemel et al., 2024). These results suggested that Lophelia pertusa could only survive a long-term temperature increase of < 3°C, as a long-term increase of >3°C would limit the capacity of the coral to maintain or regulate its microbiome under elevated temperature, which results in a proliferation of potentially pathogenic bacteria (Chemel et al., 2024). It is not yet known whether Lophelia pertusa in the Atlantic are already living at their thermal optimum, making them highly vulnerable to increases in temperature, or whether they can thrive in waters as warm as their Mediterranean counterparts. However, as Chapron et al. (2021) observed, Mediterranean Lophelia, normally living at 13°C, were strongly affected by water temperatures of 17°C.

Any parasitic infestation is likely to reduce the viability of the host, even if only a few or possibly hundreds of polyps were affected. Limited evidence is available for the lone effect of pathogens on Lophelia pertusa. However, evidence exists that shows pathogens to be the main result of Lophelia mortality in aquaria scenarios of increasing temperature (Chemel, 2023; Chemel et al., 2024). Since an increase in temperature can encourage the development of pathogens in Lophelia to its detriment, resistance is assessed as ‘Medium’ (as a worst-case scenario), resilience as ‘Very low’, and sensitivity as ‘Medium’, albeit with ‘Low’ confidence.

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’.

The American slipper limpet, Crepidula fornicata

Evidence

Crepidula fornicata larvae require hard substrata for settlement. It prefers muddy, gravelly, shell-rich substrata that include gravel, or shells of other Crepidula, or other species, e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. Yet, it was also recorded from rock, artificial substrata, and Sabellaria alveolata reefs (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011b; Helmer et al., 2019; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Tillin et al., 2020). Close examination of the literature (2023) shows that evidence of its colonization and density on bedrock in the infralittoral or circalittoral was lacking. Tillin et al. (2020) suggested that Crepidula could colonize circalittoral rock due to its presence on tide-swept rough grounds in the English Channel (Hinz et al., 2011b). However, Hinz et al. (2011b) reported that Crepidula fornicata only dominated one assemblage (with an average of 181 individuals per trawl) on gravel substratum with boulders. Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas dominated by boulders, and Bohn et al. (2013a, 2013b, 2015) and Preston et al. (2020) showed that while Crepidula could settle on slate panels or ‘stone’, it preferred shell, especially that of conspecifics.

Sensitivity assessment. The lower circalittoral rock and cold-water coral characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata due to its depth and the moderately strong tidal conditions it experiences, which may mitigate or prevent the colonization by Crepidula at high densities.  Although Crepidula has been recorded from gravelly sediments in areas of strong tidal streams at 160 m (Hinz et al., 2011b), no evidence was found of the effect of Crepidula populations on cold-water coral-dominated, or infralittoral or circalittoral rock habitats (Tillin et al., 2020). At present, there is 'Insufficient evidence' to suggest that the lower circalittoral rock and cold-water coral biotopes are sensitive to colonization by Crepidula fornicata or other invasive species; further evidence is required. 

The carpet sea squirt, Didemnum vexillum

Evidence

The carpet sea squirt Didemnum vexillum (syn. Didemnum vestitum; Didemnum vestum) is a colonial ascidian with rapidly expanding populations that have invaded most temperate coastal regions around the world (Kleeman, 2009; Stefaniak et al., 2012; Tillin et al., 2020). It is an ‘ecosystem engineer’ that can change or modify invaded habitats and alter biodiversity (Griffith et al., 2009; Mercer et al., 2009). Didemnum vexillum has colonized and established populations in the northeast Pacific, Canadian and USA coast; New Zealand; France, Spain, and the Wadden Sea, Netherlands; the Mediterranean Sea and Adriatic Sea (Bullard et al., 2007; Coutts & Forrest, 2007; Dijkstra et al., 2007; Valentine et al., 2007a; Valentine et al., 2007b; Lambert, 2009; Hitchin, 2012; Tagliapietra et al., 2012; Gittenberger et al., 2015; Vercaemer et al., 2015; Mckenzie et al., 2017; Cinar & Ozgul, 2023; Holt, 2024). In the UK, Didemnum vexillum has colonized Holyhead marina and Milford Haven, Wales; the west coast of Scotland (marinas around Largs, Clyde, Loch Creran and Loch Fyne), South Devon (Plymouth, Yealm, and Dartmouth estuaries), the Solent, northern Kent, Essex, and Suffolk coasts (Griffith et al., 2009; Lambert, 2009; Hitchin, 2012; Minchin & Nunn, 2013; Bishop et al., 2015; Mckenzie et al., 2017; Tillin et al., 2020, Holt, 2024; NBN, 2024).

Although a widespread invader, Didemnum vexillum has a limited ability for natural dispersal since the pelagic larvae remain in the water column for a short time (up to 36 hours). Therefore, it has a short dispersal phase that can allow the species to build localized populations (Herborg et al., 2009; Vercaemer et al., 2015; Holt, 2024). However, Bullard et al. (2007) suggested that Didemnum vexillum can form new colonies asexually by fragmentation. Colonies can produce long tendrils from an encrusting colony, which can fragment, disperse and settle, attaching to suitable hard substrata elsewhere (Bullard et al., 2007; Lambert, 2009; Stefaniak & Whitlatch, 2014). A fragmented colony can spread naturally for up to three weeks, transported by ocean currents, attached to floating seaweed, seagrass or other floating biota, or as free-floating spherical colonies (Bullard et al., 2007; Lengyel et al., 2009; Stefaniak & Whitlatch, 2014; Holt, 2024). Fragments can reattach to suitable substrata within six hours of contact. Fragments have the potential to disperse around 20 km before reattachment (Lengyel et al., 2009). Valentine et al. (2007a) reported that colonies of Didemnum vexillum enlarged by 6 to 11 times by asexual budding after 15 days and enlarged 11 to 19 times after 30 days. Valentine et al. (2007a) concluded fragments could successfully grow, survive, and help to spread Didemnum vexillum.

While natural fragmentation of tendrils is thought to allow Didemnum vexillum to invade longer distances and increase its dispersal potential, Stefaniak & Whitlatch (2014) found that only one tendril out of 80 reattached to the flat, bare substrata used in their study, because tendrils required an extensive (at least eight-hour) period of contact to reattach. Stefaniak & Whitlatch (2014) suggested that once fragmented from a colony, the success of tendril reattachment was limited, and reattachment was not a major contributor to the invasive success of Didemnum vexillum. However, Stefaniak & Whitlatch (2014) also found that larvae-packed tendril fragments may increase natural dispersal distance, reproduction, and invasive success of Didemnum vexillum, and increase the distance larvae can travel. Not all colonies produce tendrils at all locations.

Human-mediated transport via aquaculture facilities, boat hulls, commercial fishing vessels, and ballast water is probably the most important vector that has aided the long-distance dispersal of Didemnum vexillum and explains its prevalence in harbours and marinas (Bullard et al., 2007; Dijkstra et al., 2007; Griffith et al., 2009; Herborg et al., 2009). Fragmentation of colonies during transport or human disturbance (such as trawling or dredging) could indirectly disperse the species and enable it to find suitable conditions for establishment (Herborg et al., 2009). For example, in oyster farms in British Columbia, large fragments of Didemnum sp. come off oyster strings when they are pulled out of water, and other fragments can be pulled off oysters and mussels and thrown back into the water, which is likely to aid dispersal of the invasive species (Bullard et al., 2007). Dijkstra et al. (2007) hypothesised that Didemnum sp. was introduced to the Gulf of Maine with oyster aquaculture in the Damariscotta River and transported via Pacific oysters.

Didemnum vexillum was likely introduced into the UK from northern Europe or Ireland via poorly maintained or not antifouled vessels, movement of contaminated shellfish stock and aquaculture equipment, or via marine industries such as oil, gas, renewables, and dredging (Holt, 2024). Recent evidence from genetic material suggests that human-mediated dispersal, between marinas and shellfish culture sites, is the most likely pathway for connectivity of Didemnum vexillum populations throughout Ireland and Britain (Prentice et al., 2021; Holt, 2024). Didemnum vexillum can disperse away from artificial substrata, invading and colonizing natural substrata in surrounding areas (Tillin et al., 2020). Holt (2024) noted that Didemnum vexillum had not spread as far as feared in the UK since it was first recorded. The current evidence of Didemnum vexillum’s ability to spread on natural habitats in this area is sparse and often conflicting, complicated by genetics and its apparent variable habitat preferences and tolerances and its variable ability to adapt to ‘new’ conditions (Holt 2024).

Didemnum vexillum has a seasonal growth cycle that is influenced by temperature (Valentine et al., 2007a). In warmer months (June and July), colonies may be large and well-developed encrusting mats. Populations experience more rapid growth from July to September, sometimes continuing into December. Colonies begin to decline in health and ‘die-off’ when temperatures drop below 5°C during winter months from around October to April (Gittenberger, 2007; Valentine et al., 2007a; Herborg et al., 2009). Cold water months cause colonies to regress and reduce in size, yet they often regenerate as temperatures warm (Griffith et al., 2009; Kleeman, 2009; Mercer et al., 2009), although some populations may not survive winter at all (Dijkstra et al., 2007). The early growth phase, from May to July, is initiated by smaller colonies developing from remnants of colonies that survived the cold water (Valentine et al., 2007a). The seasonal growth cycle is also likely influenced by location. For example, the Didemnum sp. growth cycle for colonies in Sandwich tide pool (temperature range from -1°C to 24°C, with daily fluctuations), probably does not occur in deep offshore subtidal habitats in Georges Bank (annual temperature range from 4°C to 15°C, and daily fluctuations are minimal) (Valentine et al., 2007a). Larval release and recruitment typically occur between 14°C to 20°C and slow or cease below 9°C to 11°C as summer ends (Griffith et al., 2009; McKenzie et al., 2017). In New Zealand, recruitment occurs from November to July, where the highest average temperatures were recorded in February (18°C to 22°C) and the lowest average temperatures were recorded in July (9°C to 10°C) (Fletcher et al., 2013a). In this New Zealand study, higher water temperatures were associated with a higher level of recruitment (Fletcher et al., 2013a).

Didemnum vexillum requires suitable hard substrata for successful settlement and the establishment of colonies. It can grow quickly and establish large colonies of dense encrusting mats on a variety of hard substrata (Valentine et al., 2007a; Griffith et al., 2009; Lambert, 2009; Groner et al., 2011; Cinar & Ozgul, 2023). Gittenberger (2007) stated that invasive Didemnum sp. was a threat to native ecosystems because of its ability to overgrow virtually all hard substrata present. Suitable hard substrata can include rocky substrata such as bedrock, gravel, pebble, cobble, or boulders or artificial substrata such as a variety of maritime structures, such as pontoons, docks, wood and metal pilings, chains, ropes and moorings, plastic and ship hulls and at aquaculture facilities (Valentine et al., 2007a&b; Bullard et al., 2007; Griffith et al., 2009; Lambert, 2009; Tagliapietra et al., 2012; Tillin et al., 2020). Didemnum vexillum has been reported colonizing these types of hard substrata in the USA, Canada, northern Kent, and the Solent (Bullard et al., 2007; Valentine et al., 2007a; Valentine et al., 2007b; Hitchin, 2012; Vercaemer et al., 2015; Tillin et al., 2020).

Didemnum vexillum has the ability to rapidly overgrow and displace on other sessile organisms such as other colonial ascidians (Ciona intestinalis, Styela clava, Ascidiella aspera, Botrylloides violaceus, Botryllus schlosseri, Diplosoma listerianium and Aplidium spp.), bryozoan, hydroids, sponges (Clione celata and Halichrondria sp.), anemone (Diadumene cincta), calcareous tube worms, eelgrass (Zostera marina), kelp (Laminaria spp. and Agarum sp.), green algae (Codium fragile subsp. fragile), red algae (Plocamium, Chondrus crispus and bush weed Agardhiella subulata), brown algae (Ascophyllum nodosum, Sargassum, Halidrys, Fucus evanescens and Fucus serratus), calcareous algae (Corallina officinalis), mussels (Mytilus galloprovincialis, Perna canaliculus  and Mytilus edulis), barnacles, oysters (Magallana gigas, Ostrea edulis and Crassostrea virginica), sea scallops (Placopecten magellanicus), or dead shells (Dijkstra et al., 2007; Gittenberger, 2007; Valentine et al., 2007a; Valentine et al., 2007b; Griffith et al., 2009; Carman & Grunden, 2010; Dijkstra & Nolan, 2011; Groner et al., 2011; Hitchin, 2012; Tagliapietra et al., 2012; Minchin & Nunn, 2013; Gittenberger et al., 2015; Long & Groholz, 2015; Vercaemer et al., 2015).

In contrast, Didemnum vexillum’s preference for sheltered conditions, established colonies observed in Georges Bank and Long Island Sound were exposed to moderately strong tidal currents (1 to 2 knots; ca 0.5 to 1 m/s recorded at both sites) that may mobilise sediment (Valentine et al., 2007b; Mercer et al., 2009; Tillin et al., 2020). However, Valentine et al. (2007b) describe the substratum as immobile, presumably consolidated, gravel, cobbles, and pebbles. Kleeman (2009) stated that the presence of a consistent mild wave action or ‘swash zone’ appears to favour Didemnum sp. establishment in the intertidal. Although some evidence suggests that waves and currents can facilitate the fragmentation and spread of Didemnum vexillum (Mckenzie et al., 2017), the tidal current velocities at some sites where Didemnum vexillum has been reported (for example, New England, where current velocities reach up to around 3 m/s) is lower than the current velocity required for the dislodgement of Didemnum vexillum fragments (around 7.6 m/s) (Reinhardt et al., 2012). This suggests that not all tidal currents are likely to dislodge Didemnum vexillum fragments. When on boat hulls, the species can experience higher current velocities, which are enough to cause dislodgement (Reinhardt et al., 2012).  

Didemnum vexillum has been recorded in the sublittoral to depths of 81 m in Georges Bank and 30 m in Long Island, USA (Bullard et al., 2007; Valentine et al., 2007b; Mercer et al., 2009). This cold-water coral biotope occurs on bedrock, which could provide a suitable hard substratum for colonization by Didemnum sp. Didemnum vexillum is reported to prefer sheltered conditions but has also been recorded in moderately strong currents (Valentine et al., 2007b; Mercer et al., 2009; Tillin et al., 2020) and is predicted to survive stronger currents, as the current velocity which will dislodge Didemnum vexillum is around 7.6 m/s (Reinhardt et al., 2012). This biotope experiences weak to moderately strong water flow (0.5 to 1.5 m/s) and is extremely sheltered from wave exposure, which could allow Didemnum settlement. Didemnum vexillum regresses as temperatures decline in winter, so shallow examples may be able to recover their condition in winter (Gittenberger, 2007; Valentine et al., 2007a; Herborg et al., 2009). However, deeper examples may not experience enough temperature change to trigger the decline in Didemnum vexillum (Valentine et al., 2007a). If Didemnum sp. could gain a 'foothold', it might overgrow, smother or cause mortality of corals, bryozoans, and sponges. Holt (2024) noted that Didemnum vexillum had not spread as far as feared in the UK since it was first recorded. Therefore, a resistance of 'Medium' (some, <25% mortality) is suggested as a precaution in case Didemnum vexillum could colonize the biotope, but with 'Low' confidence due to the lack of direct evidence. Resilience is assessed as 'Very low' as recovery would require the physical removal of Didemnum sp., so sensitivity is assessed as 'Medium'. 

The Pacific oyster, Magallana gigas

Evidence

The majority of the evidence indicates that infralittoral rock and other habitats that occur at depths more than 10 m are unlikely to be suitable for Magallana gigas because it is considered an intertidal and shallow subtidal species rarely recorded below extreme low water (Herbert et al., 2012, 2016; Tillin et al., 2020). Therefore, this INIS is probably 'Not relevant' in this biotope. 

Wireweed, Sargassum muticum

Evidence

The depth and sedimentation probably exclude macroalgae from this biotope. Hence, it is unlikely to be colonized by Sargassum. Therefore, this INIS is probably 'Not relevant' in this biotope. 

Wakame, Undaria pinnatifida

Evidence

The depth and sedimentation probably exclude macroalgae from this biotope. Hence, it is unlikely to be colonized by Undaria. Therefore, this INIS is probably 'Not relevant' in this biotope.

Other INIS

Evidence

No other alien or non-native species are known to compete with Lophelia pertusa or other cold-water corals, at present. Therefore, there is ‘No evidence’ for the effect of other INIS on this biotope.