The Marine Life Information Network

Global warming (extreme)

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

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

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

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

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

Evidence

Deep waters off the continental shelf (200 – 2,500 m) are expected to see a lower temperature rise (ca 1°C) than shallow water habitats by the end of this century, regardless of scenario (FAO, 2019). Scleractinian corals such as Caryophyllidae may be more affected by temperature increases than ocean acidification stress (FAO, 2019).  Gori et al. (2016) found that when the Caryophyllidae species, Desmophyllum dianthus, was exposed to an elevated temperature of 15°C, relative to a 12°C ambient benchmark, calcification rates were significantly reduced. When exposed to both this elevated temperature and an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark), respiration rates were significantly reduced. As such, the study concluded that Desmophyllum dianthus is more sensitive to thermal than pCO₂ stress.

Global habitat suitability modelling for black corals, including the family Leiopathidae, Myriopathidae and Antipathidae (relevant for Leiopathes spp., Antipathella spp. and Stichopathes spp., respectively) found that temperature was the most important variable (with some influence from topography, surface productivity and oxygen level; Yesson et al., 2017). Seabed temperatures above 3°C found to be most suitable, although a model response to depth was also noted. Leiopathes spp. was recorded in a canyon in the southern Bay of Biscay, where temperatures ranged from 10-11°C (Sánchez et al., 2014). Leiopathes glaberrima was found alongside Lophelia pertusa in areas where temperatures ranged between 8.5 and 10.6°C over five days of measurements in the Gulf of Mexico (Davies et al., 2010). Within this five-day period, internal waves caused temperature fluctuations of 0.8°C over 5-11 hrs (Davies et al., 2010). Furthermore, high-frequency temperature variability over even shorter periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred within 20-30-minutes, followed by a slower temperature decline. Habitat suitability modelling for Leiopathes glaberrima in the Gulf of Mexico was undertaken by Etnoyer et al. (2018). The study found that mean annual bottom temperature (together with slope and depth) was the most important environmental predictor variable for model fitting. The predicted likelihood of suitable habitat was greatest at a mean annual bottom temperature range of 6 to 16°C.

For the genus Antipathella, evidence is available for Antipathella subpinnata, Antipathella wollastoni and Antipathella fiordensis. Antipathella subpinnata colonies have been found in the Tyrrhenian Sea at water temperatures between 14-16°C (Gaino & Scoccia, 2010). Bo et al. (2008) suggest that temperature is the main environmental factor influencing the bathymetric distribution of Antipathella subpinnata in the Mediterranean, where the species doesn’t occur shallower than 50 m and temperatures are greater than 15°C. The authors state that this indicates that the species is stenothermal and unable to survive at temperatures in excess of 15°C. CTD (conductivity, temperature and depth) profiles from the Azores within the depth range where Antipathella subpinnata gardens occur, recorded temperatures of 14.5-14.9°C (Tempera, unpublished data, cited in de Matos et al., 2014). Similarly, ROV temperature sensors during the de Matos et al. (2014) study logged 15 and 16°C (±1°C) during the warmest months of the year. The seamounts and island slopes where colonies were collected also experience pronounced surface cooling (Bashmachnikov et al., 2004 cited in de Matos et al., 2014). This evidence further indicates that Antipathella subpinnata has a temperature tolerance of <15°C.

Antipathella wollastoni occurs in the Azores, where summer temperatures are 18°C (Rakka et al., 2017). The gamete maturation of Antipathella wollastoni was positively correlated to sea surface temperature (SST). However, spawning appeared to happen after the temperature peak in September of 21.1°C. This indicated that high temperatures might be a cue for final gamete maturation, rather than spawning.

Antipathella fiordensis occurs off New Zealand, where Parker et al. (1997) recorded temperatures between 11 and 15°C over the course of a year. It is worth noting that these temperatures were 2-3°C lower on average than those recorded in previous years by Grange et al. (1991, cited in Parker et al., 1997). Spawning also appeared to be linked to temperature,  occurring after the highest temperature peak (February). The authors also noted that spawning occurred a month later than in the previous year, when the temperature was higher. Antipathella fiordensis therefore shows a reliance on temperature for control of oogenesis (Parker et al., 1997), meaning that fluctuating temperatures may interfere with reproduction. However, the inter-annual temperature variations suggest that the benchmark of an increase in temperature of 1°C is unlikely to negatively affect the species.

Acanthogorgia armata has been found off the south of Iceland, where the maximum water temperature is 10.7°C on average (Madsen, 1944 & The Icelandic Benthos database, 2007, cited in Buhl-Mortensen et al., 2015). Buhl-Mortensen et al. (2015) also recorded the temperature range of Acanthogorgia armata to be from 1 to 12°C, although most occurrences were within 3-4°C.

Specimens of Stichopathes spp. were observed in the Whittard Canyon (at 633-762 m depths), where temperatures were recorded at ca 9°C (Johnson et al., 2013). Stichopathes spp. have also been recorded in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where bottom temperatures were 21.6°C (Qurban et al., 2014).  Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where temperatures vary from 3.97-7.62°C across the seamount (Henry et al., 2015).  These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks are subject to high short-term variability in water temperature down to 1,500 m deep, consistent with an internal tide led oceanographic regime.

Sensitivity assessment. Under all three scenarios (middle and high emission, and extreme scenarios), waters off the continental shelf are expected to increase marginally by approximately 1°C. The characterizing species Stichopathes gravieri, Antipathella spp., Acanthogorgia armata and Leiopathes spp. naturally occur within a range of bottom water temperatures, so are not likely to be affected by a change in bottom temperature at the pressure benchmark (a 1°C rise in temperature in the deep-sea). In particular, Leiopathes glabberima has been shown to inhabit areas subjected to natural high-frequency temperature variations of up to 1°C over periods of 20-30 minutes, 2.5 hours and 5-11 hours (Davies et al., 2010; Sánchez et al., 2014). However, evidence for one species within the family Caryophylliidae spp. (also characterizing), does show sensitivity to increased temperatures (Gori et al., 2016). Although the 3°C increase in temperature used in the study is higher than the 1°C benchmark for this pressure, significant reductions in calcification rates were observed. When subjected to both elevated pCO₂ and temperature, respirations rates were significantly reduced. Hence, as Caryophylliidae spp. are potentially sensitive to changes in temperature. Therefore, resistance for this biotope is assessed as ‘Medium’, resilience as ‘Very low’ and sensitivity is assessed as ‘Medium’.

Global warming (high)

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

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

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

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

Evidence

Deep waters off the continental shelf (200 – 2,500 m) are expected to see a lower temperature rise (ca 1°C) than shallow water habitats by the end of this century, regardless of scenario (FAO, 2019). Scleractinian corals such as Caryophyllidae may be more affected by temperature increases than ocean acidification stress (FAO, 2019).  Gori et al. (2016) found that when the Caryophyllidae species, Desmophyllum dianthus, was exposed to an elevated temperature of 15°C, relative to a 12°C ambient benchmark, calcification rates were significantly reduced. When exposed to both this elevated temperature and an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark), respiration rates were significantly reduced. As such, the study concluded that Desmophyllum dianthus is more sensitive to thermal than pCO₂ stress.

Global habitat suitability modelling for black corals, including the family Leiopathidae, Myriopathidae and Antipathidae (relevant for Leiopathes spp., Antipathella spp. and Stichopathes spp., respectively) found that temperature was the most important variable (with some influence from topography, surface productivity and oxygen level; Yesson et al., 2017). Seabed temperatures above 3°C found to be most suitable, although a model response to depth was also noted. Leiopathes spp. was recorded in a canyon in the southern Bay of Biscay, where temperatures ranged from 10-11°C (Sánchez et al., 2014). Leiopathes glaberrima was found alongside Lophelia pertusa in areas where temperatures ranged between 8.5 and 10.6°C over five days of measurements in the Gulf of Mexico (Davies et al., 2010). Within this five-day period, internal waves caused temperature fluctuations of 0.8°C over 5-11 hrs (Davies et al., 2010). Furthermore, high-frequency temperature variability over even shorter periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred within 20-30-minutes, followed by a slower temperature decline. Habitat suitability modelling for Leiopathes glaberrima in the Gulf of Mexico was undertaken by Etnoyer et al. (2018). The study found that mean annual bottom temperature (together with slope and depth) was the most important environmental predictor variable for model fitting. The predicted likelihood of suitable habitat was greatest at a mean annual bottom temperature range of 6 to 16°C.

For the genus Antipathella, evidence is available for Antipathella subpinnata, Antipathella wollastoni and Antipathella fiordensis. Antipathella subpinnata colonies have been found in the Tyrrhenian Sea at water temperatures between 14-16°C (Gaino & Scoccia, 2010). Bo et al. (2008) suggest that temperature is the main environmental factor influencing the bathymetric distribution of Antipathella subpinnata in the Mediterranean, where the species doesn’t occur shallower than 50 m and temperatures are greater than 15°C. The authors state that this indicates that the species is stenothermal and unable to survive at temperatures in excess of 15°C. CTD (conductivity, temperature and depth) profiles from the Azores within the depth range where Antipathella subpinnata gardens occur, recorded temperatures of 14.5-14.9°C (Tempera, unpublished data, cited in de Matos et al., 2014). Similarly, ROV temperature sensors during the de Matos et al. (2014) study logged 15 and 16°C (±1°C) during the warmest months of the year. The seamounts and island slopes where colonies were collected also experience pronounced surface cooling (Bashmachnikov et al., 2004 cited in de Matos et al., 2014). This evidence further indicates that Antipathella subpinnata has a temperature tolerance of <15°C.

Antipathella wollastoni occurs in the Azores, where summer temperatures are 18°C (Rakka et al., 2017). The gamete maturation of Antipathella wollastoni was positively correlated to sea surface temperature (SST). However, spawning appeared to happen after the temperature peak in September of 21.1°C. This indicated that high temperatures might be a cue for final gamete maturation, rather than spawning.

Antipathella fiordensis occurs off New Zealand, where Parker et al. (1997) recorded temperatures between 11 and 15°C over the course of a year. It is worth noting that these temperatures were 2-3°C lower on average than those recorded in previous years by Grange et al. (1991, cited in Parker et al., 1997). Spawning also appeared to be linked to temperature,  occurring after the highest temperature peak (February). The authors also noted that spawning occurred a month later than in the previous year, when the temperature was higher. Antipathella fiordensis therefore shows a reliance on temperature for control of oogenesis (Parker et al., 1997), meaning that fluctuating temperatures may interfere with reproduction. However, the inter-annual temperature variations suggest that the benchmark of an increase in temperature of 1°C is unlikely to negatively affect the species.

Acanthogorgia armata has been found off the south of Iceland, where the maximum water temperature is 10.7°C on average (Madsen, 1944 & The Icelandic Benthos database, 2007, cited in Buhl-Mortensen et al., 2015). Buhl-Mortensen et al. (2015) also recorded the temperature range of Acanthogorgia armata to be from 1 to 12°C, although most occurrences were within 3-4°C.

Specimens of Stichopathes spp. were observed in the Whittard Canyon (at 633-762 m depths), where temperatures were recorded at ca 9°C (Johnson et al., 2013). Stichopathes spp. have also been recorded in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where bottom temperatures were 21.6°C (Qurban et al., 2014).  Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where temperatures vary from 3.97-7.62°C across the seamount (Henry et al., 2015).  These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks are subject to high short-term variability in water temperature down to 1,500 m deep, consistent with an internal tide led oceanographic regime.

Sensitivity assessment. Under all three scenarios (middle and high emission, and extreme scenarios), waters off the continental shelf are expected to increase marginally by approximately 1°C. The characterizing species Stichopathes gravieri, Antipathella spp., Acanthogorgia armata and Leiopathes spp. naturally occur within a range of bottom water temperatures, so are not likely to be affected by a change in bottom temperature at the pressure benchmark (a 1°C rise in temperature in the deep-sea). In particular, Leiopathes glabberima has been shown to inhabit areas subjected to natural high-frequency temperature variations of up to 1°C over periods of 20-30 minutes, 2.5 hours and 5-11 hours (Davies et al., 2010; Sánchez et al., 2014). However, evidence for one species within the family Caryophylliidae spp. (also characterizing), does show sensitivity to increased temperatures (Gori et al., 2016). Although the 3°C increase in temperature used in the study is higher than the 1°C benchmark for this pressure, significant reductions in calcification rates were observed. When subjected to both elevated pCO₂ and temperature, respirations rates were significantly reduced. Hence, as Caryophylliidae spp. are potentially sensitive to changes in temperature. Therefore, resistance for this biotope is assessed as ‘Medium’, resilience as ‘Very low’ and sensitivity is assessed as ‘Medium’.

Global warming (middle)

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

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

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

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

Evidence

Deep waters off the continental shelf (200 – 2,500 m) are expected to see a lower temperature rise (ca 1°C) than shallow water habitats by the end of this century, regardless of scenario (FAO, 2019). Scleractinian corals such as Caryophyllidae may be more affected by temperature increases than ocean acidification stress (FAO, 2019).  Gori et al. (2016) found that when the Caryophyllidae species, Desmophyllum dianthus, was exposed to an elevated temperature of 15°C, relative to a 12°C ambient benchmark, calcification rates were significantly reduced. When exposed to both this elevated temperature and an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark), respiration rates were significantly reduced. As such, the study concluded that Desmophyllum dianthus is more sensitive to thermal than pCO₂ stress.

Global habitat suitability modelling for black corals, including the family Leiopathidae, Myriopathidae and Antipathidae (relevant for Leiopathes spp., Antipathella spp. and Stichopathes spp., respectively) found that temperature was the most important variable (with some influence from topography, surface productivity and oxygen level; Yesson et al., 2017). Seabed temperatures above 3°C found to be most suitable, although a model response to depth was also noted. Leiopathes spp. was recorded in a canyon in the southern Bay of Biscay, where temperatures ranged from 10-11°C (Sánchez et al., 2014). Leiopathes glaberrima was found alongside Lophelia pertusa in areas where temperatures ranged between 8.5 and 10.6°C over five days of measurements in the Gulf of Mexico (Davies et al., 2010). Within this five-day period, internal waves caused temperature fluctuations of 0.8°C over 5-11 hrs (Davies et al., 2010). Furthermore, high-frequency temperature variability over even shorter periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred within 20-30-minutes, followed by a slower temperature decline. Habitat suitability modelling for Leiopathes glaberrima in the Gulf of Mexico was undertaken by Etnoyer et al. (2018). The study found that mean annual bottom temperature (together with slope and depth) was the most important environmental predictor variable for model fitting. The predicted likelihood of suitable habitat was greatest at a mean annual bottom temperature range of 6 to 16°C.

For the genus Antipathella, evidence is available for Antipathella subpinnata, Antipathella wollastoni and Antipathella fiordensis. Antipathella subpinnata colonies have been found in the Tyrrhenian Sea at water temperatures between 14-16°C (Gaino & Scoccia, 2010). Bo et al. (2008) suggest that temperature is the main environmental factor influencing the bathymetric distribution of Antipathella subpinnata in the Mediterranean, where the species doesn’t occur shallower than 50 m and temperatures are greater than 15°C. The authors state that this indicates that the species is stenothermal and unable to survive at temperatures in excess of 15°C. CTD (conductivity, temperature and depth) profiles from the Azores within the depth range where Antipathella subpinnata gardens occur, recorded temperatures of 14.5-14.9°C (Tempera, unpublished data, cited in de Matos et al., 2014). Similarly, ROV temperature sensors during the de Matos et al. (2014) study logged 15 and 16°C (±1°C) during the warmest months of the year. The seamounts and island slopes where colonies were collected also experience pronounced surface cooling (Bashmachnikov et al., 2004 cited in de Matos et al., 2014). This evidence further indicates that Antipathella subpinnata has a temperature tolerance of <15°C.

Antipathella wollastoni occurs in the Azores, where summer temperatures are 18°C (Rakka et al., 2017). The gamete maturation of Antipathella wollastoni was positively correlated to sea surface temperature (SST). However, spawning appeared to happen after the temperature peak in September of 21.1°C. This indicated that high temperatures might be a cue for final gamete maturation, rather than spawning.

Antipathella fiordensis occurs off New Zealand, where Parker et al. (1997) recorded temperatures between 11 and 15°C over the course of a year. It is worth noting that these temperatures were 2-3°C lower on average than those recorded in previous years by Grange et al. (1991, cited in Parker et al., 1997). Spawning also appeared to be linked to temperature,  occurring after the highest temperature peak (February). The authors also noted that spawning occurred a month later than in the previous year, when the temperature was higher. Antipathella fiordensis therefore shows a reliance on temperature for control of oogenesis (Parker et al., 1997), meaning that fluctuating temperatures may interfere with reproduction. However, the inter-annual temperature variations suggest that the benchmark of an increase in temperature of 1°C is unlikely to negatively affect the species.

Acanthogorgia armata has been found off the south of Iceland, where the maximum water temperature is 10.7°C on average (Madsen, 1944 & The Icelandic Benthos database, 2007, cited in Buhl-Mortensen et al., 2015). Buhl-Mortensen et al. (2015) also recorded the temperature range of Acanthogorgia armata to be from 1 to 12°C, although most occurrences were within 3-4°C.

Specimens of Stichopathes spp. were observed in the Whittard Canyon (at 633-762 m depths), where temperatures were recorded at ca 9°C (Johnson et al., 2013). Stichopathes spp. have also been recorded in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where bottom temperatures were 21.6°C (Qurban et al., 2014).  Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where temperatures vary from 3.97-7.62°C across the seamount (Henry et al., 2015).  These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks are subject to high short-term variability in water temperature down to 1,500 m deep, consistent with an internal tide led oceanographic regime.

Sensitivity assessment. Under all three scenarios (middle and high emission, and extreme scenarios), waters off the continental shelf are expected to increase marginally by approximately 1°C. The characterizing species Stichopathes gravieri, Antipathella spp., Acanthogorgia armata and Leiopathes spp. naturally occur within a range of bottom water temperatures, so are not likely to be affected by a change in bottom temperature at the pressure benchmark (a 1°C rise in temperature in the deep-sea). In particular, Leiopathes glabberima has been shown to inhabit areas subjected to natural high-frequency temperature variations of up to 1°C over periods of 20-30 minutes, 2.5 hours and 5-11 hours (Davies et al., 2010; Sánchez et al., 2014). However, evidence for one species within the family Caryophylliidae spp. (also characterizing), does show sensitivity to increased temperatures (Gori et al., 2016). Although the 3°C increase in temperature used in the study is higher than the 1°C benchmark for this pressure, significant reductions in calcification rates were observed. When subjected to both elevated pCO₂ and temperature, respirations rates were significantly reduced. Hence, as Caryophylliidae spp. are potentially sensitive to changes in temperature. Therefore, resistance for this biotope is assessed as ‘Medium’, resilience as ‘Very low’ and sensitivity is assessed as ‘Medium’.

Marine heatwaves (high)

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

Evidence

Marine heatwaves caused by increased air-sea flux of heat are only expected to penetrate surface waters (≤ 50 m) (Cerrano et al., 2000, Garrabou et al., 2009; Dan Smale, pers. comms.). Mixed coral assemblages on Lophelia pertusa reef framework are deep-sea biotopes, relevant to the Atlantic mid and upper bathyal zone, at depths of 200 – 1300 m. Therefore, the biotope will not be affected by changes arising from marine heatwaves, and the assessment at the pressure benchmark is ‘Not relevant’.

Marine heatwaves (middle)

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

Evidence

Marine heatwaves caused by increased air-sea flux of heat are only expected to penetrate surface waters (≤ 50 m) (Cerrano et al., 2000, Garrabou et al., 2009; Dan Smale, pers. comms.). Mixed coral assemblages on Lophelia pertusa reef framework are deep-sea biotopes, relevant to the Atlantic mid and upper bathyal zone, at depths of 200 – 1300 m. Therefore, the biotope will not be affected by changes arising from marine heatwaves, and the assessment at the pressure benchmark is ‘Not relevant’.

Ocean acidification (high)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping to 8.14 in the 1990s (Jacobson, 2005). By the end of this century, pH is predicted to decrease by a further 0.15 – 0.35 units depending on the emission scenario used (Bopp et al., 2013; Ostle et al., 2016), meaning surface pH could reduce to between ~7.99 to 7.79 pH units. Aragonite undersaturation is also likely to occur seasonally under the high emission scenario (Ostle et al., 2016). The mixed coral assemblage biotope is characterized by a number of different cold-water coral species, including black corals, gorgonians and scleractinians. Ocean acidification could pose a threat to these species, especially scleractinian corals such as Caryophillidae, which have a skeleton formed by aragonite (Maier et al., 2011 in Kenchington et al., 2012) and gorgonians such as Acanthogorgia armata that secrete magnesium carbonate (Kenchington et al., 2012).

Cold-water coral resilience to ocean acidification has been shown to relate to their ability to increase pH within their internal calcifying fluid, which will in turn induce carbonate precipitation (McCulloch et al., 2012; Wall et al., 2015). However, it is possible that under low food supply conditions (e.g. reductions in POC (particulate organic carbon) flux), shifts in energy allocation could occur to prioritise physiological functions rather than calcification and growth (Maier et al., 2016), meaning acidification may still have a negative effect. It should be noted these studies are more specific to scleractinian corals than black corals and gorgonians.

For the family Caryophylliidae, direct experimental evidence is available on the deep-sea solitary cup coral species Desmophyllum dianthus. Gori et al. (2016) found that at ambient temperatures, an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark) did not cause any change in the instantaneous calcification, respiration or ammonium excretion rates of the species. When exposed to both this elevated pCO₂ of 750 ppm and an elevated temperature of 15°C (relative to a 12°C ambient benchmark), respiration rates were significantly reduced. The study concluded that Desmophyllum dianthus is, therefore, more sensitive to thermal stress than pCO₂ stress. This species can also be found within naturally acidic waters, where pH ranges from 8.4 to 7.4 (Fillinger & Richter, 2013). Calcification rates of other non-reef forming species within the Caryophylliidae family similarly do not appear to be affected by decreases in pH including Desmophyllum cornigera (Movilla, 2015; Rodolfo-Metalpa et al., 2015), Caryophyllia smithii (Rodolfo-Metalpa et al., 2015) and Enallopsammia rostrate (McCulloch et al., 2012).

Gorgonians may be more sensitive to ocean acidification than scleractinians (FAO, 2019). A study undertaken by Carreiro-Silva et al. (in press) detailed in FAO (2019), to investigate the effects of ocean acidification on the deep-sea gorgonian Dentomuricea meteor found that the species showed a depressed metabolism and tissue necrosis. However, as this is the only study available on gorgonian species, they also highlighted the need to increase the range of deep-sea species tested for climate change impacts. In a shallow water study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had a mean pH of >8.1 and a minimum pH >7.9. The areas where octocorals and black corals were rarely found were characterized by high pH (maximum pH >8.4, mean pH >8.2). However, a range of other environmental factors were also measured, so pH is unlikely to be the sole cause of this pattern.  

In the Gulf of Mexico, the black coral Leiopathes glaberrima was found to occur alongside Lophelia pertusa (Davies et al., 2010). ROV dives concentrated in the areas with the densest coral cover had a consistent pH throughout all the dives, with values between 7.95 and 7.97. The other ROV dives over areas of coral had pH of 8.04 to 8.10 and 7.92 to 8.01.

As the oceans absorb carbon dioxide from the atmosphere, leading to a decrease in pH and an increase in acidity, the shoaling of the aragonite saturation horizon (ASH) is a further concern. The ASH is defined as the depth in the oceans at which aragonite saturation equals 1. Below this depth, aragonite saturation will fall below 1, and dissolution of calcified structures may occur. Currently the depth of the ASH in the North Atlantic is approximately 2,000 m (Jiang et al., 2015). This depth has already become 80-150 m shallower over the past two centuries (Chung et al., 2003, Feely et al., 2004). By the end of this century, the depth of the ASH is expected to become shallower still, reaching depths of up to 400 m under the high emission scenario (RCP 8.5) and 600 m for the middle emission scenario (RCP 4.5) (Zheng & Long, 2014). In addition to the shallowing of the aragonite saturation horizon, the calcite saturation horizon will also become shallower as ocean acidification occurs (Feely et al., 2004). The calcite saturation horizon is more relevant for octocorals, as they require calcium carbonate for structural development and calcite is essential in the skeletal structure (specifically for their sclerites; (Bayer & Macintyre, 2001).

The black coral Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where aragonite saturation levels vary from 0.77-1.40 across the seamount (Henry et al., 2015). These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks were subject to high short-term variability in aragonite down to 1,500 m deep, consistent with an internal tide led oceanographic regime.

In the Red Sea, at depths of 240-700 m, where records of an unidentified species of Caryophyllidae occur, aragonite saturation levels were recorded as 3.44-3.61 (Roder et al., 2013). Despite these high aragonite saturation levels, the study found that calcification rates were particularly low in this species of Caryophyllidae, suggesting that other factors may limit the growth of deep-sea corals, such as low oxygen levels or limited food availability. Another Caryophyllidae species, Desmophyllum dianthus, has been recorded at deep-sea Pacific upwelling locations with aragonite saturation levels of ≤0.6, however these specimens had depleted skeletal P/Ca, which is attributed to this undersaturation effect and linked to pH levels (Anagnostou et al., 2011). The tissue layer of deep-sea corals is also noted to protect the skeleton against dissolution.  However, under stress the coral may retract its polyps to expose the corallite skeleton, putting it at risk from erosion and dissolution (Lazier et al., 1999, cited in Anagnostou et al., 2011). Anagnostou et al. (2012) further suggest that Desmophyllum dianthus can partially compensate for a range of pH and aragonite saturation levels through its physiological modification mechanisms. This adaptation to low pH allows the species to enhance aragonite precipitation. In their study, specimens of Desmophyllum dianthus were from depths of 274-1,470 m in the Atlantic, Pacific and Southern Ocean, where the seawater pH ranged from 7.57-8.05 and aragonite saturation ranged from 0.6 to 2.1.

Sensitivity assessment. The characterizing species Leiopathes spp. naturally occurs within a pH range of 7.95- 8.10 (Davies et al., 2010) and in shallow waters. Yeung et al. (2014) found black corals were at highest abundance at minimum pH of 7.9.  As such, black corals are not likely to be affected by a change in pH at the middle emission scenario pressure benchmark (a further decrease of 0.15 to approx. 7.99) but may be affected at the high emission scenario benchmark (a further decrease of 0.35 to approx. 7.8). The black coral Stichopathes cf. abyssicola has been found at aragonite saturation levels <1. As such, this species may not be affected by shoaling of the ASH under the middle or high emission scenarios.

Evidence suggests that a number of species within the family Caryophylliidae can tolerate decreases in pH (Gori et al., 2016) and some occur naturally in areas with low pH (Fillinger & Richter, 2013) and low aragonite saturations levels (Anagnostou et al., 2011). Physiological adaptions have been observed in Desmophyllum dianthus to compensate for such conditions, and the tissue layer of deep-sea corals can protect against dissolution (Anagnostou et al., 2011). As such, this genus is unlikely to be affected by ocean acidification at the middle or high emission scenarios.

Kenchington et al. (2012) note that Acanthogorgia armata may be at risk from acidification due to its magnesium carbonate skeleton and Carreiro-Silva et al. (in press; detailed in Xavier et al. (2019), found that a deep-sea gorgonian species did show lower resistance to ocean acidification. Yeung et al. (2014) found highest species richness, including the genus Acanthogorgia, in areas with a minimum pH >7.9. As such, the characterizing species Acanthogorgia armata may be affected by ocean acidification at the high emission scenario but may be less affected at the middle emission scenario.

Therefore, resistance for the biotope at the middle emission scenario is assessed as ‘High’, with ‘High’ resilience, with an overall sensitivity of ‘Not sensitive’. However, at the high emission scenario the biotope is assessed as ‘Medium’. Resilience is assessed as ‘Very low’ as the pressure is expected to be long-term so recovery is not possible, therefore overall sensitivity is ‘Medium’.

Ocean acidification (middle)

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

Evidence

Increasing levels of CO₂ in the atmosphere have led to the average pH of sea surface waters dropping to 8.14 in the 1990s (Jacobson, 2005). By the end of this century, pH is predicted to decrease by a further 0.15 – 0.35 units depending on the emission scenario used (Bopp et al., 2013; Ostle et al., 2016), meaning surface pH could reduce to between ~7.99 to 7.79 pH units. Aragonite undersaturation is also likely to occur seasonally under the high emission scenario (Ostle et al., 2016). The mixed coral assemblage biotope is characterized by a number of different cold-water coral species, including black corals, gorgonians and scleractinians. Ocean acidification could pose a threat to these species, especially scleractinian corals such as Caryophillidae, which have a skeleton formed by aragonite (Maier et al., 2011 in Kenchington et al., 2012) and gorgonians such as Acanthogorgia armata that secrete magnesium carbonate (Kenchington et al., 2012).

Cold-water coral resilience to ocean acidification has been shown to relate to their ability to increase pH within their internal calcifying fluid, which will in turn induce carbonate precipitation (McCulloch et al., 2012; Wall et al., 2015). However, it is possible that under low food supply conditions (e.g. reductions in POC (particulate organic carbon) flux), shifts in energy allocation could occur to prioritise physiological functions rather than calcification and growth (Maier et al., 2016), meaning acidification may still have a negative effect. It should be noted these studies are more specific to scleractinian corals than black corals and gorgonians.

For the family Caryophylliidae, direct experimental evidence is available on the deep-sea solitary cup coral species Desmophyllum dianthus. Gori et al. (2016) found that at ambient temperatures, an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark) did not cause any change in the instantaneous calcification, respiration or ammonium excretion rates of the species. When exposed to both this elevated pCO₂ of 750 ppm and an elevated temperature of 15°C (relative to a 12°C ambient benchmark), respiration rates were significantly reduced. The study concluded that Desmophyllum dianthus is, therefore, more sensitive to thermal stress than pCO₂ stress. This species can also be found within naturally acidic waters, where pH ranges from 8.4 to 7.4 (Fillinger & Richter, 2013). Calcification rates of other non-reef forming species within the Caryophylliidae family similarly do not appear to be affected by decreases in pH including Desmophyllum cornigera (Movilla, 2015; Rodolfo-Metalpa et al., 2015), Caryophyllia smithii (Rodolfo-Metalpa et al., 2015) and Enallopsammia rostrate (McCulloch et al., 2012).

Gorgonians may be more sensitive to ocean acidification than scleractinians (FAO, 2019). A study undertaken by Carreiro-Silva et al. (in press) detailed in FAO (2019), to investigate the effects of ocean acidification on the deep-sea gorgonian Dentomuricea meteor found that the species showed a depressed metabolism and tissue necrosis. However, as this is the only study available on gorgonian species, they also highlighted the need to increase the range of deep-sea species tested for climate change impacts. In a shallow water study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had a mean pH of >8.1 and a minimum pH >7.9. The areas where octocorals and black corals were rarely found were characterized by high pH (maximum pH >8.4, mean pH >8.2). However, a range of other environmental factors were also measured, so pH is unlikely to be the sole cause of this pattern.  

In the Gulf of Mexico, the black coral Leiopathes glaberrima was found to occur alongside Lophelia pertusa (Davies et al., 2010). ROV dives concentrated in the areas with the densest coral cover had a consistent pH throughout all the dives, with values between 7.95 and 7.97. The other ROV dives over areas of coral had pH of 8.04 to 8.10 and 7.92 to 8.01.

As the oceans absorb carbon dioxide from the atmosphere, leading to a decrease in pH and an increase in acidity, the shoaling of the aragonite saturation horizon (ASH) is a further concern. The ASH is defined as the depth in the oceans at which aragonite saturation equals 1. Below this depth, aragonite saturation will fall below 1, and dissolution of calcified structures may occur. Currently the depth of the ASH in the North Atlantic is approximately 2,000 m (Jiang et al., 2015). This depth has already become 80-150 m shallower over the past two centuries (Chung et al., 2003, Feely et al., 2004). By the end of this century, the depth of the ASH is expected to become shallower still, reaching depths of up to 400 m under the high emission scenario (RCP 8.5) and 600 m for the middle emission scenario (RCP 4.5) (Zheng & Long, 2014). In addition to the shallowing of the aragonite saturation horizon, the calcite saturation horizon will also become shallower as ocean acidification occurs (Feely et al., 2004). The calcite saturation horizon is more relevant for octocorals, as they require calcium carbonate for structural development and calcite is essential in the skeletal structure (specifically for their sclerites; (Bayer & Macintyre, 2001).

The black coral Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where aragonite saturation levels vary from 0.77-1.40 across the seamount (Henry et al., 2015). These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks were subject to high short-term variability in aragonite down to 1,500 m deep, consistent with an internal tide led oceanographic regime.

In the Red Sea, at depths of 240-700 m, where records of an unidentified species of Caryophyllidae occur, aragonite saturation levels were recorded as 3.44-3.61 (Roder et al., 2013). Despite these high aragonite saturation levels, the study found that calcification rates were particularly low in this species of Caryophyllidae, suggesting that other factors may limit the growth of deep-sea corals, such as low oxygen levels or limited food availability. Another Caryophyllidae species, Desmophyllum dianthus, has been recorded at deep-sea Pacific upwelling locations with aragonite saturation levels of ≤0.6, however these specimens had depleted skeletal P/Ca, which is attributed to this undersaturation effect and linked to pH levels (Anagnostou et al., 2011). The tissue layer of deep-sea corals is also noted to protect the skeleton against dissolution.  However, under stress the coral may retract its polyps to expose the corallite skeleton, putting it at risk from erosion and dissolution (Lazier et al., 1999, cited in Anagnostou et al., 2011). Anagnostou et al. (2012) further suggest that Desmophyllum dianthus can partially compensate for a range of pH and aragonite saturation levels through its physiological modification mechanisms. This adaptation to low pH allows the species to enhance aragonite precipitation. In their study, specimens of Desmophyllum dianthus were from depths of 274-1,470 m in the Atlantic, Pacific and Southern Ocean, where the seawater pH ranged from 7.57-8.05 and aragonite saturation ranged from 0.6 to 2.1.

Sensitivity assessment. The characterizing species Leiopathes spp. naturally occurs within a pH range of 7.95- 8.10 (Davies et al., 2010) and in shallow waters. Yeung et al. (2014) found black corals were at highest abundance at minimum pH of 7.9.  As such, black corals are not likely to be affected by a change in pH at the middle emission scenario pressure benchmark (a further decrease of 0.15 to approx. 7.99) but may be affected at the high emission scenario benchmark (a further decrease of 0.35 to approx. 7.8). The black coral Stichopathes cf. abyssicola has been found at aragonite saturation levels <1. As such, this species may not be affected by shoaling of the ASH under the middle or high emission scenarios.

Evidence suggests that a number of species within the family Caryophylliidae can tolerate decreases in pH (Gori et al., 2016) and some occur naturally in areas with low pH (Fillinger & Richter, 2013) and low aragonite saturations levels (Anagnostou et al., 2011). Physiological adaptions have been observed in Desmophyllum dianthus to compensate for such conditions, and the tissue layer of deep-sea corals can protect against dissolution (Anagnostou et al., 2011). As such, this genus is unlikely to be affected by ocean acidification at the middle or high emission scenarios.

Kenchington et al. (2012) note that Acanthogorgia armata may be at risk from acidification due to its magnesium carbonate skeleton and Carreiro-Silva et al. (in press; detailed in Xavier et al. (2019), found that a deep-sea gorgonian species did show lower resistance to ocean acidification. Yeung et al. (2014) found highest species richness, including the genus Acanthogorgia, in areas with a minimum pH >7.9. As such, the characterizing species Acanthogorgia armata may be affected by ocean acidification at the high emission scenario but may be less affected at the middle emission scenario.

Therefore, resistance for the biotope at the middle emission scenario is assessed as ‘High’, with ‘High’ resilience, with an overall sensitivity of ‘Not sensitive’. However, at the high emission scenario the biotope is assessed as ‘Medium’. Resilience is assessed as ‘Very low’ as the pressure is expected to be long-term so recovery is not possible, therefore overall sensitivity is ‘Medium’.

Sea level rise (extreme)

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

Evidence

Mixed coral assemblages on Lophelia pertusa reef framework are deep-sea biotopes, relevant to the Atlantic mid and upper bathyal zone, at depths of 200 – 1300 m. Therefore, the biotope will not be affected by changes arising from sea-level rise, and the assessment at the pressure benchmark is ‘Not relevant’.

Sea level rise (high)

High emission scenario benchmark: a 70 cm rise in average UK by the end of this century (2018-2100). Further detail.

Evidence

Mixed coral assemblages on Lophelia pertusa reef framework are deep-sea biotopes, relevant to the Atlantic mid and upper bathyal zone, at depths of 200 – 1300 m. Therefore, the biotope will not be affected by changes arising from sea-level rise, and the assessment at the pressure benchmark is ‘Not relevant’.

Sea level rise (middle)

Middle emission scenario benchmark: a 50 cm rise in average UK sea-level rise by the end of this century (2081-2100). Further detail.

Evidence

Mixed coral assemblages on Lophelia pertusa reef framework are deep-sea biotopes, relevant to the Atlantic mid and upper bathyal zone, at depths of 200 – 1300 m. Therefore, the biotope will not be affected by changes arising from sea-level rise, and the assessment at the pressure benchmark is ‘Not relevant’.

Temperature increase (local)

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

Evidence

There is little direct evidence of the resistance of the characterizing species to temperature change. In the absence of this information, the temperature tolerances of the species (based on their current geographical range, environmental preferences and habitat suitability modelling) can be used as a proxy.

Global habitat suitability modelling for black corals, including the family Leiopathidae, Myriopathidae and Antipathidae (relevant for Leiopathes spp., Antipathella spp. and Stichopathes spp., respectively) was undertaken by Yesson et al., (2017). The study found that temperature was the most important variable (with some influence from topography, surface productivity and oxygen level). Seabed temperatures above 3°C were found to be most suitable, although a model response to depth was also noted.

Leiopathes sp. was recorded in a canyon in the southern Bay of Biscay, where temperatures ranged from 10-11°C over a 2.5-hour period (Sánchez et al., 2014). In the Gulf of Mexico, Leiopathes glaberrima occurred alongside Lophelia pertusa at depths of 400-500 m, in areas where temperatures ranged between 8.5 and 10.6°C over five days of measurements (Davies et al., 2010). Within these five days, internal waves caused temperature fluctuations of 0.8°C over 5-11 hours (Davies et al., 2010). Furthermore, a high-frequency temperature variability over even shorter periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred within 20-30 minutes, followed by a slower temperature decline. Habitat suitability modelling for Leiopathes glaberrima in the Gulf of Mexico was undertaken by Etnoyer et al. (2018). The study found that mean annual bottom temperature (together with slope and depth) was the most important environmental predictor variable for model fitting. The predicted likelihood of suitable habitat was greatest at a mean annual bottom temperature range of 6 to 16°C.

For the genus Antipathella, evidence was available for the species Antipathella subpinnata, Antipathella wollastoni and Antipathella fiordensis. Antipathella subpinnata colonies have been found in the Tyrrhenian Sea at water temperatures between 14-16°C (Gaino & Scoccia, 2010). Bo et al. (2008) suggested that temperature is the main environmental factor influencing the bathymetric distribution of Antipathella subpinnata in the Mediterranean, where the species does not occur shallower than 50 m, where temperatures are greater than 15°C. The authors state that this indicates that the species is stenothermal and unable to survive at temperatures over 15°C. CTD (conductivity, temperature and depth) profiles from the Azores within the depth range where Antipathella subpinnata gardens occur, recorded temperatures of 14.5-14.9°C (Tempera, unpublished data, cited in de Matos et al., 2014). Similarly, ROV temperature sensors during the de Matos et al. (2014) study logged 15 and 16°C (±1°C) during the warmest months of the year. The seamounts and island slopes where colonies were collected also experienced pronounced surface cooling (Bashmachnikov et al., 2004 cited in de Matos et al., 2014). This evidence further indicates that Antipathella subpinnata has a temperature tolerance of <15°C.

Antipathella wollastoni occurs in the Azores, where summer temperatures are 18°C (Rakka et al., 2017). This study found that gamete maturation of Antipathella wollastoni was positively correlated to sea surface temperature (SST). However, spawning appeared to happen after a temperature peak in September of 21.09°C. This indicated that high temperatures might be a cue for final gamete maturation, rather than spawning. Antipathella fiordensis occurs off New Zealand, where Parker et al. (1997) recorded temperatures between 11 and 15°C over the course of a year. It is worth noting that these temperatures were 2-3°C lower on average than those recorded in previous years by Grange et al. (1991; cited in (Parker et al., 1997). Spawning also appeared to be linked to temperature, and occurred after the highest temperature peak (in February). The authors also noted that spawning occurred a month later than in the previous year when the temperature was higher. Antipathella fiordensis therefore shows a reliance on temperature for control of oogenesis (Parker et al., 1997), meaning that fluctuating temperatures may interfere with reproduction. However, the inter-annual temperature variations suggest that the benchmark of an increase in temperature of 2°C is unlikely to negatively affect the species.

Acanthogorgia armata has been found off the south of Iceland, where the maximum water temperature is 10.7°C on average (Madsen, 1944; The Icelandic Benthos database, 2007, cited in Buhl-Mortensen et al., 2015). Buhl-Mortensen et al. (2015) also recorded the temperature range of Acanthogorgia armata to be from 1 to 12°C, although most occurrences were within 3-4°C. Specimens of Stichopathes sp. were observed in the Whittard Canyon (at 633-762 m depths), where temperatures were recorded as ca 9°C (Johnson et al., 2013). Stichopathes spp. have also been recorded in the northern Red Sea (depths of 357-437m and 362-594m), where bottom temperatures were 21.6°C (Qurban et al., 2014).  Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where temperatures vary from 3.97-7.62°C across the seamount (Henry et al., 2015).  These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks are subject to high short-term variability in water temperature down to 1,500 m deep, consistent with an internal tide-led oceanographic regime.

The family Caryophylliidae are highly cosmopolitan and found in a wide range of UK habitats. However direct experimental evidence was only available for the deep-sea solitary cup coral species Desmophyllum dianthus. Gori et al. (2016) found that when Desmophyllum dianthus was exposed to an elevated temperature of 15°C, relative to a 12°C ambient benchmark, calcification rates were significantly reduced. When exposed to both this elevated temperature and an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark), respiration rates were significantly reduced. As such, the study concluded that Desmophyllum dianthus is more sensitive to thermal than pCO₂ stress.

Sensitivity assessment. Records of the biotope ‘Mixed coral assemblage on Lophelia reef framework’ from Anton Dohrn Seamount, East Rockall Bank, and Hatton Bank have been recorded in temperatures ranging from 5-9°C (Howell et al., 2007; Long et al., 2010). The characterizing species for the biotope appear to have a wide range of temperature tolerances. Acanthogorgia armata occurs in temperatures ranging from 1 to 12°C (Buhl-Mortensen et al., 2015), whilst Stichopathes spp. have been recorded around the UK in 4-9°C temperatures (Henry et al., 2015; Johnson et al., 2013). In waters outside of the UK, Leiopathes spp. have been recorded in temperatures of 8.5-11°C (Sánchez et al., 2014; Davies et al., 2010). The three species of Antipathella have varying temperature tolerances of 11-15°C, <15°C and 18-21°C (de Matos et al., 2014; Bo et al., 2008; Rakka et al., 2017; Parker et al., 1997).

Overall, if the biotope occurs in an area corresponding to the middle or lower limit of its temperature range then it is probably able to tolerate a long-term increase in temperature of 2°C. As the majority of the characterizing species appear to have wide temperature tolerances, a short-term increase in temperature of 5°C is also unlikely to affect the biotope. Similarly, if the biotope occurs at the upper limit of its temperature range, then it is probably able to tolerate an increase in temperature of 2°C. However, at the upper limit of the biotope’s temperature range, a short-term increase in temperature of 5°C may negatively affect some of the characterizing species and hence the classification of the biotope. In particular, one species within the Caryophylliidae family experienced significant reductions in calcification rates when exposed to a 3°C increase in temperature from 12°C (Gori et al., 2016). Therefore, resistance is assessed as ‘Medium’ as a precaution based on possible long-term effects of increased temperature or exposure to localised thermal effluent. Hence, resilience is assessed as ‘Very Low’ and sensitivity as ‘Medium’. 

Temperature decrease (local)

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

Evidence

There is little direct evidence of the resistance of the characterizing species to temperature change. In the absence of this information, the temperature tolerances of the species (based on their current geographical range, environmental preferences and habitat suitability modelling) can be used as a proxy.

Global habitat suitability modelling for black corals, including the family Leiopathidae, Myriopathidae and Antipathidae (relevant for Leiopathes spp., Antipathella spp. and Stichopathes spp., respectively) was undertaken by Yesson et al., (2017). The study found that temperature was the most important variable (with some influence from topography, surface productivity and oxygen level). Seabed temperatures above 3°C were found to be most suitable, although a model response to depth was also noted.

Leiopathes sp. was recorded in a canyon in the southern Bay of Biscay, where temperatures ranged from 10-11°C over a 2.5-hour period (Sánchez et al., 2014). In the Gulf of Mexico, Leiopathes glaberrima occurred alongside Lophelia pertusa at depths of 400-500 m, in areas where temperatures ranged between 8.5 and 10.6°C over five days of measurements (Davies et al., 2010). Within these five days, internal waves caused temperature fluctuations of 0.8°C over 5-11 hours (Davies et al., 2010). Furthermore, a high-frequency temperature variability over even shorter periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred within 20-30 minutes, followed by a slower temperature decline. Habitat suitability modelling for Leiopathes glaberrima in the Gulf of Mexico was undertaken by Etnoyer et al. (2018). The study found that mean annual bottom temperature (together with slope and depth) was the most important environmental predictor variable for model fitting. The predicted likelihood of suitable habitat was greatest at a mean annual bottom temperature range of 6 to 16°C.

For the genus Antipathella, evidence was available for the species Antipathella subpinnata, Antipathella wollastoni and Antipathella fiordensis. Antipathella subpinnata colonies have been found in the Tyrrhenian Sea at water temperatures between 14-16°C (Gaino & Scoccia, 2010). Bo et al. (2008) suggested that temperature is the main environmental factor influencing the bathymetric distribution of Antipathella subpinnata in the Mediterranean, where the species does not occur shallower than 50 m, where temperatures are greater than 15°C. The authors state that this indicates that the species is stenothermal and unable to survive at temperatures over 15°C. CTD (conductivity, temperature and depth) profiles from the Azores within the depth range where Antipathella subpinnata gardens occur, recorded temperatures of 14.5-14.9°C (Tempera, unpublished data, cited in de Matos et al., 2014). Similarly, ROV temperature sensors during the de Matos et al. (2014) study logged 15 and 16°C (±1°C) during the warmest months of the year. The seamounts and island slopes where colonies were collected also experienced pronounced surface cooling (Bashmachnikov et al., 2004 cited in de Matos et al., 2014). This evidence further indicates that Antipathella subpinnata has a temperature tolerance of <15°C.

Antipathella wollastoni occurs in the Azores, where summer temperatures are 18°C (Rakka et al., 2017). This study found that gamete maturation of Antipathella wollastoni was positively correlated to sea surface temperature (SST). However, spawning appeared to happen after a temperature peak in September of 21.09°C. This indicated that high temperatures might be a cue for final gamete maturation, rather than spawning. Antipathella fiordensis occurs off New Zealand, where Parker et al. (1997) recorded temperatures between 11 and 15°C over the course of a year. It is worth noting that these temperatures were 2-3°C lower on average than those recorded in previous years by Grange et al. (1991; cited in (Parker et al., 1997). Spawning also appeared to be linked to temperature, and occurred after the highest temperature peak (in February). The authors also noted that spawning occurred a month later than in the previous year when the temperature was higher. Antipathella fiordensis therefore shows a reliance on temperature for control of oogenesis (Parker et al., 1997), meaning that fluctuating temperatures may interfere with reproduction. However, the inter-annual temperature variations suggest that the benchmark of an increase in temperature of 2°C is unlikely to negatively affect the species.

Acanthogorgia armata has been found off the south of Iceland, where the maximum water temperature is 10.7°C on average (Madsen, 1944; The Icelandic Benthos database, 2007, cited in Buhl-Mortensen et al., 2015). Buhl-Mortensen et al. (2015) also recorded the temperature range of Acanthogorgia armata to be from 1 to 12°C, although most occurrences were within 3-4°C. Specimens of Stichopathes sp. were observed in the Whittard Canyon (at 633-762 m depths), where temperatures were recorded as ca 9°C (Johnson et al., 2013). Stichopathes spp. have also been recorded in the northern Red Sea (depths of 357-437m and 362-594m), where bottom temperatures were 21.6°C (Qurban et al., 2014).  Stichopathes cf. abyssicola has been recorded on the Hebrides Terrace seamount in the Northeast Atlantic, where temperatures vary from 3.97-7.62°C across the seamount (Henry et al., 2015).  These values were recorded at depths between 1,040-3,157 m, at the summit and flank. The study found that the flanks are subject to high short-term variability in water temperature down to 1,500 m deep, consistent with an internal tide-led oceanographic regime.

The family Caryophylliidae are highly cosmopolitan and found in a wide range of UK habitats. However direct experimental evidence was only available for the deep-sea solitary cup coral species Desmophyllum dianthus. Gori et al. (2016) found that when Desmophyllum dianthus was exposed to an elevated temperature of 15°C, relative to a 12°C ambient benchmark, calcification rates were significantly reduced. When exposed to both this elevated temperature and an elevated pCO₂ of 750 ppm (relative to a 390 ppm ambient benchmark), respiration rates were significantly reduced. As such, the study concluded that Desmophyllum dianthus is more sensitive to thermal than pCO₂ stress.

Sensitivity assessment. Records of the biotope ‘Mixed coral assemblage on Lophelia reef framework’ from Anton Dohrn Seamount, East Rockall Bank, and Hatton Bank have been recorded in temperatures ranging from 5-9°C (Howell et al., 2007; Long et al., 2010). The characterizing species for the biotope appear to have a wide range of temperature tolerances. Acanthogorgia armata occurs in temperatures ranging from 1 to 12°C (Buhl-Mortensen et al., 2015), whilst Stichopathes spp. have been recorded around the UK in 4-9°C temperatures (Henry et al., 2015; Johnson et al., 2013). In waters outside of the UK, Leiopathes spp. have been recorded in temperatures of 8.5-11°C (Sánchez et al., 2014; Davies et al., 2010). The three species of Antipathella have varying temperature tolerances of 11-15°C, <15°C and 18-21°C (de Matos et al., 2014; Bo et al., 2008; Rakka et al., 2017; Parker et al., 1997).

Overall, if the biotope occurs in an area corresponding to the middle or lower limit of its temperature range then it is probably able to tolerate a long-term increase in temperature of 2°C. As the majority of the characterizing species appear to have wide temperature tolerances, a short-term increase in temperature of 5°C is also unlikely to affect the biotope. Similarly, if the biotope occurs at the upper limit of its temperature range, then it is probably able to tolerate an increase in temperature of 2°C. However, at the upper limit of the biotope’s temperature range, a short-term increase in temperature of 5°C may negatively affect some of the characterizing species and hence the classification of the biotope. In particular, one species within the Caryophylliidae family experienced significant reductions in calcification rates when exposed to a 3°C increase in temperature from 12°C (Gori et al., 2016). Therefore, resistance is assessed as ‘Medium’ as a precaution based on possible long-term effects of increased temperature or exposure to localised thermal effluent. Hence, resilience is assessed as ‘Very Low’ and sensitivity as ‘Medium’. 

Salinity increase (local)

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

Evidence

No direct experimental evidence was available on the effects of changes in salinity on the characterizing species. In areas off the south of Iceland, where Acanthogorgia armata occurs, salinities range from 34.87‰ to 35.05‰ at 300-400 m (Buhl-Mortensen et al., 2015). In La Gaviera Canyon (part of the Aviles Canyon System in the Cantabrian Sea), Leiopathes sp., Acanthogorgia armata and Desmophyllum dianthus (Caryophylliidae family) have been found at depths of 700-1,200 m living on both dead and living coral framework (Sánchez et al., 2014). Salinity at the sites varied between 35.6 and 35.8 PSS. Leiopathes glaberrima has also been observed in the Gulf of Mexico at 400-500 m, alongside Lophelia pertusa, in areas where salinity ranged between 35.0 and 35.3 (Davies et al., 2010). These small-scale variations in salinity over 5-11 hour periods (alongside temperature fluctuations) were associated with internal waves.

Other records indicate more extreme tolerances of some of the characterizing species. Stichopathes sp. and Acanthogorgia sp. have been recorded on rocky habitat in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where salinity was ca 40.56, with very little seasonal variation (Qurban et al., 2014). These deep-water corals were therefore found to be able to cope with high salinity. In a study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had a salinity range of 34.5 and 31.9.

Sensitivity assessment. Changes in salinity defined in the benchmark are unlikely due to the highly stable nature of water masses found at mid and upper bathyal depths at which mixed coral assemblages are found, combined with distance from shore and the low potential for brine or freshwater discharge. The natural salinity conditions at which the characterizing species occur exhibit minimal variation in salinity. However,  there is some evidence to suggest that Stichopathes sp. and Acanthogorgia sp. can tolerate more extreme salinities (ca. 40.56 for both species, as well as 31.9 for Acanthogorgia sp.). Overall, most of the characteristic species are likely to be stenohaline and not adapted to hypersaline, variable or reduced salinity regimes. Therefore, resistance is assessed as 'Low' as a precaution in the unlikely event of localised hypersaline (>40) or reduced (<30) salinity effluents from offshore installations, albeit with 'Low' confidence. Hence, resilience is assessed as 'Very low' and sensitivity 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

No direct experimental evidence was available on the effects of changes in salinity on the characterizing species. In areas off the south of Iceland, where Acanthogorgia armata occurs, salinities range from 34.87‰ to 35.05‰ at 300-400 m (Buhl-Mortensen et al., 2015). In La Gaviera Canyon (part of the Aviles Canyon System in the Cantabrian Sea), Leiopathes sp., Acanthogorgia armata and Desmophyllum dianthus (Caryophylliidae family) have been found at depths of 700-1,200 m living on both dead and living coral framework (Sánchez et al., 2014). Salinity at the sites varied between 35.6 and 35.8 PSS. Leiopathes glaberrima has also been observed in the Gulf of Mexico at 400-500 m, alongside Lophelia pertusa, in areas where salinity ranged between 35.0 and 35.3 (Davies et al., 2010). These small-scale variations in salinity over 5-11 hour periods (alongside temperature fluctuations) were associated with internal waves.

Other records indicate more extreme tolerances of some of the characterizing species. Stichopathes sp. and Acanthogorgia sp. have been recorded on rocky habitat in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where salinity was ca 40.56, with very little seasonal variation (Qurban et al., 2014). These deep-water corals were therefore found to be able to cope with high salinity. In a study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had a salinity range of 34.5 and 31.9.

Sensitivity assessment. Changes in salinity defined in the benchmark are unlikely due to the highly stable nature of water masses found at mid and upper bathyal depths at which mixed coral assemblages are found, combined with distance from shore and the low potential for brine or freshwater discharge. The natural salinity conditions at which the characterizing species occur exhibit minimal variation in salinity. However,  there is some evidence to suggest that Stichopathes sp. and Acanthogorgia sp. can tolerate more extreme salinities (ca. 40.56 for both species, as well as 31.9 for Acanthogorgia sp.). Overall, most of the characteristic species are likely to be stenohaline and not adapted to hypersaline, variable or reduced salinity regimes. Therefore, resistance is assessed as 'Low' as a precaution in the unlikely event of localised hypersaline (>40) or reduced (<30) salinity effluents from offshore installations, albeit with 'Low' confidence. Hence, resilience is assessed as 'Very low' and sensitivity as 'High'.

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

Cold-water corals are typically filter or suspension feeders (Chang-Feng & Ming-Chao, 1993; Roberts et al., 2006), and are reliant on water flow for the dispersal of larvae (Lacharité & Metaxas, 2013; Parker et al., 1997; Rakka et al., 2017). Hence, changes in water flow may have a profound impact on the success of these groups. Studies in Lophelia pertusa have shown greatest capture rates at low flow (<0.07 m/s) (Orejas et al., 2016) and while Lophelia pertusa reefs have been shown to survive under extreme flow conditions (0.6 m/s) (Mienis et al., 2014) the majority of cold-water coral sites experience current speeds of less than 0.15 m/s (Orejas et al., 2016). It is also possible that changing the current regime will alter the morphology of both gorgonians (Mortensen & Buhl-Mortensen, 2005) and scleractinians (Chindapol et al., 2013).

There is some evidence that cold-water coral groups may be able to adapt behaviourally to short-term changes in water flow (Oevelen et al., 2016; Orejas et al., 2016) but the evidence surrounding the long-term resistance and resilience of cold-water corals to changing currents is lacking. Given the occurrence of cold-water corals groups in areas with often turbulent and variable natural flow, increases in flow may prove advantageous through increased food availability while a decrease in flow may be deleterious for the opposite reason.  In Italian waters, Leiopathes glaberrima had a preference for areas of stronger currents (Bo et al., 2014b) while other species were less tolerant of strong currents. This may point to a change in habitat suitability in a reduced or increased flow scenario, however, a lack of quantitative data makes assessing this pressure at benchmark levels difficult.

Parrish & Oliver (2020) investigated the flow characteristics of deep-sea coral patches, with coral communities. They found that there were more Acanthogorgia sp. where there was higher than average flow at the given site. Antipathella subpinnata populations in the Mediterranean were found on slopes of rock pinnacles exposed to the prevailing main deep current in the area, at depths of 50-100 m (Bo et al., 2009). This indicated that Antipathella subpinnata was adapted to strong currents, as evidenced by its flexible and resistant chitinous skeleton (Bo et al., 2009). There is further evidence for the presence of black corals within areas of strong currents on North Pacific seamounts, where upwelling currents occur. Such currents are beneficial, as they can supply resuspended organic matter from the seabed to suspension feeding corals, such as Antipathella spp. (Kaufmann et al., 1989 cited in Bo et al., 2009; Genin et al., 1986). Antipathella fiordensis is found in southern fiords of New Zealand at depths of 5-35 m (Grange 1985, 1988, 1990, Grange & Singleton 1988, cited in Bo et al., 2009) has a similar ecology to Antipathella subpinnata and also appears to have a preference for areas with fast currents. The presence of the species on steeper slopes, however, indicates an avoidance of detritus falling down the fjord (Grange 1985, 1988, 1990, Grange & Singleton 1988, cited in Bo et al., 2009). Off California, Stichopathes sp. occupies rocky substrata at depths of 550-1,150 m and it is found in much higher densities in areas exposed to strong currents (Genin et al., 1986). Therefore, the heightened position off the seafloor given by the dead Lophelia framework is beneficial for the species.

Leiopathes glaberrima was observed in the Gulf of Mexico, alongside Lophelia pertusa, in areas where temperatures were 8.5-10.6°C, salinity 35.0–35.3, difference in water density (σΘ, 27.1–27.2 kg/m³), O₂ was 2.6–2.8 ml/l and turbidity revealed at 150, 240 and 450 m from the 5-hour yo-yo CTD (Davies et al., 2010). Temperature variations of 0.8°C were observed over 5-11 hour periods, associated with internal waves. Furthermore, high-frequency temperature variability over 20-30-minute periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred, followed by a slower temperature decline. These fluctuations exhibit 5-11-hour cycles. The ROV dives were concentrated in the areas with the densest coral cover and had a consistent pH throughout all the dives, with values between 7.95 and 7.97. The other ROV dives over areas of coral had pH of  8.04 to 8.10 and 7.92 to 8.01 (Davies et al., 2010).

Gilkinson & Edinger (2009) noted that Acanthogorgia armata occurred in areas of low-current strength but did not define that current strength. Mortensen & Buhl-Mortensen (2004) reported that Acanthogorgia armata in the Northeast Channel (Atlantic Canada), an area characterized by strong semidiurnal currents with a maximum speed of 0.4 to 0.5 m/s at 16 m above the bottom. Their study concluded that the abundance of corals was determined by large-scale surface topography (e.g. cobbles) that in turn affected localised surface currents. Deidun et al. (2015) found that a dense forest of Leiopathes glaberrima occurred off Malta within areas with high turbulence and strong currents but did not define the current speed. 

Ruiz-Ramos et al. (2015) suggest that the recruitment of the different lineages of Leiopathes glaberrima in the Gulf of Mexico (248-674 m depths), might be influenced by local patterns of topography and current velocity. This was based upon an observed segregation pattern, where a barrier for gene flow was evident between sites 36.4 km apart. One of the lineages appeared capable of long-distance dispersal and indicated an out-bred species, whereas the other indicated more localised recruitment (self-fertilisation with relative isolation, limited habitat, and individuals being highly inbred. 

Stichopathes sp. and Acanthogorgia sp. were recorded on rocky habitat in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where bottom temperatures were 21.6°C, salinity (40.56), dissolved oxygen (1.75 ml/l ) and velocities ranging from 0.6 to 34.5 cm/s (mean 9.5 cm/s ) (Qurban et al., 2014). 

Sensitivity assessment. Antipatharian corals are generally upright and erect corals that are dependent on water flow to suspension feed. Each species probably varies in its preference for current strength, and their growth form and morphology vary with current flow, which in turn can be affected by local topography and their position relative to the seabed (Mortensen & Buhl-Mortensen, 2004, 2005). Therefore, changes in water flow may affect feeding, growth form, and growth rates in these species. The above evidence provides flow rates typically between 0.4-0.5 m/s in some areas or a mean of 0.95 m/s in others, while the majority of cold-water coral sites experience current speeds of less than 0.15 m/s. Therefore, changes in water flow of 0.1 to 0.2 m/s for more than a year (the benchmark) may affect feeding, growth form, and growth rates in these species but would probably need to be prolonged to result in mortality in these long-lived species. However, each characteristic species may respond differently. Hence, resistance has been assessed as 'Medium' as a precaution to represent reduced growth and possible reduction in the abundance of a few members of the coral community, and the biotope may only be slightly impoverished as a result. Resilience is assessed as 'Very low' due to their slow growth rates and sensitivity is assessed as 'Medium' but with 'Low' confidence. 

Emergence regime changes

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

Evidence

The M.AtMB.Bi.CorRee.LopFra biotope is found at mid bathyal depths and as such will not be affected by changes in the emergence regime.

Wave exposure changes (local)

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

Evidence

The M.AtMB.Bi.CorRee.LopFra biotope is found at mid bathyal depths and as such will not be affected by changes in nearshore wave exposure.

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

There is limited evidence surrounding the effect of transition elements and organometals on the characterizing black corals and octocorals. There is some limited evidence of other contaminants in coral tissues, where trace elements have been found sequestered in Antipatharian and Gorgonian tissue (Raimundo et al., 2013). The results of this study point to natural enrichment from hydrothermal sources and do not refer to the health of the sampled organisms. More recently, the uptake of organo-iodine has been documented in Leiopathes sp. (Prouty et al., 2018) but the science is at an elementary stage. In shallow waters in Oman, there is some evidence of TBT and heavy metal contamination in Antipatharian tissue. However, this study targeted geochemical monitoring and thus did not assess the effect of TBT/heavy metal contamination on Antipatharians (Jupp et al., 2017). The longevity and slow growth rate of cold-water coral communities may make them susceptible to contamination but the evidence of sequestration in hard tissues may point to greater resistance than other soft-bodied organisms.

The results of a Rapid Evidence Assessment on the effects of 'Transitional metals and organometal' contaminants on Anthozoa (Watson & Tyler-Walters, 2023) are also summarized below. The full 'Anthozoa evidence review' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Transitional metals and organometal' contaminant examined, together with an overall pressure assessment. 

Transitional metals. The Actinaria were reported to experience ‘Severe’ or ‘Significant’ mortality due to transitional metal exposure but to be of ’Medium’ sensitivity due to their reasonable recovery rates. Nematostella vectensis is an exception due to its inability to disperse over long distances or between sites without human intervention (see above). Therefore, while resistance is assessed as ‘Low’, resilience is probably ‘Medium’ and sensitivity is assessed as ‘Medium’, albeit with ‘Low’ confidence.

The Scleractinia (true corals) also show a varied response to transitional metal exposure. However, resistance is probably ‘Low’ or ‘Very low’ based on the ‘worst-case’ mortality reported, the metals, and their dose. Hence, resilience is assessed as ‘Very low’ and sensitivity as ‘High’ albeit with ‘Low’ confidence due to the variation in response. The Octocorallia and Zoantharia were each represented by a single study, in which only sublethal effects were observed so, no sensitivity assessment for these groups was suggested.

Reichelt-Brushett & Michalek-Wagner (2005) reported fertilization success in the Octocoral Lobophytum compactum was more resistant to copper exposure than other species studies but also reported a significant decrease in fertilization success.  Overall, the effects of transitional metal exposure were varied but metals have the potential to cause ‘Severe’ or ‘Significant’ mortalities in Anthozoa as a group. Therefore, the worst-case resistance of Anthozoa and, hence, black corals and octocorals to transitional metal exposure is assessed as ‘Low’, resilience as ‘Low’ and sensitivity as ‘High’ but with ‘Low’ confidence due to the lack of direct evidence and the variation in response. 

Nanoparticulate metals. The effects of nanoparticulate copper oxide exposure on Aiptasia spp. were examined by Henderson & Salazar (1996) and Siddiqui et al. (2015). Only sublethal effects were reported. The evidence is probably too limited to assess the sensitivity of other groups of Anthozoa.

Organometals. The Anthozoa (Actinaria and Scleractinia) were reported to experience ‘Severe’ or ‘Significant’ mortality from organometals (organozinc, organotin, and organocopper) exposure in 87% of the results reviewed (Watson & Tyler-Walters, 2023). Therefore, the resistance of Anthozoa as a group to organometal exposure is assessed as ‘None.’ The resilience of Actinaria is probably ‘Medium’, so sensitivity is assessed as ‘Medium. However, the resilience of Scleractinia is probably ‘very low’ so sensitivity is assessed as ‘High.’  No direct evidence of the effects of organometals on black corals or octocorals was found. Resistance is assessed as ‘Low’, based on the assumption that Anthozoa share similar hormonal and biochemical pathways. Hence, resilience is assessed as ‘Low’ and sensitivity as ‘High’ but with ‘Low’ confidence due to the lack of direct evidence.

Overall sensitivity assessment. No direct evidence of the effects of 'transitional metals and organometals' on black corals or octocorals was found.  However, the evidence from Anthozoa as a group suggests that the worst-case resistance of black corals or octocoral species, and hence the biotope, to transitional metals and organometals, is ‘Low’, based on the assumption that Anthozoa share similar hormonal and biochemical pathways. Hence, resilience is assessed as ‘Low’ and sensitivity as ‘High’ but with ‘Low’ confidence due to the lack of direct evidence. The evidence of the effects of nanoparticulate metals was too limited to inform a sensitivity assessment. 

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

In the wake of the Deepwater Horizon oil spill, there is a wealth of evidence surrounding hydrocarbon contamination on cold-water corals from the Gulf of Mexico (Boehm & Carragher, 2012; Cordes et al., 2016a; Fisher et al., 2014; Goodbody-Gringley et al., 2013; Hsing et al., 2013; Ruiz-Ramos et al., 2017; Silva et al., 2016; White et al., 2012). Potential effects of hydrocarbon contamination observed in the Gulf of Mexico on a range of coral taxa (Porites, Madrepora, Lophelia, Paramuricea, Callogorgia and Leiopathes) include tissue loss, sclerite enlargement, excess mucous production and a covering of hydrocarbon-based flocculate as well as potential impacts on the larval stages of cold-water corals, which has significant implication for the resilience of the biotope to hydrocarbon contamination. In addition, there is concern over the longevity of pollution effects combined with the longevity and slow growth rate of cold-water coral communities. 

The results of a Rapid Evidence Assessment on the effects of 'Hydrocarbons and PAH' contaminants on Anthozoa (Watson & Tyler-Walters, 2023) are summarized below. The full 'Anthozoa evidence review' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Hydrocarbon and PAH' contaminant examined, together with an overall pressure assessment. 

Oil spills. The effects of an oil spill on Anthozoa were only reported in two papers. It was unclear if the effects of the Torrey Canyon spill on Anthozoa (Smith, 1968) were due to the oil and dispersant or oil alone. Etnoyer et al. (2016) examined the health and condition of species of large gorgonian octocorals before and after a Deepwater Horizon (DWH) oil spill. Although the octocoral reefs occurred at depth below the resultant oil slick, they suggested that the octocorals could come into contact with contaminants in the form of particulates or contaminated phytoplankton in the water column. Etnoyer et al. (2016) reported a significant increase in injury to several species of octocoral after the spill (38-50% of large gorgonians) but no direct mortality at the end of their study in 2014, four years after the spill. They suggested that the chance of recovery from injury was unlikely, which implies that mortality may have occurred in the longer term. Therefore, although their paper reported only sublethal effects (resistance is ‘High’) it may be prudent to assess the resistance of Octocorals to oil spills as at least ‘Medium’ resistance, albeit with ‘Low’ confidence. Hence, resilience is assessed as ‘Low' and sensitivity as ‘Medium’.

Petroleum hydrocarbons – oils and dispersed oils.  Frometa et al. (2017) reported ‘no’ mortality in Swiftia exserta exposed to DWH WAF but ‘Severe’ mortality after exposure to dispersant and oil mixtures (CEWAF). They concluded that combinations of dispersants and oils were more toxic to octocorals than oils alone. Smith (1968) reported that Actinia equina and Urticina (as Tealia) felina were the most common and the most resistant animals on the shore after the oil spill and clean up, while some specimens of Cereus pedunculatus, Sagartia elegans and Anemonia sulcata were found dead and few survived. However, in the true coral examples mortality ranged from ‘Severe’ to ‘None’ depending on the study.

Overall, in most of the studies reviewed, the resistance of true corals (Scleractinia) and Octocorals to petroleum hydrocarbons, oils, and dispersed oils would be assessed as ‘Low’ or ‘None’ and, due to their ‘Low’ resilience, sensitivity would be assessed as ‘High’ but with ‘Low’ confidence due to the limited number of studies examined. 

Dispersants. All but one of the species examined in the articles reviewed (Acropora millepora) were reported to experience either ‘Severe’ or ‘Significant’ mortality due to exposure to dispersants. Therefore, the resistance of Anthozoa, as a group, to dispersants is assessed as ‘None’ or ‘Low’ depending on the species. Hence, resilience is assessed as ‘Low’ or ‘Very low’ in the Octocorals and true corals but ‘Medium’ in the Actinaria. Therefore, sensitivity to dispersants is assessed as ‘High’ in Octocorals and true corals but ‘Medium’ in the Actinaria, but with ‘Low’ confidence due to the limited number of studies examined. 

Others. One study (Mercurio et al., 2004) examined the effects of vegetable oils on Acropora microphthalma and one other (Farina et al., 2008) examined the effect of the PAH B[a]P on Porites astreoides. ‘Severe’ or ‘Significant’ mortality was reported, respectively. Therefore, the resistance of true corals to vegetable oil or PAH exposure may be ‘Low’ or ‘None’ and sensitivity may be ‘High’. This assessment may represent the sensitivity of other Anthozoa, including sea pens, but with only ‘Low’ confidence due to the limited number of studies found.

Overall sensitivity assessment.  Etnoyer et al. (2016) reported that octocorals could be contaminated by oil spills even at depth, in the form of particulates or contaminated phytoplankton in the water column. In addition, the evidence from studies of the aftermath of the DWH spill on many coral taxa, together with experimental studies, suggested that Anthozoa and octocorals (and by inference black corals) were sensitive to petroleum hydrocarbons, oils, dispersed oils and dispersants.  Therefore, the worst-case resistance of black corals and octocorals and their associated biotope to 'Hydrocarbons and PAHs' is assessed as 'Low' but with 'Low' confidence due to the lack of direct evidence. Hence, resilience is assessed as ‘Very low’ and sensitivity as ‘High. 

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

The results of the Rapid Evidence Assessment on the effects of 'Synthetic compound' contaminants on Anthozoa (Watson & Tyler-Walters, 2023) are summarized below. The full 'Anthozoa evidence review' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Synthetic compound' contaminant examined, together with an overall pressure assessment. 

Pesticides/biocides. ‘Pesticides/biocides’ exposure was reported to result in mortality (‘Severe’, ‘Significant’ or ‘Some’ mortality) in only 23% of the worst-case results collated on species of Anthozoa. The majority (77%) of studies reported ‘no’ mortality or sublethal effects. In the case of Actinaria, Aiptasia spp. was reported to experience significant mortality after exposure to 19 mg/l Diuron (Bao et al., 2011) but only sublethal effects to paraformaldehyde or the bactericide Suflo-B33 (Tagatz et al., 1979), while Anthopleura spp. was reported to experience only sublethal effects after exposure to Chlordane (Pridmore et al., 1992). Similarly, the Scleractinia were reported to experience only sublethal effects from pesticide/biocide exposure, except in a few species/pesticide combinations.

Overall, the evidence suggests that pesticides/biocides may be toxic to some species of Anthozoa depending on the dose and life stage and that sensitivity should be assessed on a species-specific and chemical-specific basis. Therefore, the ‘worst-case’ resistance of Actinaria as a group to pesticide/biocide exposure is potentially ‘Low’ so resilience is probably ‘Medium’, and sensitivity is assessed as ‘Medium. However, the ‘worst-case’ resistance of Scleractinia as a group to pesticide/biocide exposure is potentially ‘None’, and as the resilience of Scleractinia is probably ‘Very low’, sensitivity is assessed as ‘High’. But the confidence in the assessment is ‘Very low’.  

No direct evidence of the effects of pesticides/biocides on black corals or octocorals. In addition, the reported effects of pesticides on the Anthozoa are species and chemical-specific. It is precautionary to assume that black corals or octocorals may be affected adversely by some pesticides, in the same way as some Anthozoa. Therefore, the resistance to pesticides/biocides is assessed as ‘Low’ as a precaution, so resilience is assessed as ‘Low’ and sensitivity as ‘High’ but with ‘Low’ confidence. Further study is required.

Personal Care Products (PCPs). The effects of UV filters (benzophenone-3 and benzophenone-2) on the planulae of true corals were examined by Downs et al. (2014, 2016). They reported significant mortality of planulae in all the species studied. Loss of planulae and hence recruitment may not be detrimental in the short term because true corals are long-lived. However, if unchecked it may result in population decline in the long term depending on the species. Therefore, resistance is assessed as ‘Low’, resilience as ‘Very low’ and sensitivity as ‘High’.

No direct evidence of the effects of personal care products on black corals or octocorals was found. It is precautionary to assume that they may be affected adversely by some personal care products. Therefore, the resistance to personal care products is assessed as ‘Low’ as a precaution, so resilience is assessed as ‘Low’ and sensitivity as ‘High’ but with ‘Low’ confidence. Further study is required.

Others. The effects of ‘Pharmaceuticals’, ‘Phthalates’, ‘PFAS/PFAS’ and other synthetics were examined by a limited number of studies in only four species. The evidence was not adequate to make an overall assessment of sensitivity or to inform an assessment of the effects on sea pen species. 

Overall sensitivity assessment. The evidence for Anthozoa varies between species and the chemical contaminant studied. No direct evidence of the effects of 'Synthetic compounds' on black corals or octocorals was found.  It is precautionary to assume that they may be affected adversely by some pesticides, or PCPs in the same way as some Anthozoa. Therefore, the resistance to 'Synthetic compounds' is assessed as ‘Low’ as a precaution, so resilience is assessed as ‘Very low’ and sensitivity as ‘High’ but with ‘Low’ confidence. 

Radionuclide contamination

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

Evidence

No evidence could be found regarding the effect of radionuclide contamination on the M.AtMB.Bi.CorRee.LopFra biotope.

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

The results of the Rapid Evidence Assessment on the effects of 'Other substance' contaminants on Anthozoa (Watson & Tyler-Walters, 2023) are summarized below. The full 'Anthozoa evidence review' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Other substance' contaminant examined, together with an overall pressure assessment. 

Exposure to cyanide was reported to result in ‘Severe’ mortality in both of the true corals examined. Therefore, it is assumed that cyanide is probably toxic to all Anthozoa, depending on concentration. Hence, resistance is assessed as ‘None’. Sensitivity assessment is dependent on resilience. Therefore, sensitivity is assessed as ‘High’ in Octocorallia and Scleractinia. The effects of wastewater or production formation water ‘effluent’ exposure (Negri & Heyward, 2000; Howe et al., 2015) are shown in the ‘Anthozoa evidence summary’. However, in both cases, the active ingredients of the effluents were not specified. Hence, no assessment was attempted.

Carrerio-Silva et al. (2022) examined the effects of elevated suspended polymetallic sulphide (PMS) particles and suspended quartz particles on the cold water octocoral Dentomuricea meteor. These particulates may be generated during deep-sea mining activities for PMS. They reported ‘Severe’ mortality of the octocoral after exposure to PMS, together with an increase in the concentration of metals associated with the particulates in the water column and the tissue of the octocoral. Therefore, the resistance of Octocorallia to suspended polymetallic sulphide (PMS) particles is assessed as ‘None’, resilience as ‘Very low’ and sensitivity as ‘High’. Further study is required.

Overall sensitivity assessment. The effects of 'Other substances' as a pressure will vary depending on the chemical contaminant and the species studied. The evidence above suggests that black corals and octocorals are likely to be sensitive to cyanide, depending on the concentration and duration of exposure. The evidence from the study of an Octocoral also suggests that black corals are also likely to be sensitive to exposure to suspended polymetallic sulphide (PMS) particles due to both physical damage and the chemical toxicity of associated metals. Therefore, the worst-case resistance of black corals and octocorals to 'other substances' is assessed as 'Low'. Hence, resilience is assessed as 'Very low' and sensitivity as 'High'.  The confidence in the assessment is 'Low' due to the limited number of studies reviewed and the lack of direct evidence on the effects of the contaminants on black corals. 

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

Deoxygenation is known to cause mortality in a range of benthic organisms, especially sessile taxa that cannot escape unfavourable conditions. Whilst there is no direct experimental evidence on deoxygenation on the characterizing species, it has been suggested that low O₂ levels could be a limiting factor on the distribution of Lophelia pertusa reefs (Dodds et al., 2007). In addition, direct experimentation on Lophelia pertusa found that oxygen concentrations below 1.5 ml/l (2.1 mg/l) led to 100% mortality while concentrations of 5 and 3 ml l^-1 (7.14 and 4.2 mg/l) resulted in 100% survivorship in seven-day treatments (Lunden et al., 2014). This would suggest resistance to a critical point where the coral cannot survive. Assessing this against benchmark pressure suggests that a deoxygenation event of 2 mg/l for one week may create significant stress but is unlikely to cause 100% mortality in Lophelia pertusa.  

The dissolved oxygen (DO) concentrations at Viosca Knoll, in the Gulf of Mexico, where Leiopathes sp. were collected (depths 310-317 m) were measured as 27 to 28 ml/l (38  to 40 mg/l) (Prouty et al., 2011). This is relatively low. Hong Kong has a large annual temperature variation, from 30°C in summer to 13°C in winter (Ang et al., 2005 cited in (Yeung et al., 2014)) and relatively high turbidity (Yeung et al., 2014). In a study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had temperature ranges of 16.0-27.2°C and 16.6-26.6°C (mean pH >8.1 and minimum pH >7.9). This area was exposed to waves and currents. It was characterized by low levels of suspended solids (max. <16.2 mg/l, mean <6.1 mg/l, min. <1.4 mg/l), low levels of nutrients and microbiologically related variables and high levels of salinity (max. >34.5 and min. >31.9). However, at the study's top five sites, a high diversity of corals was found in deep water regions with higher amounts of relatively fine sediments. Octocoral and black coral community compositions were marginally correlated with the overall environmental dataset. The areas where octocorals and black corals were rarely found had low wave exposure (protected environments) and were characterized by high pH (maximum pH >8.4, mean pH >8.2), in addition to high DO (mean >87.3%), high phaeo-pigments (minimum >0.2 ug/l), low nitrate nitrogen (max. <0.059 mg/l, mean <0.013 mg/l, min. <0.001 mg/l), high total Kjeldahl nitrogen (max. >0.40 mg/l, mean >0.26 mg/l, minimum >0.17 mg/l).

Leiopathes glaberrima was observed in the Gulf of Mexico, alongside Lophelia pertusa, in areas where temperatures were 8.5-10.6°C, salinity 35.0–35.3, seawater density σ_Θ, 27.1–27.2 kg m^-3, O₂ was 2.6 to 2.8 ml/l (3.7 to 4 mg/l) and turbidity revealed at 150, 240 and 450 m from the 5-hour yo-yo CTD (Davies et al., 2010). Temperature variations of 0.8°C were observed over 5 to 11-hour periods, associated with internal waves. Furthermore, high-frequency temperature variability over 20-30-minute periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred, followed by a slower temperature decline. These fluctuations exhibit 5 to 11-hour cycles. The ROV dives which were concentrated in the areas with the densest coral cover had a consistent pH throughout all the dives, with values between 7.95 and 7.97. The other ROV dives over areas of coral had pH of 8.04 to 8.10 and 7.92 to 8.01.

Stichopathes sp. and Acanthogorgia sp. were recorded on rocky habitat in the northern Red Sea (depths of 357-437 m and 362-594 m, respectively), where bottom temperatures were 21.6°C, salinity (40.56), dissolved oxygen (1.75 ml/l, 2.5 mg/l) and velocities ranging from 0.6 to 34.5 cm/s (mean 9.5 cm/s) (Qurban et al., 2014). 

Sensitivity assessment. The evidence above suggests that Lophelia is probably sensitive to a reduction in DO below 2 mg/l. However, in this biotope (M.AtMB.Bi.CorRee.LopFra) the Lophelia framework is provided by mostly dead Lophelia so it is unlikely to affect the underlying coral framework. In Hong Kong water, the black corals and octocorals were rarely found in areas of high DO, which suggests other environmental factors were responsible for their rarity. In the Gulf of Mexico, Leiopathes glaberrima was reported from areas where DO was 3.7 to 4 mg/l.  Stichopathes sp. and Acanthogorgia sp. were recorded in the northern Red Sea where dissolved oxygen was ca 2.5 mg/l. The evidence review by Vaquer-Sunyer & Duarte (2008) suggested that Cnidaira (as a group) had the lowest sublethal LC50's (ca 0.69 mg/l DO) of all the groups examined (based on only) 19 studies and one of the highest LT50 (based on eight studies). Overall, resistance to hypoxia is probably variable between species. It might be expected that organisms adapted to high mass transport of water and good water flow may be sensitive to reduced oxygen concentrations but the evidence of the defect of hypoxia on cold-water coral communities is lacking.  Therefore, there is 'Insufficient evidence' on which to base an assessment against the benchmark. 

Nutrient enrichment

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

Evidence

Evidence on the effects of nutrient enrichment on the characterizing species is limited.  While effluent signatures have been observed in stable isotopic ratios both in the Gulf of Mexico (Williams et al., 2007) and the Arabian Peninsula (Risk et al., 2009) these studies did not address the impacts of nutrient enrichment at benchmark pressure for the characterizing species. In deep-water gorgonians, variation in the structure of the skeleton may be related to food availability (Sherwood, 2002; cited in Williams et al., 2006). Under nutrient-rich conditions, the animal forms a protein-rich organic skeleton, whereas calcite forms under nutrient-poor conditions (Sherwood, 2002; cited in Williams et al., 2006).  There is 'Insufficient evidence' on which to base an assessment against the benchmark. 

Organic enrichment

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

Evidence

Evidence on the effects of carbon deposition on the characterizing species is limited. While organic content is known to be an important food source to cold-water coral communities in the Viosca knoll, Gulf of Mexico (Mienis et al., 2012), changes at the benchmark pressure have not been investigated. Leiopathes glaberrima relies upon particulate organic carbon for its skeleton (Roark et al., 2006; Prouty et al., 2011).  While there is some evidence surrounding depositional events as a trigger for spawning in Phelliactis spp., overall, there is Insufficient evidence to make an assessment.  

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 available habitat (resilience is ‘Very low’). The squat lobster assemblage biotopes are therefore considered to have ‘High’ sensitivity to 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

A change from sediment to hard rock substratum is likely to impact the characterizing species and the physical habitat. As dead coral debris defines the biotopes, a change in substratum type will result in a change in the biotope classification and therefore the loss of the original biotope. De Matos et al. (2014) reported that Antipathella subpinnata was able to colonize other invertebrates (e.g. bivalves, hydrocorals and sponges) and another colony had incorporated two stones (~2 cm diameter) into its stem, which suggested that the coral ‘covered’ loose rocks that it was touching. This may indicate that the species could create a new fixation point on the substratum if the original is destroyed (de Matos et al., 2014). Nevertheless, resistance is assessed as 'None'. As this pressure is considered a permanent change, resilience is assessed as 'Very Low', and sensitivity is, therefore, assessed as 'High'.

Physical change (to another sediment type)

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

Evidence

This biotope is defined by the presence of an extensive, mostly dead, framework of Lophelia pertusa debris on hard substrata. However, as this species requires a hard substratum onto which to anchor, a change in soft sediment type is 'Not relevant' to this biotope. Hence, the pressure is assessed as ‘Not relevant’. 

Habitat structure changes - removal of substratum (extraction)

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

Evidence

This biotope is defined by the presence of an extensive, mostly dead, framework of Lophelia pertusa debris on hard substrata, which is unlikely to be 'extracted', However, where the framework has collapsed or grown over sediment, it may be subject to this pressure. Hence, the extraction of the sediment (to 30 cm) may further fragment and/or remove the Lophelia framework and any associated corals in the affected area resulting in the loss of the biotope. Therefore, resistance is assessed as 'None', resilience as 'Very low' and sensitivity as 'High'. 

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

The effects of abrasion/disturbance on cold-water coral communities are well documented (Bo et al., 2014a; Cau et al., 2017; Collie et al., 1997; Freiwald et al., 2004; Murillo et al., 2016; Roberts, 2002; Watling & Auster, 2005). Studies from areas where fishing using trawl gear is commonplace, such as Irish, Scottish and Norwegian waters have found that the use of trawl gear can cause widespread damage to cold-water coral communities, especially in deep-sea areas which are environmentally stable and the gear used is often much heavier (Clark et al., 2016). In addition, research into the effects of other fishing methods, such as longlining (Mytilineou et al., 2014; Orejas et al., 2009; Sampaio et al., 2012) and gill netting (Clark et al., 2016; Fosså et al., 2002) have also found negative impacts, although it is hypothesised that the use of these other methods is far less spatially damaging to the biotope (Pham et al., 2014). Other forms of abrasion or disturbance, such as prop wash, anchoring, grounding of vessels, placement of structures or other miscellaneous forms are not likely to affect this biotope due to the depth at which it is found. For example, Deidun et al. (2015) reported the entanglement of Leiopathes glaberrima specimens by discarded long lines and large ropes in the black coral forests off Malta. Although individual specimens did not exhibit significant degradation due to entanglement, the authors noted numerous dead and removed specimens in their study, probably due to entanglement.  

In addition, the longevity (Prouty et al., 2015; Roark et al., 2009) and slow growth rate (Larcom et al., 2014; Mortensen and Buhl-Mortensen, 2005; Prouty et al., 2015) of the species associated with this biotope, as well as the slow growth of the underlying Lophelia pertusa framework mean that this biotope shows very low resilience to abrasion/disturbance (Althaus et al., 2009; Clark et al., 2016; Freiwald et al., 2004; Massi et al., 2018). As of 2018, research into the effectiveness of protection for cold-water coral communities is at an elementary stage (Bennecke & Metaxas, 2017).

Sensitivity assessment. The evidence above suggests that resistance is 'Low', so resilience is assessed as 'Very low' and sensitivity as '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 above (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 the cold-water coral community 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

Bo et al. (2008) suggest that any resuspension of sediment that increases water turbidity may damage Antipathella assemblages. There is a lack of evidence on the effects of suspended solids on the characteristic species. Limited laboratory experimentation on Lophelia pertusa has shown that turbidity rated a ‘medium’ on the WFD ranking system caused 30-50% mortality and an increase in sediment load to ‘very turbid’ caused 100% mortality (Brooke et al., 2009). Nevertheless, suspended solids are an important cold-water coral food supply, as shown by isotopic evidence (Roark et al., 2006, 2009, Sherwood et al., 2008, cited in Carreiro-Silva et al., 2013).

The waters of Hong Kong have a large annual temperature variation, from 30°C in summer to 13°C in winter (Ang et al., 2005; cited in Yeung et al., 2014)) and relatively high turbidity (Yeung et al., 2014). In a study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had temperature ranges of 16.0 to 27.2°C and 16.6 to 26.6°C (mean pH >8.1 and minimum pH >7.9). This area was exposed to waves and currents. It was characterized by low levels of suspended solids (max. <16.2 mg/l, mean <6.1 mg/l, min. <1.4 mg/l), low levels of nutrients and microbiologically related variables and high levels of salinity (max. >34.5 and min. >31.9). However, at the study's top five sites, a high diversity of corals was found in deep water regions with higher amounts of relatively fine sediments. Octocoral and black coral community compositions were marginally correlated with the overall environmental dataset. The areas where octocorals and black corals were rarely found had low wave exposure (protected environments) and were characterized by high pH (maximum pH >8.4, mean pH >8.2), in addition to high DO (mean >87.3 mg/l), high phaeo-pigments (minimum >0.2 ug/l), low nitrate nitrogen (max. <0.059 mg/l, mean <0.013 mg/l, min. <0.001 mg/l), and high total Kjeldahl nitrogen (max. >0.40 mg/l, mean >0.26 mg/l, minimum >0.17 mg/l) (Yeung et al., 2014).

Sensitivity assessment. The turbidity range given for Hong Kong waters sits in the 'Clear' and 'Intermediate' ranks under the WFD (Water Framework Directive). A decrease in turbidity may decrease the food supply to the corals but is unlikely to cause mortality within a year (see benchmark). An increase to 'Medium' or 'High' turbidity may be detrimental, especially if it blocks or smothers the feeding apparatus of the corals. Therefore, resistance is assessed as 'Medium' to represent the loss of small individuals or particularly sensitive members of the community, given the longevity of corals, which will probably survive a short-term (one year; see benchmark) increase in turbidity. However, prolonged changes in turbidity may be more severe. Resilience is assessed as 'Very low' and sensitivity as 'Medium' but with 'Low' confidence due to the lack of direct evidence on the background levels of suspended solids experienced by the biotope and the effect of changing sediment load on the characteristic species.

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

Information on the effect of sediment deposition on the charactersitic species is limited. However, experimental and monitoring studies based on the exposure of Lophelia pertusa to drill cuttings from oil drilling activities on the Norwegian continental shelf indicate that coral polyps can tolerate the enhanced particle deposition rates and suspended matter concentrations up to a point, thereafter the polyps are unable to clear sediment and become anoxic (Allers et al., 2013; Larsson et al., 2013; Purser, 2015 in Fernandez-Arcaya et al., 2017). Direct laboratory experimentation on the deposition of 6.5 mm of drill cuttings onto Lophelai pertusa polyps found significant mortality of individual polyps (Cordes et al., 2016b; Larsson & Purser, 2011). In addition, a small pilot experiment indicated that coral larvae might be particularly vulnerable to high particle concentrations (Larsson et al., 2013 cited in Fernandez-Arcaya et al., 2017; Järnegren et al., 2017).

Antipathella subpinnata occurs in hard substrata. However (Bo et al., 2008) found records of the species growing on rocks covered by fine muddy sediments (e.g. off Stromboli island, in the Mediterranean). Antipathella fiordensis is found on steeper slopes in New Zealand fjords, compared to Anitpathella subpinnata in the Mediterranean, despite having a similar ecology (Grange 1985, 1988, 1990, Grange & Singleton 1988). It was suggested that its distribution was to avoid detritus falling down the fiord. Limited evidence from British Colombia reported that Caryophyllia spp. were “remarkably tolerant of high turbidity” (Farrow et al., 1983).

The waters of Hong Kong have a large annual temperature variation, from 30°C in summer to 13°C in winter (Ang et al., 2005; cited in Yeung et al., 2014)) and relatively high turbidity (Yeung et al., 2014). In a study by Yeung et al. (2014), the areas with the highest species richness (primarily azooxanthellate octocorals, including the genus Acanthogorgia, and black corals) had temperature ranges of 16.0 to 27.2°C and 16.6 to 26.6°C (mean pH >8.1 and minimum pH >7.9). This area was exposed to waves and currents. It was characterized by low levels of suspended solids (max. <16.2 mg/l, mean <6.1 mg/l, min. <1.4 mg/l), low levels of nutrients and microbiologically related variables and high levels of salinity (max. >34.5 and min. >31.9). However, at the study's top five sites, a high diversity of corals was found in deep water regions with higher amounts of relatively fine sediments. Octocoral and black coral community compositions were marginally correlated with the overall environmental dataset. The areas where octocorals and black corals were rarely found had low wave exposure (protected environments) and were characterized by high pH (maximum pH >8.4, mean pH >8.2), in addition to high DO (mean >87.3 mg/l), high phaeo-pigments (minimum >0.2 ug/l), low nitrate nitrogen (max. <0.059 mg/l, mean <0.013 mg/l, min. <0.001 mg/l), and high total Kjeldahl nitrogen (max. >0.40 mg/l, mean >0.26 mg/l, minimum >0.17 mg/l) (Yeung et al., 2014).

Leiopathes glaberrima has been noted to thrive on exposed rocky terraces with low silting levels (Deidun et al., 2015, Mytilineou et al., 2014). Leiopathes glaberrima was observed in the Gulf of Mexico, alongside Lophelia pertusa, in areas where temperatures were 8.5-10.6°C, salinity 35.0–35.3, the difference in seawater density (σ_Θ, 27.1–27.2 kg m^-3), O₂ was 2.6–2.8 ml^-1 and turbidity revealed at 150, 240 and 450 m from the 5-hour yo-yo CTD  (Davies et al., 2010). Temperature variations of 0.8°C were observed over 5-11 hour periods, associated with internal waves. Furthermore, high-frequency temperature variability over 20-30-minute periods was also recorded at one of the coral sites (476 m depth), where a temperature rise of 0.5°C occurred, followed by a slower temperature decline. These fluctuations exhibit 5 to 11-hour cycles. The ROV dives concentrated in the areas with the densest coral cover had a consistent pH throughout all the dives, with values between 7.95 and 7.97. The other ROV dives over areas of coral had pH of 8.04 to 8.10 and 7.92 to 8.01.

Sensitivity assessment. The vertical growth of the characterizing species (5 cm above the attachment point) would protect most individual polyps from the effect of 5 cm of deposited sediment. The current regimes typical of cold water coral sites are likely to remove deposited sediment material quickly. Therefore, resistance is assessed as 'High', resilience as 'High' and sensitivity as 'Not sensitive' at the benchmark level. However, there is limited specific evidence on the effects of this pressure on the characteristic species so confidence in the assessment is 'Low'.

Smothering and siltation rate changes (heavy)

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

Evidence

Information on the effect of sediment deposition on the characteristic species is limited. However, experimental and monitoring studies based on the exposure of Lophelia pertusa to drill cuttings from oil drilling activities on the Norwegian continental shelf indicate that coral polyps can tolerate the enhanced particle deposition rates and suspended matter concentrations up to a point, thereafter the polyps are unable to clear sediment and become anoxic (Allers et al., 2013; Larsson et al., 2013; Purser, 2015 in Fernandez-Arcaya et al., 2017). Direct laboratory experimentation on the deposition of 6.5 mm of drill cuttings onto Lophelai pertusa polyps found significant mortality of individual polyps (Cordes et al., 2016b; Larsson & Purser, 2011). In addition, a small pilot experiment indicated that coral larvae might be particularly vulnerable to high particle concentrations (Larsson et al., 2013 cited in Fernandez-Arcaya et al., 2017; Järnegren et al., 2017).

In Italian waters, the preference of Leiopathes spp. for more wave exposed areas may indicate a preference for stronger current and possibly greater resistance to heavy sediment load (Bo et al., 2014b). Rueda et al. (2014) reported that Stichopathes sp and Antipathes sp. were more resistant to burial in submarine flows due to submarine volcanism than other corals. However, the effects of discrete volcanism also include changes in water chemistry changes and other effects that are difficult to quantify and disentangle. 

Sensitivity assessment. Cold-water black corals (Antipatharia) can grow up to several metres in height (Freiwald et al., 2004), depending on growth form and species. Their large size may allow the bulk of the individual to avoid smothering by 30 cm of deposited sediment (the benchmark). However, smaller individuals or low-growing species may be adversely affected. Also, the severity of the impact will also depend on the local hydrography and how long the sediment remains on the seabed. Therefore, resistance is assessed as 'Low' as a precaution to represent the loss of juveniles and or low-growing species from the community. Hence, resilience is assessed as 'Very low' and sensitivity as 'High'. Confidence in the assessment is 'Low' as the impact is likely to be dependent on local conditions, and vary between species. 

Litter

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

Evidence

The impact of lost fishing gear on cold-water coral communities, is documented (Consoli et al., 2018; Sampaio et al., 2012). Its distribution can be widespread (especially in fishing grounds) and the persistence of lost gear and plastics means a longer timeframe for recovery. In addition, there is potential for submarine canyons to act as “repositories for derelict fishing gear” and other litter (Cau et al., 2017). Lost fishing gear and other litter have the potential to entangle individual corals and cause damage or restrict growth (Brown & Macfadyen, 2007; Cau et al., 2017; Consoli et al., 2018; Fosså et al., 2002). For example, Deidun et al. (2015) reported the entanglement of Leiopathes glaberrima specimens by discarded long lines and large ropes in the black coral forests off Malta. Although individual specimens did not exhibit significant degradation due to entanglement, the authors noted numerous dead and removed specimens in their study, probably due to entanglement.  

The deposition of artificial hard substratum (e.g. coal clinker; Briggs et al., 1996), or shipwrecks (Hiscock et al., 2010)) can provide additional habitat for sessile filter feeders. In addition, oil and gas infrastructure can provide additional habitat on short timescales (Gass & Roberts, 2006; Roberts, 2002). In addition, de Matos et al. (2014) recorded a colony of Antipathella subpinnata growing on an old discarded rag off the Azores.

Sensitivity assessment. Little evidence of the effects of litter, especially microplastics, was found. However, the evidence of the effects of discarded fishing gear (ghost fishing) on the black coral Leiopathes glaberrima suggests that similar species may also be adversely affected. Therefore, resistance is assessed as 'Low', resilience as 'Very low' and sensitivity as 'High'. However, confidence in the assessment is 'Low' due to the limited direct evidence. 

Electromagnetic changes

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

Evidence

No evidence was found regarding the effect of electromagnetic change on the M.AtMB.Bi.CorRee.LopFra biotope.

Underwater noise changes

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

Evidence

The M.AtMB.Bi.CorRee.LopFra biotope is characterized by invertebrates with no known means to detect noise and as such will not be affected by changes in underwater noise as defined under this pressure.

Introduction of light or shading

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

Evidence

Physico-chemical factors potentially causing band formation in A. fiordensis were reviewed in Grange & Goldberg (1993). However, no correlations were found between band formation and surface or underwater light levels, salinity, or temperature (Williams et al., 2006). Gorgonian and black coral larvae are negatively phototrophic (Grigg, 1974; Oakley, 1988; cited in Yeung et al., 2014). Yeung et al. (2014) also noted that octocorals and black corals (azooxanthellate corals) were important habitats for other species at depth in the relatively turbid waters of Hong Kong where other scleractinian corals did not grow. 

Sensitivity assessment.  Natural light rarely penetrates to the depth this biotope is found in the North East Atlantic, so changes in incident light due to shading are probably irrelevant. Offshore installations, especially at depth, might add extremely localized artificial light. However, no evidence could be found on the effect of anthropogenic light on the M.AtMB.Bi.CorRee.LopFra biotope.

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

The M.AtMB.Bi.CorRee.LopFra biotope is characterized by sessile invertebrates and as such will not be affected by barriers to species movement. Barriers to the movement of propagules (e.g. larvae) are not considered under this pressure. 

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

The M.AtMB.Bi.CorRee.LopFra biotope is characterized by sessile invertebrates and as such will not be affected by increased risk of collision. It might be adversely affected by large falling marine debris such as barrels, containers, and even shipwrecks but the effects are probably addressed under 'abrasion' above. 

Visual disturbance

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

Evidence

The M.AtMB.Bi.CorRee.LopFra biotope is characterized by invertebrates that are not reliant on vision and as such will not be affected by visual disturbance, as defined under this pressure.

Genetic modification & translocation of indigenous species

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

Evidence

No evidence was found to suggest that any of the characteristic species were subject to translocation or genetic modification, nor the introduction of genetically distinct organisms. Therefore, this pressure is assessed as 'Not relevant'. 

Introduction or spread of invasive non-indigenous species

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

Evidence

No evidence was found on the introduction of non-native species on the characteristic species or the M.AtMB.Bi.CorRee.LopFra biotope. In a single study from the Hawaiian Islands, there is evidence of non-native colonization by an Antipatharian coral (Kahng & Grigg, 2005). However, the authors cite a lack of anthropogenic vector and depauperate existing fauna as reasons for the unique nature of this colonization.

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

In Mexico, nutrient enrichment was found to be positively correlated to the presence of aspergillosis disease in gorgonian corals (Bruno et al., 2003; cited in Yeung et al., 2014). However, no evidence was found for the effects of the introduction of microbial pathogens or disease vectors on the M.AtMB.Bi.CorRee.LopFra biotope or its characteristic species. 

Removal of target species

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

Evidence

In cold-water coral regions globally, several small-scale fisheries for Leiopathes spp. and Antipathes spp. have been documented, specifically for jewellery (Grigg, 2001; Deidun et al., 2010; Tsounis et al., 2010). Grigg (2001) suggested that the fishery for precious corals around Hawaii was sustainable (in 2001). Deidun et al. (2010) noted that the targetted fishery for black corals in Maltese waters had ceased in 1987 and that the coral resources had not suffered greatly from past harvesting but also noted potential concerns over damage caused by ghost fishing (see abrasion above). Friewald et al. (2004) noted that the unspecific 'drags' used to harvest corals also damages the entire community. However, there is no current or historical evidence of such a fishery in the UK. Therefore the assessment of fishery pressure for the M.AtMB.Bi.CorRee.LopFra biotope as a target species is assessed as ‘Not relevant’.

Removal of non-target species

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

Evidence

There is extensive evidence of cold-water coral communities as bycatch from numerous longline and trawl fisheries (Bo et al., 2014a; Roberts, 2002; Sampaio et al., 2012). Fishing activity, especially trawling, has been reported to be deleterious to Lophelia pertusa reefs globally. There is evidence that trawling effects are orders of magnitude greater (296–1,719) than long-lining (Pham et al., 2014). Gilkinson & Edinger (2009) observed both upright and overturned Acanthogorgia armata in an area of heavy trawling. Wareham & Edinger (2007) recorded the by-catch frequencies of Acanthogorgia armata. Crab pots, gillnet and longline fixed gears caught two, three and 12 individuals of Acanthogorgia armata corals, respectively, whilst otter trawl mobile gear caught 27 between April 2004 and January 2006. Similarly, Antipatharia individuals were caught as bycatch by gillnet (14), longline (1), otter trawl (17) and twin trawl (3) (Wareham & Edinger, 2007). Similarly, Diedun et al. (2014) reported that two specimens of Leiopathes glaberrima were caught as bycatch by long-line fishermen off Malta.

Sensitivity assessment. The above evidence suggests that the black corals that dominate this biotope are subject to bycatch. Also, passing dredges/trawls may also damage or remove the underlying Lophelia framework, scattering or removing the hard substratum required by the rest of the coral community. Therefore, resistance is assessed as 'Low'.  Resilience is assessed as 'Very low' due to the slow growth rate and longevity of cold-water coral communities and also the time required for the replacement of the underlying 'framework' from any existing Lophelia reef in the area; assuming that is possible. Hence, sensitivity is assessed as 'High'.