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information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Mixed coral assemblage on Atlantic upper bathyal Lophelia pertusa reef framework (biogenic structure)

Summary

UK and Ireland classification

UK and Ireland classification

Description

This biotope represents the extensive, mostly dead, framework of Lophelia pertusa that support a high diversity of species including various other corals such as Caryophylliidae, Stichopathes gravieri, Antipathella, Acanthogorgia armarta and Leiopathes. Other conspicuous taxa include anemone Phelliactis and encrusting sponges. This may be found associated with Lophelia pertusa reef summit or may form beneath escarpments where live colonies of Lophelia pertusa grow but subsequently break off and form a rubble framework. The same assemblage is found in the mid bathyal but associated species are likely to vary. Characterizing species listed refer to all mixed coral on Lophelia reef framework assemblages not just those found associated with the zone and substrate specified in this biotope. (Information from JNCC, 2015).

Depth range

200-600 m

Additional information

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Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

The mixed coral assemblage on Lophelia pertusa reef framework occurs at a range of depths in the deep sea. The M.AtMB.Bi.CorRee.LopFra biotope occurs in the Atlantic mid bathyal zone and the M.AtUB.Bi.CorRee.LopFra biotope in the Atlantic upper bathyal zone. The sensitivity of these biotopes is assessed as a group, on the assumption that their sensitivity is very similar in terms of substratum and functional groups present. Any differences in species or biotope response to pressures are highlighted.

The biotopes are primarily composed of mixed corals. The assessment focuses on the coral species listed within the description (Caryophylliidae spp., Stichopathes gravieri, Antipathella spp., Acanthogorgia armata and Leiopathes spp.), with additional reference to the anemone Phelliactis.  Encrusting sponges are common on a range of hard substrata and are not specific to this biotope. Therefore, these are not considered significant to the assessment of sensitivity. Very little information was available on deep-sea Caryophylliidae, particularly due to the lack of genus or species level information for the biotope. Where found, evidence has been included below. The underlying framework, formed by the scleractinian coral Lophelia pertusa, is crucial to these biotopes. The following assessment only considers the sensitivity of the framework itself, as it is composed mainly of dead coral. Further information on the ecology and sensitivity of live Lophelia pertusa can be found within the Atlantic upper bathyal live Lophelia pertusa reef (biogenic structure) assessment (M.AtUB.Bi.CorRee.LopPer).

Resilience and recovery rates of habitat

The formation of Lophelia framework is a long-term process (Roberts, 2002), dependent on natural degradation processes and natural minor damage or fragmentation. Reef formation is described in detail by Roberts et al. (2009). The reef structure created by Lophelia pertusa modifies the water flow regime within the reef (Mullins et al., 1981).  The complex structure of the reef slows down water flow and can cause sediments to fall out of suspension. The reef also provides a wide range of niches for other species and the increase in biological activity within the reef can also increase sedimentation (Roberts et al., 2009).

Species overview, distribution and habitat preferences

Stichopathes gravieri, Antipathella spp. and Leiopathes spp. are all black corals, Caryophylliidae spp. are cup-corals, Acanthogorgia armata is a gorgonian and Phelliactis is an anemone. Acanthogorgia armata has a fan-like skeleton composed primarily of gorgonin, with some scleritic calcite, and a hollow-cross chambered, consolidated central axis (De Moura Neves, 2016; Wareham & Edinger, 2007). The species is confined to the Atlantic, and occurs off the Azores (Braga-Henriques et al., 2013), the UK, southern Iceland, Davis Strait (Buhl-Mortensen et al., 2015) and Canada (Gilkinson & Edinger, 2009; Kenchington et al., 2012; Mortensen & Buhl-Mortensen, 2004). It is notably absent from the Norwegian shelf, which is thought to be because the temperature range, currents and substrata around the Greenland-Scotland topographical barrier (Faroe-Shetland Channel) restrict the transport of larvae (Buhl-Mortensen et al., 2015). Wareham & Edinger (2007) found individual colonies <50 cm in height off Canada, in depths ranging from 171-1,415 m. Baker et al. (2012) found the maximum height of Acanthogorgia armata colonies off Newfoundland to be 51 cm, although the average height was 8 cm. In Canadian waters, Acanthogorgia armata was found in high abundance on cobbles (Mortensen & Buhl-Mortensen, 2004), and in Newfoundland, Baker et al. (2012) found Acanthogorgia armata associated with boulders, cobbles, gravel and mud-sand. Off the south of Iceland, the species occurs down to 2,137 m (Madsen, 1944 & The Icelandic Benthos database, 2007, cited in Buhl-Mortensen et al., 2015). The maximum water temperature was 10.7°C on average, and salinity in ranged from 34.87‰ to 35.05‰ at 300-400 m. Buhl-Mortensen et al. (2015) recorded the temperature range of Acanthogorgia armata to be from 1 to 12°C, although most records were within 3-4°C.

Stichopathes gravieri has a whip-like morphology with an unbranched corallum, a single row of polyps on the axis and a number of spine rows visible from one side (Tsounis et al., 2010). On a seamount in the Pacific abyssal seafloor southwest of California, Stichopathes sp. was found to occupy rocky substrata at depths of 550-1,150 m but was absent from sediment areas (Genin et al., 1986). The Eastern North Pacific seamounts also support Stichopathes sp. aggregations, where they occur down to 1,150 m (Opresko and Genin, 1990, cited in de Matos et al., 2014).

Leiopathes spp. have a feathered, branched morphology (Tsounis et al., 2010). Habitat suitability modelling for Leiopathes glaberrima in the Gulf of Mexico (Etnoyer et al., 2018) found that mean annual bottom temperature, slope and depth were the most important environmental predictor variables for model fitting. The model suggested that the preferred depth range of the species was 200-1,000 m. By-caught specimens of Leiopathes spp. in the Azores at depths of 183-512 m were recorded to have a mean height of 31.1 (±24) cm, a mean width of 62 (±47.8) cm and a mean length of 78.7 (±58) cm (Sampaio et al., 2012). One specimen from the Azores has been reported with a height of 3 m and an axis diameter of 4 cm (Carreiro-Silva et al., 2013). In the Mediterranean, the species Leiopathes glaberrima occurs from 100 m, but only forms dense forests at depths of 200 m or more (Bo et al., 2014). These assemblages occur on hard bedrock or on rocky boulders (Angeletti et al., 2015; Deidun et al., 2015). Colonies can be up to 2 m in height, with a basal diameter of approx. 7 cm (Angeletti et al., 2015; Bo et al., 2015).  Deidun et al. (2015) observed newly settled colonies of Leiopathes glaberrima in the Mediterranean that were less than 5 cm high. In the UK, Leiopathes spp. colonies have been found at 1,280 m depth on silty bedrock slopes (Hughes & Narayanaswamy, 2013).  There are many different phenotypes of Leiopathes spp., resulting in colonies of different colours (Deidun et al., 2015). The study by Carreiro-Silva et al. (2013) comprised three distinct morphotypes and the authors note that the Leiopathes genus in the NE Atlantic requires revision. However, Ruiz-Ramos et al. (2015) found that the different colour morphs of Leiopathes glaberrima, which also show variation in branching pattern and polyp size, do not represent different species in the Gulf of Mexico (at 248-674 m depths). Instead, the authors concluded that the species is phenotypically plastic. For example, different sites had significantly different branch densities and the colour morphs appeared to be influenced by depth, and potentially slope. Plasticity may be linked to variations in the local environment, such as food and water flow (Ruiz-Ramos et al., 2015).

There are five species within the genus Antipathella. Three occur off New Zealand (Antipathella aperta, Antipathella strigosa and Antipathella fiordensis), one in the Atlantic and Mediterranean (Antipathella subpinnata) and the other is common in the Macaronesian archipelagos (Antipathella wollastoni; Ocaña et al., 2006; Opresko, 2001). However, Ocaña et al. (2006) also observed Antipathella wollastoni in the Mediterranean. It is worth noting that the distinction between Antipathella wollastoni and Antipathella subpinnata has only recently been clarified (Opresko, 2001). Information on Antipathella subpinnata and Antipathella wollastoni is used for this sensitivity assessment, with additional reference to Antipathella fiordensis where appropriate.

Antipathella subpinnata is tree-like in shape with a flexible and resistant chitinous skeleton (Bo et al., 2009). In the Mediterranean basin, the species occurs from 54 to 500 m depths on exposed hard substrata (Bo et al., 2009, 2008). Bo et al. (2008) also found records of the species growing on rocks covered by fine muddy sediments (e.g. off Stromboli island, in the Mediterranean) and numerous large colonies on the artificial substratum of an iron wreck in the Ligurian Sea. Deidun et al. (2015) observed small colonies of Antipathella subpinnata within large colonies of Leiopathes glaberrima. De Matos et al. (2014) also observed the species colonizing other invertebrates (e.g. bivalves, hydrocorals and sponges). The species can occur as single, sparse or grouped colonies (Bo et al., 2008), as well as part of large mixed assemblages (Bo et al., 2009). Specimens of 80 to 120 cm in height have been observed in the Mediterranean, however, most were in the size classes 0-20 and 20-40 cm (Bo et al., 2009). Bo et al., (2008, 2009) determined that depth was likely to be the main parameter affecting the density of Antipathella subpinnata, whilst settlement and growth was likely to be affected by the substratum slope. For example, colony densities were low when the gradient was 30-60° (Bo et al., 2008). In contrast, Antipathella fiordensis is found on steeper slopes in New Zealand fiords, despite having a similar ecology (Bo et al., 2009; Grange & Singleton, 1988).

Stichopathes spp., Antipathella subpinnata, Antipathella wollastoni and Antipathella fiordensis have been shown to prefer areas exposed to strong currents (Bo et al., 2009, 2008; Tempera et al., 2001 cited in de Matos et al., 2014; Genin et al., 1986; Grange, 1988; Grange and Singleton, 1988). Even on a small scale, the density of Stichopathes spp. on a seamount southwest of California was higher on small knobs and pinnacles (Genin et al., 1986). The heightened position off the sea floor given by the dead Lophelia framework is therefore crucial for the species.

Two species within the genus Phelliactis are known to occur in the Porcupine Seabight, at depths of 719-1668 m (Phelliactis hertwigi) and 1600-2173 m (Phelliactis robusta; Van Praet et al., 1990). Phelliactis robusta was found on hard substrata, with a preference for steep slopes and canyon walls. At Hatton Bank, Phelliactis sp. was observed at depths of ca 500-650 m, where it was colonising coral rubble, coral framework and steeply sloping rock (Roberts et al., 2008).

Reproduction and development

Antipathella fiordensis and Antipathella subpinnata are both dioecious (Gaino and Scoccia, 2010; Parker et al., 1997). Antipathella wollastoni and Antipathella fiordensis are likely to be gonochoric broadcast spawners, where gametogenesis follows an annual cycle (Parker et al., 1997; Rakka et al., 2017). The reproductive cycle for Antipathella fiordensis was highly synchronous between and within colonies (Parker et al., 1997), however intra-colonial variation (e.g. polyp fecundity) was observed by both Parker et al. (1997) and Rakka et al. (2017) for Antipathella fiordensis and Antipathella wollastoni, respectively. Black corals are also thought to have very limited larval dispersal ability (Bo et al., 2014).

Antipathella subpinnata and Antipathella wollastoni both reproduce in summer (Gaino & Scoccia, 2010; Rakka et al., 2017). For Antipathella wollastoni, oogenesis has been shown to begin in June (when seawater temperature reaches 18°C), and spermatogenesis in July, with gametes reaching maturity by October, when the maximum oocyte size is reached (Rakka et al., 2017). In this study, gametes started disappearing from the polyps by November. Gamete maturation was positively correlated with sea surface temperature, however, spawning appeared to happen after the temperature peak of 21.1°C in September. The presence of multiple oocyte size cohorts in the mature stage (October), together with empty vesicles, suggested that repetitive spawning was likely to occur within a prolonged overall spawning period. Gaino & Scoccia (2010) noted that simultaneous spawning was also likely. Gametes are released as tight buoyant clusters of eggs and sperm from both the tentacles and mouth (Gaino & Scoccia, 2010). Fecundity for Antipathella wollastoni varied from 1 to 309 oocytes per polyp for the spent (November) and maturing (July) stages (Rakka et al., 2017). Polyp fecundity had a weak positive correlation with sea surface temperature but was positively correlated with colony height. The reproductive output of a single colony is a function of the polyp fecundity and the number of gravid polyps, therefore larger colonies are likely to have increased reproductive success and a higher contribution to recruitment.

Gametogenesis in Antipathella fiordensis (in New Zealand), was shown to occur in summer, from late November to February, with oocytes maintained until spawning in March (Parker et al., 1997). During the study, between November to February sea temperatures increased from 12 to 15°C, and then decreased to 14°C in March. It is worth noting that these temperatures were 2-3°C lower on average than those previously recorded by Grange et al. (1991, cited in Parker et al., 1997). Spawning is likely to have occurred over several weeks, after the highest temperature peak (February). Parker et al. (1997) noted a polyp fecundity range of 12-173 oocytes per polyp for Antipathella fiordensis. The largest oocytes were 100-140 µm. Female colonies were found to produce between 1.3 and 16.9 million oocytes, increasing with the size of the colony. The recruitment of Antipathella fiordensis has been noted to occur sporadically, at very low frequencies, with colonies <10 years having very high mortality rates (Grange, 1997, cited in Miller, 1998). Survivorship of colonies was found to increase with colony height and age (Grange, 1997, cited in Miller, 1998).

The planula larvae of Antipathella fiordensis are lecithotrophic, negatively buoyant, short-lived (10 days) and poor swimmers, hence they crawl on the substratum (Miller, 1997). Miller (1997) found that ciliated planulae of 200 µm in length developed within 36 hours after external fertilization of Antipathella fiordensis eggs. Miller (1998) suggested that the dispersal of black coral larvae, specifically Antipathella fiordensis (previously Antipathes fiordensis) was highly philopatric, that is, larvae settle close to parent colonies (within <5-10 m). However, the study also found that larvae or gametes may be more widely dispersed (>50 m) at certain sites. The scale of larval dispersal is, therefore, likely to be variable, with water flow playing a key role. Significant genetic differences have been found between sites 10-15 km apart within fiords, however as populations in geographically separated fiords were found to be genetically similar, Miller (1997) suggested that this is not evidence of isolation by distance.

Antipathella fiordensis also reproduces asexually via ‘polyp bailout’, forming highly mobile and ciliated planulae (Parker et al., 1997). This has been observed in the laboratory when the species is under stress (pers. comm./pers. obs., cited in Parker et al., 1997). Asexual reproduction can also occur via fragmentation, and evidence of this exists for Antipathella subpinnata (Coppari et al., 2019). Over seven months in aquaria, fast growth rates of up to 1.85 and 1.58 cm/month for whole fragments and new branchlets, respectively, were observed for this species. de Matos et al. (2014) recorded a colony of Antipathella subpinnata growing on an old discarded rag off the Azores. This colony specifically appeared to be a branch broken off from a larger colony that was beginning to regenerate, as no base or stem was present. A new branchlet was evident growing from the centre of the thickest part of the axis, presumably where the branch had broken off the mother colony (de Matos et al., 2014).

Sexual maturity in Antipathella fiordensis was found to occur at colony heights of 70 and 105 cm (Parker et al., 1997), which corresponded to a minimum age for sexual maturity of ~31 yrs, based on growth rate estimates (24.4 mm/year; Grange, 1997, cited in Parker et al., 1997). All colonies over 100 cm were mature, and colonies <49 cm were sexually immature, however, the largest immature colony was 90 cm (corresponding to an age of 37 years). However, slower growth rates of 16 mm/year have also been recorded for Antipathella fjordensis (Grange & Goldberg, 1993, cited in Love et al., 2007; Miller, 1998). Bo et al. (2008) collected two specimens of Antipathella subpinnata off Italy at a depth of 55-70 m. Despite one colony being 78 cm in height, neither of the colonies were sexually mature. In the Adriatic Sea (51 m), small colonies of Antipathella subpinnata (42 cm high) were found to be sexually immature, however, colonies 120 cm in height from the Tyrrhenian Sea (at 70 m) in August (at a water temperature of 16°C) were fertile (Gaino and Scoccia, 2010). When the water temperature was 14°C, between September to November, no fertile colonies were observed (Gaino & Scoccia, 2010).

Stichopathes spp. (two species in Puerto Rico) were reported to be gonochoric, with peak oocyte maturity in May-June (Goenaga, 1977, cited in Wagner et al., 2012). This study also reported that all of the female colonies spawned one day after the spawning of a male colony in the same aquarium. Therefore, females probably release oocytes in response to male pheromones, and fertilization is probably external (Goenaga, 1977, cited in Wagner et al., 2012). Oocyte size in these two Stichopathes spp. were ≤150 µm (Goenaga, 1977, cited in Wagner et al., 2011), and due to their high yolk content, Goenaga (1977, cited in Wagner et al., 2011) suggested that the larvae were likely to be short-lived and non-feeding. Mixed colonies of Stichopathes saccula with both male and female polyps were found by Pax et al. (1987, cited in Wagner et al., 2011) so the potential for simultaneous hermaphrodites cannot be excluded.

Leiopathes glaberrima has a mixed reproductive strategy and can reproduce through fragmentation as well as through long-distance dispersal of larvae (Ruiz-Ramos et al., 2015). Etnoyer et al. (2018) found that distinct classes were present in the size-frequency distribution of Leiopathes glaberrima, suggesting that the species reproduces through both periodic and episodic recruitment events. In the Gulf of Mexico (at 248-674 m depths), Ruiz-Ramos et al. (2015) suggested that there was a barrier for gene flow in Leiopathes glaberrima between sites 36.4 km apart. This was based upon sympatric individuals being assigned to two lineages. One lineage appeared capable of long-distance dispersal and indicated an out-bred species, whereas the other indicated more localized recruitment (self-fertilization, with relative isolation and limited habitat) with individuals being highly inbred. This mixed mating strategy is common in long-lived species, to maintain genetic diversity and colonize new habitats (ChybickiI & Burczyk, 2010, cited in Ruiz-Ramos et al., 2015). The authors also suggest that the recruitment of the different lineages might be influenced by local patterns of topography and current velocity.

Growth rates of Leiopathes glaberrima have been recorded as <10 µm/year off Hawaii, giving some specimens with a basal radial diameter of approx. 12 mm an age of approx. 2,377 years (Roark et al., 2006). The initial 5 mm of growth is thought to be faster, potentially ca 13 µm/year (i.e. over the first 400 years of growth), compared to the outer 8 mm of growth (Roark et al., 2006, 2009). The faster initial growth rates may help the colony establish (Roark et al., 2009). Another colony of Leiopathes spp. was found by Roark et al. (2009) to have an age of ~4,200 years. However, the living polyps are likely to be continuously replaced, as 14C dating has shown the carbon contained within these polyps is only a few years old. Prouty et al. (2011) reported different growth rate ranges of 8 to 22 µm/year for Leiopathes spp. in the Gulf of Mexico (at 300 m depth). They also found that growth rates decreased as the life span increased. For example, in the oldest specimen (of 2,040 years), growth decreased from 16 µm/year for the first 600 years, to an average of 8 µm/year throughout the colonies life span. Carreiro-Silva et al. (2013) also measured the growth rates of Leiopathes spp. from the Azores, at depths of 293-366 m. Radial growth rates for the smallest and largest colonies were 5-7 µm/year, however other colonies had growth rates of ca 20-30 µm/year. The study found that growth rates varied through the lifespan of a colony. In contrast to the results of Roark et al. (2006, 2009), Carreiro-Silva et al. (2013) found that, in a 2,320 year old specimen, growth rates were slowest over the initial 1,600 years and the last 300 years. The middle period (400 years) was characterized by a higher growth rate of 20 µm/year. Therefore, radial growth rates don’t correlate linearly to colony axis diameter or height. Williams et al. (2006) have also estimated that Leiopathes glaberrima (tentative ID) has a slightly radial growth rate of 14.5 µm/year, based upon specimens collected from 307-679 m depth off the southeastern continental slope of the United States and the north-central Gulf of Mexico, which were found to have ages of 198, 290, 386 and 483 years. However, this is still extremely slow.

Phelliactis hertwigi and Phelliactis robusta in the Porcupine Seabight, are known to be dioecious and are thought to spawn in cycles related to the rate and seasonality of organic matter depositions (Van Praet et al., 1990). This study found that, for both species, the gonads were developed in the mesoglea of the secondary mesenteries, with the twelve primary mesenteries being sterile. Oogenesis was found to take 8–9 months in Phelliactis hertwigi and 15-19 months in Phelliactis robusta, with spawning occurring in October/November and April/May, respectively (Van Praet et al., 1990).

Resilience assessment. Where resistance of the characterizing species is ‘None’, ‘Low’ or ‘Medium’, and the habitat has not been altered, resilience is assessed as ‘Very low’ (10-25 years). This is based upon the very slow growth rates and extreme life spans (maximum recorded is 4,200 years) of Leiopathes spp. (Carreiro-Silva et al., 2013; Prouty et al., 2011; Roark et al., 2006, 2009; Williams et al., 2006). Although the growth rates of Antipathella fiordensis are faster (24.4 mm/year; Grange, 1997, cited in Parker et al., 1997), sexual maturity isn’t reached until a minimum age of ~31 yrs (Parker et al., 1997) and recruitment occurs sporadically, at very low frequencies (Grange, 1997, cited in Miller, 1998). Colonies of Antipathella fiordensis <10 years old also have very high mortality rates, although survivorship increases with colony height (Grange, 1997, cited in Miller, 1998). Observations of Antipathella subpinnata in the Mediterranean also suggest that regeneration can occur from broken branches (de Matos et al., 2014). The confidences associated with this score are ‘High’ for Quality of Evidence, ‘Medium’ for Applicability of Evidence and ‘High’ for Degree of Concordance. An exception is made for permanent or ongoing (long-term) pressures where recovery is not possible as the pressure is irreversible, in which case resilience is assessed as ‘Very low’ by default.

Climate Change Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
Medium Very Low Medium
Q: High
A: Medium
C: High
Q: High
A: Medium
C: High
Q: High
A: Medium
C: High

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’.

Medium Very Low Medium
Q: High
A: Medium
C: High
Q: High
A: Medium
C: High
Q: High
A: Medium
C: High

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’.

Medium Very Low Medium
Q: High
A: Medium
C: High
Q: High
A: Medium
C: High
Q: High
A: Medium
C: High

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’.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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’.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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’.

Medium Very Low Medium
Q: High
A: Medium
C: Medium
Q: High
A: Medium
C: Medium
Q: High
A: Medium
C: Medium

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’.

High High Not sensitive
Q: High
A: Medium
C: Medium
Q: High
A: High
C: High
Q: High
A: Medium
C: Medium

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’.

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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’.

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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’.

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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’.

Hydrological Pressures

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Chemical Pressures

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Physical Pressures

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Biological Pressures

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Not assessed

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Citation

This review can be cited as:

Last, E.K., Ferguson, M. & Robson, L.M. 2019. Mixed coral assemblage on Atlantic upper bathyal [Lophelia pertusa] reef framework (biogenic structure). In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21-10-2020]. Available from: https://www.marlin.ac.uk/habitat/detail/1194

Last Updated: 21/11/2019