The Marine Life Information Network

Temperature increase (local)

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

Evidence

Solenosmilia variabilis has a wide thermal niche from 2.5 to 14.5°C (Os’kina et al., 2010; Thresher et al., 2015). However, the Solenosmilia variabilis reef biotope occurs in a narrower thermal niche, 5.0-5.5°C, than the species’ thermal tolerances (Davies et al., 2015) – a phenomenon also seen in Lophelia pertusa (syn. Desmophyllum pertusum) (Howell et al., 2011). There is no evidence of Solenosmilia variabilis tolerance to changes in local temperatures.

There is some evidence that Lophelia pertusa – as a proxy for Solenosmilia variabilis – has some tolerance for variable local temperatures, particularly when occurring in the presence of internal waves. Mienis et al. (2007) recorded temperature fluctuations greater than 3°C caused by internal waves on cold-water coral carbonate mounds on Rockall Bank (North-East Atlantic). Furthermore, Davies et al. (2009) observed internal waves breaking over Mingulay Reef, with temperatures varying by 0.75°C. Oceanographic models used by Pearman et al. (2020) that incorporate internal tides indicate that cold-water corals in Whittard Canyon occupy temperatures between 5.6-9.6°C, a range of 4°C. This evidence indicates that these corals tolerate relatively large changes in local temperatures at tidal frequencies but at temporal scales smaller (hours) than that of the benchmark (6 or 12 months).

Other evidence suggests (Guihen et al., 2012; Brooke et al., 2013) that Lophelia reefs in the North-East Atlantic could probably survive a localized short-term change in temperature of 5°C for a month, as long as the temperature did not exceed its thermal tolerance limit. The effects of a prolonged chronic increase in temperature (e.g. 2°C for a year, the benchmark) would probably depend on the location of the reef and other factors, e.g. food supply, but there is no empirical evidence of the effect of temperature changes at the level of the benchmark.

Sensitivity assessment. Based on the available evidence, including Lophelia reefs as a proxy, resistance is assessed as ‘Medium’ as a precaution based on possible long-term effects of increased temperature. Therefore, 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

Solenosmilia variabilis has a wide thermal niche from 2.5 to 14.5°C (Os’kina et al., 2010; Thresher et al., 2015). However, the Solenosmilia variabilis reef biotope occurs in a narrower thermal niche, 5.0-5.5°C, than the species’ thermal tolerances (Davies et al., 2015) – a phenomenon also seen in Lophelia pertusa (syn. Desmophyllum pertusum) (Howell et al., 2011). There is no evidence of Solenosmilia variabilis tolerance to changes in local temperatures.

There is some evidence that Lophelia pertusa – as a proxy for Solenosmilia variabilis – has some tolerance for variable local temperatures, particularly when occurring in the presence of internal waves. Mienis et al. (2007) recorded temperature fluctuations greater than 3°C caused by internal waves on cold-water coral carbonate mounds on Rockall Bank (North-East Atlantic). Furthermore, Davies et al. (2009) observed internal waves breaking over Mingulay Reef, with temperatures varying by 0.75°C. Oceanographic models used by Pearman et al. (2020) that incorporate internal tides indicate that cold-water corals in Whittard Canyon occupy temperatures between 5.6-9.6°C, a range of 4°C. This evidence indicates that these corals tolerate relatively large changes in local temperatures at tidal frequencies but at temporal scales smaller (hours) than that of the benchmark (6 or 12 months).

Other evidence suggests (Guihen et al., 2012; Brooke et al., 2013) that Lophelia reefs in the North-East Atlantic could probably survive a localized short-term change in temperature of 5°C for a month, as long as the temperature did not exceed its thermal tolerance limit. The effects of a prolonged chronic decrease in temperature (e.g. 2°C for a year, the benchmark) would probably depend on the location of the reef and other factors, e.g. food supply, but there is no empirical evidence of the effect of temperature changes at the level of the benchmark.

Sensitivity assessment. Based on the available evidence, including Lophelia reefs as a proxy, resistance is assessed as ‘Medium’ as a precaution based on possible long-term effects of decreased temperature. Therefore, 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

The depths at which Solenosmilia variabilis occurs in the North-East Atlantic are characterized by full salinity (30-35 psu) seawater. In situ salinity measurements at Solenosmilia reefs have ranged from 34.3 to 35.0 psu (Bostock et al., 2015; Ramiro-Sanchez et al., 2019; Raddatz et al., 2020). At these depths, Solenosmilia reefs are unlikely to encounter natural changes in salinity.

Sensitivity assessment.  Due to the highly stable conditions in which Solenosmilia variabilis reef is usually found, a change in salinity due to human activities is likely to cause mortality of the coral polyps.  Consequently, resistance has been assessed as ‘Low’, resilience as ‘Very low’, and sensitivity assessed as ‘High’.

Salinity decrease (local)

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

Evidence

The depths at which Solenosmilia variabilis occurs in the North-East Atlantic are characterized by full salinity (30-35 psu) seawater. In situ salinity measurements at Solenosmilia reefs have ranged from 34.3 to 35.0 psu (Bostock et al., 2015; Ramiro-Sanchez et al., 2019; Raddatz et al., 2020). At these depths, Solenosmilia reefs are unlikely to encounter natural changes in salinity.

Sensitivity assessment.  Due to the highly stable conditions in which Solenosmilia variabilis reef is usually found, a change in salinity due to human activities is likely to cause mortality of the coral polyps.  Consequently, resistance has been assessed as ‘Low’, resilience as ‘Very low’, and sensitivity assessed as ‘High’.

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 coral reefs are associated with strong tidal currents. Reefs are often associated with topographical features that enhance tidal currents, such as raised seabed features (e.g. seamounts and banks) and narrow channels or canyons (Rogers, 1999). Higher flow rates are thought to improve food supply to reefs, as well as reduce the accumulation of sediment (Roberts et al., 2009).

No evidence of the effects of variable tidal currents on Solenosmilia variabilis reefs was found, but the evidence is available for Lophelia reef as a proxy. Cold-water coral carbonate mounds on Rockall Bank are linked to the presence of internal waves and tidal currents, and shaped by the local hydrodynamic regime (Mienis et al., 2007). The residual currents around the mounds are 0.1 m/s, with maximum current speeds of 0.45 m/s. Davies et al. (2009) also reported variable current speeds across Mingulay Reef (Scotland) that were also tidally induced, with a residual current speed of 0.29 m/s and a maximum of 0.81 m/s.

Mortensen (2001) investigated the growth and behaviour of Lophelia pertusa in an aquarium with flowing seawater.  No polyp mortality was observed in the vicinity of aquaria inlets (0.06 m/s) but high mortality occurred at the opposite end where the current was slower (0.02 m/s) due to sediment accumulation. Similar in situ observations were made by Davies et al. (2015) on Anton Dohrn Seamount where, in low current areas, sedimentation had smothered the Solenosmilia reef.

Sensitivity assessment. The available evidence suggests that in the North-East Atlantic, Solenosmilia variabilis reefs are likely to tolerate of an increase in tidal currents at the benchmark. Considering the fluctuating currents speeds that reefs experience, the benchmark increase is relatively small compared to the variance already experienced. Both resistance and resilience have been assessed as ‘High’, and sensitivity assessed as ‘Not sensitive’ at the benchmark level.

Emergence regime changes

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

Evidence

Solenosmilia variabilis reefs are found at lower bathyal depths, therefore they will not be impacted by a change in emergence. As a result, this pressure is assessed as ‘Not relevant’.

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

Solenosmilia variabilis reefs are found at lower bathyal depths, therefore they will not be impacted by changes in wave exposure. As a result, this pressure is assessed as ‘Not relevant’.

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

Not assessed.

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

Not assessed.

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

Not assessed.

Radionuclide contamination

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

Evidence

Currently, the effect of radioactive waste on cold-water corals is unknown. Local leakage of radioactive waste would likely impact the reef (Ragnarsson et al., 2016). However, ‘no evidence’ was found.

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

Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

No direct evidence is available on the resistance of Solenosmilia variabilis reef to de-oxygenation. However, in situ measurements of dissolved oxygen concentrations at Solenosmilia variabilis reefs vary from 5.76 mg/l  in the SW Pacific (Bostock et al., 2015), to 6.57 mg/l on Solenosmilia variabilis carbonate mounds off Brazil (Raddatz et al., 2020). Observations from Thresher et al. (2014) suggest that on Tasmanian seamounts, the lower extent of live Solenosmilia variabilis reef is determined by the oxygen minimum zone (3.8 mg/l). Above the oxygen-minimum zone (1,400 m) sub-fossil Solenosmilia variabilis rubble was present that had been blackened by ferromanganese oxide deposits. Above this depth, live Solenosmilia variabilis reef was present, with a relatively high abundance of epifauna.

Similarly to Solenosmilia variabilis reefs, the oxygen-minimum zone is believed to delimit the lower distribution of Lophelia reefs in the North-East Atlantic is (Freiwald, 1998; Rogers, 1999). Dodds et al. (2007) investigated the metabolic tolerance of Lophelia pertusa to temperature and dissolved oxygen change in the laboratory. They found that Lophelia could survive anoxia for one hour, and hypoxia (2-3 kPa; 0.88-1.32 mg/l) for 96 hours (four days). Lophelia was able to increase its uptake of oxygen by the expansion of the surface area of its polyp in response to low oxygen concentrations (Dodds et al., 2007). Lunden et al. (2014) also studied the effect of decreasing oxygen concentration of Lophelia collected from the Gulf of Mexico.  Oxygen concentrations within the Gulf of Mexico are lower than those recorded in the North-East Atlantic, with records ranging from 1.5 - 3.2 ml/l (2.14 – 4.57 mg/l) (Lunden et al., 2014) and, therefore, have a higher tolerance through local adaptation to lower dissolved oxygen concentrations compared to North-East Atlantic populations. Laboratory experiments exposed Lophelia to different oxygen concentrations for seven days.  The Lophelia samples survived (100%) exposure to 5.3 and 2.9 ml/l, but experienced 100% mortality at 1.57 ml/l (2.24 mg/l) after seven days. 

Sensitivity assessment. A change in oxygen concentration at the benchmark (2 mg/l or less for a week) has the potential to cause significant mortality in cold-water reefs in North-East Atlantic. Evidence suggests that Solenosmilia variabilis reefs do not persist where oxygen concentration is below 3.8 mg/l, and direct evidence from Lunden et al. (2014) suggest that exposure to 2.24 mg/l (1.57 ml/l) conditions resulted in complete mortality of the proxy, Lophelia. Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low, so that sensitivity assessment is probably ‘High’.

Nutrient enrichment

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

Evidence

Nutrient availability is important for cold-water coral reef growth. Raddatz et al. (2020) showed that periods of enhanced Solenosmilia variabilis mound formation off Brazil were linked to nutrient-rich intermediate waters, which facilitate coral growth. In addition, Bahr et al. (2020) have linked strong monsoon seasons with increased Solenosmilia variabilis growth. Heavy monsoon seasons bring elevated run-off enhanced by terrigenous nutrients and organic matter. This material is transported to the continental margin of Brazil, boosting productivity and ultimately providing more organic materials for cold-water corals. Although it is understood that Solenosmilia variabilis can withstand and capitalise on fluctuating pulses of nutrient enrichment, there is no available evidence of the effect of nutrient enrichment on Solenosmilia variabilis reef. As a result, this pressure is recorded as ‘No evidence’.

Organic enrichment

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

Evidence

Dissolved and particulate organic matter (DOM/POM) are important food sources for cold-water coral reefs (Bahr et al., 2020; Gori et al., 2014; van Ovelen et al., 2016). However, there is no evidence was found on the effect of organic enrichment at the level of the benchmark on Solenosmilia variabilis reefs. Therefore, ‘No evidence’ is recorded.

Physical loss (to land or freshwater habitat)

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

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of available habitat (resilience is ‘Very low’). The Solenosmilia variabilis reef 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

Solenosmilia variabilis larvae, like Lophelia pertusa, require hard substratum to settle and form a solid anchoring point, such as bedrock, existing reef or artificial substrata (e.g. oil and gas platforms). For a change in substrata to occur, the original substratum would have to be removed and, therefore, remove living coral and/or coral framework. This would destroy the reef and suitable substratum for recovery.

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

Physical change (to another sediment type)

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

Evidence

Solenosmilia variabilis larvae, like Lophelia pertusa, must settle onto bedrock or other hard substrata. This allows a solid anchoring point to be established, from which the coral skeleton can grow. Although a growing reef structure may extend over soft substrata, an initial presence of a hard substratum is essential. As Solenosmilia variabilis reef occurs on rock or hard substrata, this pressure is deemed ‘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

Solenosmilia variabilis larvae, like Lophelia pertusa, must settle onto bedrock or other hard substrata. However, Solenosmilia variabilis reefs may grow out across adjacent soft sediment, which could be extracted.  In addition, the reef structure will have low local currents, resulting in the deposition and accumulation of suspended sediments which may also be extracted. Removal of these softer sediments would destroy any Solenosmilia variabilis reef.

Sensitivity review. Solenosmilia variabilis reef has no resistance to the removal of 30 cm of substrata, therefore, resistance is assessed as ‘None’. The long-lived nature (Hall-Spencer et al., 2002) and slow growth rates (Gammon et al., 2018) of Solenosmilia variabilis means that resilience is ‘Very Low’, giving this habitat an overall sensitivity of ‘High’. 

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

The main sources of potential abrasion and disturbance relevant to Solenosmilia variabilis reef are from bottom fishing, e.g. beam trawls, deep-sea mining activity, e.g. mining vehicles (Miller et al. 2018), anchoring or positioning of offshore structures (Angiolillo et al., 2015).

The abrasive action of bottom-contacting fishing nets can break Solenosmilia variabilis colonies. Hall-Spencer et al. (2001) documented the bycatch of Solenosmilia variabilis fragments, along the West Ireland continental slope. Recoverability tests on Tasmanian seamounts indicate no signs of Solenosmilia variabilis recovery, 10 years after bottom-trawling has ceased (Williams et al., 2010). Across the same seamounts, Althaus et al. (2009) reported that bottom-trawling reduced Solenosmilia variabilis cover by two orders of magnitude. Althaus et al. (2009) also provided evidence that megabenthic assemblage structures have wide divergence between trawled and untrawled seamounts. On these trawled seamounts, Solenosmilia variabilis biotopes have been replaced, resulting in a three-fold decline in richness, diversity and density of other megabenthos – a trend also observed by Koslow et al. (2001).  The wider evidence on the effects of abrasion and disturbance on other cold-water coral reefs, such as Lophelia reef (Fossa et al., 2002; Hall-Spencer et al., 2002; Rogers, 1999) also support this evidence.

Sensitivity assessment. There is significant evidence of damage by abrasion to Solenosmilia variabilis reef and other cold-water coral reefs caused by deep-sea trawling. Therefore, resistance is assessed as ‘None’, and resilience is ‘Very Low’, giving the biotope a sensitivity of ‘High’.

Penetration or disturbance of the substratum subsurface

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

Evidence

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

Sensitivity assessment. A resistance of ‘None’ has been given.  If the substratum were penetrated or disturbed, then the overlying reef would be affected.  The extremely long-lived (Hall-Spencer et al., 2002) and slow-growing nature (Gammon et al., 2018) of Solenosmilia variabilis, the characterizing species within this biotope, means that damage incurred would take a 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

As a suspension feeder, Solenosmilia variabilis relies upon the delivery of food particles (suspended solids) via currents. The known effects of varying amounts of suspended particles on Solenosmilia variabilis is limited to Davies et al. (2015). Their study suggested that Solenosmilia variabilis on Anton Dohrn Seamount was not effective at removing sediment from its polyps. Davies et al. (2015) observed the high accumulation of sediments in the reef where there was low current flow. They explain that the accumulation of sediment (which would be exacerbated with a change in WFD scale, e.g. from clear to intermediate or intermediate to medium) can smother polyps and cause tissue loss. Tissue loss can expose the coral skeleton, making it vulnerable to fouling.

Lophelia pertusa (another reef-forming cold-water coral species distributed in the North-East Atlantic and is similar to Solenosmilia variabilis) reef can withstand periodic fluctuation in turbidity over short temporal scales. Davies et al. (2009) consistently observed high loads of suspended matter transported by tidal currents over Lophelia pertusa reef (Mingulay Reef complex) during peak tides, enhancing the delivery of particles, including food, to the coral and associated fauna. This association between hydrodynamics, suspended particles and cold-water coral occurrence is also confirmed by Mienis et al. (2007) and Pearman et al. (2020).

Brooke et al. (2009) tested the tolerance of two Lophelia morphotypes, ‘brachycephala’ (heavily calcified) and ‘gracilis’ (fragile), to five different levels of turbidity in aquaria over 14 days. The results suggested that both Lophelia morphotypes were tolerant to ‘fairly heavy’ sediment conditions, but that mortality increased rapidly with higher sediment loads or longer burial time. Both morphotypes had 100% survival rates in clear conditions (<10 mg/l), and over 80% of Lophelia kept at intermediate turbidity conditions (10 –100 mg/l) survived. Two of the experimental turbidities fell within the medium turbidity WFD ranks; these were 103 mg/l and 245 mg/l.  In the former, both morphotypes had a survival rate of >50%, and the latter had a survival rate of >30%.  The ‘gracilis’ morphotype (fragile) experienced 100% mortality at the highest turbidity examined (ca 362 mg/l) while the ‘brachycephala’ morphotype had an extremely low survival rate (<10%).

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

A decrease in suspended material at the level of the benchmark could lead to a reduction in the availability of food. However, Larsson et al. (2013) reported that Lophelia was highly tolerant of living on minimal resources (food) for several months. In their experiments, Lophelia survived (100%) starvation for 28 weeks (Larsson et al., 2013).

Sensitivity assessment.  Direct evidence of the effects of suspended material on Solenosmilia variabilis is not available, but it is known that it is not resistant to high accumulation of sediments (Davies et al., 2015). Using Lophelia as a proxy, evidence suggests that a change in turbidity from clear to intermediate (10 mg/l to 10-100 mg/l) for a year could result in limited or some mortality. However, a change from intermediate to medium turbidity (100-300 mg/l) for a year could result in significant mortality depending on duration and the local hydrographic regime. For example, Brooke et al., (2009) demonstrated significant mortality after only 14 days at 103 and 245 mg/l.  Therefore, resistance is assessed as ‘Low’, resilience as ‘Very low’, and sensitivity is assessed as ‘High’ at the benchmark level.

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

There is limited evidence of the direct effects of smothering on Solenosmilia variabilis. Davies et al. (2015) suggest that Solenosmilia variabilis occurring on Anton Dohrn Seamount is not effective at removing sediment from its polyps. Davies et al. (2015) observed the high accumulation of sediments in the reef where there was low current flow. They explain that the accumulation of sediment – although the amount was not quantified – can smother polyps and cause tissue loss, which can expose the coral skeleton and make it vulnerable to fouling.

Direct evidence of the effect of smothering is available for Lophelia pertusa – another reef-forming cold-water coral species distributed in the North-East Atlantic and is similar to Solenosmilia variabilis. Rogers (1999) suggested that an increase in sedimentation would be likely to interfere with feeding, and therefore also growth. This would alter the balance between growth and bioerosion, resulting in potential degradation of the reef. However, more recent studies suggest that Lophelia pertusa are highly tolerant to living on minimal resources (food). Observations by Larsson et al. (2013) suggest that Lophelia pertusa is highly tolerant to starvation, with all polyps surviving starvation for 28 weeks (6 months).

Lophelia larvae would also be unable to settle on reefs smothered in soft sediment and, therefore, affect recruitment (Rogers, 1999). In addition, if high sediment loads occur during larval development, e.g. exposure to drill cuttings, all or part of the larval cohort may be lost (Jarnegren et al., 2017).

Larsson & Purser (2011) exposed Lophelia pertusa fragments to 6.5 (0.65 cm) and 19.0 mm (1.90 cm) of fine sediments (<63 µm drill cuttings) for three weeks. Under 6.5 mm conditions, 0.5% of polyps (1) died, whilst 3.7% of polyps died under 19.0 mm. Coral tissue was smothered and polyp mortality occurred where polyps became completely covered by material. Larsson & Purser (2011) concluded that the burial of coral by drill cuttings to the current threshold level used in environmental risk assessment models by the offshore industry (6.3 mm) may result in damage to colonies.

Allers et al. (2013) observed in laboratory experiments that sediment accumulates slowly on Lophelia because of its branching structure and mucus production. Under high sedimentation rates (462 mg/cm²) fragments were not completed covered by sediment, and no detrimental short-term effects from exposure to sediment were observed, despite reduced access to oxygen (as H₂S production was detected). These results suggest that Lophelia has some tolerance to low-oxygen and anoxic conditions for short periods. However, in further experiments, the complete burial of coral branches for >24 hrs in anoxic sediment resulted in suffocation. After removal, rinsing and 24 hrs recovery, these polyps were considered dead. Allers et al. (2013) concluded that Lophelia was resilient to sediment-induced oxygen stress, but that resilience is conditional. If polyps are completely covered and smothering is long-lasting (>24 hrs), then the coral will die. Naturally occurring sedimentation rates are less than those used in this study, but sedimentation from anthropogenic activities may be more comparable.

Sensitivity assessment. At this benchmark level, it is unlikely that the many Solenosmilia variabilis polyps will be severely affected because they are raised above the seabed. It is also likely that at this benchmark, a significant proportion of the deposited material will be re-suspended. However, if polyps remain buried for more than 24 hours, polyp mortality may occur. The resistance of this biotope to the pressure at the benchmark is assessed as ‘Medium’, resilience as ‘Very low’, and sensitivity is assessed as ‘Medium’.

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

There is limited evidence of the direct effects of smothering on Solenosmilia variabilis. Davies et al. (2015) suggest that Solenosmilia variabilis occurring on Anton Dohrn Seamount is not effective at removing sediment from its polyps. Davies et al. (2015) observed the high accumulation of sediments in the reef where there was low current flow. They explain that the accumulation of sediment – although the amount was not quantified – can smother polyps and cause tissue loss, which can expose the coral skeleton and make it vulnerable to fouling.

Direct evidence of the effect of smothering is available for Lophelia pertusa– another reef-forming cold-water coral species distributed in the North-East Atlantic and is similar to Solenosmilia variabilis. Rogers (1999) suggested that an increase in sedimentation would be likely to interfere with feeding, and therefore also growth. This would alter the balance between growth and bioerosion, resulting in potential degradation of the reef. However, more recent studies suggest that Lophelia pertusa are highly tolerant to living on minimal resources (food). Observations by Larsson et al. (2013) suggest that Lophelia pertusa is highly tolerant to starvation, with all polyps surviving starvation for 28 weeks (6 months).

Lophelia larvae would also be unable to settle on reefs smothered in soft sediment and, therefore, affect recruitment (Rogers, 1999). In addition, if high sediment loads occur during larval development, e.g. exposure to drill cuttings, all or part of the larval cohort may be lost (Jarnegren et al., 2017).

Larsson & Purser (2011) exposed Lophelia pertusa fragments to 6.5 (0.65 cm) and 19.0 mm (1.90 cm) of fine sediments (<63 µm drill cuttings) for three weeks. Under 6.5 mm conditions, 0.5% of polyps (1) died, whilst 3.7% of polyps died under 19.0 mm. Coral tissue was smothered and polyp mortality occurred where polyps became completely covered by material. Larsson & Purser (2011) concluded that the burial of coral by drill cuttings to the current threshold level used in environmental risk assessment models by the offshore industry (6.3 mm) may result in damage to colonies.

Allers et al. (2013) observed in laboratory experiments that sediment accumulates slowly on Lophelia because of its branching structure and mucus production. Under high sedimentation rates (462 mg/cm²) fragments were not completed covered by sediment, and no detrimental short-term effects from exposure to sediment were observed, despite reduced access to oxygen (as H₂S production was detected). These results suggest that Lophelia has some tolerance to low-oxygen and anoxic conditions for short periods. However, in further experiments, the complete burial of coral branches for >24 hrs in anoxic sediment resulted in suffocation. After removal, rinsing and 24 hrs recovery, these polyps were considered dead. Allers et al. (2013) concluded that Lophelia was resilient to sediment-induced oxygen stress, but that resilience is conditional. If polyps are completely covered and smothering is long-lasting (>24 hrs), then the coral will die. Naturally occurring sedimentation rates are less than those used in this study, but sedimentation from anthropogenic activities may be more comparable.

Sensitivity assessment. It can be assumed that the burial of Solenosmilia variabilis in 30 cm of sediment would cause considerable damage to the health of a reef.  If the sediment were to remain in place for more than 24 hours, polyps mortality is likely to occur. At the pressure benchmark, resistance is assessed as ‘Low’, resilience as ‘Very low’, and sensitivity as ‘High’. 

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

No evidence was found.

Underwater noise changes

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

Evidence

Species characterizing this habitat do not have hearing perception but vibrations may cause an impact. However, no evidence was found. Therefore, this pressure is assessed as ‘Not relevant’.

Introduction of light or shading

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

Evidence

Solenosmilia variabilis reef occurs at lower bathyal depths at which no light penetrates from the surface. Therefore, Solenosmilia variabilis reef is unlikely to be impacted by the introduction of light. As such, the biotope will not be affected by changes in the light regime and this pressure is assessed as ‘Not relevant’.

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

Solenosmilia variabilis has a planktonic larval stage and therefore connectivity and recruitment could be affected by a permanent or temporary barrier to propagule dispersal. However, no evidence is available to assess 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

Solenosmilia variabilis reefs are characterized by sessile invertebrates and are unlikely to be affected by an increased risk of collision as defined under the pressure. This pressure is therefore assessed as ‘Not relevant’.

Visual disturbance

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

Evidence

Solenosmilia variabilis reefs are characterized by invertebrates that are not reliant on vision, as such, the biotope will not be affected by 'Visual disturbance'. This pressure is assessed as ‘Not relevant’.

Genetic modification & translocation of indigenous species

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

Evidence

This pressure is not relevant to the characterizing species within this biotope.  Therefore, an assessment of ‘Not relevant’ has been given.

Introduction or spread of invasive non-indigenous species

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

Evidence

No alien or non-native species are known to compete with Solenosmilia variabilis or other cold-water corals.  As a result, ‘No relevant’ has been recorded.

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

No information on diseases was found in Solenosmilia variabilis. However, the parasitic foraminiferan Hyrrokkin sarcophaga was reported growing on polyps of Lophelia pertusa in aquaria (Mortensen, 2001). The foraminiferan dissolves a hole in the coral skeleton and invades the polyp. Two polyps became infested but did not seem to be influenced by the infestation (Mortensen, 2001). Any parasitic infestation is likely to reduce the viability of the host, even if only a few or possibly hundreds of polyps were affected but in the absence of additional evidence, an assessment of ‘No evidence has been given.

Removal of target species

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

Evidence

The characterizing species associated with Solenosmilia variabilis reef are not commercially targeted. Therefore, this pressure 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 strong evidence that Solenosmilia variabilis and other cold-water corals species are significantly impacted by bottom-fishing activities, within the North-East Atlantic and globally. Hall-Spencer et al. (2002) recorded Solenosmilia variabilis bycatch and photographed destroyed dead cold-water coral reefs on the West Ireland continental slope and in Norwegian waters. In addition, Durán Muñoz et al. (2012) found that in Hatton Bank, 0.1 to 25.7 kg of Solenosmilia variabilis was trawled as bycatch during 163 trawls. Extensive damage to Solenosmilia variabilis is also documented across New Zealand (Clark et al., 2019; Williams et al., 2010), with bycatch evidence (Anderson & Clark, 2003), and Tasmanian seamounts (Althaus et al., 2009; Clark & Rowden, 2009; Koslow et al., 2001; Williams et al., 2010). Althaus et al. (2009) reported that bottom-contact trawling on Tasmanian seamounts had reduced the bottom cover of Solenosmilia variabilis by two orders of magnitude over the previous decade.

Sensitivity assessment. Removal of Solenosmilia variabilis through bycatch is detrimental to the survivorship of the reef. As the characterizing species are sessile, Solenosmilia variabilis is unable to avoid the pressure. Coupled with its fragility, resistance is assessed as ‘None’. The resilience is assessed as ‘Very low’ as recovery when the pressure is fully removed, is slow (Clark et al., 2019). Therefore, sensitivity is assessed as ‘High’.