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

Psolus squamatus is widely distributed in the North Atlantic (from Svalbard, Iceland, south through the North Sea, into the Kattegat, and southern England, and Labrador south to the Bay of Fundy) and western Pacific from the Bering Sea, south to Mexico. A few records occur off the coasts of South Africa, Chile, Argentina and the Falkland Islands (OBIS, 2024). The majority of records have sea surface temperatures of ca 10 to 15°C (OBIS, 2024). However, sea surface temperatures are not relevant to deep water species.

For example, in the Rockall Trough, the deep water temperature and salinity are determined by the ocean currents, such as the Eastern North Atlantic Water, Wyville Thompson Ridge Overflow Water, the Labrador Sea Water and the Antarctic Bottom Water (Gage, 1986; Sherwin et al., 2012). Sherwin et al. (2012) reported that the temperature of the seawater in Rockall Trough was 10°C at ca 500 m and dropped to 5°C at ca 1,500 m (in October 2006). In addition, the North East Atlantic exhibits seasonal thermoclines and winter mixing but a permanent thermocline at ca 500 m (Tyler & Young, 1998). In the Rockall Trough, the seasonal thermocline develops at ca 200 m and winter mixing occurs to about 600 m, while the permanent thermocline extends from ca 800 m to ca 1,000 m (Gage, 1986). 

Psolus squamatus is recorded from 60 m to ca 1000 m in depth, although most records are from 180 m to ca 1000 m (OBIS, 2024) and is typical of the upper slope (200 m to 1000 m) holothurian fauna in the Porcupine Seabight (Billett, 1991; Wagstaff et al., 2014). Carney (2005) suggested that the upper slope from the shelf break to ca 500 m is an area of vertical food influx and possibly upwelling (depending on location) or influx from the adjacent shelf. The transition at about 1000 m is influenced by decreased cooling from the permanent thermocline and decreased food influx and sees the loss of most upper boundary species (Carney, 2005). 

Sensitivity assessment. No information on the temperature tolerances of adult or larval Psolus squamatus was found. Examples of this biotope were reported from ca 330 m to ca 1,345 m in UK waters (Weinberg et al., 2008; Roberts et al., 2008; Howell et al., 2010; Davies et al., 2015) and a similar biotope was reported at 170 to 370 m on the Oregon continental shelf (Hemery et al., 2018). On the Anton Dohr seamount the biotopes occurred from 4.3 to 7.9°C depending on location (Davies et al., 2015) and at a range of 7 to 10°C at several UK locations (Howell et al., 2010). At depth, and especially below the permanent thermocline, temperatures are likely to be stable and organisms are unlikely to be exposed to the range of temperatures and, in particular, the rapidity of temperature change experienced at the sea surface. Sherwin et al. (2012) reported that the seawater temperature of the upper 800 m of the Rockall Trough had fluctuated between ca 9.0 and 10.5°C from 1948 to 2010. While larvae may be tolerant of a range of temperatures, adults may be more stenothermal, but no direct evidence was found. Hence, while natural temperature changes are unlikely, exposure to localised thermal effluents at the benchmark level (e.g. from deep-sea installations or operations, however unlikely) may be detrimental. Therefore, resistance is assessed as 'Medium' as a precaution, albeit with 'Low' confidence. Resilience is probably 'Medium' so sensitivity is assessed as 'Medium'. 

Temperature decrease (local)

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

Evidence

Psolus squamatus is widely distributed in the North Atlantic (from Svalbard, Iceland, south through the North Sea, into the Kattegat, and southern England, and Labrador south to the Bay of Fundy) and western Pacific from the Bering Sea, south to Mexico. A few records occur off the coasts of South Africa, Chile, Argentina and the Falkland Islands (OBIS, 2024). The majority of records have sea surface temperatures of ca 10 to 15°C (OBIS, 2024). However, sea surface temperatures are not relevant to deep water species.

For example, in the Rockall Trough, the deep water temperature and salinity are determined by the ocean currents, such as the Eastern North Atlantic Water, Wyville Thompson Ridge Overflow Water, the Labrador Sea Water and the Antarctic Bottom Water (Gage, 1986; Sherwin et al., 2012). Sherwin et al. (2012) reported that the temperature of the seawater in Rockall Trough was 10°C at ca 500 m and dropped to 5°C at ca 1,500 m (in October 2006). In addition, the North East Atlantic exhibits seasonal thermoclines and winter mixing but a permanent thermocline at ca 500 m (Tyler & Young, 1998). In the Rockall Trough, the seasonal thermocline develops at ca 200 m and winter mixing occurs to about 600 m, while the permanent thermocline extends from ca 800 m to ca 1,000 m (Gage, 1986). 

Psolus squamatus is recorded from 60 m to ca 1000 m in depth, although most records are from 180 m to ca 1000 m (OBIS, 2024) and is typical of the upper slope (200 m to 1000 m) holothurian fauna in the Porcupine Seabight (Billett, 1991; Wagstaff et al., 2014). Carney (2005) suggested that the upper slope from the shelf break to ca 500 m is an area of vertical food influx and possibly upwelling (depending on location) or influx from the adjacent shelf. The transition at about 1000 m is influenced by decreased cooling from the permanent thermocline and decreased food influx and sees the loss of most upper boundary species (Carney, 2005). 

Sensitivity assessment. No information on the temperature tolerances of adult or larval Psolus squamatus was found. Examples of this biotope were reported from ca 330 m to ca 1,345 m in UK waters (Weinberg et al., 2008; Roberts et al., 2008; Howell et al., 2010; Davies et al., 2015) and a similar biotope was reported at 170 to 370 m on the Oregon continental shelf (Hemery et al., 2018). On the Anton Dohr seamount the biotopes occurred from 4.3 to 7.9°C depending on location (Davies et al., 2015) and at a range of 7 to 10°C at several UK locations (Howell et al., 2010). At depth, and especially below the permanent thermocline, temperatures are likely to be stable and organisms are unlikely to be exposed to the range of temperatures and, in particular, the rapidity of temperature change experienced at the sea surface. Sherwin et al. (2012) reported that the seawater temperature of the upper 800 m of the Rockall Trough had fluctuated between ca 9.0 and 10.5°C from 1948 to 2010. While larvae may be tolerant of a range of temperatures, adults may be more stenothermal, but no direct evidence was found. Hence, while natural temperature changes are unlikely, exposure to localised thermal effluents at the benchmark level (e.g. from deep-sea installations or operations, however unlikely) may be detrimental. Therefore, resistance is assessed as 'Medium' as a precaution, albeit with 'Low' confidence. Resilience is probably 'Medium' so sensitivity is assessed 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

This biotope is characterized by the sea cucumber Psolus squamatus. Echinoderms are osmoconformers and generally stenohaline due to their lack of an excretory organ, and their poor ability to osmoregulate (Binyon, 1966; Stickle & Diehl, 1987), while several species are recorded from extreme salinities (Stickle & Diehl, 1987; Russell, 2013). However, no information on the salinity tolerance of the characteristic species was found.  

Roberts et al. (2010b) suggested that hypersaline effluent dispersed quickly but was more of a concern at the seabed and in areas of low energy where widespread alternations in the community of soft sediments were observed. In several studies, echinoderms and ascidians were amongst the most sensitive groups examined (Roberts et al., 2010b). Fernández-Torquemada et al. (2013) suggested that echinoderms could be a useful early bioindicator for the effects of increased salinity.  In the Mediterranean, echinoderms were absent within one year in the areas affected by hypersaline effluent from a desalination plant but returned after dilution of the discharge with seawater (Fernández-Torquemada et al., 2013).

However, seawater salinity in the deep sea is more stable than inshore waters. For example, in the Rockall Trough, the deep water temperature and salinity are determined by ocean currents, such as the Eastern North Atlantic Water, Wyville Thompson Ridge Overflow Water, the Labrador Sea Water and the Antarctic Bottom Water (Gage, 1986; Sherwin et al., 2012). Sherwin et al. (2012) reported that the seawater salinity of the upper 800 m of the Rockall Trough had fluctuated between ca 35.25 and 35.45 from 1948 to 2010. Sherwin et al. (2012) reported that the salinity of the seawater in Rockall Trough was 35.4 at ca 500 m and dropped to 35.15 at ca 1,500 m (in October 2006).

Sensitivity assessment. The species that dominate this biotope (e.g. Psolus squamatus, sponges, and serpulid) are probably adapted to stable salinity conditions and have limited tolerance to salinity change. An increase in salinity from full to >40 psu is probably detrimental to the important characteristic species of the biotope. However, it is unlikely that this biotope would be exposed to hypersaline conditions (or effluent) unless from a newly opened brine seep or an unknown deep-sea operation. Although there is no direct evidence of the effects of hypersaline water on the characteristic species, the stenohaline nature of the echinoderms suggests that hypersaline conditions may cause mortality. Therefore, resistance is assessed as 'Low' but at Low confidence. Resilience would probably be 'Low' so sensitivity is 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

This biotope is characterized by the sea cucumber Psolus squamatus. Echinoderms are osmoconformers and generally stenohaline due to their lack of an excretory organ, and their poor ability to osmoregulate (Binyon, 1966; Stickle & Diehl, 1987), while several species are recorded from extreme salinities (Stickle & Diehl, 1987; Russell, 2013). However, no information on the salinity tolerance of the characteristic species was found.  

However, seawater salinity in the deep sea is more stable than inshore waters. For example, in the Rockall Trough, the deep water temperature and salinity are determined by ocean currents, such as the Eastern North Atlantic Water, Wyville Thompson Ridge Overflow Water, the Labrador Sea Water and the Antarctic Bottom Water (Gage, 1986; Sherwin et al., 2012). Sherwin et al. (2012) reported that the seawater salinity of the upper 800 m of the Rockall Trough had fluctuated between ca 35.25 and 35.45 from 1948 to 2010. Sherwin et al. (2012) reported that the salinity of the seawater in Rockall Trough was 35.4 at ca 500 m and dropped to 35.15 at ca 1,500 m (in October 2006). 

Sensitivity assessment. The species that dominate this biotope (e.g. Psolus squamatus, sponges, and serpulid) are probably adapted to stable salinity conditions and have limited tolerance to salinity change. An increase in salinity from full to >40 psu is probably detrimental to the important characteristic species of the biotope. However, it is unlikely that this biotope would be exposed to hypersaline conditions (or effluent) unless from a newly opened brine seep or an unknown deep-sea operation. Although there is no direct evidence of the effects of hypersaline water on the characteristic species, the stenohaline nature of the echinoderms suggests that hyposaline conditions may cause mortality. Therefore, resistance is assessed as 'Low' but at Low confidence. Resilience would probably be 'Low' so sensitivity is 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

Psolus squamatus and the other characteristic species are suspension feeders, dependent on current flow to transport or resuspend organic particulates or phytodetritus. Psolus squamatus is recorded from 60 m to ca 1000 m in depth, although most records are from 180 m to ca 1000 m (OBIS, 2024) and is typical of the upper slope (200 m to 1000 m) holothurian fauna in the Porcupine Seabight (Billett, 1991; Wagstaff et al., 2014). Carney (2005) suggested that the upper slope from the shelf break to ca 500 m is an area of vertical food influx and possibly upwelling (depending on location) or influx from the adjacent shelf. The transition at about 1000 m is influenced by decreased cooling from the permanent thermocline and decreased food influx and sees the loss of most upper boundary species (Carney, 2005). 

Deep sea habitats are probably dominated by mass water transport due to oceanic currents. For example, water flow in the Rockall Trough is dominated by the Eastern North Atlantic Water, Wyville Thompson Ridge Overflow Water, the Labrador Sea Water and the Antarctic Bottom Water (Gage, 1986; Sherwin et al., 2012), except near Feni Ridge or Anthon Dohrn seamount which are also influenced by tidal oscillation. Gage (1986) reported Psolus squamatus from the top of the current swept Anton Dohr Seamount and Psolus sp. from Ferni Ridge. Gage (1986) reported maximum flow rates of ca 0.5 m/s within 150 m of the bottom on the Feni Ridge west of the Anthon Dohrn seamount, mostly due to tidal oscillation, and associated with current-moulded bedforms (e.g. ripples). However, lower tidal currents <0.05 m/s with a maximum of ca 0.21 m/s were recorded within 400-500 m of the bottom elsewhere. Wienberg et al. (2008) described assemblages of Psolus sp., serpulids and bryozoans on gravel to large boulder-sized fields of 'dropstones', mainly on soft sediment on the flanks of the Franken Mound, Rockall Bank. Wienberg et al. (2008) noted that the eastern flank of Franken Mound was subject to strong but variable bottom currents, indicated by extensive areas of soft sediment, exhumed dropstones, rocky outcrops, and mobile rippled sediment, characteristic of active sediment transport. Flow speeds in the Rockall Trough are typically 0.15 to 0.3 m/s (Wienberg et al., 2008) but localised flow over mounds, sea mount and other physical features probably affect local currents. 

Sensitivity assessment. These biotopes are characterized by hard substrata (rocky outcrops, boulders, pebbles and gravel) on coarse or mobile sediments. A localized change in water flow of 0.1 to 0.2 m/s (the benchmark) might reduce the suitability of the habitat for the suspension feeders but also might be insignificant in the "strong but variable currents" suggested by Wienberg et al. (2008). The benchmark level of change lies within the range of water flow velocities recorded in parts of the Rockall Trough but no information on flow rates at the seabed was available. Therefore, there is insufficient evidence on which to base an assessment. 

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

This deep-sea biotope is not exposed to changes in emersion. 

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

These deep-sea biotopes are recorded from the upper and mid bathyal and will not be affected by changes in nearshore wave exposure.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

Bryan (1984) reported that early work had shown that echinoderm larvae were sensitive to heavy metals, e.g. the intolerance of larvae of Paracentrotus lividus to copper (Cu) had been used to develop a water quality assessment. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu) and heavy metals caused reproductive anomalies in the starfish Asterias rubens (Besten, et al., 1989, 1991). Sea urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Crompton (1997) reported that mortalities occurred in echinoderms after 4-14 day exposure to above 10-100 µg/l Cu, 1-10 mg/l Zn and 10-100 mg/l Cr but that mortalities occurred in echinoderm larvae above10-100 µg/ l Ni.

Sensitivity assessment. No evidence of the effects of transitional metals or organometal on the characteristic sea cucumbers or other species was found. However, evidence from other echinoderms suggests that the dominant sea cucumber in this biotope is also likely to be adversely affected by transitional metals. Therefore, resistance is assessed as 'Low', so resilience is probably 'Medium' and sensitivity is assessed as 'Medium', albeit with 'Low' confidence due to lack of directly relevant evidence. Further evidence is required for this pressure.

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

Sea urchins, especially the eggs and larvae are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Therefore, echinoderms, especially their larvae, may be sensitive to a range of contaminants. Echinoderms seem especially intolerant of the toxic effects of oil, likely because of the large amount of exposed epidermis (Suchanek, 1993).

Sea urchin eggs showed developmental abnormalities when exposed to 10-30 mg/l of hydrocarbons and crude oil: Corexit dispersant mixtures have been shown to cause functional loss of tube feet and spines in sea urchins (Suchanek, 1993). Olsgard & Gray (1995) found the brittlestar Amphiura filiformis very sensitive to oil pollution. During monitoring of sediments in the Ekofisk oilfield, Addy et al. (1978) suggest that reduced abundance of Amphiura filiformis within 2-3 km of the site was related to discharges of oil from the platforms and to physical disturbance of the sediment. Although acute toxicity tests showed that drill cuttings containing oil-based muds had a very low toxicity (LC50 52,800 ppm total hydrocarbons in test sediment), Newton & McKenzie (1998) suggest these are poor predictors of chronic response. Chronic sub-lethal effects were detected around the Beryl oil platform in the North Sea where the levels of oil in the sediment were very low (3 ppm) and Amphiura filiformis was excluded from areas nearer the platform with higher sediment oil content. Similarly, in Ophiothrix fragilis, exposure to 30,000 ppm oil reduces its load of symbiotic bacteria by 50% and brittle stars begin to die (Newton & McKenzie, 1995).

Crude oil from the Torrey Canyon and the detergent used to disperse it caused mass mortalities of echinoderms; Asterias rubens, Echinocardium cordatum, Psammechinus miliaris, Echinus esculentus, Marthasterias glacialis and Acrocnida brachiata (Smith, 1968). Large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m in the vicinity of Sennen after the Torrey Canyon oil spill, presumably due to a combination of wave exposure and heavy spraying of dispersants in that area (Smith 1968). Smith (1968) also demonstrated that 0.5 to 1 ppm of the detergent BP1002 resulted in developmental abnormalities in echinopluteus larvae of Echinus esculentus. Echinus esculentus populations in the vicinity of an oil terminal in A Coruna Bay, Spain, showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gomez & Miguez-Rodriguez 1999). However, the observed effects may have been due to a single contaminant or synergistic effects of all present.

A study by Brils et al. (2002) into the toxicity of C10-19 hydrocarbons found that the shallow irregular echinoid Echinocardium cordatum was susceptible to oil-contaminated sediments at as low as 190 mg/kg dry weight of Echinocardium cordatum. The high intolerance of Echinocardium cordatum to hydrocarbons was seen by the mass mortality of animals, down to about 20 m, shortly after the Amoco Cadiz oil spill (Cabioch et al., 1978). Reduced abundance of the species was also detectable up to >1,000 m away one year after the discharge of oil-contaminated drill cuttings in the North Sea (Daan & Mulder, 1996).  The polyaromatic hydrocarbon (PAH) fluoranthene was shown to cause mortality in larvae of Arbacia punctulata (purple-spined sea urchin) with 48-hour LC50 of 3.9 µg/l in the presence of UV light (Spehar et al., 1999). 

TBT was shown to inhibit arm regeneration in the brittlestar Ophioderma brevispina, at 10 ng/l and produce significant inhibition at 100 ng/l. It was suggested that TBT acts via the nervous system, although direct action on the tissues at the point of breakage could not be excluded (Bryan & Gibbs, 1991)

Sensitivity assessment. No evidence of the effects of hydrocarbon or PAH contamination on the characteristic echinoderms was found. However, evidence from other echinoderms, suggests that the dominant sea cucumbers in this biotope are also likely to be adversely affected by hydrocarbon or PAH exposure. Therefore, resistance is assessed as 'Low', so resilience is probably 'Medium' and sensitivity is assessed as 'Medium', albeit with 'Low' confidence due to lack of directly relevant evidence. Further evidence is required for this pressure.

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

Little information on the toxicity of synthetic chemicals to holothurians was found. Newton & McKenzie (1995) suggested that echinoderms tend to be very intolerant of various types of marine pollution but gave no detailed information. Cole et al. (1999) reported that echinoderm larvae displayed adverse effects when exposed to 0.15 mg/l of the pesticide Dichlorobenzene (DCB). Smith (1968) demonstrated that 0.5 -1 ppm of the detergent BP1002 resulted in developmental abnormalities in echinopluteus larvae of Echinus esculentus. Therefore, holothurians and their larvae may also be intolerant of synthetic chemicals.

Sensitivity assessment. Little evidence of the effects of synthetic contamination on the characteristic urchins was found. There is 'Insufficient evidence' above to support an assessment and further evidence is required for this pressure.

Radionuclide contamination

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

Evidence

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

No evidence was found.

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

Lawrence (1996) reported mass mortality of echinoderms in the Gulf of Trieste due to hypoxia caused by a strong thermocline combined with high pelagic productivity and eutrophication. The brittlestar Ophiura quinquemaculata was killed within a few days, and holothurians including Ocnus planci (as Cucumaria planci), starfish Asteropecten sp. and the remaining brittlestars were killed within a week. In experiments, Amphiura filiformis only left its protected position in the sediment when oxygen levels fell below 0.85mg/l (Rosenberg et al., 1991). Mass mortality of Amphiura filiformis was observed during severely low oxygen events (<0.7 mg/l) (Nilsson, 1999). However, at oxygen concentrations between 0.85 mg/l and 1.0 mg/l Rosenberg et al. (1991) observed the species survived for several weeks. Echinoderms were shown to be intolerant of the effects of algal blooms, resulting in mortalities of the sea urchins Echinus esculentus and Paracentrotus lividus, and the holothurian Labidoplax digitata amongst other echinoderms, probably due to hypoxia caused by death of the algal bloom algae (Boalch, 1979; Forster, 1979; Griffiths et al., 1979; Lawrence, 1996). Vaquer-Sunyer & Duarte (2008) suggested a median sublethal oxygen concentration of 1.22 mg O₂/l (± 0.25) for a number of echinoderms reviewed in their study. Echinoderms were neither the most nor the least sensitive of the taxonomic groups examined.  Riedel et al. (2012) examined the effects of hypoxia and anoxia on macrofauna in the North Adriatic, using in situ experimental apparatus.  They concluded that decapods, echinoderms and polychaetes were among the most sensitive to hypoxia while ascidians and anthozoans were among the most resistant of the species encountered in their study. 

Sensitivity assessment. Overall, the above evidence suggests echinoderms are intolerant of hypoxic conditions. However, In the deep sea oxygen levels are probably determined by mass transport of water by deep currents. For example, Ellett & Martin (1973) reported that the dissolved oxygen levels in the Rockall Trough varied between ca 5 and 6 ml/l (ca 7 and 8.4 mg/l) between the surface and ca 2,000 m in depth. In addition, the short-term acute hypoxia, represented by the benchmark, may also be mitigated by the large water masses and strong currents typical of areas in which these biotopes occur. Therefore, resistance is assessed as ‘Medium’ to represent some mortality under the worst-case scenario. Hence, resilience is assessed as ‘Medium' and sensitivity as 'Medium' but with 'Low' confidence. 

Nutrient enrichment

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

Evidence

Psolus squamatus is typical of the upper slope (200 m to 1000 m) holothurian fauna in the Porcupine Seabight (Billett, 1991; Wagstaff et al., 2014). This zonation is typical of marine invertebrates in deep-sea habitats and corresponds to the upper boundary biota identified by Carney (2005). Carney (2005) suggested that the upper slope from the shelf break to ca 500 m is an area of vertical food influx and possibly upwelling (depending on location) or influx from the adjacent shelf.  These biotopes are probably dependent on seasonal phytodetritus and suspended organic particulates. For example, Maier et al. (2023) concluded that local hydrography produces periodic pulses of food due to internal waves operating on seasonal, multi-year, decadal or millennial cycles, with currents that interact with the deep-sea topography (such as sea mounts, continental shelf margins, fjord sills) or cold-water reefs to form internal waves, hydraulics jumps and trapped waves. The resultant downwelling can rapidly transport surface productivity (such as plankton or POM) to the reef (Maier et al., 2023). For example, fresh organic matter can be transported from the surface in less than one hour to 140 m on Mingulay Reef (reviewed by Maier et al., 2023). Internal waves also resuspend deposited organic matter into the bottom or intermediate layers (Maier et al., 2023). Similarly, the nutrient levels (e.g. nitrates, phosphates, and ammonia) and inorganic carbon in the vicinity of cold-water coral reefs in the North East Atlantic vary with the tidal cycle and depth (Findlay et al., 2014). 

However, no evidence of the nutrient levels typical of these biotopes was found and no information on the effect of nutrient enrichment on the characteristic species was found. Therefore, 'No evidence' is recorded. 

Organic enrichment

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

Evidence

Psolus squamatus is typical of the upper slope (200 m to 1000 m) holothurian fauna in the Porcupine Seabight (Billett, 1991; Wagstaff et al., 2014). This zonation is typical of marine invertebrates in deep-sea habitats and corresponds to the upper boundary biota identified by Carney (2005). Carney (2005) suggested that the upper slope from the shelf break to ca 500 m is an area of vertical food influx and possibly upwelling (depending on location) or influx from the adjacent shelf.  These biotopes are probably dependent on seasonal phytodetritus and suspended organic particulates. For example, Maier et al. (2023) concluded that local hydrography produces periodic pulses of food due to internal waves operating on seasonal, multi-year, decadal or millennial cycles, with currents that interact with the deep-sea topography (such as sea mounts, continental shelf margins, fjord sills) or cold-water reefs to form internal waves, hydraulics jumps and trapped waves. The resultant downwelling can rapidly transport surface productivity (such as plankton or POM) to the reef (Maier et al., 2023). For example, fresh organic matter can be transported from the surface in less than one hour to 140 m on Mingulay Reef (reviewed by Maier et al., 2023). Internal waves also resuspend deposited organic matter into the bottom or intermediate layers (Maier et al., 2023). Similarly, the nutrient levels (e.g. nitrates, phosphates, and ammonia) and inorganic carbon in the vicinity of cold-water coral reefs in the North East Atlantic vary with the tidal cycle and depth (Findlay et al., 2014). 

However, no evidence of the organic carbon levels typical of these biotopes was found and no information on the effect of organic enrichment on the characteristic species was found. Therefore, 'No evidence' is recorded. 

Physical loss (to land or freshwater habitat)

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

Evidence

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

The loss of hard substrata and its replacement with sediment would cause the biotope to be lost. In addition, the mechanical removal of hard substratum would destroy any characterizing organisms present and ultimately result in the loss and reclassification of the biotope. Therefore, resistance is assessed as 'None'. As this pressure is considered a permanent change, resilience is assessed as 'Very Low', and sensitivity is assessed as 'High'.

Physical change (to another sediment type)

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

Evidence

The loss of hard and mixed substrata and its replacement with sediment alone would cause the biotope to be lost. In addition, the mechanical removal of hard substratum would destroy any characterizing organisms present and ultimately result in the loss and reclassification of the biotope. Therefore, resistance is assessed as 'None'. As this pressure is considered a permanent change, resilience is assessed as 'Very Low', and sensitivity is assessed as 'High'.

Habitat structure changes - removal of substratum (extraction)

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

Evidence

The important characteristic epifauna (Psolus squamatus) position themselves on stones, pebbles, shells, and other hard substrata to avail themselves of the passing current. the other suspension-feeding brittlestars may do the same. The extraction of sediment to a depth of 30 cm would remove the infauna, surface hard substrata such as dropstones, cobbles and pebbles, remove or relocate boulders and, hence,  the characteristics surface epifauna of sea cucumbers, ophiuroids, sponges, serpulids, anomiids in the affected area.  Therefore, a resistance of 'None' is suggested based on expert judgment. Resilience is probably 'Medium' so the sensitivity is assessed as 'Medium'. 

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

Erect epifaunal species are particularly vulnerable to physical disturbance (Jennings & Kaiser, 1998). Veale et al. (2000) reported that the abundance, biomass, and production of epifaunal assemblages decreased with increasing fishing effort. Mobile gears also result in modification of the substratum, including the removal of shell debris, cobbles and rocks, and the movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998) on which many of the species in this community depend. Picton & Goodwin (2007) noted that an area of boulders with a rich fauna of sponges and hydroids on the east coast of Rathlin Island, Northern Ireland was significantly altered since the 1980s.  Scallop dredging had begun in 1989 and boulders were observed to have been turned and the gravel harrowed. In addition, many of the boulders had disappeared and rare hydroid communities were greatly reduced (Picton & Goodwin, 2007). Prior records indicated the presence of large sponges, mainly Axinella infundibuliformis (Picton & Goodwin, 2007). Freese (2001) studied deep cold-water sponges in Alaska a year after a trawl event;  46.8% of sponges exhibited damage with 32.1% having been torn loose.  None of the damaged sponges displayed signs of regrowth or recovery.  This was in stark contrast to early work by Freese et al. (1999) on shallow sponge communities, with impacts of trawling activity being much more persistent due to the slower growth/regeneration rates of deep, cold-water sponges. 

Sensitivity assessment. No evidence of the effects of fishing activities on these deep-sea biotopes was found. However, the above evidence from shallow sea demonstrates that bottom trawling can relocate and turn boulders, and relocate or remove cobbles, pebbles and presumably 'dropstones' that are required for the development of this community. The resultant abrasion and disturbance may kill or break up sponges, in particular, although it is unclear if Psolus squamatus would survive or be displaced. Nevertheless, the removal of hard substratum (boulders, pebbles etc.) would result in the loss of suitable habitat. Therefore, resistance is assessed as 'Low'. Resilience is probably 'Medium', so sensitivity is assessed as 'Medium'. 

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

The effects of penetrative fishing gear on the biotope are probably at least as severe as surface abrasion above.  Therefore, resistance is assessed as 'Low'. Resilience is probably 'Medium', so sensitivity is assessed as 'Medium'. 

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

The SpaEnc.PsoSpo and SpaEnc.PsoAno biotopes are defined by the abundance of Psolus squamatus and hard substrata (bedrock, boulders, and cobbles) and sparse encrusting species; sponges in PsoSpo and saddle oysters and serpulids in PsoAno (JNCC, 2022). No information on the ecology of this habitat was found. However, the lack of long-lived species on the available hard substrata suggests the current flow does not support large sponge or cold-water corals and that the habitat is exposed to periodic disturbance, probably due to sediment mobility, scour and burial. The habitat is characterized by exposed rock outcrops amongst sediment, or mixed hard substratum (boulders, pebbles, and gravel etc.) on the surface of potentially mobile sediment (Wienberg et al., 2008; Roberts et al., 2008; Davis et al., 2015). 

Sensitivity assessment. The characteristic species are suspension feeders so a decrease in suspended particulates could be detrimental but possibly seasonal (see Maier et al., 2023). However, the physical nature of the habitat suggests that it could be subject to periodic sediment resuspension, mobility and burial.  Therefore, resistance is assessed as 'Medium' assuming that a reduction in suspended particulates may reduce the food supply for the characteristic species but with 'Low' confidence due to the lack of evidence. Hence, resilience is assessed as 'Medium' and sensitivity as 'Medium'. 

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

The SpaEnc.PsoSpo and SpaEnc.PsoAno biotopes are defined by the abundance of Psolus squamatus and hard substrata (bedrock, boulders, and cobbles) and sparse encrusting species; sponges in PsoSpo and saddle oysters and serpulids in PsoAno (JNCC, 2022). No information on the ecology of this habitat was found. However, the lack of long-lived species on the available hard substrata suggests the current flow does not support large sponge or cold-water corals and that the habitat is exposed to periodic disturbance, probably due to sediment mobility, scour and burial. The habitat is characterized by exposed rock outcrops amongst sediment, or mixed hard substratum (boulders, pebbles, and gravel etc.) on the surface of potentially mobile sediment (Wienberg et al., 2008; Roberts et al., 2008; Davis et al., 2015). 

Sensitivity assessment. The physical nature of the habitat suggests that it could be subject to periodic sediment resuspension, mobility and burial.  In areas of strong current flow, burial may be short-term. If this assumption is correct, and the habitat is structured by periodic smothering, then resistance is assessed as 'High' but with 'Low' confidence due to the lack of evidence. Hence, resilience is assessed as 'High' and sensitivity as 'Not sensitive'. 

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

The SpaEnc.PsoSpo and SpaEnc.PsoAno biotopes are defined by the abundance of Psolus squamatus and hard substrata (bedrock, boulders, and cobbles) and sparse encrusting species; sponges in PsoSpo and saddle oysters and serpulids in PsoAno (JNCC, 2022). No information on the ecology of this habitat was found. However, the lack of long-lived species on the available hard substrata suggests the current flow does not support large sponge or cold-water corals and that the habitat is exposed to periodic disturbance, probably due to sediment mobility, scour and burial. The habitat is characterized by exposed rock outcrops amongst sediment, or mixed hard substratum (boulders, pebbles, and gravel etc.) on the surface of potentially mobile sediment (Wienberg et al., 2008; Roberts et al., 2008; Davis et al., 2015). 

Sensitivity assessment. The physical nature of the habitat suggests that it could be subject to periodic sediment resuspension, mobility and burial.  In areas of strong current flow, burial may be short-term. If this assumption is correct, and the habitat is structured by periodic smothering, then resistance is assessed as 'High' but with 'Low' confidence due to the lack of evidence. Hence, resilience is assessed as 'High' and sensitivity as 'Not sensitive'. 

Litter

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

Evidence

No evidence could be found regarding the introduction of litter on this biotope

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

This biotope is characterized by invertebrates with no known means to detect noise, which will not be affected by changes in underwater noise, as defined under this pressure.

Introduction of light or shading

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

Evidence

This biotope is characterized by invertebrates with limited ability to detect light and is aphotic.

Barrier to species movement

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

Evidence

The benthic lifestyle and widespread deep-sea habitat of the characteristic species mean they will not be affected by barriers as defined under this pressure. Physical and hydrographic barriers may limit the dispersal of larvae but larval dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

This biotope is characterized by benthic invertebrates that are not at risk of collision with artificial structures. It might be affected adversely by falling marine debris such as barrels, containers, and even shipwrecks but the effects are probably addressed under 'abrasion' above. 

Visual disturbance

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

Evidence

This biotope is characterized by invertebrates that do not rely on visual cues and will not be affected by visual disturbance, as defined under this pressure.

Genetic modification & translocation of indigenous species

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

Evidence

No evidence was found to suggest that any of the characteristic species were subject to translocation or genetic modification, nor the introduction of genetically distinct organisms. 

Introduction or spread of invasive non-indigenous species

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

Evidence

No information on the effect of the introduction of one or more invasive non-indigenous species on this biotope was found.

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 the effect of pathogens or disease on the characterizing species was found.

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 of these biotopes are not targeted by commercial or recreational fisheries.

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

The physical effects of fisheries or dredging activities are addressed under abrasion, penetration and extraction pressures above. No clear biological relationships between the important characteristic species were found. Therefore, the removal of any one species may not affect other members of the community adversely.  However, if the important characterizing species were removed as by-catch, the character of the biotope would change. A significant decline in the abundance of Psolus squamatus would result in the loss of the biotope as recognised by the habitat classification. Therefore, a resistance of 'Medium' is recorded, albeit at Low confidence. As resilience is probably 'Medium' sensitivity is assessed as 'Medium'.