Gracilechinus alexandri, Psilaster and Plinthaster assemblage on Atlantic upper abyssal mud

Summary

UK and Ireland classification

Description

This biotope consists of urchin Gracilechinus alexandri with seastars on mud substrata. Gage (1986) describes an assemblage from the continental slope west of the Hebrides (Rockall Trough) between 1,400 and 2,500m on pelagic ooze and terbidite dominated by echinoderms. The same epifaunal assemblage is also found in the lower bathyal but associated infauna are likely to differ. The characterizing species listed refer to all Gracilechinus alexandriPsilaster and Plinthaster assemblages not just those found associated with the zone and substratum specified in this biotope.

Depth range

2100-3100 m

Additional information

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Listed By

- none -

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

The biotopes formed by the urchin Gracilechinus alexandri with Psilaster and Plinthaster seastars occur on mud at a range of depths in the Atlantic deep-sea. Assemblages occur on mud within the lower bathyal zone (M.AtLB.Mu.UrcCom.GraAle biotope) and upper abyssal zone (M.AtUA.Mu.UrcCom.GraAle biotope). The sensitivity of these Gracilechinus alexandri, Psilaster and Plinthaster biotopes is therefore 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 predominant species for the biotopes are the urchin Gracilechinus alexandri and the seastars Psilaster and Plinthaster, specifically Persephonaster patagiatus (previously known as Psilaster patagiatus) and Plinthaster dentatus. Loss of these species may result in loss or degradation of the bi­­otope. Therefore, the sensitivity of the biotope is dependent on the sensitivity of these species alone.

Other species present in the assemblages can include the crustaceans Munidopsis curvirostra, Polycheles sculptus, and Neolithodes grimaldii, and the sea snails Colus jeffreysianus and Troschelia berniciensis. As these are all ubiquitous organisms and are not unique to these biotopes, they are not considered significant to the assessment of sensitivity. Furthermore, the presence of all these species is not essential for the classification of these biotopes. More information on many of these species can be found in other biotope assessments available on this website.

Resilience and recovery rates of habitat

Limited information on the biology and development of Gracilechinus alexandri (syn. Echinus alexandri) was found. Tyler (1986) suggested that Gracilechinus alexandri reproduced seasonally and released larvae. Tyler & Gage (1986) suggested that the reproductive cycle of Gracilechinus alexandri and Gracilechinus acutus norvegicus was similar to that of Gracilechinus affinis, albeit based on a limited number of samples. Gracilechinus affinis has a minimum larval life of 89 days and exhibits a distinct seasonality with the oogenesis initiated in winter followed by vitellogenesis in summer. Spawning in both Gracilechinus affinis and Echinus esculentus occurs at the same time, in late winter to spring of the following year (Gage et al.,1986). Gracilechinus acutus norvegicus was reported to spawn a little later than Gracilechinus affinis. However, Tyler & Gage (1986) suggested the gametic cycle of Gracilechinus alexandri and Gracilechinus acutus norvegicus was similar to that of Gracilechinus affinis. Their gametogenic and spawning cycle is thought to be related to the arrival of phytodetrital material from surface primary production. Gage et al. (1986) ran analyses of oocyte-size-frequencies of female Gracilechinus (as Echinus) acutus norvegicus and Gracilechinus elegans and found that spawning was possible in March and a seasonal cycle in oogenesis. A conservative estimate of the distance travelled in a unidirectional flow by larvae of Gracilechinus affinis was reported as 370 km. All species of Gracilechinus have been found to produce a similar sized ovum (100 µm diameter) (Tyler, 1986; Tyler & Gage, 1986).

One of the main physiological variations between Gracilechinus species was the response of early embryos to pressure. Tyler & Young (1998) discovered that the eggs of Gracilechinus acutus var norvegicus developed at pressures of up to 150 atm, whereas the embryos of Gracilechinus affinis required higher pressure for successful early embryogenesis and failed to develop at lower pressures. Embryos of Gracilechinus acutus norvegicus also show a greater tolerance to a range of temperatures and pressures compared to that of Gracilechinus acutus from shallow subtidal habitats (Tyler & Young, 1998; Villalobos et al., 2006). Gracilechinus alexandri has a similar depth range compared with Gracilechinus affinis (that is ca 1,200 to 2,400 m compared to ca 1,600 to 2,600 m respectively; Gage, 1986) so their larvae may show similar behaviour, although no evidence was found.

Gage & Tyler (1985) suggest that successful settlement of juvenile Gracilechinus affinis following their planktonic larval stage may be very rare, with post-larvae observed in only one year of the ten years in which samples were obtained from the Rockall Trough. They noted that other deep-sea urchins had been reported to exhibit unpredictable recruitment. The distribution of size classes was consistent with a series of years of unsuccessful recruitment followed by a series of successful ones. They also noted that Graciliechinus (as Echinusaffinis in Rockall Trough was slow-growing and long-lived compared to other sea urchins then known (Gage & Tyler, 1985). Gage (1986) also suggested that Graciliechinus (as Echinusaffinis was probably subject to low mortality in Rockall.

Growth and longevity of Gracilechinus acutus var. norvegicus and Gracilechinus elegans are intermediate between that of Gracilechinus affinis and Echinus esculentus, suggesting that these life-history traits may be related to the greatly differing depth range of the species (Gage et al., 1986). Gracilechinus affinis has a slightly deeper depth range than Gracilechinus elegans, and hence a slower growth rate. Growth bands in Gracilechinus affinis are formed in response to the annual deposition of phytodetritus to the deep-sea floor. Any seasonal changes in food supply to urchin populations can therefore cause variations in growth. Gracilechinus affinis is a deposit feeder, grazing on deposited phytodetritus on the deep-sea floor. Larger urchins may be able to cope with food particles too large for smaller urchins to feed on, so larger urchins have greater effective food availability and thus achieve greater assimilation rates. Therefore, the food available to individual urchins changes with their size. There appears to be no significant growth reaching an asymptotic level with increasing age, nor is there any sign of growth in volume slowing with age for Gracilechinus affinis (Middleton et al.,1998). Middleton et al. (1998) reported an initial period of very slow growth lasting until about year four of development, followed by a period where growth appeared essentially linear. The transition between these two phases of growth appears to be roughly coincident with the onset of sexual maturity (Middleton et al.,1998). Rather than saturating growth in volume in mature urchins by allocating an increasing proportion of net assimilate to reproduction, growth in Gracilechinus affinis is linear (Middleton et al., 1998). For Gracilechinus elegans there is an accelerating phase of growth amongst smaller sizes. Gracilechinus acutus var norvegicus has slow growth and can take 20 years to reach maximum size (Gage et al., 1986). Whereas, Gracilechinus elegans can reach maximum size at 10 years (Gage et al., 1985). Gage et al. (1986) concluded that both species showed variation in size structure that was unrelated to bathymetry or time of year.

Information on feeding behaviour for Gracilechinus alexandri is restricted to a diet study conducted by Stevenson & Mitchell (2016). Gut contents showed that Gracilechinus alexandri fed on sediment but also preyed on cold-water corals Lophelia pertusa and Madrepora oculata, in the NE Atlantic (Stevenson & Mitchell, 2016). In particular, Stevenson & Mitchell (2016) noted that seasonal phytodetritus was used to form reproductive tissue.

Two other echinoderm species characterize the biotopes: Persephonaster patagiatus (syn. Psilaster patagiatus) and Plinthaster dentatus. Both species are sea stars from the family Astropectinidae. This family typically adopts an infaunal mode of life and is found at a wide range of depths globally. They are typically predators, using a feeding mechanism which allows them to swallow prey intact (Christensen, 1970). Persephonaster patagiatus has been recorded widely throughout the North Atlantic but is also present in the Caribbean Sea and the Gulf of Mexico. Persephonaster patagiatus adults are most abundant at depths between 1,650 m and 1,750 m, but can be found between 1,650 m and 2,500 m( Howell et al., 2002). Howell et al. (2002) note that the maximum abundance of Persephonaster patagiatus found was six individuals per hectare.

Species-specific studies on Persephonaster patagiatus and Plinthaster dentatus are limited, so evidence has been taken from congeneric or co-familiar species. Tyler & Pain (1982) reported that Psilaster andromeda, had a relatively low fecundity and formed large eggs, indicative of direct lecithotrophic development, although no evidence of brooding was found. Tyler & Pain (1982) also found that Psilaster andromeda did not demonstrate reproductive synchrony. Persephonaster patagiatus may adopt a similar reproductive strategy to its co-familiar Psilaster andromeda. However, Tyler & Pain (1982) also reported that other Astropectinidae, Dytaster insignis and Plutonaster bifrons produced numerous small eggs, and were probably planktotrophic with reproduction synchronized with the seasonal influx of surface productivity. Tyler & Pain (1982) noted that the population of Plutonaster bifrons was dominated by large size classes (5.5 to 9 cm), which was probably explained by rapid juvenile growth.

Information on the biology of Plinthaster dentatus is lacking. Howell et al. (2002) reported that adult Plinthaster dentatus were most abundant between depths of 1,650 and 1,740 m (the same depth as Persephonaster patagiatus). However, unlike Persephonaster patagiatus, juveniles were also found during sampling at depths between 1,130 m and 4,045 m (Howell et al., 2002). Sumida et al. (2001) described the early growth of Plinthaster dentatus as isometric, meaning all body parts remain proportionate. Both Sumida et al. (2001) and Howell et al. (2002) suggest that juveniles have a larger depth range than adults, which may point to both depth and diet shifts throughout development. However, specific work on Plinthaster dentatus is sparse. Deep-sea species from the same family as Plinthaster dentatus, the Goniasteridae, may provide insight into the reproductive biology of the species. Paragonaster subtilis and Pseudarchaster parelii are deep-sea species belonging to Goniasteridae. They show a distinct reproductive cycle which likely includes continuous spawning and lecithotrophic development (Tyler et al., 1982). However,  the evidence should be used with caution due to the known variation in modes of reproduction within the Goniasteridae family (Naughton & O’Hara, 2009). Goniasterids are among the most frequently observed sponge predators in both shallow and deep water (Mah, 2020, 2006). Information relating to the diet and ecology of Plinthaster dentatus is minimal, but recent observational evidence from remotely operated vehicles suggests they predate encrusting organisms (Mah, 2020; NOAA, 2019). 

Resilience assessment. No direct information on the recovery rates of the characteristic species in these habitats (biotopes) was found. The dominant urchin species Gracilechinus spp. appear to be slow-growing and long-lived reaching sexual maturity in ca five years with annual spawning but high larval mortality and unpredictable recruitment (e.g. only one year in ten in Gracilechinus affinis) (Tyler & Gage, 1984; Gage & Tyler, 1985). However, they are mobile species so adults could recolonize affected areas from neighbouring habitats. The dominant sea stars either produce planktotrophic larvae and reproduce in synchrony with the seasonal influx of surface productivity (e.g. Dytaster insignis and Plutonaster bifrons) or produce relatively few, lecithotrophic larvae that develop close to the seabed (and presumably do not disperse far) and show no reproductive synchrony (e.g. Persephonaster patagiatus and Plinthaster dentatus). However, no information on growth rates and age at sexual maturity was found. The sea stars are also highly mobile predators, probably feeding on infaunal and epifaunal invertebrates, and capable of recolonizing the habitat from the surrounding area. 

Therefore, where resistance is 'Medium' and some of the population is lost resilience is probably 'Medium' (2-10 years) due to recolonization by adults together with larval recruitment. However, where resistance is 'Low' (a significant reduction in the population) or 'None' (a severe decrease in the population) then resilience may be 'Low' (10-25 years) as recruitment is unpredictable and urchin recruits could take over five years to reach maturity. Sea stars may recover more rapidly but the evidence is lacking. Confidence in the assessment is 'Low' due to the lack of direct evidence. 

Hydrological Pressures

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ResistanceResilienceSensitivity
Temperature increase (local) [Show more]

Temperature increase (local)

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

Evidence

Tyler & Young (1998) examined the temperature (4, 7, 11, & 15°C) and pressure (1, 50, 100, 200 atm) tolerances of Echinus spp. They concluded that the embryos of Echinus esculentus and Gracilechinus (syn. Echinus) acutus from shallow water were limited by pressure to depths above 1,000 m. Early embryos of Gracilechinus (syn. Echinus) acutus from 900 m tolerated higher pressures than those from shallow water. The embryos of Gracilechinus (syn. Echinus) affinis were truly barophilic and only developed at pressures over 100 atm. The tolerance of their embryos matched the depth distribution of the adults. Tyler & Young (1998) examined pressure and temperature in combination rather than alone. However, they noted that larval development was abnormal in both Echinus esculentus and Gracilechinus (syn. Echinus) acutus from shallow water at 15°C. The embryos of Gracilechinus (syn. Echinus) acutus from the bathyal zone were the most tolerant of pressure and temperature compared to other Echinus spp. and developed rapidly at lower temperatures (4°C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. 

Gracilechinus (syn. Echinus) alexandri is recorded from Iceland and the Davis Strait in the North Atlantic, south to the Azores and the Gulf of Mexico; the majority of records with sea surface temperatures of ca 15 to 20°C (OBIS, 2024). Gracilechinus (syn. Echinus) alexandri was also recorded in the Lucky Strike hydrothermal vent area and Cape Hatteras; probably off Tristan da Cunha (Mironov 2014). The typical depth ranges from 365–3,509 m but David & Sibuet (1985) recorded the species at depths up to 4,700 m in the Bay of Biscay. Persephonaster patagiatus is recorded in the North Atlantic from northern Norway and south into the Caribbean and the northern coast of South America; records with sea surface temperatures ranging from ca 5 to 30°C (OBIS, 2024). However, Plinthaster dentatus is sparsely recorded in the North East Atlantic from off the west coast of Scotland south to Morroco, with a few records from Australia and New Zealand but the majority of records from the Gulf of Mexico and the Caribbean; the majority of records with sea surface temperatures of ca 25 to 30°C (OBIS, 2024).

However, sea surface temperatures are not relevant to deep water species. While there is evidence to suggest aspects of seasonality in deep-sea environments, temperature is not typically a parameter that varies throughout the year (Tyler, 1988). 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 seawater temperature 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). 

Sensitivity assessment. Gage (1986) reported that Gracilechinus (syn. Echinus) alexandri, Persephonaster (as Psilaster) patagiatus and Plinthaster dentatus dominated the fauna from ca 1,400 m to the base of Herbidean slope at about 2,000 to 2,500 m in the Rockall Trough. At this 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 and pressures, 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. However, these urchins and sea stars are mobile and may be able to move out of the affected area before mortality occurs. Therefore, resistance is assessed as 'Medium' as a precaution, albeit with 'Low' confidence. Resilience is probably 'Medium' so sensitivity is assessed as 'Medium'

Medium
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Medium
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Medium
Low
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Temperature decrease (local) [Show more]

Temperature decrease (local)

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

Evidence

Tyler & Young (1998) examined the temperature (4, 7, 11, & 15°C) and pressure (1, 50, 100, 200 atm) tolerances of Echinus spp. They concluded that the embryos of Echinus esculentus and Gracilechinus (syn. Echinus) acutus from shallow water were limited by pressure to depths above 1,000 m. Early embryos of Gracilechinus (syn. Echinus) acutus from 900 m tolerated higher pressures than those from shallow water. The embryos of Gracilechinus (syn. Echinus) affinis were truly barophilic and only developed at pressures over 100 atm. The tolerance of their embryos matched the depth distribution of the adults. Tyler & Young (1998) examined pressure and temperature in combination rather than alone. However, they noted that larval development was abnormal in both Echinus esculentus and Gracilechinus (syn. Echinus) acutus from shallow water at 15°C. The embryos of Gracilechinus (syn. Echinus) acutus from the bathyal zone were the most tolerant of pressure and temperature compared to other Echinus spp. and developed rapidly at lower temperatures (4°C). Tyler & Young (1998) concluded that embryos and larvae were more tolerant of depth and temperature than adults. 

Gracilechinus (syn. Echinus) alexandri is recorded from Iceland and the Davis Strait in the North Atlantic, south to the Azores and the Gulf of Mexico; the majority of records with sea surface temperatures of ca 15 to 20°C (OBIS, 2024). Gracilechinus (syn. Echinus) alexandri was also recorded in the Lucky Strike hydrothermal vent area and Cape Hatteras; probably off Tristan da Cunha (Mironov 2014). The typical depth ranges from 365–3,509 m but David & Sibuet (1985) recorded the species at depths up to 4,700 m in the Bay of Biscay. Persephonaster patagiatus is recorded in the North Atlantic from northern Norway and south into the Caribbean and the northern coast of South America; records with sea surface temperatures ranging from ca 5 to 30°C (OBIS, 2024). However, Plinthaster dentatus is sparsely recorded in the North East Atlantic from off the west coast of Scotland south to Morroco, with a few records from Australia and New Zealand but the majority of records from the Gulf of Mexico and the Caribbean; the majority of records with sea surface temperatures of ca 25 to 30°C (OBIS, 2024).

However, sea surface temperatures are not relevant to deep water species. While there is evidence to suggest aspects of seasonality in deep-sea environments, temperature is not typically a parameter that varies throughout the year (Tyler, 1988). 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 seawater temperature 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). 

Sensitivity assessment. Gage (1986) reported that Gracilechinus (syn. Echinus) alexandri, Persephonaster (as Psilaster) patagiatus and Plinthaster dentatus dominated the fauna from ca 1,400 m to the base of Herbidean slope at about 2,000 to 2,500 m in the Rockall Trough. At this 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 and pressures, 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. However, these urchins and sea stars are mobile and may be able to move out of the affected area before mortality occurs. Therefore, resistance is assessed as 'Medium' as a precaution, albeit with 'Low' confidence. Resilience is probably 'Medium' so sensitivity is assessed as 'Medium'

Medium
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Medium
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Medium
Low
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Salinity increase (local) [Show more]

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 dominated by echinoderms. 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 echinoderms that dominate this biotope 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 echinoderm-dominated community 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'.

Low
Low
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Low
Low
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High
Low
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Salinity decrease (local) [Show more]

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 dominated by echinoderms. 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 echinoids that dominate this biotope are probably adapted to stable salinity conditions and have limited tolerance to salinity change. A decrease in salinity from full to reduced (18-30 psu) is probably detrimental to the important characteristic species of the biotope. However, it is unlikely that this biotope would be exposed to hyposaline conditions (or effluent) unless from a newly opened freshwater seep or an unknown deep-sea operation. Although there is no direct evidence of the effects of hyposaline water on the characteristic species, the stenohaline nature of the echinoderm-dominated community 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'.

Low
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Low
Low
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High
Low
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Water flow (tidal current) changes (local) [Show more]

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

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. Gage (1986) noted this assemblage of echinoderms that characterizes this biotope was found below 1,400 m Hebrideean slope where the sediment is dominated by a mixture of 'pelagic ooze' and 'turbidite'. The echinoderm assemblage probably occurs because of the abundance of organic matter in the 'ooze'. For example, Gage et al. (1986) noted that growth rates in Gracilechinus affinis depended on the annual deposition of phytodetritus to the deep-sea floor.

Sensitivity assessment. The biotope is probably dependent on the presence of the 'pelagic ooze' and the seasonal deposition of organic material (marine snow), which is itself dependent on low water flow rates. Water flow in the Rockall Trough is probably dominated by mass water transport due to oceanic currents, for example, 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 (as above). An increase in water flow of 0.1 to 0.2 m/s (the benchmark) has the potential to resuspend and remove the 'ooze' and hence adversely affect the biotope. However, no information on water flow rates in examples of this biotope was available. 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. 

Insufficient evidence (IEv)
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Not relevant (NR)
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Insufficient evidence (IEv)
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Emergence regime changes [Show more]

Emergence regime changes

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

Evidence

The M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are found at upper abyssal and lower bathyal depths and will not be affected by changes in the emergence regime.

Not relevant (NR)
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Not relevant (NR)
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Not relevant (NR)
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Wave exposure changes (local) [Show more]

Wave exposure changes (local)

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

Evidence

The M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are found at upper bathyal depths and will not be affected by changes in nearshore wave exposure.

Not relevant (NR)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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Chemical Pressures

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ResistanceResilienceSensitivity
Transition elements & organo-metal contamination [Show more]

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

Sea urchins, especially the eggs and larvae are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). It is likely, therefore, that Echinus spp. and other urchins, especially their larvae are sensitive to a range of contaminants. For example:

  • Aluminium and mercury were reported to cause 100% mortality in the blastulae of Arbacia punctulata (purple-spined sea urchin) at 200 µg/l after 2.5 hours and 2 ng/l after 15 hours respectively;
  • Copper exposure resulted in 96-hour LC50 of 25 µg/l in Diadema antillarum (long-spined sea urchin) ;
  • Cooper resulted in a 50% mortality in the gametes or several species of sea urchin at varying concentrations; and
  • Zine resulted in developmental changes in the embryos of Sphaerechinus granularis exposed to 60 µg/l for 1.5 days (ECOTOX, Olker et al., 2022, cited 2024).

Bryan (1984) reported that early work had shown that echinoderm larvae were intolerant of 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). 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 single study into the effects of tributyl tin (TBT) on the shallow water urchin Echinocardium cordatum found that its biology meant it did not bioaccumulate TBT to the expected degree, but that TBT was still highly toxic with a 28-day pore water LC50 of 222 ng Sn/l (Stronkhorst et al., 1999). Alteration to the female gonad and smaller oocyte production was reported in the starfish Leptasterias polaris due to a concentration of tributyltin over 0.26 μg/gm/wwt (Mercier et al., 1994). In addition, the disposal of tributyltin in the Bay of Brest (France) was linked to a delay of embryonic development in the urchin Sphaerechinus granularis (Quiniou et al., 1999).

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

Low
Low
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NR
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Low
Low
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NR
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High
Low
NR
NR
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Hydrocarbon & PAH contamination [Show more]

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). It is likely therefore that Echinus spp. and similar urchins, especially their larvae are 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).

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 esculentusEchinus 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). 

Sensitivity assessment. No evidence of the effects of hydrocarbon or PAH contamination on the characteristic urchins was found. However, evidence from other sea urchins, in particular Echinus spp., suggests that the dominant urchins 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 'Low' and sensitivity is assessed as 'High', albeit with 'Low' confidence due to lack of directly relevant evidence. Further evidence is required for this pressure.

Low
Low
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NR
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Low
Low
NR
NR
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High
Low
NR
NR
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Synthetic compound contamination [Show more]

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

Sea urchins, especially the eggs and larvae are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). It is likely therefore that Echinus spp. and similar urchins,  especially their larvae are sensitive to a range of contaminants. 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.

Sensitivity assessment. No evidence of the effects of hydrocarbon or PAH contamination on the characteristic echinoderms was found. There is 'Insufficient evidence' above to support an assessment and further evidence is required for this pressure.

Insufficient evidence (IEv)
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Not relevant (NR)
NR
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NR
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Insufficient evidence (IEv)
NR
NR
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Radionuclide contamination [Show more]

Radionuclide contamination

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

Evidence

No evidence could be found on the effect of radionuclide contamination on the M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes. Hutchins et al. (1996) demonstrated that the sea star Asteria forbesi bioaccumulated radioactive waste disposal isotopes in a range of temperature settings. Warnau et al. (1999) suggested that the sea star Asterias rubens can retain radiocobalt contamination for a few months. Radionuclide uptake is thought to be through seawater rather than diet. However, no effects on the species studied were reported.

No evidence (NEv)
NR
NR
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No evidence (NEv)
NR
NR
NR
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No evidence (NEv)
NR
NR
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Introduction of other substances [Show more]

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

George (2017) reported that vast patches of Gracilechinus affinis were found dead after the sinkage of a ship with nerve gas cylinders onboard in a deep-sea dumpsite off New Jersey. No other evidence could be found for the effects of the introduction of other substances on the M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes.

Insufficient evidence (IEv)
NR
NR
NR
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Not relevant (NR)
NR
NR
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Insufficient evidence (IEv)
NR
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De-oxygenation [Show more]

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

Nilsson & Rosenberg (1994) reported that Echinocardium cordatum (in box cores) experienced 100% mortality after exposure to moderate (1.0 mg/l) and severe (0.5 mgl/l) hypoxia in the laboratory after a 14-day experiment in which hypoxia was achieved after eight days. Nichols (1959) noted that Echinocardium cordatum left the sediment when aeration of their water supply in the laboratory was interrupted for 24 hours. Similarly, Diaz & Rosenberg (1995) reported that benthic invertebrates, such as the echinoderms Brissopis lyrifera and Echinocardium cordatum left the sediment at a bottom water oxygen concentration of ca 1 ml/l (1.4 mg/l).  Diaz & Rosenberg (1995) suggested that Brissopis lyrifera was sensitive to hypoxia. Death of a bloom of the phytoplankton Gyrodinium aureolum in Mounts Bay, Penzance in 1978 produced a layer of brown slime on the sea bottom. This resulted in the death of fish and invertebrates, including Echinus esculentus, presumably due to anoxia caused by the decay of the dead dinoflagellates (Griffiths et al., 1979).

Sato et al. (2017) examined the effects of climate change-related changes in dissolved oxygen (DO), temperature, pH and pCO2 on the distribution of deep-water sea urchins on the Californian continental shelf using trawl data from the Southern California Bight, 1994-2013.  They concluded that deep water species had expanded upslope in the upper 500 m  while shallower-dwelling species had experienced habitat compression in the upper 200 m in the last 21 years due to temperature change, DO, pH and pCO2. They suggested that the deeper dwelling species (e.g. Brissopis pacifica and Spatangus fragilis) may have an adaptive advantage in a more deoxygenated, acidic future due to their adaption to hypoxic and hypercapnic conditions (Sato et al., 2017). They noted that the oxygen limited zone in the study area was naturally <60 µmol/kg (ca <1.9 mg/l). However, Ellet & 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. 

Sensitivity assessment. Evidence from the South California Bight suggests that deep water species may be adapted to low oxygen conditions. However, similar low oxygen conditions are not recorded from the Rockall Trough from where this biotope is recorded (Ellet & Martin, 1973). However, the evidence from familial species of Echinocardium, Brissopsis and Echinus suggests that urchins may be sensitive to hypoxia. Resistance to deoxygenation is probably species-specific but in the absence of more specific evidence, resistance is assessed as 'Low' at the benchmark level, as a precaution. Hence, resilience is assessed as 'Low' and sensitivity as 'High' albeit with 'Low' confidence. 

Low
Low
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Low
Low
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NR
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High
Low
NR
NR
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Nutrient enrichment [Show more]

Nutrient enrichment

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

Evidence

Nutrient enrichment can have significant impacts on benthic communities (Abdelrhman & Cicchetti, 2012; Rosenberg et al., 1987). However, there is no direct evidence regarding the effect of increased nutrient concentrations on the characterizing species.

Insufficient evidence (IEv)
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Not relevant (NR)
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Insufficient evidence (IEv)
NR
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Organic enrichment [Show more]

Organic enrichment

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

Evidence

Organic enrichment can have significant impacts on benthic communities (Rosenberg et al., 1987). It is known that deposit-feeding urchins like the characterizing species can be affected by increases in organic material.  Results from the west coast of the USA have shown that chemical signals from sewage dumping could be detected in the deep-sea urchin Gracilechinus affinus (Dover et al., 1992)A review of common shallow water fauna from the Netherlands placed the shallow irregular echinoid Echinocardium cordatum in group 2, “Species indifferent to enrichment”, which would suggest that the species is resistant to enrichment pressure (Gittenberger & Van Loon, 2011). Furthermore, studies from aquaculture in NW Europe have found that urchin species such as Gracilechinus acutus and Echinus esculentus can and will feed off waste organic material from finfish aquaculture (White et al., 2017; Woodcock et al., 2018). Urchins are known to rapidly respond to patches of drift kelp (Harrold & Reed, 1985; cited in Tissot et al., 2006), which provide organic material to deep-sea habitats (Harrold et al., 1998).

However, these studies make limited attempts to describe whether or not the impact of organic enrichment would be positive or negative for the urchins. White et al. (2017) have suggested that organic enrichment from fish farming can act as an energy-rich subsidy for urchins while Woodcock et al. (2018) do not assess the effect of enrichment on the species under study. 

Sensitivity assessment. This biotope is characterized by aggregations of sea urchins feeding on 'pelagic ooze' (dependent on phytodetritus) which is presumably an organic-rich substratum. The evidence that Gracilechinus acutus can feed on waste organic material, and the assessment of Gittenberger & Van Loon (2011) suggests that the biotope is resistant to organic enrichment.  However, no quantitative values were available for comparison with the benchmark. Therefore, resistance is assessed as 'High', resilience as 'High' and sensitivity is assessed as 'Not sensitive' but with 'Low' confidence. 

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
NR
NR
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Physical Pressures

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ResistanceResilienceSensitivity
Physical loss (to land or freshwater habitat) [Show more]

Physical loss (to land or freshwater habitat)

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

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of available habitat (resilience is ‘Very low’). The squat lobster assemblage biotopes are therefore considered to have ‘High’ sensitivity to this pressure.

None
High
High
High
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Very Low
High
High
High
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High
High
High
High
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Physical change (to another seabed type) [Show more]

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

Change from sedimentary to hard substrata would cause loss of the biotope. In addition, the mechanical process of changing to a 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, therefore, assessed as 'High'.

None
High
High
High
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Very Low
High
High
High
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High
High
High
High
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Physical change (to another sediment type) [Show more]

Physical change (to another sediment type)

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

Evidence

The biotope is characterized by mud, in the form of pelagic ooze and turbidites (Gage, 1986). A change in 1 Folk class, for example, from mud to sandy mud, or muddy sand would lead to either loss of the biotope or reclassification, irrespective of impacts from the mechanical agents of change.

None
High
High
High
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Very Low
High
High
High
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High
High
High
High
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Habitat structure changes - removal of substratum (extraction) [Show more]

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

Removal to benchmark levels of 30 cm would remove the biological community as well as the underlying substratum. Evidence from shallow water scallop dredging experiments has shown that the shallow water irregular echinoid Echinocardium was substantially reduced from the dredged area (Eleftheriou & Robertson, 1992) and that significant additional unobserved mortality and depredation/scavenging occurs after dredging events (Jenkins et al., 2001; Öndes et al., 2016). Baird et al. (2015) classified Psilaster acuminatus as fragile, surface living, and not highly mobile in response to trawling. Assuming Persephonaster patagiatus adopts a similar mode of life to shallow water conspecifics, then sensitivity to trawling will likely be similar in a deep-sea setting. Therefore, resistance is assessed as 'Low' within the affected area. Resilience is probably 'Low' and sensitivity is assessed as 'High' but with 'Low' confidence due to the lack of evidence on the effects of this pressure on similar habitats. 

Low
Low
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Low
Low
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NR
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High
Low
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Abrasion / disturbance of the surface of the substratum or seabed [Show more]

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

Houghton et al. (1971), Graham (1955), de Groot & Apeldoorn (1971) and Rauck (1988) refer to significant trawl-induced mortality of the heart urchin Echinocardium cordatum. A substantial reduction in the numbers of Brissopsis lyrifera due to physical damage from scallop dredging was reported by Eleftheriou & Robertson (1992). Overall, species with brittle, hard tests are regarded to be sensitive to impact with scallop dredges (Kaiser & Spencer, 1995; Bradshaw et al., 2000; Bergman & van Santbrink, 2000).

Kaiser et al. (2006) concluded that the footprint of the impact and the recovery of communities varied with gear and habitat types. For example, beam trawling and scallop dredging had significant negative short-term impacts in sand and muddy-sand habitats; and mud habitats were shown to have substantial initial impacts by otter trawling but the effects tended to be short-lived with an apparent long-term positive post-trawl disturbance response from the increase of small-bodied fauna. When used over fine muddy sediments, trawls are often fitted with shoes designed to prevent the boards from digging too far into the sediment (M.J. Kaiser, pers. obs., cited in Jennings & Kaiser, 1998). The effects may persist for variable lengths of time depending on tidal strength and currents and may result in a loss of biological organization and reduce species richness (Hall, 1994; Bergman & van Santbrink, 2000; Reiss et al., 2009). 

González-Irusta et al. (2014) examined populations of Gracilechinus acutus from trawled and non-trawled areas, at ca 80 m in the central Cantabrian Sea continental shelf (southern Bay of Biscay). They reported that populations from trawled areas exhibited significantly lower biomass, smaller mean size of Gracilechinus acutus, and significantly higher values of fullness (an estimate of gut volume compared to body volume). Urchins in non-trawling areas also had a significantly lower value of δ15N compared to trawled areas. The shift in size suggests that the larger, older urchins were more susceptible to trawling. The authors suggested that the 'fullness index' and shift in isotopic nitrogen indicated small urchins fed preferentially on small phytodetritus while larger urchins preferred small epibenthic invertebrates (González-Irusta et al., 2014). Serrano et al. (2011) also reported a significant increase in the abundance of Gracilechinus acutus after anti-trawling reefs were installed at two sites in the Cantabrian Sea, Bay of Biscay after ca two to five years. The abundance of starfish also increased. 

Sensitivity assessment. Gracilechinus spp. are epifaunal surface deposit feeders and scavengers that feed at the surface of the sediment, while the characteristic starfish are scavengers and predators. Therefore, all of the dominant echinoderms are probably susceptible to damage from passing fishing gear. González-Irusta et al. (2012) demonstrated a significant reduction in body size and biomass of Gracilechinus in trawled vs. untrawled sites in the central Cantabrian Sea continental shelf, while Serrano et al. (2011) reported an increase in urchin and starfish abundance after trawling was prevented. Therefore, resistance is assessed as 'Low'. Resilience is probably 'Low' due to the slow growth rate and sporadic recruitment of Gracilechnus in the deep waters of Rockall Trough where this biotope is recorded. Hence, sensitivity is assessed as 'High'

Low
High
Medium
Medium
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Low
Low
NR
NR
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High
Low
NR
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Penetration or disturbance of the substratum subsurface [Show more]

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

Gracilechinus spp. are epifaunal surface deposit feeders and scavengers that feed at the surface of the sediment, while the characteristic starfish are scavengers and predators. Therefore, all of the dominant echinoderms are probably susceptible to damage from passing fishing gear. 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 'Low' due to the slow growth rate and sporadic recruitment of Gracilechnus in the deep waters of Rockall Trough where this biotope is recorded. Hence, sensitivity is assessed as 'High'

Low
High
Medium
Medium
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Low
Low
NR
NR
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High
Low
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Changes in suspended solids (water clarity) [Show more]

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

No evidence on the impact of suspended particles was available for the three characterizing species of this biotope Gracilechinus alexandri, Persephonaster patagiatus, Plinthaster dentatus. This biotope is characterized by 'pelagic ooze' deposited seasonally as marine snow and the growth rates of Gracilechinus spp. are linked to the seasonal deposition of phytodetritus. Hence, the urchins are probably adapted to seasonal peaks in suspended solids. In addition, they are mainly deposit feeders (depending on age) and their tube feet probably maintain their tests clear of sediment and other debris. The Astropectinidiae (such as Persephonaster patagiatus, Plinthaster dentatus) immerse themselves in soft sediments, such as mud, where they scavenge or prey on smaller species. Therefore, the echinoderm-dominated community is probably not sensitive to increases in suspended sediment at the benchmark level. A decrease in suspended sediment may reduce food availability, especially if it was due to an interruption in the seasonal phytodetritus but due to their longevity, the population is unlikely to be adversely affected by a decrease for one year and could switch to alternative food sources in the meantime. Hence, resistance is assessed as 'High', resilience as 'High' and sensitivity as 'Non-sensitive'. 

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
NR
NR
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Smothering and siltation rate changes (light) [Show more]

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

Gracilechinus spp. are epifaunal surface deposit feeders and scavengers that feed at the surface of the sediment. Gracilechinus alexandri is flattened on the upper side and can reach ca 7 cm in diameter (Mortensen, 1927). The sea stars lie flat on or in the sediment. Psilaster andromeda can grow up to 10 cm across, while Persephonaster patagiatus can reach 10.5 cm across and Plinthaster dentatus can grow up to 9.8 cm across (Mortensen, 1927). The dominant echinoderms are probably active borrowers or large and mobile (Gracilechinus sp.)Therefore, resistance to the deposition of 5 cm of fine sediment is assessed as 'High', resilience as 'High' and sensitivity assessed as 'Not sensitive'

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
NR
NR
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Smothering and siltation rate changes (heavy) [Show more]

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

Hughes et al. (2010) found that Gracilechinus acutus norvegicus abundance declined significantly within 50 m of the drill site associated with a hydrocarbon exploration site in the North Sea. However, it was unclear if the effect was due to burial sediment deposition or the levels of other contaminants in the drill spoil such as barite (Hughes et al., 2010). Gracilechinus spp. are epifaunal surface deposit feeders and scavengers that feed at the surface of the sediment. Gracilechinus alexandri is flattened on the upper side and can reach ca 7 cm in diameter (Mortensen, 1927). The sea stars lie flat on or in the sediment. Psilaster andromeda can grow up to 10 cm across, while Persephonaster patagiatus can reach 10.5 cm across and Plinthaster dentatus can grow up to 9.8 cm across (Mortensen, 1927). 

The dominant echinoderms are probably active borrowers or large and mobile (Gracilechinus sp.)However, sudden burial by 30 cm of fine sediment is likely to adversely affect the population, especially smaller specimens, and no information on the dominant species' ability to burrow up through fine sediment was found. Therefore, resistance is assessed as 'Medium' on the assumption that some individuals may be lost in the affected arearesilience as 'Medium' and sensitivity is assessed as 'Medium' but with 'Low' confidence due to the lack of direct evidence. 

 

Medium
Low
NR
NR
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Medium
Low
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NR
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Medium
Low
NR
NR
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Litter [Show more]

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 the M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes.

No evidence (NEv)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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No evidence (NEv)
NR
NR
NR
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Electromagnetic changes [Show more]

Electromagnetic changes

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

Evidence

 Vareshin (2007) exposed the gametes and larvae of Strongylocentrotus intermedius to high frequency (EHF) electromagnetic radiation (42.2 GHz, 100 µW/cm2, impulse modulation 1000 Hz) for 17 or 34 minutes. They reported that the fertilization rate of gametes and the development of early embryos to the pluteus larval stage was 2.3 times lower than in controls, without exposure to EHF. Ravera et al. (2006) exposed newly fertilized embryos of Paracentrotus lividus to an electromagnetic field of 75 Hz and low amplitudes (from 0.75 to 2.20 mT magnetic component) for 150 min. The exposure disrupted mitosis and resulted in abnormal larvae (ca 80% of cases).  They also noted that the first 5 min of exposure was enough to adversely affect chromatin distribution in the embryos. The authors reported that other studies had found that electromagnetic fields of 5kHz, 450 MHz, and 60 Hz had also resulted in abnormal larval development in sea urchin embryos (Ravera et al., 2006). Ravera et al. (2006) found that exposure to 0.45 mT or 0.75 ± 0.01 mT resulted in the same low percentage of anomalous embryos of the controls. However, exposure to 0.80 ± 0.01 mT or 1.80 ± 0.07 mT or above the percentage of anomalous embryos was about 80%. The amplitude of 0.80 ± 0.01 mT was the lowest value that produced anomalous embryos. 

Sensitivity assessment. The evidence above suggests that sea urchin embryos are susceptible to electromagnetic fields. No information on the effects on sea stars was found. The evidence from Ravera et al. (2006) suggests that electromagnetic fields could severely impact embryo development and, hence, larval recruitment. The dominant population of Gracilechnius spp. is long-lived, spawns annually and is characterized by sporadic or decadal pulses of recruitment so may be able to withstand short-term (e.g. one year) exposure but may be adversely affected if the magnetic fields were prolonged (e.g. from a subsea cable). However, the threshold value given by Ravera et al. (2006) is an order of magnitude greater than the benchmark (0.80 mT vs. 0.01 mT). Also, information on the electromagnetic fields that may be generated by subsea cables was not available.  Therefore, there is 'Insufficient evidence' on which to base an assessment. 

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Underwater noise changes [Show more]

Underwater noise changes

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

Evidence

Mauro et al. (2018) reported that the urchin Arbacia lixula increased the expression of stress proteins when exposed to sonic stress for three hours (100 to 200 kHz emitted every one second). However, the 'sonic stress' reported is difficult to compare with the benchmark level based on the MSFD indicator, which is primarily relevant to sea mammals and sea birds. 

M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are characterized by invertebrates with no known means to detect noise and as such will not be affected by changes in underwater noise as defined under this pressure.

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Introduction of light or shading [Show more]

Introduction of light or shading

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

Evidence

M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are characterized by invertebrates with limited ability to detect light and are aphotic. 

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Barrier to species movement [Show more]

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

Whilst the M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are characterized by mobile invertebrates, their benthic lifestyle and widespread deep-sea habitat means 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.

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Death or injury by collision [Show more]

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

M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are characterized by benthic invertebrates that are not at risk of collision with artificial structures. It might be adversely affected by large falling marine debris such as barrels, containers, and even shipwrecks but the effects are probably addressed under 'abrasion' above. 

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Visual disturbance [Show more]

Visual disturbance

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

Evidence

M.AtUA.Mu.UrcCom.GraAle and M.AtLB.Mu.UrcCom.GraAle biotopes are characterized by invertebrates that are not reliant on visual cues and as such will not be affected by visual disturbance, as defined under this pressure.

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Biological Pressures

Use [show more] / [show less] to open/close text displayed

ResistanceResilienceSensitivity
Genetic modification & translocation of indigenous species [Show more]

Genetic modification & translocation of indigenous species

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

Evidence

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

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Introduction or spread of invasive non-indigenous species [Show more]

Introduction or spread of invasive non-indigenous species

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

Evidence

The introduction of predatory asteroids in shallow Australian waters was detrimental to populations of Echinocardium cordatum (Ross et al., 2002)However, no direct comparable evidence was available for the characterizing species of the biotope. There is the potential for colonization by shallow water analogues of predatory starfish such as Asterias rubens or Marthasterias glacialis, but this is extremely unlikely in the short term due to oceanographic constraints on the adult forms of these species (Villalobos et al., 2006). Furthermore, there is no evidence to suggest that non-indigenous species will directly compete with the characterizing species. No information on the effect of the introduction of one or more invasive non-indigenous species on this biotope was found.

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Introduction of microbial pathogens [Show more]

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.

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Removal of target species [Show more]

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 are not targeted by commercial or recreational fisheries.

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Removal of non-target species [Show more]

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 characteristic species are not targeted by fishing efforts but several commercially important species are fished from the sand found at upper bathyal depths. Direct removal of individuals is likely to be deleterious. No evidence exists on the survivability of deep-sea echinoids as bycatch, likely, the stress of decompression, sharp temperature changes, mechanical damage, handling and time spent out of the water will negatively affect their survival. The effect of mechanical damage by mobile gear, such as trawls, is known to have a significant negative impact on echinoids, reducing coverage density by up to 68% (Collie, 2000). Recent studies into the distribution of Gracilechinus acutus in the Cantabrian Sea found that the characterizing species was sensitive to trawl damage, with untrawled areas supporting more abundant communities with a larger body size (González-Irusta et al., 2012). Additional work from the Cantabrian Sea found that trawling disturbance had a detectable impact on the isotopic signature of Gracilechinus acutus, but the study did not make any attempt to explain the mechanism behind this observation (González-Irusta et al., 2014). Serrano et al. (2011) also reported a significant increase in the abundance of Gracilechinus acutus after anti-trawling reefs were installed at two sites in the Cantabrian Sea, Bay of Biscay after ca two to five years. The abundance of starfish also increased.  Furthermore, there is a body of evidence to suggest that bycatch impacts go largely unobserved, with significant in-situ damage and subsequent mortality and predation by opportunistic scavengers being highly significant (Evans et al., 1996; Kaiser & Spencer, 1994; Philippart, 1998). 

Baird et al. (2015) classified Psilaster acuminatus as fragile, surface living, and not highly mobile in response to trawling. Assuming Persephonaster patagiatus adopts a similar mode of life to shallow water conspecifics, then sensitivity to trawling may be similar in a deep-sea setting. Evidence on the effects of fishing activities on Plinthaster dentatus is limited but as an epifaunal relatively slow-moving species sensitivity may be similar to Persephonaster patagiatus.

Sensitivity assessment. The slow growth rate, susceptibility to mechanical damage and impact of scavenging makes the characterizing urchin species of this biotope highly sensitive to incidental fisheries damage.  Therefore, resistance is assessed as 'Low', resilience as 'Low' and sensitivity as 'High'

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Citation

This review can be cited as:

Bull, G., & Tyler-Walters, H., 2024. Gracilechinus alexandri, Psilaster and Plinthaster assemblage on Atlantic upper abyssal mud. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 16-06-2024]. Available from: https://www.marlin.ac.uk/habitat/detail/1273

Last Updated: 29/02/2024