Gracilechinus acutus norvegicus assemblage on Atlantic lower bathyal mud

Summary

UK and Ireland classification

Description

These biotopes consist of aggregations of Gracilechinus acutus norvegicus (previously Echinus acutus norvegicus) on sand substrata in the upper bathyal, mid bathyal or lower bathyal zone, or on mud substrata in the mid and lower bathyal. Associated infauna are likely to differ between the different substrata and depth zones. Gage (1986) reports this assemblage from 700-1,400 m on pelagic ooze and suggests it is present in a ribbon-like distribution around the continental margin of Europe down to about 1,400 m. Le Danois also describes this assemblage from 150-500+ m but emphasises that shallower than 500 m Spatangus raschi dominates and below Gracilechinus acutus norvegicus dominates. The characterizing species named refer to all Gracilechinus acutus norvegicus assemblages.

Depth range

1300-2100 m

Additional information

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Listed By

- none -

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

Gracilechinus acutus norvegicus assemblages are associated with mud and sand substrata and occur at a range of depths in the Atlantic deep sea. Assemblages occur on sand in the Atlantic upper bathyal zone (M.AtUB.Sa.UrcCom.GraAcu biotope), the mid-bathyal zone (M.AtMB.Sa.UrcCom.GraAcu) and the lower-bathyal zone (M.AtLB.Sa.UrcCom.GraAcu). Mud substratum biotopes for this assemblage only occur in the mid-bathyal and lower-bathyal zones (M.AtMB.Mu.UrcCom.GraAcu and M.AtLB.Mu.UrcCom.GraAcu respectively). The sensitivity of the Gracilechinus acutus norvegicus dominated 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 dominant species in these biotopes is Gracilechinus acutus norvegicus (previously Echinus acutus norvegicus), which forms aggregations. Loss of this species may result in loss or degradation of the biotopes; therefore, the sensitivity of the biotopes is dependent on the sensitivity of Gracilechinus acutus norvegicus. However, there are possible changes in the dominant species with depth, as Spatangus raschi dominates in depths shallower than 500 m, and Gracilechinus acutus norvegicus dominates below. It is also noted that Gracilechinus acutus may be replaced by Gracilechinus elegans in some areas. Therefore, all three echinoid species have been considered for this sensitivity assessment; Gracilechinus acutus norvegicus, Spatangus raschi and Gracilechinus elegans. Where information was unavailable for the main echinoid species, however, other suitable proxy deep-sea echinoid species have been used. The echinoid Calveriosoma hystrix is also a characteristic of the biotope but since it is likely to be very similar to other echinoids being assessed for this biotope, it was not considered necessary to include this species in the assessment specifically.

Other species that can be found within this biotope include the decapods Nematocarcinus ensifer, Pontophilus norvegicus, Geryon trispinosus, Nephropsis atlantica; the holothuroids Bathyplotes natans, Laetmogone violacea and Benthogone rosea, and the ophiuroid Ophiocten gracilis. These species are ubiquitous and not unique to this biotope. They are therefore not considered significant to the assessment of sensitivity. Furthermore, the presence of all these species is not essential for the classification of this biotope.

Resilience and recovery rates of habitat

Gracilechinus acutus has two sub-species, Gracilechinus acutus actus and Gracilechinus acutus norvegicus. This sensitivity assessment focuses on Gracilechinus acutus norvegicus, but the sensitivity of these sub-species are likely to be very similar. Gracilechinus acutus and Gracilechinus elegans have been found on the Hebrides-Malin slope, west Scotland, at depths ranging from 400 to 1,075 m (Gage et al.,1986). Gracilechinus elegans has an overlapping distribution from the shelf into bathyal depths, with a geographic range from Lofoten, Norway to the Moroccan shelf, covering a depth range of 50 to 1,710 m. However, an upper bathyal distribution of 704 to 1,210 m (as found in the Rockall Trough) appears to be more typical.

Gracilechinus affinis (previously Echinus affinis), another deep-sea urchin of the same genus, was noted by Tyler & Gage (1984) to have a similar reproductive cycle to that of Gracilechinus acutus norvegicus. 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 is known to spawn a little later than Gracilechinus affinis. This gametogenic and spawning cycle are 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 Echinus acutus var. norvegicus and Gracilechinus elegans and found that spawning was possible 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). One of the main physiological variations between Gracilechinus species is 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 var 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). 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 Echinus) affinis in Rockall was slow-growing and long-lived compared to other sea urchins then known (Gage & Tyler, 1985). Gage (1986) also suggested that Graciliechinus (as Echinus) affinis 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.

Spatangus raschi has a very restricted distribution off the west coast of Ireland and the Shetland Islands in the North East Atlantic and has only been found in depths below 183 m. The species lives in fine sand and is generally not completely buried. Instead, Spatangus raschi is known to plough along the sediment surface, burrowing shallowly with about half of its corona exposed above the surface, sometimes deeply, but maintaining a respiratory funnel to the surface. Spatangus raschi has very similar larvae to Echinocardium fascioles. Spatangus raschi larvae are present at a very early stage of development (0.7 mm test length), and these develop to form adult fascioles. The ventral horizontal rod arises from the body rod posterior to the anterior transverse rod.

Nichols (1959) noted that Spatangus raschi attains a larger size than Spatangus purpureus, Echinocardium cordatum, Echinocardium pennatifidumEchinocardium flavescens, or Brissopsis lyrifera, yet apparently builds only one subanal tube. As the respiratory tube feet are not confined in a burrow, there is no need for a large soak-away for the respiratory water, and the cross-section of the sanitary device can be smaller (Nichols, 1959). Two other species, Hemiaster expergitus and Brissopsis lyrifera, show a similar peristomial structure to Spatangus raschi, with a similar arrangement of spines, tube feet and sphaeridia around the peristome. Nichols (1959) deduced that the reduction in size of tube feet was a countermeasure to predation, enabled by a higher number of isomicrasters in Spatangus raschi. His theory was also supported by other features, in particular the reduction in ciliary currents in the subanal region.

Goode et al. (2020) reviewed the effects of trawling on seamount communities. They reported that urchins (echinoids) as a group, corresponded best (based on limited data) with their 'no recovery' category, which they defined as 'little to no difference in abundance between actively trawled seamounts and those that have been protected at each time point' typical of 'small and/or fragmented populations, with slow growth, and limited dispersal'. Goode et al. (2020) noted that two studies of seamount trawling (Williams et al., 2010; Clark et al., 2019) had predicted that echinoids (as a group) had a high recovery potential, but that they (Goode et al., 2020) did not observe any significant recovery over time in this group due to their association with the scleractinian corals. However, it is unclear how recovery rates on rocky seamounts relate to sedimentary habitats such as this biotope. 

Resilience assessment. No direct information on the recovery rates of the characteristic species in these habitats (biotopes) was found. The dominant 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. 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 recruits would take over five years to reach maturity. 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 (as 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 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) acutus is recorded from the White Sea, south through the North East Atlantic, in the Mediterranean and south along the Atlantic coast of Africa; the majority of records with sea surface temperatures of ca 10 to 15°C (OBIS, 2024). Gracilechinus (syn. Echinus) affinis is recorded from the North East Atlantic, the Mediterranean, and the Atlantic coast of North America; the majority of records with sea surface temperatures of ca 10 to 20°C (OBIS, 2024). Similarly, Spatangus raschi is recorded in the North East Atlantic from northern Norway, south to the Bay of Biscay and into the Mediterranean; the majority of records with sea surface temperatures of ca 5 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). 

Sensitivity assessment. Tyler & Young (1998) reported that Gracilechinus (syn. Echinus) acutus embryos from the bathyal zone had the broadest range of pressure and temperature (between 4, 7, and 11°C) tolerances of the Echinus sp. studied and was probably in the process of invading the deep sea. Gage (1986) reported this biotope (assemblage) in the form of 'enormous' populations of Gracilechinus (syn. Echinus) acutus var. norvegicus from 150 to 1,400 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 echinoids 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 (as 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 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) acutus is recorded from the White Sea, south through the North East Atlantic, in the Mediterranean and south along the Atlantic coast of Africa; the majority of records with sea surface temperatures of ca 10 to 15°C (OBIS, 2024). Gracilechinus (syn. Echinus) affinis is recorded from the North East Atlantic, the Mediterranean, and the Atlantic coast of North America; the majority of records with sea surface temperatures of ca 10 to 20°C (OBIS, 2024). Similarly, Spatangus raschi is recorded in the North East Atlantic from northern Norway, south to the Bay of Biscay and into the Mediterranean; the majority of records with sea surface temperatures of ca 5 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). 

Sensitivity assessment. Tyler & Young (1998) reported that Gracilechinus (syn. Echinus) acutus embryos from the bathyal zone had the broadest range of pressure and temperature (between 4, 7, and 11°C) tolerances of the Echinus sp. studied and was probably in the process of invading the deep sea. Gage (1986) reported this biotope (assemblage) in the form of 'enormous' populations of Gracilechinus (syn. Echinus) acutus var. norvegicus from 150 to 1,400 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 echinoids 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
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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 echinoids. 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 echinoids 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 that 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 echinoids. 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 that sensitivity is assessed as 'High'.

Low
Low
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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 that aggregations of Gracilechinus acutus var. norvegicus were found along the 700 m contour of the Hebrides-Donegal slope where the sediment is dominated by 'pelagic ooze'. The urchin aggregations probably occur because of the abundance of organic matter in the 'ooze'. For example, Gage et al. (1986) noted that growth rates in Gracilechinus affinis were dependent 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.AtUB.Sa.UrcCom.GraAcu biotope is found at upper bathyal depths and as such 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.AtUB.Sa.UrcCom.GraAcu biotope is found at upper bathyal depths and as such will not be affected by changes in nearshore wave exposure.

Not relevant (NR)
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Not relevant (NR)
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Not relevant (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 similar 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 (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. 

There is limited evidence available on the effect of transition element or organo-metal contamination on the characterizing species. A single study into the effects of tri-butyl 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). 

Sensitivity assessment. No evidence of the effects of transitional metals or organometal 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 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
NR
NR
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Low
Low
NR
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
NR
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 esculentus and especially its 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 urchins was found. There is 'Insufficient evidence' above to support an assessment and further evidence is required for this pressure.

Insufficient evidence (IEv)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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Insufficient evidence (IEv)
NR
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.AtUB.Sa.UrcCom.GraAcu biotope.

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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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.AtUB.Sa.UrcCom.GraAcu biotope.

Insufficient evidence (IEv)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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Insufficient evidence (IEv)
NR
NR
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 change in temperature, 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. 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
NR
NR
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Low
Low
NR
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)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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Insufficient evidence (IEv)
NR
NR
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
Help
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

Tissot et al. (2006) found that off Southern California one species of urchin (Lytechinus anamesus) was most dense in sand habitats, whilst another (Allocentrotus fragilis) was most dense in mud habitats (mean depth of occurrence for A. fragilis was 185m). While the characteristic species are known to occur on both sand and muddy sediments, the change in 1 Folk class, for example from sand to mixed sediment or mud/sandy mud, 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). 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
NR
NR
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Low
Low
NR
NR
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High
Low
NR
NR
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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). 

Duran Munoz et al. (2012) reported large by-catches of Spatangus raschi amongst other echinoids in deep-sea bottom trawls at the top of Hatton Bank but did not discuss their survival. 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 and a 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. Spatangus raschi ploughs through the surface of the sediment and is only buried to a shallow depth of ca 2.5 cm (Nichols, 1959). Therefore, all of the dominant urchins are probably susceptible to damage from passing fishing gear. González-Irusta et al. (2012) demonstrated a significant reduction in body size and biomass 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
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. Spatangus raschi ploughs through the surface of the sediment and is only buried to a shallow depth of ca 2.5 cm (Nichols, 1959). Therefore, all of the dominant urchins 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
NR
NR
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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

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. Spatangus raschi is also a deposit feeder living in the first few centimetres of the sediment.  Therefore, the urchin-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. Spatangus raschi ploughs through the surface of the sediment and is only buried to a shallow depth of ca 2.5 cm (Nichols, 1959). Gage et al. (1986) reported that the population of Gracilechinus acutus var. norvegicus from the Hebridean-Malin slope ranged in size from ca 2 to 6 cm. Nichols (1959) reported that Spatangus raschi was about 4 cm high (based on a single specimen) but actively ploughed through shell gravel in the laboratory.  The dominant species in the shallow range of the biotope, Spatangus raschi, is known to be an important bioturbator in soft sediments. Similarly, communities of the shallow proxy Echinocardium in New Zealand were found to be able to rework surface sediments in three days (Lohrer et al., 2005).

The dominant echinoids are probably active borrowers Spatangus raschi 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

Gracilechinus spp. are epifaunal surface deposit feeders and scavengers that feed at the surface of the sediment. Spatangus raschi ploughs through the surface of the sediment and is only buried to a shallow depth of ca 2.5 cm (Nichols, 1959). Gage et al. (1986) reported that the population of Gracilechinus acutus var. norvegicus from the Hebridean-Malin slope ranged in size from ca 2 to 6 cm. Nichols (1959) reported that Spatangus raschi was about 4 cm high (based on a single specimen) but actively ploughed through shell gravel in the laboratory.  The dominant species in the shallow range of the biotope, Spatangus raschi, is known to be an important bioturbator in soft sediments. Similarly, communities of the shallow proxy Echinocardium in New Zealand were found to be able to rework surface sediments in three days (Lohrer et al., 2005).

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).

The dominant echinoids are probably active borrowers Spatangus raschi 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
NR
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.AtUB.Sa.UrcCom.GraAcu biotope.

No evidence (NEv)
NR
NR
NR
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No evidence (NEv)
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. 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. 

Insufficient evidence (IEv)
NR
NR
NR
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Not relevant (NR)
NR
NR
NR
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Insufficient evidence (IEv)
NR
NR
NR
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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

The M.AtUB.Sa.UrcCom.GraAcu biotope is characterized by invertebrates with no known means to detect noise and as such will not be affected by changes in underwater noise as defined under this pressure.

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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Introduction of light or shading [Show more]

Introduction of light or shading

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

Evidence

The M.AtUB.Sa.UrcCom.GraAcu biotope is characterized by invertebrates with limited ability to detect light and is aphotic.  

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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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.AtUB.Sa.UrcCom.GraAcu biotope is 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.

Not relevant (NR)
NR
NR
NR
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Not relevant (NR)
NR
NR
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Not relevant (NR)
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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

The M.AtUB.Sa.UrcCom.GraAcu biotope is 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. 

Not relevant (NR)
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Not relevant (NR)
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Not relevant (NR)
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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

The M.AtUB.Sa.UrcCom.GraAcu biotope is 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.

Not relevant (NR)
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Biological Pressures

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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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Not relevant (NR)
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Not relevant (NR)
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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 the 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.

Insufficient evidence (IEv)
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Not relevant (NR)
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Insufficient evidence (IEv)
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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.

No evidence (NEv)
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No evidence (NEv)
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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 of the M.AtUB.Sa.UrcCom.GraAcu biotopes 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). 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). 

Sensitivity assessment. The slow growth rate, susceptibility to mechanical damage and impact of scavenging makes the characterizing 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:

Baron-Cohen, L.,, Fergusson, M., & Tyler-Walters, H., 2024. Gracilechinus acutus norvegicus assemblage on Atlantic lower bathyal 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/1278

Last Updated: 03/04/2024