The Marine Life Information Network

Temperature increase (local)

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

Evidence

Ophiura ophiura is a common boreo-lusitanian brittlestar recorded from North Norway and Iceland, south to the Azores, Madeira and into the Mediterranean and the Black Sea, frequent in the North Sea and Scandanavian waters and into the transitional area between the North Sea and the Baltic (Mortensen, 1927; Ursin, 1960; Tyler, 1977a; Feder, 1981; Southward & Campbell, 2006; OBIS, 2022). Therefore, the species is likely to experience a wide range of temperature regimes. OBIS (2022) lists records of Ophiura ophiura from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C. 

Temperature is a common spawning trigger in Ophiuroids but while Ophiura ophiura spawned at 12.5°C in 1974 but in 1973 larvae were found at 7.25°C in the coldest month of the year, so Tyler (1977a) suggested another environmental factor was involved.  Wood et al. (2010) exposed Ophiura ophiura to 10.5°C and 15°C in the laboratory; temperatures that they suggested were normal for spring and summer in the waters of Plymouth, UK. They reported a seven-fold increase in metabolic rate (measured as oxygen uptake) between 10.5°C and 15°C (an increase of 4.5°C), together with an increase in speed of movement, but no mortality in the 40-day experiment. However, Wood et al. (2010) suggested that the increase in metabolic rate could result in a reduction in arm regeneration and growth, and impact the survivorship of individuals in the long term. 

Sensitivity assessment. The distribution of Ophiura ophiura suggests that it is probably resistant to a 2°C change in temperature for a year.  Exposure to a short-term acute increase of 5°C may have an effect on the metabolism of Ophiura ophiura but there is no evidence to suggest that mortality would result.  Therefore, a resistance of 'High' is suggested but with Low confidence. Therefore, resilience is 'High', so the biotope is probably 'Not sensitive' at the benchmark level.

Temperature decrease (local)

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

Evidence

Ophiura ophiura is a common boreo-lusitanian brittlestar recorded from North Norway and Iceland, south to the Azores, Madeira and into the Mediterranean and the Black Sea, frequent in the North Sea and Scandanavian waters and into the transitional area between the North Sea and the Baltic (Mortensen, 1927; Ursin, 1960; Tyler, 1977a; Feder, 1981; Southward & Campbell, 2006; OBIS, 2022). Therefore, the species is likely to experience a wide range of temperature regimes. OBIS (2022) lists records of Ophiura ophiura from sea surface temperatures of 5 to 25°C although the majority of records were from 10-15°C. 

Temperature is a common spawning trigger in Ophiuroids but while Ophiura ophiura spawned at 12.5°C in 1974 but in 1973 larvae were found at 7.25°C in the coldest month of the year, so Tyler (1977a) suggested another environmental factor was involved. Crisp (1964 ed.) reported mass mortalities of Ophiura ophiura (as texturata) in South Wales, the Menai Straits and Nort-east Scotland after the severe winter of 1962/63 in which temperatures fell ca 5°C below average. 

Sensitivity assessment. The distribution of Ophiura ophiura suggests that it is probably resistant to a 2°C change in temperature for a year.  Exposure to a short-term acute increase of 5°C may may result in mass mortality of Ophiura ophiura in the affected area.  However, the biotope is probably protected by its depth and only the most shallow example may be vulnerable. Therefore, resistance is assessed as 'None', resilience as 'Medium, and sensitivity assessed as 'Medium' at the benchmark level.

Salinity increase (local)

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

Evidence

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). Information on the effects of hypersaline effluents (>40) is limited (Roberts et al., 2010b). Fernandez-Torquemada et al. (2008) reported that echinoderms (unspecified) were lost from Posidonia beds exposed to hypersaline effluents. Sanchez-Lizaso et al. (2008) reported increased mortality of Paracentrotus lividus at 40.5 to 41 psu in experimental aquaria. Chesher (1971, 1975) also reported significant mortality of echinoderms in Posidonia beds due to brine effluent but the mortality was attributed to copper contamination in the effluent. Roberts et al. (2010b) noted that, in most cases, the effects of brine effluents were limited to within 10s of metres of the outfalls. 

Sensitivity assessment. This biotope is unlikely to be exposed to hypersaline (brine) effluents unless the outfalls are placed at depth (although hypersaline effluents will sink) and it is a mobile species, likely to move away from the vicinity of the outfall. However, there is no evidence of the effect of hypersaline conditions on Ophiura ophiura or its aggregations on which to base an assessment. 

Salinity decrease (local)

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

Evidence

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).  However, several species are recorded from extreme salinities (Stickle & Diehl, 1987; Russell, 2013). Ophiura ophiura (as texturata) was recorded from 18 ppt in the Black Sea, from an average of 20 ppt in the transitional area between the North Sea and the Baltic Sea, from 21 to 31 ppt in the German Waddensea, and from 27 ppt from the delta region of the Netherlands (Ursin, 1960; Stickle & Diehl, 1987; Russell, 2013). Ursin (1960) cites records from the estuaries of the rivers Crouch and Roach on the south English coast. Mortensen (1927) notes that it may be found in the lower intertidal, where it buries itself in the sand as the tide recedes. OBIS (2022) lists records of Ophiura ophiura at sea surface salinities between 5 and 35 psu although the majority are from 30-35 psu. However, Ursin (1960) commented it was uncertain if it could reproduce at low salinities (ca 20 ppt) because Thorson (1946) did not find any larvae in the Øresund.  

Sensitivity assessment. Ophiura ophiura can probably survive a change in salinity from full (30-35) to reduced (18-30) for a year, perhaps more. However, it is unclear what density of individuals or populations occurred at the low salinities recorded above. This biotope is only recorded from full salinity (30-35) conditions. If, (as Ursin, 1960 suggests) low salinities impair recruitment, where good recruitment is required to maintain the dense aggregation of this species a change to reduced salinity conditions may result in a reduction in the population density in the short-term due to loss of recruitment or the species moving to more suitable conditions. Therefore, resistance is assessed as 'Medium' but with 'Low' confidence. Hence, resilience is 'High' and sensitivity is assessed as 'Low'. 

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

No information on tidal streams in this biotope (SS.SSa.CMuSa.Ooph) was available (JNCC, 2022).  However, Ophiura ophiura was recorded in biotopes from very weak to moderately strong (negligible to 1.5 m/s) tidal streams (Connor et al., 2004; Tillin & Tyler-Walters, 2014b). In addition, Ophiura ophiura is a sediment generalist recorded from silty mud, fine to very fine muddy sand, sandy mud and clean fine sands (Connor et al., 2004; Tillin & Tyler-Walters, 2014b). Local hydrography is important for recruitment in ophiuroids (Tyler, 1977b; Tyler & Banner, 1977; Balch et al., 1999). Olivier & Retiere (1998) noted that Ophiura ophiura was transported (drifted) during the tidal cycle in the English Channel. Extreme increases in water flow, that could remove the sediment, would adversely affect the biotope and cause the characteristic brittlestar population to relocate.  However, a change in the water flow of 0.1 to 0.2 m/s may reduce fines and favour more sandy sediments but Ophiura ophiura is recorded from muddy sands and sands. Therefore, resistance is assessed as 'High' based on expert judgement. Hence, resilience is assessed as 'High' and sensitivity as 'Not sensitive' at the benchmark level. 

Emergence regime changes

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

Evidence

This biotope (SS.SSa.CMuSa.Ooph) is recorded from 10-100 m in depth. Hence, emergence is 'Not relevant'.

Wave exposure changes (local)

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

Evidence

This biotope (SS.SSa.CMuSa.Ooph) is recorded from very exposed to moderately exposed wave conditions (JNCC, 2022), where depth probably attenuates wave-mediated water movement to allow the muddy muddy sands that characterize the biotope to persist.  Local hydrography is important for recruitment in ophiuroids (Tyler, 1977b; Tyler & Banner, 1977; Balch et al., 1999). Olivier & Retiere (1998) noted that Ophiura ophiura was transported (drifted) during the tidal cycle in the English Channel.  Extreme wave action from seasonal storms may be detrimental. For example, Rees et al. (1977) examined shallow benthic communities after major storms in the winter of  1975-1976 in North Wales. In Red Wharf Bay, Anglesey Ophiura ophiura (as texturata) was one of the most numerous species washed ashore. In Colwyn Bay, the muddy sands were scored away to the underlying gravel and Ophiura albida was removed in the process (0% survival). The sediments in Red Wharf Bay and Beaumaris Bay were modified but remained muddy (Rees et al., 1977). Therefore, seasonal storms have the potential to move and/or resuspend sediment and move and/or strand dense populations of brittlestars and result in loss of the biotope, depending on their depth and the severity of the storm. However, a 3-5% change in significant wave height (the benchmark) is unlikely to have a significant on the biotope, especially in the deeper examples.  Therefore, resistance is assessed as 'High', resilience as 'High' and sensitivity as 'Not sensitive'. 

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

Adult echinoderms such as Ophiothrix fragilis are known to be efficient concentrators of heavy metals including those that are biologically active and toxic (Ag, Zn, Cd and Co) (Hutchins et al., 1996). There was no information on the effect of this bioaccumulation. Gounin et al. (1995) studied the transfer of heavy metals (Fe, Mn, Pb, Cu and Cd) through Ophiothrix beds. They concluded that heavy metals ingested or absorbed by the animals transited rapidly through the body and were expelled in the faeces and did not appear to accumulate in their tissues. Studies by Deheyn & Latz (2006) at the Bay of San Diego found that heavy metal accumulation in brittlestars occurs both through dissolved metals as well as through diet, to the arms and disc, respectively. Similarly, Sbaihat et al. (2013) measured concentrations of heavy metals (Cu, Ni, Cd, Co, Cr and Pb) in the body of Ophiocoma scolopendrina collected from the Gulf of Aqaba, and found that most concentration was found in the central disc rather than arms and no simple correlations could be found between contaminant and body length. It is logical to suppose that brittlestar beds would be adversely affected by major pollution incidents such as oil spills, or by continuous exposure to toxic metals, pesticides, or the antiparasite chemicals used in cage aquaculture. However, there are no field observations of epifaunal brittlestar beds being damaged by any of these forms of pollution, and no evidence of the toxicity effects of heavy metal accumulation on brittlestars was found.

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

Echinoderms tend to be very sensitive to various types of marine pollution (Suchanek, 1993; Newton & McKenzie, 1995). Adult Ophiothrix fragilis have been documented to be intolerant to hydrocarbons (Newton & McKenzie, 1995). The sub-cuticular bacteria that are symbiotic with Ophiothrix fragilis are reduced in number following exposure to hydrocarbons. Exposure to ca 30,000 ppm oil reduces the bacterial load by 50% and brittlestars begin to die. All the Ophiothrix were dead after 6 days at ca 30,000 ppm but showed some recovery at ca 300 ppm.  (Newton & McKenzie, 1995).  Specimens of Amphiura filiformis, Ophiofrix fragilis and Ophiura ophiura collected from the North Sea in June 1993 after the Braer oil spill were found to have a reduced number of sub-cuticular bacteria as the oil contamination in the sediment increased, although sample size meant that the results were only significant for Amphiura (Newton & McKenzie, 1995). The water-accumulated fraction of diesel oil was acutely toxic to Ophiothrix fragilis and Ophiocomina nigra, although no field observations of beds being damaged by hydrocarbon pollution have been found (Hughes, 1998b). The majority of specimens of Ophiocomina nigra were killed by experimental exposure to 5 ppm of the dispersant BP1005 (Smith, 1968).  However, no direct evidence of resultant mortality in Ophiura spp. was found.

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

Echinoderms tend to be very sensitive to various types of marine pollution (Newton & McKenzie, 1995) but there was no more detailed information than this broad statement. Brittlestar beds may be damaged by chemical pollutants such as pesticides or anti-parasite chemicals used in aquaculture, but no direct evidence was found. 

Radionuclide contamination

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

Evidence

Adult echinoderms such as Ophiothrix fragilis were reported to be efficient concentrators of radionuclides (Hutchins et al., 1996). However, there was no information available about the effect of this bioaccumulation.

Introduction of other substances

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

Evidence

No evidence was found

De-oxygenation

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

Evidence

In their review of hypoxia, Vaquer-Sunyer & Duarte (2008) noted that echinoderms were amongst the most resistant to hypoxia after molluscs, and cited a sublethal threshold for Ophiura albida of 0.79 mg/l O₂ or 2.0 mg/l O₂ depending on the source. Diaz & Rosenberg (1995) listed Ophiura albida among species resistant to severe hypoxia. Riedel et al. (2012) used in situ chambers to manipulate oxygen concentrations at the sediment surface. They reported that mortality of Ophiura quinquemaculata occurred at the transition between hypoxia (median of 0.03 ml/l) and anoxia (median duration 6.1 hours). However, 13 species, including Ophiura spp. only died after 8.2 to 19.1 hours of anoxia.

Theede et al. (1969) reported an LD50 of 32 hours when Ophiura albida was exposed to 0.15 ml O₂/l (ca 0.21 mg/l O₂) which decreased to 30 hours with the addition of 50 mg/l of sodium sulphide. Theede et al. (1969) suggested that Ophiura albida was one of the three most resistant species they tested.  However, Vistisen & Vismann (1997) suggested that Theede et al. underestimated mortality rates due to methodological problems. Vistisen & Vismann (1997; cited in Gray et al., 2002) reported LT₅₀s of <0.1 mg/l O₂ (60 hours), 0.3 mg/l O₂ (144 hours), 0.5 mg/l O₂ (336 hours) in Ophiura albida, which also exhibited an initial escape response and lifted their disc's into the water column at 0.1 to 1.1 mg/l O₂. The presence of hydrogen sulphide decreased the lethal time.  At <0.1 mg/l O₂  and 2 µM H₂S, the LT₅₀ was 43.2 hours and decreased to 8 hours at 0.1 mg/l O₂ and 200 µM H₂S (Vistisen & Vismann, 1997; cited in Gray et al., 2002). Vistisen & Vismann (1997) noted that even very small increases in H₂S decreased survivability significantly. 

Belley et al. (2010) reported a high abundance of surface-feeding Ophiura spp. in the persistently hypoxic waters of the lower St Lawrence estuary. Ophiura spp. dominated (61.32 individuals/m²) in the hypoxic waters (<20% O₂, ca <6.5 mg/l) but was less abundant in normoxic waters.

Stachowitsch (1984) observed the mass mortality of benthic organisms in the Gulf of Trieste, northern Adriatic Sea, caused by the onset of severe hypoxia (oxygen depletion) in the near-bottom water. A wide variety of organisms was affected, including burrowing invertebrates, sponges, and the brittlestar Ophiothrix quinquemaculata, a dominant component of the local epifaunal community. All of the brittlestar Ophiothrix quinquemaculata were dead within 2-3 days, whereas Ophiura ophiura (as texturata) survived until day 3 at some stations. This event was likely caused by a combination of unfavourable weather and tidal conditions, at the same time as a period of maximal organic input from coastal pollution and dying phytoplankton. Water exchange in the Gulf was poor, and the area tended to accumulate sediment and suspended organic material, however, no estimate of oxygen concentrations was given (Stachowitsch, 1984). Mass mortality of Ophiura albida was also reported after eutrophication and a thermocline in the eastern German Bight in 1982 (Lawrence, 1996). Summer mass mortalities in the 1980s due to hypoxia caused by eutrophication and stratification were reported in the fjords of western Sweden in which Ophiura spp. were killed. Ophiura albida was the only echinoderm to recover after 1988 (Lawrence, 1996). 

Sensitivity assessment. The above evidence suggests that Ophiura spp. are resistant to severe hypoxia and only die once conditions become anoxic, under controlled conditions. However, Ophiura ophiura was reported to have died after three days during the severe hypoxia in the Gulf of Trieste, although the level of hypoxia was not quantified. Ophiura ophiura would probably survive at 2 mg/l O₂ for a week (see benchmark) but survival would decrease as the oxygen concentration decreased, the duration of the event increased and hydrogen sulphide increased in concentration. However, Ophiura ophiura is a mobile species capable of moving away from unsuitable local conditions. Therefore, resistance is assessed as 'Low' to represent the potential for significant mortality of Ophiura ophiura within the biotope after prolonged exposure (several days) to oxygen concentrations below 2 mg/l. Resilience is probably 'High' so sensitivity is assessed as 'Low'. 

Nutrient enrichment

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

Evidence

Mass mortalities of brittlestars, including Ophiura spp. have been attributed to eutrophication, in combination with stratification and resultant hypoxia (see Lawrence, 1996 above). Caspers (1980) reported a monoculture on Ophiura ophiura (as texturata) in parts of a sewage dumping site in the southern North Sea, composed of adults and juveniles with a density of up to 140 per 0.1 m² (1,400 /m²⁾ where it fed on the rich organic nutrients present. However, high densities of bivalves (Abra alba) or polychaetes in other parts of the dump site excluded Ophiura ophiura, probably due to space limitations (Caspers, 1980). Ursin (1960) noted that Ophiura ophiura reached high densities in the Limfjord where it did not grow very large feeding on detritus, but that it grew larger, in low densities, in the Kattegat where it was carnivorous. Hence growth rate and density were probably related to the food source (Ursin, 1960).

Feder & Pearson (1988) examined the benthic epifauna of Loch Eil and Loch Linnhe, 16-18 years after pulp mill effluent was discharged into the Lochs. Ophiura ophiura was found to feed on detritus, plant material and pulp fibres in the Loch Linnhe, in addition to its usual prey items.  However, Ophiura ophiura was common in Loch Linnhe and rare in Loch Eil. Feder & Pearson (1988) concluded that the absence of Ophiura and other species from Loch Eil was due to the change in sedimentary conditions from the pre-pollution (1963) to intermittently deoxygenated surface sediments by 1980. Pulp mill effluent ceased in 1980, and several species returned by 1982 but not Ophiura. 

Sensitivity assessment. The evidence suggests that eutrophication, organic enrichment and resultant hypoxia have resulted in mass mortalities of ophiuroids, including Ophiura ophiura (see 'deoxygenation' above).  No evidence of the effect of nutrient enrichment (nitrogen and phosphorus) on the biotope was found. However, the mass mortalities reported in the past subject that eutrophication (e.g. a change from 'good' to 'moderate' water quality, see benchmark) could result in mortality if local conditions allowed for hypoxia to occur. Therefore, resistance is assessed as 'Medium', as a precaution, albeit with 'Low' confidence since the level of enrichment is not quantified in the evidence. Hence, resilience is 'High' and sensitivity is assessed as 'Low'. 

Organic enrichment

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

Evidence

Mass mortalities of brittlestars, including Ophiura spp. have been attributed to eutrophication, in combination with stratification and resultant hypoxia (see Lawrence, 1996 above). Caspers (1980) reported a monoculture on Ophiura ophiura (as texturata) in parts of a sewage dumping site in the southern North Sea, composed of adults and juveniles with a density of up to 140 per 0.1 m² (1,400 /m²⁾ where it fed on the rich organic nutrients present. However, high densities of bivalves (Abra alba) or polychaetes in other parts of the dump site excluded Ophiura ophiura, probably due to space limitations (Caspers, 1980). Ursin (1960) noted that Ophiura ophiura reached high densities in the Limfjord where it did not grow very large feeding on detritus, but that it grew larger, in low densities, in the Kattegat where it was carnivorous. Hence growth rate and density were probably related to the food source (Ursin, 1960).

Feder & Pearson (1988) examined the benthic epifauna of Loch Eil and Loch Linnhe, 16-18 years after pulp mill effluent was discharged into the Lochs. Ophiura ophiura was found to feed on detritus, plant material and pulp fibres in the Loch Linnhe, in addition to its usual prey items.  However, Ophiura ophiura was common in Loch Linnhe and rare in Loch Eil. Feder & Pearson (1988) concluded that the absence of Ophiura and other species from Loch Eil was due to the change in sedimentary conditions from the pre-pollution (1963) to intermittently deoxygenated surface sediments by 1980. Pulp mill effluent ceased in 1980, and several species returned by 1982 but not Ophiura. 

Sensitivity assessment. The evidence suggests that eutrophication, organic enrichment and resultant hypoxia have resulted in mass mortalities of ophiuroids, including Ophiura ophiura (see 'deoxygenation' above).  However, the observation of high densities of Ophiura ophiura in a sewage sludge dumping ground, on organically enriched sediment (Caspers, 1980) suggests that Ophiura ophiura and, hence, this biotope may be resistant to and even benefit from areas of organic enrichment (Ursin, 1960; Caspers, 1980; Feder & Pearson, 1988) in the absence of hypoxia. Therefore, resistance is assessed as 'High', albeit with 'Low' confidence since the level of enrichment is not quantified in the evidence. Hence, resilience is 'High' and sensitivity is assessed as 'Not sensitive'. 

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 habitat (Resilience is Very Low). Sensitivity within the direct spatial footprint of this pressure is therefore High. Although no specific evidence is described, confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

f the sediment that characterizes the biotopes was replaced with rock substrata, this would represent a fundamental change to the physical character of the biotope. The characterizing species would no longer be supported and the biotopes would be lost and/or reclassified.  Therefore, resistance to the pressure is considered 'None', and resilience 'Very low', given the permanent nature of this pressure. Sensitivity has been assessed as 'High'. Although no specific evidence is described, confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another sediment type)

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

Evidence

Ophiura ophiura is a sediment generalist recorded from silty mud, fine to very fine muddy sand, sandy mud, clean fine sands, gravels and broken shells (Connor et al., 2004; Boos & Franke, 2006; Boos et al., 2010 Tillin & Tyler-Walters, 2014b), while this biotope (SS.SSa.CMuSa.Ooph) is recorded from muddy sands (JNCC, 2022). Caspers (1980) reported a dense population of Ophiura ophiura (as texturata) on fine, organically-rich, mud at a sewage sludge dumpsite. Boos et al. (2010) concluded that Ophiura ophiura was relatively unselective of sediment type, as it did not rely on burrowing to escape predators and escaped by quickly moving across the substratum. Hence, a change in sediment type from muddy sands to mud or coarse sediment is unlikely to affect Ophiura ophiura.  It is unclear if muddy sands are a prerequisite for the development of the dense aggregations of Ophiura ophiura that characterize this biotope. As this species is a widespread, common, member of the sedimentary epifauna and a sediment generalist it seems unlikely that sediment type is a prerequisite for the development of the biotope.  Therefore, resistance is assessed as 'High' but with 'Low' confidence. Hence, resilience is assessed as 'High' and sensitivity as 'Not sensitive'. 

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

Ophiura ophiura is epifaunal, living on the sediment surface and occasionally burrowing into the surface layer. Removal of the sediment to a depth of 30 cm (the benchmark) would remove all of the benthos within the affected area, and result in the loss of the biotope.  Therefore, resistance is assessed as 'None', resilience as 'Medium' (assuming suitable sediment remains)  and sensitivity is assessed as 'Medium'. 

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

The effect of fishing gear on sedimentary epifauna has been studied by numerous authors in the past few decades. The effect of trawling on Ophiura spp. and other epifauna varies between studies depending on the gear used and sediment type and the survival of bycatch on the gear type and duration of aerial exposure.

Bergman & Van Santbrink (2000b) examined the effect of different types of beam trawls and otter trawls in sandy sediments in the Dutch North Sea. They reported that megafauna (>1 cm) experienced annual fishing mortality of 5-35% mainly due to the direct impact of the trawl on the trawl track or indirectly due to disturbance and predation. In particular, Ophiura ophiura experienced between 2 and 12% mortality but there were no significant differences between trawl types examined. Bergman & Van Santbrink (2000b) reported that Ophiura ophiura experienced a 7% mortality, across all trawl fisheries in1994 in the Dutch sector of the North Sea.   Bradshaw et al. (2000) noted that animals with hard tests, e.g. brittlestars such as Ophiura spp. were badly damaged by contact with scallop dredges or beam trawls, although they also reported that the abundance of Ophiura albida increased in dredge tracks. Bergman & Hup (1992) reported that the number of small Ophiura (0.1-0.4 cm) in the surface sediment did not change after three-fold experimental trawling, probably because they escaped undamaged through meshes. Hinz et al. (2012) also reported significant negative effects of queen dredges (for scallops) on Ophiura ophiura in the dredge tracks. The significant differences between the two types of queen dredge were not seen in bycatch but in the tracks, which suggested the effect was due to the direct impact of the dredges used.  Smith et al. (2000) noted that epifaunal abundance was reduced in otter-trawl tracks during the trawling season (October-March) in the Mediterranean but increased again after the trawling season.

Constantino et al. (2009) examined the effect of clam dredging on the sediment community at different depths. At 18 m that noted that Ophiura ophiura was removed from dredge tracks directly after trawling but had returned within 1 day and were present at least 96 days after trawling. However, as scavengers Ophiura ophiura may be expected to be attracted to discards and injured organisms in the path of fishing gear. Kaiser & Spencer (1995) reported that 96% of Ophiura ophiura bycatch were alive after experimental trawling with a 4 m beam trawl but that mortality increased to 19% after 120 hours. Mortality was due to >50% damage to the disc (Kaiser & Spencer, 1995). Bergmann & Moore (2001b) reported 100% mortality in the Ophiura ophiura brought onboard as bycatch 14 days after trawling and aerial exposure and high mortality (91%) in specimens returned to the water immediately after trawling. They concluded that earlier studies underestimated mortality because they only monitored mortality for up to five days. 

Rumohr & Kujawski (2000) compared historical data on epifauna in the southern North Sea from  1900-1912 with data from 1986. They noted that bivalve populations had declined while scavengers and predators  (sea stars, crustaceans and gastropods) have increased in frequency due to the effects of fishing activities. However, they reported that Ophiura ophiura was absent from their stations in 1986 but had occurred in 55% of stations in 1900-1912, while other Ophiura spp. had increased in frequency. Bradshaw et al. (2002) reported that Ophiura albida was one of a number of species that increased in abundance over a 60-year period from ca 1939 and 1950 to 1994 in areas of the Irish Sea subject to scallop dredging. They suggested that the life-history characteristics of Ophiura spp. (mobility and good regeneration from non-fatal injuries) provided resilience against the long-term impacts of trawling. Callaway et al. (2007) reported that Ophiura ophiura was one of 12 species to double their spatial presence (distribution) in the North Sea from 1902 to 2000, in spite of fishing activity.

Sensitivity assessment. In their summary, Bergmann & Moore (2001b) noted that while some studies concluded that Ophiura ophiura was resilient to fishing gear due to their high capacity for regeneration and some studies had found a significant increase in Ophiura ophiura densities after experimental trawling, other studies had shown a significant reduction in ophiuroid densities due to fishing disturbance. They concluded that the species continued abundance in the Clyde Sea suggested that populations exposed to trawling could be restocked from adjacent populations and that brittlestar mortality from trawling could be outweighed by the species' reproductive resilience and the possible reduction in the density of its predators or competitors by fishing activities (Bergmann & Moore, 2001b). Therefore, resistance is assessed as 'Low' based on the potential mortality from direct contact with fishing gear or as bycatch. However, resilience is probably 'High' so sensitivity is assessed as 'Low'. 

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

Ophiura ophiura is epifaunal but can burrow into the surface of the sediment. The effects of penetrative gear are likely to be very similar to the effects of fishing gear that only disturbs the surface of the sediment (see 'abrasion' above). Therefore, resistance is assessed as 'Low' based on the potential mortality from direct contact with fishing gear or as bycatch. However, resilience is probably 'High' so sensitivity is assessed as 'Low'. 

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

Ophiura ophiura is a sediment generalist recorded from silty mud, fine to very fine muddy sand, sandy mud, clean fine sands, gravels and broken shells (Connor et al., 2004; Boos & Franke, 2006; Boos et al., 2010 Tillin & Tyler-Walters, 2014b), while this biotope (SS.SSa.CMuSa.Ooph) is recorded from muddy sands (JNCC, 2022). Schäfer (1972) noted that brittlestars were usually free from areas of frequent sedimentation but often preserved by rapid sedimentation events and burial (see smothering below). However, no direct evidence of the effects of suspended sediment on Ophiura ophiura was found.  Ophiura ophiura is an omnivore, active predator, scavenger, and detritivore and is not dependent on suspended sediment for its food supply. Therefore, resistance is assessed as 'High' but with Low confidence. Hence, resilience is 'High' and sensitivity is assessed as 'Not sensitive'.  

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

Lawrence (1996) noted that smothering was the only main cause of mass mortality for fossil echinoderms.  Schäfer (1972) noted that brittlestars were usually free from areas of frequent sedimentation but often preserved by rapid sedimentation events and burial, for example, during and after storms. Schäfer (1972) suggested that the sudden deposition of only 5 cm of sediment was enough to immobilize and kill brittlestars. However, experimental studies suggested that Ophiura ophiura was resistant of burial (Last et al., 2011; Henrick et al., 2016). In experimental chambers, Ophiura ophiura were buried under 2, 5 or 7 cm of fine, medium or coarse sediment. Mortality after burial depended on the depth and duration of burials as well as the sediment type. Mortality was highest after 32 days of burial (18.5%), in the fine sediment (16.7%) and at 7 cm (22.2%) but was also highest in the largest individuals (6 to 9.7 cm across). However, overall mortality was low (ca 9.9%) due to its ability to emerge from burial. Emergence exceeded 60% in all durations and depths of burial, but was highest in medium sediment (94.4%) and low depths (94.4%) and lowest under coarse sediment (40.7%) decreasing with increasing depth (Last et al., 2011; Henrick et al., 2016).

Sensitivity assessment. Last et al. (2011) and Henrick et al. (2016) concluded that Ophiura ophiura was highly tolerant (resistant) of burial under 2-7 cm of fine to coarse sediment for up to 32 days. Therefore, this Ophiura ophiura dominated biotope is likely to experience some mortality due to the sudden deposition of 5 cm of fine sediment (the benchmark) and resistance is assessed as 'Medium' (<25% mortality). Hence, resilience is probably 'High' and sensitivity is assessed as 'Low'.

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

Lawrence (1996) noted that smothering was the only main cause of mass mortality for fossil echinoderms. Schäfer (1972) noted that brittlestars were usually free from areas of frequent sedimentation but often preserved by rapid sedimentation events and burial, for example, during and after storms. Schäfer (1972) suggested that the sudden deposition of only 5 cm of sediment was enough to immobilize and kill brittlestars.  However, experimental studies suggested that Ophiura ophiura was resistant of burial (Last et al., 2011; Henrick et al., 2016). In experimental chambers, Ophiura ophiura were buried under 2, 5 or 7 cm of fine, medium or coarse sediment. Mortality after burial depended on the depth and duration of burials as well as the sediment type. Mortality was highest after 32 days of burial (18.5%), in the fine sediment (16.7%) and at 7 cm (22.2%) but was also highest in the largest individuals (6 to 9.7 cm across). However, overall mortality was low (ca 9.9%) due to its ability to emerge from burial. Emergence exceeded 60% in all durations and depths of burial, but was highest in medium sediment (94.4%) and low depths (94.4%) and lowest under coarse sediment (40.7%) decreasing with increasing depth (Last et al., 2011; Henrick et al., 2016).

Sensitivity assessment. Last et al. (2011) and Henrick et al. (2016) concluded that Ophiura ophiura was highly tolerant (resistant) of burial under 2-7 cm of fine to coarse sediment for up to 32 days. However, the sudden deposition of 30 cm of fine sediment (the benchmark) is likely to be more damaging. Therefore, this Ophiura ophiura dominated biotope is likely to experience significant mortality and resistance is assessed as 'None' based on evidence from palaeoecology (Schäfer, 1972).  Nevertheless, resilience is probably 'Medium' and sensitivity is assessed as 'Medium'.

Litter

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

Evidence

No evidence was found and no assessment was made. 

Electromagnetic changes

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

Evidence

No evidence was found

Underwater noise changes

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

Evidence

Ophiura spp. probably reacts to vibration but is unlikely to respond to noise as defined by the benchmark. 

Introduction of light or shading

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

Evidence

Fell (1966) noted that brittlestars were negatively phototactic and avoided visual predators by taking shelter under stones, in crevices or hollows, burrowing or using cryptic colouration. Moore & Cobb (1985) reported that Ophiura ophiura immediately 'freeze' any movement in response to shading but that this response was overridden by the presence of food. Sköld (1985) reported that approaching Ophiura ophiura with the plan of the hand, without contact, was enough to elicit a phototactic escape response.  Therefore, a phototactic response to shading is probably a response to a potential predator.  Sköld (1985) and Boos et al. (2010) noted that Ophiura ophiura did not avoid predators by burrowing but rather rapidly escaped across the substratum surface, except in aquaria where other Ophiura ophiura were consumed by fish and predation was intense, in which case they did burrow (Sköld, 1985). However, shading or illumination of this biotope is unlikely to have any negative effects, especially at depth and the pressure is assessed as 'Not relevant'. 

Barrier to species movement

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

Evidence

Not relevant. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of larvae but larval dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

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

Evidence

Not relevant to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

Visual disturbance

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

Evidence

Fell (1966) noted that brittlestars were negatively phototactic and avoided visual predators by taking shelter under stones, in crevices or hollows, burrowing or using cryptic colouration. Moore & Cobb (1985) reported that Ophiura ophiura immediately 'freeze' any movement in response to shading but that this response was overridden by the presence of food. Sköld (1985) reported that approaching Ophiura ophiura with the plan of the hand, without contact, was enough to elicit a phototactic escape response.  Therefore, a phototactic response to shading is probably a response to a potential predator.  Sköld (1985) and Boos et al. (2010) noted that Ophiura ophiura did not avoid predators by burrowing but rather rapidly escaped across the substratum surface, except in aquaria where other Ophiura ophiura were consumed by fish and predation was intense, in which case they did burrow (Sköld, 1985).  Therefore, short-range visual disturbance due to the presence of a potential predator or from the hands of divers may be expected to elicit an escape response. However, their visual range is probably very limited and visual disturbance from passing machinery, vessels or boats is unlikely to be relevant.

Genetic modification & translocation of indigenous species

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

Evidence

No evidence was found to suggest that Ophiura ophiura is translocated or subject to genetic modification. Therefore, this pressure is assessed as 'Not relevant'. 

Introduction or spread of invasive non-indigenous species

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

Evidence

The American slipper limpet Crepidula fornicata was introduced to the UK and Europe in the 1870s from the Atlantic coasts of North America with imports of the eastern oyster Crassostrea virginica. It was recorded in Liverpool in 1870 and the Essex coast in 1887-1890. It has spread through expansion and introductions along the full extent of the English Channel and into the European mainland (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Helmer et al., 2019; Hinz et al., 2011; McNeill et al., 2010; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015).

Crepidula fornicata is recorded from shallow, sheltered bays, lagoons and estuaries or the sheltered sides of islands, in variable salinity (18 to 40) although it prefers ca 30 (Tillin et al., 2020). Larvae require hard substrata for settlement. It prefers muddy gravelly, shell-rich, substrata that include gravel, or shells of other Crepidula, or other species e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. But it also recorded in a wide variety of habitats including clean sands, artificial substrata, Sabellaria alveolata reefs and areas subject to moderately strong tidal streams (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015; Tillin et al., 2020).

High densities of Crepidula fornicata cause ecological impacts on sedimentary habitats. The species can form dense carpets that can smother the seabed in shallow bays, changing and modifying the habitat structure. At high densities, the species physically smothers the sediment, and the resultant build-up of silt, pseudofaeces, and faeces is deposited and trapped within the bed (Tillin et al., 2020, Fitzgerald, 2007, Blanchard, 2009, Stiger-Pouvreau & Thouzeau, 2015). The biodeposition rates of Crepidula are extremely high and once deposited, form an anoxic mud, making the environment suitable for other species, including most infauna (Stiger-Pouvreau & Thouzeau, 2015, Blanchard, 2009). For example, in fine sands, the community is replaced by a reef of slipper limpets, that provide hard substrata for sessile suspension-feeders (e.g., sea squirts, tube worms and fixed shellfish), while mobile carnivorous microfauna occupy species between or within shells, resulting in a homogeneous Crepidula dominated habitat (Blanchard, 2009). Blanchard (2009) suggested the transition occurred and became irreversible at 50% cover of the limpet. De Montaudouin et al. (2018) suggested that homogenization occurred above a threshold of 20-50 Crepidula /m².

Impacts on the structure of benthic communities will depend on the type of habitat that Crepidula colonizes. De Montaudouin & Sauriau (1999) reported that in muddy sediment dominated by deposit-feeders, species richness, abundance and biomass increased in the presence of high densities of Crepidula (ca 562 to 4772 ind./m²), in the Bay of Marennes-Oléron, presumably because the Crepidula bed provided hard substrata in an otherwise sedimentary habitat. In medium sands, Crepidula density was moderate (330-1300 ind./m²) but there was no significant difference between communities in the presence of Crepidula. Intertidal coarse sediment was less suitable for Crepidula with only moderate or low abundances (11 ind./m²) and its presence did not affect the abundance or diversity of macrofauna. However, there was a higher abundance of suspension–feeders and mobile Crustacea in the absence of Crepidula (De Montaudouin & Sauriau, 1999). The presence of Crepidula as an ecosystem engineer has created a range of new niche habitats, reducing biodiversity as it modifies habitats (Fitzgerald, 2007). De Montaudouin et al. (1999) concluded that Crepidula did not influence macroinvertebrate diversity or density significantly under experimental conditions, on fine sands in Arcachon Bay, France. De Montaudouin et al. (2018) noted that the limpet reef increased the species diversity in the bed, but homogenised diversity compared to areas where the limpets were absent. In the Milford Haven Waterway (MHW), the highest densities of Crepidula were found in areas of sediment with hard substrata, e.g., mixed fine sediment with shell or gravel or both (grain sizes 16-256 mm) but, while Crepidula density increased as gravel cover increased in the subtidal, the reverse was found in the intertidal (Bohn et al., 2015). Bohn et al. (2015) suggested that high densities of Crepidula in high-energy environments were possible in the subtidal but not the intertidal, suggesting the availability of this substratum type is beneficial for its establishment. Hinz et al. (2011) reported a substantial increase in the occurrence of Crepidula off the Isle of Wight, between 1958 and 2006, at a depth of ca 60 m, on hard substrata (gravel, cobbles, and boulders), swept by strong tidal streams. Presumably, Crepidula is more tolerant of tidal flow than the oscillatory flow caused by wave action which may be less suitable (Tillin et al., 2020).

The availability of hard substrata (e.g., gravel) may only restrict initial colonization as higher densities of Crepidula function as substrata for subsequent colonization (Thieltges et al., 2004; Blanchard, 2009). However, Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas of homogenous fine sediment and areas dominated by boulders. Bohn et al. (2015) suggested that wave action (exposure) probably prevented the establishment of large numbers of Crepidula in high-energy areas. Blanchard (2009) noted that sandy areas in the Bay of Saint-Mont Michel were not colonized by Crepidula because of surface sand mobility. Thieltges et al. (2003) also noted that storm events removed some clumps of mussels and presumably Crepidula onto tidal flats where they disappeared, which caused their abundance to fluctuate. Similarly, Crepidula was absent from sandy substrata in Swansea Bay but was most abundant in the shelter of the breakwater at the Swansea east site (Powell-Jennings & Calloway, 2018). Powell-Jennings & Calloway (2018) noted that Crepidula is killed by sudden burial and possibly burial due to deposition, which could mitigate Crepidula density.

Sensitivity assessment. The sediments characterizing this biotope are likely to be unsuitable for most of the invasive non-indigenous species currently recorded in the UK. However, the above evidence also suggests that mud and fine sediments are unsuitable for the colonization of Crepidula fornicata due to the lack of gravel, shells, or any other hard substrata used for larvae settlement (Bohn et al., 2015; Tillin et al., 2020). This biotope is exposed to wave action and the resultant sediment mobility may also prevent colonization by Crepidula. In addition, Ophiura ophiura is an omnivore, feeding on a range of other species, including their larvae. It is unlikely that Crepidula larvae will survive settlement in this habitat due to the presumed high level of larval predation by the high density of the Ophiura ophiura.  Therefore, this resistance to colonization by Crepidula is assessed as 'High', resistance as 'High', and sensitivity as 'Not sensitive'. However, Crepidula has not yet been reported to occur in this biotope so the confidence in the assessment is 'Low' and further evidence is required. 

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

Ophiura ophiura is associated with the parasitic copepod Parartotrogus richardi (Mortensen, 1927; Southward & Campbell, 2006).  Mortensen (1927) reported that Ophiura ophiura (as texturata) was infested with the parasitic green alga Coccomyxa ophiurae in the Limfjord. The alga dissolves the brittlestar's skeleton, presumably leading to death (Mortensen, 1927). Any parasitic infestation/disease may result in some mortality within the population. Therefore, resistance is assessed as 'Medium' based on limited evidence. Hence, resilience is 'High' and sensitivity is assessed as 'Low' but with 'Low' confidence. 

Removal of target species

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

Evidence

Ophiura ophiura is not subject to a targetted fishery. Hence, this pressure is 'Not relevant' in this biotope. 

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

Ophiura spp. are often removed as bycatch.  Bergman & Van Santbrink (2000b) examined the effect of different types of beam trawls and otter trawls in sandy sediments in the Dutch North Sea. They reported that megafauna (>1 cm) experienced annual fishing mortality of 5-35% mainly due to the direct impact of the trawl on the trawl track or indirectly due to disturbance and predation. In particular, Ophiura ophiura experienced between 2 and 12% mortality but there were no significant differences between trawl types examined. Bergman & Van Santbrink (2000b) reported that Ophiura ophiura experienced a 7% mortality, across all trawl fisheries in1994 in the Dutch sector of the North Sea.   Bradshaw et al. (2000) noted that animals with hard tests, e.g. brittlestars such as Ophiura spp. were badly damaged by contact with scallop dredges or beam trawls, although they also reported that the abundance of Ophiura albida increased in dredge tracks. Bergman & Hup (1992) reported that the number of small Ophiura (0.1-0.4 cm) in the surface sediment did not change after three-fold experimental trawling, probably because they escaped undamaged through meshes. Hinz et al. (2012) also reported significant negative effects of queen dredges (for scallops) on Ophiura ophiura in the dredge tracks. The significant differences between the two types of queen dredge were not seen in bycatch but in the tracks, which suggested the effect was due to the direct impact of the dredges used.  Smith et al. (2000) noted that epifaunal abundance was reduced in otter-trawl tracks during the trawling season (October-March) in the Mediterranean but increased again after the trawling season.

Constantino et al. (2009) examined the effect of clam dredging on the sediment community at different depths. At 18 m that noted that Ophiura ophiura was removed from dredge tracks directly after trawling but had returned within 1 day and were present at least 96 days after trawling. However, as scavengers Ophiura ophiura may be expected to be attracted to discards and injured organisms in the path of fishing gear. Kaiser & Spencer (1995) reported that 96% of Ophiura ophiura bycatch were alive after experimental trawling with a 4 m beam trawl but that mortality increased to 19% after 120 hours. Mortality was due to >50% damage to the disc (Kaiser & Spencer, 1995). Bergmann & Moore (2001b) reported 100% mortality in the Ophiura ophiura brought onboard as bycatch 14 days after trawling and aerial exposure and high mortality (91%) in specimens returned to the water immediately after trawling. They concluded that earlier studies underestimated mortality because they only monitored mortality for up to five days. 

Rumohr & Kujawski (2000) compared historical data on epifauna in the southern North Sea from  1900-1912 with data from 1986. They noted that bivalve populations had declined while scavengers and predators  (sea stars, crustaceans and gastropods) have increased in frequency due to the effects of fishing activities. However, they reported that Ophiura ophiura was absent from their stations in 1986 but had occurred in 55% of stations in 1900-1912, while other Ophiura spp. had increased in frequency. Bradshaw et al. (2002) reported that Ophiura albida was one of a number of species that increased in abundance over a 60-year period from ca 1939 and 1950 to 1994 in areas of the Irish Sea subject to scallop dredging. They suggested that the life-history characteristics of Ophiura spp. (mobility and good regeneration from non-fatal injuries) provided resilience against the long-term impacts of trawling. Callaway et al. (2007) reported that Ophiura ophiura was one of 12 species to double their spatial presence (distribution) in the North Sea from 1902 to 2000, in spite of fishing activity.

Sensitivity assessment. In their summary, Bergmann & Moore (2001b) noted that while some studies concluded that Ophiura ophiura was resilient to fishing gear due to their high capacity for regeneration and some studies had found a significant increase in Ophiura ophiura densities after experimental trawling, other studies had shown a significant reduction in ophiuroid densities due to fishing disturbance. They concluded that the species continued abundance in the Clyde Sea suggested that populations exposed to trawling could be restocked from adjacent populations and that brittlestar mortality from trawling could be outweighed by the species' reproductive resilience and the possible reduction in the density of its predators or competitors by fishing activities (Bergmann & Moore, 2001b). Therefore, resistance is assessed as 'Low' based on the potential mortality from direct contact with fishing gear or as bycatch. However, resilience is probably 'High' so sensitivity is assessed as 'Low'.