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Corymorpha, Gersemia, Zoantharia and Heliometra glacialis on Arctic mid bathyal rock and other hard substrata

Distribution MapBIO Map Legend

Summary

UK and Ireland classification

Description

This biotope has been recorded on a cobble matrix at the base of the Wyville-Thomson Ridge. The most conspicuous fauna is an unidentified orange zoanthid, Corymorpha and Gersemia, although there is a dense ophiuroid bed present also. It is found in the cold Arctic waters.

Depth range

600-1100 m

Additional information

-

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

This biotope occurs in the Arctic mid bathyal zone on a cobbles matrix at the base of the Wyville-Thomson Ridge and is characterized by four species, Corymorpha sp., Gersemia sp., Zoantharia sp. and Heliometra glacialis. Other species and taxa present in the assemblage include Ophiuroidea indet., encrusting Porifera, Sabellidae, Asbestopluma lycopodium, Hydrozoa (bushy), Cyclostomatida, Actiniaria (sediment-dwelling),  Actiniaria indet., Tubularia and Actinostolidae.

The important characterizing species are the focus for the sensitivity assessment, as the loss of these species and/or change in substrata will result in a change of biotope.  The potential sensitivity of other species is mentioned where relevant. 

Resilience and recovery rates of habitat

Corymorpha is a genus of solitary athecate hydroid. Two species may inhabit the M.ArMB.Ro.MixCor.CorGer biotope; Corymorpha glacialis and Corymorpha groenlandica. Corymorpha glacialis has two forms, a shallow (<200 m) and deep-water (<1,050 m), and is an Arctic species with a southern limit of the Faroe-Shetland region (Schuchert, 2010). Corymorpha groenlandica is also an Arctic species, occurring as south as the Faroe-Shetland region (Schuchert, 2010), with polyps up to 10 cm long. Corymorpha groenlandica has a deeper distribution than Corymorpha glacialis, occurring down to 2,000 m (Schuchert, 2010). However, there is limited evidence available for both of these species and evidence in this assessment includes other species within Corymorpha and other athecate hydroids.

Hydroids are characterized by having a life cycle involving sexual and asexual reproduction. Most hydroids have a benthic, colonial polyp stage which reproduces asexually by budding. Asexual multiplication of Corymorpha groenlandica polyps via frustules has been reported (Schuchert, 2010). Dutto et al. (2019) observed signs in Corymorpha januarii – a shallow-water species of Corymorpha – of budding in an Argentinean estuary, with smaller polyps attached to bigger ones. Corymorpha januarii polyps show strong seasonality in temperate waters, cycling through periods of senescence and regeneration, often making them visually absent from the benthos for prolonged periods (Dutto et al., 2019). This behaviour is also observed in Corymorpha palma and Corymorpha nutans (Torrey, 1910; Svoboda, 1973). This process may allow polyps to survive during winter months when seawater temperatures decrease, entering a resting stage in the substrata. Polyps may then regenerate when temperatures increase, restarting the cycle (Dutto et al., 2019). The dormant stages of hydroid life cycles are very resistant to environmental perturbation (Gili & Huges, 1995). Although polyps may be destroyed or removed, the resting stages may survive, providing a mechanism for rapid recovery (Cornelius, 1995a; Kosevich & Marfenin, 1986). Regeneration from damage is also possible among hydroids.  For example, Schmidt & Warner (1991) observed the distal regeneration of Sertularia culpressina from broken colony stems. In addition, Corymorpha can reproduce sexually. The medusa of some Corymorpha species, such as Corymorpha nutans, release sperm and eggs and fertilization occurs externally, developing a planula larvae that eventually settles onto the seabed. Other species, such as Corymorpha glacialis, are viviparous. Embryos develop in sporosac, resulting in the release of 2 mm sized polyps (Schuchert, 2010). Schuchert (2010) reports that Corymorpha groenlandica has both male and female gonophores, with females containing 10-12 eggs. There were no reports of viviparity or medusa stage in this species. Therefore, Corymorpha groenlandica polyps likely directly release sperm and eggs, which fertilize externally, with no medusa stage, developing planula larvae that subsequently settle and metamorphose into a polyp.

There is little direct evidence of Corymorpha ability to recover from disturbance. Teixidó et al. (2004) described the recovery of the benthos in the SE Weddell Sea shelf from iceberg scour. Corymorpha parvula was among the first species to recolonize disturbed areas that Teixidó et al. (2004) categorised as ‘R0’, where the mega-epifauna of the colonized area represented <10% of that in the equivalent undisturbed areas (Gutt & Starmans, 2001). Jones et al. (2012) studied the rate of recovery after drilling activity in the Faroe-Shetland Channel.  Two former drilling sites were investigated; Site A (three years post drilling) and Site C (ten years post drilling), as well as representative background sites outside the influence of drilling activity. Corymorpha groenlandica was recorded as absent from Site A but present at Site C. Corymorpha groenlandica was present at the background sites. This study suggests that in this region, Corymorpha groenlandica recovers between three and ten years after drilling activity. However, these results in Site A must be used with caution, as hydroids may appear absent from the benthos when in a reduced resting phase.

Soft corals, Alcyonacea, reproduce both sexually and asexually. Runners, fragments, buds and splitting techniques, facilitate asexual reproduction. Sexual reproduction occurs by either broadcast spawning or brooding. Sun et al. (2011) observed the direct release of 79 planulae from Gersemia fruticosa (after brooding) in aquaria between 1.5 and 2.5 mm long. Metamorphosis and settlement of the larvae occurred 3-70 days post-release. Polyps grew 6-10 mm tall within two to three months. However, after this period, growth was virtually null. Sun et al. (2011) suggest that this species is slow-growing, and emphasised the vulnerability of soft coral populations to anthropogenic and natural disturbances. However, Sun et al. (2011) stated that sexual maturity may be reached at a small size, possibly offsetting slow growth. For example, the smallest sized fertile colony of Gersemia fruticose measured 2 cm in height, 1 cm in diameter and comprised of only 10 polyps.

Henry et al. (2003) simulated disturbance caused by bottom fishing on Gersemia rubiformis. Four colonies were rolled and crushed 10 times, once every day, for two months. Crushing induced an immediate retraction of the colony. Daughter colonies were also produced in crushed corals, however, contrary to expectation, these colonies were derived sexually and not by budding or fragmentation. Henry et al. (2003) hypothesized that when crushed, colonies prematurely expulse larvae to dispose of the energy-intensive planulae in favour of colony repair. Between 18 and 21 days after disturbance, new tissue had completely covered wounds on the coral surface. Within 25-30 days, new polyps emerged from the regenerated tissues. Henry et al. (2003) concluded that the ability to regenerate from acute localised injuries, contract and survive crushing may benefit Gersemia rubiformis in heavily disturbed habitats, e.g. where bottom fishing occurs and mechanical disturbance is high. The investigation of recovery after drilling (Jones et al. 2012; above) observed the recovery of Gersemia sp. Similarly, to Corymorpha groenlandica, Gersemia sp. had recovered between three and ten years post-disturbance.

There is limited evidence of the reproduction, life history, dispersal or ecology of deep-sea zoanthids. Gametogenesis is a continual process for two colonial deep-sea species, Epizoanthus paguriphilus and Epizoanthus abyssorum (Muirhead et al., 1986). Within the Porcupine Seabight (Ireland), the former is distributed 600-1,550 m and the latter at 3,500-4,350 m, and are associated with the carapace of Parapagurus pilosimanus (Muirhead et al., 1986). Continual gametogenesis in deep-sea Epizoanthus species differs from shallow water and tropical zoanthids, which typically spawn in summer, driven by rises in temperature (Ryland, 1997). Macronemina, a suborder that contains the Epizoanthus genus, are usually gonochoric, however, hermaphroditic Epizoanthus areanaceus have been observed (Ryland, 1997). Asexual reproduction is also observed in zoanthids. Ryland (1997) described budding occurring in zoanthids in a similar manner seen in Hydrozoans and Scyphozoans. In addition, fragmentation is also known to occur in zoanthids (Ascota et al., 2001). Deep-sea zoanthids are also found associated with corals and sponges. Epizoanthus norvegicus is a commensal of corals Paragorgia arborea and Primnoa resedeaformis in the Norwegian Sea (Carreiro-Silva et al., 2011), and the stalks of Hexactinellid sponges (Beaulieu, 2001; Hajdu et al., 2017). Deep-sea zoanthids are also often described as parasitic. Zoanthids can kill cold-water coral colonies by growing over the top of coral polyps, such as Gorgonians, and progressively eliminate the host tissue, whilst the skeletal support continues to offer support and protection to the zoanthid. There is also a limited amount of available data on the recovery of zoanthids. Asch & Collie (2008) reported a reduction in zoanthid density in areas disturbed by mobile fishing gear. The mean density per photograph of the unidentified zoanthid in undisturbed transects was 1.74, compared to 0.23 in disturbed transects (Asch & Collie, 2008).

There is also very limited data available on Heliometra glacialis, so where available, evidence of another deep-water crinoid genus, Leptometra, is used as a proxy. A review of OBIS distribution data suggests Heliometra glacialis is only distributed in the northern hemisphere and limited to regions characterized by cold, Arctic waters. The majority of records come from the North Atlantic, such as the Labrador Sea, Norwegian Sea and the Barents Sea, but there are also some records from the North Pacific. The majority of records are from depths between 200 and 700 m. Both Leptometra celtica and Leptometra phalangium are capable of swimming up into the water column and moving across the seabed (Hill, 2008; Smith et al., 2000). However, how long swimming can be sustained is unknown, but it is likely to be short. Heliometra glacialis is a suspension feeder. Kharlamenko et al. (2013) characterized the likely food sources of Heliometra glacialis by analysing nitrogen and carbon isotopes, and lipids. The results indicated that Heliometra glacialis feeds on fresh suspended organic matter, largely diatoms and zooplankton (primarily copepods).

Although some crinoids brood embryos, most are broadcast spawners, releasing sperm and eggs for external fertilization. Fertilized eggs hatch into larvae and attach to suitable substrata within a few days (estimated between one to ten days), before metamorphosing into its benthic post-larva stage. Gallego et al. (2013), from inshore Marine Protected Areas, modelled the potential distribution of Leptometra celtica larvae. The potential distribution of the larvae was small because of the short pelagic larval duration. Therefore, Leptometra celtica could be at risk from local pressures due to the low connectivity. Furthermore, it is increasingly perceived that Leptometra phalangium is easily disturbed by activities such as trawling (Gofas et al., 2014).

Resilience assessment. There is very little direct evidence available for each of the characterizing species/taxa of this biotope (M.ArMB.Ro.MixCor.CorGer). The above evidence suggests that Corymorhpa and Gersemia may take between three and ten years to recover from disturbance from drilling.  Although hydroids such as Corymorhpa are reported to recover quickly from disturbance, or seasonally, due to resting stages (Gili & Hughes, 1995), disturbance or burial or the substratum may remove or inhibit resting stages and prolong recovery. Recovery in feather stars is unclear but if  Heliometra glacialis behaves in a similar way as Leptometra sp., then local recruitment is probably good but, although adults are mobile, long distance recruitment is poor.  The recovery of zoanthids is probably dependent on the recovery of their host, that is, the soft corals in the biotope. The overall recovery of the biotope following disturbance is likely within 2-10 years. Therefore, where resistance is ‘None’, ‘Low’, or ‘Medium’, resilience is assessed as ‘Medium’.  However, as the evidence on recovery is limited and the assessment is based on life histories and similar species or genera, confidence in the assessment is ‘Low’. 

Hydrological Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

No direct evidence was found on the effect of local temperature change on any of the characterizing species.

Gersemia fruticosa colonies were kept at ambient temperatures from December 2006 to April 2007, which ranged from 0°C to 9°C, during aquaria-based studies by Sun et al. (2011). This suggests that Gersemia fruticosa can withstand large natural fluctuations in temperature. Furthermore, planulation occurred in Gersemia fruticosa when the temperature was still at its annual minimum, suggesting that temperature is not the driving force. Dyer et al. (1984) recorded over 100 Heliometra glacialis specimens in Svalbard waters, in temperatures ranging from -1.5°C to 4°C. This suggests that Heliometra glacialis is also tolerant to some natural variation in temperature.

This biotope in UK and Irish waters is only known to occur at the Wyvile-Thompson Ridge, a bathymetric feature that separates deep Atlantic and Arctic water masses. This biotope is distributed on the northern (Arctic) side of the Wyvile-Thompson Ridge. This biotope is characterized and strongly influence by Arctic water masses, and does not occur in the Atlantic division of the habitat classification.

Sensitivity assessment. This biotope likely occurs in the UK and Ireland at the most southern limit of its distribution. Despite some evidence for tolerance in temperature fluctuations, a biotope characterized by cold arctic waters, distributed at its most southerly limit would likely be adversely affected by increases in temperature at the benchmark level. Therefore, resistance is assessed as ‘Low’, resilience is assessed as ‘Medium’, and overall sensitivity is assessed as ‘Medium’

High High Not sensitive
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

No direct evidence was found on the effect of local temperature change on any of the characterizing species.

Gersemia fruticosa colonies were kept at ambient temperatures from December 2006 to April 2007, which ranged from 0°C to 9°C, during aquaria-based studies by Sun et al. (2011). This suggests that Gersemia fruticosa can withstand large natural fluctuations in temperature. Furthermore, planulation occurred in Gersemia fruticosa when the temperature was still at its annual minimum, suggesting that temperature is not the driving force. Dyer et al. (1984) recorded over 100 Heliometra glacialis specimens in Svalbard waters, in temperatures ranging from -1.5°C to 4°C. This suggests that Heliometra glacialis is also tolerant to some natural variation in temperature.

This biotope in UK and Irish waters is only known to occur at the Wyvile-Thompson Ridge, a bathymetric feature that separates deep Atlantic and arctic water masses. This biotope is distributed on the northern (Arctic) side of the Wyvile Thompson Ridge. This biotope is characterized and strongly influence by Arctic water masses, and does not occur in the Atlantic division of the Habitat Classification.

Sensitivity assessment. This biotope is likely to occur in the UK and Ireland at the most southern limit of its distribution. In addition, there is some evidence for some of the characterizing species can tolerate fluctuation in temperature. Therefore, resistance is assessed as ‘High’, resilience is assessed as ‘High’, and overall sensitivity is assessed as ‘Not sensitive’.

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

This biotope (M.ArMB.Ro.MixCor.CorGer) occurs at depths characterized by full salinity (30-35 psu) seawater. As a deep-sea biotope, it is unlikely that it will experience natural fluctuations in salinity.  Hence, due to the highly stable conditions in which this deep-sea biotope (M.ArMB.Ro.MixCor.CorGer) occurs, a change in salinity due to human activity is likely to cause mortality in the characterizing species and taxa. Therefore, resistance has been assessed as ‘Low’, resilience assessed as ‘Medium’, with an overall sensitivity assessment of ‘Medium’

Low Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

This biotope (M.ArMB.Ro.MixCor.CorGer) occurs at depths characterized by full salinity (30-35 psu) seawater. As a deep-sea biotope, it is unlikely that it will experience natural fluctuations in salinity. Hence, due to the highly stable conditions in which this deep-sea biotope (M.ArMB.Ro.MixCor.CorGer) occurs, a change in salinity due to human activity is likely to cause mortality in the characterizing species and taxa. Therefore, resistance has been assessed as ‘Low’, resilience assessed as ‘Medium’, with an overall sensitivity assessment of ‘Medium’.

High High Not sensitive
Q: Low
A: NR
C: NR
Q: High
A: High
C: High
Q: Low
A: Low
C: Low

The substrata of this biotope (M.ArMB.Ro.MixCor.CorGer) is characterized by a cobble matrix, indicating a high current flow environment and the Wyvile-Thompson Ridge is described as a ‘high energy environment’. Using the Hjulstrom-Sundborg diagram, minimum mean current speeds are estimated as at least 1 m/s. A decrease at the benchmark level will change the substrata, introducing finer particles such as sand. This will ultimately change the characterizing substrata and therefore the biotope.

An increase in water flow is unlikely to change the characterizing substrata or adversely affect the characterizing species/taxa. The species and taxa that characterize this biotope are adapted to the high-energy environment of the Wyvile Thompson Ridge. Dutto et al. (2019) suggested that Corymorpha januarii show plasticity in their feeding behaviour, allowing them to act opportunistically to exploit variable food sources which are typical of the dynamic environment they inhabit. Corymorpha januarii are capable of capturing active swimming zooplankton prey with good evasion capacity. This would be beneficial if an increase in water flow at the benchmark were to occur. Furthermore, crinoids, such as Leptometra celtica, show plasticity in their feeding behaviour in response to changes in bottom-current flow, arranging their arms in various planar, conical, or parabolic postures in response to laminar, near-bottom flow (e.g. La Touche, 1978; Macurda & Meyer, 1974; Meyer & Macurda Jr., 1980).

A decrease in water flow could potentially facilitate the deposition of finer sediments (e.g. sands) and ultimately change the characterizing substrata and, therefore, the biotope.  However, the biotope is characteristic of the high-energy environment of the Wyvile-Thompson Ridge and probably exposed to tidal streams greater than 1 m/s, and considerable mass water transport.  Therefore, a change in the water flow of 0.1 – 0.2 m/s is probably not significant, and resistance is assessed as ‘High’. Hence, resilience is also ‘High’ and sensitivity is assessed as ‘Not sensitive’ at the benchmark level.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This biotope (M.ArMB.Ro.MixCor.CorGer) is found at mid bathyal depths; therefore, it will not be impacted by a change in emergence. Hence this pressure is assessed as ‘Not relevant’.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This biotope (M.ArMB.Ro.MixCor.CorGer) occurs at mid bathyal depths and therefore will not be impacted by wave exposure. Hence, this pressure is assessed as ‘Not relevant'. 

Chemical Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not assessed.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not assessed.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not assessed.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

‘No evidence’ was found.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Not assessed.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No specific evidence on the effects of deoxygenation on the characterizing species/taxa id this biotope was available. This pressure is assessed as ‘No evidence’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Nutrient availability will be important to this biotope (M.ArMB.Ro.MixCor.CorGer), however, no evidence was found on the effect of nutrient enrichment on the biotope. Therefore, this pressure is recorded as ‘No evidence’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

As suspension feeders, particulate organic matter (POM) is a food source for the species and taxa that characterize this biotope. However, no evidence was found on the effect of organic enrichment at the level of the benchmark on the biotope. Therefore, ‘No evidence’ is recorded.

Physical Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

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’). This biotope (M.ArMB.Ro.MixCor.CorGer) is therefore considered to have ‘High’ sensitivity to this pressure.

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

This biotope (M.ArMB.Ro.MixCor.CorGer) is characterized by hard rock (consolidated cobbles) substrata (JNCC, 2015). If the hard rock (cobbles) were replaced by a soft rock or sedimentary substrata, this would represent a fundamental change to the physical characteristics of the biotope, whilst also removing suitable habitat.

Sensitivity assessment. Resistance is assessed as ‘None’, resilience as ‘Very low’ and overall sensitivity as ‘High’

None Very Low High
Q: High
A: High
C: High
Q: High
A: High
C: High
Q: High
A: High
C: High

This biotope (M.ArMB.Ro.MixCor.CorGer) is characterized by a hard rock (cobble matrix). A change in seabed type to anything but cobble and gravel dominated coarse substrata at the benchmark level would result in the introduction of finer sediments. This would permanently change the characterizing substrata and, therefore, change the biotope. Hence, resistance is assessed as ‘None’, resilience as ‘Very low’ and overall sensitivity assessed as ‘High’

None Medium Medium
Q: Low
A: NR
C: NR
Q: Medium
A: Low
C: Medium
Q: Low
A: Low
C: Low

The only mobile characteristic species/taxa of this biotope (M.ArMB.Ro.MixCor.CorGer) is Heliometra glacialis. As this pressure is not permanent, Heliometra glacialis has the potential to move out of the area when disturbed but quickly recolonize the area once the pressure has reversed, providing there is another suitable habitat available locally. However, Corymorpha, Gersemia and zoanthids will likely be killed/crushed during the removal of the substrata (cobble matrix). As a result, the resistance of this biotope is assessed as ‘None’, resilience as ‘Medium’, with an overall sensitivity of ‘Medium’.

Low Medium Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Low
C: Medium
Q: Medium
A: Low
C: Medium

The main sources of potential abrasion and physical disturbance relevant to this biotope (M.ArMB.Ro.MixCor.CorGer) are from bottom fishing activities (e.g. beam trawls), deep-sea mining and drilling activities (e.g. mining vehicles; Miller et al., 2018), and anchoring and positioning of offshore structures (e.g. offshore wind turbines).

There is currently no direct evidence available to assess Corymorpha.  However, hydroids are capable of regeneration and rapid repair from injuries (Sparks, 1972). Furthermore, hydroids also produce dormant, resting stages that are resistant to environmental pressures (Gili & Hughes, 1995). Hydroid polyps may be damaged beyond repair or removed completely – this is quite likely given the delicacy of the polyps. However, the resting stages of hydroids can provide a mechanism for rapid recovery, e.g. after experiencing physical damage to the seabed.

Direct evidence for Gersemia is also limited. In aquaria, Henry et al. (2003) simulated disturbance caused by bottom fishing to test the resistance of Gersemia rubiformis. This was carried out by rolling and crushing four colonies, once every two weeks over four months. Colony responses were recorded after four and seven days. Crushing immediately induced retraction in the colonies. Colonies exhibited the ability to regenerate well from acute localised injuries. The authors concluded that Gersemia rubiformis’ ability to regenerate, temporarily contract and survive crushing, will be of benefit in heavily disturbed habitats, i.e. bottom trawling areas where mechanical disturbance is high (Henry et al., 2003). Furthermore, Gilkinson et al. (2002) investigated the susceptibility of Gersemia rubiformis to capture by hydraulic clam dredges. Post-dredging, no changes in abundance were recorded. The capture rate was relatively low (2-19%), but 84% of Gersemia rubiformis were attached to discarded gastropod shells. Gilkinson et al. (2002) hypothesised that the pressure wave produced by the dredge, displaced corals, on their shells, out of the dredge pathways and resettled nearby. This would not occur in this biotope, as the underlying substrata are cobble matrix and will not be re-suspended, and would therefore be more likely to experience adverse effects. Prena et al. (1999) found that experimental otter trawls decreased biomass by 24% when compared to reference areas, including a consistently significant decrease in Gersemia sp. Similarly, Asch & Collie (2008) reported a reduction in the density of an unidentified Zoantharia after being disturbed by mobile fishing gear.

Although mobile, there is evidence that this pressure could adversely affect Leptometra spp. (a proxy for Heliometra glacialis). Gofas et al. (2014) stated that Leptometra phalangium is ‘easily disturbed’ by trawling activity. Furthermore, McCormack & O’Connor (2016) reported Leptometra celtica bycatch in ground fish surveys off the west coast of Ireland. Leptometra celtica is also vulnerable to direct physical injury from trawls, as well as sensitive to the resuspended sediment caused by the passing of a trawl (Blanchard et al., 2004). Dyer et al. (1984) also recorded over 100 Heliometra glacialis adult specimens (up to 20 cm arm length) as bycatch in trawls over three stations in Svalbard waters.

Sensitivity assessment. There is evidence to suggest that the action of abrasion or physical disturbance can cause a significant decline (at least 25%) in the abundance of characterizing species/taxa in this biotope (M.ArMB.Ro.MixCor.CorGer). Therefore, resistance is assessed as ‘Low’, resilience is assessed as ‘Medium’, and overall sensitivity of ‘Medium’.

Low Medium Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Low
C: Medium
Q: Medium
A: Low
C: Medium

Penetration and/or disturbance of the substratum would result in similar, if not identical, results as an abrasion and/or disturbance of the substratum on the surface of the seabed (see abrasion/disturbance above).  Therefore, resistance has been assessed as ‘Low’, resilience assessed as ‘Medium’, and overall sensitivity of ‘Medium’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Suspended solids are important to all the characterizing species and taxa of this biotope, specifically because they are filter feeders. As a result, these species/taxa are reliant upon currents transporting food items, e.g. copepods or diatoms (Dutto et al., 2019; Kharlamenko et al., 2013), to them for capture. An increase in suspended solids may increase the food supply to organisms. For example, a high abundance of Leptometra phalangium indicates a good supply of particulate organic matter (Gofas et al., 2014). On the other hand, a decrease in suspended solids may see a reduction in available food. Too much suspended sediment may also clog feeding appendages and, if combined with high-energy environments, cause damage and injury to organisms.

Dutto et al. (2019) recorded the occurrence of Corymorpha januarii in a highly turbid coastal ecosystem (50 to 300 NTU) in the south-western Atlantic. Udalov et al. (2019) studied the effects of glacier discharge on benthic community structure in Oga Bay, Kara Sea (Russia). The glacier discharge was characterized by high concentrations of suspended sediment. Gersemia fruticosa was absent from stations with high turbidity (24.5 FTU) but was present in stations where turbidity was significantly less (<2 FTU). Blanchard et al. (2004) described Leptometra celtica as a ‘fragile species’, citing, as a filter feeder, the species is sensitive to the resuspension of particles by the passage of trawls.  However, deep-sea Leptometra celtica assemblages occur around shelf edges areas characterized by high concentrations of suspended material (Lavaleye et al., 2002). Leptometra phalangium and Leptometra celtica live in direct contact with mobile sandy-gravel substrata in turbid areas where strong currents deliver particles for suspension-feeding (Colloca et al., 2004; Davies et al., 2014).

Overall, there is limited evidence on the effects at the benchmark level of a change in suspended solids. Therefore, an assessment cannot be made on this pressure at the benchmark level and is recorded as ‘No evidence’

Low Medium Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Low
C: Medium
Q: Medium
A: Low
C: Medium

There is no direct evidence available to assess the pressure at the benchmark. As suspension feeders, the characterizing species and taxa need to be able to maintain contact with free-flowing currents to continue successfully feeding and avoid suffocation. Smothering through the disposition of material can cause this and therefore have detrimental effects.

Jones et al. (2012) studied the rate of recovery after drilling activity in the Faroe-Shetland Channel. Two former drilling sites were investigated; Site A (three years post drilling) and Site C (ten years post drilling), as well as representative background sites outside the influence of drilling activity. The main impact from the drilling activity is the deposition of ‘drill cuttings’ on the seabed in the surrounding area – primarily ‘downstream’. At Site A, soon after drilling, the area of seabed completely covered by cuttings totalled 30,700 m2, the area of complete and partial cuttings 70,890 m2, with an extended area of just partial cuttings. Three years later, the area affected by cuttings had reduced; the area of complete cuttings to 5,570 m2; and the area of complete and partial cuttings to 10,980 m2. In terms of the distance from the drill site, the effect had reduced from an average of 90 m to 40 m. At Site C (after 10 years), complete cuttings extending from the drill location was 18 m on average (area of complete cuttings 920 m2; area of complete and partial cuttings 2,700 m2).

Corymorpha groenlandica was recorded as absent from Site A (three years) but present at Site C (10 years), at the same abundances as background sites (0.3 m2). This study suggests that in this region, Corymorpha groenlandica recovers between three and ten years after drilling activity and cutting deposition. However, the Corymorpha groenlandica results in Site A must be used with caution as hydroids may appear absent from the benthos when in a reduced resting phase. In the case of Gersemia sp., early signs of recovery were observed after three years (abundance of <0.4 m2). In Site C (10 years), a far more significant recovery was observed, with abundance counts over 50 per m2. The results suggest that the effects of drilling – which are largely the deposition of drill cuttings – have negative impacts on abundance and recovery of Corymorpha groenlandica and Gersemia sp. is observed between three and ten years.

No direct evidence was found for any deep-sea zoanthids. However, Barreira e Castro et al. (2012) observed the high abundance of Palythoa caribaeorum on tropical Brazilian coral reefs that were associated with high sedimentation rates (maximum of 35 mg cm2 per day, mean of 15 mg cm2 per day). This species is well adapted to areas of high sedimentation, incorporating fine sediment into its tissues (up to 45% of its wet weight). In addition, this species produces high volumes of mucus and has a smooth surface, reducing its friction that aids sediment removal. However, this is a large, colonial, zooxanthellate zoanthid species, compared to the solitary, small, azooxanthellate zoanthid in this biotope.

As a semi-mobile species, Heliometra glacialis may be able to swim up from the seabed during the deposition of material, providing respiratory structures do not become blocked. The species could move out of the area or potentially resettle onto the affected seabed.

Sensitivity assessment. Although direct evidence is limited across all characterizing species/taxa, the evidence available for Corymorpha and Gersemia provided by Jones et al. (2012) suggests there will be adverse effects. However, the biotope occurs in a high-energy environment (Wyvile-Thompson Ridge) so it is likely that fine sedimentation of 5 cm will be quickly removed, mitigating the severity of the impacts. Therefore, for this pressure at the benchmark level, resistance is assessed as ‘Low’ instead of ‘None’. Resilience is, therefore, assessed as ‘Medium’ and overall sensitivity as ‘Medium’.

None Medium Medium
Q: Medium
A: Medium
C: Medium
Q: Medium
A: Low
C: Medium
Q: Medium
A: Low
C: Medium

There is no direct evidence available to assess the pressure at the benchmark. As for suspension feeders, the characterizing species and taxa need to be able to maintain contact with free-flowing currents to continue successfully feeding and avoid suffocation. Smothering through the disposition of material can cause this and therefore have detrimental effects.

Jones et al. (2012) studied the rate of recovery after drilling activity in the Faroe-Shetland Channel. Two former drilling sites were investigated; Site A (three years post drilling) and Site C (ten years post drilling), as well as representative background sites outside the influence of drilling activity. The main impact from the drilling activity is the deposition of ‘drill cuttings’ on the seabed in the surrounding area – primarily ‘downstream’. At Site A, soon after drilling, the area of seabed completely covered by cuttings totalled 30,700 m2, the area of complete and partial cuttings 70,890 m2, with an extended area of just partial cuttings. Three years later, the area affected by cuttings had reduced; the area of complete cuttings to 5,570 m2; and the area of complete and partial cuttings to 10,980 m2. In terms of the distance from the drill site, the effect had reduced from an average of 90 m to 40 m. At Site C (after 10 years), complete cuttings extending from the drill location was 18 m on average (area of complete cuttings 920 m2; area of complete and partial cuttings 2,700 m2).

Corymorpha groenlandica was recorded as absent from Site A (three years) but present at Site C (10 years), at the same abundances as background sites (0.3 m2). This study suggests that in this region, Corymorpha groenlandica recovers between three and ten years after drilling activity. However, the Corymorpha groenlandica results in Site A must be caveated with the knowledge that hydroids may appear absent from the benthos when in a reduced resting phase. In the case of Gersemia sp., early signs of recovery were observed after three years (abundance of <0.4 m2). In Site C (10 years), a far more significant recovery had been observed, with abundance counts over 50 per m2. The results suggest that the effects of drilling – which are largely the deposition of drill cuttings – have negative impacts on abundance and recovery of Corymorpha groenlandica and Gersemia sp. is observed between three and ten years.

No direct evidence was found for any deep-sea zoanthids. However, Barreira e Castro et al. (2012) observed the high abundance of Palythoa caribaeorum on tropical Brazilian coral reefs that were associated with high sedimentation rates (maximum of 35 mg cm2 per day, mean of 15 mg cm2 per day). This species is well adapted to areas of high sedimentation, incorporating fine sediment into its tissues (up to 45% of its wet weight). Additionally, this species produces high volumes of mucus and has a smooth surface, reducing its friction that aids sediment removal. However, this is a large, colonial, zooxanthellate zoanthid species, compared to the solitary, small, azooxanthellate zoanthid in this biotope.

As a semi-mobile species, providing respiratory structures do not become blocked, Heliometra glacialis may be able to swim up from the seabed during the deposition of material. The species could move out of the area or potentially resettle onto the affected seabed.

Sensitivity assessment. Although direct evidence is limited across all characterizing species/taxa, the evidence available for Corymorpha and Gersemia provided by Jones et al. (2012) suggests there will be adverse effects – particularly at the benchmark level of 30 cm. It is also likely that severe mortality will occur in Zoantharia sp., particularly given its small size.  Therefore, for this pressure at the benchmark level, resistance is assessed as ‘None’, resilience is as ‘Medium’, and an overall sensitivity as ‘Medium’.

Not Assessed (NA) Not assessed (NA) Not assessed (NA)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

A black microfiber was found embedded in the surface of a deep-sea zoanthid, attached to a bamboo coral in the Equatorial mid-Atlantic (Taylor et al., 2016). However, this pressure is ‘Not assessed’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

‘No evidence’ was found.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

Whilst no evidence could be found on the effects of noise or vibrations on the characterizing species, it is unlikely that these species would be adversely affected by noise. This pressure is assessed as ‘Not relevant’.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

This biotope (M.ArMB.Ro.MixCor.CorGer) occurs at mid bathyal depths at which no light penetrates from the surface. Although Leptometra celtica assemblages occur at considerable depths where little or no incident light penetrates from the surface, and where the movement of surface vessels is not likely to affect the species, evidence shows that they respond to changes in anthropogenic light. Observations by Messing (2019, pers. comms., 30 April), Eleaume (2019, pers. comm., 5 May) and Morais et al. (2007) suggest that Leptometra celtica and other crinoids display a likely avoidance response (i.e. crown rotation, arm-waving, ‘crouching’ or ‘flying’ behaviour) to approaching ROVs or submersibles (bright lights).  As there is no evidence of mortality, and effects are limited to behavioural responses, resistance is assessed as ‘High’, resilience as ‘High’ and overall the biotopes are considered to be ‘Not sensitive’ at the benchmark level.  No evidence was found to suggest that the other characteristic species could be affected by artificial light.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The characterizing species/taxa of this biotope have a larval stages and therefore connectivity and recruitment could be affected by a permanent or temporary barrier to propagule dispersal. However, ‘No evidence’ is available to assess this pressure.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

This biotope is mainly characterized by sessile invertebrates (Corymorpha, Gersemia and Zoanthids), or species with limited swimming capacity (Heliometra glacialis), in deep water and is unlikely to be affected by an increased risk of collision as defined under the pressure. This pressure is therefore assessed as ‘Not relevant’.

High High Not sensitive
Q: Medium
A: Medium
C: Medium
Q: High
A: High
C: High
Q: Medium
A: Medium
C: Medium

Observations by Messing (2019, pers. comms., 30 April), Eleaume (2019, pers. comm., 5 May) and Morais et al. (2007) suggest that Leptometra celtica and other crinoids display a likely avoidance response (i.e. crown rotation, arm-waving, ‘crouching’ or ‘flying’ behaviour) to approaching ROVs or submersibles (bright lights). As there is no evidence of mortality, and effects are limited to behavioural responses, resistance is assessed as ‘High’, resilience as ‘High’ and overall the biotopes are considered to be ‘Not sensitive’ at the benchmark level.  The other characteristic species are not reliant on vision, as such, and unlikely to be affected by 'Visual disturbance'. 

Biological Pressures

Use / to open/close text displayedResistanceResilienceSensitivity
Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

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

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No alien or non-native species are known to compete with the characterizing species or taxa of this biotope.  Hence, this pressure is recorded as ‘No evidence’.

No evidence (NEv) Not relevant (NR) No evidence (NEv)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

No evidence’ was found on diseases that may affect the characterizing species or taxa.

Not relevant (NR) Not relevant (NR) Not relevant (NR)
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR
Q: NR
A: NR
C: NR

The characterizing species and taxa associated with the biotope are not commercially targeted. Therefore, this pressure is assessed as ‘Not relevant’.

Low Medium Medium
Q: High
A: High
C: Medium
Q: Medium
A: Low
C: Medium
Q: Medium
A: Low
C: Medium

The available evidence suggests that this biotope is sensitive to removal through bycatch. Experimental trawling by Prena et al. (1999) on the Grand Banks (Newfoundland) indicated that Gersemia sp. biomass was consistently lower (average 24%) than reference areas. Jørgensen et al. (2015) also found that Gersemia sp. biomass was also reduced in trawled areas and provided evidence of trawl-induced direct mortality of Gersemia sp.

There is also available evidence for the capture of crinoids with bottom fishing gear. Sanchez et al. (2008) recorded bycatch of Leptometra celtica in beam trawls off Le Danois Bank (southern Spain) and Heliometra glacialis has been in scientific trawls (Kolpakov et al., 2018). Dyer et al. (1984) caught over 100 specimens of Heliometra glacialis over three stations in Svalbard waters. Asch & Collie (2008) also observed a reduction in the density of unidentified Zoanthids in areas disturbed by mobile fishing gears.

Sensitivity assessment. The available evidence suggests that the characterizing species/taxa of this biotope are readily caught as bycatch by bottom fishing gear, i.e. trawls. However, there is evidence that suggests that the same individuals may evade capture (Prena et al., 1999). Therefore, resistance is assessed as ‘Low’ (25-75% reduction in abundance/cover). As a result, resilience is assessed as ‘Medium’ and overall sensitivity as ‘Medium’.

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Citation

This review can be cited as:

Graves, K.P., 2022. Corymorpha, Gersemia, Zoantharia and Heliometra glacialis on Arctic mid bathyal rock and other hard substrata. 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 04-02-2023]. Available from: https://marlin.ac.uk/habitat/detail/1239

Last Updated: 03/03/2022