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

Berman et al. (2013) monitored sponge communities off Skomer Island, UK over three years with all characterizing sponges for this biotope assessed.  seawater temperature, turbidity, photosynthetically active radiation and wind speed were all recorded during the study. It was concluded that, despite changes in species composition, primarily driven by the non-characterizing Hymeraphia stellifera and Halicnemia patera, no significant difference in sponge density was recorded in all sites studied.  Morphological changes most strongly correlated with a mixture of water visibility and temperature.  Lemoine et al. (2007) studied the effects of thermal stress on the holobiont of the sponge Halichondria bowerbanki collected from Virginia, USA.   Whilst no apparent change in density or diversity of symbionts was detected over the range of temperatures (29 °C, 30 °C and 31 °C), the presence of particular symbionts was temperature dependent.  Barthel (1986) reported that reproduction and growth in Halichondria panicea in the Kiel Bight were primarily driven by temperature, with higher temperatures corresponding with highest growth. 

Dendrodoa grossularia gamete release occurs from spring-autumn, with peaks in early spring and another in late summer. Gamete release is reduced at temperatures above 15 °C and totally suppressed above ca 20 °C (Millar, 1954). No information was found on the upper temperature threshold of mature Dendrodoa grossularia. Whilst widespread throughout the British Isles (NBN, 2015),  Dendrodoa grossularia is close to its southern range limit and  a dramatic increase in temperature that is outside the normal range for the UK may cause mortality.  All of the characteristic anemones (Corynactis viridis, Cylista elegans, Urticina felina, Alcyonium digitatum, Metridium senile) are widely distributed across the British Isles (NBN, 2015).

Sensitivity assessment. Typical surface water temperatures around the UK coast vary, seasonally from 4-19°C (Huthnance, 2010). The biotope is considered to tolerate a 2°C increase in temperature for a year.  The majority of characterizing species would be unaffected by an increase in temperature at the benchmark level.  Whilst the ascidian Dendrodoa grossularia is widespread throughout the British Isles (NBN, 2015), it is close to its distribution limit and mortality may occur in dramatic temperature increases, as may some of the anemones. At the benchmark level, resistance is likely to be ‘Medium’, resilience is therefore ‘High’ and sensitivity is assessed as ‘Low’.

Temperature decrease (local)

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

Evidence

All characterizing sponges, anemones and the ascidian Dendrodoa grossularia are widely distributed across the coasts of the British Isles and are all found from the Channel Isles to Northern Scotland (NBN, 2015).  Berman et al. (2013) monitored sponge communities off Skoma Island, UK over three years with all characterizing sponges for this biotope assessed.  seawater temperature, turbidity, photosynthetically active radiation and wind speed were all recorded during the study.  It was concluded that, despite changes in species composition, primarily driven by the non-characterizing Hymeraphia Stellifera and Halicnemia patera, no significant difference in sponge density was recorded in all sites studied.  Morphological changes most strongly correlated with a mixture of visibility and temperature.

Some sponges exhibit morphological strategies to cope with winter temperatures e.g.  Halichondria bowerbanki goes into a dormant state below 4°C, characterized by major disintegration and loss of choanocyte chambers with many sponges surviving mild winters in more protected areas from where it can recolonize (Vethaak et al., 1982).

Crisp (1964) studied the effects of an unusually cold winter (1962-63) on the marine life in Britain, including porifera in North Wales.   Whilst difficulty in distinguishing between mortality and delayed development was noted, Crisp found that Pachymastia johnstonia and Halichondria panicea were wholly or partly killed by frost and several species appeared to be missing including Amphilectus fucorum. Others, including Hymeniacidon perleve were unusually rare and a few species, including Polymastia boletiformis, were not seriously affected.  It should be noted that Crisp’s general comments on all marine life state that damage decreased the deeper the habitat.  Barthel (1986) reported that Halichondria panicea in the Kiel Bight degenerated and disintegrated after reproduction before winter, however young colonies were observed from September. Dendrodoa grossularia has been recorded as an abundant component of benthic fauna in Nottinghambukta, Svalbard (Różycki & Gruszczyński, 1991).

Sensitivity assessment

There is evidence of sponge mortality at extreme low temperatures in the British Isles(Crisp, 1964a).  Given this evidence, it is likely that a cooling of 5°C for a month could potentially affect the characterizing sponges in shallow examples of this biotope. Resistance has been assessed as ‘Medium’, with a resilience of ‘High’.  Sensitivity has, therefore, been assessed as ‘Low’ 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

The biotope is recorded in Full salinity. An increase at the benchmark level would result in hypersaline conditions.  Marin (1998) described the presence of the ascidian Dysidea fragilis in a hypersaline coastal lagoon (42-47 g/l) in La Mar Menor, Spain.  ‘No evidence‘ for the characterizing sponges, Dendrodoa grossularia or other epifauna in hypersaline conditions was found.

Salinity decrease (local)

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

Evidence

These biotopes have only been recorded in full salinity (Connor et al., 2004), and any low salinity events would probably be short-lived due to the high-energy conditions. 

Castric-Fey & Chassé (1991) conducted a factorial analysis of the subtidal rocky ecology near Brest, France and rated the distrubution of species from estuarine to offshore conditions.  Dysidea fragilis and Raspailia ramosa were rated as unaffected by salinity at this range.  Cliona celata and Pachymatisma johnstonia had a slight preference for more estuarine conditions. Mean salinity difference across the study was low (35.1 and 33.8 ‰ respectively) but a greater range was experienced in the Inner Rade (± 2.4‰ compared with± 0.1‰).  It should be noted that the range of salinities identified in this study do not reach the lower benchmark level.   Some of the characterizing species occur in harbours and estuaries, including Halichondria spp. and Hymeniacidon perleve (Ackers et al., 1992).  Of the characterizing sponges present in this biotope, all except Clathrina coriacea have been recorded in variable salinity of lower (Connor et al., 2004)

Dendrodoa grossularia has been recorded as an abundant component of benthic fauna in Nottinghambukta, Svalbard where salinity can range between 6 and 20‰ (Różycki & Gruszczyński, 1991).

Although Urticina felina is predominantly marine, the species does penetrate into estuaries (e.g. the Thames estuary at Mucking (NMMP, 2001) and the River Blackwater estuary (Davis, 1967). Braber & Borghouts (1977) found that Urticina (as Tealia) felina penetrated to about the 11 ppt Chlorinity (about 20 psu) isohaline at mid tide during average water discharge in the Westerschelde estuary, suggesting that during high river flow, it would be tolerant of reduced salinity conditions.

Although Metridium senile is predominantly marine, the species also penetrates into estuaries. Braber & Borghouts (1977) found that Metridium senile occurred in about 10ppt Chlorinity (about 19 psu) in the Delta Region of the Netherlands suggesting that it would be tolerant of reduced salinity conditions. Shumway (1978) found that, during exposure to 50% seawater, animals retracted their tentacles whilst animals exposed to fluctuating salinity, contracted their body wall and produced copious mucus.

Sensitivity assessment

This biotope is subtidal and characterized by high energy and any low salinity events would probably be short lived.  However, some mortality is likely, with some of the sponges (Clathrina coriacea) affected.  Resistance is assessed as ‘Medium’, resilience as ‘High’ and sensitivity is ‘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

These biotopes are characterized by their high energy wave surge.  There is a progression within this group of biotopes, with IR.FIR.SG.CrSp occurring in the areas most subject to wave surge (found in the narrow-most gullies).  In slightly less surge affected areas, ascidians (primarily Dendrodoa grossularia) become more abundant and therefore important in defining the character of the biotopes CrSpAsAn, DenCcor and CrSpAsDenB.

Sensitivity assessment. All the biotopes within this complex are characterized by their high energy  due to wave surge, and a change in water flow is unlikely to affect the hydrodynamics of the biotope.  Change at the benchmark level (0.1-0.2 m/s) is unlikely to be significant enough to alter the biotope and resistance is, therefore, assessed as ‘High’, resilience is ‘High’ and the biotope is ‘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 occurs in the infralittoral, however it has been recorded in the 0-5 m depth band and may therefore be subject to emergence.

Increased emergence may reduce habitat suitability for characterizing species through greater exposure to desiccation and reduced feeding opportunities for the faunal community while.   Given the subtidal nature of the biotope, emergence is likely to result in a significant decline in the characterizing species.  However, the topography of vertical walls, caves and gullies may afford some resistance to areas within these biotopes and resistance is therefore assessed as ‘Low’. Recovery is assessed as ‘High’, and sensitivity as 'Low'.

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

All the biotopes within this complex are defined by their exposure to wave action. As sublittoral biotopes, a change in wave height would affect the wave surge experienced by characterizing species.  A decrease in wave surge could result in succession of the IR.FIR.SG.CrSp to biotopes more dominated by ascidians and/or anemones.

Conversely, an increase in wave surge could result in loss of the IR.FIR.SG.CrSpAsAn, IR.FIR.SG.CrSpAsDenB and IR.FIR.SG.DenCcor to more impoverished or scoured biotopes. 

Sensitivity assessment. All the biotopes within this complex are characterized by their high energy and significant changes, particularly decreases would probably result in a fundamental change in the nature of the biotope and hence reclassification would be required.  However, at the benchmark level, changes are unlikely to be significant enough to alter the biotope and resistance is, therefore, assessed as ‘High’, resilience is ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

This pressure is Not assessed but evidence is presented where available.

While some sponges, such as Cliona spp. have been used to monitor heavy metals by looking at the associated bacterial community (Marques et al., 2007; Bauvais et al., 2015), no literature on the effects of transition element or organo-metal pollutants on the characterizing sponges could be found.

Mercier et al. (1998) exposed Metridium senile to tri-butyl tin contamination in surrounding water and in contaminated food. The species produced mucus 48 hours after exposure to contaminated seawater. TBT was metabolised but the species accumulated levels of butyl tins leading the authors to suggest that Metridium senile seemed vulnerable to TBT contamination. However, Mercier et al., (1998) did not indicate any mortality and, since Metridium senile is a major component of jetty pile communities immediately adjacent to large vessels coated with TBT antifouling paints.

Ascidians may be intolerant of synthetic chemicals such as tri-butyl-tin anti-foulants. Rees et al. (2001), working in the Crouch estuary, observed that six ascidian species were recorded at one station in 1997 compared with only two at the same station in 1987, shortly following the banning of TBT in antifouling paints. Also, there was a marked increase in the abundance of ascidians especially Ascidiella aspersa and Ascidia conchilega in the estuary after the ban on TBT was introduced.

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

This pressure is Not assessed but evidence is presented where available

Tethya lyncurium concentrated BaP (benzo[a ]pyrene )to 40 times the external concentration and no significant repair of DNA was observed in the sponges, which, in higher animal, would likely lead to cancers. As sponge cells are not organized into organs the long-term effects are uncertain (Zahn et al., 1981). No information was found on the intolerance of the characterizing sponges or barnacles to hydrocarbons. However, other littoral barnacles generally have a high tolerance to oil (Holt et al., 1995) and were little impacted by the Torrey Canyon oil spill (Smith, 1968).

Ignatiades & Becacos-Kontos (1970) found that the ascidian Ciona intestinalis can resist the toxicity of oil polluted water and ascidia are frequently found in polluted habitats such as marinas and harbours, etc. (Carver et al., 2006) as well as Ascidia mentula (Aneiros et al., 2015).

Ryland & de Putron (1998) found no detectable damage to under-boulder communities, which are similar to some overhang communities, in Watwick Bay, Pembrokeshire following the Sea Empress oil spill. Part of the resistance to effects might be because oil does not settle onto overhanging surfaces. However, some species, especially gastropods are likely to be narcotised and killed and some damage is likely. Return to a previous species composition would occur from new settlement from larval sources although some gastropods have no or only a short dispersal phase so that recovery will be slow.

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

This pressure is Not assessed but evidence is presented where available.

Hoare & Hiscock (1974) reported that the anemone Urticina felina survived near to an acidified halogenated effluent discharge in a 'transition' zone where many other species were unable to survive, suggesting a tolerance to chemical contamination. However, Urticina felina was absent from stations closest to the effluent, which were dominated by pollution tolerant species (such as polychaetes). Those specimens closest to the effluent discharge appeared generally unhealthy.

Radionuclide contamination

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

Evidence

‘No evidence’ was found.

Introduction of other substances

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

Evidence

This pressure is Not assessed.

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

It is likely that as this biotope occurs in areas that experience significant wave surge, re-oxygenation is likely which would limit the effects of any de-oxygenation events. However, this may mean that the species present have little exposure to low oxygen and may be sensitive to this pressure.

Halichondria panicea has been reported to survive under oxygen levels as low as 0.5-4 % saturation (ca 0.05-0.4 mg/l) for up to 10 days (Mills et al., 2014).  Wahl (1984, 1985) noted that the LC₅₀ value for Metridium senile in anoxic conditions is about three weeks and that none survive beyond six weeks. He observed that anemones detached from the substratum during the first week of deoxygenation in the Inner Flensburg Fjord and may drift away. When oxygen is lacking, Metridium senile diminishes body surface area. At the level of the benchmark, Metridium senile is not sensitive and even in extreme conditions seems able to survive for some time and then detach. No specific evidence for the other species characterizing this biotope were found.

Sensitivity assessment. The hydrodynamics of this biotope would likely mean that hypoxic events would be rare and short lived.  The available evidence suggests that Halichondria panicea and Metridium senile  are tolerant of de-oxygenation and resistance is therefore recorded as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.  Lack of evidence for other characterizing species results in a ‘Low’ confidence score.

Nutrient enrichment

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

Evidence

This pressure relates to increased levels of nitrogen, phosphorus and silicon in the marine environment compared to background concentrations.  The benchmark is set at compliance with WFD criteria for good status, based on nitrogen concentration (UKTAG, 2014).   Therefore the biotope is assessed as 'Not sensitive' at the pressure benchmark that assumes compliance with good status as defined by the WFD.

Organic enrichment

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

Evidence

Organic enrichment leads to organisms no longer being limited by the availability of organic carbon.  The consequent changes in ecosystem function can lead to the progression of eutrophic symptoms (Bricker et al., 2008), changes in species diversity and evenness (Johnston & Roberts, 2009) and decreases in dissolved oxygen and uncharacteristic microalgae blooms (Bricker et al., 1999, 2008).  Indirect adverse effects associated with organic enrichment include increased turbidity, increased suspended sediment and the increased risk of deoxygenation. 

Johnston & Roberts (2009) undertook a review and meta-analysis of the effect of contaminants on species richness and evenness in the marine environment.  Of the 49 papers reviewed relating to sewage as a contaminant, over 70% found that it had a negative impact on species diversity, <5% found increased diversity, and the remaining papers finding no detectable effect.  It was found that any single pollutant reduced species richness by 30-50% within any of the marine habitats considered (Johnston & Roberts, 2009).  Throughout their investigation there were only a few examples where species richness was increased due to the anthropogenic introduction of a contaminant.  These examples were almost entirely from the introduction of nutrients, either from aquaculture or sewage outfalls.

Rose & Risk, 1985 described an increase in abundance of the sponge Cliona delitrix in an organically polluted section of Grand Cayman fringing reef affected by the discharge of untreated faecal sewage.  Fu et al. (2007) described Hymeniacidon perleve in aquaculture ecosystems in sterilized natural seawater with different concentrations of total organic carbon (TOC), at several concentrations between 52.9 and 335.13 mg/l).   Hymeniacidon perleve removed 44–61% TOC during 24 h, with retention rates of ca. 0.19–1.06 mg/hr ·g-fresh sponge. Hymeniacidon perleve removed organic carbon excreted by Fugu rubripes with similar retention rates of ca. 0.15 mg/h · g-fresh sponge, and the sponge biomass increased by 22.8%. Some of the characterizing species occur in harbours and estuaries, including Halichondria panicea (Ackers et al., 1992).

There is some suggestion that there are possible benefits to the ascidians from increased organic content of water; 'ascidian richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996). 

Sensitivity assessment. These biotopes occur in high energy conditions and it is likely that the deposited organic content would be rapidly removed.  There is also evidence that the filter-feeding characterizing species would tolerate an increase in organic content.  Resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

If rock were replaced with sediment, this would represent a fundamental change to the physical character of the biotope and the species would be unlikely to recover. The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very low’. Sensitivity has been assessed as ‘High’.

Physical change (to another sediment type)

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

Evidence

‘Not relevant’ to biotopes occurring on bedrock.

Habitat structure changes - removal of substratum (extraction)

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

Evidence

The species characterizing this biotope are epifauna or epiflora occurring on rock and would be sensitive to the removal of the habitat. However, extraction of rock substratum is considered unlikely and this pressure is considered to be ‘Not relevant’ to hard substratum habitats.

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 species characterizing this biotope occur on the rock and therefore have no protection from surface abrasion. For this assessment, the focus is on the effects of trampling and scour.

Halichondria panicea is compressible but crumbly in texture and easily broken (Ackers et al, 1992) and is typically found in cryptic or semi-cryptic areas (Hayward & Ryland, 1995b).  Abrasion events are therefore likely to remove the sponge, however specific evidence was not found.

Boulcott & Howell (2011) conducted experimental Newhaven scallop dredging over a circalittoral rock habitat in the sound of Jura, Scotland and recorded the damage to the resident community. The results indicated that, whilst damage to faunal crusts tended to be restricted, the sponge Pachymatisma johnstoni was highly damaged by the experimental trawl.  

The abundance of Urticina felina increased in gravel habitats on the Georges Bank, (Canada) closed to trawling by bottom gears (Collie et al., 2005) which suggested that this species was sensitive to fishing.  In a recent review, assigning species to groups based on tolerances to bottom disturbance from fisheries, the anemone Urticina felina and the sponge Halichondria panacea were assigned to AMBI Fisheries Group II, described as ‘species sensitive to fisheries in which the bottom is disturbed, but their populations recover relatively quickly’ (Gittenberger & van Loon, 2011). Urticina felina also occurs in highly scoured  habitats in the English Channel (Holme & Wilson, 1985).

Sensitivity assessment. These biotopes are defined by their high energy wave surge which prohibits succession. However they occur above cave and gully floors which experience significant scour and biotopes containing scour resistant barnacles and spirobids tend to prevail.  Any activity that physically abrades the faunal crust is likely to result in localized damage.  Increase in scour or other abrasion events are likely to remove the sponge, ascidian and anemone components. Resistance is ‘Low’, resilience is ‘High’ and sensitivity is ‘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

The species characterizing this biotope group are epifauna or epiflora occurring on rock which is resistant to subsurface penetration.  The assessment for abrasion at the surface only is therefore considered to equally represent sensitivity to this pressure. This pressure is thought ‘Not Relevant’ to hard rock biotopes.

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

An increase in suspended solids is unlikely to have direct effects on the characterizing species due to light penetration or clogging. However, given the high energy associated with the biotope, suspended particulates could increase the scour experienced by the characterizing species.

Despite sediment being considered to have a negative impact on suspension feeders (Gerrodette & Flechsig 1979), many encrusting sponges appear to be able survive in highly sediment conditions (Schönberg, 2015; Bell & Barnes 2000; Bell & Smith 2004).  Some of the characterizing species occur in harbours and estuaries, including Halichondria panicea (Ackers et al., 1992). 

Urticina felina is found in highly turbid areas associated with biotopes such as CR.MCR.SfR.Pol (Connor et al., 2004; Holme & Wilson, 1985) and is therefore considered to be unaffected by an increase in suspended solids at the benchmark. 

An increase in suspended sediment could result in scour due to wave action and tidal flow.  Overall, resistance is assessed as ‘Medium’, mainly due to the scour effect.  Resilience is ‘High’ and sensitivity is ‘Low’.

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

This biotope typically occurs on vertical walls, with more scour resistant biotopes occurring on cave and gully floors.  The majority of the examples of this biotope are therefore unlikely to be affected by smothering following an increase in sediment deposition.  This being said, where the biotope does occur on the shallow or flat lower  surfaces, mortality could occur, depending on the level and rate of removal of the sediment. 

Despite sediment being considered to have a negative impact on suspension feeders (Gerrodette & Flechsig 1979), many encrusting sponges appear to be able survive in highly sedimented conditions, and in fact many species prefer such habitats (Schönberg, 2015; Bell & Barnes 2000; Bell & Smith, 2004).  Whilst complete smothering may result in loss of the sponges, the biotope often occurs on cave walls and ceilings and thus burial is unlikely.  Dendrodoa grossularia is a small ascidian, capable of reaching a size of approx 8.5 mm (Millar, 1954) and is therefore likely to be inundated by deposition of 5 cm of sediment. If inundation is long lasting then the understorey community may be adversely affected.

Communities dominated by the anemone Urticina felina were described on tide swept seabed, exposed to high levels of suspended sediment, sediment scour and to periodic smothering by thin layers of sand, up to ca 5 cm in the central English Channel (Holme & Wilson, 1985).  Urticina felina is abundant in the sediment-scoured, silty rock communities CR.HCR.XFa.FluCoAs and CR.MCR.EcCr.UrtScr (Connor et al., 2004).

Sensitivity assessment. Overall, the biotope is unlikely to be affected by smothering, as deposited sediment would be emoved rapidly.  Therefore, resistance is assessed as ‘Medium’, mainly due to the scour effect as the sediment is removed.  Therefore, resilience is ‘High’ and sensitivity is ‘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

This biotope typically occurs on vertical walls, with more scour resistant biotopes occurring on cave and gully floors.  The majority of the examples of this biotope are therefore unlikely to be affected by smothering following an increase in sediment deposition.  This being said, where the biotope does occur on the shallow or flat lower  surfaces, mortality could occur, depending on the level and rate of removal of the sediment. 

Despite sediment being considered to have a negative impact on suspension feeders (Gerrodette & Flechsig 1979), many encrusting sponges appear to be able survive in highly sedimented conditions, and in fact many species prefer such habitats (Schönberg, 2015; Bell & Barnes 2000; Bell & Smith, 2004).  Whilst complete smothering may result in loss of the sponges, the biotope often occurs on cave walls and ceilings and thus burial is unlikely. 

Dendrodoa grossularia is a small ascidian, capable of reaching a size of approx 8.5 mm (Millar, 1954) and is therefore likely to be inundated by deposition of 5 cm of sediment. If inundation is long lasting then the understorey community may be adversely affected.

Communities dominated by the anemone Urticina felina were described on tide swept seabed, exposed to high levels of suspended sediment, sediment scour and to periodic smothering by thin layers of sand, up to ca 5 cm in the central English Channel (Holme & Wilson, 1985).  Urticina felina is abundant in the sediment-scoured, silty rock communities CR.HCR.XFa.FluCoAs and CR.MCR.EcCr.UrtScr (Connor et al., 2004).

Sensitivity assessment. Overall, the biotope is unlikely to be affected by smothering, however, an increase in sediment could result in scour following re-suspension due to wave and tidal flow.  Removal of the sediment is likely to be rapid.  Overall, resistance is assessed as ‘Medium’, mainly due to the scour effect as the sediment is removed, although the risk that some parts of the biotope that exist on flat or gently sloping areas may experience burial.  Resilience is ‘High’ and sensitivity is ‘Low’.

Litter

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

Evidence

Not assessed.

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

Whilst no evidence could be found for the effect of noise or vibrations on the characterizing species of these biotopes, it is unlikely that these species have the facility for detecting or noise vibrations.

Sensitivity assessment

The characterizing sponges are unlikely to respond to noise or vibrations and resistance is therefore assessed as ‘High’, Resilience as ‘High’ and Sensitivity as ‘Not Sensitive’.

Introduction of light or shading

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

Evidence

These biotopes have very limited algal abundance, although Connor et al. (2004) notes that kelps are unable to colonize the biotope primarily due to the level of wave surge and vertical topography.  The impact of introduction of light may therefore be of limited importance to increasing the algal component of the biotope.

 Jones et al. (2012) compiled a report on the monitoring of sponges around Skomer Island and found that many sponges, particularly encrusting species, preferred vertical or shaded bedrock to open, light surfaces.  However, it is possible that this relates to decreased competition with algae.  Whilst no evidence could be found for the effect of light on the other faunal species present within these biotopes, it is unlikely that they would be impacted. While increase in light could potentially promote algal growth, light may not be the limiting factor when considering the lack of algae.  In any case, growth ceases for a number of red algae  below ca 1.0 μmol m^-2l^-1 (ca 50 Lux), whereas this value is 2 μmol m^-2l^-1 (ca 100 Lux) for green algae (Leukart & Lüning, 1994) . 

Sensitivity assessment. A change at the benchmark level (0.1 Lux) is therefore unlikely to be significant.  Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive' at the benchmark level.

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

Barriers and changes in tidal excursion are 'Not relevant' to biotopes restricted to open waters.

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

'Not 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.

Introduction or spread of invasive non-indigenous species

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

Evidence

Wave surge in this biotope will probably limit establishment of all but the most surge resistant invasive non-indigenous species (INIS) and no direct evidence was found for effects of INIS on this biotope.  The low levels of light within this biotope, particularly the rear walls of caves, are considered to also inhibit invasive algal species.

The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second World War. The species does well in estuaries and bays, where it can displace Semibalanus balanoides. However, on exposed shores the native species out-compete this invasive species (Raffaelli & Hawkins, 1999).

Two non-native spirobids – Dexiospira oshoroensis and Pileolaria rosepigmentata - were found on the non-native algae Sargassum muticum in Portsmouth (Knight-Jones et al., 1975). Invasive tubeworms are reported from UK harbours (Thorp et al., 1986)  and are likely to be well established in areas with large volumes of ship traffic.

Didemnum vexillum is an invasive colonial sea squirt native to Asia which was first recorded in the UK in Darthaven Marina, Dartmouth in 2005. Didemnum vexillum can form extensive mats over the substrata it colonizes; binding boulders, cobbles and altering the host habitat (Griffith et al., 2009). Didemnum vexillum can also grow over and smother the resident biological community. Recent surveys within Holyhead Marina, North Wales have found Didemnum vexillum growing on and smother native tunicate communities (Griffith et al., 2009). Due to the rapid-re-colonization of Didemnum vexillum eradication attempts have to date failed. 

Presently Didemnum vexillum is isolated to several sheltered locations in the UK (NBN, 2015), however, Didemnum vexillum has successfully colonized the offshore location of the Georges Bank, USA (Lengyel et al., 2009) which is more exposed than the locations which Didemnum vexillum have colonized in the UK. It is, therefore, possible that Didemnum vexillum could colonize more exposed locations within the UK and could, therefore, pose a threat to these biotopes. 

There was ‘No evidence’ regarding known invasive species that may pose a threat to IR.FIR.SG.CrSpAsAn, IR.FIR.SG.CrSpAsDenB, IR.FIR.SG.DenCcor or IR.FIR.SG.CrSp.  Due to the constant risk of new invasive species, the literature for this pressure should be revisited.  Due to the constant risk of new invasive species, the literature for this pressure should be revisited.

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

Gochfeld et al. (2012) found that diseased sponges hosted significantly different bacterial assemblages compared to healthy sponges, with diseased sponges also exhibiting significant decline in sponge mass and protein content.  Sponge disease epidemics can have serious long-term effects on sponge populations, especially in long-lived, slow-growing species (Webster, 2007).  Numerous sponge populations have been brought to the brink of extinction including cases in the Caribbean (with 70-95% disappearance of sponge specimens) (Galstoff,1942) and  the Mediterranean (Vacelet, 1994; Gaino et al., 1992).  Decaying patches and white bacterial film were reported in Haliclona oculata and Halichondria panicea in North Wales, 1988-89 (Webster, 2007).  Specimens of Cliona spp. exhibited blackened damage since 2013 in Skomer. Preliminary results have shown that clean, fouled and blackened Cliona all have very different bacterial communities. The blackened Cliona are effectively dead and have a bacterial community similar to marine sediments. The fouled Cliona have a very distinct bacterial community that may suggest a specific pathogen caused the effect (Burton, pers comm; Preston & Burton, 2015).  Hydroids exhibit astonishing regeneration and rapid recovery from injury (Sparks, 1972) and the only inflammatory response is active phagocytosis (Tokin & Yaricheva, 1959;1961, as cited in Sparks, 1972).  No record of diseases in the characterizing hydroids could be found.  There appears to be little research into ascidian diseases particularly in the Atlantic.  The parasite Lankesteria ascidiae targets the digestive tubes and can cause ‘long faeces syndrome’ in Ciona intestinalis (although it has also been recorded in other species). Mortality occurs in severely affected individuals within about a week following first symptoms. (Mita et al., 2012).

Sensitivity assessment. Whilst evidence for disease in ascidians and sponges exists, ‘No evidence’ for mortality in the characterizing species was found.

Removal of target species

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

Evidence

No evidence of targeting of the characterizing species could found and the pressure is ‘Not relevant’ to this biotope group.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

The characteristic species probably compete for space within the biotope, so that loss of one species would probably have little if any effect on the other members of the community. However, the incidental removal of the characteristic epifauna is likely to remove a proportion of the biotope and change the biological character of the biotope. These direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of non-target species on this biotope. 

Sensitivity assessment. Based on broad agreement  of trawl impacts on sponge communities and the likely disturbance to the sessile epifaunal species, resistance is recorded as ‘Low’, resilience is recorded as ‘High’ and Sensitivity is ‘Low’