The Marine Life Information Network

The sponge Dysidea fragilis has been recorded from the Arctic to the Mediterranean, Pachymatisma johnstonia has been recorded from the Orkneys to Spain is ubiquitous across the western and southern coasts of Britain and Cliona celata has been recorded from Sweden to the Mediterranean (Ackers et al., 1992). The sea anemone Sargatia elegans is found from Scandinavia to the Mediterranean (Picton & Morrow 2015), Actinothoe sphyrodeta is distributed from the northern coast of Scotland to Spain (Ramos, 2010; NBN, 2015) and Metridium senile has been reported in the Adriatic (Manual, 1988). 

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. Research by Webster et al. (2008, 2011), Webster & Taylor (2012) and Preston & Burton (2015) suggested that many sponges rely on a holobiont of many synergistic microbes. Webster et al. (2011) described a much higher thermal tolerance to sponge larval holobiont when compared with adult sponges. 

Sensitivity assessment. The characterizing species are widely distributed across the British Isles. Morphological changes were observed in UK sponge communities, with temperature a factor, but the characterizing sponges assessed were not listed as the most highly contributing to these changes (Berman et al., 2013).  Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity as ‘Not Sensitive’ at the benchmark level.

The sponge Dysidea fragilis has been recorded from the Arctic to the Mediterranean, Pachymatisma johnstonia has been recorded from the Orkneys to Spain is ubiquitous across the western and southern coasts of Britain and Cliona celata has been recorded from Sweden to the Mediterranean (Ackers et al., 1992).  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 visibility and temperature.  Some sponges do 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) reported the effects of an unusually cold winter (1962-3) on the marine life in Britain, including Porifera in North Wales.  Whilst difficulty distinguishing between mortality and delayed development was noted, Crisp (1964) found that Pachymastia johnstonia and Halichondria panicea were wholly or partly killed by frost, 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.  The anemone Sargatia elegans is found from Scandinavia to the Mediterranean (Picton & Morrow, 2015), while Actinothoe sphyrodeta is distributed from the northern coast of Scotland to Spain (Ramos, 2010; NBN, 2015) and could, therefore, be affected by a reduction in temperature.

The sea anemone Cylista elegans is found from Scandinavia to the Mediterranean (Picton & Morrow, 2015), Actinothoe sphyrodeta is distributed from the northern coast of Scotland to Spain (Ramos, 2010; NBN, 2015).  Crisp (1964) reported that Metridium senile was unaffected by the cold winter of 1962-63. The characterizing bryozoans Alcyonidium diaphanum has been recorded across the British Isles, from the Channel Isles to the northern coast of Scotland (NBN, 2015).

Sensitivity assessment. There is evidence of sponge mortality at extreme low temperatures in the British Isles.  Given this evidence, it is likely that rapid cooling of 5°C would affect some of the characterizing species, and resistance is assessed as ‘Medium’.  A resilience of ‘High’ is recorded and sensitivity is assessed as ‘Low’.

Marin (1997) describes the presence of Dysidea fragilis in a hypersaline coastal lagoon (42-47 g/l) in La Mar Menor, Spain. ‘No evidence’ for other characterizing species was found.

Castric & Chassé (1991) conducted a factorial analysis of the subtidal rocky ecology near Brest, France and rated the distribution of species from estuarine to offshore conditions.  Dysidea fragilis and Raspailia ramosa were rated as indifferent to this range.  Cliona celata and Pachymatisma johnstonia had a slight preference for more estuarine conditions.  Mean salinity difference between the two farthest zones was low (35.1 and 33.8 ‰ respectively) but with a greater range being experienced in the Inner Rade (±2.4‰ compared with ±0.1‰).  It should be noted that the range of salinities identified in this study does not reach the lower benchmark level, and at least some of the characterizing sponges are likely to be affected at the benchmark level. 

Although Metridium senile is predominantly marine, the species also penetrates into estuaries. Braber & Borghouts (1977) found that Metridium senile occurred in about 10 ppt 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. Cylista elegans and Actinothoe sphyrodeta occur in the littoral (Picton & Morrow, 2015) and are therefore likely to experience both higher and lower salinities than ‘Full’ (30-35 ppt) as per the biotope description (Connor et al., 2004).

Ryland (1970) stated that, with a few exceptions, the Gymnolaemata bryozoans were fairly stenohaline and restricted to full salinity (30-35 ppt), noting that reduced salinities result in an impoverished bryozoan fauna. Dyrynda (1994) noted that Alcyonidium diaphanum was probably restricted to the vicinity of the Poole Harbour entrance by their intolerance to reduced salinity.

Sensitivity assessment. Some of the characterizing bryozoans and sponges are likely to be adversely affected by a reduction in salinity.  Resistance is assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’.

Riisgard et al. (1993) discussed the low energy cost of filtration for sponges and concluded that passive current-induced filtration may be of insignificant importance for sponges.  Pumping and filtering occurs in choanocyte cells which generate water currents in sponges using flagella (de Vos et al., 1991). The sponges Pachymatisma johnstonia and Dysidea fragilis have been recorded in biotopes from very weak to very strong water flow (0->3 m/s).  The anemones Corynactis viridis and Metridium senile have been recorded in biotopes from very weak to very strong water flow (0->3 m/s). 

Water flow has been shown to be important for the development of bryozoan communities and the provision of suitable hard substrata for colonization (Eggleston, 1972b; Ryland, 1976). In addition, areas subject to the high mass transport of water such as the Menai Strait and tidal rapids generally support large numbers of bryozoan species (Moore, 1977). Although, active suspension feeders, their feeding currents are probably fairly localized and they are dependent on water flow to bring adequate food supplies within reach (McKinney, 1986). A substantial decrease in water flow will probably result in impaired growth due to a reduction in food availability, and an increased risk of siltation (Tyler-Walters, 2005c).

Sensitivity assessment. This biotope is defined as a moderate to high energy and occurs in areas of moderately strong to strong tidal water flow (0.5- 3 m/s).  Bryozoan communities rely on movement of water for feeding and a severe reduction in water flow over an extended period of time could cause mortality.  Characterizing sponges and anemones are present in biotopes with both stronger and weaker tidal flow and are, therefore, unlikely to be affected by a change in water flow at the benchmark level (0.1-0.2 m/s).  Resistance is, therefore, recorded as ‘High’ with resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Changes in emergence are 'Not relevant' to this biotope as it is restricted to fully subtidal/circalittoral conditions - the pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

Roberts et al. (2006) studied deep sponge reef communities (18-20 m) in sheltered and exposed locations in Australia. They reported greater diversity and cover (>40% cover) of sponges in wave-sheltered areas compared with a sparser and more temporal cover in exposed sites (25% cover).

Sensitivity assessment. The SpAnVt complex is found in extreme wave exposure so that a further increase is 'Not relevant'. However, a reduction in wave exposure is likely to result in faunal communities typical of moderate to low energy, and less wave exposed, habitats, e.g. the BrAs complex dominated by ascidians and brittlestars or echinoderm grazed faunal turfs. Hence, a significant reduction in wave exposure could result in reclassification and loss of the biotope.  However, a 3-5% change in significant wave height (the benchmark) is probably not significant. Resistance is, therefore, recorded as ‘High’ with resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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

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.

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

CR.HCR.XFa.SpAnVt is a subtidal biotope (Connor et al., 2004). Oil pollution is mainly a surface phenomenon its impact upon circalittoral turf communities is likely to be limited. However, as in the case of the Prestige oil spill off the coast of France, high swell and winds can cause oil pollutants to mix with the seawater and potentially negatively affect sublittoral habitats (Castège et al., 2014).

Filter feeders are highly sensitive to oil pollution, particularly those inhabiting the tidal zones which experience high exposure and show correspondingly high mortality, as are bottom dwelling organisms in areas where oil components are deposited by sedimentation (Zahn et al., 1981). There is little information on the effects of hydrocarbons on bryozoans. Ryland & Putron (1998) did not detect adverse effects of oil contamination on the bryozoan Alcyonidium spp. in Milford Haven or St. Catherine's Island, south Pembrokeshire, although it did alter the breeding period. Banks & Brown (2002) found that exposure to crude oil significantly impacted recruitment in the bryozoan Membranipora savartii.

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 animals would likely lead to cancers. As sponge cells are not organized into organs the long-term effects are uncertain (Zahn et al., 1981).

Hoare & Hiscock (1974) suggested that polyzoa (bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay, Anglesey and reported that Flustra foliacea did not occur less than 165 m from the effluent source. The evidence, therefore, suggests that Securiflustra securifrons would be sensitive to synthetic compounds.

'No evidence' was found.

This pressure is Not assessed.

In general, respiration in most marine invertebrates does not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates, this concentration is about 2 ml/l (Herreid, 1980; Rosenberg et al., 1991; Diaz & Rosenberg, 1995). Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l.

Little information on the effects of oxygenation on bryozoans was found. Sagasti et al. (2000) reported that epifauna communities, including dominant species such as the bryozoans were unaffected by periods of moderate hypoxia (ca 0.35 -1.4 ml/l which corresponds to ca 0.5 - 2 mg/l ) and short periods of hypoxia (<0.35 ml/l which corresponds to <0.5 mg/l) in the York River, Chesapeake Bay, although bryozoans were more abundant in the area with generally higher oxygen. However, estuarine species are likely to be better adapted to periodic changes in oxygenation. 

Hiscock & Hoare (1975) reported an oxycline forming in the summer months (Jun-Sep) in a quarry lake (Abereiddy, Pembrokeshire) from close to full oxygen saturation at the surface to <5% saturation (ca <0.5 mg/l) below ca 10 m.  No sponges were recorded at depths below 10 - 11 m.  Demosponges maintained under laboratory conditions can tolerate hypoxic conditions for brief periods, (Gunda & Janapala, 2009) investigated the effects of variable dissolved oxygen (DO) levels on the survival of the marine sponge, Haliclona pigmentifera. Under hypoxic conditions (1.5-2.0 ppm DO which corresponds to ca 1.5-2.0 mg/l), Haliclona pigmentifera with intact ectodermal layers and subtle oscula survived for 42 ± 3 days.  Sponges with prominent oscula, foreign material, and damaged pinacoderm exhibited poor survival (of 1-9 days) under similar conditions. Complete mortality of the sponges occurred within 2 days under anoxic conditions (<0.3 ppm DO = ca <0.3 mg/l).

Wahl (1984, 1985) noted that the LC₅₀ value for Metridium senile in anoxic conditions is about three weeks and that none survived beyond six weeks. He observed that anemones detached from the substratum during the first week of deoxygenation in the Inner Flensburg Fjord and could 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 was found.

Sensitivity assessment. The evidence suggests that the sponge communities would be severely affected by hypoxic conditions.  Resistance is therefore recorded as ‘Low’, with a resilience of ‘Medium’ and sensitivity is classed as 'Medium' at the benchmark level.

Hartikainen et al. (2009) reported that increased nutrient concentrations resulted in freshwater bryozoans achieving higher biomass.  O’Dea & Okamura (2000) found that annual growth of Flustra foliacea in western Europe substantially increased since 1970.  They suggested that this could be due to eutrophication in coastal regions due to organic pollution, leading to increased phytoplankton biomass (see Allen et al., 1998). 

Gochfeld et al. (2012) studied the effect of nutrient enrichment (≤0.05 to 0.07 μM for nitrate and ≤0.5 μM for phosphate)  as a potential stressor in Aplysina caulifornis and its bacterial symbionts and found that nutrient enrichment had no effects on sponge or symbiont physiology when compared to control .  This study does contradict findings in Gochfeld et al. (2007) in which Aplysina spp. sponges were virtually absent from a site of anthropogenic stress in Bocas del Toro, Panama which experienced high rainfall and terrestrial runoff.  The author suggested that whilst this site did include elevated nutrient concentrations, other pressures and stresses could be contributing.

Rose & Risk (1985) described an increase in abundance of Cliona delitrix in organically polluted section of Grand fringing reef affected by the discharge of untreated faecal sewage.  Ward-Paige et al. (2005) described the greatest size and biomass of clionids corresponded with the highest nitrogen, ammonia and δ¹⁵N levels. 

Nevertheless, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

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. 

De Goeij et al. (2008) used ¹³C to trace the fate of dissolved organic matter in the coral reef sponge Halisarca caerulea. Biomarkers revealed that the sponge incorporated dissolved organic matter through both bacteria mediated and direct pathways, suggesting that it feeds, directly and indirectly, on dissolved organic matter. Mayer-Pinto & Junqueira (2003) studied the effects of organic pollution on fouling communities in Brazil and found that tolerance of polluted/unpolluted artificial reefs varied among bryozoan species.  It should be noted that Bugula spp. preferred the polluted sites.

O’Dea & Okamura (2000) found that annual growth of Flustra foliacea in western Europe has substantially increased since 1970.  They suggest that this could be due to eutrophication in coastal regions due to organic pollution, leading to increased phytoplankton biomass (see Allen et al., 1998).

Sensitivity assessment. This biotope occurs 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.

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.

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’.

‘Not relevant’ to biotopes occurring on bedrock.

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.

Physical disturbance by fishing gear has been shown to adversely affect emergent epifaunal communities with hydroid and bryozoan matrices reported to be greatly reduced in fished areas (Jennings & Kaiser, 1998). Heavy mobile gears could also result in movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998).   

Van Dolah et al. (1987) studied the effects on sponges and corals of one trawl event over a low-relief hard bottom habitat off Georgia, US.  The densities of individuals taller than 10 cm of three species of sponges in the trawl path and in adjacent control area were assessed by divers and were compared before, immediately after and 12 months after trawling.  Of the total number of sponges remaining in in the trawled area, 32% were damaged.  Most of the affected sponges were the barrel sponges Cliona spp., whereas Haliclona oculata and Ircina campana were not significantly affected.  Twelve months after trawling, the abundance of sponges had increased to pre-trawl densities, or greater. Tilnant (1979) found that, following a shrimp trawl in Florida, US, over 50% of sponges, including Neopetrosia, Spheciospongia, Spongia and Hippiospongia, were torn loose from the bottom.  Highest damage incidence occurred to the finger sponge Neopetrosia longleyi. Size did not appear to be important in determining whether a sponge was affected by the trawl.  Recovery was ongoing, but not complete 11 months after the trawl, although no specific data was provided.

Freese et al. (1999) studied the effects of trawling on seafloor habitats and associated invertebrates in the Gulf of Alaska.  They found that a transect following a single trawling event showed a significant reduction in ‘vase’ sponges (67% expressed damage) and ‘morel’ sponges (total damage could not be quantified as their brittle nature meant that these sponges were completely torn apart and scattered).   The ‘finger’ sponges, the smallest and least damaged of the sponges assessed (14 %), were damaged by being knocked over. Freese (2001) studied deep cold-water sponges in Alaska a year after a trawl event; 46.8% of sponges exhibited damage with 32.1% having been torn loose.  None of the damaged sponges displayed signs of regrowth or recovery.  This was in stark contrast to early work by Freese (1999) on warm shallow sponge communities.  Impacts of trawling activity in Alaska study were more persistent due to the slower growth/regeneration rates of deep, cold-water sponges. Given the slow growth rates and long lifespans of the rich, diverse fauna, it was considered likely to take many years for deep sponge communities to recover if adversely affected by physical damage (Freese, 2001).

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 vulnerable epifauna, including the sponge Pachymatisma Johnstoni, were highly damaged by the experimental trawl.  It should be noted that other epifaunal turfs on uneven rock substrata were more resistant to damage than populations on sediment. Please note, Boulcott & Howell (2011) did not mention the abrasion caused by fully loaded collection bags on the Newhaven dredges. A fully loaded Newhaven dredge may cause higher damage to the community as indicated in their study. Hall-Spencer & Moore, (2000a) reported that sessile epifauna including sponges and the anemone Metridium senile, where present, were significantly reduced in abundance in dredged areas for four years post-dredging.

The abundance of the non-characterizing anemone 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).

Sensitivity assessment. Given the sessile, emerged nature of the sponges and bryozoans, damage and mortality following a physical disturbance effect are likely to be significant, however, some studies have brought into question the extent of damage to the faunal turf. The physiology of the bryozoans affords some protection in the event of abrasion events and recovery is likely to be rapid if stolons remain undamaged. However, based on the damage to sponges, resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity has been assessed as ‘Medium’.

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

Despite sediment being generally considered to have a negative impact on suspension feeders (Gerrodette & Flechsig, 1979), many encrusting sponges appear to be able to survive in highly sedimented conditions, and many species prefer such habitats (Bell & Barnes, 2001; Bell & Smith, 2004).  Castric & Chassé (1991) conducted a factorial analysis of the subtidal rocky ecology near Brest, France and rated the distribution of species in varying turbidity (corroborated by the depth at which laminarians disappeared).  Cliona celata was classed as indifferent to turbidity but Pachymatisma johnstonia had a slight preference for clearer water.   Dysidea fragilis had a strong preference for turbid water.  Storr (1976) observed the sponge Sphecispongia vesparium backwashing to eject sediment and noted that other sponges (such as Condrilla nucula) use secretions to remove settled material.  Tjensvoll (2013) found that the non-characterizing Geodia barretti physiologically shuts down when exposed to sediment concentrations of 100 mg /l (86% reduction).  Rapid recovery to initial respiration levels directly after the exposure indicated that Geodia barretti can cope with a single short exposure to elevated sediment concentrations.

Sensitivity assessment. CR.HCR.XFa.SpAnVt tends to occur in areas of high energy, therefore an increase in suspended sediment will result in an increase in scour. The biotope contains a rich and diverse group of species and an increase in scour would likely result in loss of abundance or diversity (particularly of the sponges), with the biotope coming to resemble a more grazed or scoured example.  The sponges and anemones would likely suffer significant decline and resistance is therefore assessed as ‘Low’, resilience as ‘Medium’ and sensitivity is assessed as ’Medium’.

Smothering by 5 cm of sediment is likely to prevent feeding, and hence growth and reproduction, as well as respiration in the bryozoans. In addition, associated sediment abrasion may remove the bryozoan colonies. A layer of sediment will probably also interfere with larval settlement (Tyler-Walters, 2005c). Despite sediment being generally considered to have a negative impact on suspension feeders (Gerrodette & Flechsig, 1979), many encrusting sponges appear to be able to survive in highly sedimented conditions, and in fact, many species prefer such habitats (Bell & Barnes, 2001; Bell & Smith, 2004). However, Wulff (2006) described mortality in three sponge groups following four weeks of burial under sediment.  16% of Amphimedon biomass died compared with 40% and 47% in Iotrochota and Aplysina respectively. The complete disappearance of the sea squirt Ascidiella aspersa biocoenosis and associated sponges in the Black Sea near the Kerch Strait was attributed to siltation (Terent'ev, 2008 cited in Tillin & Tyler-Walters, 2014). Holme & Wilson (1985) examined the fauna in a tide-swept region of the central English Channel. Flustra foliacea dominated communities subject to sediment transport (mainly sand) and periodic, temporary, burial (ca <5 cm).

Sensitivity assessment. Smothering by 5 cm of sediment is likely to cause limited mortality amongst some of characterizing species of this biotope (particularly the smaller sponges).  This biotope tends to occur on vertical rock with moderate to strong water movement. Therefore, resistance has been assessed as ‘High’.  Hence, resilience has been assessed as ‘High’ and sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Smothering by 30 cm of sediment is likely to prevent feeding, and hence growth and reproduction, as well as respiration in the bryozoans. In addition, associated sediment abrasion may remove the bryozoan colonies. Sediment will probably also interfere with larval settlement (Tyler-Walters, 2005c). Despite sediment being generally considered to have a negative impact on suspension feeders (Gerrodette & Flechsig 1979), many encrusting sponges appear to be able to survive in highly sedimented conditions, and in fact, many species prefer such habitats (Bell & Barnes 2001; Bell & Smith 2004). However, Wulff (2006) described mortality in three sponge groups following four weeks of burial under sediment.  16% of Amphimedon biomass died compared with 40% and 47% in Iotrochota and Aplysina respectively. The complete disappearance of the sea squirt Ascidiella aspersa biocoenosis and associated sponges in the Black Sea near the Kerch Strait was attributed to siltation (Terent'ev 2008 cited in Tillin & Tyler-Walters, 2014).  Whilst the majority of the characterizing species are likely to be buried in 30 cm of sediment deposition, the biotope occurs on vertical rock in high energy conditions and burial is unlikely.

Sensitivity assessment. Smothering by 30 cm of sediment could cause mortality amongst the majority of characterizing species of this biotope if it settled.  However, this biotope occurs on vertical rock in areas with moderate to strong water movement and deposition is unlikely. Resistance at the benchmark has been assessed as ‘High’.  Resilience has been assessed as ‘High’, assuming sediment removal and the biotope is assessed as ‘Not sensitive’ at the benchmark level.

Not assessed.

'No evidence'.

Stanley et al. (2014) studied the effects of vessel noise on fouling communities and found that the bryozoans Bugula neritina, Watersipora arcuate and Watersipora subtorquata responded positively.  More than twice as many bryozoans settled and established on surfaces with vessel noise (128 dB in the 30–10,000 Hz range) compared to those in silent conditions.  Growth was also significantly higher in bryozoans exposed to noise, with 20% higher growth rate in encrusting and 35% higher growth rate in branching species. Whilst no evidence could be found for the effect of noise or vibrations on the characterizing sponges, it is unlikely that these species would be adversely affected by noise.

Sensitivity assessment. Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive'. 

Jones et al. (2012) found that many sponges, around Skomer Island, particularly encrusting species, preferred vertical or shaded bedrock to open, light surfaces, presumably due to lack of competition from algae.

Sensitivity assessment. Whilst sponges seem to favour shaded areas in which to settle, it is unlikely that changes at the benchmark pressure would be significant.  Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive'. 

'Not relevant' as barriers and changes in tidal excursion are not relevant to biotopes restricted to open waters.

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

'Not relevant'

‘No evidence’ was found.

This biotope is classified as circalittoral and therefore no algal species have been considered. 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 smothering native tunicate communities, including Ciona intestinalis (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.

A number of invasive bryozoans are of concern, including Schizoporella japonica (Ryland et al., 2014) and Tricellaria inopinata (Dyrynda et al., 2000; Cook et al., 2013b), however, evidence of potential effects is sparse. However, there is ‘No evidence’ regarding known invasive species posing a threat to this biotope. 

Gochfeld et al. (2012) found that diseased sponges hosted significantly different bacterial assemblages compared to healthy sponges, with diseased sponges also exhibiting a 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 in the Mediterranean (Vacelet,1994 cited in Cebrian et al., 2011; 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. have 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 were effectively dead and had a bacterial community similar to marine sediments. The fouled Cliona had a very distinct bacterial community which may suggest a specific pathogen caused the effect (Burton, pers. comm.; Preston & Burton, 2015).   No evidence for disease in the characterizing bryozoans could be found.

Sensitivity assessment Sponge diseases have caused limited mortality in the characterizing genus Cliona in the British Isles. However, there is ‘No evidence’ to support an assessment of mortality due to diseases in the characterizing species of this biotope.

Spongia officinalis (a Mediterranean species) has been targeted as a commercial species for use as bath sponges, although this species does not occur in the British Isles and no record of commercial exploitation of sponges in the British Isles could be found.  No evidence for commercial exploitation of bryozoans could be found.  Should removal of target species occur, the sessile, epifaunal nature of the characterizing species would result in little resistance to this pressure.

This pressure is ‘Not relevant’ as none of the characterizing species are targeted.

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, removal of the characteristic epifauna due to by-catch 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.  The sponge community is likely to be severely affected by accidental by-catch and, based on the abrasion pressure above, resistance is, therefore, assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’.