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

Suberites ficus has been recorded throughout the British Isles (NBN, 2015) and is widely distributed in north west Europe (Fish & Fish, 1996).  Suberites carnosus and Hymeniacidon perlevis have been reported across the western, southern and northern British Isles (NBN, 2015) and more widely as southerly as Cape Verde (Van Soest, 1993) and the Azores (Boury-Esnault & Lopes, 1985) respectively.  Bachinski et al. (1997) studied heat response in Suberites domunculu, noting stress response within 5 minutes of exposure to 31°C. 

Bugula spp. grow and reproduce in the summer months. However, day length and/or the phytoplankton bloom characteristic of temperate waters are probably more important than temperature (Ryland, 1967; 1970; Tyler-Walters, 2005).  Cocito & Sgorbini (2014) studied spatial and temporal patterns of colonial bryozoans in the Ligurian Sea over 9 years.  High temperature events were recorded, the first causing mass mortality among a number of species.  Flustra foliacea is perennial Stebbing (1971a) and widespread throughout the British Isles (NBN, 2015).  It is distributed across north-west Europe (Fish& Fish, 1996).  Stebbing (1971a) noted that Flustra foliacea on the Gower peninsular, South Wales had an annual growth season between March and November.

Sensitivity assessment. All characterizing species are found across the British Isles and (considering that this biotope occurs off Anglesey) it is unlikely that a high temperature event at the benchmark level would result in mortality and resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Temperature decrease (local)

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

Evidence

Suberites ficus has been recorded throughout the British Isles (NBN, 2015) and is widely distributed in north west Europe (Fish & Fish, 1996).  Suberites carnosus and Hymeniacidon perlevis have been reported across the western, southern and northern British Isles (NBN, 2015) and more widely from northern Norway (Hentschel, 1929) and Svalbard, as Hymerniacidon caruncula (Hentschel, 1929) respectively.

Crisp (1964) studied the effects of an unusually cold winter (1962-3) 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, several species appeared to be missing including Amphilectus fucorum. Others, including the characterizing Hymeniacidon perlevis 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 and that the extremely cold temperatures (sea temperatures between 4-6°C colder than the 5 year mean over a period of 2 months) is more extreme than the benchmark level for assessment. 

Berman et al. (2013) monitored sponge communities off Skomer Island, UK over three years.  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 with a Rho value of 0.171 (P = 0.01%; 9999 permutations).

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).

Characterizing bryozoans including Flustra foliacea,  Bugula plumosa and Bugula flabellata have been recorded across the British Isles, from the Channel Isles to the northern coast of Scotland (NBN, 2015).

Flustra foliacea is perennial Stebbing (1971a) and widespread throughout the British Isles (NBN, 2015) and north-west Europe (Fish& Fish, 1996).  Stebbing (1974) noted that Flustra foliacea on the Gower peninsular, South Wales had an annual growth season between March and November, with a dormant winter period, when no growth occurred.  Growth resumed in spring, leading to a line forming across the fronds which can be used to age specimens (Stebbing, 1971a).

Sensitivity assessment. All characterizing species are found across the British Isles and (considering that this biotope occurs off Anglesey) it is unlikely that a low temperature event at the benchmark level would result in mortality and resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’.

Salinity increase (local)

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

Evidence

Marin et al. (1998) describes the presence of Dysidea fragilis in a hypersaline coastal lagoon (42-47 g/l) in La Mar Menor, Spain. 

Soule & Soule (1979) cite Hastings (1927) who described the presence of 5 bryozoans in hypersaline conditions in the Suez Canal. No evidence could be found for characterizing species.

Sensitivity assessment. ‘No evidence’ for mortality or tolerance of the characterizing bryozoans or sponges in hypersaline conditions could be found.

Salinity decrease (local)

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

Evidence

Castric-Fey & 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 unaffected at 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 do not reach the lower benchmark level.   Some of the sponges occur in harbours and estuaries, including Hymeniacidon perlevis (Ackers et al., 1992).  Suberites ficus is generally found in oceanic water, where there is no freshwater influence (Ackers et al., 1992) and is therefore unlikely to be tolerant of a decrease in salinity.   

Ryland (1970) stated that, with a few exceptions, the Gymnolaemata were fairly stenohaline and restricted to full salinity (30-35 ppt), noting that reduced salinities result in an impoverished bryozoan fauna. Flustra foliacea appears to be restricted to areas with high salinity (Tyler-Walters & Ballerstedt 2007; Budd 2008).

Dyrynda (1994) noted that Flustra foliacea was probably restricted to the vicinity of the Poole Harbour entrance by their intolerance to reduced salinity. Although, protected from extreme changes in salinity due to their subtidal habitat, severe hyposaline conditions could adversely affect Flustra foliacea colonies.

Sensitivity assessment. Whilst there is contradictory evidence amongst the sponges, Suberites ficus and the bryozoans are unlikely to resist a reduction in salinity.  Resistance is therefore ‘Low’, resilience is ‘Medium’ and the sensitivity is ‘Medium’.

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

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 that generate water currents in sponges using flagella (De Vos et al., 1991). 

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 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, 2005).

Okamura (1984) reported that an increase in water flow from slow flow (0.01-0.02 m/s) to fast flow (0.1 – 0.12 m/s) reduced feeding efficiency in small colonies but not in large colonies of Bugula stolonifera. 

Flustra foliacea colonies are flexible, robust and reach high abundances in areas subject to strong currents and tidal streams Stebbing, 1971a; Eggleston, 1972b; Knight-Jones & Nelson-Smith, 1977; Hiscock, 1983, 1985; Holme & Wilson, 1985). Dyrynda (1994) suggested that mature fronded colonies do not occur on unstable substratum due to the drag caused by their fronds, resulting in rafting of colonies on shells or the rolling of pebbles and cobbles, resulting in destruction of the colony. Dyrynda (1994) reported that the distribution of Flustra foliacea in the current swept entrance to Poole Harbour was restricted to circalittoral boulders, on which it dominated as nearly mono-specific stands. While, the pumping activity of the lophophores provide the greatest proportion of the colonies food requirements (Hayward & Ryland, 1998), the current generated is probably very localized and the colonies are likely to be dependent on water currents for food supply.  A significant decrease in water flow is likely to result in a decrease in the abundance of bryozoans.

It should be noted that a decrease in water flow would result in more deposition of suspended sediment, and consequently, a change in turbidity which could result in colonization by algal species.

Sensitivity assessment. CR.HCR.XFa.SubCriTf occurs in moderately strong water flow (0.5 – 1.5 m/sec).  Whilst an increase at the benchmark level could result in increased scour and result in a change to more opportunistic hydroids and bryozoans, a decrease would reduce scour and could favour more slow growing faunal groups. However, a decrease of 0.1- 0.2 m/sec is unlikely to be significant and resistance is therefore assessed as ‘High’, resilience as ‘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 can occur in the 0-5 m range.   Suberites ficus occurs on the lower shore, Hymeniacidon perlevis up to the middle shore and Bugula turbinata on the lower shore (Fish & Fish, 1996; Dyrynda & Ryland, 1982) and mortality is likely to be low for these species in the event of an increase in emergence at the benchmark level.  However, Flustra foliacea is recorded as a sublittoral species (Fish & Fish, 1996) and mortality is likely to occur in the shallow examples of this biotope.  Resistance is, therefore, assessed as ‘Low’, resilience is ‘High’ and sensitivity is assessed 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

Flustra foliacea occurs from very wave exposed to sheltered waters, although probably limited to deeper waters in very wave exposed conditions (Tyler-Walters & Ballerstedt ,2007) The oscillatory water flow generated by wave action may be more damaging than constant strong currents, e.g. strong wave action may generate an oscillatory flow of 2m/sec at 20m (Hiscock, 1983, 1985). Flustra foliacea is a common member of the flotsam, having been removed from its substratum by storms. Whilst the biotope is circalittoral, a severe increase in wave exposure (e.g. storms) could affect bryozoans colonies.  Cocito et al (1998) described a severe winter storm of 1993 had devastating effects on the same Flustra foliacea population, sweeping away most of the colonies down to 11 m.   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).  Erect sponges dominated the sheltered sites, while encrusting sponges dominated in exposed locations. 

Sensitivity assessment. CR.HCR.XFa.SubCriTf is characterized by the presence of ‘massive’ sponge forms which tend to be associated with less wave exposed locations and a significant increase in wave action could result in change in sponge morphology and may result in reclassification of the biotope.  However, a change at the benchmark level is unlikely to be significant enough to affect the biotope and resistance is therefore assessed as ‘High’, resilience as ‘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.

Whilst some sponges, such as Cliona spp. have been used to monitor heavy metals by looking at the associated bacterial community (Marques et al., 2006; Bauvais et al., 2015), no literature on the effects of transition element or organo-metal pollutants on the characterizing sponges could be found. TBT has been reported to induce apoptotic processes in the tissue of the marine sponge Geodia cydonium (Batel et al., 1993).

Bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1979; Holt et al., 1995). Bryan & Gibbs (1991) reported that there was little evidence regarding TBT toxicity in bryozoa with the exception of the encrusting Schizoporella errata, which suffered 50% mortality when exposed for 63 days to 100ng/l TBT. Rees et al. (2001) reported that the abundance of epifauna (including bryozoans) had increased in the Crouch Estuary in the 5 years since TBT was banned from use on small vessels. This last report suggests that bryozoans may be at least inhibited by the presence of TBT. 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 165m from the effluent source. The evidence therefore suggests that Securiflustra securifrons would be sensitive to synthetic compounds.

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.

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). 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 sub-littoral habitats (Castège et al., 2014). 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).

Little information on the effects of hydrocarbons on bryozoans was found. Ryland & e Putron (1998) did not detect adverse effects of oil contamination on the bryozoan Alcyonidium spp. or other sessile fauna in Milford Haven or St. Catherine's Island, south Pembrokeshire. Houghton et al. (1996) reported a reduction in the abundance of intertidal encrusting bryozoa (no species given) at oiled sites after the Exxon Valdez oil spill. Soule & Soule (1979) reported that the encrusting bryozoan Membranipora villosa was not found in the impacted area for 7 months after the December 1976 Bunker C oil spill in Los Angeles Harbour. Additionally, Soule & Soule (1979) reported that Bugula neritina was lost from breakwater rocks in the vicinity (in December 1979) of the Bunker C oil spill and had not recovered within a year. However, Bugula neritina had returned to a nearby area within 5 months (May 1977) even though the area was still affected by sheens of oil. Furthermore, only three of eight recorded species were present two weeks after the incident in April within the affected breakwater area. All the species had been replaced by dense growths of the erect bryozoan Scrupocellaria diegensis by June. Banks & Brown (2002) found that exposure to crude oil significantly impacted recruitment in the bryozoan Membranipora savartii.

Mohammad (1974) reported that Bugula spp. and Membranipora spp. were excluded from settlement panels near an oil terminal in Kuwait subject to minor but frequent oil spills. Encrusting bryozoans are also probably intolerant of the smothering effects of acute hydrocarbon contamination and pollution, resulting in suffocation of colonies and communities may be lost or damaged. Circalittoral communities are likely to be protected from the direct effects of oil spills by their depth. However, the biotope may be exposed to emulsified oil treated with dispersants, especially in areas of turbulence, or may be exposed to water soluble fractions of oils, PAHs or oil adsorbed onto particulates (Tyler-Walters, 2002).

Little information of the effects of hydrocarbons on hydroids was found although hydroid species adapted to a wide variation in environmental factors and with cosmopolitan distributions tend to be more tolerant of polluted waters (Boero, 1984; Gili & Hughes, 1995).

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.

Schröder et al. (1998) demonstrated that exposure to selected classes of PCBs induced DNA damage in the Suberites domuncula. Bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1979; Holt et al., 1995). 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 165m from the effluent source.

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

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) and short periods of hypoxia (<0.35 ml/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 below ca 10 m.  Despite the presence of Tethya aurantia, Kirchenpaueria pinnata, Hymeniacidon perlevis and Suberites carnosus in shallower depths, no sponges were recorded at depths below the oxycline at 10 - 11 m. 

Demosponges maintained under laboratory conditions can tolerate hypoxic conditions for brief periods. Gunda & Janapala (2009) investigated the effects of variable oxygen levels on the survival of the marine sponge, Haliclona pigmentifera. Under hypoxic conditions (1.5-2.0 ppm O₂), 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 O₂).

Sensitivity assessment

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

Nutrient enrichment

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

Evidence

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 conditions.  This study does contradict findings in Gochfeld et al. (2007) in which Aplysina spp. 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 increase in abundance of Cliona delitrix in organically polluted section of Grand Cayman fringing reef  affected  by  the  discharge of untreated  faecal  sewage.  Ward-Paige et al., 2005 described greatest size and biomass of Clionids corresponding with highest nitrogen, ammonia and δ¹⁵N levels.  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 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).

Nevertheless, this biotope is considered to be '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

Fu et al. (2007) described Hymeniacidon perlevis (as Hymeniacidon perleve) in aquaculture ecosystems in sterilized natural seawater at several different concentrations of total organic carbon (TOC)  ranging from 52.9 to 335.13 mg/l.   Hymeniacidon perlevis removed 44–61% TOC during 24 h, with retention rates of ca. 0.19–1.06 mg/h per g-fresh sponge  Hymeniacidon perlevis removed organic carbon excreted by Fugu rubripes with similar retention rates over a 15 day study and the sponge biomass increased by 22.8%.  Some of the characterizing  sponges occur in harbours and estuaries, including Halichondria spp. and Hymeniacidon perlevis (Ackers et al., 1992).  Rose & Risk, 1985 described 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.

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).  Mayer-Pinto & Junqueira (2003) studied the effects of organic pollution on fouling communities in Brazil and found that some tolerance of polluted/unpolluted artificial reefs varied among bryozoan species.  It should be note that Bugula spp. preferred the polluted sites.

Sensitivity assessment

Whilst an increase in organic matter would likely be removed relatively rapidly by water movement in this biotope, such an increase is likely be beneficial to the characterizing species.  Resistance is therefore ‘High’ resilience is ‘High’ and the biotope is ‘Not sensitive’.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very low’). Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

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

Evidence

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 rock.

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

Freese et al. (1999) studied the effects of trawling on a seafloor habitats and associated invertebrates in the Gulf of Alaska.  They found that a transect following a single trawling event showed significantly reduced abundance of ‘vase’ sponges (67% expressed damage) and ‘morel’ sponges, although 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 (14%) of the sponges assessed, were damaged by being knocked over.

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 oculta and Ircina campana were not significantly affected.  The abundance of sponges had increased to pre-trawl densities, or greater 12 months after trawling

Tilmant (1979) found that over 50% of sponges, including Neopetrosia, Spheciospongia, Spongia and Hippiospongia, were torn loose from the bottom following a shrimp trawl in Florida, US.  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 (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 epifaunal species, including the sponge Pachymatisma johnstoni, were highly damaged by the experimental trawl.  Coleman et al. (2013) described a 4 year study on the differences between a commercially potted area in Lundy within a no take zone.  No significant difference in Axinellid populations was observed.  The authors concluded that lighter abrasion pressures, such as potting, were far less damaging than heavier gears, such as trawls.

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. 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.  Based on the damage to sponges, Resistance has been assessed as ‘Low’, Resilience as ‘Medium’ and sensitivity has been assessed as ‘Medium’.

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 sediment may have a deleterious effect on the suspension feeding community. It is likely to clog their feeding apparatus to some degree, resulting in a reduced ingestion over the benchmark period and, subsequently, a decrease in growth rate (Jackson, 2004).  Bryozoans are suspension feeders that may be adversely affected by increases in suspended sediment, due to clogging of their feeding apparatus.  However, Tyler-Walters & Ballerstedt (2007) reported Flustra foliacea as tolerant to increased suspended sediment based on its occurrence in areas of high suspended sediment e.g. abundant in turbid, fast flowing waters of the Menai Straits (Moore 1977). Communities dominated by Flustra foliacea were described on tide swept seabeds, exposed to high levels of suspended sediment and sediment scour in the English Channel (Holme & Wilson, 1985). Flustra foliacea is also characteristic of sediment-scoured, silty rock communities CR.HCR.XFa.FluCoAs and CR.MCR.EcCr.UrtScr (Connor et al., 2004). 

Despite sediment being 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 (Schönberg, 2015; Bell & Barnes, 2000; Bell & Smith, 2004).  Castric-Fey & 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 and Stelligera rigida were classed as indifferent to turbidity, Tethya aurantium, Pachymatisma johnstonia and Polymastia boletiformis (as Polymastia robusta) had a slight preference for clearer water, while Dysidea fragilis, Polymastia mamillaris, and Raspailia ramosa had a strong preference for turbid water.   Some sponges occur in harbours and estuaries, including Hymeniacidon perlevis (Ackers et al., 1992).  Storr (1976) observed the sponge Sphecispongia vesparium back washing to eject sediment and noted that other sponges (such as Condrilla nucula) use secretions to remove settled material.

The very high silt loading in the water column means that this circalittoral biotope occurs at unusually shallow depths (0 - 20 m below Chart Datum).  However, a decrease in suspended sediment at the depth range at which this biotope occurs could result in an algal component colonizing this biotope.  This would result in a change in biotope classification, however, following return to heavily silted conditions, it is probable that the algal species would disappear and return to CR.HCR.XFa.SubCriTf would subsequently occur.

Sensitivity assessment

CR.HCR.XFa.SubCriTf is a heavily silted biotope which occurs at shallow depths.  A decrease in suspended sediment could result in colonization by algal species, the biotope would therefore have to be reclassified and resistance would be ‘None’.  Following return to heavily silted conditions, it is likely that the algae would disappear and the biotope would recover.  Resistance is ‘Medium’ and sensitivity is assessed as ‘Medium’.

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

Flustra foliacea dominated communities were reported in a tide-swept region of the central English Channel subject to sediment transport (mainly sand) and periodic, temporary, burial (ca <5 cm) (Holme & Wilson, 1985).

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).  However, Wulff (2006) described mortality in three sponge groups following four weeks of complete 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 aspera 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).  Hymeniacidon perlevis is encrusting (up to 2.5 mm height) or cushion forming up to 15 cm across and 2-5 cm thick (Hayward & Ryland, 1995b).  It can tolerate smothering of the main body, with the papillae protruding through the silt layer (Hayward & Ryland, 1995b). It should be noted that this biotope is characterized by ‘massive’ sponge forms and the majority should remain unburied at the benchmark level.

Sensitivity assessment: Deposition of 5 cm of sediment may bury some of the characterizing species.  However, the biotope experiences moderate water flow so that and depostied sediment is prbably removed with a few tidal cycles. Resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is 'Not sensitive' at the benchmark level.

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

Flustra foliacea dominated communities were reported in a tide-swept region of the central English Channel subject to sediment transport (mainly sand) and periodic, temporary, burial (ca <5 cm) (Holme & Wilson, 1985).

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).  However, Wulff (2006) described mortality in three sponge groups following four weeks of complete 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 aspera 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).  Hymeniacidon perlevis is encrusting (up to 2.5 mm height) or cushion forming up to 150 mm across and 20-50 mm thick (Hayward & Ryland, 1995b).  It can tolerate smothering of the main body, with the papillae protruding through the silt layer (Hayward & Ryland, 1995b). 

Sensitivity assessment: Deposition of 30 cm of sediment would bury the characterizing species.  However, the biotope experiences moderate water flow.  Resistance is assessed as ‘Medium’, resilience as ‘High’ and sensitivity as ‘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'

Underwater noise changes

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

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 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, while the bryozoan turf may benefit.  Resistance is, therefore, assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

Introduction of light or shading

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

Evidence

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, probably due to reduced competition from algae.  Flustra foliacea larvae are positively phototactic on release, swimming for only short periods (Hayward & Ryland, 1998) however, at the depths Flustra foliacea can occur, light may not be important.  Given the highly turbid nature of the biotope, it is unlikely that an increase in light or shade at the benchmark level would affect the biotope. Resistance is, therefore, assessed as 'High', resilience as 'High' and the biotope is 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

Not relevant: 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

Bugula spp. are classed as fouling bryozoans, and may be found in the intake pipes of ships or power stations, and on ships hulls. The geographic distribution of Bugula species has been extended by transportation by shipping (Ryland, 1967), however 'No evidence' of genetic modification was found. No evidence for the characterizing sponges 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

This biotope is classified as circalittoral and therefore no algal species have been considered. Crepidula fornicata larvae require hard substrata for settlement. It prefers muddy gravelly, shell-rich, substrata that include gravel, or shells of other Crepidula, or other species e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. But it also recorded from rock, artificial substrata, and Sabellaria alveolata reefs (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Helmer et al., 2019; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Tillin et al., 2020). Close examination of the literature (2023) shows that evidence of its colonization and density on bedrock in the infralittoral or circalittoral was lacking. Tillin et al. (2020) suggested that Crepidula could colonize circalittoral rock due to its presence on tide-swept rough grounds in the English Channel (Hinz et al., 2011). However, Hinz et al. (2011) reported that Crepidula fornicata only dominated one assemblage (with an average of 181 individuals per trawl) on gravel substratum with boulders. Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas dominated by boulders, and Bohn et al. (2013a, 2013b, 2015) and Preston et al. (2020) showed that while Crepidula could settle on slate panels or ‘stone’ it preferred shell, especially that of conspecifics. In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats. It was only recorded at low density (0.1-0.9/m²) in one faunal turf biotope (CR.MCR.CFaVS.CuSpH.As) (JNCC, 2015). Faunal turfs are dominated by suspension feeders so larval predation is probably high, which may prevent colonization by Crepidula. Also, faunal turf species actively compete for space and many are fast growing and opportunistic, so may out-compete Crepidula for space even if it gained a foothold in the community. 

Several invasive bryozoans are of concern including Schizoporella japonica (Ryland et al., 2014) and Tricellaria inopinata (Dyrynda et al., 2000; Cook et al., 2013b), although no evidence for the effects on the biotope were found. CR.HCR.XFa.SubCriTf occurs close to a population of Crepidula fornicata at their northerly distribution limit. 

Sensitivity assessment. The circalittoral rock characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata due to the moderately wave exposed conditions, in which wave action and storms may mitigate or prevent the colonization by Crepidula at high densities, although Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats or infralittoral or circalittoral rock habitats. At present, there is 'Insufficient evidence' to suggest that the circalittoral rock biotopes are sensitive to colonization by Crepidula fornicata or other invasive species; further evidence is required. 

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

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. 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 that 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. Whilst mass mortality and even extinction have been reported further afield, sponge diseases have caused limited mortality in some species in the British Isles.  Resistance is, therefore, assessed as 'Medium', resilience as 'High' and sensitivity as 'Low' .  Given the on-going work described above, this pressure should be revisited in light of any new evidence.

Removal of target species

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

Evidence

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

This pressure is 'Not relevant' as no characterizing species are targeted.

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, accidental removal of the characteristic epifauna is likely to remove a proportion of the biotope and change the biological character of the biotope. 

Based on the potential loss of sponges, resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity has been assessed as ‘Medium’.