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

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 (1974) noted that Flustra foliacea on the Gower peninsular, South Wales had an annual growth season between March and November.  Polyclinum aurantium is distributed across the British Isles and from Norway to the Mediterranean (Picton & Morrow, 2004b).

Reproduction of Clavelina lepadiformis is temperature dependant (Berrill, 1975; Millar, 1970).  A change in temperature could affect time and duration of spawning, however, the distribution of Clavelina lepadiformis extends to the north and south of the British Isles from Norway to the Adriatic (Hayward & Ryland, 1996).

Sensitivity assessment

All characterizing species are not at their southerly limit in the British Isles.  Resistance is ‘High’, resilience is ‘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

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 (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).

Polyclinum aurantium regresses into an overwintering phase when it divides, reproducing asexually before beginning to feed again in the spring and is distributed across the British Isles and from Norway to the Mediterranean (Picton & Morrow, 2004).

Clavelina lepadiformis undergoes stolonic asexual budding. At the end of the sexual breeding season, towards the end of the summer, zooids disappear or are resorbed. Over winter the colony survives as 'winter buds' from which new zooids develop in spring (Berrill, 1950; Fish & Fish, 1996; Picton, 1997). In the winter months, when the zooids undergo de-differentiation, the resulting cylindrical bodies of many species of Clavelinidae are often found on rocky shores (Millar, 1970).  During the severe winter of 1962-63, although no significant mortality of Clavelina lepadiformis was noted, Crisp (1964) found that many compound ascidians were retarded in renewal of the colony after 'winter budding', and some individuals may have been killed.

Sensitivity assessment

Flustra foliacea is not at its northerly limit in the British Isles and growth, which is halted in the winter, resumes in spring (Stebbing, 1971a).  The characterizing species have mechanisms in place to cope with cold conditions and no evidence of mortality due to low temperature in the British Isles was found.  Sensitivity is therefore assessed as ‘High’, Resilience as ‘High’ and the biotope is ‘Not Sensitive’ 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

This biotope occurs in full salinity and an increase in salinity would result in hypersaline conditions.  Soule & Soule (1979) cite Hastings (1927) who described the presence of five bryozoans in the Suez Canal at salinities of up to 49‰.  No other evidence for bryozoans, including Flustra foliacea, in hypersaline conditions was found.   Marin et al. (1998) describes the presence of Dysidea fragilis in a hypersaline coastal lagoon (42-47 g/l) in La Mar Menor, Spain.  No other evidence could be found for characterizing sponges.

Sensitivity assessment

CR.HCR.XFa.FluCoAs and associated biotopes occur in the circalittoral and are recorded at full salinity. No evidence was found to assess the effects of hypersaline conditions on Flustra foliacea or other characterizing species.

Salinity decrease (local)

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

Evidence

Ryland (1970) reported that, with a few exceptions, the Gymnolaemata were stenohaline and restricted to full salinity (30-35 ppt), noting that reduced salinities resulted in an impoverished bryozoan fauna. Flustra foliacea appears to be restricted to areas with full salinity (Tyler-Walters & Ballerstedt, 2007; Budd, 2008). Dyrynda (1994) noted that Flustra foliacea and Alcyonidium diaphanum were probably restricted to the vicinity of Poole Harbour entrance by their intolerance to reduced salinity. No evidence for the presence of Haliclona oculata in lower salinity conditions was found, and the species appears to be limited to open coasts and the outer reaches of estuaries (Hayward & Ryland, 1995a). Clavelina lepadiformis can tolerate a relatively broad range of salinities from 14 – 35 psu (Millar, 1971).

Sensitivity assessment. Although protected from extreme changes in salinity due to their subtidal habitat, distribution suggests that hyposaline conditions would probably affect Flustra foliacea and Haliclona oculata adversely.  Resistance is assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘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

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, 1977a). 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 (1-2 cm/s) to fast flow (10-12 cm/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, 1985b; 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 and 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 localized and the colonies are likely to be dependent on water currents for food supply.  Flustra foliacea abundance is lower in weak currents (Stebbing, 1971a). A significant decrease in water flow is likely to result in a decrease in the abundance of bryozoans.

Increased competition and sedimentation could also affect the community.  Riisgard et al. (1993) discussed the low energy cost of filtration for sponges and concluded that passive current-induced filtration may be insignificant for sponges. Pumping and filtering occurs in choanocyte cells that generate water currents in sponges using flagella (De Vos et al., 1991). 

Clavelina lepadiformis thrives in areas where there is little water movement (Hiscock & Hoare, 1975; De Caralt et al., 2002). Naranjo et al. (1996) found that the species was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations. High water flow rates may be detrimental to feeding ability and posture but are unlikely to cause detachment.

Sensitivity assessment

The CR.HCR.XFa.FluCoAs biotope complex occurs in a range of water flow conditions, from weak (>1kn) to strong (3-6kn) (Connor et al., 2004).  Flustra foliacea has been reported in areas subject to high water flow, with greater abundance in stronger water flow (Stebbing , 1971a).  Significant decrease in water flow would likely result in a reduction in the abundance of Flustra foliacea.  But a change in flow  benchmark level (0.1-0.2 m/s) are unlikely to result in mortality.  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

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, 1977a). 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 (1-2cm/s) to fast flow (10-12cm/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 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.

Flustra foliacea abundance is lower in weak currents (Stebbing, 1971a). 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 dependent on water currents to carry food particles to them.  Increased competition and sedimentation could also affect the community.  Riisgard et al. (1993) discussed the low energy cost of filtration for sponges and concluded that passive current-induced filtration may be insignificant for sponges. Pumping and filtering occurs in choanocyte cells that generate water currents in sponges using flagella (De Vos et al., 1991). 

Clavelina lepadiformis thrives in areas where there is little water movement (Hiscock & Hoare, 1975; De Caralt et al., 2002). Naranjo et al. (1996) found that the species was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations. High water flow rates may be detrimental to feeding ability and posture but are unlikely to cause detachment.

Sensitivity assessment

The CR.HCR.XFa.FluCoAs biotope complex occurs in a range of water flow conditions, from weak (>1kn) to strong (3-6kn) (Connor et al., 2004).  Flustra foliacea has been reported in areas subject to high water flow, with greater abundance in stronger water flow (Stebbing , 1971a).  Significant decrease in water flow would likely result in a reduction in the abundance of Flustra foliacea, but changes at the benchmark level are unlikely to result in mortality.  Resistance is therefore assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

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 2 m/s at 20 m (Hiscock, 1983, 1985). Dead colonies of Flustra foliacea are commonly found washed up, having been removed from its substratum by storms (Hayward & Ryland, 1995a). Whilst the biotope is circalittoral, a severe increase in wave exposure (e.g. storms) could affect bryozoans colonies.

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 (Roberts et al., 2006).  Erect or massive sponge forms possess a relatively small basal area relative to volume and do poorly in high energy environments (Wulff, 1995; Bell & Barnes, 2000).  Haliclona oculata is found in biotopes up to moderately exposed (Connor et al., 2004)

Clavelina lepadiformis is tolerant of a wide range of exposure, but is most abundant in moderately exposed sites (Picton, 1997).

Sensitivity assessment:

The CR.HCR.XFa.FluCoAs biotope complex is exposed or moderately exposed to wave action (Connor et al., 2004).  Whilst there is evidence that storm damage has significantly affected Flustra foliacea populations (Cocito et al., 1998b), changes in wave action at the benchmark level (a 3-5% change in significant wave height) are unlikely to be significant.  Resistance is therefore recorded as ‘High’, with 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.

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. Bryozoans were shown to bioaccumulate heavy metals to a certain extent (Holt et al., 1995). For example, Bowerbankia gracialis and Nolella pusilla accumulated Cd, exhibiting sublethal effects (reduced sexual reproduction and inhibited resting spore formation) between 10-100 µg Cd /l and fatality above 500 µg Cd/l (Kayser, 1990).

De Caralt et al. (2002) reported that Clavelina lepadiformis accumulated copper, lead and vanadium (vanadium is used in ascidian metabolism). A harbour population contained significantly more copper and lead than an open littoral population despite its abundance being an order of magnitude higher in the harbour (De Caralt et al., 2002). Neither reproduction nor growth were affected in this harbour population compared with a population outside of the harbour.

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.

CR.HCR.XFa.FluCoAs is a sub-tidal biotope complex (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 sub-littoral 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 & De 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.

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.

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 within 165m of the effluent source.

Radionuclide contamination

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

Evidence

No evidence

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 (ca 2.66 mg/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 epifaunal communities, including dominant species such as bryozoans (Membranipora tenuis and Conopeum tenuissimum), were unaffected by periods of moderate hypoxia (ca 0.35 -1.4 ml/l) and short periods of anoxia (<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.    An anoxic event in the northern Adriatic (1989–1990) exterminated the Pentapora fascialis population (McKinney & Jaklin, 2000; Hayward and McKinney, 2002). Colonies of Pentapora fascialis established after that anoxic event exceeded 15 cm in diameter by the summer of 1998 (Hayward & McKinney, 2002).

Demosponges maintained under laboratory conditions can tolerate hypoxic conditions for brief periods. Gunda & Janapala (2009) investigated the effects of variable DO levels on the survival of the marine sponge, Haliclona pigmentifera. Under hypoxic conditions (1.5-2.0 ppm DO), 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).  Stefaniak et al. (2014) reported that the sponge population at Stratford Shoal persisted despite multiple hypoxic events, however, the length and magnitude of these events was uncertain.  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.  No sponges or ascidians were recorded at depths below 10 - 11 m.

Sensitivity assessment

There is evidence that bryozoans and sponges may tolerate short periods of hypoxia, although moderate to long-term events or anoxia is likely to cause significant mortality.  Resistance at the benchmark level is likely to be ‘Medium’, resilience is ‘High’ and sensitivity is ‘Low’.

Nutrient enrichment

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

Evidence

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 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). 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 and ammonia and δ¹⁵N levels. 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 with 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.

Koopmans & Wijffels (2008) reported that concentrations of nitrate, nitrite, ammonium and phosphate correlated negatively with growth rate of Haliclona oculata. 

Clavelina lepadiformis was found to dominate Spanish harbours and nearby zones with highly transformed substrata, low rate of water renewal and excess silting and suspended matter and was described as biofouling and opportunist (Naranjo et al., 1996).

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

O’Dea & Okamura (2000) found that annual growth of Flustra foliacea in western Europe has 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).  

Koopmans & Wijffels (2008) found no correlation between growth rate of Halilcona oculata and dissolved organic carbon, suggesting that Haliclona oculata is more dependent on particulate organic carbon.  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.  Koopmans & Wiffjels (2008) reported that there was no correlation of Haliclona oculata growth rate and dissolved organic carbon concentration, suggesting that Haliclona oculata is more dependent on particulate organic carbon.

Clavelina lepadiformis was found to dominate Spanish harbours and nearby zones with highly transformed substrata, low rate of water renewal, excess silting and suspended matter.  The species was described as biofouling and opportunist (Naranjo et al., 1996).

Sensitivity assessment

Therefore, the important characteristic species could probably resist organic enrichment at the benchmark level. Resistance to this pressure is assessed as 'High', but with Low confidence, and resilience as 'High'. This biotope is therefore considered to be '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 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

Flustra foliacea is tolerant of sediment abrasion (Stebbing, 1971a; Knight-Jones & Nelson-Smith, 1977), but physical disturbance by fishing gear has been shown to adversely affect emergent epifaunal communities with 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).  Although Flustra foliacea is flexible, physical disturbance by a passing scallop dredge is likely to damage fronds and remove some colonies. Colonies on hard substrata are probably less vulnerable to fishing activity but would probably be damaged or partially removed. Colonies of Flustra foliacea are capable of regenerating areas of the frond which have been removed by grazing, which can result in new branches (Stebbing, 1971a).  Silén (1981) reported that Flustra foliacea could repair physical damage (a notch) to its fronds within 5-10 days, and regenerated at ca 4-5 zooid lengths per month.  As long as the holdfast remains intact, Flustra foliacea would survive and grow back.

Haliclona oculata is a branching erect sponge which is soft and elastic near the branch tips, becoming firmer near the base (Ackers et al., 1992).  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.  Twelve months after trawling, the abundance of sponges had increased to pre-trawl densities, or greater.  Freese (2001) studied deep cold-water sponges in Alaska a year after a trawl event and found that 46.8% of sponges exhibited damage and 32.1% were torn loose.  None of the damaged sponges displayed signs of regrowth or recovery.  This was in stark contrast to early work by Freese et al. (1999) on warm shallow sponge communities.  Impacts of trawling activity in Alaska study being much more persistent due to the slower growth/regeneration rates of deep, cold-water sponges.  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. 

Clavelina lepadiformis is permanently attached to the substratum and is unable to move out of the way from abrasive objects. The body of the species is soft and delicate, so abrasion is likely to cause physical damage and possibly death.

Sensitivity assessment

Whilst disturbance would damage the sessile Flustra foliacea, the flexibility and ability to regenerate damaged fronds (as long as the holdfast is undamaged) would result in a significant proportion of the colonies to survive disturbance.  Therefore, resistance is assessed as ‘Medium’, resilience is ‘High’ and sensitivity as ‘Low’.

Penetration or disturbance of the substratum subsurface

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

Evidence

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

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 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 seabed, exposed to high levels of suspended sediment and sediment scour in the English Channel subject to sediment transport (mainly sand) and periodic, temporary, submergence by thin layers of sand (ca <5 cm) (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 generally 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 many species prefer such habitats (Bell & Barnes 2001; Bell & Smith 2004).  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.  Raspailia ramosa and Stelligera stuposa have a reduced maximum size in areas of high sedimentation (Bell et al, 2002).  Tjensvoll et al. (2013) found that 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.  Schönberg (2015) reviewed and observed the interactions between sediments and marine sponges and described the lack of research on Porifera, with most studies grouping them together when looking at sediment effects.  Her findings were that, whilst many sponges are disadvantaged by sedimentation, many examples exist of sponges adapting to sediment presence, including through sediment incorporation, sediment encrusting, soft sediment anchoring using spicules and living, at least partially, embedded within the sediment.  Schönberg (2015) found that Polymastiida interacted with sediment in 18.9% of observations (primarily through spicules), Clionaida had a highly variable interaction with sediment, with 5.7±11.4 %, Tethyida interacted in 13.1±21.1%. However no Haliclonids were considered as part of the study.   De Kluijver & Leewis (1994) monitored the marine species before and two years after construction of a storm barrier in the Oosterschelde Estuary.  The barrier resulted in lower tidal flow, higher sedimentation and increased Haliclona oculata abundance.

Increased siltation can cause clogging of ascidians respiratory organs (Bakus, 1968). Clavelina lepadiformis has relatively wide apertures that help prevent clogging from particles (Naranjo et al., 1996). The simplistic structure of its branchial sac (Fiala-Medioni, 1978) may be less efficient in expelling particles, and more likely to suffer from clogging of feeding apparatus than other forms of sea squirts, such as Ciona intestinalis.  Clavelina lepadiformis was found to dominate Spanish harbours and nearby zones with low rate of water renewal, excess silting and suspended matter and the species was described as biofouling and opportunist (Naranjo et al., 1996).

Sensitivity assessment

Sediment scour within CR.HCR.XFa.FluCoAs and associated biotopes is an important factor in the dominance of the scour tolerant Flustra foliacea (Connor et al., 2004).  Whilst an increase is unlikely to have an effect, a reduction in suspended sediment could reduce scour and allow other species to colonize the biotope.  On return to the original sediment levels, it is probable that Flustra foliacea would again dominate the biotope.

Resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not Sensitive’ at the benchmark level.

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

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, 2005).  Communities dominated by Flustra foliacea were described on tide swept seabed, exposed to high levels of suspended sediment and sediment scour in the English Channel subject to sediment transport (mainly sand) and periodic, temporary, submergence by thin layers of sand (ca <5 cm) (Holme & Wilson 1985). 

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 aspera and associated sponges in the Black Sea near the Kerch Strait was attributed to siltation (Terent'ev, 2008 cited in Tillin & Tyler-Walters, 2014).  Some sponges are likely to be buried in 5cm of sediment deposition.  Haliclona oculata grows to ca 30 cm in height (Hayward & Ryland, 1995a) and smothering by 5 cm depth of sediment would bury only the smallest individuals.

Clavelina lepadiformis reaches up to 2 cm in height and often colonizes vertical surfaces and overhangs (Fish & Fish, 1992). Smothering by 5 cm depth of sediment would completely cover the majority of the population, with only those colonizing overhangs and vertical surfaces protected.

Sensitivity assessment

A deposit of 5 cm of fine sediment could smother and damage many of the smaller individulas of the faunal community. For example, Flustra foliacea is probably resistant while Clavelina lepadiformis is probably not resistant. However, in the high energy environment that the biotope occurs, deposited sediment would probably be removed quickly.  Therefore, resistance is ‘Medium’, resilience is ‘High’ and the 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

Smothering by 30 cm of sediment is likely to prevent feeding, 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, 2005).

Holme & Wilson (1985) examined the bottom fauna in a tide-swept region of the central English Channel. Flustra foliacea dominated communities were reported to form in areas subject to sediment transport (mainly sand) and periodic, temporary, submergence by thin layers of sand (ca <5 cm). If inundated by 30cm of sediment respiration and larval settlement are likely to be blocked until the deposited sediment is removed.  Haliclona oculata grows to ca 300 mm in height (Hayward & Ryland, 1995a) and smothering by 30 cm of sediment would cover the majority of the population.

Clavelina lepadiformis reaches up to 20 mm in height and often colonizes vertical surfaces and overhangs (Fish & Fish, 1992). Smothering by 30 cm of sediment would completely cover the majority of the population, with only those colonizing overhangs and vertical surfaces protected.

Sensitivity assessment

A deposit of 30 cm of fine sediment would smother and damage the majority of the faunal community.  In the high energy environment that the biotope occurs, deposited sediment would probably be removed fairly quickly.

Resistance is therefore assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’. 

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. No evidence could be found for the effects of noise on sponges but they are unlikely to be sensitive.

Sensitivity assessment. 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.

Introduction of light or shading

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

Evidence

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.

Jones et al. (2012) compiled a report on the monitoring of sponges around Skomer Island and found that many sponges, particularly encrusting species, were more abundant on vertical or shaded bedrock to open, light surfaces, probably due to reduced competition with algae.

Sensitivity assessment

The biotope occurs in the ciraclittoral and, whilst increase in light could result in competition with algae, it is unlikely that an increase at the benchmark level would 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

There is currently ‘No evidence’ on which to assess this pressure.

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. 

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 and 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 successfully colonized offshore in Georges Bank, USA (Lengyel et al., 2009), which is more exposed than the locations that Didemnum vexillum has colonized in the UK. It is therefore possible that Didemnum vexillum could pose a threat to these biotopes.

Several invasive bryozoans are of concern including Schizoporella japonica (Ryland et al., 2014) and Tricellaria inopinata (Dyrynda et al., 2000; Cook et al., 2013).  Tricellaria inopinata has been reported to colonize the byssal threads of the mussel Mytilus galloprovincialis, Hymeniacidon perleve and the ascidian Styela plicata (Dyrynda et al., 2000). Tricellaria inopinata dominated the fouling community in the Lagoon of Venice, within seven years of being introduced (Ambrogi, 2000).

Sensitivity assessment. The circalittoral rock characterizing this biotope is likely to be unsuitable for the colonization by Crepidula fornicata due to the wave exposed to 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

Pukall et al. (2001) studied the microbial community associated with Flustra foliacea and reported colonization of surfaces by bacteria typical of the marine environment and which may have been transferred into this environment from terrestrial sites.  No information on diseases was found. Stebbing (1971a) reported that encrusting epizoites reduced the growth rate of Flustra foliacea by ca 50%.  The bryozoan Bugula flabellata produces stolons that grow in and through the zooids of Flustra foliacea, causing "irreversible degeneration of the enclosed polypide" (Stebbing, 1971b).

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 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). 

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). Ooishi (2010) reported the copepod Enterocola hessei parasitizing Clavelina lepadiformis, however no evidence for microbial infection was found.

Sensitivity assessment

Current research on disease indicates that Flustra foliacea and some sponges are susceptible to disease, although the extent and long term implications are still being researched.  There is no evidence to suggest mortality of sponges in the British Isles, although mass mortality and even extinction have been reported further afield.  Resistance has been assessed as ‘Medium' with a resilience of ‘Medium’ and sensitivity is therefore ‘Medium’.

Removal of target species

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

Evidence

Flustra foliacea is not presently known to be subject to extraction. However, many bryozoans have been recently found to contain pharmacologically active substances (Hayward & Ryland, 1998; Lysek et al., 2002; Peters et al., 2003). 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.  Many different bioactive compounds have been found in the Haliclona order, such as lectins, peptides, ketosteroids, and sterol esters (Pajic et al. 2002; Aoki et al. 2003; Santalova et al. 2003; Koopmans & Wijffels, 2008), and it is possible that these sponges may be subject to future harvesting.

Sensitivity assessment

Whilst not presently harvested, it is possible that Flustra foliacea and Haliclonids may be subject to harvesting in the future.  Flustra foliacea and the sponges are sessile epifauna and would therefore have no defence against targeted extraction. Therefore a precautionary resistance of ‘None’ is suggested with Low confidence. Resilience is ‘Medium’ and overall sensitivity is therefore ‘Medium’.

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, 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.

Whilst disturbance would damage the sessile Flustra foliacea, the flexibility and ability to regenerate damaged fronds (as long as the holdfast is undamaged) would result in survival of a significant proportion of the colonies. Resistance is therefore ‘Medium’, resilience is ‘High’ and sensitivity is ‘Low’.