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

Novocrania anomala extends as far south as the Mediterranean. Radolović et al. (2015) describe the gregarious settlement of Novocrania anomala in a cave in the Adriatic coast of Croatia. Despite this geographical range, Hiscock (1985 cited in Hartnoll, 1998), noted that seasonal shallow thermoclines may form, particularly in sheltered areas such as sea lochs, and extend down to 15 m. Some animals such as the brachiopods Crania (syn. Novocrania) and Terebratulina seem restricted to below this thermocline.  It is, therefore, possible that geographical populations may acclimate to local temperature (Hartnoll, 1998).

Protanthea simplex is a northerly species, with its southern distribution limit typically in Scotland, although one record exists off Connemara, Ireland (Seeley, 2006). Protanthea simplex experienced a marked long-term decline in Swedish and Norwegian sites between 1972 and 1982, experiencing ca 50% mortality (density of ca 600 to ca 300) at 20 m and virtual population collapse at 15 m (reduction in density from 400-500 to <50) over ten years (Heip et al., 1985).  This decline appeared to coincide with a warm period between 1973 and 1978 of up to ca +2°C deviation and an increase in Novocrania anomala (Heip et al., 1985). 

Ciona intestinalis is considered a cold water or temperate species but has been found as far south as Cape Verde, although these tropical populations are likely transitory (Monniot & Monniot, 1994). Temperature tolerance varies among geographical populations or ecotypes. Adult Ciona intestinalis is reported as tolerant of temperatures up to 30°C (Dybern, 1965; Therriault & Herborg, 2008), although Petersen & Riisgard (1992) noted that filtration rates declined above 21°C, which suggested thermal stress, and indicated that long-term survival was likely to require temperatures lower than the 30°C.  Other studies also indicated that Ciona intestinalis exhibits a decline in ammonia excretion rate and oxygen consumption rate above 18°C (Zhang and Fang 1999, Zhang et al., 1999).

The effect of higher temperatures on Ascidia mentula is not as well researched.  It is distributed from Norway through to the Mediterranean and the Black Sea, and the species appears to tolerate a broad range of temperatures.  Svane (1984) found that in Sweden, whilst lower temperatures decreased recruitment, populations responded positively to the “warm period” of 1972-1976 (Glantz, 2005), with an increase in population density across all sites in the study and a gradual decrease during the ensuing “cold period”, and minor fluctuations throughout.  Unusually high mean temperatures in 1975 did result in higher recruitment, with colder temperatures in January 1976 and spring 1979 coinciding with very little recruitment.  Svane (1984) found that, unlike recruitment, mortality was regulated locally and independent of temperature within the range of the study (mean monthly deviation of ±3°C)(Svane, 1984).

Sensitivity assessment.  Whilst Novocrania anomala and the ascidians are unlikely to be affected by a temperature increase at the benchmark level, Protanthea simplex, already at its southern-most limit, is unlikely to tolerate a long-term increase in temperature e.g. 2°C for a year. Population collapse has been recorded at 15 m in Sweden during an extended warm period (longer than the benchmark level).  Resistance has therefore been assessed as ‘Low’, Resilience has been assessed as ‘Medium’ and sensitivity is therefore recorded as ‘Medium’.

Temperature decrease (local)

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

Evidence

The characterizing brachiopod Novocrania anomala has been recorded as far north as Svalbard (Greig, 1924, cited in Prestrud et al., 2004) and the anemone Protanthea simplex is a northerly species, occurring in Scandinavia and recorded in across Scotland (Wood, 2005; NBN, 2015).  A reduction in temperature would probably be beneficial and could result in distribution expansion of Protanthea simplex.

Tolerance for low temperatures varies among geographical populations of ascidians. In the Mediterranean, most adult Ciona intestinalis die when temperatures fall below 10°C, and the population is maintained by the survival of younger individuals, which are more tolerant of colder temperatures (Marin et al., 1987).  Observation of Scandinavian populations indicated a higher mortality rate of Ciona intestinalis during the coldest period of the year (temperatures down to 1°C) (Dybern, 1965). 

In Scandinavian populations, normal egg development requires 8-22°C and larval development occurs between 6-24°C (Dybern, 1965).   Larval temperature tolerances may play a part in successful recruitment in unseasonable temperature fluctuations.  Ciona savigny larvae were found to acclimate to temperature, with embryos collected in the summer dividing normally between 14 - 27°C and embryos collected in the winter dividing normally between 10 - 20°C  (Nomaguchi et al., 1997).

Ascidia mentula is distributed from Norway through to the Mediterranean and the Black Sea, and the species appears to tolerate a broad range of temperatures.  Svane (1984) found that in Sweden, whilst lower temperatures (of ±3°C of the monthly mean) decreased recruitment, mortality did not significantly increase. Shallow populations (15 m) experiencing much greater seasonal variability did exhibit seasonal spawning rather than year-round spawning that occurs in more temperate and deeper populations (Svane, 1984).

Populations responded positively to the ‘warm period’ of 1972-1976 (Glantz, 2005), with an increase in population density across all sites in the study and a gradual decrease during the ensuing ‘cold period’, with minor fluctuations throughout.  Unusually high mean temperatures in 1975 did result in higher recruitment, with colder temperatures in January 1976 and spring 1979 coinciding with very little recruitment.  Svane (1984) found that, unlike recruitment, mortality was regulated locally and independent of temperature within the range of the study (mean monthly deviation of ±3°C).

Sensitivity assessment. None of the characterizing species for this biotope are at their northern distribution limit and are unlikely to be affected by a reduction in temperature at the benchmark level.  Resistance is therefore assessed as ‘High’, Resilience as ‘High’ and Sensitivity is therefore recorded as ‘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

Novocrania anomala occurs in biotopes ranging across all salinity regimes – from Low (<18 ppt) through to Full (30-35 ppt).  No literature could be found relating to this brachiopod in hypersaline conditions. Protanthea simplex prefers full salinity habitats over lower salinity as, whilst it is characterizing in NovPro.FS, it is only occasionally found in the variable salinity biotope NovPro.VS (Connor et al., 2004). No evidence could be found for the effect of hypersaline conditions.

Ciona intestinalis has been classified as euryhaline with a high salinity tolerance range (12-40‰) although it typically occurs in full salinity conditions (>30‰) (Tillin & Tyler-Walters, 2014).  Ciona intestinalis has been found in salinities ranging from 11 to 33 PSU in Sweden, although the same study found that parent acclimation to salinity (high or low) has an overriding and significant effect on larval metamorphic success, independent of parent origins (Renborg, 2014).

Sensitivity assessment. NovPro.FS is found in full salinity, but 'No evidence' for the characterizing species 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

Novocrania anomala occurs in biotopes ranging across all salinity variants, from Low (<18 ppt) through to full (30-35 ppt).  Whilst Novocrania anomala and the ascidians are likely to be unaffected by a decrease in salinity at the benchmark level, the reduced presence of Protanthea simplex from the variable salinity NovPro.VS indicates that it is at least partially intolerant of salinity decrease.  It should also be noted that, given the biotope descriptions, a change from NovPro.FS to NovPro.VS would occur in the event of a permanent salinity reduction at the benchmark level.  Whilst no evidence could be found directly for Novocrania anomala, Hammond (1983) reported that Lingula anatina could tolerate salinities ranging from 20‰ to 50‰ for prolonged periods (more than four weeks) and survived in salinities as low as 5‰ for short periods of time (snap response failed at 1 day) and 11.5‰ for 19 days.  Other studies report tolerances of ca 16 to 18‰ (Emig, 1997 and references therein) reported more conservative tolerance.  It should be noted that the ability for brachiopods to respire anaerobically within their closed shell would enable them to survive short-term changes (James et al., 1992).  Ciona intestinalis has been classified as euryhaline with a high salinity tolerance range (12-40‰) although it typically occurs in full salinity conditions (>30‰) (Tillin & Tyler-Walters, 2014) but has been found in Scandinavian waters in salinities as low as 11 PSU (Renborg, 2014, Dybern, 1967).  Adult acclimation to salinity was shown to have an overriding and significant effect on larval metamorphic success, independent of parent origins (Renborg, 2014).  ‘Massive die-offs’ of Ciona intestinalis were observed following winter rains in Californian harbours with ‘massive recolonizations usually following in the spring’ (Lambert & Lambert, 1998).  Population collapses of Ciona intestinalis in the Mediterranean have also been reported, and whilst the drivers for these events are not well understood, it has been postulated that low salinity could play a part (Péres, 1943; Caputi et al., 2015).  Oxygen consumption rate has been shown to decline with decreasing salinity and ceased at 19‰ with siphons tightly closed. (Shumway, 1978).  Ascidia mentula is found on the West coast of Norway in salinities greater than 20‰ (Dybern, 1969) and found in a brackish lake in Corsica with a salinity gradient of 6.5 to 18.5‰ Cl^- (Verhoeven, 1978).  Dendrodoa was observed as one of the dominant species in a study area in Lübeck Bay, Norway, where salinity was recorded as between 11.1 -15.0‰ (Gulliksen, 1977).

Sensitivity assessment. The abundance of Protanthea simplex is reduced from NovPro.FS (Full salinity of 35 ppt) to NovPro.VS (Low- Variable salinity, <18– 35ppt) while the abundance of Dendrodoa grossularia increases (JNCC, 2014). Therefore, resistance is assessed as ‘Medium, resilience as ‘High’ and sensitivity as ‘Low’. 

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

The CR.LCR.BrAs.NovPro biotope exists in weak to negligible tidal flow conditions (<0.5 m/sec.) Connor et al. (2004).  High flow rates may reduce the abundance of Novocrania anomala and Protanthea simplex, although Novocrania anomala may inhabit areas with water flow rates of up to 3 knots (Jackson, 2000; 2008b). Decreases in water flow are unlikely to have any effect but increases in flow rate above weak may prevent the animals from maintaining posture and interfere with feeding. Increased flow rates may also sweep individuals off the substratum.

As sessile filter feeders, ascidians generally require a reasonable water flow rate in order to ensure sufficient food availability.  It was shown that in stagnant water, phytoplankton density became reduced in a 20-30 cm layer immediately above a dense colony of Ciona intestinalis (Riisgård et al., 1996).  However, Ciona intestinalis has been recognised as tolerant of low water flow environments which it uses as a competitive advantage in areas with minimal water exchange and renewal such as harbours, marinas and docks, (Carver et al., 2006).

Whilst Ciona intestinalis is typically found in areas of low flow, it can reportedly withstand flow rates up to 3 knots (1.5 m/s) (Jackson 2008b). If dislodged, juveniles and adults have a limited capability to re-attach, given calm conditions and prolonged contact with the new substrata (Millar 1971; Carver et al., 2006; Jackson, 2008).  Hiscock (1983) found that, for the solitary ascidian Ascidia mentula, siphons closed when current velocity rose above about 0.15 m/s.

Sensitivity assessment.  Significant increases in water flow are likely to negatively affect the characterizing species, but mortality at the benchmark level is unlikely.  Therfore, resistance is assessed as ‘High’, resilience as ‘High’ and the biotope is considered ‘Not sensitive’ at the pressure benchmark.

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

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

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

The NovPro biotope complex is found in sheltered to extremely sheltered wave exposure conditions. Novocrania anomala is unlikely to tolerate wave action and is found in sheltered.  Increases in wave exposure above moderately exposed would probably cause death (Jackson, 2000).

High energy wave action can be detrimental to ascidian populations. This is mainly through physical damage to the sea squirts and through the abrasive action of suspended sediment (Jackson, 2008).  Ciona intestinalis is often dominant in highly sheltered areas such as harbours (Carver et al., 2006). Decreases in wave exposure are unlikely to have any effect.  If dislodged, juvenile and adult Ciona intestinalis have a limited capability to re-attach, given calm conditions and prolonged contact with the new substratum (Millar 1971; Carver et al., 2006; Jackson 2008;) but increases in wave exposure above moderately exposed are likely to cause a proportion of the population to die, especially in the shallower examples of the biotope if the cobbles and pebbles on which the biotope occurs are mobilized by wave action.  Ascidia mentula has rarely been recorded at depths shallower than 15 m (Svane, 1984), it is possible that damage could occur if subjected to increased wave exposure.

Sensitivity assessment. Whilst the characterizing species are likely to be affected by an increase in wave exposure, the NovPro biotope complex is found in sheltered to extremely sheltered wave exposure conditions and a change at the benchmark level is unlikely to increase mortality.  Resistance is therefore assessed as ‘High’, with resilience as ‘High’ and the biotope is therefore assessed as ‘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

Mercier et al. (1998) studied response to TBT exposure of temperate anemones (Metridium senile and Bunodactis stella), which metabolised and regulated butyl-tin uptake, and accumulated less than mussels (Fent, 1996) or symbiotic anemones (Mercier et al., 1996). Regulation of butyl-tin compounds in temperate sea anemones seemed to parallel that of trace metals (Mercier et al., 1998). Nevertheless, this pressure is Not assessed but evidence is presented where available.

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.LCR.BrAs.NovPro is a sub-tidal biotope (Connor et al., 2004). Oil pollution is mainly a surface phenomenon its impact upon circalittoral turf communities is likely to be limited. However, as in the case of the Prestige oil spill off the coast of France, high swell and winds can cause oil pollutants to mix with the seawater and potentially negatively affect sublittoral habitats (Castège et al., 2014). Filter feeders are highly sensitive to oil pollution, particularly those inhabiting the tidal zones that 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). Smith (1968) studied the aftermath of the Torrey Canyon oil spill and subsequent use of dispersants in that area. The beadlet anemone Actinia equine and the dahlia anemone Tealia feline were considered some of the most resistant animals on the shore, being commonly found alive, and on 26^th April they were found in pools between the tide-marks which appeared to be devoid of all other animals. Some Anemonia sulcata, Cylista elegans and Cereus pedunculatus were found dead; few survived. Little evidence for brachiopod resistance to hydrocarbon contamination could be found.

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.

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

The brachiopod Terebratulina unguicula is dominant in a fjord that shows annual upwelling of anoxic waters; it is one of the few animals found in areas with oxygen levels frequently below 0.1 ml/l (Tunnicliffe & Wilson, 1988).  The inarticulate Crania californica has a restricted distribution that may be a function of low dispersal. Over a number of years, one monitored brachiopod population was stable although a gradual retreat from the low oxygen waters was observed (Tunnicliffe & Wilson, 1988). 

The brachiopod Terebratulina septentionalis has been shown to survive in anoxic conditions for 3.5 days (through anaerobic respiration), however, its activity may be reduced (Hammen, 1977, cited in James et al., 1992).  Thayer (1981) found that the brachiopods L. californianus and Terebratulina unguicula survived more than two weeks in anoxic conditions.

Ellington(1982)  reviewed the effects of hypoxia and anoxia on anemones and noted that survival was several days to weeks depending on species. Mazouni et al. (2001) noted that whilst oysters (Magallana gigas) can survive short-term exposure to periods of anoxia (Thau Lagoon, France), the associated biofouling community dominated by Ciona intestinalis suffered heavy mortality.  It should be noted, however, that this species is frequently found in areas with restricted water renewal where oxygen concentrations may drop (Carver et al., 2006). While adverse conditions could affect health, feeding, reproductive capability and could eventually lead to mortality, recovery should be rapid.

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.

The ability of solitary ascidians to withstand decreasing oxygen levels has not been well documented.

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.  During these summer events, no echinoderms or Ascidia mentula were recorded at depths below 10 - 11 m.

Sensitivity assessment. No direct evidence was found on the effect of hypoxia on Novocrania anomala or Protanthea simplex. Based on the evidence of other brachiopods, and anemones, a proportion of the community is likely to be able to survive a short-term anoxic episode. An event at the benchmark level is likely to cause limited mortality among all the characterizing species.  Resistance is, therefore recorded as ‘Medium’, resilience as ‘High’ and sensitivity as ‘Low’.

Nutrient enrichment

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

Evidence

James et al. (1992) conducted a review of brachiopod literature, including brachiopod sensitivity to turbidity and cited Rhodes & Thayer (1991), highlighting the ability of brachiopods to sort and reject particles.  The rejected material was removed using mucous streamers, although the extra energy cost of this mechanism was noted.  The importance of dissolved organic matter is debated (see James et al., 1992).  Steele & Petrovic (1975, 1976, 1979) and Thayer (1986) discussed the importance of the unfused lophophore tentacles in adaptation to highly turbid environments, although whether this makes them better suited to excessive turbidity than bivalves is questioned (Thayer, 1991).  Ascidia mentula has been reported in Iberian bays subject to both nutrient-rich upwelling events and anthropogenic pollution (Aneiros et al., 2015).  There is some suggestion that there are possible benefits to ascidians from the increased organic content of water; ascidian ‘richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996). 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

Rhodes & Thayer (1991, cited in James et al.,1992) highlighted the ability of brachiopods to sort and reject particles.  The rejected material was removed using mucous streamers, although the extra energy cost of this mechanism was noted.  The importance of dissolved organic matter is debated (see James et al., 1992). The lophophore in some brachiopods appears to be able to absorb directly dissolved organic matter from seawater (Storch & Welsch, 1976 cited in Emig, 1997).  Steele & Petrovic (1975, 1976, 1979) and Thayer (1986) discussed the importance of the unfused lophophore tentacles in adaptation to highly turbid environments, although whether this makes them better suited to excessive turbidity than bivalves is questioned (Thayer, 1991). 

Shick (2012) reviewed the uptake of dissolved organic matter in sea anemones and noted (citing Robbins & Shick, 1980) that this feeding mechanism is likely to particularly important for small anemones, which have a proportionally large tentacle surface area.

There is some suggestion that there are possible benefits to the ascidians from the increased organic content of water. Ascidian ‘richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996).  Kocak & Kucuksezgin (2000) noted that Ciona intestinalis was one of the rapid breeding opportunistic species that tended to be dominant in Turkish harbours enriched by organic pollutants and was frequently found in polluted environments (Carver et al., 2006).  Ascidia mentula has been reported in Iberian bays subject to both nutrient-rich upwelling events and anthropogenic organic pollution (Aneiros et al., 2015).

Sensitivity assessment. All of the characterizing species are filter feeders and dissolved organic matter is an important food source.  However, organic enrichment can lead to eutrophication or hypoxia.  But ‘No evidence’ as to the effects of organic enrichment in sublittoral rock was found.

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

The replacement of rock by sediment would be a fundamentally change the physical character of the biotope, which would be lost.  Resistance to the pressure is considered ‘None’, and resilience ‘Very low’ (a permanent change). 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

Novocrania anomala is a sessile brachiopod protected by a calcified shell. However its shell is not massively strong and physical disturbance (such as a passing scallop dredge) will probably cause damage and death (Long & Stricker, 1991; James et al., 1992; Jackson, 2000).  Protanthea simplex is delicate and soft-bodied. Abrasion is highly likely to cause mortality. Both Ciona intestinalis and Ascidia mentula are large, emergent, sessile ascidians, and physical disturbance is likely to cause damage and mortality.  Emergent epifauna are generally very intolerant of disturbance from fishing gear (Jennings & Kaiser, 1998).  However, studies have shown Ascidia spp. to become more abundant following disturbance events (Bradshaw et al., 2000). 

Sensitivity assessment. Whilst the hard shell of Novocrania anomala would afford some protection from a lighter abrasion event, both the ascidians and the soft-bodied Protanthea simplex are likely to be significantly affected.  Resistance is, therefore, assessed as ‘Low’, resilience as ‘Medium’, and sensitivity 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

Rhodes and Thayer’s (1991, cited in James et al., 1992)  highlighted the ability of brachiopods to sort and reject particles.  The rejected material was removed using mucous streamers, although the extra energy cost of this mechanism was noted.  The importance of dissolved organic matter as a food source was debated (see James et al., 1992).  Steele-Petrović (1975, 1976, 1979) and Thayer (1986) discussed the importance of the unfused lophophore tentacles in adaptation to turbid environments, although whether this makes them better suited to excessive turbidity than bivalves was questioned (Thayer, 1991).  Whilst brachiopods appear well suited to cope with turbid conditions, Rudwick (1965, 1970, cited in James et al., 1992) noted that the sessile brachiopods, unable to maintain themselves at the surface of a rapidly accreting substratum, would not tolerate sedimentation.    Increased siltation may clog the anemone's tentacles and interfere with feeding. Clearing the sediment will require increased energetic expenditure and loss of condition may result.  Ciona intestinalis frequently occurs in habitats close to harbours and marinas with high levels of silt and suspended matter (Carver et al., 2006; Kocak & Kucuksezgin, 2000). Naranjo et al. (1996) described Ciona intestinalis as having a large body and siphons that have wide apertures that helps prevent blocking. Increased suspended sediment may potentially have some detrimental effects in clogging up feeding filtration mechanisms, however, there are possible benefits from increased suspended sediment as ascidian ‘richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996). In high (up to 300 mg/l of inorganic and 2.5 x10⁷ cells/l) suspended particulate concentrations, the active rejection mechanism (squirting) is increased in Ciona intestinalis with no discrimination between organic and inorganic particulates observed in any of the ascidians in the study (Robbins, 1984a).  Despite these observations, the turbidity tolerance level for this species is not well established. Robbins (1985a) found that continual exposure to elevated levels of inorganic particulates (>25 mg/l) arrested the growth rate of Ciona intestinalis and exposure to 600 mg/l resulted in 50% mortality after 12-15 days and 100% mortality after 3 weeks.  It was suggested that because this species can only “squirt” to clear the branchial sac, it may be vulnerable to clogging under heavy sediment loads.  Ascidia mentula has been shown to decrease absolute (instantaneous) rate of pumping in high suspended particulate concentrations, whilst filtration efficiency remained unchanged (Robbins, 1984a).  However, specific data on the sensitivity to suspended sediment is lacking.

Sensitivity assessment. Whilst increase in turbidity may result in increased energy expenditure for some of the characterizing species, all have methods to cope with increased turbidity.  Assuming the biotope typically occurs in intermediate turbidity (10-100 mg/l), an increase at the benchmark level (to medium, 100-300 mg/l) is unlikely to cause significant mortality amongst the characterizing species and Resistance is assessed as ‘High’, Resilience as ‘High’ and the biotope is considered to be ‘Not sensitive’.

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

Protanthea simplex is a small (2 cm high), delicate anemone (Jackson, 2008). Smothering with 5 cm of sediment is likely to cause physical damage to the anemone as well as restricting respiration and preventing feeding.  In the event of burial, Novocrania anomala is up to 1.5 cm in size (Jackson, 2000), can close their shell and survive in low oxygen concentrations, which can be tolerated for a few days (Thayer, 1981 cited in James et al., 1992).  Longer term, smothering by sediment will prevent feeding and result in anoxic conditions, eventually resulting in mortality. Adults are sessile, being permanently cemented to the substratum (Jackson, 2000) and Rudwick (1965, 1970, cited in James et al., 1992) noted that the sessile brachiopods, unable to maintain themselves at the surface of a rapidly accreting substratum, would not tolerate sedimentation.  The solitary ascidians considered in this report are permanently attached to the substratum and are active suspension feeders. Smothering with 5 cm of sediment is likely to only affect a small proportion of the population because the adults reach up to 15 cm and 18 cm in length for Ciona intestinalis and Ascidia mentula respectively (Rowley, 2008; Jackson, 2008) and frequently inhabit vertical surfaces (Jackson, 2008), Recovery should be rapid, facilitated by the remaining adults.

Sensitivity assessment.  Smothering by 5 cm of sediment is likely to impact the characterizing species of this biotope including the sessile ascidians and Novocrania anomala.  The biotope often occurs on vertical walls which would protect the characterizing species from sedimentation effects.  In flatter areas where sedimentation could occur, given the low water flow rates experienced by these biotopes (Weak to very weak), it is unlikely that the sediment would be removed very rapidly and it is unlikely that Novocrania anomala could survive.  Resistance has been assessed as ‘Medium’, resilience as ‘High’ and sensitivity has been assessed as ‘Low’ 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

Protanthea simplex is a small (2 cm high), delicate anemone (Jackson, 2008). Smothering with 30 cm of sediment is highly likely to cause physical damage to the anemone as well as restricting respiration and preventing feeding.  In the event of burial, the dorsal valve of Novocrania anomala is up to 1.5 cm in size (Jackson, 2000), can close their shell and survive in low oxygen concentrations, which can be tolerated for a few days (Thayer, 1981 cited in James et al., 1992).  Longer term, smothering by sediment will prevent feeding and result in anoxic conditions, eventually resulting in mortality. Adults are sessile, being permanently cemented to the substratum (Jackson, 2000) and Rudwick (1965, 1970, cited in James et al., 1992) noted that the sessile brachiopods, unable to maintain themselves at the surface of a rapidly accreting substratum, would not tolerate sedimentation.  The solitary ascidians considered in this report are permanently attached to the substratum and are active suspension feeders. Smothering with 30 cm of sediment is likely to affect a proportion of the population because, although the adults reach up to 15 cm and 18 cm in length for Ciona intestinalis and Ascidia mentula respectively (Rowley, 2008; Jackson, 2008), they frequently inhabit vertical surfaces (Jackson, 2008). Recovery should be rapid, facilitated by the remaining adults. 

Sensitivity assessment. Smothering by 30 cm of sediment is likely to impact the characterizing species of this biotope especially the sessile ascidians and Novocrania anomala.  The biotope often occurs on vertical walls which would protect the characterizing species from sedimentation effects.  In flatter areas where sedimentation could occur, given the low water flow rates experienced by these biotopes (weak to very weak), it is unlikely that the sediment would be removed very rapidly and few Novocrania anomala and ascidians would survive.  The resilience assessment assumes removal of the sediment, however, depending on the conditions, this may not be possible.  Resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity has been assessed as ‘Medium’ at the benchmark level.

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

No evidence could be found for the effects of noise or vibrations on Novocrania anomala or Protanthea simplex but they are considered unlikely to be sensitive to this pressure.  McDonald (2014) studied the effect of generator noise on fouling of four vessels by Ciona intestinalis and found that fouling was highest at locations closest to the generators and lowest furthest away from the generators.  Subsequent in vitro experiments demonstrated that larvae settled much faster in the presence of noise (2 h- 20 h compared with 6 h-26 h for control), underwent metamorphosis more rapidly (between 10 and 20 h compared with ca 22 h) and had a markedly increased survival rate to maturity (90-100% compared with 66%).   Other studies also reported that noise emissions from vessels promoted fouling by organisms including ascidians (Stanley et al., 2016). 

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

Introduction of light or shading

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

Evidence

Whilst most brachiopods are believed to detect light, the means of detection has been questioned and few studies have been undertaken (James et al., 1992).  It should be noted that McCammon (1973) reported that Magellania venosa was not sensitive to light.  Anemones have been reported to respond to light (Parker, 1919 cited in Sebens, 1981).  The ascidian Dendrodoa spp. larvae do not possess an eye spot, and light does not appear to affect locomotion (Mackie & Bone, 1976).

Sensitivity assessment. Whilst there is evidence that some characterizing species respond to light, either as larvae or as adults, change at the benchmark level is unlikely to cause mortality among any of the species assessed, and resistance and resilience are both recorded as ‘High’, and the biotope is considered ‘Not sensitive’ to this pressure.

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

Ciona intestinalis is considered a fouling species and adheres readily to the hulls of vessels, and is considered an invasive species in the USA, Chile, Western Australia, New Zealand, Canada and South Africa (Millar 1966; McDonald 2004; Blum et al. 2007; Ramsay et al. 2008, 2009; Dumont et al.,2011).  Whilst there have been novel proposals to farm Ciona intestinalis as a potential feedstock for aquaculture in Sweden (Laupsa, 2015), there is no evidence to suggest such farming exists.  No evidence for Novocrania anomala or Protanthea simplex could be found. Therefore, 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 has successfully colonized offshore in Georges Bank, USA (Lengyel et al., 2009). Styela clava, another INIS ascidian, was first recorded in the UK at Plymouth in 1952 (Eno et al., 1997).

Sensitivity assessment. The circalittoral rock characterizing this biotope could be suitable for colonization by Crepidula fornicata due to the sheltered to extremely sheltered wave conditions, where water is mediated by tidal flow rather than wave actions. Crepidula has been recorded from the lower intertidal to ca 160 m in depth but is most common in the shallow subtidal above 50 m (Blanchard, 1997; Thieltges et al., 2003; Bohn et al., 2012, 2015; Hinz et al., 2011; OBIS, 2023; Tillin et al., 2020), therefore, colonization of Crepidula would be limited to low densities in deeper examples of the biotope. In addition, no evidence was found of the effect of Crepidula populations on faunal turf-dominated habitats or infralittoral or circalittoral rock habitats. Didemnum vexillum could pose a potential threat. 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

Little is known about brachiopod disease, therefore there is 'No evidence' on which to base an assessment.  However, James et al. (1992) highlighted significant shell and soft tissue regenerative capabilities.  McCammon (1973) recorded infection of the lophophore tentacles of Magellania venosa by an unidentified protist which destroyed connective tissues and ultimately resulted in death.  McCammon (1972) also observed brachiopods subject to stress being prone to fungal infection which exhibited black spots forming on the shell.  More generally, James et al. (1992) discussed brachiopod success in aquaria and suggests that they are relatively hardy.  No evidence for diseases affecting Protanthea simplex could be found.  There appears to be little research into ascidian diseases, particularly in the Atlantic.  The parasite Lankesteria ascidiae targets the digestive tubes and can cause ‘long faeces syndrome’ in Ciona intestinalis (although it has also been recorded in other species).  Mortality occurs in severely affected individuals within about a week following first symptoms. (Mita et al., 2012).  There is ‘No evidence’ to support an assessment of this pressure.

Removal of target species

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

Evidence

Among brachiopods, only the lingulids (Lingula spp.) have been fished commercially, and on a very small scale (Printrakoon & Kamlung-ek, 2013). No evidence for brachiopod extraction in the British Isles was found.  Whilst unlikely, should targeted extraction occur, it is likely to have a significant impact on the characterizing species. Whilst anemones are not sessile, they are very slow moving and are therefore likely to be as exposed to extraction as the sessile Novocrania anomala and ascidians. 'Not relevant' as none of the 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.  Removal of the characteristic epifauna due to by-catch is likely to remove a proportion of the biotope and change the biological character of the biotope. These direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures. The sensitivity assessment for this pressure considers any biological/ecological effects resulting from the removal of non-target species on this biotope. Therefore, resistance is assessed as ‘Low’, resilience as ‘Medium’ and sensitivity assessed as ‘Medium’.  This biotope may be removed or damaged by static or mobile gears that are targeting other species (see physical pressures above).