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

Murina (1997) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe, which extends into the warmer waters of Portugal and Italy (Pardal et al., 1993; Sordino et al., 1989). In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata at temperatures of 7.5 to 11.5°C and in Whitstable, in Kent, where sea temperatures varied between 0.5 and 17°C (Dorsett, 1961). Growth rates may increase if the temperature rises. For example, at Whitstable in Kent, Dorsett (1961) found that a rapid increase in growth coincided with the rising temperature of the seawater during March.

Amphipods were reported to have a low tolerance to temperature changes (Bousfield, 1973) although lethal limits were not given. However, the amphipods that occur within this habitat are mobile and can avoid unfavourable conditions to some extent. Furthermore, Corophium volutator is widely distributed in the North Atlantic, American and European coasts; from western Norway to the Mediterranean and the Black Sea and Azov Sea (Neal & Avant, 2006). The amphipod is subject to temperatures of 1°C in the winter to 17°C in the summer (Wilson & Parker, 1996) but can resist much higher temperatures (Meadows & Ruagh, 1981). Temperature increases may lead to indirect effects on populations of the characterizing species, through changes in the distribution and prevalence of parasites and pathogens (see microbial pathogens pressure). Using a simulation model, Mouritsen et al. (2005) demonstrated that a 3.8 °C increase in ambient temperature would probably result in a parasite‐induced collapse of the amphipod population in the Wadden Sea. This indirect effect is assessed in the introduction of microbial pathogens pressure.

Other polychaetes species in the biotope, e.g. Scoloplos armiger and Pygospio elegans, show a relationship between the timing of reproduction and temperature. Studies on the polychaete Scoloplos armiger in the Wadden Sea (North Sea) displayed that intertidal ‘Type I’ Scoloplos armiger reproduced in spring, through holobenthic development, triggered by a rise in seawater temperature above 5°C (Kruse et al., 2004). Gibson & Harvey (2000), in a study on asexual reproduction of Pygospio elegans in Nova Scotia, Canada, found temperature did not influence reproduction strategy (planktotrophy, lecithotrophy or asexual reproduction) but that environmental conditions, including temperature, influenced the timing of reproduction. Furthermore, Pygospio elegans has been recorded in seas with a temperature range of 1.6°C to 12.5°C (OBIS, 2016). Scoloplos armiger occurs in seas with a temperature range of between 8.8°C and 13°C (OBIS, 2016). Both Scoloplos armiger and Pygospio elegans tolerate a wide temperature range although optimal temperature ranges, based on feeding and reproductive success are more restricted, suggesting a 5°C increase in temperature over a month may increase temperatures above the preferred range, but not cause widespread mortality. These temperature ranges are not derived from peer-reviewed studies and, therefore, caution should be used with the interpretation.  No information was found regarding the intolerance of Spiophanes bombyx to temperature. Spiophanes bombyx is found in the Mediterranean (Hayward & Ryland, 1995b), which is likely to be warmer than the waters around Britain and Ireland.

Sensitivity assessment. Typical surface water temperatures around the UK coast vary seasonally from 4-19°C (Huthnance, 2010). Reproduction may be affected but no mortality is expected and the characterizing species of this biotope are likely to be able to resist a long-term increase in temperature of 2°C and may resist a short-term increase of 5°C. Resistance and resilience are, therefore, assessed as 'High' and the biotope assessed as '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

Murina (1997) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe. In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata at temperatures of 7.5 to 11.5°C and in Whitstable, Kent, abundance was high when winter water temperatures dropped to 0.5°C (Dorsett, 1961). During the extremely cold winter of 1962/63, Polydora ciliata was unaffected (Crisp, 1964).

Amphipods were reported to have a low tolerance to temperature changes (Bousfield, 1973) although lethal limits were not given. Mills (1967) reported that gonadal growth of Ampelisca vadorum and Ampelisca abdita was retarded by low temperatures, thus delaying maturity, and feeding rate was reduced below 10°C. Corophium volutator is subject to temperatures of 1°C in the winter to 17°C in the summer (Wilson & Parker, 1996), but the population may equally reduce activity and delay reproduction if the temperature drops below 7°C. Sudden pulses of very cold water can disrupt the circa-tidal rhythms of Corophium volutator by resetting the onset of swimming behaviour. For example, a six hour cold spell would lead to the population trying to swim at low tide and leave them vulnerable to increased predation. However, it took temperatures of 15-20°C below ambient temperature to induce this response (Holmström & Morgan, 1983b). Furthermore, Drolet et al. (2013) sampled two intertidal mudflats in the upper Bay of Fundy, Canada, over two consecutive winters (2009–2011), where sediment temperature, 5 cm deep, reached −2°C. The authors’ concluded Corophium volutator survived winter through physiological adaptations. Additionally, Crisp (1964) reported that species of amphipod and isopods seemed to be unharmed by the severe winter of 1962-1963, which may be due to burial in sediments buffering temperature or seasonal migration to deeper waters to avoid freezing.

The other polychaete species that are common in the biotope, Scoloplos armiger and Pygospio elegans, show a relationship between the timing of reproduction and temperature. Studies on the polychaete Scoloplos armiger in the Wadden Sea (North Sea) demonstrated that intertidal ‘Type I’ Scoloplos armiger reproduce in spring, through holobenthic development triggered by a rise in seawater temperature above 5°C (Kruse et al., 2004). In a study from the Baltic Sea, the timing of reproduction of Pygospio elegans was linked to environmental conditions including temperature (Anger, 1984). No information was found regarding the intolerance of Spiophanes bombyx to temperature. However, Spiophanes bombyx is found in waters off Denmark (Thorson, 1946) which are likely to be colder than British and Irish waters.

Sensitivity assessment. Typical surface water temperatures around the UK coast vary seasonally from 4-19°C (Huthnance, 2010). Reproduction may be affected but no mortality is expected and the characterizing species of this biotope are likely to be able to resist a long-term decrease in temperature of 2°C and may resist a short-term decrease of 5°C. Resistance and resilience are, therefore, assessed as 'High' and the biotope judged as '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

Corophium volutator occupies a greater variety of habitats and is found in fine sediments of mudflats, saltmarsh pools and brackish ditches. It is therefore exposed in its natural range to salinity extremes, from freshwater flushing during periods of high rainfall and increases in salinity during periods of high evaporation. Corophium volutator is, therefore, an exceptionally euryhaline species able to tolerate 2-50 psu (McLusky, 1968) but growth is fastest at 15-20 psu (McLusky, 1967; McLusky, 1970 cited in Meadows & Ruagh, 1981). The interstitial salinity is more important for Corophium volutator than that of the overlying water. Sustained periods of increased salinity are required to alter that of the interstitial water and there is a lag between salinity changes and the response of Corophium volutator (McLusky, 1968). Sudden increases in salinity delay swimming activity (Harris & Morgan, 1984a). Corophium volutator will also migrate from areas of unfavourable salinity (McLusky, 1968).

Monitoring at a Spanish desalination facility where discharges close to the outfall reached a salinity of 53, found that amphipods, including Ampelisca spp. were sensitive to the increased salinity and that species free-living in the sediment were most sensitive (De-la-Ossa-Carretero et al., 2016).  Roberts et al. (2010b) reported that the effects of brine discharge were dependent on the receiving environment but that the effects were limited to with 10s of metres of the outfall. In their review, they reported that polychaete abundance and diversity decreased adjacent to a brine outfall in Alicante, Spain and that the family Ampharaetidae were the most sensitive while the family Paraonidae were the least sensitive (Ruso et al., 2008 cited in Roberts et al., 2010b).  

In the western Baltic Sea, Scoloplos armiger abundance was greatest between 12 psu and 17 psu and reduced abundance with increasing salinity was observed (Gogina et al., 2010). As Scoloplos armiger is a species complex and is not a cosmopolitan species there may be inconsistencies between general environmental settings found in literature and observed and predicted distribution limits within study sites (Bleidorn et al., 2006 cited in Gogina et al., 2010). Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. Pygospio elegans is common in both marine and brackish waters in the Schelde Estuary (Netherlands) suggesting in European habitats the species tolerates a broad salinity range (Ysebaert et al., 1993). Studies of Pygospio elegans population structure in the Baltic Sea and the North Sea also found larvae were not hampered by changes in salinity (Kesaniemi et al., 2012). Although case studies are lacking for British and Irish coasts, the existing evidence suggests Pygospio elegans would tolerate salinity changes at the pressure benchmark level. However, an increase in one MNCR salinity category above the usual range of the biotope may reduce abundance as both species are most abundant in variable and fully marine salinity categories (and Scoloplos armiger has displayed negative responses to increasing salinity). No information was found concerning the reaction of Spiophanes bombyx or Pygospio elegans to hypersaline conditions (>40 psu). It is unlikely that Spiophanes bombyx would experience hypersaline conditions, therefore unlikely to be adapted to such conditions.

Sensitivity assessment. The characterizing species of this biotope are euryhaline and likely to be resistant to increases in salinity. However, the biotope occurs full saline conditions (Connor et al., 2004) and is unlikely to experience hypersaline conditions. Therefore, exposure to hypersaline effluent (>40) it might result in the death of a portion of the individuals in the population, especially Ampelisca and some polychaetes species. Therefore, resistance is assessed as 'Low' but with low confidence. Resilience is likely to be High, so the biotope is assessed as 'Low' sensitivity to an increase in salinity at the pressure benchmark.

Salinity decrease (local)

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

Evidence

Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. In an area of the western Baltic Sea, where bottom salinity was between 11.1 and 15.0 psu Polydora ciliata was the second most abundant species with over 1000 individuals per m² (Gulliksen, 1977). Corophium volutator is an exceptionally euryhaline species able to tolerate 2-50 psu (McLusky, 1968) but growth is fastest at 15-20 psu (McLusky, 1970 cited in Meadows & Ruagh, 1981). Corophium volutator is a hyperosmotic regulator and the tolerance of its tissues is 13-50 psu but it needs a salinity of above 5 psu in order to moult since the ability to osmoregulate is lost during moulting (McLusky, 1967). A salinity of at least 7.5 psu is required for reproduction (McLusky, 1968). Females undergoing a pre-copulatory moult failed to lay eggs below salinities of 3‰, and the lowest salinity at which all females moulted and laid eggs was 20‰ (Mills & Fish, 1980). Changes in salinity are very unlikely to cause mortality but may alter population distribution and abundances within the biotope as the species is likely to move to more favourable conditions or to suffer some effects on reproduction with resulting decreases in abundance.

Other polychaete species in the biotope are likely to tolerate decreases in salinity. Scoloplos armiger shows a lower salinity limit of 10.5 psu (Gogina et al., 2010), suggesting the species is tolerant of a decrease in salinity. Pygospio elegans was common in both marine and brackish waters in the Schelde Estuary (Netherlands) suggesting in European habitats the species tolerates a broad salinity range (Ysebaert et al., 1993). Studies of Pygospio elegans population structure in the Baltic Sea and the North Sea also found larvae were not hampered by changes in salinity (Kesaniemi et al., 2012). Spiophanes bombyx is a euryhaline species (Bailey-Brook, 1976; Maurer & Lethem, 1980), inhabiting fully saline and estuarine habitats.

Sensitivity assessment. SS.SSa.IFiSa.TbAmPo occurs in full salinity conditions (Connor et al., 2004). However, the evidence presented indicates that the species indicative of sensitivity occur in environments of lower salinities and are, therefore, likely to resist a decrease in salinity at the pressure benchmark level (to reduced 18-30 ppt). Therefore, resistance is assessed as 'High' and resilience as 'High' (by default) so the biotope is assessed as 'Not Sensitive' to a decrease in salinity at the pressure benchmark level.

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

Changes in water flow are likely to change the sediment characteristics in which the biotope occurs, primarily by resuspending and preventing deposition of finer particles (Hiscock, 1983). A decrease in water flow is unlikely to cause any impact on the biotope as species are adapted to incremental deposition, typical of low energy environments such as those where the biotope occurs. However, an increase would likely result in a decrease in tube-building material for the characterizing species, and the lack of deposition of particulate matter at the sediment surface would reduce food availability for the deposit feeders in the biotope. The resultant energetic cost over one year would be likely to result in some mortality of tube-builders and infauna. For example, Polydora ciliata was present and colonized test panels in Helgoland in three areas; two exposed to strong tidal currents and one site sheltered from currents (Harms & Anger, 1983). However, very strong water flows may sweep away Polydora colonies, often in a thick layer of mud on a hard substratum. Small Corophium volutator cannot resettle after swimming at current speeds approx. 0.1 m/s (Ford & Paterson, 2001), which probably explains why they mainly swim at high tide (Hughes, 1988). An increase in water flow rate could cause swimming Corophium volutator to be swept away from suitable habitat and cause high mortality. The species has been reported as not using flow velocity as a cue to stimulate swimming (Ford & Paterson, 2001).

The most damaging effect of increased flow rate would be the erosion of the medium to fine muddy sand substratum as this could eventually lead to loss of the habitat. Emergent species, such as the Polydora ciliata tubes that characterize this biotope, may create turbulent flow leading to particle resuspension. However, the medium to fine muddy sands offer increased cohesiveness and resistance to erosion and, because of their high numbers, amphipods are thought to stabilize the intertidal sediments in which they reside (Mouritsen et al., 1998). Additionally, where a change in water flow rate changes sediment characteristics, with increased deposits of coarser sediments, characterizing species may no longer be supported due to particular substratum preferences. For example, Spiophanes bombyx preferred substratum is fine sands, and Scoloplos armiger and Pygospio elegans thrive in medium particle size, therefore a change in sediment characteristics may result in a reduced distribution and extent of the populations.

Mills (1967, 1969) noted that the tubes of Ampelisca increased the surface complexity of the sandflat in Barnstable Harbour, Maine. Also, their feeding decreased the median grain size of the sediment, towards fine particulates, and resulted in instability. Mills (1969) stated that minor breaks in the mat of Ampelisca tubes were sufficient to cause large areas to wash out, especially on windy days in a rising or falling tide.

Sensitivity assessment. SS.SSa.IFiSa.TbAmPo is recorded in weak (<0.5 m/s) and very weak (negligible) tidal streams (Connor et al., 2004). Sand particles are likely to be eroded at about 0.20 m/s (based on Hjulström-Sundborg diagram, Sundborg, 1956). This biotope occurs on medium to very fine muddy sand (Connor et al., 2004), and the very fine muddy sands will require greater critical erosion velocities than fine sand because of their cohesiveness. Although a decrease in water flow rate is likely to be irrelevant, an increase in water flow at the pressure benchmark is likely to result in loss of parts of the characterizing mat of tubes formed by Polydora, Ampelisca, and Corophium spp.  Furthermore, stronger currents (e.g. due to storms) are likely to wash away the community of semi-permanent tube-building amphipods and polychaetes that characterize the biotope. Therefore, resistance is assessed as 'Low' and resilience as 'High' so that sensitivity is assessed as 'Low' sensitivity to a change in water flow at the pressure 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

SS.SSa.IFiSa.TbAmPo occurs in the shallow subtidal fringe and a change in emergence could potentially affect the upper extent of shallow examples of the biotope that are emersed on extreme low tides. All characterizing species would probably survive an increase in emergence. However, the species can only feed when immersed and, therefore, may experience reduced feeding opportunities. Over the course of a year, the resultant energetic cost is likely to cause some mortality. In addition, increased emergence is likely to increase the vulnerability to predation from shore birds, particularly of Corophium spp. which form an important food source for several species of birds and mobile predators (Hughes, 1988; Jensen & Kristensen, 1990; Raffaelli et al., 1991; Flach & De Bruin, 1994; Brown et al., 1999). A decrease in emergence is likely to allow the biotopes to extend their upper limits, where suitable substrata exist.

Sensitivity assessment. Species within the biotope exhibit physiological and behavioural adaptations to changes in emergence and the biotope is unlikely to be very sensitive. Furthermore, although some mortality of the characterizing species is likely to occur, it is considered that populations in the mid-range examples of the biotope are likely to be unaffected by changes in the emergence regime. Resistance and resilience (by default) are, therefore, assessed as 'High', and the biotope considered 'Not Sensitive'.

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

Where the biotope occurs in the shallow subtidal, it is likely to be affected by winter storms. Storms may cause dramatic changes in the distribution of macro-infauna by washing out dominant species, opening the sediment to recolonization by adults and/or available spat/larvae (Eagle, 1975; Rees et al., 1976; Hall, 1994) and by reducing the success of recruitment by newly settled spat or larvae (see Hall, 1994 for review). However, the biotope is found in moderately exposed and sheltered sites (Connor et al., 2004), which is likely to be an important factor in allowing for the development of the characteristic sedimentary regime and associated fauna that characterize this biotope.

Feeding of the characterizing species may be impaired in strong wave action and changes in wave exposure may also influence the supply of particulate matter for tube-building polychaetes and amphipods. Mills (1967, 1969) noted that the tubes of Ampelisca increased the surface complexity of the sandflat in Barnstable Harbour, Massachusetts. Also, their feeding decreased the median grain size of the sediment, towards fine particulates, and resulted in instability. Mills (1969) stated that minor breaks in the mat of Ampelisca tubes were sufficient to cause large areas to wash out, especially on windy days in a rising or falling tide and reported that Ampelisca flats were damaged noticeably by winter storms (Mills, 1967, 1969). 

Potentially the most damaging effect of increased wave heights would be the erosion of the medium to fine muddy sand substrata as this could eventually lead to loss of the habitat. Increased wave action may disturb the mud in which Corophium volutator lives and make it impossible for them to maintain burrows and may affect their ability to settle after swimming. Increased erosion would lead to the loss of habitat and removal of the characterizing species.

Sensitivity assessment. The tube mat that characterizes this biotope is probably very susceptible to damage or removal by during winter storms or on windy days in the shallow examples of the habitat. Mills (1969) considered that the  Ampelisca dominated tube mat demonstrated 'dynamic instability' due to its need to move from areas of physical disturbance and sediment modification.  However, the biotope occurs in moderately exposed and sheltered conditions (Connor et al., 2004), and a 3-5% change in significant wave height (the benchmark level) is unlikely to be significant. Therefore resistance is assessed as 'High', resilience as 'High' and sensitivity is 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

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

Experimental studies with various species suggest that polychaete worms are quite resistant to heavy metals (Bryan, 1984). Polydora ciliata occurred in an area of the southern North Sea polluted by heavy metals but was absent from sediments with very high heavy metal levels (Diaz-Castaneda et al., 1989). For most metals, toxicity to crustaceans increases with decreased salinity and elevated temperature, therefore marine species living within their normal salinity range may be less susceptible to heavy metal pollution than those living in salinities near the lower limit of their salinity tolerance (McLusky et al., 1986). In laboratory investigations, Hong & Reish (1987) observed 96-hour LC₅₀ water column concentrations of between 0.19 and 1.83 mg/l for several species of amphipod. Corophium volutator is highly intolerant of metal pollution at levels often found in estuaries from industrial outfalls and contaminated sewage. A concentration of 38 mg Cu/l was needed to kill 50% of Corophium volutator in 96-hour exposures (Bat et al., 1998). Other metals are far more toxic to Corophium volutator, e.g. zinc is toxic over 1 mg/l and toxicity to metals increases with increasing temperature and salinity (Bryant et al., 1985). Mortality of 50% is caused by 14 mg/l (Bat et al., 1998). Although exposure to zinc may not be lethal, it may affect the perpetuation of a population by reducing growth and reproductive fitness. Mercury was found to be very toxic to Corophium volutator, e.g. concentrations as low as 0.1 mg/l caused 50% mortality in 12 days. Other metals known to be toxic include cadmium, which causes 50% mortality at 12 mg/l (Bat et al., 1998); and arsenic, nickel and chromium which are all toxic over 2 mg/l (Bryant et al., 1984; Bryant et al., 1985a; 1985).

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 any evidence is presented where available.

In general, soft-sediment inhabitants, especially infaunal polychaetes, are particularly affected by oil pollution (Suchanek, 1993). For example, Jacobs (1980) investigated the effects of the Amoco Cadiz oil spill in 1978 and noted that the numbers of spionidae polychaetes decreased after the spill. In an analysis of kelp holdfast fauna following the Sea Empress oil spill in Milford Haven the fauna present, including Polydora ciliata, showed a strong negative correlation between numbers of species and distance from the spill (SEEEC, 1998). After the extensive oil spill in West Falmouth, Massachusetts, Grassle & Grassle (1974) followed the settlement of polychaetes in the disturbed area. Species with the most opportunistic life histories, including Polydora ligni, were able to settle in the area. This species has some brood protection which enables larvae to settle almost immediately in the nearby area (Reish, 1979). Furthermore, Gray et al. (1990) found that Scoloplos armiger was a dominant species in uncontaminated soft sediments at a case study site adjacent to the Ekofisk oil field but was not present at contaminated sites, suggesting Scoloplos armiger are also intolerant to hydrocarbon contaminates.

Amphipods in general and ampeliscid amphipods, in particular, seem particularly intolerant of contamination with oil. Dauvin (1998) reported reductions in abundance, biomass and production of Ampelisca sp. following the Amoco Cadiz oil spill. Furthermore, light fractions (C10 - C19) of oils are much more toxic to Corophium volutator than heavier fractions (C19 - C40). In exposures of up to 14 days, light fraction concentrations of 0.1 g/kg sediment caused high mortality. It took 9 g/kg sediment to achieve similar mortalities with the heavy fraction (Brils et al., 2002). In the Forth Estuary, Corophium volutator was excluded for several hundred metres around the outfalls from hydrocarbon processing plants. Roddie et al. (1994) found high levels of mortality of Corophium at sites contaminated with crude oil.

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 any evidence is presented where available.

In general, crustaceans are widely reported to be intolerant of synthetic chemicals (Cole et al., 1999) and intolerance to some specific chemicals has been observed in amphipods. Species of a different genus are likely to differ in their susceptibility to synthetic chemicals and that this may be related to differences in their physiology (Powell, 1979). Corophium volutator is paralysed by pyrethrum based insecticide sprayed onto the surface of the mud (Gerdol & Hughes, 1993) and pyrethrum would probably cause significant mortalities if it found its way into estuaries from agricultural runoff. Nonylphenol is an anthropogenic pollutant that regularly occurs in water bodies, it is an oestrogen mimic that is produced during the sewage treatment of non-ionic surfactants and can affect Corophium volutator (Brown et al., 1999). Nonylphenol is a hydrophobic molecule and often becomes attached to sediment in water bodies. This will make nonylphenol available for ingestion by Corophium volutator in estuaries where much of the riverine water-borne sediment flocculates and precipitates out of suspension to form mudflats. Nonylphenol is not lethal to Corophium volutator but does reduce growth and has the effect of causing the secondary antennae of males to become enlarged, which can make the amphipods more vulnerable to predators (Brown et al., 1999). Corophium volutator is killed by 1% ethanol if exposed for 24 hours or more but can withstand higher concentrations in short pulses. Such short pulses, however, have the effect of rephasing the diel rhythm and will delay the timing of swimming activity for the duration of the ethanol pulse (Harris & Morgan, 1984b).

The anti-parasite compound ivermectin is highly toxic to benthic polychaetes and crustaceans (Black et al., 1997; Collier & Pinn, 1998; Grant & Briggs, 1998, cited in Wilding & Hughes, 2010). OSPAR (2000) stated that, at that time, ivermectin was not licensed for use in mariculture but was incorporated into the feed as a treatment against sea lice at some farms. Ivermectin has the potential to persist in sediments, particularly fine-grained sediments at sheltered sites. Data from a farm in Galway, Ireland indicated that ivermectin was detectable in sediments adjacent to the farm at concentrations up to 6.8 μm/kg and to a depth of 9 cm (reported in OSPAR, 2000). Infaunal polychaetes have been affected by deposition rates of 78-780 mg ivermectin/m². Furthermore, Polydora ciliata was abundant at polluted sites close to acidified, halogenated effluent discharge from a bromide-extraction plant in Amlwch, Anglesey (Hoare & Hiscock, 1974). Spionid polychaetes were found by McLusky (1982) to be relatively resistant of distillation and petrochemical industrial waste in Scotland.

Radionuclide contamination

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

Evidence

Corophium volutator readily absorbs radionuclides such as americium and plutonium from water and contaminated sediments (Miramand et al., 1982). However, the effect of contamination of the individuals was not known but accumulation through the food chain was assumed (Miramand et al., 1982). There was 'No evidence' on which to base an assessment.

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

Polydora ciliata is repeatedly found at localities with oxygen deficiency (Pearson & Rosenberg, 1978). For example, in polluted waters in Los Angeles and Long Beach harbours Polydora ciliata was present in the oxygen range 0.0-3.9 mg/l and the species was abundant in hypoxic fjord habitats (Rosenberg, 1977). Furthermore, in a study investigating a polychaete community in the north-west Black Sea, Polydora ciliata was observed in all four study sites, including those severely affected by eutrophication and hypoxia as a result of the discharge of waste waters (Vorobyova et al., 2008). However, Polydora ciliata is unlikely to be able to resist anoxic conditions. Hansen et al. (2002) reported near total extinction of all metazoan in the Mariager Fjord (Denmark), including Polydora spp. after a severe hypoxia event that resulted in complete anoxia in the water column for two weeks. Additionally, Como & Magni (2009) investigated seasonal variations in benthic communities known to be affected by episodic events of hypoxia. The authors observed that the abundance of Polydora ciliata varied seasonally, decreasing during the summer months, and suggested it could be explained by the occurrence of hypoxic/anoxic conditions and sulphidic sediments during the summer. No details of the levels of dissolved oxygen leading to these community responses were provided. Other polychaetes in the biotope are also likely to be able to deal with hypoxia. For example, during low tide, the polychaete Scoloplos armiger survives deoxygenation by ascending into the oxidative layer where it can maintain aerobic metabolism. In laboratory conditions, Scoloplos armiger survived low oxygen conditions for 40 hours (Schöttler & Grieshaber, 1988).

Amphipods appear not to be tolerant of reduced oxygenation. For example, Ampelisca agassizi is reported to be intolerant of hypoxia (Diaz & Rosenberg, 1995) and Jassa falcata, another tube building amphipod species, was absent from Californian harbours with low oxygen concentrations (0-2.5 mg/l). Corophium volutator is highly sensitive to hypoxia and suffers 50% mortality after just four hours in hypoxic conditions, or two hours if there is a rapid build-up of sulphide (Gamenick et al., 1996). These conditions often occur in estuaries where drifting macroalgae (such as Fucus sp.) settle on the mudflats in small patches. These results agree with other work by Gamble (1970) who found that survival rates were temperature-dependent, with individuals surviving longer at lower temperatures. The level of oxygen was not assessed by Gamenick et al. (1996) and the description of the experimental set-up suggests that anoxic test conditions were used rather than hypoxic. Gamble (1970) found that at 5^oC most individuals were inactive after 30 minutes exposure to anaerobic seawater and that mortality occurred later; the inactivity may have allowed the species to survive longer (Gamble, 1970).

Riedel et al. (2012) assessed the response of benthic macrofauna to hypoxia advancing to anoxia in the Mediterranean. The hypoxic and anoxic conditions were created for 3-4 days in a box that enclosed in-situ sediments. Polychaetes appeared to be sensitive to hypoxia, as only 10% of polychaetes survived. In general, epifauna were more sensitive than infauna, mobile species more sensitive than sedentary species and predatory species more sensitive than suspension and deposit feeders. The test conditions did not lead to the production of hydrogen sulphide that may have reduced mortalities compared to other observations.

Nierman et al. (1990) reported changes in a fine sand community for the German Bight in an area with regular seasonal hypoxia. In 1983, oxygen levels were exceptionally low (<3 mg O₂/l) in large areas and <1 mg O₂/l in some areas. Species richness decreased by 30-50% and overall biomass fell. Spiophanes bombyx was found in small numbers at some, but not all areas, during the period of hypoxia. Once oxygen levels returned to normal Spiophanes bombyx increased in abundance. The evidence suggests that at least some individuals would survive hypoxic conditions.

Sensitivity assessment. Cole et al. (1999) suggested possible adverse effects on marine species exposed to dissolved oxygen concentrations below 4 mg/l and probable adverse effects below 2 mg/l. Polydora ciliata is repeatedly found at localities with oxygen deficiency (Pearson & Rosenberg, 1978) and seems to only be affected by severe deoxygenation episodes. Furthermore, opportunistic Polydora spp. were also reported to be amongst the first to recover from hypoxic events (Hansen et al., 2002; Van Colen et al., 2010). Other polychaetes in the biotope are likely to behave similarly. However, the mortality of tube building Corophium and other amphipod species is likely to occur. Therefore, resistance to deoxygenation at the pressure benchmark level is assessed as 'Low' but resilience is likely to be 'High so that biotope sensitivity is assessed as 'Low' sensitivity to exposure to a dissolved oxygen concentration of less than or equal to 2 mg/l for 1 week.

Nutrient enrichment

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

Evidence

Connor et al. (2004) suggested that many of the sites featuring this biotope are situated near fish farms, so it is possible that it may have developed as the result of moderate nutrient enrichment. Polydora ciliata is often found in environments subject to high levels of nutrients. For example, the species was abundant in areas of the Firth of Forth exposed to high levels of sewage pollution (Smyth, 1968), in nutrient-rich sediments in the Mondego Estuary, Portugal (Pardal et al., 1993), and the coastal lagoon Lago Fusaro, Naples (Sordino et al., 1989). The extensive growths of Polydora ciliata in mat formations were recorded at West Ganton, in the Firth of Forth, prior to the introduction of the Sewage Scheme (Read et al., 1983). The abundance of the species was probably associated with their ability to use the increased availability of nutrients as a food source and silt for tube building.

Similarly, amphipods appear to be tolerant of and indeed prefer, high nutrient levels. However, in the Ythan Estuary, Scotland, nutrient enrichment causes the mudflats to become covered with algal mats consisting mainly of the gutweed Ulva intestinalis. These mats physically perturb Corophium volutator by preventing burrowing and normal feeding. In areas where the mats did not occur, the density of Corophium volutator was 11 times higher than under the algae. When the algae died-back in the winter, the areas were rapidly recolonized by Corophium volutator from adjacent patches where the gutweed could not grow and population growth was high from feeding on the rotting algae. In the spring, the gutweed returned and the Corophium volutator were excluded once again (Raffaelli et al., 1991).

Sensitivity assessment. This pressure relates to increased levels of nitrogen, phosphorus and silicon in the marine environment compared to background concentrations. The characterizing species of this biotope are likely to be able to resist and be favoured by nutrient enrichment where increased availability of nutrients may be used as a source of food (Hiscock et al., 2005a). However, where nutrient enrichment causes proliferation of algal mats, Corophium volutator densities are likely to be reduced as a result of smothering. Nevertheless, the biotope is considered Not Sensitive at the pressure benchmark level, which is set at compliance with Water Framework Directive (WFD) criteria for good status, based on nitrogen concentration (UKTAG, 2014).

Organic enrichment

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

Evidence

Polydora ciliata is often found in environments subject to high levels of nutrients. For example, the species was abundant in areas of the Firth of Forth exposed to high levels of sewage pollution (Smyth, 1968), in nutrient-rich sediments in the Mondego Estuary, Portugal (Pardal et al., 1993), and the coastal lagoon Lago Fusaro in Naples (Sordino et al., 1989). The extensive growths of Polydora ciliata in mat formations were recorded at West Ganton, in the Firth of Forth, prior to the introduction of the Sewage Scheme (Read et al., 1983). The abundance of the species was probably associated with their ability to use the increased availability of nutrients as a food source and silt for tube building. In colonization experiments in an organically polluted fjord receiving effluent discharge from Oslo, Polydora ciliata had settled in large numbers within the first month (Green, 1983). However, Callier et al. (2007) investigated the spatial distribution of macrobenthos under a suspended mussel culture, in eastern Canada, where the sedimentation of organic matter to the bottom was approx. 1-3 gC/m²/day. Polydora ciliata was recorded as absent in the sites under the suspended mussel farm after one year and as dominant in reference areas of the study.  Como & Magni (2009) investigated seasonal variations in benthic communities known to be affected by episodic events of sediment over-enrichment. The authors observed that abundance of Polydora ciliata varied seasonally, and suggested this could be a result major accumulation of organic carbon-binding fine sediments in the study site.  Studies by Almeda et al. (2009) and Pedersen et al. (2010) investigated larval energetic requirements for Polydora ciliata and suggested maximum growth rates were reached at food concentrations ranging from 1.4 to 2.5 μg C/ml depending on larval size, and energetic carbon requirements of 0.09 to 3.15 μg C l/d, respectively. Borja et al. (2000) and Gittenberger & Van Loon (2011) both assigned Polydora ciliata to their AMBI Ecological Group IV ‘second-order opportunistic species (slight to pronounced unbalanced situations)’, and Corophium volutator to Group III ‘Species tolerant to excess organic matter enrichment; these species may occur under normal conditions, but their populations are stimulated by organic enrichment (slight unbalance situations)’. However, Polydora ciliata can also occur in organically poor areas (Pearson & Rosenberg, 1978).

Sensitivity assessment. Connor et al. (2004) suggested that as many of the sites featuring this biotope are situated near fish farms, it may have developed as the result of moderate nutrient enrichment. Furthermore, the evidence presented suggests that the characterizing species of this biotope are likely to be stimulated by enrichment and only affected by excessive organic enrichment (above the benchmark level). Therefore, resistance and resilience are assessed as 'High', and the biotope is assessed as 'Not Sensitive' to organic enrichment involving deposition of 100 gC/m²/yr.

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

SS.SSa.IFiSa.TbAmPo is characterized by the medium to very fine muddy sand substratum which supports the characterizing species. These species have very specific preference of suitable substrata. A change to a rock or artificial substratum would result in the loss of the characterizing species, significantly altering the character of the biotope. The biotope would be lost and/or reclassified.

Sensitivity assessment. Resistance to the pressure is considered 'None', and resilience 'Very Low' based on the permanent loss of suitable substratum to support the community of the characterizing tube-building polychaete and amphipod species. Sensitivity has been assessed as '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 sediment type)

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

Evidence

The biotope occurs in medium to very fine muddy sand (Connor et al., 2004). A change in sediment type by one Folk Class (based on the Long, 2006 simplification) would result in an increase in the fraction of sand and gravel in the substratum. The characterizing species would no longer be supported and the biotope would be lost and/or reclassified. For example, Polydora ciliata preferably settles on mud; Corophium spp. prefers muddier sediments (Watkin, 1941; Flach, 1993); Scoloplos armiger prefers sediments 200-350 µm that are enriched with mud (Degraer et al., 2006).

Sensitivity assessment. Resistance to the pressure is considered None, and resilience 'Very Low' based on the permanent loss of suitable substratum to support the community of the characterizing species. Sensitivity has been assessed as 'High'.

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

Removal of the substratum to 30 cm would result in the loss of the mat of Polydora ciliata tubes and of Corophium volutator that borrows up to 5 cm deep (Meadows & Reid, 1966). Recovery of sediments will be site-specific and will be influenced by currents, wave action and sediment availability (Desprez, 2000). Except in areas of mobile sands, the process tends to be slow (Kenny & Rees, 1996; Desprez, 2000). Boyd et al. (2005) found that in a site subject to long-term extraction (25 years), extraction scars were still visible after six years and sediment characteristics were still altered in comparison with reference areas with ongoing effects on the biota. The strongest currents are unable to transport gravel. A further implication of the formation of these depressions is a local drop in current strength associated with the increased water depth, resulting in deposition of finer sediments than those of the surrounding substrate (Desprez, 2000).

Sensitivity assessment. Resistance is assessed as 'None' as the extraction of the sediment will remove the characterizing and associated species present. Resilience is assessed as 'Medium' (see resilience section) and sediments may need to recover (where exposed layers are different). Biotope sensitivity is, therefore, assessed as 'Medium'.

Abrasion / disturbance of the surface of the substratum or seabed

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

Evidence

The tubes of the polychaetes and amphipods are bound only with mucous and are therefore likely to be damaged or removed by abrasion. The soft-bodied polychaetes are most likely to suffer mortality, while the more robust amphipods are likely to be more resistant, and mobile enough to avoid impact. The infaunal annelids are predominantly soft-bodied, live within a few centimetres of the sediment surface and may expose feeding or respiration structures where they could easily be damaged by a physical disturbance such as a dredge. For example, Ferns et al. (2000) reported a decline of 31% in populations of Scoloplos armiger (initial density 120/m²) in muddy sands and an 83% decline in Pygospio elegans (initial density 1850/m²) when a mechanical tractor towed harvester was used (in a cockle fishery). Pygospio elegans was significantly depleted for >100 days after harvesting (surpassing the study monitoring timeline). Scoloplos armiger demonstrated recovery >50 days after harvesting in muddy sands (Ferns et al., 2000).

Additionally, attached epifauna, such as the characterizing Polydora community in this biotope, can be entangled and removed by abrasion. Veale et al. (2000) reported that the abundance, biomass and production of epifaunal assemblages decreased with increasing fishing effort. Resampling of grounds that were historically studied (from the 1930s) indicates that some upright species have increased in areas subject to scallop fishing (Bradshaw et al., 2002).

The burrowing life habits of Corophium volutator are likely to provide some protection from abrasion at the surface only. However, any abrasion or physical disturbance is likely to reduce the density of Corophium volutator by emigration and increased mortality. For example, the sediment turnover caused by cockles and lugworms disturbed the burrows of Corophium volutator and caused a significant negative effect on the species density as a result of the increased rate of swimming that made the amphipod more vulnerable to predation (Flach & De Bruin, 1993, 1994). Furthermore, a number of studies have assessed the effects of trampling on other intertidal amphipods and these assessments are used as a proxy. Ugolini et al. (2008) carried out a controlled trampling experiment on Talitrus saltator. Plastic cylinders of 110 cm diameter (area 0.95 m²) were placed in the sand and all individuals trapped and counted, and 400 steps were made in a cylinder in 15 minutes after the amphipods had reburied. The trampling rate was based on the observed number of beach users and therefore represents a realistic level of exposure. Live individuals were counted at the end of the experiment and 24 hours after. Trampling significantly reduced abundance of the amphipods and after 24 hours the percentage of surviving amphipods dropped to almost zero, while survival rates of control (untrampled) amphipods were unaffected. Abrasion and compaction can, therefore, kill buried amphipods within sediments.

Sensitivity assessment. The evidence presented suggests that erect epifauna and soft-bodied individuals, such as those characterizing this biotope are directly exposed to this pressure, which would displace, damage and kill individuals. However, some individuals are likely to survive as individuals can withdraw into burrows.  Although the burrowing life habits of the infaunal community are likely to provide some protection from abrasion at the surface only, physical disturbance is likely to have adverse impacts on the community. Abrasion may also damage the substratum resulting in loss of habitat. Resistance to abrasion is considered 'Low' and resilience of the biotope is considered as 'High'. The biotope is, therefore, assessed as 'Low' sensitivity to abrasion or disturbance of the surface of the seabed.

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

Activities that penetrate below the surface are likely to tear up and remove a significant proportion of the tube building community that characterize this biotope. Additionally, Corophium volutator burrows to 5 cm deep and is also likely to be removed. However, in the Columbia river, no significant difference was found in Corophium volutator densities before and after dredging a channel and no difference between the dredged site and a control site (McCabe et al., 1998). Presumably, the dredging did cause mortality of Corophium volutator but recolonization was so rapid that no difference was found. Additionally, the extraction of cockles by sediment raking and mechanical disturbance and digging for lugworms for bait is likely to cause significant mortality of Corophium volutator. Bait digging was found to reduce Corophium volutator densities by 39%.  Juveniles were most affected and suffered a 55% reduction in dug areas (Shepherd & Boates, 1999). Bergman & Van Santbrink (2000) found that direct mortality of gammarid amphipods, following a single passage of a beam trawl (in silty sediments where penetration is greater) was 28%. Furthermore, stomach analysis of fish caught scavenging in the tracks of beam trawls found parts of Ampelisca spp. indicating that these had been damaged and exposed by the trawl (Kaiser & Spencer, 1994).

Experiments in shallow, wave disturbed areas, using a toothed, clam dredge, found that deposit-feeding polychaetes were more impacted than carnivorous species. Dredging resulted in reductions of >90% of Spiophanes bombyx immediately post dredging compared with before impact samples and the population reduction persisting for 90 days (although results may be confounded by storm events within the monitoring period which caused sediment mobility). The passage of the dredge across the sediment floor will have killed or injured some organisms that will then be exposed to potential predators/scavengers (Frid et al., 2000; Veale et al., 2000) providing a food source to mobile scavengers including these species. Bergman & Hup (1992) carried out a pre and post-experimental investigation using a 12 m beam trawl. The area was trawled three times over two days and samples taken up to two weeks after trawling. Some benthic species showed a 10-65% reduction in density after trawling the area three times. There was a significant lower of density (40-60%) of polychaete worms, including Spiophanes bombyx.

Sensitivity assessment. The evidence presented suggests that the community of characterizing species may suffer significant mortality (>75%) as a result of penetrative activities of the seabed. Biotope resistance is, therefore, assessed as 'None' and recovery is assessed as 'Medium so that sensitivity is assessed as 'Medium'.

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

The biotope is likely to occur in relatively turbid waters that allow sediment deposition to support the community of characterizing tube-building polychaetes and amphipods, and, therefore, the species in the biotope are likely to be adapted to turbid conditions. Amphipods are tolerant of high turbidity and gather suspended sediment for the construction of tubes. Mills (1967) reported that feeding by Ampelisca vadorum and Ampelisca abdita were initiated by the turbidity of the water surrounding the tubes. However, the feeding structures of suspension feeders such as Ampelisca spp. may become clogged by large increases in suspended sediment or feeding may be terminated, compromising growth. Corophium volutator lives in areas with very high sediment loads and it might be postulated that an increase would not affect them.

Tube-building polychaetes are likely to be tolerant of high turbidity as they normally inhabit waters with high levels of suspended sediment which they actively fix in the process of tube making. For example, in the Firth of Forth, Polydora ciliata formed extensive mats in areas that had an average of 68 mg/l suspended solids and a maximum of approximately 680 mg/l indicating the species can tolerate different levels of suspended solids (Read et al., 1982; Read et al., 1983). Daro & Polk (1973) reported that the success of Polydora is directly related to the quantities of muds of any origin carried along by rivers or coastal currents. Deposit feeders and tube builders rely on siltation of suspended sediment. A decrease in suspended sediment will reduce this supply and therefore may compromise growth and reproduction.

Spiophanes bombyx is found in estuarine regions which experience high levels of turbidity. Spiophanes bombyx is a surface deposit feeder and relies on a supply of nutrients at the sediment surface. An increase in turbidity, reducing light availability may reduce primary production by phytoplankton in the water column. Although productivity in the biotope is secondary, a reduction in primary production in the water column may result in reduced food supply to deposit and suspension feeders, which in turn may affect growth rates and fecundity.

Sensitivity assessment. An increase in suspended solids at the pressure benchmark level is unlikely to affect the characterizing species of this biotope. However, a decrease in the suspended matter in the biotope could result in limitation of material for tube building activities and the loss of suitable substratum for colonization by new recruits of Polydora ciliata, in particular. Therefore, resistance is assessed as 'Low' (loss of 25-75%) and resilience is 'High' so that sensitivity is assessed as 'Low' 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

A Polydora mud can be up to 50 cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes or have left them to rebuild close to the surface. Munari & Mistri (2014) investigated the spatio-temporal variation pattern of a benthic community following deposition of dredged material, at a maximum thickness of 30–40 cm. Polydora ciliata was amongst the first colonizers of the newly deposited sediments. The authors suggested that individuals may have migrated vertically through the deep layer of dredged sand. This was based on the results of Roberts et al. (1998) who suggested 15 cm as the maximum depth of overburden through which benthic infauna can successfully migrate. After one year, no adverse impact of sand disposal on the benthic fauna was detected on the study site (Munari & Mistri, 2014).

Corophium volutator was categorized in AMBI sedimentation Group III – ‘species insensitive to higher amounts of sedimentation, but don’t easily recover from strong fluctuations in sedimentation’ (Gittenberger & Van Loon, 2011). Experimental fences placed on mudflats caused sedimentation rates of 2-2.5 cm/month and reduced Corophium volutator densities from approximately 1700 m² to approximately 400 m². In areas without fences, Corophium volutator numbers increased from approximately 1700 per m² to 3500 per m² (Turk & Risk, 1981 cited in Neal & Avant, 2006).

The characterizing polychaetes Spio filicornis and Spiophanes bombyx were characterized by Gittenberger & Van Loon (2011) in their index of sedimentation tolerance as Group IV species: ‘Although they are sensitive to strong fluctuations in sedimentation, their populations recover relatively quickly and even benefit. This causes their population sizes to increase significantly in areas after a strong fluctuation in sedimentation’ (Gittenberger & Van Loon, 2011). Pygospio elegans was classified as ‘Group III’ which do tolerate disturbance and excess organic content by Borja et al. (2000).

Where a coarse/impermeable layer was added to the seabed the suitability of the habitat for Corophium volutator would be reduced if these could not reach the surface or maintain burrows. Furthermore, the deposition of fine sediment is likely to take several tidal cycles to clear in the low energetic conditions where this biotope occurs.

Sensitivity assessment. Based on the evidence presented, Polydora ciliata and other characterizing polychaetes are likely to resist or relocate after smothering by 5 cm of sediment. However, the same ‘light’ deposition of fine sediment is likely to cause some mortality of Corophium spp.. Therefore, resistance is assessed as 'Medium', resilience as High, and biotope is assessed as 'Low' sensitivity to a ‘light’ deposition of up to 5 cm of fine material in a single discrete event.

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

A Polydora mud can be up to 50 cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes or have left them to rebuild close to the surface. Munari & Mistri (2014) investigated the spatio-temporal variation pattern of a benthic community following deposition of dredged material, at a maximum thickness of 30–40 cm. Polydora ciliata was amongst the first colonizers of the newly deposited sediments. The authors suggested that it was possible that the individuals migrated vertically through the deep layer of dredged sand. This was based on the results of Roberts et al. (1998) who suggested 15 cm as the maximum depth of overburden through which benthic infauna can successfully migrate. After one year, no adverse impact of sand disposal on the benthic fauna was detected on the study site (Munari & Mistri, 2014).

Corophium volutator was categorized in AMBI sedimentation Group III – ‘species insensitive to higher amounts of sedimentation, but don’t easily recover from strong fluctuations in sedimentation’ (Gittenberger & Van Loon, 2011). Experimental fences placed on mudflats caused sedimentation rates of 2-2.5 cm/month and reduced Corophium volutator densities from approximately 1700 m² to approximately 400 m². In areas without fences, Corophium volutator numbers increased from approximately 1700 per m² to 3500 per m² (Turk & Risk, 1981 cited in Neal & Avant, 2006). Pygospio elegans was classified as ‘Group III’ by Borja et al. (2000) as tolerant of disturbance and excess organic content.

Where a coarse/impermeable layer was added to the seabed the suitability of the habitat for Corophium volutator would be reduced if these could not reach the surface or maintain burrows. Furthermore, the deposition of fine sediment is likely to take several tidal cycles to clear in the low energetic conditions where this biotope occurs.

Sensitivity assessment. Based on the evidence presented, Polydora ciliata and other characterizing polychaetes are probably likely to resist and relocate the following smothering by 30 cm of sediment. However, the same ‘heavy’ deposition of fine sediment is likely to result in mortality of Corophium volutator. Resistance is, therefore, assessed as 'Low' and resilience as 'High' and the biotope sensitivity is assessed as 'Low' to a ‘heavy’ deposition of up to 30 cm of fine material in a single discrete event.

Litter

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

Evidence

Corophium volutator is widely used in ecotoxicological studies and know to uptake nanoplastics but toxicity at the current environmental relevant concentrations has yet to be confirmed (Booth et al., 2015). However, Corophium volutator forms an important food source for several species of birds and mobile predators such as fish and crabs (Hughes, 1988; Jensen & Kristensen, 1990; Raffaelli et al., 1991; Flach & De Bruin, 1994; Brown et al., 1999), which is likely to result in transition of the particles up the marine food chain. Nevertheless, there was insufficient evidence on which to assess the sensitivity of this biotope to the introduction of litter.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

No evidence was available on which to assess this pressure. However, Arendse & Barendregt (1981) manipulated magnetic fields to alter the geomagnetic orientation of the talitrid amphipod Orchestia cavimana.

Underwater noise changes

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

Evidence

Polydora ciliata may respond to vibrations from predators or bait diggers by retracting their palps into their tubes. Corophium volutator is probably sensitive to surface vibrations but little is known about the effects of noise on invertebrates. However, there is no evidence to suggest that any of the species that characterize the biotope respond to noise or vibration at the level of the benchmark, so the biotope is assessed as Not relevant.

Introduction of light or shading

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

Evidence

SS.SSa.IFiSa.TbAmPo is a sublittoral biotope (Connor et al., 2004) and therefore not directly dependent on sunlight. Although Polydora spp. can perceive light, this pressure is not considered relevant. Although changes in light may alter predation rates on Corophium volutator (Meadows, 1964), it is unlikely to be relevant for the overall composition of the biotope given the species is already likely to be adapted to sustain high levels of predation. The biotope is considered to have 'High' resistance and, by default, 'High' resilience and is, therefore, is assessed as 'Not Sensitive' to the introduction of light.

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 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

Polydora ciliata exhibits shadow responses and withdraws its palps into its burrow, which is believed to be a defence against predation. The withdrawal of the palps interrupts feeding and possibly respiration, although the species also shows habituation of the response (Kinne, 1970).  Polydora is unlikely to be sensitive to visual disturbance caused by passing shipping but may respond to passing divers at close range.  Other characterizing polychaetes, such as Spiophanes bombyx, also inhabit a tube so visual range is probably very limited.  Corophium volutator has limited visual acuity and since it spends most of its life in a burrow it is unlikely to be affected by visual disturbances. Furthermore, in substratum choice experiments, Corophium volutator preferred substrata independently of whether the dishes were in darkness or illuminated (Meadows, 1964) suggesting visual acuity is low.  Therefore, visual disturbance (as defined by the benchmark) is probably '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

The important characterizing species in the biotope are not cultivated or likely to be translocated. This pressure is, therefore considered 'Not relevant'.

Introduction or spread of invasive non-indigenous species

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

Evidence

The American slipper limpet Crepidula fornicata was introduced to the UK and Europe in the 1870s from the Atlantic coasts of North America with imports of the eastern oyster Crassostrea virginica. It was recorded in Liverpool in 1870 and the Essex coast in 1887-1890. It has spread through expansion and introductions along the full extent of the English Channel and into the European mainland (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Helmer et al., 2019; Hinz et al., 2011; McNeill et al., 2010; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015).

Crepidula fornicata is recorded from shallow, sheltered bays, lagoons and estuaries or the sheltered sides of islands, in variable salinity (18 to 40) although it prefers ca 30 (Tillin et al., 2020). 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 in a wide variety of habitats including clean sands, artificial substrata, Sabellaria alveolata reefs and areas subject to moderately strong tidal streams (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015; Tillin et al., 2020).

High densities of Crepidula fornicata cause ecological impacts on sedimentary habitats. The species can form dense carpets that can smother the seabed in shallow bays, changing and modifying the habitat structure. At high densities, the species physically smothers the sediment, and the resultant build-up of silt, pseudofaeces, and faeces is deposited and trapped within the bed (Tillin et al., 2020, Fitzgerald, 2007, Blanchard, 2009, Stiger-Pouvreau & Thouzeau, 2015). The biodeposition rates of Crepidula are extremely high and once deposited, form an anoxic mud, making the environment suitable for other species, including most infauna (Stiger-Pouvreau & Thouzeau, 2015, Blanchard, 2009). For example, in fine sands, the community is replaced by a reef of slipper limpets, that provide hard substrata for sessile suspension-feeders (e.g., sea squirts, tube worms and fixed shellfish), while mobile carnivorous microfauna occupy species between or within shells, resulting in a homogeneous Crepidula dominated habitat (Blanchard, 2009). Blanchard (2009) suggested the transition occurred and became irreversible at 50% cover of the limpet. De Montaudouin et al. (2018) suggested that homogenization occurred above a threshold of 20-50 Crepidula /m².

Impacts on the structure of benthic communities will depend on the type of habitat that Crepidula colonizes. De Montaudouin & Sauriau (1999) reported that in muddy sediment dominated by deposit-feeders, species richness, abundance and biomass increased in the presence of high densities of Crepidula (ca 562 to 4772 ind./m²), in the Bay of Marennes-Oléron, presumably because the Crepidula bed provided hard substrata in an otherwise sedimentary habitat. In medium sands, Crepidula density was moderate (330-1300 ind./m²) but there was no significant difference between communities in the presence of Crepidula. Intertidal coarse sediment was less suitable for Crepidula with only moderate or low abundances (11 ind./m²) and its presence did not affect the abundance or diversity of macrofauna. However, there was a higher abundance of suspension–feeders and mobile Crustacea in the absence of Crepidula (De Montaudouin & Sauriau, 1999). The presence of Crepidula as an ecosystem engineer has created a range of new niche habitats, reducing biodiversity as it modifies habitats (Fitzgerald, 2007). De Montaudouin et al. (1999) concluded that Crepidula did not influence macroinvertebrate diversity or density significantly under experimental conditions, on fine sands in Arcachon Bay, France. De Montaudouin et al. (2018) noted that the limpet reef increased the species diversity in the bed, but homogenised diversity compared to areas where the limpets were absent. In the Milford Haven Waterway (MHW), the highest densities of Crepidula were found in areas of sediment with hard substrata, e.g., mixed fine sediment with shell or gravel or both (grain sizes 16-256 mm) but, while Crepidula density increased as gravel cover increased in the subtidal, the reverse was found in the intertidal (Bohn et al., 2015). Bohn et al. (2015) suggested that high densities of Crepidula in high-energy environments were possible in the subtidal but not the intertidal, suggesting the availability of this substratum type is beneficial for its establishment. Hinz et al. (2011) reported a substantial increase in the occurrence of Crepidula off the Isle of Wight, between 1958 and 2006, at a depth of ca 60 m, on hard substrata (gravel, cobbles, and boulders), swept by strong tidal streams. Presumably, Crepidula is more tolerant of tidal flow than the oscillatory flow caused by wave action which may be less suitable (Tillin et al., 2020).

The availability of hard substrata (e.g., gravel) may only restrict initial colonization as higher densities of Crepidula function as substrata for subsequent colonization (Thieltges et al., 2004; Blanchard, 2009). However, Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas of homogenous fine sediment and areas dominated by boulders. Bohn et al. (2015) suggested that wave action (exposure) probably prevented the establishment of large numbers of Crepidula in high-energy areas. Blanchard (2009) noted that sandy areas in the Bay of Saint-Mont Michel were not colonized by Crepidula because of surface sand mobility. Thieltges et al. (2003) also noted that storm events removed some clumps of mussels and presumably Crepidula onto tidal flats where they disappeared, which caused their abundance to fluctuate. Similarly, Crepidula was absent from sandy substrata in Swansea Bay but was most abundant in the shelter of the breakwater at the Swansea east site (Powell-Jennings & Calloway, 2018). Powell-Jennings & Calloway (2018) noted that Crepidula is killed by sudden burial and possibly burial due to deposition, which could mitigate Crepidula density.

Sensitivity assessment. The sediments characterizing this biotope are likely to be too mobile and unsuitable for most of the invasive non-indigenous species currently recorded in the UK. The above evidence suggests that this biotope is unsuitable for the colonization of Crepidula fornicata due to a lack of gravel, shells, or any other hard substrata used for larvae settlement (Tillin et al., 2020). The aggregations of tube-building amphipods and polychaetes characterizing this biotope might exclude the settlement of Crepidula rather than provide a suitable substratum as the amphipods may eat the Crepidula larvae and their tube mats may exclude limpet spat. This habitat is moderately exposed to sheltered, in which wave action and storms may mobilise the sediment (JNCC, 2022), which may mitigate or prevent colonization by Crepidula at high densities, although Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). Hence, resistance is assessed as 'High' and resilience as 'High' so that the biotope is assessed as 'Not sensitive'. Crepidula has not yet been reported to occur in this biotope so the confidence in the assessment is 'Low' and 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

Introduced organisms (especially parasites or pathogens) are a potential threat in all coastal ecosystems. However, no information was found on microbial pathogens affecting Polydora ciliata. Amphipods may be infected by a number of parasites or pathogens that alter population numbers through changes in host condition, growth, behaviour and reproduction (Green Extabe & Ford, 2014). For example, infection by acanthocephalan larvae may alter the behaviour and responses of gammarid amphipods (Bethel & Holmes, 1977). The amphipod Orchestia gammarellus is host to the parasitic protist Marteilia that has a feminizing effect on populations, with higher ratios of females and intersex males in infected, estuarine populations (Ginsburger-Vogel & Desportes, 1979). Corophium volutator is parasitized by several species of trematodes in Europe and North American (McCurdy et al., 2000a; McCurdy et al., 2000b; Mouritsen & Jensen, 1997, cited in Shim et al., 2013). Mass mortalities of Corophium volutator have been associated with infestation by trematodes in the Wadden Sea (Jensen & Mouritsen, 1992). A dense field of Corophium volutator disappeared completely, and the density of the mud snail Hydrobia ulvae declined by 40% during spring 1990 as a result of an epizootic by trematodes. High spring temperature accelerated both the development rate and the release of infective larval stages of an infectious trematode from the snail Hydrobia ulvae (Poulin & Mouritsen, 2006). Studies conducted in the Baltic Sea suggested that increased parasitism by trematode species has a detrimental effect on local amphipods (Meissner & Bick, 1999; Mouritsen & Jensen, 1997 cited in Shim et al., 2013).  

Sensitivity assessment. Although there are no records of the biotope being affected by the introduction of microbial pathogens in the British Isles, there are reports of mass mortality of characterizing species Corophium volutator (Jensen & Mouritsen, 1992). Therefore, the biotope may be at risk and is assessed with a 'Low' resistance to this pressure. Hence, resilience is assessed as 'High' and the biotope is assessed as 'Low' sensitivity to the introduction of microbial pathogens.

Removal of target species

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

Evidence

Fowler (1999) reviewed the effects of bait digging on intertidal fauna including Arenicola marina, which occurs in SS.SSa.IFiSa.TbAmPo. Diggers have been reported to remove 50 or 70% of the blow lug population. Heavy commercial exploitation in Budle Bay in winter 1984 removed 4 million worms in 6 weeks, reducing the population from 40 to <1 per m². Recovery occurred within a few months by recolonization from surrounding sediment (Fowler, 1999). However, Cryer et al. (1987) reported no recovery for six months over summer after mortalities due to bait digging. Mechanical lugworm dredgers have been used in the Dutch Wadden Sea where they removed 17-20 million lugworms/year. A near doubling of the lugworm mortality in dredged areas was reported, resulting in a gradual substantial decline in the local population over a four year period. The effects of mechanical lugworm dredging are more severe and can result in the complete removal of Arenicola marina (Beukema, 1995; Fowler, 1999). Beukema (1995) noted that the lugworm stock recovered slowly reaching its original level in at least three years. McLusky et al. (1983) examined the effects of bait digging on blow lug populations in the Forth Estuary. Dug and infilled areas and unfilled basins left after digging repopulated within one month, whereas mounds of dug sediment took showed a reduced population. Basins accumulated fine sediment and organic matter and showed increased population levels for about 2-3 months after digging. Overall, recovery is generally regarded as rapid.

Sensitivity assessment. Arenicola marina may be targeted by fisheries and the evidence presented suggests that the species abundance can be severely affected. However, Arenicola marina is not considered an important characterizing species indicative of the sensitivity of SS.SSa.IFiSa.TbAmPo. As the direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures, and this pressure considers only the ecological or biological effects of the removal of the targeted species, it is considered that removal of Arenicola marina is unlikely to have an impact on the character of the biotope. Furthermore, the biotope occurs in the shallow sublittoral and is unlikely to be exposed at low tide and hence targeted by bait diggers. Resistance and resilience are, therefore, assessed as 'High', and the biotope considered Not Sensitive to this pressure.

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

Direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures, while this pressure considers the ecological or biological effects of by-catch. The characterizing species in this biotope are highly likely to be damaged or directly removed by static or mobile gears that are targeting other species (see abrasion and penetration pressures).

Sensitivity assessment. Loss of the characterizing species of this biotope is likely to occur as a result of unintentional removal. Removal of the characterizing species would result in the biotope being lost. Thus, the biotope is considered to have a resistance of 'Low' to this pressure.  However, resilience is probably  'High' so that sensitivity is assessed as 'Low'.