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

Species found high on the shore are generally able to tolerate a greater range of temperatures than those confined to lower shore levels (Davenport & Davenport, 2005), however, the timing of site-specific factors such as low tides will influence local acclimation. For intertidal species increased temperatures may also result in desiccation when exposed (see changes in emergence pressure).

Limited information on the thermal tolerance of Lanice conchilega was found. Lanice conchilega occurs in temperate regions all around UK and Irish shores in the intertidal and shallow subtidal, populations also occur in the Mediterranean, in the Arabian Gulf and the Pacific and along the south east of the North Sea, but the species is absent from Arctic waters (Ropert & Dauvin, 2000; Connor et al., 2004; Degraer et al., 2008). The geographical range suggests that the species is adapted to variable temperature conditions but local populations are likely to be acclimated to prevailing temperatures.

Cerastoderma edule is found from Norway to Mauritania (Honkoop et al., 2008) and through the Baltic, Mediterranean and Black Sea (Longshaw & Malham, 2013). The eastern border of distribution is the Murmansk coast of the Barents sea (Genelt-Yanovskiy et al., 2010). The species is therefore likely to be exposed to warmer and colder water and air temperatures than experienced in the UK over its geographic range. Kristensen (1958) reported that Cerastoderma edule from the Dutch Wadden Sea have an upper temperature tolerance of 31°C for 24 hrs while Wilson (1981) reported an upper lethal temperature of 42.5°C. These temperatures are likely to exceed the pressure benchmark. Wilson (1993) concluded that Cerastoderma edule was probably tolerant of a long-term temperature rise of 2°C associated with climate change. Warmer temperatures during winter result in increased metabolic rate, hence depletion of energy reserves in a time of low food availability and may contribute to post winter mortality of adult cockles (Wilson & Elkaim, 1991). Therefore, the tolerance of Cerastoderma edule to temperature change will be dependent on season, so an acute, short-term temperature rise in summer or decrease in winter may be detrimental.

Nephtys hombergii has been reported from as far south as South Africa, suggesting the species can tolerate temperatures above a 5°C increase on UK and Irish coasts. Records are limited but Emery et al. (1957) found that Nephtys hombergii could withstand summer temperatures of 30-35°C. Pygospio elegans are summer visitors to an effluent exposed habitat in the UK where effluents are typically 8-12°C warmer than the receiving waters (Bamber & Spencer, 1984), and this species is considered tolerant of acute and chronic increases in temperature.

Sensitivity assessment. Typical surface water temperatures around the UK coast vary seasonally from 4-19 ^oC (Huthnance, 2010). The associated species are considered likely to be tolerant of acute and chronic increases in temperature at the pressure benchmark. Lanice conchilega, Nephtys hombergii and Cerastoderma edule have a wide geographic range. As species inhabiting the intertidal, they are likely to experiences rapid fluctuations in temperature over the tidal cycle. The lack of evidence for mass mortalities in very hot summers (compared with reports for low winter temperatures) suggest that the characterizing and associated species are likely to tolerate a chronic increase at the pressure benchmark (2°C for one year). An acute increase in temperature for one month may lead to changes in reproductive success and predation, particularly on spat and juveniles. Adults may, however, survive. Biotope resistance is therefore assessed as ‘High’ and residence is ‘High’ (by default), the biotope is therefore 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

Many intertidal species are resistant of freezing conditions as they are exposed to extremes of low air temperatures during periods of emersion. They must also be able to cope with sharp temperature fluctuations over a short period of time during the tidal cycle. Species that occur in the intertidal are generally adapted to periods of freezing conditions during winter months and have evolved mechanisms of survival to withstand rapid cooling (Loomis, 1995; Davenport & Davenport, 2005).

Infaunal species such as Pygospio elegans and Nephtys hombergii and including Lanice conchilega may be protected to some extent for short periods by the ability to burrow deeper within the sediment. Prolonged freezing temperatures may, however, result in mortalities. In the German coastal area during 1978-79 winter, water temperature remained below 0°C on 45 successive days and resulted in the eradication of Lanice conchilega. Up to July 1980 no recolonization of the area had taken place (Buhr, 1981). An intertidal population of Lanice conchilega, in the northern Wadden Sea, was wiped out during the severe winter of 1995/96 (Strasser & Pielouth, 2001), and Crisp (1964) described mortality of Lanice conchilega between the tidemarks but not at lower levels during the severe winter of 1962/63. These severe winters probably exceed the pressure benchmark. Beukema (1990) had noted that the recovery of most species including Lanice conchilega, was rapid (within 1 and 2 years) and total-biomass value increased faster as a consequence of generally high successful recruitment in the Wadden Sea. Whilst Heuers et al. (1998) observed Lanice conchilega re-established abundance within 3 to 4 years in the Spiekeroog area of the Wadden Sea following severe freezing.

High mortalities of Cerastoderma edule populations attributed to severe winters have been reported by many authors (Kristensen, 1958; Hancock & Urquhart, 1964; Beukema, 1990; Ducrotoy et al., 1991) and high shore populations are likely to be more vulnerable to extremes of temperature owing to their longer emergence time. Strasser et al. (2001) noted mortalities ranging on average between 80% and 100% in the high tidal zone. Mortalities that occurred during spring and summer may have constituted a time-lag effect of the preceding winter. Beukema (1990) suggested that Cerastoderma edule was more sensitive to low winter temperatures than other bivalves (e.g. Mya arenaria, and Mytilus edulis) which make up 50% of the macrobenthic biomass (Reise & Lackschewitz, 1998).

Nephtys hombergii are found as far north as the Barents Sea, and would be expected to be resistant to a 5°C decrease in temperature for one month period, or 2°C for one year.  However, during the winter of 1978- 79, Nephtys hombergii in the River Tyne estuary (north-east England) did not spawn but instead reabsorbed the gametes, reducing the Nephtys hombergii population for subsequent years. In previous years, recruitment had been good and it was considered probable that this was a result of the extremely cold conditions experienced in 1978-1979 (Olive et al., 1981).

Sensitivity assessment. Resistance has been assessed to be ‘Low’ as evidence suggests that intertidal populations of Lanice conchilega and Cerastoderma edule and other polychaetes are likely to be vulnerable to acute decreases in temperature during winter. However, resilience is assessed as ‘High’ where some adults remain and sensitivity is assessed as ‘Low’.

Salinity increase (local)

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

Evidence

This biotope occurs in full (30-35 ppt) and variable salinity biotopes (18-35 ppt). Biotopes occurring in variable salinity are not considered to be sensitivie to an increase to full salinity as this falls within the natural range. At the pressure benchmark, an increase from full to hypersaline (>40 ppt) is considered. Local populations may be acclimated to the prevailing salinity regime and may exhibit different tolerances, therefore caution should be used when inferring tolerances from populations in different regions.

No direct evidence was found to assess the sensitivity of this biotope. Salinities within tide swept habitats vary due to weather conditions such as rain fall at low tide and evaporation causing hypersaline conditions on hot days. Intertidal shores within estuarine environments can also experience considerable short-term changes in salinities. During summer, the Atlantic French coast rapidly increased in salinity and reached hypersaline conditions (48 ppt) in the upper sediment layer within 1.5 hrs (Juneau et al., 2015). However, increased salinity is not restricted to hot summer conditions. This can occur at moderate optimal temperatures (16-20°C), due to wind-driven desiccation in spring in the first 0.5 cm of the sediment where Lanice conchilega, Nephtys hombergii, Pygospio elegans and Scoloplos armiger and the cockle Cerastoderma edule occur. This may interfere with the sediment cohesion and composition and possibly the ability to retain pore-water at the surface to modulate the species activity (Paterson & Hagerthey, 2001). Lanice conchilega as a tube dwelling polychaete has the ability to retract deeper into the sediment to avoid unfavourable conditions.

Verdelhos et al. (2015) assessed the saline optimal ranges of Cerastoderma edule (a euryhaline species) from 0-35 ppt. High activity was initially observed in conditions above the optimal range (15, 30 and 35 ppt) for Cerastoderma edule, but activity decreased after 72 hrs. Results suggest that high saline conditions over short periods is tolerated. Responses involved reduced activity through osmo-regulations and behaviours such as valve closure to prevent exposure.

Sensitivity assessment. Species within the biotope may tolerate short periods of high salinity, however, prolonged exposure to hypersalinity may lead to changes in species richness, abundance and biomass and loss of characterizing and associated species. Sensitivity to this pressure is not assessed due to lack of evidence.

Salinity decrease (local)

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

Evidence

The subtidal biotope is found in full salinity (JNCC, 2015), and the intertidal biotope and associated species are found in full and variable salinity. It is therefore considered that a decrease in salinity at the pressure benchmark, from full to variable (18-35 ppt), would not result in loss of the biotope. Since the intertidal biotope is found in full and variable salinity (18-35 ppt), the biotope is not considered sensitive to a change from full to variable salinity, as this falls within the natural habitat distribution. However, the biotope may be sensitive to a change from variable to low salinity (<18 ppt).

There is limited information on the effects of decreased salinity on Lanice conchilega. Salinities within tide swept habitats vary due to weather conditions such as rain fall at low tide and evaporation causing hypersaline conditions on hot days. Intertidal shores within estuarine environments can also experience considerable short-term changes in salinities.

Substantial salinity fluctuations due to heavy rains leading to scouring are common in intertidal areas and shallow coastal areas inhabited by adult Cerastoderma edule. Kristensen (1958) reported death of young cockle spat (1-2 mm) in the Dutch Wadden Sea due to heavy rain, although adults were able to dig deeper to avoid the freshwater influx (reduced salinities).

Boyden & Russell (1972) stated that Cerastoderma edule prefers salinities between 15 and 35 psu, whilst Russell & Peterson (1973) reported lower median salinity limits of 12.5 psu and upper median salinity limits of 38.5 psu. Rygg (1970) noted that Cerastoderma edule did not survive 23 days exposure to <10 psu. Rygg (1970) also demonstrated that salinity tolerance was temperature dependant (after 3 days, 100% survival at 33 psu and 35-38°C, but 50% mortality occurred at 20 psu and 37°C and 100% mortality at 13 psu and 37°C). Wilson (1984) noted that Cerastoderma edule remained open during 1 hour exposure to salinities between 13.3 and 59.3 psu. It should be noted that the tolerances reported above depended on the duration of the experiment.

Gogina et al. (2010) reported the lower limit of Scoloplos armiger was resistant of salinities of 8 psu, yet mortalities have been observed in the Baltic region, suggesting a lower limit of 10.5 psu. However, it was noted that Pygospio elegans can survive in salinities as low as 2 psu.

Nephtys hombergii has been shown to be highly resistant of a wide range of salinities (as low as 16 psu) (Clarke & Haderile, 1960; Davey & George, 1986), extending from the Mediterranean to the western Baltic Sea (Hartmann-Schroéder, 1996). Nephtys hombergii is considered to be a brackish water species (Barnes, 1994), but where the species occurs in open coastal locations the species would have to tolerate salinities of 25 psu and above. Within a few months of the closure of a dam across the Krammer-Volkerak estuary in the Netherlands, Wolff (1971b) observed that species with pelagic larvae or a free-swimming phase, including Nephtys hombergii, expanded rapidly with a concomitant increase of salinity to 9-15 psu everywhere. Prior to the closure of the dam the estuary demonstrated characteristics of a typical 'salt-wedge' estuary with a salinity gradient from 0.3 to 15 psu. Hence, Nephtys hombergii is likely to survive increases in salinity within estuarine environments. Nephtys hombergii may still be found in fully marine locations but may be competitively inferior to other species of Nephtyidae (e.g. Nephtys ciliata and Nephtys hystricis) and occur in lower densities. An increase to fully marine (30-40 ‰) would therefore be likely to lead to a reduction in density of Nephtys hombergii.

Pygospio elegans has been found in brackish water in high abundances, with salinities as low as 2 psu (Bolam & Fernandes, 2003).

Sensitivity assessment. Little empirical evidence was found to assess sensitivity of Lanice conchilega to this pressure at the benchmark level and therefore the assessment was made based on the biotopes associated species. The available evidence suggests that adult Cerastoderma edule may survive a reduction in salinity to just below 18 psu and populations may become locally acclimated to reduced salinities. Other species such as Pygospio elegans and Nephtys hombergii are also likely to be tolerant of a reduction at the pressure benchmark. As a reduction may lead to some mortalities and a reduction in growth and reproductive success of the key characterizing species, biotope resistance is assessed as ‘Medium’, recovery is assessed as ‘High’ (following restoration of typical conditions) and resilience is ‘High’. Biotope sensitivity is therefore assessed 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

This biotope is found in areas exposed to tidal streams varying from very strong (>3 m/s) to negligible (JNCC, 2015). There is limited evidence to assess changes in water flow rates for >1 year at the benchmark level. It should be noted that Lanice conchilega occupies shores with variable exposed flow speeds ranging from sheltered (<0.5 m/sec) to very strong (>3 m/sec) (Connor et al., 2004). Laboratory flume studies have showed that Lanice conchilega feeding rates on diatoms alter according to flow (Denis et al., 2007). Feeding rates were optimal at 0.15 m/s and lower at flow speeds of 0.04 m/s and 0.27 m/s (Denis et al., 2007). Changes in current velocity at the pressure benchmark are relevant to feeding rates, however, impacts are likely to depend on food supply, population density and proportion of inorganic particles.

The motion of the water is the dominant factor in the transportation of sediment, facilitating erosion and redistribution of materials (Hjulström, 1939). This may change the sediment structure and have associated effects on the intertidal community. Lanice conchilega alter between passive and active feeding depending on the tidal regimes, i.e. in still water, they move their tentacles or in high velocities the fringed tentacles are supported. A switch from active to passive feeding behaviour was observed during the experiments between 4 and 8 cm/s (Denis et al., 2007). Moderate to high velocities of water flow have been reported to enhance settlement of Lanice conchilega larvae (Harvey & Bourget, 1997), increasing average particle size in favour of gravels and pebbles.

Increase particle movement is likely to increase sediment scour (see abrasion and sedimentation), re-suspension of material (see organic enrichment, and suspended sediment), and potentially a decrease in clearance in filter feeders. Populations of Lanice conchilega and Pygospio elegans may decline in part due to a lack of suitable substrata to build its tubes. The biotope would probably become dominated by water flow resistant species that prefer coarse substratum.

Reduced water flow is a factor that has been identified as affecting the density of Lanice conchilega, as recruitment to the benthos is reduced (Harvey & Bourget, 1995). The average grain size of the sediment would also be reduced and probably favour deposit feeders and detritivores, to the detriment of the suspension feeders.

Sensitivity assessment.  A change in water flow rate at the pressure benchmark level of 0.1-0.2 m/s is considered to fall within the range of flow speeds experienced by the biotope. Resistance and resilience are assessed as ‘High’ and the biotope considered ‘Not sensitive’ 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

The biotope and characterizing species occur in the mid to low intertidal. All characterizing species would probably survive an increase in emergence. However, Lanice conchilega can only feed when immersed and therefore likely to 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. A decrease in emergence is likely to allow the biotope to extend its upper limit, where suitable substrata exist.

The dense Lanice biotope LS.LSa.MuSa.Lan on certain lower shores may be a littoral extension of the biotope SS.SCS.ICS.SLan. A decrease in emergence may lead to some shifts in species present but a Lanice conchilega dominated biotope is likely to persist.

Sensitivity assessment. Emergence is a key factor structuring intertidal biotopes (JNCC, 2015). The Lanice conchilega biotope is likely to shift distribution during periods of altered sea levels. Some changes in the structure of the biological assemblage would be predicted. Resistance is assessed as ‘Low’ and resilience is ‘High’, following habitat recovery and sensitivity is assessed as ‘Low’.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

The biotope is recorded from locations that have variable wave exposures (moderately exposed to extremely sheltered) (Connor et al., 2004). The degree of wave exposure influences wave height, as in more exposed areas with a longer fetch waves would be predicted to be higher. 

Sensitivity assessment. As this biotope is found across a range of wave exposed shores, resistance is assessed as ‘High’ and resilience as ‘High’ to a 3 to 5% change in wave height at the pressure benchmark. Therefore, the biotope is considered ‘Not sensitive’.

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

The results of the Rapid Evidence Assessment on the effects of 'Transitional metal or organometal' contaminants on selected polychaete and mollusc species are summarized below. The full 'evidence reviews' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Transitional metal or organometal' contaminant examined, together with an overall pressure assessment. 

Transitional metals. No direct evidence of the direct effects of 'transitional metals' on Lanice spp. was found in the literature reviewed. Overall, the effects of metal exposure vary depending on the type of metal, its chemical form (e.g., salt), the environmental conditions (e.g., pH, salinity, and temperature), and the concentration and duration of exposure. The effects also vary between species, depending on their habitat (e.g., sedimentary), feeding mechanism (i.e., the method of ingestion of the metals), and any metal detoxification pathways the species possess. Bryan (1984) reported that short-term toxicity in polychaetes was highest to Hg, Cu, and Ag, declined with Al, Cr, Zn, and Pb with Cd, Ni, Co and Se being the least toxic. It was reported that polychaetes have a range of tolerances to heavy metal levels of Cu, Zn, As, and Sn being in the order of 1500-3500 µg/g. An analysis of organisms from Restronguet Creek revealed that Nephtys hombergii from the middle and lower reaches of the creek contained appreciably higher concentrations of Cu (2227 µg/g dry wt), Fe, and Zn than comparable specimens of Hediste diversicolor.

In addition, there is evidence that some polychaete species can adapt to metal contamination in the long term (Bryan & Hummerstone, 1973; Grant et al., 1989; Hateley et al., 1988; Mouneyrac et al., 2003; Alla et al., 2006b; Burlinson & Lawrence, 2007; McQuillan et al., 2014). For example, Rainbow & Phillips (1993) noted that Hediste (Nereis) diversicolor was able to regulate its tissue concentration of several trace elements including manganese and zinc.  McQuillan et al. (2014) suggested that some species (Nephtys hombergii) had developed metal-resistant populations as a functional genetic trait to Cu homeostasis. However, Alve (1991) and Ellison et al. (1986) concluded that there is a shift in the abundance of biodiversity away from the source of contamination, which is indicative of metal contamination (Stubbles, 1993).

The 'evidence review' of selected polychaetes found evidence of 'severe' or 'significant' mortality due to 'transitional metal' exposure in Arenicola spp, Hediste spp., and Nereis spp., depending on the metal but only sublethal effects in Nephtys spp, and Eteone spp. albeit based on a few studies. Therefore, the worst-case resistance of polychaetes to transitional metal exposure is probably 'None' or 'Low' depending on the species, the metal, its concentration and the duration of exposure. Hence, resilience is assessed as 'Medium' or 'High' and sensitivity as 'Medium or Low respectively but with 'Low' confidence due to the variation between species. 

‘Severe’ or ‘Significant’ mortality was reported in 88% of the results from studies of the effects of ‘Transitional metal’ exposure on Cerastoderma edule in the 'evidence review' depending on the exposure concentration or duration of all the ‘metals’ studied, with the exception of manganese (Mn). Bryan (1984) stated that Hg was the most toxic metal to bivalves. Studies of Cerastoderma edule transplanted populations from polluted and uncontaminated sites resulted in 10-15% mortality within 63 days but 100% within 4 months at the Restronguet Creek (Bryan & Gibbs, 1983). In addition, Cu and Zn are believed to inhibit the settlement of juvenile Cerastoderma edule, leading to patchy distributions (Langston et al., 2003). Barite (in the form of drilling mud barite) was shown to cause 100% mortality of C. edule within 12 days at a depth of 2- and 3-mm dosage but the cause may have been due to physical damage of their gill filaments rather than chemical toxicity (Barlow & Kingston, 2001). Ladhar-Chaabouni et al. (2009) was the only article to examine C. glaucum but reported that cadmium (Cd) exposure resulted in 100% mortality 18 days after exposure to 100 µg/l Cd. Overall, the evidence suggests that the worst-case resistance of Cerastoderma spp. to ‘transitional metals’ exposure is ‘None’. Therefore, the resilience of Cerastoderma spp. is assessed as ‘Medium’ and sensitivity as ‘Medium’.

Organometal. No direct evidence of the direct effects of 'organometals' on Lanice spp. was found in the literature reviewed. The evidence on the effects of tributyltin on selected polychaetes was limited to two papers, one of which was not accessible (Walsh et al., 1986b). Beaumont et al. (1989) TBT was introduced into three microcosms at high (1-3 µg/l) concentrations and three microcosms at low (0.06-0.17 µg/l) concentrations. Non-introduced Nereis diversicolor, Arenicola marina, and Eteone sp. occurred in the low-level TBT and the control treatments but not in the high-level TBT treatments. High mortalities of Nereis diversicolor were recorded in all microcosms including the control, so the results were inconclusive. Overall, only sublethal effects were reported in the evidence reviewed. Therefore, the sensitivity of Arenicola spp. and Nereis spp. to TBT is assessed as ‘Not sensitive’ but with ‘Low’ confidence due to the lack of evidence.

Beaumont et al. (1989) examined the effects of tributyltin (TBT) exposure in Cerastoderma edule. In their flow-through mesocosm studies, all Cerastoderma edule died within two weeks at high concentrations of TBT (1-3 µg/l) and progressive mortality was observed in the low TBT treatments (0.06-0.17 µg/l) over time with 80% mortality after 17 weeks. Therefore, the worst-case resistance of Cerastoderma spp. to TBT exposure is assessed as ‘None’, resilience as ‘Medium’ and sensitivity as ‘Medium’, especially long-term exposure. However, confidence in the assessment is ‘Low’ due to the limited number of studies reviewed.

Nanoparticulate metals. No direct evidence of the direct effects of 'nanoparticulate metal' on Lanice spp. was found in the literature reviewed. Sublethal effects and ‘no’ mortality were reported in all but one of the studies reviewed that examined the effects of nanoparticulate metals on polychaetes. The nanoparticulates did result in reduced burrowing speed or activity, where an effect was reported. While a reduction in burrowing ability may reduce feeding or increase the susceptibility to predation, ‘no’ direct mortality was reported. For example, Galloway et al. (2010) reported sublethal effects due to exposure to nanoparticulate titanium in Arenicola marina. Therefore, the sensitivity of A. marina to nanoparticulate titanium is assessed as ‘Not sensitive’ but with ‘Low’ confidence due to the lack of evidence. However, Cozzari et al. (2015) reported that silver nanoparticles caused 8% and 16% mortalities in the 2.5 and 10 µg/g treatments after 4 days, respectively, and the 5 µg/g treatments caused 12% mortality by day seven. Therefore, the worst-case resistance of Nereis spp. to nanoparticulate silver is assessed as ‘Medium’, resilience as ‘High’ and sensitivity as ‘Low’ but with ‘Low’ confidence due to the lack of evidence.

Overall sensitivity assessment. No direct evidence of the effects of 'transitional metals and organometals' on the dominant characteristic species, Lanice spp., was found. However, there is considerable evidence to suggest that polychaetes as a group can be sensitive to transitional metal contamination and the assumption that polychaetes share similar biochemical and hormonal pathways.  The evidence on the effect of organometals and nanoparticulate metals is limited but some polychaetes may be sensitive.  Therefore, the worst-case resistance of Lanice spp. dominated habitat is assessed as 'Low', albeit with 'Low' confidence due to the lack of direct evidence, the potential variation in response between species and the chemical in question, and the possibility of local adaptation.  Hence, resilience is assessed as 'High' and sensitivity as 'Low'. Where Cerastoderma spp. is present, resident populations of cockles may take longer to recover so the worst-case sensitivity is 'Medium' but with 'Low' confidence. 

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

The results of the Rapid Evidence Assessment on the effects of 'Hydrocarbon and PAHs' contaminants on selected polychaete and mollusc species are summarized below. The full 'evidence reviews' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Hydrocarbon and PAH' contaminant examined, together with an overall pressure assessment. 

Oil spills. Suchanek (1993) reviewed the effects of oil spills and concluded that soft sediment polychaetes, bivalves, and amphipods were particularly sensitive. Dauvin (2000) noted that 20 years after the Amoco Cadiz oil spill in 1978, Lanice conchilega was re-established between 1978 and 1984 but disappeared after 1985, although the cause of its disappearance was uncertain. A similar delayed response was observed by Sanders (1980) as a result of the Florida oil spill and the Braer oil spill (Kingston et al., 1995; Gómez Gesteira & Dauvin, 2000).  The Amoco Cadiz oil spill resulted in reductions in abundance, biomass, and production of the invertebrate communities, however, Nephtys hombergii and other polychaetes (cirratulids and capitellids) were largely unaffected by the Amoco Cadiz oil spill (Conan, 1982). The sediment rapidly recovered and in 1981, benthic recruitment occurred under normal conditions (Dauvin, 1998). The evidence suggests that some polychaetes are largely unaffected, especially if opportunistic or mobile, and/or able to recover quickly after the initial spill. 

Petroleum hydrocarbons and PAHs. Lewis et al. (2008) reported that both the WAF of crude oil and the PAH fluoranthene adversely affected fertilization success and caused larval mortality in A. marina. Morales-Caselles et al. (2008) noted that sediment contaminated with fuel oil from a sunken tanker caused significant mortality in Arenicola marina, for example, 8% fuel oil / dry weight sediment resulted in 100% mortality after 21 days. Farke & Gunther (1984) and Morales-Caselles et al. (2009) demonstrated that oil-contaminated sediment reduced burrowing activity in A. marina. Farke & Gunther (1984) noted that dispersed oil also reduced burrowing activity but the dispersant used showed no effect. The evidence suggests that oil contamination could also reduce recruitment to contaminated sediment, and hence prolong recovery.  However, exposure of adult A. marina to PAHs (Casado-Martinez et al., 2008) did not contribute to mortality. Lewis et al. (2008) also reported that both the WAF of crude oil and the PAH fluoranthene adversely affected fertilization success in N. virens, while the WAF caused larval mortality. No mortality due to PAH exposure was reported in the evidence reviewed. McLusky & Martins (1998) investigated the long-term effects of petrochemical discharge on the faunal composition of an estuarine mudflat over a 20-year period. The abundance of N. diversicolor varied over the 20 years and no but no significant trends were recorded. The evidence reviewed suggested that dispersed oils and dispersants only caused sublethal effects in Arenicola marina. 

Savari et al. (1991a) observed that the density and growth of Cerastoderma edule decreased with increasing hydrocarbon concentration. The studies of the effects of 'Hydrocarbons or PAHs’ reviewed (see 'evidence reviews') on Cerastoderma edule contributed 98% of the results (worst-case ranked mortalities) on this pressure, of which 27% reported ‘Severe’ mortality and 73% reported ‘Significant’ mortality. Most (74%) of the results were from studies that examined the effects of dispersants and emulsified oils, which reported ‘Severe’ or ‘Significant’ mortality in all cases. ‘Severe or ‘Significant’ mortality was also reported due to exposure to complex hydrocarbons, phenols and a PAH (phenanthrene) in C. edule. ‘Significant mortality was also reported in C. glaucum. Therefore, the worst-case resistance of Cerastoderma spp. to ‘Hydrocarbons and PAHs’ is assessed as ‘None’. Hence, resilience is assessed as ‘Medium’ and sensitivity as ‘Medium’. Confidence in the assessments is assessed as ‘Medium’ because only the data rather than the original data sources were accessible.

Overall sensitivity assessment. Little direct evidence of the effects of 'Hydrocarbons and PAHs' on Lanice sp. was found. Evidence suggests that soft sediment communities are highly susceptible to hydrocarbon contamination. In the littoral zone especially, oil spills resulting from tanker accidents are likely to be deposited directly on the sediment of the biotope, preventing oxygen transport to the substratum and oil pushed into the substratum by tidal-pulsing will destabilize the sediment (Elliott et al., 1998). Other members of the community may be more sensitive, eg., amphipods. The evidence from the Amoco Cadiz oil spill suggests that Lanice spp. has a 'Low' sensitivity to oil spills (resistance is 'Medium' or 'Low' and resilience is 'High') as it recolonized and became abundant within a few years of the spill. Other polychaetes are probably sensitive. For example, the worst-case resistance of Arenicola spp. to petroleum hydrocarbons is probably 'None' and to PAH (fluoranthene) is also 'None' while the evidence suggests it is non-sensitive to the dispersants and dispersed oils examined in the articles reviewed. Similarly, the resistance of Nereis spp. (and Hediste spp.) to petrochemical hydrocarbons are assessed as ‘Low’ based on the worst-case results reviewed.  Overall, the worst-case resistance of this Lanice-dominated community to 'Hydrocarbons and PAHs' contamination is assessed as 'Low'.  However, recovery is potentially rapid and resilience is assessed as 'High' and, hence, sensitivity is assessed as 'Low' based on the assumption that polychaetes share similar biochemical and hormonal pathways. However, confidence in the assessment is 'Low' due to the lack of evidence on the effects of hydrocarbons, and dispersants, PAHs on Lanice spp.  Where present, Cerastoderma spp. are probably more sensitive. 

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

The results of the Rapid Evidence Assessment on the effects of 'Synthetic compound' contaminants on selected polychaete and mollusc species are summarized below. The full 'evidence reviews' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Synthetic compound' contaminant examined, together with an overall pressure assessment. 

Overall, ‘Severe’ mortality was reported in 8.7% of the results of the effects of pesticides/biocides on the polychaetes reviewed, ‘Significant’ in 30.4%, ‘Some’ in 4%, ‘no’ mortality in 10.8% and sublethal effects in 45.6% of the results from the evidence reviewed. However, the toxicity and, hence, sensitivity varied between polychaete species and the chemical examined. Also, each individual chemical/species combination was only examined in a small number of studies, so the evidence for each combination is limited. No evidence concerning the specific effects of synthetic chemical contaminants on Lanice conchilega or Nephtys hombergii was found.

Pesticides/biocides. The effect of 'Pesticides/biocides' on Arenicola spp. was studied in six of the articles reviewed. Garnas et al. (1977) reported 100% mortality in Arenicola cristata exposed to 1,000 µg/l Kepone for 5 days. Similarly, Rubenstein (1979) reported 100% mortality in A. cristata exposed to 29.5 µg/l of Kepone, for 144 hours.  Exposure to 2.8, 4.5, 6.6, 7.4, and 29.5 µg/l Kepone for 144 hours also reduced feeding behaviour significantly. However, Mirex and sodium pentachlorophenate reduced feeding and burrowing behaviour in A. cristata significantly (Schoor & Newman, 1976; Rubinstein, 1978). Carbaryl, Ivermectin and Parathion-ethyl were reported to cause significant mortality in A. marina (Conti, 1987; Allen et al., 2007). Ivermectin had a significant effect on the survival of the lugworms; the 10-day LC50 was 17.9 µg IVM/kg wet sediment in Test 1 and 14.8 µg IVM/kg wet sediment in Test 2 and Ivermectin reduced the mean casting rate (Allen et al., 2007). Conti (1987) reported 48-hour LC50s of 2,700 µg/l for Parathion-ethyl and 7,200 µg/l for Carbaryl. 

Seven articles examined the effects of ‘Pesticides/biocides’ on Hediste (Nereis) diversicolor.  For example, Collier & Pinn (1998) reported that Nereis diversicolor was the most sensitive of the species in their experiment, as 8.0 mg/m² Ivermectin caused 100% mortality within 14 days. Mayor et al. (2008) reported that the sea-lice insecticide Emamectin benzoate had significant effects on the survival of Hediste diversicolor with an LC50 value of 1,367.71 µg/kg (wet sediment). Scaps et al. (1997) reported that However, by day 21, 20% of Nereis diversicolor exposed to 10^-6 and 10^-8 M Malathion died, and 33.5 and 62.5% mortality occurred in the 10^-8 and 10^-6 M parathion-ethyl treatments.  Only sublethal effects were reported in the other pesticides reviewed.  Underwood & Paterson (1993) reported that Nereis diversicolor was absent from areas of sediment treated with formaldehyde. Although not studied directly, the observation suggests that Nereis diversicolor was excluded from the treatment site due to the toxicity of the formaldehyde or the lack of microalgal food.

Nephtys spp., Eteone longa, and Streblospio benedicti were examined in only two of the articles reviewed. In all cases, only sublethal effects were reported. For example, Dumbauld et al. (2001) observed the effects of the application of the pesticide Carbaryl on the estuarine benthic community in oyster culture sites but did not detect trends or significant differences in the abundance of the polychaetes Streblospio benedicti and Eteone longa. Similarly, Scanes et al. (1993) reported no significant changes in polychaete abundance after an accidental spill of the pesticide Aldrin on an estuarine beach in New South Wales, Australia.

The worst-case resistance of Arenicola spp. , Nereis spp. and Hediste spp. to ‘Pesticides/biocides’ is assessed as ‘None’, resilience as ‘Medium’ and sensitivity assessed as ‘Medium’. The confidence is assessed as ‘low’ due to the limited evidence and the variation in toxicity between species and the chemical studied.  

All three of the studies that examined exposure of Cerastoderma edule to ‘Pesticides/biocides’ reported ‘severe’ or ‘significant’ mortality. Goncalves et al. (2016) reported 96-hour LC50 values of 28.78 mg/l (large) and 27.25 mg/l (small) and 100% mortality at 60 mg/l in Cerastoderma edule exposed to the herbicide Primextra® Gold TZ. Portmann & Wilson (1971) and Portmann (1972) exposed Cerastoderma edule to a range of different ‘Pesticides/biocides’ (see Mollusc Evidence Summary). Overall, the evidence suggested that Cerastoderma edule was sensitive to all the ‘Pesticides/biocides’ tested. Therefore, the worst-case resistance of Cerastoderma edule to ‘Pesticides/biocides’ is assessed as ‘None’. Hence, resilience is assessed as ‘Medium’ and sensitivity as ‘Medium’. However, confidence in the assessment is ‘Medium’ due to the limited number of studies reviewed.

Pharmaceuticals. Only two papers in the evidence review examined the effects of ‘Pharmaceuticals’ on Arenicola marina. Zanuri et al. (2017) investigated the impacts of Diclofenac, Ibuprofen, and Sildenafil citrate (Viagra®) on the fertilization biology of spawning marine invertebrates, including A. marina. Sperm motility and swimming speed were reduced when exposed to >1 µg/l Diclofenac for over 90 minutes. Ibuprofen exposure significantly increased the swimming speed of the sperm when exposed to >10 µg/l for 30 minutes or longer. Diclofenac negatively affected the fertilization success of the polychaetes but neither Ibuprofen nor Sildenafil citrate exposure affected fertilization success significantly. Pre-incubation of both sperm and oocytes caused significant decreases in fertilization success of the polychaetes at Diclofenac concentrations of 1 µg/l and above. Ibuprofen caused significant reductions in fertilization success when gametes were exposed to Ibuprofen at 1000 µg/l. Pre-incubation with Sildenafil citrate had no effects on fertilization success. Lewis & Galloway (2009) reported that methyl methanesulfonate exposure did not affect fertilization success at all tested concentrations but abnormal development occurred at all tested concentrations (18, 32, and 52 mg/l for 24 hours and 72 hours prior to the induction of spawning) in Arenicola marina.

Eight articles examined the effects of several ‘Pharmaceuticals’ on Hediste (Nereis) diversicolor. For example, Maranho et al. (2014) reported that the survival of the Hediste diversicolor was negatively correlated with concentrations of Carbamazepine and 17α-ethynylestradiol. Significant mortality (>25%) was observed in the Carbamazepine (0.05 and 0.5 µg/l), Fluoxetine (0.001 µg/l) and 17α-ethynylestradiol (0.01 and 0.1 µg/l) treatment groups.  Pires et al. (2016) reported that Hediste diversicolor experienced 8.3% mortality at concentrations 0.3 and 3.0 µg/l after 28 days of exposure to carbamazepine, 25% mortality at 6.0 µg/l and 16.7% mortality at 18.0 µg/l after 28 days of exposure carbamazepine. Some mortality occurred after exposure to the beta-blocker Propranolol (Maranho et al., 2014). However, the other studies reported only sublethal effects, including a reduction in burrowing activity.

Others. Casado-Martinez et al., 2008 examined the effects of Hg, PCB and PAH contamination on Arenicola marina but PAH and PCB sediment concentrations were not correlated with mortality.  Therefore, no assessment of its sensitivity to PCBs is attempted. Conti (1987) examined the effects of surfactants on A. marina. The 48-hour LC50s of the two anionic detergents were 15,200 µg/l for sodium dodecyl benzene sulphonate and 12,500 µg/l for sodium dodecylbenzenesulphonate. The 48-hour LC50 of the non-ionic detergent Triton X-100 was 15,200 µg/l. 

Overall sensitivity assessment.  The effects of 'Synthetics compounds' on other polychaete species are used in the absence of direct evidence of their effect on Lanice spp. Pesticides were reported to be the most toxic of the chemicals studied in the polychaetes reviewed.  Therefore, the worst-case resistance of Lanice-dominated habitat to 'synthetic compounds' is assessed as 'None', resilience as 'Medium' and sensitivity as 'Medium' based on the assumption that polychaetes share similar biochemical and hormonal pathways. However, confidence in the assessment is 'Low' due to the lack of direct evidence and the variation in toxicity between the chemicals studies and the species exposed. 

Radionuclide contamination

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

Evidence

No evidence found

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

The results of the Rapid Evidence Assessment on the effects of 'Other substances' contaminants on selected polychaete and mollusc species are summarized below. The full 'evidence reviews' should be consulted for details of the studies examined and their results. A sensitivity assessment is provided for each type or source of 'Other substances' contaminant examined, together with an overall pressure assessment. 

Galloway et al. (2010) investigated the sublethal toxicity of nano-titanium dioxide and carbon nanotubes on the marine polychaete Arenicola marina. The lugworms were exposed through natural sediments to a 10-day OECD/ASTM 1990 acute toxicity test. Sediment was prepared with either single-walled carbon nanotubes (0.003–0.03 g/kg), nano-titanium dioxide (1–3 g/kg), or seawater alone. The lugworms were fed every other day and feeding behaviour was monitored every 48 hours. Casts were collected, dried overnight and weighed, with seawater renewals every 48 hours following cast collection. After 10 days of exposure, the lugworms were removed from the exposure sediment and the lugworm's ability to re-bury into clean sediment was assessed following the OECD/ICES A. marina burrowing bioassay. Sediment exposure to single-walled carbon nanotubes or nano-titanium dioxide had no effects on the burrowing behaviour of the lugworm. During the exposure period, single-walled carbon nanotubes had no effects on the feeding behaviour of the lugworms. However, nano-titanium dioxide exposure caused a significant impact on feeding behaviour with reductions in casting rate at 2 g/kg nano-titanium dioxide.

De Marchi et al. (2017) investigated the effects of different multi-walled carbon nanotubes (MWCNTs) (at 0.01; 0.10 and 1.00 mg/l) on Diopatra neapolitana and Hediste diversicolor. The effects on physiological and biochemical performance were assessed after 28 days of exposure. The respiration rate of Hediste diversicolor was measured after 28 days of exposure. Exposure to 0.01 mg/l MWCNTs increased the respiration rate compared to the controls. However, respiration rates significantly decreased at 0.1 mg/L MWCNTs compared to the control, but respiration rate increased at the highest tested concentration (1.00 mg/L) of MWCNTs. Mortality of H. diversicolor individuals exposed to 0.01, 0.10 and 1.00 mg/l was 11% at each of the tested concentrations. In the control treatment, there was 100% survival recorded after bioassay.

Pires et al. (2022) investigated the effects of graphene oxide (GO) nanosheets on the behavioural, physiological and biochemical responses of Hediste diversicolor. Polychaetes were exposed to a range of concentrations of graphene oxide nanosheets (10, 100, 1000, and 10,000 µg/l) for 28 days. The study assessed the effects on the behaviour, feeding activity, mucus production, regenerative capacity, antioxidant status, biochemical damage and metabolism. Body regeneration was significantly influenced by GO exposure, with all individuals exposed to GO exhibiting reductions in the number of regenerated segments when compared to the controls. Feeding activity was influenced by GO exposure with increased feeding times for exposed individuals. The segregation of mucus was significantly higher in individuals exposed to GO when compared to the controls. Burrowing rates of polychaetes exposed to GO were significantly slower than those in the control, with 20-35% of individuals in the highest tested concentrations unable to burrow by the end of the 30-minute assay. Mortality was around 40% in the GO-exposed treatments, with 30% mortality in the 10 and 100 µg/l treatments, but only 5% in the highest tested concentration of 10,000 µg/l. No mortality occurred in the control.

Therefore, while Arenicola spp may be 'Not sensitive to carbon nanotubules Hediste diversicolor probably has a resistance of ‘Low’ to graphene oxide nanosheets and ‘Medium’ resistance to multi-walled carbon nanotubes. Hence, resilience is probably ‘High’ and sensitivity is assessed as ‘Low’ but with ‘Low’ confidence.

Pires et al. (2016) investigated the biochemical effects of single and combined exposure to Carbamazepine and caffeine on Hediste diversicolor. Polychaetes were exposed to a range of concentrations of carbamazepine (0.3, 3.0, 6.0 and 9.0 µg/l) and caffeine (0.5, 3.0, and 18.0 µg/l) for 28 days. 8.3% of mortality at concentrations 0.3 and 3.0 µg/l after 28 days of exposure to carbamazepine, 25% at 6.0 µg/l and 16.7% at 18.0 µg/l. Specimens experienced 8.3% of mortality after 28 days of exposure to caffeine at 0.5 and 18.0 µg/l, and polychaetes exposed to 0.3 µg/l carbamazepine + 0.5 µg/l caffeine had 8.3% mortality. No mortality was recorded in the 3 µg/l caffeine or 3 µg/l caffeine + 6 µg/l carbamazepine treatment. The above evidence suggests that Hediste diversicolor has a ‘Low’ sensitivity to caffeine exposure but confidence in the assessment is ‘Low’ due to the lack of evidence. The effects of pesticides/biocides are discussed above. 

Muller-Karanassos et al. (2021) investigated the effects of environmental concentrations of antifouling paint particles on sediment-dwelling invertebrates. Adult ragworms and cockles were exposed to three types of antifouling paint particles (APP), two biocidal (‘historic’ and ‘modern’) and one biocide-free (‘silicone’). Two laboratory-based 18-day and 5-day exposure experiments were carried out. The APPs ranged in particle size and included varying concentrations of Cu, Sn, Pb, Hg, and Zn. Trial experiments carried out using the maximum environmental APP concentration (18.8 g/l) caused 100% mortality of all ragworms and cockles in the modern treatment within 6 days. In the 18-day exposure, antifouling paint particle concentrations were 4.2 g/l for the historic biocidal treatment; 3.0 g/l for the modern biocidal treatment; and 2.1 g/l for the non-biocidal silicone treatment. The burrowing rate of the ragworms was reduced by 29% in the modern biocidal treatment. However, there were no significant differences between treatments. Ragworms decreased in weight and feeding rates significantly, but significant differences were only seen between the modern biocidal treatment and the control. Modern biocidal antifouling paint particles were used at concentrations ranging from 0 to 30 g/l (ragworms) and 0 to 6 g/l (cockles) to estimate the 5-day LC50 exposure. The 5-day LC50 values were 19.9 g/l for the ragworms and 2.3 g/l for cockles. The 5-day EC50 values were 14.6 g/l for the ragworms and 1.4 g/l for cockles.

The evidence Muller-Karanassos et al. (2021) suggests that antifouling paint particles remain toxic in the environment. Therefore, the resistance of Hediste diversicolor to APPs is assessed as ‘None’. Hence, resilience is assessed as ‘Medium’ and sensitivity as ‘Medium’ but confidence in the assessment is ‘Low’ due to the lack of evidence.

Wastewater discharge was shown to reduce the abundance of Cerastoderma edule in the affected area (Bergayou et al., 2019). Exposure to pulverised fuel ash was reported to result in ‘Severe’ mortality in Cerastoderma edule (Jenner & Bowmer, 1990; Bowmer et al., 1994), while pollution in Southampton Water resulted in reduced scope for growth (Savari et al., 1991). However, the exact nature of the contaminants in each mixture was unclear.  Therefore, the worst-case resistance of Cerastoderma edule to pulverised fuel ash exposure is assessed as ‘None’, resilience as ‘Medium’ and sensitivity as ‘Medium’ but with ‘Low’ confidence. However, its resistance to wastewater discharge may be ‘Medium’ and its sensitivity ‘Low’ depending on the nature of the contaminants involved but confidence is ‘Low’ due to the lack of evidence.

Overall sensitivity assessment.  The effects of 'other substances' on other polychaete species are used in the absence of direct evidence of their effect on Lanice spp.  Therefore, the worst-case resistance of Lanice-dominated habitat to 'other substances' such as antifouling paint particles (APP) assessed as 'None', and resilience as 'Medium' and sensitivity as 'Medium' based on the assumption that polychaetes share similar biochemical and hormonal pathways. However, confidence in the assessment is 'Low' due to the lack of direct evidence and the variation in toxicity between the chemicals studies and the species exposed and the assessment should be used with caution.  The resistance to graphene oxide sheets may be 'Low' (resulting in a resilience of 'High' and a sensitivity of 'Low') but the mode of action is unclear and, in particular, how GOs act between species within taxonomic groups, Hence, no assessment of sensitivity is Lanice spp. is made. 

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

Niermann et al. (1990) reported that the abundance of Lanice conchilega in a subtidal fine sand community in the German Bight area, was significantly reduced during a period of hypoxia (1-3 mg/O₂/dm³). However, the period of hypoxia lasted for about a month and, therefore, exceeds the pressure benchmark. The activities of Lanice conchilega oxygenate sediments (Forster & Graf, 1995) and this species may not, therefore, be adapted to anoxic/hypoxic conditions unlike burrowing infauna such as Nephtys spp. and oligochaetes.

Nilsson & Rosenberg (1994) summarized that Nephtys hombergii have the potential to be tolerant of severe hypoxia and hydrogen sulphide (Alheit, 1978; Arndt & Schiedek, 1997). Nephtys hombergii survived 5 days in pure artificial anoxic seawater, not shifting from the aerobic to anaerobic metabolic pathways before oxygen saturation decreases to 112% (Schottler, 1982). Other experiments demonstrated that 50% of Nephtys hombergii survived 23 days in almost anaerobic conditions (10.2 mg/l), whereas Nephtys ciliata survived 11 days in the same tests (Fallesen & Jorgensen, 1991). 

Rosenberg et al. (1991) observed that Cerastoderma edule migrated to the sediment surface in response to reduced oxygen concentrations in the upper sediment layers and reported 100% mortality of Cerastoderma edule exposed to 0.5-1.0 ml/l oxygen for 43 days. Theede et al. (1969) reported 50% mortality after 4.25 days at 1.5 ml/l oxygen. Theede et al. (1969) added that Cerastoderma edule only survived 4 days’ exposure of <6.1 cm²/l of hydrogen sulphide, which is associated with anoxic conditions. Cerastoderma edule fatalities are likely to occur at the benchmark.

Sensitivity assessment. Although some species associated with the biotope, such as Nephtys hombergii, are tolerant of hypoxia and anoxia, other species that occur in oxygenated sediments or at the surface may be more sensitive. As the biotope occurs in the intertidal, oxygen recharge during immersion may ameliorate the effects of hypoxia and anoxia. Biotope resistance is therefore assessed as ‘Medium’ and resilience as ‘High’ (following the restoration of typical habitat conditions). Biotope resistance is therefore assessed as ‘Low’. Due to the lack of evidence for Lanice conchilega, confidence is assessed as ’Low’.

Nutrient enrichment

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

Evidence

This pressure relates to increased levels of nitrogen, phosphorus and silicon in the marine environment compared to background concentrations. The benchmark is set at compliance with WFD criteria for good status, based on nitrogen concentration (UKTAG, 2014). 

Moderate enrichment increases food supply, enhancing productivity and abundance. Mudflats can be sensitive to nutrient enrichment which can result in blooms of opportunistic ephemeral seaweeds such as Enteromorpha spp. Macoma balthica has been shown experimentally to be able to resist time periods of nine weeks under algal clover as their long siphon allows them to reach oxygenated water, although other bivalves decreased in abundance (Thiel et al., 1998). Organic enrichment beneath oyster cultivation trestles and mussel cultivation sites and fish cages has led to community replacement/dominance by Cirratulid, Capitellid and Spionid polychaetes, particularly Manayunkia aesturina in mudflats, which characterize disturbed areas enriched in organic matter (Pearson & Rosenberg, 1978; Samuelson, 2001, see Bouchet & Saurier, 2008 for references). Local hydrodynamics and topographic features will mediate or strengthen biodeposition effects. Gross effects will lead to anoxic, defaunated sediments which may be covered by sulphur reducing bacteria such as Beggiatoa spp. (Elliott et al., 1998). Diatom density may be reduced by organic enrichment potentially reducing the stability of mudflats (Elliott et al., 1998).

Sensitivity assessment. '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

There is limited evidence to assess the effects of organic enrichment directly on Lanice conchilega, other polychaetes (Pygospio elegans, Scoloplos armiger and Nephtys hombergii) and Cerastoderma edule. The response of benthic communities and of the sediment to increased organic carbon can be determined by the physical composition of the substrata and the availability of dissolved oxygen.

Cromey et al. (1998) found that organic loading rates <36 g C/m²/year had little effect on the macrobenthic communities; the sediment became enriched up to inputs of 365 g C/m²/year and organic loading >500 g C/m²/year led to degraded conditions probably due to lower oxygen concentrations. 

Lanice conchilega has been categorised by Borja et al. (2000) as AMBI Group II - 'Species indifferent to enrichment, always present in low densities with non-significant variations with time (from initial state, to slight unbalance)'. This assessment was reviewed by Gittenberger & Van Loon (2011) and changed to AMBI 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)'. From the AMBI index group, Cerastoderma edule and Pygospio elegans are identified in the Ecological Group III reflecting feeding type and other traits: 'Tolerant of excessive organic matter enrichment and populations are stimulated by organic enrichment' (Borja et al., 2000).

Sensitivity assessment. There is little empirical evidence to quantify the effect of organic enrichment deposits of 100 g C/m^²/yr on Lanice conchilega. Based on the ranges presented by Cromey et al. (1998), this benchmark pressure is unlikely to have an influence upon Lanice conchilega and associated species. The resistance of ‘High’ and a resilience of ‘High’ may also be assigned and by default the biotope is ‘Not sensitive’.

Physical loss (to land or freshwater habitat)

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

Evidence

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

Physical change (to another seabed type)

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

Evidence

The species characterizing this biotope occur within the upper layers of the soft sediment (JNCC, 2015). This biotope does not occur on artificial substrata or rock habitats, although patches of sediment may support some of the species associated with this biotope. Any substratum other than the sediments on which this biotope is found would therefore lead to a loss of this biotope. Consequently, biotope resistance is assessed as 'None’, resilience is assessed as ‘Very Low’ (as the change, at the benchmark is permanent), and biotope sensitivity is 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

This biotope is found in medium to fine muddy sand and mixed sediments (Connor et al., 2004). The biotope would not be considered sensitive to a change to mixed sediments from muddy sands or vice versa, as the sediment would still be likely to support the biotope. A change to coarse sediments or clean sands could, however, lead to loss of habitat suitability for the associated species that are restricted to sediments with a high proportion of fine factions, such as the burrowing polychaetes. 

The characterizing species Lanice conchilega occurs in a range of sediments, including clean sands and coarser, clean sediments and pockets of sediment within otherwise unsuitable habitats. It is therefore likely to still occur in habitats where there has been a change in Folk class at the pressure benchmark. However, abundances of Lanice conchilega and the species richness and abundances of other species present are likely to alter. Degraer et al. (2006) report that Lanice conchilega displays a preference for fine to medium-grained sediments (100 to 500 μm) with relatively high mud content (10 to 40%), and other sediment types are therefore likely to be sub-optimal.

Dense aggregations of Lanice conchilega facilitate the deposition of fine materials as the tubes reduce the velocity of flow. Some increase in fine sediment fraction to muds is likely to be tolerated. Sylvand (1995) highlighted the dominant presence of Lanice conchilega in areas of oyster cultivation where fine particles were deposited.

High densities of Nephtys hombergii were found in substrata of 0.3% particles >0.25 mm and 5.8% <0.125 mm in diameter, but tolerated up to 3.8% 0.25 mm and 2.2-15.9% <0.125 mm (Clark et al., 1962). Nephtys hombergii may be found in higher densities in muddy environments. An increase in gravel content, although tolerated by Nephtys hombergii, may lead to increased abundance of Nephtys cirrosa and decreased abundance of Nephtys hombergii. Degraer et al. (2006) summarized that the higher the medium grain size of the sediment the lower the relative occurrence of Nephtys hombergii and in grain sizes over 0.5 mm the species was absent in the Belgium part of the North Sea.

Habitat partitioning has been observed between Corophium volutator and Corophium arenarium on the basis of sediments, although modified by disturbance from other species (see removal of target species). Corophium arenarium is associated with areas of sandy sediment whilst Corophium volutator prefers muddier sediments (Watkins, 1941; Meadows, 1964; Flach, 1993), changes in sediment type may, therefore, lead to shifts in the species present.

Sensitivity assessment.  Changes to increased finer sediments are likely to be tolerated, however, a change in the sediment Folk class classification at the pressure benchmark to gravel is likely to alter the abundance of Lanice conchilega and the composition of the species assemblage, resulting in loss of this biotope. Resistance is therefore assessed as 'None' and resilience as 'Very Low' (as the change at the pressure benchmark is permanent). The biotope is considered to have 'High' sensitivity to this pressure.

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

Sedimentary communities are likely to be highly intolerant of substratum removal, which will lead to partial or complete defaunation, exposure of underlying sediment which may be anoxic and/or of a different character or bedrock and lead to changes in the topography of the area (Dernie et al., 2003). Any remaining species, given their new position at the sediment/water interface, may be exposed to conditions to which they are not suited, i.e. unfavourable conditions. Newell et al. (1998) state that removal of 0.5 m depth of sediment is likely to eliminate benthos from the affected area.

Removal of 30 cm of sediment will remove species that occur at the surface and within the upper layers of sediment. The extraction of sediment would remove the characterizing species Lanice conchilega, and the associated species present, including Cerastoderma edule, which is found to a depth of 5 cm and Nephtyid species and other polychaetes, such as Scoloplos armiger and Pygospio elegans that burrow between 5 and 20 cm into the sediment (Schӧttler, 1982; Pedersen, 1991; Kruse et al., 2004).   

Hydrodynamics and sedimentology (mobility and supply) influence the recovery of soft sediment habitats (Van Hoey et al., 2008). Recovery of the sedimentary habitat would occur via infilling, some recovery of the biological assemblage may take place before the original topography is restored, if the exposed, underlying sediments are similar to those that were removed.

Sensitivity assessment. Extraction of 30 cm of sediment will remove the characterizing biological component of the biotope. Resistance is assessed as ‘None’ and biotope resilience is assessed as ‘Medium’ as some sediment recovery may be required before recovery processes begin. 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 characterizing species of this biotope (Lanice conchilega) has robust, flexible tubes and may retract below the surface. They are also able to rapidly rebuild or repair tubes (Nickolaidou, 2003). These characteristics reduce exposure to this pressure and enhance recovery. Rabaut et al. (2008) studied fisheries impacts at the species level in temperate sandy bottom areas. A controlled field manipulation experiment was designed focusing on areas with high densities of Lanice conchilega (i.e. Lanice conchilega reefs). A treatment zone was exposed to a one-off experimental trawling and the impact on, and recovery of, the associated fauna was investigated for a period of 9 days post-impact. Community analysis showed a clear impact on associated species such as Eumida sanguinea, followed by a relatively quick recovery. The passage of a single beam trawl did not significantly alter the density of Lanice conchilega (Rabaut et al., 2008).

Muddy sand sediments, in general, tend to be cohesive, although high levels of water content will reduce this and destabilise sediments. Sediment cohesion provides some sediment stabilisation to resist erosion following surface disturbance. Surface compaction can collapse burrows and reduce the pore space between particles, decreasing penetrability and reducing stability and oxygen content (Sheehan, 2007). The tops of burrows may be damaged and repaired subsequently at energetic cost to their inhabitants. Experiments have shown that areas subject to compaction from trampling tend to have reduced species abundance and diversity (Sheehan, 2007; Rossi et al., 2007). Sheehan (2007) proposed that following compaction, organisms avoid or emigrate from affected areas.

Rossi et al. (2007) investigated the effects of continuous trampling (a source of abrasion) on intertidal soft sediments, with on average of 5 people for 3-5 hrs, twice a month between March and September (2005). The abundance of Cerastoderma edule was reduced presumably by sediment compression, leading to asphyxia in adults. Rossi et al. (2007) conducted the investigation during spawning periods, when juveniles where present in the water column. There was therefore little observable effect on juvenile Cerastoderma edule abundances due to continuous recruitment. Rossi et al. (2007) noted that during the growing season, recovery can be fast but in the long-term trampling increased the recruitment of Macoma balthica at the expense of Cerastoderma edule.

Abrasion is likely to reduce the density of Corophium spp. by emigration and increased mortality, as this species is sensitive to sediment disturbance from bioturbating species (Flach, 1993).

Exposure to abrasion may vary according to life stage. For example, the egg cocoons of Scoloplos armiger and Nephtys hombergii are laid on the sediment surface before hatching and entering into their planktonic stages of development. The juveniles found a few millimetres below the surface (Reise, 1979; Kruse et al., 2004) are sensitive to the effects of abrasion.

Sensitivity assessment. The experiments by Rabaut et al. (2008) suggest that Lanice conchilega has ‘High’ resistance to abrasion, however, other associated species may be more impacted. Biotope resistance to a single abrasion event is assessed as ‘High’ based on the key characterizing species Lanice conchilega. There may be some damage to tubes but this is expected to be sub-lethal and tubes are likely to be rapidly repaired. Recovery from impacts of associated species is predicted to be ‘High’ and the biotope is assessed as ‘Not sensitive’.  

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 characterizing species of this biotope (Lanice conchilega) has robust, flexible tubes and may retract below the surface. They are also able to rapidly rebuild or repair tubes (Nickolaidou, 2003). These characteristics reduce exposure to this pressure and enhance recovery.

Rabaut et al. (2008) studied fisheries impacts at the species level in temperate sandy bottom areas. A controlled field manipulation experiment was designed focusing on areas with high densities of Lanice conchilega (i.e. Lanice conchilega reefs). A treatment zone was exposed to a one-off experimental trawling, and the impact on and recovery of the associated fauna was investigated for a period of 9 days post-impact. Community analysis showed a clear impact followed by a relatively quick recovery. The passage of a single beam trawl did not significantly alter the density of Lanice conchilega. Rabaut et al. (2009) also studied the direct mortality of Lanice  conchilega as a consequence of sustained physical disturbance at varying frequencies to reflect the effect of beam trawl fisheries. Research was based on a laboratory experiment in which four different disturbance regimes were applied (disturbance every other 12, 24 and 48 h and no fishing disturbance as a control). Survival dropped significantly after 10 and 18 days (with a disturbance frequency of every 12 and 24 h, respectively). The results indicate that Lanice conchilega is relatively resistant to physical disturbance but that reef systems can potentially collapse under continuous high frequency disturbance.

Ferns et al. (2000) investigated the effect of tractor dredging for cockles on an intertidal muddy sand at Burry Inlet, South Wales mechanical cockle harvesting. The tubes of Lanice  conchilega were damaged but this damage was rapidly repaired. Associated species were more vulnerable and a decline of 31% in populations of Scoloplos armiger (initial density 120/m²) was recorded  in muddy sands and an 83% decline in Pygospio elegans (initial density 1850/m²). Pygospio elegans were significantly depleted for >100 days after harvesting (surpassing the study monitoring timeline). Whilst Nephtys hombergii and Scoloplos armiger demonstrated recovery >50 days after harvesting in muddy sands. Cerastoderma edule recovered more quickly than those in muddy sand with a more structured community, which included Pygospio elegans and Lanice conchilega in clean sands (Ferns et al., 2000).

Hand raking for cockles on intertidal silty sandflats, using rakes that penetrated the surface by 5-10 cm, resulted in a three-fold increase in the damage rate of cockles compared to control plots and, in the short-term, led to a relative decrease in the overall abundance of fauna (Kaiser et al., 2001). After 56 days, the small (9 m²) plots had recovered but the larger (36 m²) plots remained in an altered state. Results collected over a year after the disturbance suggested that while effects of hand-raking may be significant within a year, they are unlikely to persist beyond this time-scale unless there are larger long-lived species present within the community (Kaiser et al., 2001). Effects may be longer lasting where sediment damage occurs without recovery. A study in the Dutch Wadden Sea showed that suction-dredging for cockles (Cerastoderma edule) led to a significant long-term reduction in settlement and stocks of the target bivalve species (Piersma et al., 2001). Analysis of sediment characteristics before and after dredging showed an increase in median grain size and a reduction of silt content, and that these changes were most pronounced in the area dredged for cockles. Sediment characteristics only returned to pre-impact conditions 8-11 years after the suction dredging.

Sensitivity assessment. The experiments by Rabaut et al. (2008, 2009) suggest that Lanice conchilega has ‘High’ resistance to abrasion and penetration, however, other associated species may be more impacted. Biotope resistance to a single abrasion event is assessed as ‘High’ based on the key characterizing species Lanice conchilega. There may be some damage to tubes but this is expected to be sub-lethal and tubes are likely to be rapidly repaired. Recovery from impacts of associated species is predicted to be ‘High’ and the biotope is assessed as ‘Not sensitive’.  

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

Production within the biotope is predominantly secondary, derived from detritus and to some extent phytoplanktonic production. Characteristic infauna do not require light and therefore the effects of increased turbidity on light attenuation are not directly relevant. However, an increase in turbidity may affect primary production in the water column and therefore reduce the availability of phytoplankton as food but phytoplankton would also be transported in to the biotope from distant areas, so the effect of increased turbidity may be mitigated. As soon as light levels return to normal, phytoplanktonic primary production would increase, the species would resume optimal feeding, so recoverability has been assessed to be very high. A decrease in suspended organic particles may reduce food supply to Lanice conchilega, however, this species can switch from suspension to deposit feeding and vice versa (Buhr & Winter, 1977). Supply of materials needed to build the tubes may be affected with a decrease in suspended solids but wave action would be likely to continue to re-suspend and transport sediments.

Sensitivity assessment. A decrease in turbidity and hence increased light penetration may result in increased phytoplankton production and hence increased food availability for suspension feeders, including Lanice conchilega and Cerastoderma edule. Therefore, reduced turbidity may be beneficial. In areas of high suspended sediment, a decrease may result in improved condition and recruitment due to a reduction in the clogging of filtration apparatus of suspension feeders and an increase in the relative proportion of organic particulates. However, a decrease in suspended organic particles in some areas may reduce food availability for deposit feeders resulting in lower growth or reduced energy for reproduction. 

Where increased turbidity results from organic particles then subsequent deposition may enhance food supply for suspension and deposit feeders within the biotope. Alternatively, if turbidity results from an increase in suspended inorganic particles then energetic costs may be imposed on these species as sorting and feeding becomes less efficient, reducing growth rates and reproductive success. Lethal effects are considered unlikely given the occurrence of Lanice conchilega and Cerastoderma edule and other associated species in estuaries where turbidity is frequently high from suspended organic and inorganic matter. Resistance and resilience are therefore assessed 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

The tube of Lanice conchilega protrudes above the sediment by 1–4 cm, an adaptation to trap suspended particles (Zühlke, 2001). Furthermore, Ziegelmeier (1952) showed that the tubes of Lanice conchilega increased the height with increasing sedimentation so that it could continue feeding and metabolising aerobically. This enables Lanice conchilega to switch between deposit and suspension feeding (Buhr, 1976). Therefore, Lanice conchilega is suitably adapted to discrete events of sedimentation, characteristic of sandy, muddy sand intertidal flats. Lanice conchilega  has dominated areas of Manila clam cultivation where protective netting had led to an increase in sedimentation (Spencer et al.,1998) and in areas where oysters were cultivated and sedimentation increased (Sylvand, 1995).

Cerastoderma edule has short siphons and needs to keep in contact with the surface of the sediment. It will quickly burrow to the surface if covered by as little as 2 cm of sediment (Richardson et al., 1993b; Cotter et al., 1997). When buried to 5 cm depth in a series of siltation experiments most cockles returned to the surface but few were able to reposition to the surface if buried at 10 cm depth (Jackson & James, 1979). None had died after 72 hours. Additional burial experiments under 10 cm of sediment assessed movement and survival after 3, 6 and 9 days in two sediment types (a mix of surface mud and sand in two ratios 9:1 and 1:9). The movement towards the surface was slower in the predominantly muddy sediment and all cockles died between 3 and 6 days. Substantial mortality resulted in the predominantly sandy mixture, although some cockles were able to move towards the surface and survive for 9 days (Jackson & James, 1979).

The associated species Pygospio elegans is limited by high sedimentation rates (Nugues et al., 1996) and the species does not appear to be well adapted to oyster culture areas where there are high rates of accumulation of faeces and pseudofaeces (Sornin et al., 1983; Deslous-Paoli et al., 1992; Mitchell, 2006; Bouchet & Sauriau, 2008). Pygospio elegans is known to decline in areas following re-deposition of very fine particulate matter (Rhoads & Young, 1970; Brenchley, 1981). Experimental relaying of mussels on intertidal fine sands led to the absence of Pygospio elegans compared to adjacent control plots. The increase in fine sediment fraction from increased sediment deposition and biodeposition alongside possible organic enrichment and decline in sediment oxygen levels was thought to account for this (Ragnarsson & Rafaelli, 1999). Nephtys species are highly mobile within the sediment. Vader (1964) observed that Nephtys hombergii relocated throughout the tidal cycle and is unlikely to be affected by smothering with sediment consistent with that of the habitat.

Sensitivity assessment. Based upon the ability of Lanice conchilega to increase tube elevation above the sediment surface when deposition has increased, it is likely that Lanice conchilega is resistant to the effects of a single discrete event of deposition of 5 cm. Although Cerastoderma edule and Pygospio elegans may be impacted, the Lanice conchilega biotope is unlikely to be altered from a single event. Sensitivity to continuous events will depend on tidal hydrodynamics, and spawning and recruitment, prior to the event (see recover/resilience rates). As the benchmark refers to a single discrete event, resistance is ‘High’ and resilience is ‘High’, therefore this biotope is ‘Not sensitive’.

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

No evidence was found to assess sensitivity of Lanice conchilega to heavy sedimentation. It is likely that intertidal flats may sometimes be subject to sedimentation following storm events but no species-specific examples were found. Ziegelmeier (1952) showed that Lanice conchilega increased the height of its tube top with increasing sedimentation so that it could continue feeding and respire. However, heavy sedimentation of 30 cm during a single event may have a severe effect on Lanice conchilega and the associated species.

Cerastoderma edule has short siphons and needs to keep in contact with the surface of the sediment. Bait digging (for large polychaete worms) disturbs the sediment down to a depth of 30 cm (Jackson & James, 1979) and leads to repositioning within sediment or burial from piled sediments. Intensification of bait digging on intertidal flats on the north Norfolk coast for lugworm (Arenicola marina) and ragworm (Hediste diversicolor) was associated with declines in the Cerastoderma edule populations (Jackson & James, 1979). Experimental simulation of bait digging (sediment dug over to a depth of 30 cm with a garden fork) led to high mortalities of cockles in dug areas rather than undug areas (48% mortality in 9 days to a maximum of 85% after 11 days), probably due to smothering (Jackson & James, 1979). The observation was tested experimentally in the laboratory by burying 3 size-classes of cockles at 0, 5 or 10 cm depth in a mix of oxidated and deeper anoxic sands (mixed as a ratio of 3:1). Movements were recorded after 24, 48 and 72 hours. When buried to 5 cm depth, most cockles returned to the surface but few were able to reposition to the surface if buried at 10 cm depth. None had died after 72 hours. Additional burial experiments under 10 cm of sediment assessed movement and survival after 3, 6 and 9 days in two sediment types (a mix of surface mud and sand in two ratios 9:1 and 1:9). The movement towards the surface was slower in the predominantly muddy sediment and all cockles died between 3 and 6 days. Substantial mortality resulted in the predominantly sandy mixture, although some cockles were able to move towards the surface and survive for 9 days.

Sensitivity assessment. The addition of 30 cm of sediment would prevent Cerastoderma edule from extending siphons to the surface. It is unlikely that this species could emerge from this depth of sediment, although some individuals may survive and sediment may be rapidly removed by tide and wave action. It is likely, however, that there would be considerable mortality of Cerastoderma edule and other species, including Lanice conchilega. Resistance is assessed as ‘Low’ and resilience as ‘High’. Sensitivity is therefore assessed as ‘Low’. Although some polychaetes may be able to reposition following sedimentation at the pressure benchmark, this will depend on the characteristics of the overburden, and sedentary species such as Pygospio elegans are likely to suffer high levels of mortality.

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 information was found concerning the intolerance of the biotope or the characterizing species to noise. The siphons of bivalves and palps of polychaetes are likely to detect vibrations and would probably be withdrawn as a predator avoidance mechanism. However, it is unlikely that the biotope and characterizing species will be affected by noise or vibrations caused by noise at the level of the benchmark and this pressure is assessed as ‘Not relevant’.

Introduction of light or shading

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

Evidence

No evidence. As this feature is not characterized by the presence of primary producers, it is not considered that shading would alter the character of the habitat directly. However, there may be changes in microphytobenthos abundance. Littoral muddy sands support microphytobenthos on the sediment surface and within the sediment. The microphytobenthos consists of unicellular eukaryotic algae and cyanobacteria that grow within the upper several millimetres of illuminated sediments, typically appearing only as a subtle brownish or greenish shading. Mucilaginous secretions produced by these algae may stabilise fine substrata (Tait & Dipper, 1998). The biomass of the benthic microalgae often exceeds that of the phytoplankton in the overlying waters (MacIntyre et al., 1996) such that benthic microalgae play a significant role in system productivity and trophic dynamics, as well as habitat characteristics such as sediment stability. Shading will prevent photosynthesis leading to death or migration of sediment microalgae, altering sediment cohesion and food supply to higher trophic levels.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Barriers that reduce the degree of tidal excursion may alter larval supply to suitable habitats from source populations. Conversely, the presence of barriers at brackish waters may enhance local population supply by preventing the loss of larvae from enclosed habitats to environments, which are unfavourable, reducing settlement outside of the population. Resistance to this pressure is assessed as 'High' and resilience as 'High' by default. This biotope is therefore considered to be 'Not sensitive'.

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

Characterizing and associated species are not cultivated or transplanted and this pressures is 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

Intertidal flats may be colonized by the invasive non-indigenous species Crepidula fornicata and the pacific oyster Magallana gigas. The two species have not only attained considerable biomasses from Scandinavian to Mediterranean countries but have also generated ecological consequences such as alterations of benthic habitats and communities or food chain changes (OSPAR, 2009).

The Pacific oyster, Magallana (syn. Crassostrea) gigas, is native to warm temperate regions from the northwest Pacific to Japan and northeast Asia, including Cape Mariya (Russia) to Hong Kong (China) (Carrasco & Baron, 2010; GBNNSS, 2011, 2012). It is a fast-growing and tolerant species that has become a successful invader in the coastal waters of all continents, aside from Antarctica (Wrange et al., 2010; Carrasco & Baron, 2010; Padilla, 2010). Magallana gigas is recognised as a beneficial and important species in aquaculture worldwide (Padilla, 2010). It was initially introduced for aquaculture in Europe and the UK in the 1960s due to a decline in the Portuguese oyster (Crassostrea angulata) and the European flat oyster (Ostrea edulis) (Spencer et al., 1994; GBNNSS, 2011, 2012; Humphreys et al., 2014 cited in Alves et al., 2021; Hansen et al., 2023).

Since introduction, the species has invaded and established self-sustaining natural populations throughout Europe from the North Sea, Wadden Sea and Scandinavian coastlines to the Atlantic coastlines of Spain and Portugal, as well as the Mediterranean and Adriatic Sea (Wrange et al., 2010; GBNNSS, 2011, 2012; Ezgeta-Balic et al., 2019; Spagnolo et al., 2019; Bergstrom et al., 2021; Hansen et al., 2023). In the UK, the species predominantly occurs around the southern and western coastlines (OBIS, 2024; NBN, 2024). Shipping activity has also been associated with the introduction of Magallana gigas in the northeastern Adriatic Sea, where it was not introduced for aquaculture (Ezgeta-Balic et al., 2019). It was also suggested that some Magallana gigas populations were established in southwest England from France possibly via fouling on ships (GBNNSS, 2011, 2012; Padilla, 2010; Ezgeta-Balic et al., 2019).

Magallana gigas has a high fecundity, a long-lived pelagic larval phase (2 to 4 weeks) and can produce up to 200 million eggs during spawning (Herbert et al., 2012, 2016; Alves et al., 2021; Wood et al., 2021; Hansen et al., 2023). Hence, as a broadcast spawner, it has a high dispersal potential of more than 1000 km (Padilla, 2010; Wood et al., 2021). Larval mortality can be as large as 99%, as larvae are sensitive to environmental conditions (Alves et al., 2021). However, adults are long-lived so populations can survive with infrequent recruitment (Padilla, 2010). Larval dispersal and mass spawning events have facilitated the settlement and establishment of Pacific oysters, as seen in the Oosterschelde estuary, Netherlands (Hansen et al., 2023). It has been suggested that the spread of the Pacific oyster in Scandinavia is due to northward larval drift on tidal and wind-driven currents (Hansen et al., 2023). Wood et al. (2021) suggested that larval dispersal of the Pacific oyster from populations within and outside the UK was possible via unaided (passive) transport by currents, but that aquaculture and offshore structures (e.g. windfarms) increased the risk of the invasive species spreading and the geographical extent of spread.

Magallana gigas is an ecosystem engineer and can dramatically change habitat structure when it invades. Once successfully settled, groups of Pacific oysters may form dense aggregations, potentially forming a reef, which in some regions can reach densities of 700 individuals m² (Herbert et al., 2012, 2016). Once, the density of live or dead Pacific oysters reaches or exceeds 200 ind./m² little of the underlying substratum remains visible (Herbert et al., 2016). These reefs can stabilize the sediment surface locally (Troost, 2010). When such reefs are formed or, particularly when the species colonizes soft sediments such as mud or sand, it can change and affect local communities, by creating hard substrata for mobile species, which might not otherwise be present before the invasion (Padilla, 2010). However, Hansen et al. (2023) suggested that no immediate ecosystem risk is observed where the Pacific oyster occurs sporadically.

Magallana gigas requires hard substrata for successful settlement and establishment, including littoral rock, bedrock, chalk, bare boulders, cobbles and pebbles and shells (Kochmann, 2012; Kochmann et al., 2013; Mckinstry & Jensen, 2013; Herbert et al., 2016; Tillin et al., 2020). It also prefers mudflats with mixed sediment composed of shingle and sand, attaching to whatever hard substrata are available within otherwise unsuitable fine muddy sediment (Spencer et al., 1994; Mckinstry & Jensen, 2013; Tillin et al., 2020). Magallana gigas has been reported from estuaries growing on intertidal mudflats, sandflats, and other soft sediments (Padilla, 2010; Herbert et al., 2016; Cabral et al., 2020). The settlement of spat on hard substrata within sediments has been observed in the estuaries of the River Dart, Exe, Fal, Fowey, Tamar, Teign, and Yealm in Devon and Cornwall, the Menai Straits, Wales and large estuaries of Lough Swilly, Lough Foyle and the Shannon in Ireland, and the Tagus Estuary in Portugal (Spencer et al., 1994; Kochmann, 2012; Kochmann et al., 2013; Cabral et al., 2020). In Lough Swilly, Lough Foyle and the Shannon, the Pacific oyster was often associated with intertidal mud or sandflats (Kochmann et al., 2013). In contrast, the Pacific oysters were absent from sandflat areas in Poole Harbour (Mckinstry & Jensen, 2013).

Although shorelines comprised of mainly mud were suggested to be unsuitable for spat settlement (Spencer et al., 1994), the presence of smaller hard substrata, such as shells or pebbles, can enable larvae to settle (Tillin et al., 2020). For example, in the River Teign estuary, Pacific oyster settlement was observed on shell-covered ground mainly attached to mussel shells, and occasionally attached to cockles, stones and common periwinkle (Littorina littorea) shells on a mud flat in the estuarine intertidal zone otherwise mainly comprised of sand and mud (Spencer et al., 1994). In addition, the Blue Lagoon on the north shore of Poole Harbour had the highest abundance of oysters on mud mixed with shingle and shell (Mckinstry & Jensen, 2013). Outside of the Blue Lagoon, oysters were also recorded on mixed substrata composed of mud, gravel, and shell (McKinstry & Jensen, 2013). Tillin et al. (2020) concluded that while successful invasions occurred on mudflats, Magallana gigas prefers mixed substrata. Fine mud sediments without hard substrata (such as small stones, gravel, and shell) are unlikely to be suitable (Tillin et al., 2020). The speed of Magallana gigas reef formation on soft substrata seems to be dependent on the amount of hard substrata present, developing quicker once there is a sufficient amount (Troost, 2010). Bergstrom et al. (2021) reported that the presence of Magallana gigas was partially dependent on increasing gravel content up to 15% but remained stable with increasing percentages (measured up to 80%). 

The oyster reefs, in the Wadden Sea and Brittany, on littoral muddy and sandy habitats formed predominantly at lower tidal levels from Mean Low Water levels to the shallow subtidal (Herbert et al., 2012, 2016). Pacific oyster spatfall was recorded in the estuarine intertidal zone on areas with hard substrata of stone and shell, particularly between the low water of spring tides and high water of neap tides, such as in the Menai Strait (Spencer et al., 1994). At high densities the Pacific oyster reef smothers sediment, provides hard substrata in an otherwise sedimentary environment with additional niches for colonization by other species that require hard substratum (e.g. barnacles), and changes surface roughness and local hydrography (Troost, 2010; Herbert et al., 2012, 2016; Tillin et al., 2020). Lejart & Hily (2011) found the surface available for epibenthic species in the Bay of Brest, increased 4-fold when oysters were present on mud, for every 1 m² of colonized substrata the oyster reef added 3.87 m² of surface area on mud sediment. An increase in available settlement substrata, free of epibiota, could be the reason oyster reefs see an increase in macrofaunal abundance. This can change the community composition and habitat structure in reefs on soft mud sediments, creating new habitats for an increasing abundance of infaunal and epibenthic mobile species (Kochmann et al., 2008; Lejart & Hily, 2011; Zwerschke et al., 2018). Results have shown 38% of species present in the oyster reefs on mud were characteristic of rocky substratum habitats (Lejart & Hily, 2011).

In the Bay of Brest, Pacific oyster reefs had a higher diversity and species richness than surrounding mud habitats, including the mud underneath the reefs, where the population was dominated by carnivores rather than suspension the feeders found on the mudflats (Lejart & Hily, 2011; Herbert et al., 2012). In addition, in muddy habitats around the UK, Ireland and Northern France, macrofaunal diversity increased as Pacific oyster density increased but epifaunal diversity decreased as oyster densities increased (Zwerschke et al., 2018). It was suggested that the decrease in epifaunal diversity was due to a decrease in settlement space and a increase in habitat fragmentation because of dense oyster assemblages (Zwerschke et al., 2018).

Green & Crowe (2014) examined the effects of Magallana gigas density in experimental plots (0.25 m²) in Lough Swilly and Lough Foyle, Ireland. The number of species and species diversity increased with oyster cover on mudflats, depending on site and duration. The assemblage also changed due to the increased abundance of barnacles and bryozoans on the oyster shells and polychaetes within the sediment (Green & Crowe, 2014). Zwerschke et al. (2020) suggested that Pacific oyster beds could replace the ecosystem services provided by native oysters, in areas where native oysters had been lost. Morgan et al. (2021) suggested that the smothering of sediment habitats could prevent fish and bird species from feeding on infauna like worms, molluscs, and crustaceans. Also, the development of tidepools within mixed Pacific oyster and blue mussel reefs in soft sediment intertidal sites has been observed in the Wadden Sea, which can create new microhabitats within the reefs (Weniger et al., 2022).

Pacific oysters have been found to reduce the proportion of fine particles and increase the proportion of large particles in the mud under the reef (Lejart & Hily, 2011). The evidence suggests that Pacific oyster reefs change sediment characteristics, by affecting nutrient cycling and increasing the organic content of sediment, sand-to-silt ratio and levels of porewater ammonium (Kochmann et al., 2008; Padilla, 2010; Wagner et al., 2012 cited in Tillin et al., 2020; Green & Crowe, 2014; Herbert et al., 2012, 2016; Zwerschke et al., 2020; Hansen et al., 2023).  Zwerschke et al. (2020) found no significant differences in nutrient cycling rates of native oyster beds or Magallana gigas beds or their associated benthic communities, in experimental plots in Ireland. Persistent changes in the rates of nutrient cycling were driven by the density and presence of oysters (Zwerschke et al., 2020).

The deposition of faeces and pseudo-faeces by Magallana gigas can increase the toxic levels of sulphide in sediments and associated hypoxic sediment conditions, which can reduce photosynthesis and growth in eelgrass (Kelly & Volpe, 2007). Faecal deposition and hypoxia have also been suggested to explain a reduction in species diversity in the sediment underlying high density oyster reefs (Green & Crowe, 2013, 2014; Herbert et al., 2016). However, Lejart & Hily (2011) observed no organic or silt enrichment by Pacific oysters in mud beneath oyster reefs in the Bay of Brest, and no significant difference in the amount of organic matter found in the mud underneath oyster reefs and on bare mud not colonized by the oyster. The biodeposits excreted by the oyster may be washed away by powerful tides and currents seen in the Bay of Brest and the effects of organic enrichment at oyster reefs might be minimal due to wave action (Lejart & Hily, 2011).

Magallana gigas also colonizes littoral intertidal biogenic reefs formed by the blue mussel Mytilus edulis or honeycomb worm Sabellaria alveolata (GBNNSS, 2011, 2012; Kochmann, 2012; Kochmann et al., 2013; Herbert et al., 2016; Tillin et al., 2020). In chalk reefs in Kent with 50% cover of Lanice conchilega, the worm has been partially displaced by Magallana gigas, which has reached maximum densities of 14 oyster individuals per m² (Mcknight, 2011, 2012 cited in Herbert et al., 2012, 2016). 

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. In addition, in the MHW, the highest densities of Crepidula were found in areas of sediment with hard substrata, e.g., mixed fine sediment with shell, gravel or both but, while Crepidula density increased as gravel cover increased in the subtidal, the reverse was found in the intertidal (Bohn et al., 2015). However, gravel formed the base of most stacks of Crepidula in the intertidal, which suggested that initial colonization occurred on available hard substrata (i.e., gravel) in the absence of adult shells of Crepidula (Bohn et al., 2015).

Crepidula is recorded from the lower intertidal to ca 160 m in depth but it is most common in the shallow subtidal and low water springs (Blanchard, 1997; Thieltges et al., 2003; Bohn et al., 2012, 2015; Hinz et al., 2011; OBIS, 2023; Tillin et al., 2020). Bohn et al. (2012, 2013a, 2013b, 2015) suggested that extreme conditions in intertidal limited its upward distribution due to early post-settlement mortality. It reached its highest densities on the lower shore (below ca 0.7 m) and was absent from the high tidal level (ca 1.8 m) in the MHW (Bohn et al., 2015). Bohn et al. (2013b) noted that Crepidula spat in their experimental intertidal panels suffered high mortality of 78-100% during emersion by low water spring tides. Thieltges et al. (2003) noted that Crepidula abundance at the intertidal to the subtidal transition zone (ca 21/ m²) was significantly higher than in the upper, mid, and lower intertidal ca <3/ m²). Similarly, Diederich & Pechenik (2013) noted that Crepidula densities were not significantly different in the low intertidal (+0.2 m) and shallow subtidal (-1 m) but became lower at +0.4 and were absent above +0.6 m in Bissel Cove, Rhode Island where the mean high water was +1.38 m. They reported that intertidal adults experienced temperatures of ca 42°C, which were 15°C higher than subtidal adults. However, there was no significant difference in the tolerance of subtidal and intertidal adults with a lethal range of 33-37°C after three hours in the laboratory. Diederich & Pechenik (2013) suggested that adult Crepidula were living close to their upper thermal limit in Rhode Island and would be driven into the subtidal due to climate change. Diederich et al. (2015) reported that most juvenile Crepidula died after aerial exposure under laboratory conditions (20°C, 75% relative humidity), while adults from the intertidal and subtidal survived (26°C, 75% relative humidity). Franklin et al. (2023) noted that the body mass index of adult Crepidula did not decrease significantly in winter months in New Hampshire, USA, but did decrease in spring and summer, probably due to its investment in reproduction. 

The density of Crepidula populations in northern Europe (Germany, Denmark, and Norway) was significantly lower (ca <100/ m2) than in southern waters. Thieltges et al. (2004) reported that the population of Crepidula was affected strongly by cold winters in the Wadden Sea. The winters of 2001 and 2003 resulted in ca 56-64% mortality of intertidal Crepidula and up to 97% on one mussel bed, compared to only 11-14% in southern areas without frost. Crepidula almost vanished from the Wadden Sea after the 1978/79 winter and took ten years to recover due to moderate winters which regularly affected the population. Similarly, 25% mortality was observed in Crepidula populations on the south coast of the UK after the extreme 1962/63 winter (Crisp, 1964, Bohn et al., 2012). Thieltges et al. (2003) suggested that global warming may allow Crepidula populations to become more abundant in northern Europe.

In the Wadden Sea, the Pacific oyster Magallana gigas has colonized intertidal flats (Smaal et al., 2005). This species may consume larvae including the pelagic larvae of Cerastoderma edule and Macoma balthica and other species, reducing recruitment (Smaal et al., 2005). Troost et al. (2009) investigated whether Magallana gigas had a competitive feeding advantage over Cerastoderma edule and concluded that differences in feeding current characteristics were small and not considered to lead to significant differences in feeding efficiency. The most severe effects are likely to occur from impacts on sediment, where Magallana gigas create reefs on sedimentary flats that will prevent recruitment of juveniles and will restrict access of infauna to the sediment-water interface impacting respiration and feeding. Tillin et al. (2020) suggested that Magallana gigas could significantly alter intertidal sediments where adequate hard substrata or shell debris was present and the conditions allow reefs of the oyster to form, based on its occurrence in Poole Harbour, and reefs on littoral sediments in southern England, Ireland, France and the Wadden Sea (Herbert et al., 2016b).  

The Manila clam (Tapes philippinarium), which was introduced to Poole Harbour for aquaculture in 1998, has become a naturalised population on the intertidal mudflats (occurring at densities of 60 clams/m² in some locations within the harbour) (Jensen et al., 2004). Densities of Cerastoderma edule and Abra tenuis have increased since the introduction of the Manila clam, but the abundance of Scrobicularia plana and Macoma balthica has declined (Caldow et al., 2005). However, the decline of these species may have been caused by tri-butyl-tin pollution (Langston et al., 2003) and may have facilitated the naturalization of the Manila clam. The predatory veined whelk (Rapana venosa) and Hemigrapsus takinei are not established in the UK (although Hemigrapsus takinei has been recorded at two locations) and could become significant predators of Cerastoderma edule and other species associated with the biotope in the future.

Sensitivity assessment. Intertidal muddy sands may be exposed to invasive species which can alter the character of the habitat (primarily Crepidula fornicata at the sublittoral fringe and Magallana gigas), leading to re-classification of this biotope. The above evidence suggests that Crepidula could colonize muddy sand habitats, typical of this biotope, due to the presence of gravel that can be used for larvae settlement (Tillin et al., 2020). Therefore, Crepidula has the potential to colonize, and modify the habitat and its associated community due to the introduction of Crepidula shell biomass, silt, pseudofaeces and faeces (Blanchard, 2009; Tillin et al., 2020). In addition, this habitat is moderately exposed to extremely sheltered, in which wave action and storms may mobilise the sediment (JNCC, 2022), which may also mitigate or prevent colonization by Crepidula at high densities. However, Crepidula has been recorded from areas of strong tidal streams (Hinz et al., 2011). Therefore, the habitat may be more suitable for Crepidula in more sheltered examples of the biotope and where water movement is meditated by tidal flow rather than wave action. There may be higher densities of Crepidula in the lower shore examples of the biotope, but the densities may be lower in the mid-shore, and it may be absent from the upper shore due to the unsuitable extreme conditions in the intertidal zone preventing Crepidula post-settlement recruitment and mitigating colonization (Bohn et al. 2015). Therefore, resistance is assessed as 'Low', as a worst-case scenario. Resilience is assessed as 'Very low' as it would require the removal of Crepidula, probably by artificial means. Hence, sensitivity is assessed as 'High'. The confidence in the assessment is 'Low' because the sensitivity of this biotope to Crepidula is potentially site-specific, there is a risk of its introduction by artificial means and a lack of direct evidence of Crepidula's occurrence in the biotope. 

The above evidence suggests that this biotope could be suitable for the colonization of Magallana gigas due to the presence of gravel, shells, or other hard substrata required for successful settlement and establishment (Kochmann, 2012; Kochmann et al., 2013; Mckinstry & Jensen, 2013; Herbert et al., 2016; Tillin et al., 2020). However, areas of the biotope with fine sediment and a lack of hard substrata present may be less suitable. This biotope also occurs mostly in the lower-shore to mid-shore, which is the preferred depth for Magallana gigas populations. Magallana gigas populations may be limited to low densities in wave exposed to moderately wave exposed conditions (Teschke et al., 2020) typical of most (ca 60%) records of this biotope. However, Magallana gigas has been observed, in one study, to partially displace Lanice conchilega cover in chalk reefs, suggesting that Lanice conchilega dominated habitats could be invaded by the Pacific oyster (Mcknight, 2011, 2012 cited in Herbert et al., 2012, 2016). Therefore, resistance to colonization by Magallana is assessed as 'Low' as a precaution. Resilience is likely to be ‘Very low’ as the Magallana gigas population would need to be removed for recovery to occur. Therefore, sensitivity is assessed as ‘High’ for Lanice dominated sediments The confidence in the assessment is 'Low' because the assessment is based on one observation of Magallana gigas invading a Lanice conchilega habitat of soft rock, and no evidence from sedimentary habitats was found. 

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

No evidence was found for microbial pathogens, parasites or diseases of Lanice conchilega or other characterizing polychaetes.

A review of parasites, pathogens and commensals identified a range of agents impacting European cockles, including 50 conditions affecting Cerastoderma edule (Longshaw & Malham, 2013). Cockles are hosts to viruses, bacteria, fungi, Apicomplexa , Amoeba, Ciliophora, Perkinsozoa, Haplosporidia, Cercozoa, Turbellaria, Digenea, Nematoda, Crustacea and Nemertea. Mortalities are associated particularly with digeneans and some protistan infections; parasites may limit growth, reduce fecundity and alter burrowing behaviour (Longshaw & Malham, 2013). A number of examples of conditions associated with mass mortalities of Cerastoderma edule are presented below. Parasites and disease are more likely to cause mortalities in populations that are subject to suboptimal conditions or other stressors such as hot summers or cold winters (Longshaw & Malham, 2013).

The Cerastoderma edule catchment in Galicia (NW Spain) was previously a productive cockle fishery, however, cockle mortality rate increased sharply in this bed in April 2012, reaching 100% in May 2012. Marteiliosis, which was first detected in February 2012 and reached 100% prevalence in April 2012, was identified as the most probable cause. Marteiliosis had never been detected in Galician cockles. Extensive surveillance of the Galician coast in May to July 2012 detected Marteiliosis in most cockle beds of the Ría de Arousa, whereas it was not found in other rías; 2 months later, the cockle catch in the Ría de Arousa became negligible as a result of a Martelia cochillia protozoan infection (Villalba et al., 2014).

Sensitivity assessment. Based on the evidence for Cerastoderma edule, it is likely that parasitic infection may indirectly alter the species composition of the biotope, however, there is no evidence of pathogens influencing Lanice conchilega and the other characterizing polychaetes. Resistance is assessed as ‘High’ as the biotope classification would be unlikely to change and removal of Cerastoderma edule may increase the extent of Lanice conchilega patches and the abundance of species that are sensitive to its sediment disturbing activities, such as Pygospio elegans and Corophium arenarium. Resilience is therefore assessed as ‘High’ and the biotope is considered to be ‘Not sensitive’. 

Removal of target species

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

Evidence

The direct, physical impacts of removal 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 target species on this biotope. The cockle Cerastoderma edule may be targeted by recreational and commercial fishers and the polychaete Nephtys hombergii may be targeted by bait collectors. The removal of target species (Cerastoderma edule) may result in changes to the sediment structure (see physical disturbances pressures).

Dense populations of Cerastoderma edule on intertidal flats support commercial fisheries in several areas of the UK and the species is also harvested throughout Europe. Harvesting may use mechanical methods (e.g. tractor dredges or hydraulic suction dredging) or hand collection using rakes or other methods. The method of harvesting cockles will influence the proportions that are removed and damaged. Pickett (1973) found that intense dredging for a short period on a bed of cockle spat had little effect on survival and growth, although Cook (1991) found that impacts on small cockles from dredging were variable, with little reduction one year but a reduction in density observed the following year. Cotter et al. (1997) assessed the catch rates and damage and mortality of Cerastoderma edule resulting from experimental tractor dredging at the Burry Inlet (Wales). Stocks of adult cockles were reduced by 31 and 49% in low and high density areas respectively. Similarly, mechanical cockle harvesting in muddy sand reduced the abundance of Cerastoderma edule by ca 34%. Populations had not recovered to their original abundance after 174 days (Ferns et al., 2000).

Removal of adult cockles by harvesting or other factors allows other species to establish. Following experimental removal of large adult Cerastoderma edule by Cesar & Frid (2012), sediments showed increased biodiversity and assemblages dominated by traits common to opportunist taxa at a species-poor shore at Warton Sands, Morecambe Bay, and a more diverse shore at Thurstaston, Dee Estuary. The movements of cockles disturb and exclude the amphipod Corophium volutator and other species (Flach, 1996; Flach & De Bruin, 1994). The removal of cockles may, therefore, allow this species to colonize intertidal flats. During periods of low cockle density, Desprez et al. (1992) observed that Pygospio elegans established dense populations, when cockles returned these were lost within one year.

Sensitivity assessment. This biotope is characterized by Lanice conchilega, the removal of Cerastoderma edule and Nephthys hobergii may affect the biotope through physical damage (see abrasion and penetration pressures) but their loss would not lead to biotope reclassification. Resistance is therefore assessed as ‘Medium’ as removal would lead to some alteration of the biological assemblage through changes in abundance and biomass and through changes in competition for space and sediment disturbance (Cerastoderma edule) and predation (Nephtys hombergii). The densities of prey species and species sensitive to sediment disturbance such as Corophium arenarium may increase. Removal of competitors and predators may enhance recruitment of Lanice conchilega. Where sediments remain suitable cockles are likely to recolonize via adult migration, survival of small, discarded cockles or via larval recruitment. Resilience is assessed as ‘High’ so that biotope sensitivity is assessed as ‘Low’. 

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

Species within this biotope may be removed or damaged by static or mobile gears that are targeting other species. 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.

Lanice conchilega (sand mason worm) is the dominant polychaete in this biotope. It qualifies as an ‘ecosystem engineer’ in that it changes and/or creates a habitat, which affects the abundance of other species (Jones et al., 1994, 1997). The tube which Lanice conchilega builds provides structure and stabilises the sediment (Jones & Jago, 1993). The tubes also obstruct the activities of predatory burrowers enabling other sedentary animals to establish themselves (Wood, 1987). The burrows and tubes allow oxygenated water to penetrate into the sediment, the oxic upper layer of sediment to support shallow burrowing species such as amphipods (Ampelisca spp., Bathyporeia spp. & Gammarus spp.) and small Crustacea. Lanice conchilega may therefore increase species richness and abundance through habitat modification (Rabaut et al., 2007; Zuhlke, 2001). Dense aggregates of Lanice conchilega have the potential to enhance food supply to birds and fish due to increased biodiversity (Rabaut et al., 2010; Godet et al., 2008; Van Hoey et al., 2008; Callaway et al., 2010; De Smet et al., 2013).

Sensitivity assessment. The removal of non-target species may result in changes to the biological community and hence the classification of the assemblage type as assessed in the biotope. Incidental removal of Lanice conchilega would alter the biotope classification and most likely result in changes to the habitat and associated species. As Lanice conchilega is sedentary and present at the surface, resistance is ‘Low’ and resilience is ‘High’. Biotope sensitivity is therefore assessed as ‘Low’. This assessment considers the ecological effect of removal, the abrasion pressure assessment provides evidence for the robustness of tubes and the species may be resistant to removal by bottom trawls deployed at low intensity (e.g. single passes).