Source: https://www.marlin.ac.uk/habitats/detail/1125/polychaetes_in_littoral_fine_sand
Timestamp: 2019-04-24 16:41:20+00:00

Document:
Researched by Matthew Ashley Refereed by This information is not refereed.
The biotope LS.LSa.FiSa.Po occurs in moderately exposed or sheltered beaches of medium and fine, usually clean, sand, though the sediment may on rare occasions contain a small silt and clay fraction. The sediment is relatively stable, remains damp throughout the tidal cycle, and contains little organic matter. It is often rippled and typically lacks an anoxic sub-surface layer. Where an anoxic layer is present, it occurs at a depth below 10 cm and tends to be patchy. The biotope occurs mainly on the lower part of the shore, and relatively frequently on the mid shore. It is only rarely present above mid shore level, except where coastal defences cause backwash onto the upper shore. Conditions are usually fully marine, though the biotope can also occur in open lower estuarine conditions. The infaunal community is dominated by a range of polychaete species such as Nephtys cirrosa, Paraonis fulgens, Spio spp., Pygospio elegans, Ophelia rathkei and Scoloplos armiger. The presence of polychaetes may be seen as coloured burrows running down from the surface of the sediment, and Arenicola marina casts may be present on the sediment surface. The amphipods Bathyporeia spp. and Pontocrates arenarius frequently occur, and nemerteans are often present. On some North Wales shores, the presence of Arenicola species characterises the lowest part of the shore, with a range of species characteristic of the shallow sublittoral. These include sparsely distributed Echinocardium, Acrocnida brachiata, Ensis siliqua and Fabulina fabula. The Po biotope is split into three sub-biotopes, between which there can be a large degree of overlap. The bivalve Macomangulus tenuis sub-biotope, which is characterized by slightly more stable and fine sediments than the other two sub-biotopes. The infauna of this biotope may be affected significantly by seasonal changes in degree of wave exposure. During stormy winters, the sediment may become de-stabilised, leading to the disappearance of some macroinfaunal species. The lugworm Arenicola marina may be present occasionally, usually as a temporary recruitment and is likely to be washed out during storms (information from Connor et al. 2004).
The variant LS.LSa.FiSa.Po.Pful sub-biotope occurs mainly on the mid and lower shore of moderately wave-exposed coasts, with medium and fine clean sand which remains damp throughout the tidal cycle and contains little organic matter. The sediment is often rippled and typically lacks an anoxic sub-surface layer. Polychaetes make up the greater part of the community, and are dominated by Paraonis fulgens, Capitella capitata, Pygospio elegans, Ophelia rathkei and Eteone longa. The presence of polychaetes may be seen as coloured burrows running down from the surface of the sediment. Nemerteans may also be present. The amphipods Bathyporeia pilosa and Bathyporeia sarsi are often present.
The variant LS.LSa.FiSa.Po.Aten sub-biotope occurs on the mid and lower shore on moderately wave-exposed and sheltered coasts, with predominantly fine sand which remains damp throughout the tidal cycle. The sediment is often rippled, and an anoxic layer may occasionally occur below a depth of 10 cm, though it is often patchy. The infaunal community is dominated by the abundant bivalve Macomangulus tenuis together with a range of polychaetes. The presence of polychaetes may be seen as coloured burrows running down from the surface of the sediment. Polychaetes that are characterising for this biotope include Nephtys cirrosa, Paraonis fulgens and Spio filicornis. Burrowing amphipods Bathyporeia spp. may occur in some samples of this biotope.
The variant LS.LSa.FiSa.Po.Ncir biotope occurs mainly on the mid and lower shore on moderately wave-exposed and sheltered coasts, with medium to fine clean sand which remains damp throughout the tidal cycle and contains little organic matter. The sediment is not usually well sorted and may contain a fraction of coarse sand. It is often rippled and typically lacks an anoxic sub-surface layer. The polychaete infauna is dominated by Nephtys cirrosa, Magelona mirabilis, Spio martinensis, Spiophanes bombyx and Paraonis fulgens. The presence of polychaetes may be seen as coloured burrows running down from the surface of the sediment. Nemertean worms may be present. The amphipods Pontocrates spp. and Bathyporeia spp., as well as Cumopsis goodsiri and the shrimp Crangon crangon are typically present. The bivalve Macomangulus tenuis is scarce or absent.
The biotope LS.LSa.FiSa.Po occurs on moderately exposed or sheltered beaches of medium and fine, usually clean, sand, though the sediment may on rare occasions contain a small silt and clay fraction. The biotope occurs mainly on the lower part of the shore, and relatively frequently on the mid shore, remains damp throughout the tidal cycle and contains little organic matter.
The infaunal community is dominated by a range of polychaete species such as Nephtys cirrosa, Paraonis fulgens, Spio spp., Pygospio elegans, Ophelia rathkei and Scoloplos armiger. The amphipods Bathyporeia spp. and Pontocrates arenarius frequently occur, and nemerteans are often present. On some North Wales shores, the presence of Arenicola species characterizes the lowest part of the shore, with a range of species characteristic of the shallow sublittoral. These include sparsely distributed Echinocardium, Acrocnida brachiata, Ensis siliqua and Fabulina fabula. The Po biotope is split into three sub-biotopes, between which there can be a large degree of overlap. The bivalve Angulus tenuis sub-biotope, which is characterized by slightly more stable and fine sediments than the other two sub-biotopes (Conner et al. 2004).
Nephtys cirrosa, Paraonis fulgens, Spio spp., and Pygospio elegans are reviewed as characterizing species, although during stormy winters, the sediment may become de-stabilised, leading to the disappearance of some macroinfaunal species. The lugworm Arenicola marina may be present occasionally, usually as a temporary recruitment and is likely to be washed out during storms. Capitella capitella is also reviewed as it is a charctaerizing species of sub-biotopes in more exposed locations. Sub biotopes are mainly distinguished by chanegs in sediment grain size to either finer or coarser material and changes in silt fraction.
The variant LS.LSa.FiSa.Po.Pful sub-biotope occurs less often in sheltered locations but mainly on the mid and lower shore of moderately wave-exposed coasts. The medium and fine clean sand may contain less silt fraction but also remains damp throughout the tidal cycle and contains little organic matter. Polychaetes make up the greater part of the community, and are dominated by Paraonis fulgens, Capitella capitata, Pygospio elegans, Ophelia rathkei and Eteone longa. Nemerteans may also be present. The amphipods Bathyporeia pilosa and Bathyporeia sarsi are often present.
The variant LS.LSa.FiSa.Po.Aten sub-biotope occurs in similar conditions to .Po, on the mid and lower shore on moderately wave-exposed and sheltered coasts. This sub-biotope contains fine sand (in comparison to the mediuma nd fien sand with small silt content found in .Po. The infaunal community is dominated by the abundant bivalve Angulus tenuis together with a range of polychaetes. Polychaetes that are characterizing for this biotope include Nephtys cirrosa, Paraonis fulgens and Spio filicornis. Burrowing amphipods Bathyporeia spp. may occur in some samples of this biotope.
The variant LS.LSa.FiSa.Po.Ncir biotope occurs in the same position, mainly on the mid and lower shore on moderately wave-exposed and sheltered coasts. The seidment contains medium to fine clean sand, is not usually well sorted and may contain a fraction of coarse sand. The polychaete infauna is dominated by Nephtys cirrosa, Magelona mirabilis, Spio martinensis, Spiophanes bombyx and Paraonis fulgens. The presence of polychaetes may be seen as coloured burrows running down from the surface of the sediment. Nemertean worms may be present. The amphipods Pontocrates spp. and Bathyporeia spp., as well as Cumopsis goodsiri and the shrimp Crangon crangon are typically present. The bivalve Angulus tenuis is scarce or absent.
Therefore, the LS.LSa.FiSa.Po is characterized by the fine to medium sand in a moderately exposed to sheltered wave climate that remains damp throughout the tidal cycle but are occasionally affected by storms. The dominant fauna are polychaetes and mobile burrowing amphipods, although the abundance of bivalve Angulus tenuis varies between sub-biotopes. The sensitivity assessment is based on the sensitivity of the dominant polychaetes, and to a lesser extent the sensitivity of mobile amphipods and Angulus tenuis where appropriate.
Nephtys cirrosa is a relatively long-lived polychaete with a lifespan of six to possibly as much as nine years. It matures at one year and the females release over 10,000 (and up to 80,000 depending on species) eggs of 0.11-0.12 mm from April through to March. These are fertilized externally and develop into an early lecithotrophic larva and a later planktotrophic larva which spends as much as 12 months in the water column before settling from July-September. The genus Nephtys has a relatively high reproductive capacity and widespread dispersion during the lengthy larval phase. It is likely to have a high recoverability following disturbance (MES, 2010).
Paraonis fulgens, is a small polychaete, up to 3 cm in length. Paraonis fulgens displays growth and reproduction strategies typical of opportunistic species. It occurred in highly dynamic communities in German estuaries in a community of opportunistic species (Nehmer et al., 2003). Therefore, it is likely to show rapid recovery. Paraonis fulgens is thought to feed exclusively on benthic diatoms so that its abundance and recovery is likely to be affected by changes in levels of primary productivity (Gaston et al., 1992).
Spiophanes spp. (e.g. Spiophanes filicornis, Spiophanes martinensis, Spiophanes bombyx) have opportunistic life strategies (Kröencke, 1980; Niermann et al., 1990). They are characterized by small size, rapid maturation and short-lifespan of 1-2 years and produce large numbers of small propagules. It is often found at the early successional stages of variable, unstable habitats that it is quick to colonize following perturbation (Pearson & Rosenberg, 1978). For example, two years after dredging, the abundance of opportunistic species was generally elevated relative to pre-dredging levels and the communities were numerically dominated (50-70%) by Spiophanes bombyx (Gilkinson et al., 2005). Van Dalfsen et al. (2000) found that polychaetes recolonized a dredged area within 5-10 months (cited from Boyd et al., 2005) and their biomass was predicted to recover within 2-4 years.
Capitella capitata is a classic opportunist species possessing life history traits of rapid development, many reproductions per year, high recruitment and high death rates (Grassle & Grassle, 1974; McCall 1977).The Capitella species complex displays reproductive variability, planktonic larvae are able to colonize newly disturbed patches but after settlement the species can produce benthic larvae brooded within the adult tube to rapidly increase the population before displacement by more competitive species (Gray, 1979). Shull (1997) demonstrated that recolonization occurs by larval settlement, bedload transport and by burrowing. Thus, when conditions are suitable, the time for the community to reach maturity is likely to be less than six months. Bolam & Fernandes (2002) and Shull (1997) noted that Capitella capitata can colonize azoic sediments rapidly in relatively high numbers and experimental studies, using defaunated sediments, have shown that on small scales Capitella can recolonize to background densities within 12 days (Grassle &Grassle 1974; McCall 1977). In Burry Inlet, Wales, tractor towed cockle harvesting led to a reduction in density of some species but Capitella capitata had almost trebled its abundance within the 56 days in a clean sandy area (Ferns et al., 2000). In favourable conditions, maturity can be reached in <3 months and growth rate is estimated to be 3 cm per year. Adult potential dispersal is up to 1 km.
The polychaete Pygospio elegans has life history strategies that allow rapid colonization and population increase in disturbed and defaunated patches where there is little competition from other species. Pygospio elegansexhibit a number of reproductive strategies (a trait known as poecilogony). Larvae may develop directly allowing rapid population increase in suitable patches or they may have a planktonic stage (allowing colonization of new habitats). Experimental defaunation studies have shown an increase in Pygospio elegans, higher than background abundances within 2 months, reaching maximum abundance within 100 days (Van Colen et al. 2008). Following a period of anoxia in the Bay of Somme (north France) that removed cockles, Pygospio elegans increased rapidly but then decreased as cockle abundance recovered and sediments were disturbed by cockle movement (Desprez et al., 1992). Re-colonization of Pygospio elegans, was observed in 2 weeks by Dittmann et al. (1999) following a 1 month long defaunation of the sediment. However, McLusky et al. (1983) found that Pygospio elegans were significantly depleted for >100 days after harvesting (surpassing the study monitoring timeline). Ferns et al. (2000) found that tractor-towed cockle harvesting removed 83% of Pygospio elegans (initial density 1850 per m2). In muddy sand habitats, Pygospio elegans had not recovered their original abundance after 174 days (Ferns et al., 2000). These results are supported by work by Moore (1991) who also found that cockle dredging can result in reduced densities of some polychaete species, including Pygospio elegans. Rostron (1995) undertook experimental dredging of sandflats with a mechanical cockle dredger, including a site comprised of stable, poorly sorted fine sands with small pools and Arenicola marina casts with some algal growths. At this site, post-dredging, there was a decreased number of Pygospio elegans with no recovery to pre-dredging numbers after six months. Although numbers may be depleted in the short-term the evidence suggests that Pygospio elegans is likely to recvoer within two years.
All three sub-biotopes may contain amphipods of the genus Bathyporeia. Bathyporeia spp. are short lived, reaching sexual maturity within 6 months with 6-15 eggs per brood, depending on species. Reproduction may be continuous (Speybroeck et al., 2008) with one set of embryos developing in the brood pouch whilst the next set of eggs is developing in the ovaries. However, specific reproductive periods vary between species and between locations (Mettam, 1989) and bivoltine patterns (twice yearly peaks in reproduction) have been observed (Mettam, 1989; Speybroeck et al., 2008). Adult amphipods are highly mobile in the water column and recolonization by the adults is likely to be a significant recovery pathway. The life history traits of rapid sexual maturation and production of multiple broods annually support rapid local recolonization of disturbed sediments where some of the adult population remains.
Resilience assessment. The biotope is characterized by opportunistic polychaetes and mobile amphipods that are characteristic of biotopes subject to natural and/or anthropogenic disturbance. Biotope resilience is considered to be High as populations of the characterizing species are likely to recover within two years, even after severe depletion of the resident populations or community, unless the substratum or other key habitat factors are altered.
Intertidal species are exposed to extremes of high and 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. In winter air temperatures are colder than the sea, conversely in summer air temperatures are much warmer than the sea. Species that occur in the intertidal are therefore generally adapted to tolerate a range of temperatures, with the width of the thermal niche positively correlated with the height of the shore that the animal usually occurs at (Davenport & Davenport, 2005). The geographic distribution of species characteristic of this biotope extend south of the British Isles, further suggestinfg these species are likely to be resistant to an increase in temperature. Infaunal species are likely to be protected to some extent from direct effects of acute increases in temperature by sediment buffering, although increased temperatures may affect infauna indirectly by stimulating increased bacterial activity and increased oxygen consumption.
Emery & Stevensen (1957) reported that Nephtys spp. could withstand summer temperatures of 30-35°C so is likely to withstand the benchmark acute temperature increase. An acute increase in temperature at the benchmark level may result in physiological stress endured by the infaunal species but is unlikely to lead to mortality. Nephtys cirrosa is an active worm that can swim short distances and, therefore, it could avoid short-term changes in temperature by migrating away from localised warmer spots.
No direct evidence was found to assess the sensitivity of Paraonis fulgens, however, this species is recorded in warmer waters than the UK in the Gulf of Mexico. Paraonis fulgens was one of the most abundant macrobenthic organisms collected in the shallow waters off Perdido Key, Florida, where winter water temperatures average 22 °C (Gaston et al. 1992). Angulus tenuis is found off the Norwegian coasts to the Mediterranean and north-west coast of Africa and is likely to be resistant to temperature changes at the pressure benchmark.
Spiophanes bombyx is found in the Mediterranean (Hayward & Ryland, 1995), which is likely to be warmer than the waters around Britain and Ireland.
Capitella capitata is a cosmopolitan species in coastal marine and estuarine soft sediment systems. The global population is actually made up of several genetically distinct (and apparently genetically isolated) sibling species whose distributions overlap such that local Capitella capitata populations actually consist of a number of co-occurring sibling species (Grassle & Grassle, 1976). Within the complex tolerances may vary and local acclimation is possible. Capitella capitata has also been recorded in extreme environments around hydrothermal vents (Gamenick & Giere, 1997), which suggests that the species complex would be relatively tolerant to an increase in temperature.Experimental evaluation of the effects of combinations of varying salinities and temperature on Capitella capitata were carried out by Redman (1985) and Warren (1977). Redman (1985) found that, length of life decreased as follows: 59 weeks at mid-temperature and salinity (15°C, 25ppt); 43 weeks at high temperature & high salinity (18°C, 30 ppt); 33 weeks at lower temperature & high salinity (12°C, 30 ppt); 17 weeks at high temperature and low salinity (18°C, 20ppt). Redman (1985) also found that net reproduction (Ro: the mean number of offspring produced per female at the end of the cohort) decreased as follows: 41.75 control; 36.69 under high salinity, high temperature; 2.19 high temperature, low salinity; 2.16 low temperature, high salinity. Therefore, a combination of changes in temperature and salinity may decrease the viability of the population. Warren (1977) used individual worms collected from Warren Point (south-west England) to test response to high and low temperatures. Worms were acclimated to 10°C for 10 days and subsequently heated in a water bath at 1°C per 5 min. When the temperature had reached 28°C worms were removed at 0.5°C intervals and returned to a constant temperature of 10°C. The percentage mortality after 24 h was calculated. Larvae were removed from the maternal tube and tested using the same method. The experiments indicated that temperatures above 30°C were most critical; the upper lethal temperature was 31.5°C for adult worms and a little higher for the larvae.
Intertidal species are exposed to extremes of high and 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. In winter air temperatures are colder than the sea, conversely in summer air temperatures are much warmer than the sea. Species that occur in the intertidal are therefore generally adapted to tolerate a range of temperatures, with the width of the thermal niche positively correlated with the height of the shore that the animal usually occurs at (Davenport & Davenport, 2005). Some of the characterizing species are found in colder waters that the UK suggesting these can tolerate colder waters than typically encountered. Paraonis fulgens occurs in colder waters than Irish and UK seas, such as the Bay of Fundy, Canada where winter temperatures are between 0 and 4 °C (Risk & Tunnicliffe 2006). Spiophanes bombyx is found in water off Denmark (Thorson, 1946) which are likely to be colder than British and Irish waters.Angulus tenuis is found off the Norwegian coasts to the Mediterranean and north-west coast of Africa and is likely to be resistant to temperature changes at the pressure benchmark. However, Nephtys cirrosa reaches its northern limit in Scotland, and German Bight of the North Sea. A decrease in temperature may result in loss of the species from the biotope in these areas.
Wu et al. (1988) collected Capitella capitata individuals at seawater temperatures of -2° that harboured mature oocytes indicating reproductive activity even under low temperatures.Warren (1977) used Capitella captitata adults collected from Warren Point (south-west England) to test response to high and low temperatures. Worms were acclimated to 10°C for 10 days prior to testing. The worms were cooled in a water bath to experience a decrease in temperature of 1 °C per 5 min. When the final temperature was reached worms were removed at 0.5 °C intervals and returned to a constant temperature of 10 °C. The percentage mortality after 24 h was calculated. Each experiment was repeated once. Larval Capitella capitata were removed from the maternal tube and tested using the same method. Both adults and larvae of Capitella capitata were tolerant of low temperatures, 50 % of the adults and 65 % of the larvae surviving at - 1°C.
Crisp (1964) reported that species of amphipod seemed to be unharmed by the severe winter of 1962-1963. This may be due to burial in sediments buffering temperature or seasonal migration to deeper waters to avoid freezing. In the winter migrations have also been observed for Bathyporeia spp. (Fish & Fish, 1978; Fish & Preece, 1970). Preece (1971) tested temperature tolerances of Bathyporeia pilosa in the laboratory. Individuals acclimated to 15°C for 24 hours were placed in a freezer in wet sediment. As test temperatures were reached individuals were removed and allowed to recover for 24 hours at which point mortalities were tested. Amphipods were also allowed to bury into sediments and held at test temperatures of -1°C, -3°C and -5°C for 24 hours before being allowed to recover in fresh seawater at 15°C for a further 24 hours before mortalities were assessed. The lower lethal short-term tolerances of Bathyporeia pilosa were -13.6°C. Bathyporeia pilosa individuals could withstand temperatures as low as -1°C for 24 hours, at -3°C, 5% of Bathyporeia pilosa died but this rose to 82% at -5°C.
Sensitivity assessment..Typical surface water temperatures around the UK coast vary seasonally from 4-19°C (Huthnance, 2010). A chronic decrease in temperature throughout the year of 2°C may fall within the normal temperature variation but an acute decrease in water temperatures from 4°C to -1°C at the coldest part of the year may lead to freezing and lethal effects but may be tolerated by the characterizing species through deeper burrowing and/or migration. However, the abundance of Nephtys cirrosa may be reduced in northern examples of the biotope or severe winters. Therefore, biotope resistance is assessed as Medium. However, resilience is probably ‘High’ and sensitivity is assessed as Low.
This biotope is found in full salinity (30-35 ppt) habitats (18-35 ppt) (JNCC, 2015). A change at the pressure benchmark is therefore assessed as a change to hypersaline conditions (>40 ppt) from full salinity. Little evidence was found to assess responses to hypersalinity. However, monitoring at a Spanish desalination facility where discharges close to the outfall reached a salinity of 53, found that amphipods were sensitive to the increased salinity and that species free-living in the sediment were most sensitive (De-la-Ossa-Carretero et al., 2016). Roberts et al. (2010) concluded that the reported effects of brine discharges were limited and difficult to compare but identified some trends. Hypersaline effluents tend to disperse quickly in well flushed environments like the habitat this biotope occurs in. However, sediment communities were affected in the immediate vicinity of brine discharges. For example, one of the studies reviewed found that the sediment became dominated by nematodes, with polychaetes, crustaceans and molluscs only fond at a distance from the outfall. Another study noted that the diversity of polychaete communities decreased adjacent to the outfall, and that the Ampharetidae were the most sensitive while the Paranoidae were the least sensitive.
Sensitivity assessment. No direct evidence was found to assess biotope sensitivity. However, if the biotope was exposed to hypersaline effluents then a proportion of the community may be lost and species diversity and abundances are likely to decrease. Therefore, a biotope resistance of Low is suggested. Resilience is probably High (following restoration of the usual salinity regime) so that sensitivity is assessed as Low.
The biotope occurs in full salinity in approximately 80% of the records. A decrease in salinity to reduced is likely to lead to changes between sub-biotopes. LS.LSa.FiSa.Po.Ncir and LS.LSa.FiSa.Po.Pful occur in full and variable salinities, and occupy a greater range of salinities (<18 to 35 ppt),and may increase their distribution.
Sensitivity assessment Nephtys cirrosa is possibly the more sensitive to the lower range of the ‘variable’ or ‘reduced’ salinity category, although as a mobile species it will be resistant through being able to move lower down the shore or away from freshwater run-off. Nephtys cirrosa displays resistance to the pressure as the species occur at the mouths of estuaries and estuarine lagoons where salinity may fall below 20 psu (Barnes, 1994), so are unlikely to be significantly impacted by a reduction in salinity. Resistance and resilience are both ‘High’ and sensitivity is therefore, ‘Not sensitive’.
The biotope and sub biotopes occur on moderately exposed or sheltered beaches. Tidal flow velocities from very weak to moderately strong occur in the biotope LS.LSa.FiSa.Po suggesting changes in flow velocity at the benchmark level are unlikely to impact the biotope as characterizing species are likely to be resistant to a very weak to moderately strong flow velocities. Changes in flow velocity are more likely to lead to changes between sub-biotopes. For instance, 21% of records of LS.LSa.FiSa.Po.Ncir occur in moderately strong flow velocities compared to 8% of records of LS.LSa.FiSa.Po.Pful (Paraonis fulgens, Capitella capitata, Pygospio elegans) suggesting a change to LS.LSa.FiSa.Po.Ncir (Nephtys cirrosa, Magelona mirabilis, Spio martinensisI), sub-biotope is more likely under an increase in flow velocity.
A decrease in emergence may allow the biotope to extend up the shore is suitable habitat exists. However, a decreased in emergence may result in drying of sediment between tides at the upper limit of the biotope, and result in an extension o the BarSa biotope (Connor et al., 2004).
Sensitivity assessment. Increased emergence is likely to reduce the upper limit of the intertidal LS.LSa.FiSa.Po biotope. Although the individual polychaete species would probably migrate down the shore, the upper extent of the biotope may be lost. Therefore, a resistance of Medium is suggested. Resilience is probably High so sensitivity is assessed as Low.
The biotope and sub biotopes occur on moderately exposed or sheltered beaches. Increases and decreases in wave exposure may lead to increased erosion or deposition. Species in moderately exposed examples of the biotope are likely to be resistant to the dynamic nature of substratum.
Increased wave exposure is likely to resuspend finer material and may lead to reduced abundance of species, such as Capitella capitata that are absent when there is no mud content in the substratum. The circulatory motion of wave action may also wash infauna such as Nepthys cirrosa and Capitella capitata from the sediment in most exposed locations. Although increased wave action is likely to wash some individuals from the sediment, recovery would be rapid.
Sensitivity assessment. An increase in wave height at the benchmark level is unlikely to create a noticeable impact, where initial conditions are sheltered. Where conditions are moderately exposed, infauna such as Nepthys cirrosa are likely to be washed from the sediment by the largest waves. However, the biotope was reported to be naturally disturbed by winter storms (Connor et al., 2004) and a 3-5% change in significant wave height (the benchmark) is unlikely to affect the biotope adversely Therefore, resistance and resilience are assessed as ‘High’, and the biotope is assessed as , ‘Not Sensitive’ at the benchmark level.
Levels of contaminants that exceed the pressure benchmark may cause impacts. Bryan & Gibbs (1983) reported lower sediment-metal concentrations in sandy areas than mud near the mouth of Restronguet Creek, a branch of the Fal Estuary system which is heavily contaminated with metals. Although heavy metals may not accumulate in the substratum to the extent that they would in muddy substrata, characterizing infauna are likely to be susceptible. Bryan & Gibbs (1983) suggested that in populations of polychaetes exposed to heavy metal contamination for a long period, metal resistance could be acquired. For example Nephtys hombergii from Restronguet Creek seemed able to regulate copper. The head end of the worm became blackened and x-ray microanalysis by Bryan & Gibbs (1983) indicated that this was caused by the deposition of copper sulphide in the body wall. In the same study, Bryan & Gibbs (1983) presented evidence that Nephtys hombergii from Restronguet Creek possessed increased tolerance to copper contamination. Specimens from the Tamar Estuary had a 96 h LC50 of 250 µg/l, whilst those from Restronguet Creek had a 96 h LC50 of 700 µg/l (35 psu; 13°C).
Contamination at levels greater than the pressure benchmark may adversely influence the biotope. Suchanek (1993) reviewed the effects of oil spills on marine invertebrates and concluded that, in general, on soft sediment habitats, infaunal polychaetes, bivalves and amphipods were particularly affected.
Oil spills resulting from tanker accidents have caused deterioration of sandy communities in the intertidal and shallow sublittoral. Subtidal sediments, however, may be at less risk from oil spills unless oil dispersants are used, or if wave action causes dispersion of oil into the water column and sediment mobility drives oil in to the sediment (Elliott et al., 1998). Microbial degradation of the oil within the sediment would increase the biological oxygen demand and oxygen within the sediment may become significantly reduced.
Species within the biotope have been reported to be intolerant of oil pollution, e.g. amphipods (Suchanek, 1993). After the Amoco Cadiz oil spill there was a reduction in both the number of amphipod species and the number of individuals (Cabioch et al., 1978). Initially, significant mortality would be expected, attributable to toxicity. Amphipod populations have been reported not return to pre-spill abundances for five or more years, which is most likely related to the persistence of oil within sediments (Southward, 1982). Nephtys species were amongst the fauna that was eradicated from sediments following the 1969 West Falmouth spill of Grade 2 diesel fuel documented by Sanders (1978).
Multivariate analysis showed that the Prestige oil spill scarcely affected the macroinfaunal community structure during the study period (2003-2009) and its effect was limited just to the first campaign (2003), six months after the Prestige accident (Junoy et al., 2013). Opportunistic species such Capitella capitata have been shown to increase in abundance close to sources of contamination. High numbers of Capitella capitata have been recorded in hydrocarbon contaminated sediments (Ward & Young, 1982; Olsgard, 1999; Petrich & Reish, 1979) and colonization of areas defaunated by high hydrocarbon levels may be rapid (Le Moal, 1980). After a major spill of fuel oil in West Virginia Capitella capitata increased dramatically alongside large increases in Polydora ligni and Prionospio sp. (Sanders et al. 1972, cited in Gray 1979).
Boon et al. (1985) reported that Nephtys species in the North Sea accumulated organochlorines but, based on total sediment analyses, organochlorine concentrations in Nephtys species were not correlated with the concentrations in the (type of) sediment which they inhabited.
No information concerning the reduced oxygen tolerance of Nephtys cirrosa was found but evidence (Alheit, 1978; Arndt & Schiedek, 1997; Fallesen & Jørgensen, 1991) indicated a similar species, Nephtys hombergii, to be very tolerant of episodic oxygen deficiency and at the benchmark duration of one week. Nephtys cirrosa and Spio spp. were classified by Borja et al. (2000) as being indifferent to enrichment, suggesting some resilience to de-oxygenation. Dense Capitella capitata populations are frequently located in areas with greatly elevated organic content, even though eutrophic sediments are often anoxic and highly sulfidic (Tenore 1977; Warren 1977; Tenore & Chesney 1985; Bridges et al. 1994). The polychaetes Capitella capitata, Pygospio elegans and Scoloplos armiger have all been reported to recolonize habitats following periods of anoxia and hypoxia.
Scoloplos armiger has been described as being present in low oxygen areas and as a dominant species in the recolonization of previously anoxic areas (Pearson & Rosenberg, 1978). Intertidal Scoloplos armiger is, in contrast to subtidal specimens, subject to hypoxia when tidal flats are without oxygenated seawater during low tide (Kruse et al., 2004). Tolerance against hypoxia and sulfide is low (Kruse et al., 2004), and worms may ascend into the oxic layer during low tide (Schoettler & Grieshaber, 1988). Capitella capitata exhibits a relatively high tolerance for sediment hypoxia, hydrogen sulphide concentration, and other sediment conditions avoided by many infauna (Henriksson, 1969). Forbes & Lopez (1990) experimentally demonstrated that reduced oxygen concentrations (pO2 = 20 mm Hg or less) led to decreased Capitella capitata growth rates and cessation of burrowing and feeding activity even when an abundance of food was provided. The authors hypothesize that animals rely solely on anaerobic metabolism once this threshold is crossed. Magnum & Van Winkle (1973) similarly observed that Capitella capitata oxygen uptake ceased when pO2 fell to between 0-34 mm Hg. The fact that experimental worms lost body mass under these conditions supports the contention that full aerobic metabolism cannot be sustained at very low ambient oxygen conditions despite a very high affinity of Capitella capitata haemoglobin for oxygen. Diaz & Rosenberg (1995) listed Capitella capitata as resistant of moderate hypoxia.
Sensitivity assessment. The species characterizing the biotope are mobile and able to migrate vertically to escape unsuitable conditions. The biotope is characterized by well sorted and oxygenated sands, where the anoxic layer occurs below 10 cm and is patchy where it occurs (Connor et al., 2004). This suggests that the resident species may not be adapted to low oxygen levels but also that deoxygenation of the water column may be short-lived, especially as the biotope is exposed at low tide. Therefore, while some members of the community are known to be tolerant, other species may be lost or reduced in abundance and a resistance of Medium is suggested. ‘Resilience is probably ‘High’ ( and sensitivity is assessed as Low. However, hypoxia or anoxia caused by the bacterial decomposition of organic matter may be detrimental.
In-situ primary production is limited to microphytobenthos within and on sediments and the high levels of sediment mobility may limit the level of primary production as abrasion would be likely to damage diatoms (Delgado et al., 1991).
Benthic responses to organic enrichment have been described by Pearson & Rosenberg (1978) and Gray (1981). In general, moderate enrichment increases food supply and increases productivity and abundance. Nephtys cirrosa and Spio spp. were classified by Borja et al. (2000) as being indifferent to enrichment. Dense Capitella capitata populations are frequently located in areas with greatly elevated organic content such as areas of sewage disposal and below fish farms and mussel long lines, even though eutrophic sediments are often anoxic and highly sulfidic (Gray, 1979; Tenore, 1977; Warren, 1977; Tenore & Chesney, 1985; Bridges et al., 1994; Haskoning, 2006; Callier et al., 2007).
Sensitivity assessment.At the benchmark levels, resistance was assessed as ‘High’ as the main characterizing species are tolerant of organic enrichment and an input at the pressure benchmark is considered unlikely to lead to gross pollution effects . A resilience of ‘High’ is assigned (by default) and the biotope is assessed as ‘Not sensitive’.
All marine and estuarine habitats and benthic species within them 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.
A change to natural or artificial hard substratum would remove this sedimentary biotope and the species. If pockets of fine sediment accumulate in pockets within the substrata then these areas may be re-colonised by species associated with this biotope but these pockets of sediment would not be equivalent to the biotope. Recovery will depend on the re-instatement of suitable habitat.
Sensitivity assessment. Based on the loss of suitable habitat, biotope resistance to this pressure is assessed as ‘None’. Resilience is assessed as ‘Very low’ as the pressure benchmark refers to a permanent change. Biotope sensitivity is therefore ‘High’.
The benchmark for this pressure refers to a change in one Folk class. The pressure benchmark originally developed by Tillin et al., (2010) used the modified Folk triangle developed by Long (2006) which simplified sediment types into four categories: mud and sandy mud, sand and muddy sand, mixed sediments and coarse sediments. The change referred to is, therefore, a change in sediment classification rather than a change in the finer-scale original Folk categories (Folk, 1954). The change in one Folk class is considered to relate to a change in classification to adjacent categories in the modified Folk triangle (Long, 2006). As this biotope occurs within fine sands and muddy sands (JNCC, 2015), the change at the pressure benchmark refers to a potential change to coarse sediments, mixed sediments, sand and muddy sands or mud.
The particle size of sediments and correlated physical and chemical factors (such as drainage, organic matter content and hydrodynamic regime), is a key determinant of the structure of benthic invertebrate assemblages (Van Hoey et al., 2004; Yates et al., 1993). Infauna can be affected by changes in sediment as many are adapted to burrow through certain grades of sediment (Trueman & Ansell, 1969), decreased fine fractions will reduce habitat suitability for species that maintain permanent burrows. Changes in sedimentary features may also influence the proportions of suspension and deposit feeding animals (Sanders, 1968), with deposit feeders favoured by increases in the proportion of silts and clays. In North America, cultivation of clam species including the Manila clam, Tapes philippinarum usually involves some form of habitat modification in the form of adding gravel or gravel and crushed shell over mud and sand beaches, to create a more productive clam habitat (referred to as ‘gravelled clam plots’). Such habitat modifications lead to alterations in the local environment and consequently faunal composition. Simenstad and Fresh (1995, cited in Kaiser & Beadman, 2002) reported that the application of gravel to intertidal sediments resulted in a shift from a polychaete to a bivalve and nemertean dominated community, but emphasised that changes are likely to be site-specific.
Responses are also likely to be species-specific and depend on habitat preferences. Pygospio elegans prefers fine sediments such as sand and mud; increased sediment coarseness is likely to render sediments unsuitable for this species. Empirical evidence supporting this view is provided by Bolam (1999) where experimental manipulation of sediments by implanting macroalgae mats led to increased fine sediment fractions (with associated increased organic and water content) which led to the establishment of Pygospio elegans.Capitella capitata was found in fine and medium grain size sediments and was almost completely absent in sediments without mud in the Belgium part of the North Sea (Degraer et al., 2006). This suggests that a change to muddy sand is likely to result in increased abundance but a change to coarser or gravelly sand is likely to lead to reduced abundance.
Nepthys cirrosa occurs in fine to coarser sands, with greatest abundance in the Belgium part of the North Sea recorded in medium grain sizes (Degraer et al., 2006). A change to gravelly sand is unlikely to impact the species, however a change to muddy sand may limit the species abundance as the species displays a slight preference for low mud content levels < 10% (Degraer et al., 2006).
Changes to finer sand are likely to result in increased abundance of Angulus tenuis and changes to the sub-biotope LS.LSa.FiSa.Po.Aten, particularly in the low intertidal where the substratum remains damp at low tide.
Sensitivity assessment. Individual members of the community are found in a range of different sediment types, at different abundances. The character of the habitat is largely determined by the sediment type, changes to this would lead to habitat re-classification. The addition of coarse sand particles or fine particles in sufficient quantities would lead to the development of a different habitat type. Changes in sediment characteristics can lead to changes in community structure. An increase in coarse sediments would lead to the development of a community typical of mixed sediments, clean sands and/or gravels depending on the degree of change. In general, an increase to very coarse sediments may favour some amphipod species rather than burrowing polychaetes and sessile tube-dwelling polychaetes. This change would alter the character of the biotope present leading to re-classification, biotope resistance is assessed as 'None' and, as the change is permanent, resilience is assessed as 'Very Low'. Biotope sensitivity is therefore 'High'.
The process of extraction is considered to remove all biological components of the biotope group. If extraction occurred across the entire biotope, loss of the biotope would occur. Recovery would require substratum to return to sand and with a finer silt fraction.
Sensitivity assessment. Resistance of the biotope to extraction is probably ‘None’. Resilience differs between species with slower recovery likely to be displayed by Nephtys cirrosa. Resilience is assessed as ‘High’ (although if the substratum changed recovery could be prolonged) and biotope sensitivity is assessed as ‘Medium’.
This biotope is present in disturbed and well sorted sands, the associated species are generally present in low abundances and adapted to frequent disturbance. Therefore, resistance to surface abrasion is probably ‘High’. The polychaete Nephtys cirrosa is adapted to life in unstable sediments and survives through rapid burrowing (McDermott, 1983, cited from Elliott et al., 1998). This characteristic is likely to protect this species from surface abrasion.
Paraonis fulgens were found to reduce in abundance in experimental areas exposed to trampling (Reyes-Martínez et al., 2015), suggesting a lower resistance of this species to abrasion or surface disturbance. Chandrasekara and Frid (1996) found that some species including Capitella capitata and Scoloplos armiger reduced in abundance in intertidal muds,along a pathway heavily trampled for five summer months (ca 50 individuals a day Bonsdorff & Pearson (1997) found that sediment disturbance forced Capitella capitata deeper into the sediment, although the species was able to burrow back through the sediment to the surface again.Juveniles and adults of Scoloplos armiger stay permanently below the sediment surface and freely move without establishing burrows. While juveniles are only found a few millimeters below the sediment surface, adults may retreat to 10 cm depth or more (Reise, 1979; Kruse et al., 2004) and are likely to be more protected. The egg cocoons are laid on the surface and hatching time is 2-3 weeks during which these are vulnerable to surface abrasion.
A number of studies have assessed the effects of trampling on other intertidal amphipods and these assessments are used as a proxy. Comparisons between shores with low and high levels of trampling found that the amphipod Bathyporeia pelagica is sensitive to human trampling, other species including Pontocrates arenarius and the isopod Eurydice affinis also decreased in response to trampling but Bathyporeia pelagica appeared to be the most sensitive (Reyes-Martínez et al., 2015). Changes in abundance of talitrid amphipods on urban beaches subject to high levels of recreational use was also observed by Bessa et al. (2014), this study compared abundances between samples taken ten years apart and thus the trends observed were not directly attributable to trampling vs beach cleaning or other pressures although they illustrate a general trend in density patterns as recreational use increases. Ugolini et al. (2008) carried out a controlled trampling experiment on Talitrus saltator. Plastic cylinders of 110 cm diameter (area 0.95 m2) were placed in the sand and all individuals trapped and counted, and 400 steps were made in a cylinder in 15 minutes after the amphipods had reburied. The trampling rate was based on observed number of beach users and therefore represents a realistic level of exposure. Alive individuals were counted at the end of the experiment and 24 hours after. Trampling significantly reduced abundance of the amphipods and after 24 hours the percentage of surviving amphipods dropped to almost zero, while survival rates of control (untrampled) amphipods were unaffected. Abrasion and compaction can, therefore, kill buried amphipods within sediments.
Sensitivity assessment. The characterizing species Paraonis fulgens Capitella capitata and Scoloplos armiger are reduced following abrasion impacts (trampling). However, species in the biotope are adapted to disturbance. Resistance is assessed as ‘Medium’, Resilience of Capitella capitata and other opportunistic species is higher but Nephtys cirrosa is likely to show longer recovery times, overall resilience is assessed as ‘High’, although the potential for longer recovery of Nephtys cirrosa should be accounted for. Sensitivity is, therefore, assessed as ‘Low’.
Nephtys cirrosa and Spiophanes bombyx were characterizing species of infauna assemblages in both control and impact sample sites on the Thornton Bank Belgium (North Sea), before and after dredging occurred as part of the construction process for an offshore wind farm (Coates et al. 2015). Recovery of assemblages occurred within one to two years at individual dredged sites. The species potentially display resilience to dredging activities as past aggregate dredging had also occurred before wind farm construction.
Nephtys cirrosa was found to be sensitive to experimental trawling disturbance over 18 months (Tuck et al., 1998). Nephtys cirrosa is also likely to be vulnerable to dredging but can probably accommodate limited sediment deposition from the dredging process (MES, 2010).
Collie et al. (2000) found that abundance of Nephtys hombergii was negatively affected by fishing activities. Mean response of infauna and epifauna communities to fishing activities was also much more negative in mud and sand communities (such as this biotope) than other habitats. Nephtys hombergii abundance also significantly decreased in areas of the Solent, UK, where bait digging had occurred (Watson et al. 2007). Similarly, Nephtys hombergii abundance was reduced by 50% in areas where tractor towed cockle harvesting was undertaken on experimental plots in Burry inlet, south Wales, and had not recovered after 86 days (Ferns et al., 2000).
Capitella capitata, are soft bodiedrelatively fragile species inhabiting mucus tubes close to the sediment surface. Abrasion and compaction of the surficial layer may damage individuals. Capitella capitata and Pygospio elegans were categorised as AMBI fisheries Group IV- as ‘second-order opportunistic species, which are sensitive to fisheries in which the bottom is disturbed. Their populations recover relatively quickly however and benefit from the disturbance, causing their population sizes to increase significantly in areas with intense fisheries’ (Gittenberger & Van Loon 2011).
Spio filicornis is a soft bodied organism that exposes its palps at the surface while feeding. It lives infaunally in sandy sediment and any physical disturbance that penetrates the sediment, for example dredging or dragging an anchor, would lead to physical damage of Spio filicornis. However, adult worms can burrow up to 10 cm and may escape the disturbance. Juveniles can only burrow up to 2 cm into the sediment and are likely to be affected. However, individuals are likely to pass through a passing scallop dredge due to their small size. Bergman and Hup (1992) reported that the total density of spionids actually increased with increased fishing disturbance presumably due to their ability to colonize newly exposed substratum. Hall et al. (1990) investigated the impact of hydraulic dredging for razor clams. They reported that any effects only persisted for a short time, with the community restored after approximately 40 days in stormy conditions. The population density of Spio filicornis was slightly reduced in the dredged site relative to the control site but its abundance had increased over that of the control site after 40 days. However, the control site showed a similar level of variation in abundance.
Bergman and Hup (1992) found that worm species (including Scoloplos armiger) showed no change in total density after trawling a subtidal habitat. Conversely, a later study by Bergman and Santbrink (2000) found that the direct mortality of Scoloplos armiger from a single passage of a beam trawl in subtidal silty grounds was 18% of the population. Rostron (1995) undertook experimental dredging of sandflats with a mechanical cockle dredger, including a site comprised of stable, poorly sorted fine sands with small pools and Arenicola marina casts with some algal growths. At this site, post-dredging Scoloplos armiger had disappeared from some dredged plots. Fernset al. (2000) used a tractor-towed cockle harvester, to extract cockles from intertidal plots of muddy sand and clean sand, to investigate the effects on non-target organisms; 31% of the population of Scoloplos armiger (initial density of 120 per m2) were removed. Populations of Scoloplos armiger remained significantly depleted in the area of muddy sand for more than 50 days after harvesting. Ball et al. (2000) found that species includingScoloplos armiger showed a significant decrease in abundance of between 56-27% after 16 months of otter trawling at a previously unfished Scottish sea loch. Chandrasekara and Frid (1996, cited in Tyler-Walters & Arnold, 2008) found that along a pathway heavily used for five summer months (ca. 50 individuals day-1), Scoloplos armiger reduced in abundance. Recovery took place within 5-6 months. These studies suggest that Scoloplos armigeris likely to be impacted by sediment disturbance and that recovery to previous densities may require more than two years.
A number of studies have found that the abundance of the polychaete Pygospio elegans is reduced by simulated cockle dredging (Hall & Harding, 1998; Moore, 1990; Ferns et al., 2000; Rostron, 1995). Ferns et al. (2000) found that tractor towed cockle harvesting removed 83% of Pygospio elegans (initial density 1850/ m2). In muddy sand habitats, Pygospio elegans had not recovered to the original abundance after 174 days (Ferns et al.,2000). Rostron (1995) also found that Pygospio elegans had not recovered to pre-dredging numbers after six months. Conversely, Hall & Harding, (1998) found that abundance of Pygospio elegans increased significantly over 56 days following suction dredging. Pygospio elegans inhabits a fragile tube that projects above the sediment surface and is probably more vulnerable to physical disturbance and abrasion than other, more deeply buried, infaunal species.
Sensitivity assessment. 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. Resistance of the biotope is assessed as ‘Low’, as a proportion of the population of characterizing species may be removed, however, species in the biotope are adapted to disturbance and recover quickly Hence, resilience is assessed as ‘High ’, and sensitivity is assessed as ‘Low’.
The characterizing species live within the sand and are unlikely to be directly affected by an increased concentration of suspended matter in the water column. Within the mobile sands habitat storm events or spring tides may re-suspend or transport large amounts of material and therefore species are considered to be adapted to varying levels of suspended solids. Bathyporeia spp. feed on diatoms within the sand grains (Nicolaisen & Kanneworff, 1969), an increase in suspended solids that reduced light penetration could alter food supply. However, diatoms are able to photosynthesize while the tide is out and therefore a reduction in light during tidal inundation may not affect this food source, depending on the timing of the tidal cycle. Bathyporeia spp. may be regular swimmers within the surf plankton, where the concentration of suspended particles would be expected to be higher (Fincham, 1970a).
However, the biotope is characterized by a low amount of organic matter and an increase in suspended solids may cause a change in this factor if this is coupled with changes in hydrodynamics that reduce particle re-suspension. Increased suspended solids are unlikely to have a direct impact on infauna but increased organic matter may result in an increase in the abundance of opportunistic species such as Capitella capitella. Biotope resistance is assessed as ‘High’ and resilience as ‘High’ (by default), so that the biotope is assessed to be ‘Not sensitive’.
The characterizing 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 pseudo faeces (Sornin et al., 1983; Deslous-Paoli et al., 1992; Mitchell, 2006 and Bouchet & Sauriau, 2008). Pygospio elegans is known to decline in areas following re-deposition of very fine particulate matter (Rhoads & Young, 1971; 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).
Mobile and/or burrowing species (including molluscs and polychaetes such as Nephtys spp., and Scoloplos armiger) are generally considered to be able to reposition following periodic siltation events or low levels of chronic siltation. Nepthys cirrosa occurs in fine to coarser sands, with greatest abundance in the Belgium part of the North Sea recorded in medium grain sizes (Degraer et al., 2006). A light deposition of fine sediment may lead to small but insignificant changes in abundance as it will reduce the available preferred habitat with medium grain size. As the tidal flow is strong in this biotope, a light deposition of finer sediment is likely to be resuspended. Resistance is likely to be high for Nepthys cirrosa at the benchmark level as this species is likely to be able to reposition within sediments.
Capitella capitata was categorised as AMBI sedimentation Group IV as a ‘second-order opportunistic species, insensitive to higher amounts of sedimentation. Although they are sensitive to strong fluctuations in sedimentation, their populations recover relatively quickly and even benefit. This causes their population sizes to increase significantly in areas after a strong fluctuation in sedimentation’ (Gittenberger & Van Loon 2011).
Sensitivity assessment. None of the characterizing species are considered likely to be significantly impacted by deposition of up to 5 cm of fine material. Resistance is assessed as ‘High’. Resilience as ‘High’ and Sensitivity as ‘Not sensitive’.
Nephtys cirrosa is a large infaunal species, with adult size between 6 cm and 10 cm and capable of moving through the sediment, suggesting some resilience to smothering. Nephtys cirrosa is an active worm which demonstrates the characteristic swimming motion (a rapid lateral wriggling, starting from the rear and increasing in amplitude towards the head) of the Nephtyidae. Deposition of up to 30 cm of fine material is likely to bury some individuals beyond the typical 5 to 15 cm depth of tunnels. It is likely Nephtys cirrosa close to the surface may be capable of relocating in the sediment although feeding and reproduction activities are likely to be interrupted.
Nepthys cirrosa occurs in fine to coarser sands, with greatest abundance in the Belgium part of the North Sea recorded in medium grain sizes (Degraer et al., 2006). Presence of fine material may lead to small but insignificant changes in abundance as it will reduce the available preferred habitat with medium grain size. As the tidal flow is strong in this biotope, a light deposition of finer sediment is likely to be resuspended. Resistance is likely to be high to the presence of finer material for Nepthys cirrosa but initial smothering is likely to cause some mortality and interrupt feeding and reproduction activity at the benchmark level.
Capitella capitata has been categorised through expert and literature review, as AMBI sedimentation Group IV – a second-order opportunistic species, insensitive to higher amounts of sedimentation. Although they are sensitive to strong fluctuations in sedimentation, their populations recover relatively quickly and even benefit. This causes their population sizes to increase significantly in areas after a strong fluctuation in sedimentation (Gittenberger & Van Loon 2011).
Bijkerk (1988, results cited from Essink, 1999) found that the maximal overburden through which Bathyporeiacould migrate was approximately 20 cm in mud and 40 cm in sand. No further information was available on the rates of survivorship or the time taken to reach the surface and no information was available for other characterizing species.
Sensitivity assessment. Overall smothering by 30 cm of fine sediments may result in mortality of characterizing species. The introduction of fine sediment may also alter the sediment typical of the biotope causing a temporary shift in the abundance of species. However, the opportunistic species occurring in the biotope are likely to recover rapidly following sediment recovery. Biotope resistance is, therefore, assessed as ‘Low’, resilience is assessed as ‘High’, following habitat recovery to fine sands and biotope sensitivity is assessed as ‘Low’.
Plastic debris breaks up to form microplastics. Microplastics have been shown to occur in marine sediments and to be ingested by detritivores such as the amphipod Orchestia gammarellus, deposit feeders such as Arenicola marina and holothurians, as well as by suspension feeders, e.g. Mytilus edulis (Wright et al., 2013b; Browne et al., 2015).
Wright et al. (2013) showed that the presence of microplastics (5% UPVC) in a lab study significantly reduced feeding activity when compared to concentrations of 1% UPVC and controls. As a result, Arenicola marina showed significantly decreased energy reserves (by 50%), took longer to digest food, and as a result decreased bioturbation levels, which would be likely to impact colonization of sediment by other species, reducing diversity in the biotopes the species occurs within. Wright et al. (2013) suggested that in the intertidal regions of the Wadden Sea, where Arenicola marina is an important ecosystem engineer, Arenicola marina could ingest 33m3 of microplastics a year.
In a similar experiment, Browne et al. (2013) exposed Arenicola marina to sediments with 5% PVC particles or sand presorbed with pollutants nonylophenol and phenanthrene for 10 days. PVC is dense and sinks to the sediment. The experiment used Both microplastics and sand transferred the pollutants into the tissues of the lugworm by absorption through the gut. The worms accumulated over 250% more of these pollutants from sand than from the PVC particulates. The lugworms were also exposed to PVC particulates presorbed with plastic additive, the flame retardant PBDE-47 and antimicrobial Triclosan. The worms accumulated up to 3,500% of the concentration of theses contaminants when compared when to the experimental sediment. Clean sand and PVC with contaminants reduced feeding but PVC with Triclosan reduced feeding by over 65%. In the PVC with Triclosan treatments, 55% of the lugworms died. Browne et al., 2013 concluded that the contaminants tested reduced feeding, immunity, response to oxidative stress, and survival (in the case of Triclosan).
Sensitivity assessment. Impacts from the pressure ‘litter’ would depend on upon the exact form of litter or man-made object being introduced. Browne et al. (2015) suggested that if effects in the laboratory occurred in nature, they could lead to significant changes in sedimentary communities as Arenicola marina is an important bioturbator and ecosystem engineer in sedimentary habitats. Arenicola marina does not reach high abundances in this biotope but other deposit feeding polychaetes could potentially ingest microplastics, although no evidence in available at present. This pressure is 'Not assessed' as no benchmark has been defined for this pressure.
Field measurements of electric fields at North Hoyle wind farm, North Wales recorded 110µ V/m (Gill et al. 2009). Modelled results of magnetic fields from typical subsea electrical cables, such as those used in the renewable energy industry produced magnetic fields of between 7.85 and 20 µT (Gill et al. 2009; Normandeau et al. 2012). Electric and magnetic fields smaller than those recorded by in field measurements or modelled results were shown to create increased movement in thornback ray Raja clavata and attraction to the source in catshark Scyliorhinus canicular (Gill et al. 2009).
Flatfish including dab Limanda limanda and sole Solea solea are predators of many polychaete species. They have been shown to decrease in abundance in a wind farm array or remain at distance from wind farm towers (Vandendriessche et al., 2015; Winter et al. 2010). However, larger plaice increased in abundance (Vandendriessche et al., 2015). There have been no direct causal links identified to explain these results.
Sensitivity assessment. No evidence was found on effects of electric and magnetic fields on the characterizing species. However, responses by flatfish and elasmobranchs suggest changes in predator behaviour are possible. There is no evidence currently but if electromagnetic fields affect predator-prey dynamics as further marine renewable energy devices are deployed, these are likely to be over small spatial scales and unlikely to significantly impact the biotope.
Species within the biotope can probably detect vibrations caused by noise. However, at the benchmark level the community is unlikely to be sensitive to noise and this pressure is therefore ‘Not relevant’.
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. As the characterizing biological assemblage occurs within the sediment, an increase in light or shading is considered ‘Not relevant’. However, shading may reduce the microphytobenthos component of this infralittoral biotope. Mucilaginous secretions produced by these algae may stabilize fine substrata (Tait & Dipper, 1998). Shading will prevent photosynthesis leading to death or migration of sediment microalgae, which may alter sediment cohesion and food supply to higher trophic levels.
Characterizing species may have some, limited, visual perception. As they live in the sediment the species will most probably not be impacted at the pressure benchmark and this pressure is considered 'Not relevant'.
Important characterizing species within this biotope are not cultivated or translocated. This pressure is, therefore, considered ‘Not relevant’ to this biotope.
Coastal and estuarine areas are among the most biologically invaded systems in the world, especially by molluscs such as the slipper limpet Crepidula fornicata and the Pacific oyster Magallana gigas (OSPAR, 2009b). 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. In the Wadden Sea, the main issue of concern is the pacific oyster (Magallana gigas), which has also spread in the Thames estuary and along French intertidal flats. Padilla (2010) predicted that Magallana gigas could either displace or overgrown mussels on rocky and sedimentary habitats of low or high energy. In general littoral sand sediments are mobile and winter storms may remove sediments and wash-out some species (Connor et al., 2004) preventing the establishment of larger, longer -lived species and the development of bivalve reefs. However, as some beaches in which the biotope occur may be relatively sheltered some colonization may occur and sensitivity to invasive molluscs is considered.
In the Wadden Sea and the North Sea, Magallana gigas overgrows mussel beds in the intertidal zone (Diederich 2005, 2006; Kochmann et al., 2008), although they did show a preference for settling on conspecifics before the mussels and struggled to settle on mussels with a fucoid covering. However, recruitment of Magallana gigas was significantly higher in the intertidal than the shallow subtidal, although the survival of adult oysters or mussels in the subtidal is limited by predation.
Crepidula fornicata is known to colonize and smother a wide range of sediments in the subtidal, from mixed sediments to mud, especially in prior shellfish beds (e.g. of oysters and mussels) (Blanchard, 1997; Minchin et al., 1995). Crepidula fornicata larvae may out-compete oyster (Magallana gigas) larvae during summer months where the two species co-occur. Trophic competition between adult Crepidula fornicata and Magallana gigas was reported in France during winter and spring. In Mont Saint-Michel Bay, France, slipper limpet populations have affected flatfish populations. Changes in habitat structure and reduced abundance of suspension feeding organisms upon which the flatfish feed were linked to slipper limpet extent (Decottignies et al., 2007; Blanchard et al. 2008; and Kostecki et al., 2011 cited in Sewell & Sweet, 2011).
On some north Wales shores Ensis siliqua occurs (Connor et al., 2004), this species could co-occur with or be replaced by a similar, but non-native species Ensis directus. Such a change is unlikely to alter the character of the biotope.
Sensitivity assessment. Magallana gigas is predicted to invade sedimentary habitats, although no direct examples exist to date and Magallana gigas recruitment is lower in the subtidal (Diederich 2005, 2006; Padilla, 2010). Crepdiula fornicata is a major invader and colonizer of subtidal sediments. However, both species require hard substrata in the form of stones, debris or, preferably, the shells conspecifics to colonize the habitat. This biotope is dominated by fine mud and a shell fraction is not recorded in the description (Connor et al., 2004) but if artificial hard debris (e.g. litter) was introduced to the habitat then it may provide an initial point for the colonization of Crepidula in particular. Although it would probably take many years, colonization by Crepidula would result in the complete modification of the habitat, reclassification and loss of the biotope, although polychaete populations may survive in the sediment itself. Therefore, a precautionary resistance of Low has been suggested with ‘Low’ confidence due to the lack of direct evidence. Resilience is likely to be Very low as a bed of Crepidula or Magallana gigas would need to be removed before recovery could begin. Therefore, sensitivity is assessed as High.
Nephtys cirrosa is targeted by bait diggers, there is limited information on the effect of targeted removal on Nephtys cirrosa populations, however, there is evidence on effects on Nephtys hombergii. Nephtys hombergii is directly removed through commercial bait digging and by recreational anglers and abundance significantly decreased in areas of the Solent, UK, where bait digging (primarily for Nereis virens) had occurred (Watson et al. 2007). Recovery of Nephtys hombergii has been assessed to be high as re-population would occur initially relatively rapidly via adult migration and later by larval recruitment. Dittman et al. (1999) observed that Nephtys hombergii was amongst the macrofauna that colonized experimentally disturbed tidal flats within two weeks of the disturbance that caused defaunation of the sediment. However, if sediment is damaged recovery is likely to be slower, for instance, Nephtys hombergii abundance was reduced by 50% in areas where tractor towed cockle harvesting was undertaken on experimental plots in Burry inlet, south Wales, and had not recovered after 86 days (Ferns et al., 2000).
Removal of Nephtys cirrosa by bait digging may cause short-term loss of food resources for predators such as fish species including Limanda limanda and Pleuronectes platessa. As recovery is medium to high, the long-term impacts on populations are likely to be small but will be dependent upon the scale and frequency of bait digging activities.
Sensitivity assessment. Confidence in this assessment in relation to the removal of Nephtys cirrosa is low as it is based on evidence of removal of Nephtys hombergii. However, biotope resistance is assessed as ‘Low’ based on direct removal of a characterizing species, Resilience is assessed as ‘High’ as habitats that are not regularly harvested may recover rapidly, it should be noted that continued harvesting will inhibit recovery. Biotope sensitivity to a single harvesting event is assessed as ‘Low’. It is important to consider that the spatial extent and duration of harvesting is important to consider when assessing this pressure as smaller scale extraction may not impact the entire extent of the biotope but greater scale extraction over a long period would cause longer term impacts.
Direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures, while this pressure considers the ecological or biological effects of by-catch. Species in this biotope, including the characterizing species, may be damaged or directly removed by static or mobile gears that are targeting other species (see abrasion and penetration pressures).
Collie et al. (2000) identified that intertidal communities (such as this biotope) suffered impacts from impact from fishing activities. The review concluded that there were ecologically important impacts from removal of >50% of fauna from bottom towed fishing activity (dredge and trawls) (Collie et al., 2000). Kaiser et al. (2001) carried out experimental hand raking, similar to that used in intertidal cockle fisheries. Both small and large raked plots showed changed communities in comparison to control plots, smaller plots recovered in 56 days, whilst larger plots remained in an altered state.
Collie et al. (2000) found that abundance of a Nephtys hombergii was negatively affected by fishing activities. Mean response of infauna and epifauna communities to fishing activities was also much more negative in mud and sand communities (such as this biotope) than other habitats. Nephtys hombergii abundance also significantly decreased in areas of the Solent, UK, where bait digging had occurred (Watson et al. 2007). Similarly, Nephtys hombergii abundance was reduced by 50% in areas where tractor towed cockle harvesting was undertaken on experimental plots in Burry inlet, south Wales, and had not recovered after 86 days (Ferns et al., 2000).
Sensitivity assessment. The incidental damage or removal of a proportion of the population (e.g. by commercial bait digging) may change the character of the community temporarily. The biotope is disturbed seasonally by storms, (Connor et al., 2004) and may recover quickly. However, long-term disturbance from repeated events e.g. by periodic bait digging (see above) may prolong recovery. Biotope resistance is assessed as ‘Low’ based on removal or damage of characterizing species, that on commercial scales can remove a large proportion of the population and lead to an impacted community. Resilience is assessed as ‘High’ but it should be noted that continued harvesting will impact the population and Nephtys cirrosa will take longer to recover if harvesting is over extended spatial scales.Biotope sensitivity is assessed as ‘Low’. It is important to consider that the spatial extent and duration of areas impacted by removal is important to consider when assessing this pressure, as smaller scale extraction may not impact the entire extent of the biotope but greater scale extraction over a long period would cause longer term impacts. The type of fishing activity is also important to consider in relation to the type and severity of the impact.
Callier, M. D., McKindsey, C.W. & Desrosiers, G., 2007. Multi-scale spatial variations in benthic sediment geochemistry and macrofaunal communities under a suspended mussel culture. Marine Ecology Progress Series, 348, 103-115.
Coates, D.A., van Hoey, G., Colson, L., Vincx, M. & Vanaverbeke, J., 2015. Rapid macrobenthic recovery after dredging activities in an offshore wind farm in the Belgian part of the North Sea. Hydrobiologia, 756 (1), 3-18.
Collie, J.S., Hall, S.J., Kaiser, M.J. & Poiner, I.R., 2000. A quantitative analysis of fishing impacts on shelf-sea benthos. Journal of Animal Ecology, 69 (5), 785–798.
Degraer, S., Mouton, I., De Neve, L. & Vincx, M., 1999. Community structure and intertidal zonation of the macrobenthos on a macrotidal, ultra-dissipative sandy beach: summer-winter comparison. Estuaries, 22, 742-752.
Emery, K.O. & Stevenson, R.E., 1957. Estuaries and lagoons. In Treatise on marine ecology and paleoecology.1. Ecology, (ed. J.W. Hedgpeth), USA: Geological Society of America.
Fallesen, G. & Jørgensen, H.M., 1991. Distribution of Nephtys hombergii and Nephtys ciliata (Polychaeta: Nephtyidae) in Århus Bay, Denmark, with emphasis on the severe oxygen deficiency. Ophelia, Supplement 5, 443-450.
Forbes, T.L. & Lopez, G.R., 1990. The effect of food concentration, body size, and environmental oxygen tension on the growth of the deposit-feeding polychaete, Capitella species 1. Limnology and Oceanography, 35 (7), 1535-1544.
Gamenick, I. & Giere, O., 1997. Ecophysiological studies on the Capitella capitata complex: respiration and sulfide exposure. Bulletin of Marine Science, 60, 613.
Gaston, G.R., McLelland, J.A. & Heard, R.W., 1992. Feeding biology, distribution, and ecology of two species of benthic polychaetes: Paraonis fulgens and Paraonis pygoenigmatica (Polychaeta: Paraonidae). Gulf Research Reports, 8 (4), 395-399.
Grassle, J.F. & Grassle, J.P., 1974. Opportunistic life histories and genetic systems in marine benthic polychaetes. Journal of Marine Research, 32, 253-284.
Grassle, J.F. & Grassle, J.P., 1976. Sibling species in the marine pollution indicator (Capitella) (Polychaeta). Science, 192, 567-569.
Henriksson, R., 1969. Influence of pollution on the bottom fauna of the Sound (Öresund). Oikos, 20 (2), 507-523.
Le Moal, Y., 1980. Ecological survey of an intertidal settlement living on a soft substrata in the Aber Benoit and Aber Wrac'h estuaries, after the Amoco Cadiz oil spill. Universite de Bretagne Occidentale, Brest (France), 25pp.
Mangum, C. & Van Winkle, W., 1973. Responses of aquatic invertebrates to declining oxygen conditions. American Zoologist, 13 (2), 529-541.
McCall, P.L., 1977. Community patterns and adaptive strategies of the infaunal benthos of Long Island Sound. Journal of Marine Research, 35, 221-266.
Meißner, K., Darr, A. & Rachor, E., 2008. Development of habitat models for Nephtys species (Polychaeta: Nephtyidae) in the German Bight (North Sea). Journal of Sea Research, 60 (4), 276-291.
Mills, D.J.L., 1998. Liverpool Bay to the Solway (Rhos-on-Sea to the Mull of Galloway)(MNCR Sector 11). In Marine Nature Conservation Review. Benthic marine ecosystems of Great Britain and the north-east Atlantic, pp. 315-338.
Minchin, D., McGrath, D. & Duggan, C.B., 1995. The slipper limpet Crepidula fornicata (L.) in Irish waters with a review of its occurrence in the north east Atlantic. Journal of Conchology, 35, 247-254.
Nehmer, P. & Kroencke, I., 2003. Macrofaunal communities in the Wichter Ee, a channel system in the East Frisian Wadden Sea. Senckenbergiana Maritima, 32 (1-2), 1-10.
Olsgard, F., 1999. Effects of copper contamination on recolonisation of subtidal marine soft sediments - an experimental field study. Marine Pollution Bulletin, 38, 448-462.
Petrich, S.M. & Reish, D.J., 1979. Effects of aluminium and nickel on survival and reproduction in polychaetous annelids. Bulletin of Environmental Contamination and Toxicology, 23, 698-702.
Tenore, K.R., 1977. Growth of Capitella capitata cultured on various levels of detritus derived from different sources. Limnology and Oceanography, 22 (5), 936-941.
Tenore, K.R. & Chesney, E.J., 1985. The effects of interaction of rate of food supply and population density on the bioenergetics of the opportunistic polychaete, Capitella capitata (type 1). Limnology and Oceanography, 30 (6), 1188-1195.
Tuck, I.D., Hall, S.J., Robertson, M.R., Armstrong, E. & Basford, D.J., 1998. Effects of physical trawling disturbance in a previously unfished sheltered Scottish sea loch. Marine Ecology Progress Series, 162, 227-242.
Ward, T.J. & Young, P.C., 1982. Effects of sediment trace metals and particle size on the community structure of epibenthic seagrass fauna near a lead smelter, South Australia. Marine Ecology Progress Series, 9, 136-146.
Warren, L.M., 1977. The ecology of Capitella capitata in British waters. Journal of the Marine Biological Association of the United Kingdom, 57, 151-159.
Watson, G.J., Farrell, P., Stanton, S. & Skidmore, L.C., 2007. Effects of bait collection on Nereis virens populations and macrofaunal communities in the Solent, UK. Journal of the Marine Biological Association of the United Kingdom, 87 (3), 703-716.
Wu, B., Qian, P. & Zhang, S., 1988. Morphology, reproduction, ecology and isoenzyme electrophoresis of Capitella complex in Qingdao. Acta Oceanologica Sinica, 7 (3), 442-458.

References: in fine
in fine
in fine
in fine
in fine
in fine