Biodiversity & Conservation

SS.IGS.FaS.Lcon

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Characterizing species in the biotope are infaunal and would therefore be removed along with the substratum. Some epifaunal and swimming species, such as amphipods and the harbour crab Liocarcinus depurator, may be able to avoid the factor. However, because the species which characterize the biotope would be lost, intolerance has been assessed to be high and there would be a major decline in species richness. Recoverability has been assessed to be high (see additional information below).
Smothering
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The tube of Lanice conchilega rises several centimetres above the sediment surface. Ziegelmeier (1952) showed that the polychaete increased the height of the tube top with increasing sedimentation. It is therefore, unlikely that silt would smother the worm. For other polychaetes, such as Magelona mirabilis, that deposit feeds at the surface by extending contractile palps from its burrow, a layer of sediment would result in a temporary cessation of feeding activity. Abra alba and Fabulina fabula are shallow burrowers in sandy sediments. These bivalves require their inhalant siphons to be above the sediment surface for feeding and respiration. Smothering with 5 cm of sediment would temporarily halt feeding and respiration and require the species to relocate to its preferred depth. Similarly, infaunal polychaete species would move up through additional sediment without adverse effect. Intolerance has been assessed to be low as relocation would be at energetic cost and feeding activity would be inhibited. Recovery has been assessed to be immediate. Smothering by viscous or impenetrable materials would be expected to have a more severe effect.
Increase in suspended sediment
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Suspension feeding species within the biotope are likely to benefit from an increase in suspended sediment especially if there was a significant proportion of organic matter in the suspended sediment and if food was previously limiting. Lanice conchilega uses its 'feeding crown' to attain particles and unless the 'feeding crown' becomes clogged and requires excessive cleaning at energetic cost the species is unlikely to be adversely affected. Infaunal species such as Arenicola marina are unlikely to be perturbed. An assessment of not sensitive * has been made as suspension feeders may benefit from the increased availability of food.
Decrease in suspended sediment
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A decrease in suspended sediment would reduce the amount of available food for suspension feeders such as Lanice conchilega and bivalve molluscs. Deposit feeders such as Arenicola marina are unlikely to be directly affected, although a reduction in suspended sediment may eventually cause deposits of organic matter to become limiting as a consequence of reduced supply. An intolerance assessment of low has been made as suspension feeding species would experience reduced growth and fecundity rather than mortality over the period of one month. On return to prior conditions optimal feeding is likely to resume and recoverability has been assessed to be very high.
Desiccation
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Normally, exposure to direct sunlight and air is unlikely as the biotope is subtidal. However, desiccation would become a stress if sediments in the very shallow sublittoral became 'baked' by sunlight during a prolonged low tide event or the component species in the biotope were to be removed from the sediment and stranded, unable to reburrow. However, the majority of the fauna, polychaete worms and bivalves live infaunally and so are likely to be protected from desiccation stress. Bivalves respond to desiccation stress by valve adduction and it is likely that they would be able to retain enough water within their shells to avoid mortality during the benchmark period of one hour. Mobile species would migrate. In avoiding the effects of desiccation the fauna would not be able to feed and respiration would be compromised, so there is likely to be some energetic cost. Therefore intolerance has been assessed to be low. On immersion, metabolic activity should quickly return to normal and recoverability is therefore recorded as very high. There is unlikely to be a decline in species richness.
Increase in emergence regime
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The biotope occurs from the shallow sublittoral (0-5 m) down to a depth of 20 m, therefore it does not normally experience periods of emergence. An increase in emergence is unlikely to occur in this biotope, but if it did only the uppermost part of it in the very shallow sublittoral would be affected. However, on certain shores the £LGS.Lan£ (Dense Lanice conchilega in tide-swept lower shore sand) may be a littoral extension of this biotope. The LGS.Lan biotope comprises of many similar functioning species (if not the same) suggesting that species of the IGS.Lcon biotope would be not sensitive. An increase in emergence may however lead to an increase in predation (of the relatively small proportion of the biotope affected) by wading sea birds. However, on balance the major extent of the biotope would be unaffected and so an assessment of not sensitive has been made.
Decrease in emergence regime
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The biotope occurs from the shallow sublittoral (0-5 m) down to a depth of 20 m where it is continually immersed and therefore would not be affected by a decrease in emergence regime.
Increase in water flow rate
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The nature of the substratum is, in part, determined by the hydrographic regime including water flow rate. Changes in the water flow rate will change the sediment structure and have concomitant effects on the community, as many sediment dwelling species have defined substratum preferences (e.g. Bathyporeia pelagica).
However, moderate to high velocities of water flow have been reported to enhance settlement of Lanice conchilega larvae (Harvey & Bourget, 1995) (see recruitment processes). But an increase in water flow from e.g. moderately strong to very strong, would probably winnow away smaller particulates, increasing average particle size in favour of gravels and pebbles. Therefore, the density of the Lanice conchilega population may decline, in part due to lack of suitable substrata with which to build its tubes, and partly from interference with its feeding. The community would probably become dominated by water flow tolerant species, that prefer coarse substratum, while species such as Arenicola marina, Abra alba, and Spiophanes bombyx may be excluded. The biotope may start to resemble the burrowing anemone dominated community £IGS.HalEdw£. Therefore, an intolerance of high has been recorded. On return to prior conditions recoverability is likely to be high (see additional information below).
Decrease in water flow rate
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The nature of the substratum is, in part, determined by the hydrographic regime including water flow rate. Changes in the water flow rate will change the sediment structure and have concomitant effects on the community.

Reduced water flow is a factor that has been identified as affecting the density of Lanice conchilega. Recruitment to the benthos is reduced under low flow as a result of reduced turbulence (Harvey & Bourget, 1995) (see recruitment processes). Furthermore, at the benchmark level, decreased water flow rate would probably increase deposition of finer sediments, and increase siltation. The sediment would probably begin to favour deposit feeders and detritivores, to the detriment of the suspension feeders. The average grain size of the sediment would be reduced, and the community may start to be replaced over a period of one year by communities characteristic of muddy sands, with a higher proportion of deposit feeding species, perhaps e.g. £IMS.MacAbr£ or £IMS.EcorEns£. Therefore, an intolerance of high has been recorded. On return to prior conditions recoverability has been assessed to be high (see additional information below)

Increase in temperature
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The geographic distribution of polychaete and bivalve species characteristic of this biotope extend to the south of the British Isles, so are likely to be tolerant of a long-term chronic temperature increase of 2 °C. Infaunal species are likely to be protected to some extent from direct effects of acute increases in temperature, although increased temperatures may affect infauna indirectly, by stimulating increased bacterial activity and increased oxygen consumption. Depletion of oxygen from the interstitial waters would result in reduced oxygen levels (hypoxia) or more severely the complete absence of oxygen (anoxia) (see deoxygenation) in the sediment (Hayward, 1994).
Lethal temperatures (LT50) have been reported for species such as Abra alba and Fabulina fabula (see MarLIN reviews) but temperatures in excess of 20 °C are not likely around the British Isles (Hiscock, 1998). An acute increase in temperature at the benchmark level may result in physiological stress endured by the species but is unlikely to lead to mortality. The biotope is subtidal and probably protected from extremes of temperature by the depth of overlying water.
Therefore, an intolerance of low has been recorded to represent sub-lethal effects on growth and reproduction. A recoverability of very high has been suggested.
Decrease in temperature
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Lanice conchilega is intolerant of low temperatures (Beukema, 1990). An intertidal population of Lanice conchilega, in the northern Wadden Sea, was wiped out during the severe ice winter of 1995/96 (Strasser & Pielouth, 2001). The population took three years to fully recover, as there was low recruitment for the first two years. Crisp (1964) described mortality of Lanice conchilega between the tidemarks but not at lower levels during the severe winter of 1962/63.
Other characterizing species in the biotope are recorded north of the British Isles (e.g. Arenicola marina, Abra alba, and Spiophanes bombyx) and are unlikely to be affected by long term chronic decreases in temperature. However, Arenicola marina may be more intolerant, it experienced some mortality at 5 °C in laboratory studies, although in the field it would derive protection from its infaunal habit.
Overall, species within the biotope are probably protected from extremes of temperature by their infaunal habit and depth of overlying water. While some more intolerant species may be reduced in abundance or migrate to deeper water, reducing species richness, an overall intolerance of low has been recorded. Recoverability is probably very high.
Increase in turbidity
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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. The increased turbidity persists for a year, so decreased food availability would probably affect growth and fecundity of species and an intolerance of low has been recorded. 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.
Decrease in turbidity
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It is possible that decreased turbidity would increase primary production in the water column by phytoplankton and by the microphytobenthos. The resultant increase in food availability may enhance growth and reproduction of both suspension and deposit feeding species but only if food was previously limiting. An intolerance assessment of not sensitive* has been made.
Increase in wave exposure
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The biotope occurs in 'sheltered', 'very sheltered' and 'extremely sheltered' locations (Connor et al., 1997a). An increase in wave exposure is likely to have adverse effect on the biotope. Rees et al. (1977) found that only 1 % of the Lanice conchilega population in Colwyn Bay apparently survived after winter storms. Presumably the oscillatory action on the prominent tube served to dislodge the species. An increase in wave exposure would also lead to erosion of the substratum in the shallowest locations, which will alter the extent of suitable habitat available for the community. Intolerance has been assessed to be high as important characterizing species would be lost and the habitat damaged. On return to prior conditions recoverability is likely to be high (see additional information below).
Decrease in wave exposure
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The biotope occurs in 'sheltered', 'very sheltered' and 'extremely sheltered' locations (Connor et al., 1997a). A further decrease in wave exposure may result in increased siltation and a consequent change in sediment characteristics (Hiscock, 1983). A substratum with a higher proportion of fine sediment would probably result in the increased abundance of the deposit feeders within the biotope, particularly species which favour finer sediments, such as the polychaete Aphelochaeta marioni and the echinoid Echinocardium cordatum. However, in the absence of wave action, tidal flow is likely to be a more significant factor structuring the community, replenishing oxygen, supplying planktonic recruits and would maintain a supply of suspended organic matter in suspension for suspension feeders. Therefore the biotope has been assessed to be not sensitive.
Noise
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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 are probably withdrawn as a predator avoidance mechanism. However, it is unlikely that the biotope will be affected by noise or vibrations caused by noise at the level of the benchmark.
Visual Presence
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The majority of species in the biotope are infaunal and have little or no visual acuity. No evidence was found concerning intolerance to visual presence, but it is unlikely that the biotope would be affected.
Abrasion & physical disturbance
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Lanice conchilega inhabits a permanent tube and is likely to be damaged by any activity that penetrates the sediment. Ferns et al. (2000) investigated the effect of mechanical cockle harvesting. The tubes of Lanice conchilega were damaged but this damage was seen to be repaired. In the intertidal, mechanical cockle harvesting resulted in significant losses of common invertebrates in muddy sand and clean sand in the Burry Inlet (Ferns et al. , 2000). For example, losses varied from 31% of Scoloplos armiger to 83% of Pygospio elegans in dense populations. Populations of Nephtys hombergii and Scoloplos armiger took over 50 days to recover. However, recovery was more rapid in clean sand than in muddy sand. In muddy sand, Bathyporeia pilosa took 111 days to recover while Pygospio elegans and Hydrobia ulvae had not recovered their original abundance after 174 days (Ferns et al. , 2000). In a similar study, Hall & Harding (1997) found that non-target benthic fauna recovered within 56 days after mechanised cockle harvesting. However, Hall & Harding (1997) study took place in summer while Ferns et al. (2000) study occurred in winter.

Despite their apparent robust body form, bivalves are also vulnerable to physical abrasion. For example, as a result of dredging activity, mortality and shell damage has been reported in Mya arenaria and Cerastoderma edule (Cotter et al. , 1997). The most sensitive species identified was Echinocardium cordatum which has a fragile test that is likely to be damaged by an abrasive force such as movement of trawling gear over the seabed. A substantial reduction in the numbers of Echinocardium cordatum due to physical damage from scallop dredging has been observed (Eleftheriou & Robertson, 1992). The species has high fecundity, normally reproduces every year and has pelagic larvae so recovery would be expected. Intolerance has been assessed to be intermediate, as some mortality would be expected as a result of abrasion and physical disturbance. Recoverability has been assessed to be high (see additional information below).

Displacement
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Yonow (1989) observed Lanice conchilega re-establishing tubes immediately after removal from the sediment, when placed on a suitable sediment in the laboratory. Abra alba, Fabulina fabula and Magelona mirabilis are all active burrowers and are capable of reburying themselves if displaced to the surface of a suitable substratum (Jones, 1968; Salzwedel, 1979). However, while at the sediment surface they are vulnerable to predation from crabs, echinoderms (Aberkali & Trueman, 1985) and bottom feeding fish (Hunt, 1925; Hayward & Ryland, 1995) so there is likely to be some mortality. Intolerance has been assessed to be intermediate. However, it is likely that the majority of displaced specimens would obtain protection within the substratum relatively quickly so recoverability has been assessed to be immediate.

Chemical Factors

Synthetic compound contamination
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No evidence of the effects of chemical contaminant on Lanice conchilega were found. However, exposure of Hediste diversicolor and Arenicola marina to Ivermecten resulted in significant mortality (see MarLIN reviews; Collier & Pinn, 1998). Beaumont et al. (1989) investigated the effects of tri-butyl tin (TBT) on benthic organisms. At concentrations of 1-3 µg/l there was no significant effect on the abundance of Hediste diversicolor or Cirratulus cirratus after 9 weeks in a microcosm. However, no juvenile polychaetes were retrieved from the substratum suggesting that TBT had an effect on the larval and/or juvenile stages of these polychaetes. Bryan & Gibbs (1991) reported that Arenicola costata larvae were unaffected by 168 hr exposure to 2000 ng TBT/ l seawater and were probably relatively tolerant, however in another study, Scoloplos armiger exhibited a dose related decline in numbers when exposed to TBT paint particles in the sediment.

(Møhlenberg & Kiørboe, 1983) demonstrated that pesticide contamination impaired or prevented burrowing in Abra alba, which would probably result in the species being exposed to predatory starfish and fish. Beaumont et al. (1989) concluded that bivalves are particularly intolerant of tri-butyl tin (TBT). For example, when exposed to 1-3 µg TBT/l, Cerastoderma edule and Scrobicularia plana suffered 100 % mortality after 2 weeks and 10 weeks respectively. There is also evidence that TBT causes recruitment failure in bivalves, either due to reproductive failure or larval mortality (Bryan & Gibbs, 1991).

Pesticides and herbicides were suggested to be very toxic for invertebrates, especially crustaceans (amphipods, isopods, mysids, shrimp and crabs) and fish (Cole et al., 1999). Cole et al. (1999) suggested that TBT was very toxic to algae (including microalgae), molluscs, crustaceans and fish, with observable endocrine disrupting effects in gastropods. Waldock et al. (1999) examined recovery of benthic infauna of the Crouch estuary after a ban on the use of TBT on small boats. They observed marked increase in species diversity, especially of Ampeliscid amphipods and polychaetes (e.g. Tubificoides species and Aphelochaeta marioni) which mirrored the decline in sediment TBT concentration. Whilst a causal link could not be shown, the study by Waldock et al. (1999) suggested that crustacean and polychaete diversity may be inhibited by TBT contamination.

Polychaete species vary greatly in their tolerance of chemical contamination. However, evidence suggests that the polychaetes within this biotope, including the dominant species Lanice conchilega, are potentially highly intolerance of chemical contamination from pesticides or TBT. The abundance and reproduction of bivalves, crustaceans and other species in the biotope may also be adversely affected. Therefore, an intolerance of high has been recorded, albeit at low confidence. Species richness is likely to decline markedly, due to the dominance of fewer tolerant species. On return to prior conditions and assuming deterioration of the contaminants recoverability is likely to be high (see additional information below).
Heavy metal contamination
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Bryan (1984) suggested that polychaetes are fairly resistant to heavy metals based on the species studied. Short term toxicity in polychaetes was highest to Hg, Cu and Ag, declined with Al, Cr, Zn and Pb whereas Cd, Ni, Co and Se were the least toxic. However, polychaete species vary in their tolerance to heavy metals. For example, exposure to 10 ppm Cd in seawater halted feeding in Arenicola marina but continued at 1 ppm (Rasmussen et al., 1998), while median lethal concentrations (LC50) of 20 µg Cu/g, 50 µg Zn/g, and 25 µg Cd/g have been reported (Bat & Raffaelli, 1998). Arenicola marina was also found to accumulate As, Cd, Sb, Cu, and Cr when exposed to pulverised fuel ash (PFA) in sediments (Jenner & Bowmer, 1990). The spionid polychaete, Aphelochaeta marioni, is apparently very tolerant of heavy metal contamination, occurring in sediments with very high concentrations of arsenic, copper, tin, silver and zinc (Bryan & Gibbs, 1983) and accumulating remarkable concentrations of arsenic (Gibbs et al., 1983). Hediste diversicolor has been found successfully living in estuarine sediments contaminated with copper ranging from 20 µm Cu/g in low copper areas to >4000 µm Cu/g where mining pollution is encountered e.g. Restronguet Creek, Fal Estuary, Cornwall (Bryan & Hummerstone, 1971).

Bryan (1984) stated that Hg was the most toxic metal to bivalve molluscs while Cu, Cd and Zn seem to be most problematic in the field. In bivalve molluscs, Hg was reported to have the highest toxicity, mortalities occurring above 0.1-1 µg/l after 4-14 days exposure (Crompton, 1997), toxicity decreasing from Hg > Cu and Cd > Zn > Pb and As > Cr ( in bivalve larvae, Hg and Cu > Zn > Cd, Pb, As, and Ni > to Cr). However, bivalves vary in their tolerance to heavy metals.

Cole et al. (1999) suggested that Hg, Pb, Cr, Zn, Cu, Ni, and Ar were very toxic to invertebrates. Crustaceans are generally regarded to be intolerant of cadmium (McLusky et al., 1986). In laboratory investigations Hong & Reish (1987) observed 96 hour LC50 (the concentration which produces 50 % mortality) of between 0.19 and 1.83 mg/l in the water column for several species of amphipod.

Overall, polychaetes and bivalves vary in intolerance but may exhibit at least intermediate intolerance to some heavy metals, especially Hg. Amphipods are probably more intolerant, and heavy metal contamination is likely to result in a decline in species richness. On return to prior conditions, and assuming deterioration of the contaminants ,recoverability has been assessed to be high (see additional information below).
Hydrocarbon contamination
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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. A 20 year study investigating community effects after the Amoco Cadiz oil spill of 1978 (Dauvin, 2000) found that a population of Lanice conchilega was established between 1978-84 but disappeared after 1985. Hailey (1995) cited substantial kills of Hediste diversicolor, Cerastoderma edule, Macoma balthica, Arenicola marina and Hydrobia ulvae as a result of the Sivand oil spill in the Humber estuary in 1983.

Levell (1976) examined the effects of experimental spills of crude oil and oil: dispersant (BP1100X) mixtures on Arenicola marina. Single spills caused 25-50 % reduction in abundance and additional reduction in feeding activity. Up to four repeated spillages (over a 10 month period) resulted in complete eradication of the affected population either due to death or migration out of the sediment. Levell (1976) also noted that recolonization was inhibited but not prevented. Prouse & Gordon (1976) found that Arenicola marina was driven out of the sediment by waterborne concentration of >1 mg/l of fuel oil or sediment concentration of >100 µg/g fuel oil. Seawater oil concentrations of 0.7 mg oil /l reduced feeding after five hours and all worms exposed for 22 hours to 5mg/l oil left the sediment and died after three days. However, the sample size, in the experiment, was very small (6 worms). Sediment concentration >10g/g could reduce feeding. However, Nephtys hombergii, cirratulids and capitellids were largely unaffected by the Amoco Cadiz oil spill Conan (1982).

Generally, contact with oil in bivalves causes an increase in energy expenditure and a decrease in feeding rate, resulting in less energy available for growth and reproduction. Sublethal concentrations of hydrocarbons also reduce infaunal burrowing rates. After the Amoco Cadiz oil spill Fabulina fabula (studied as Tellina fabula) started to disappear from the intertidal zone a few months after the spill and from then on was restricted to subtidal levels. In the following two years, recruitment of Fabulina fabula was very much reduced (Conan, 1982).

The Amoco Cadiz oil spill also resulted in reductions in abundance, biomass and production of the community through the disappearance of the dominant populations of the amphipods Ampelisca sp. which are very sensitive to oil contamination (Dauvin, 1998) The sediment rapidly de-polluted and, in 1981, benthic recruitment occurred under normal conditions (Dauvin, 1998). However, the recovery of Ampelisca populations took up to 15 years. This was probably due to the amphipods' low fecundity, lack of pelagic larvae and the absence of local unperturbed source populations (Poggiale & Dauvin, 2001).

The above evidence suggests that soft sediment communities are highly intolerant of perturbation by oil spills. However, the biotope occurs subtidally and so the majority of the biotope is unlikely to be affected directly but may be exposed to water soluble fractions of hydrocarbons, and oils adsorbed onto particulates. Therefore, an intolerance of intermediate has been recorded. Recovery of amphipods to the biotope is likely to be slow. However, Lanice conchilega was shown to be relatively opportunistic after the Amoco Cadiz oil spill, colonizing shortly after the spill (Dauvin, 2000). Therefore, recoverability is likely to be high.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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Nutrient enrichment can lead to significant shifts in community composition in sedimentary habitats. Typically the community moves towards one dominated by deposit feeders and detritivores, such as polychaete worms (see review by Pearson & Rosenberg, 1978). The IGS.Lcon biotope includes some species tolerant of nutrient enrichment, such as the polychaete Capitella capitata (Pearson & Rosenberg, 1978). It is likely that such species would increase in abundance following nutrient enrichment (Elliott, 1994), with an associated decline in suspension feeding species, e.g. Lanice conchilega and organisms adapted to low nutrient levels, such as Magelona mirabilis (Niermann, 1996). In a sewage dumping region of the North Sea, a great increase in the abundance of Abra alba occurred in much of the dumping area because of the ecological adaptations of the species enabled it to exploit the greatly increased supply of nutrients (Caspers, 1981). In extreme cases of eutrophication, however, sediments may become anoxic and defaunated (see deoxygenation below; Elliott, 1994).
Indirect effects may include algal blooms. Algal blooms may smother the sediment and result in localised hypoxia and anoxia as a consequence of decomposition and mineralization of organic matter. Algal blooms have been implicated in mass mortalities of Arenicola marina, e.g. in South Wales where up to 99 % mortality was reported (Holt et al. 1995; Olive & Cadman, 1990; Boalch, 1979). The dinoflagellate bloom on the southwest coast of England in summer 1978 was also reported to cause mortalities in bivalves (e.g.Ensis species,) and the heart urchin Echinocardium cordatum (Forster, 1979). Overall, the structure of the community is likely to change in favour of deposit feeders, with an increase in the abundance of opportunistic species and a decrease in species richness. The dense Lanice conchilega bed is likely to be lost and an intolerance of high has been recorded. On return to prior conditions recoverability is likely to be high (see additional information below).
Increase in salinity
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IGS.Lcon occurs in full salinity conditions (Connor et al., 1997a) and therefore, a further increase in salinity is unlikely. No information was found concerning the intolerance of the characterizing species to hypersaline conditions.
Decrease in salinity
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The biotope has only been recorded in full salinity conditions (Connor et al., 1997b). Therefore, a decrease in salinity is likely to result in changes in the community. For example, although Lanice conchilega may be found in estuaries in reduced salinities its occurs at low abundance. Arenicola marina is unable to tolerate salinities below 24 psu and is excluded from areas influenced by freshwater runoff or input (e.g. the head end of estuaries) where it is replaced by Hediste diversicolor (Hayward, 1994). Abra alba is only recorded in full salinity conditions and may be intolerant of reduced salinity. Overall, a change in salinity from e.g. full to reduced (see benchmark) is likely to reduce the characteristic density of Lanice conchilega, result in loss of intolerant species and favour an increase in the abundance of species tolerant of reduced salinities e.g. Nephtys cirrosa, Scoloplos armiger, and Spiophanes bombyx. The biotope may come to resemble the reduced to low salinity biotope £IGS.Ncir£. Therefore, the biotope described may be lost and an intolerance of high has been recorded. On return to prior conditions recoverability is likely to be high (see additional information below).
Changes in oxygenation
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Nierman et al. (1990) reported changes in a fine sand community for the German Bight in an area with regular seasonal hypoxia. In 1983, oxygen levels were exceptionally low <3mg O2/l in large areas and < 1mg O/l in some areas. Species richness decreased by 30-50 % and overall biomass fell. Hypoxia is likely to result in an increase in the abundance of tolerant species. For example, Niermann et al. (1990) reported that Spiophanes bombyx was found in numbers at some, but not all areas, during the period of hypoxia. Arenicola marina is also tolerant of low oxygen concentrations and even short periods of anoxia (Dales, 1958; Hayward, 1994; Zebe & Schiedek, 1996). Abra alba was found to survive, with a decreased growth rate, exposure to 2.4 -3.5 mg O2,/ l over a 93 day experimental period (Hylland et al., 1996).

intolerance has been assessed to be intermediate as some individuals in the biotope may perish but many are likely to survive at the benchmark level. Recoverability is likely to be high (see additional information below).

Biological Factors

Introduction of microbial pathogens/parasites
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Insufficient information was found concerning microbial pathogens and parasites of polychaete species. However, more than 20 viruses have been described for marine bivalves (Sinderman, 1990). Bacterial diseases are more significant in the larval stages and protozoans are the most common cause of epizootic outbreaks that may result in mass mortalities of bivalve populations. Parasitic worms, trematodes, cestodes and nematodes can reduce growth and fecundity within bivalves and may in some instances cause death (Dame, 1996). Data concerning effects on community composition was not found.
Introduction of non-native species
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No evidence was found to suggest that important characterizing species of this biotope are threatened by alien species.
Extraction
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Commercially exploited species Ensis spp. and Cerastoderma edule occur in this biotope, but at lower densities and are not considered to be characterizing species. Shellfish of marketable size can be harvested both in the intertidal and subtidal more rapidly and efficiently using mechanical methods such as tractor-powered harvesters and suction dredgers than by traditional methods. Hydraulic suction dredgers operate by fluidising the sand using water jets and then lifting the sediment and infauna into a revolving drum for sorting. The tractor-towed dredge utilises a blade between 70 -100 cm wide that penetrates to a depth of between 20-40 cm. Sediment is sorted through a rotating drum cage (Hall & Harding, 1997). Such machinery adversely impacts on non-target infaunal species as they are sucked or displaced from the sediment and sustain damage as 'by-catch'. For instance, Ferns et al. (2000) recorded significant losses of common infaunal polychaetes from areas of intertidal muddy sand sediment worked with a tractor-towed cockle harvester: 31% of the polychaete Scoloplos armiger (initial density of 120 m²) and 83% of Pygospio elegans (initial density 1850 m²) were removed and bird feeding activity increased on harvested areas as gulls and waders took advantage of invertebrates made available. The intolerance of the biological community to this factor has been assessed to be intermediate as mortalities would occur. In the study by Ferns et al. (2000) the population of Pygospio elegans remained depleted for more than 100 days after harvesting, whilst those of Nephtys hombergi, Scoloplos armiger and Bathyporeia spp. were depleted for over 50 days. However, invertebrate populations in clean sand with relatively few Cerastoderma edule, but with more tube-dwelling species such as Lanice conchilega, recovered more quickly. Recoverability has been assessed to be very high.

Additional information icon Additional information

Recoverability
The life history characteristics of the polychaete and bivalve species that characterize the biotope suggest that the biotope would recover from major perturbations within five years. For instance;
  • Lanice conchilega spends up to 60 days in the plankton and could disperse over a wide area. Heuers & Jaklin (1999) found that areas with adult worms or artificial tubes were settled and areas without these structures were not. Strasser & Pielouth (2001) reported that larvae were seen to settle in areas where there were no adults but took 3 years to re-establish the population. Recoverability is, therefore, probably quicker in areas that already have a population of Lanice conchilega but would occur in suitable substratum within only a few years even in the absence of existing populations.
  • Abra alba demonstrates a considerable capacity for recovery. Abra alba spawns at least twice a year over a protracted breeding period, during which time an average sized animal of 11 mm can produce between 15, 000 and 17, 000 eggs. Such egg production ensures successful replacement of the population, despite high larval mortality which is characteristic of planktonic development. Timing of spawning and settlement suggests that the larval planktonic phase lasts at least a month (Dauvin & Gentil, 1989), in which time the larvae may be transported over a considerable distance. Whilst some larvae may settle back into the parent population, the planktonic presettlement period is important for dispersal of the species and spatial separation from the adults also reduces the chances of adult induced mortality on the larvae through adult filter feeding (Dame, 1996). In addition to dispersal via the plankton, dispersal of post-settlement juveniles may occur via byssus drifting (Sigurdsson et al., 1976, see adult distribution) and probably bedload transport (Emerson & Grant, 1991). Niermann et al. (1990) studied the recovery of a fine sand Fabulina fabula community from the German Bight following a severe hypoxia event. Re-establishment of faunal composition took approximately 8 months, but biomass did not fully recover for approximately 2 years.

This review can be cited as follows:

Budd, G.C. 2006. Dense Lanice conchilega and other polychaetes in tide-swept infralittoral sand. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 15/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=116&code=1997>