Biodiversity & Conservation

LS.LSa.MoSa.AmSco.Eur

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The infauna reside in the uppermost layers of the substratum and removal of the substratum would cause a major decline in species richness, as they would be removed with it. Thus all the biotopes represented by this key information review have been assessed to be highly intolerant of substratum loss at the benchmark level. Recolonization by the important characterizing species is likely following deposition of a sandy substratum, therefore recovery has been assessed to be high. However, extensive areas of intertidal mud and sand flats have been lost through land-claim (Davidson et al., 1991) and should this biotope be covered over it would never recover.
Smothering
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Smothering by 5 cm of sand is unlikely to affect adversely the important characterizing species which are able to burrow. Therefore, an intolerance of low has been recorded.

However, biotope intolerance is likely to be higher if the smothering sediment is atypical for the biotope e.g. fine silt or shingle, and assuming that the smothering materials were not rapidly removed or dispersed by the hydrographic regime, the atypical substrata would dramatically change the nature of the surface substratum. Over the duration of one month species not normally found within the biotope may find conditions favourable for colonization and the LGS.AEur biotope may start to shift to another community. The biotope would possibly not be recognized. Recovery has been assessed to be very high on return to prior conditions (see additional information below).

Increase in suspended sediment
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Increased suspended sediment derived from within the biotope, e.g. as the result of storm induced turbulence, is unlikely to be of significance to the important characterizing species as they do not suspension feed and therefore an assessment of not sensitive has been made.
Decrease in suspended sediment
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A decrease in suspended sediment may result in overall erosion of intertidal sands, where erosion is not compensated by deposition, but over the duration of one month effects are unlikely to be significant. The important characterizing species are not dependent on a supply of suspended material for feeding, so an assessment of not sensitive has been made.
Desiccation
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In most circumstances, desiccation is unlikely to prove a lethal factor to the species of an established beach fauna, since the risk of drying up follows a regular pattern to which the species of the biotope have evolved both physiological and behavioural adaptations (Eltringham, 1971). The important characterizing species are mobile, with an endogenous swimming rhythm that is coupled to circasemilunar pattern of emergence, which serves to reduce the risk of animals being stranded high on the shore (Jones & Naylor, 1970; Fish & Fish, 1972; Alheit & Naylor, 1976). Other species of the community are infaunal and their environmental position and ability to bury deeper into the sand is likely to protect them from drying out. However, a change in desiccation may result as a consequence of alteration of the water table or beach gradient and hence drainage of the beach. The population residing in the upper facies of the beach are likely to avoid conditions to which they are intolerant and move seawards. The important characterizing species are unlikely to be destroyed but in their absence from the upper facies of the biotope, the biotope may not be recognized and intolerance has been assessed to be intermediate. Recovery has been assessed to be very high, as the species will recolonize as soon as conditions become tolerable.
Increase in emergence regime
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Increased emergence (e.g. by tidal and storm surge barrages) is likely to increase the desiccation of the sediment, especially at the top of the shore and may consequently extend the extent of the barren sands biotope (£LGS.BarSnd£), and potentially allow terrestrial plants, such as pioneer saltmarsh species e.g. Salicornia sp. or Spartina spp. to invade the very top of the shore. The important characterizing species of the biotope, Eurydice pulchra and Bathyporeia pelagica are both intertidal species which experience regular periods of emersion. Individually these species were assessed to have a low intolerance to an increase in the emergence regime owing to the fact that their environmental position and ability to burrow, would protect them to a greater extent from effects of desiccation. Scolelepis squamata appears to be capable of tolerating the well-drained sediments of this biotope and generally demonstrates a high tolerance to different environmental conditions (Souza & Borzone, 2000). However, Scolelepis squamata, is normally only present in the LGS.AEur biotope in low densities, so if already at the limit of its tolerance, an increase in the emergence regime may exclude it from the biotope. Furthermore, during an increased period of emergence (see benchmark), the populations of infaunal crustaceans may be susceptible to increased predation pressure by feeding wildfowl but at the expense of fish that feed in the intertidal. Intolerance to an increase in the emergence regime has been assessed to be intermediate. The key characterizing species of the biotope are unlikely to be destroyed by the factor but may experience a reduction in viability owing to predation pressure. In addition, the biotope may be effectively squeezed to the lower part of the shore (but not necessarily lost) as the upper facies of drying sand becomes more extensive. Recovery has been assessed to be very high (see additional information below).
Decrease in emergence regime
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The key characterizing species, Eurydice pulchra and Bathyporeia pelagica, were assessed not to be intolerant of a decrease in emergence regime. A decrease in the emergence regime may have implications for other species that utilize the biotope. For instance on the Oosterschelde, construction of a storm surge barrier resulted in the loss of 33% of intertidal habitat (Meire, 1993). Such a reduction in the exposed area or tidal range may increase the area available to fish for feeding, but at the expense of the wildfowl feeding period, which in turn reduces the carrying capacity of the area for wildfowl. The carrying capacity being reached when every new individual entering the habitat causes the emigration or death of another bird (Goss Custard, 1985). Intolerance has been assessed to be intermediate.
Increase in water flow rate
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The nature of the substratum is, in part, determined by the hydrodynamic regime including water flow rate. Changes in the water flow rate will change the sediment structure and have concomitant effects on the community. The important characterizing species, Eurydice pulchra and Bathyporeia pelagica, demonstrated a preference for substrata of a specific grade (1.0-0.5 mm and 0.125-0.5 mm median diameter respectively). Although the species may not be directly exposed to the increased current, the factor would probably cause a redistribution/reduction of the preferred substrata and the species populations may become restricted or lost from a location. Consequently the biotope may no longer be identified in the location and intolerance has been assessed to be high. Recovery has been assessed 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 hydrodynamic regime including water flow rate. Changes in the water flow rate will change the sediment structure and have concomitant effects on the community. The important characterizing species, Eurydice pulchra and Bathyporeia pelagica, demonstrated a preference for substrata of a specific grade (1.0-0.5 mm and 0.125-0.5 mm median diameter respectively). Although the species may not be directly affected by decreased current, it would probably cause the accretion of finer particulate and organic matter and to which the important characterizing species are intolerant and the species populations may become restricted or lost from a location. The accretion of muds and organic matter would encourage littoral mud communities to develop and the LGS.AEur biotope, and others represented by this review would no longer be recognised. Therefore intolerance has been assessed to be high. Recovery has been assessed to be high (see additional information below).
Increase in temperature
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Many intertidal species are adapted to temperature extremes, can alter metabolic activity, burrow deeper in sediment or move to deeper water. At low tide, air temperature becomes critically important to intertidal animals, and on sandy beaches the substratum, from the surface to a depth of several centimetres, can experience large variations in temperature during a single cycle and throughout the year (Hayward, 1994). For instance, Khayrallah & Jones (1980b) reported the temperature range of sand at a depth of 1 cm during neap tides to be from -2°C in February 1973, to a maximum of 25°C in July 1977. Although adapted to temperature change, severe acute change may result in seasonal reduction in species richness and abundance, but the effects of an acute temperature increase are not necessarily direct and may be more related to the resultant changes in other factors, especially oxygen resulting from enhanced microbial activity (Hayward, 1994; Eltringham , 1971). Intolerance has therefore been assessed to be low and variable.
Decrease in temperature
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Many intertidal species are adapted to temperature extremes, can alter metabolic activity, burrow deeper in sediment or move to deeper water. Although adapted to temperature change, severe change may result in seasonal reduction in species richness and abundance. At low tide, air temperature becomes critically important to intertidal animals, and on sandy beaches the substratum, from the surface to a depth of several centimetres, can experience large variations in temperature during a single cycle and throughout the year (Hayward, 1994). For instance, Khayrallah & Jones (1980b) reported the temperature range of sand at a depth of 1 cm during neap tides to be from -2°C in February 1973, to a maximum of 25°C in July 1977. The effect of an unusually cold winter on the infauna is a simple physical one, in which body fluids freeze, causing cell and tissue damage. However, Crisp (1964) reported that species of amphipod and isopods seemed to be unharmed by the severe winter of 1962-1963 and intolerance has been assessed to be low.
Increase in turbidity
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Primary productivity due to pelagic phytoplankton and microphytobenthos contribute to intertidal benthic communities and is light limited. Incoming tides and wave action suspend sediment resulting in high local turbidity, so microphytobenthos normally experience light limiting conditions periodically. However, the majority of productivity in these biotopes is secondary (detritus) and the biotope has been assessed to be not sensitive to the light attenuating effects of an increase in turbidity.
Decrease in turbidity
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A decrease in turbidity, possibly associated with a decrease in wave action, may allow fish to hunt more efficiently, as prey items such as the crustaceans become more visible when swimming. However, as the important characterizing species are likely to be not sensitive to an increase in light penetration, the biotope has been assessed not to be sensitive.
Increase in wave exposure
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Wave action determines the slope and width of sandy intertidal areas. An increase in wave exposure would alter the habitat through increased erosion (which may not be compensated for by deposition) and ultimately the nature of the substratum would change becoming coarser, forming deposits of shingle or gravel rather than sand, creating conditions outside the species habitat preference. Intolerance has been assessed to be high as the important characterizing species would probably no longer be found. Recovery has been assessed to be very high, for instance, at Village Bay on St Kilda, an island group far out into the Atlantic west of Britain, an expanse of sandy beach was removed offshore as a result of winter storms to reveal an underlying rocky shore (Scott, 1960). Yet in the following summer the beach was gradually replaced when wave action was less severe. Eurydice pulchra was a species reported to be a frequent member of the re-colonizing fauna, its recovery being aided by the ability to survive in the shallow sublittoral zone where substrata may be deposited.
Decrease in wave exposure
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Wave action determines the slope and width of sandy intertidal areas. Decreases in wave exposure would probably cause accretion of finer sands, silts and clays and lessen the slope of the shore, which in turn would alter drainage and the oxygenation of the substratum. Opportunistic species, more typically associated with muddy littoral biotopes, may colonize the biotope. The important characterizing species of the LGS.AEur biotope, and others represented by this review, demonstrated a preference for clean relatively well drained sand, and may be exposed to unfavourable conditions. In the absence of these species the biotope may no longer be recognisable. Therefore intolerance has been assessed to be high. Recovery has been assessed to be high on return to prior conditions (see additional information below).
Noise
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Disturbance by noise and visual presence of human activities will be considered together. Disturbance causes birds that frequent the biotope to fly away. A reduction in predation pressure may benefit infaunal populations of crustaceans and polychaetes and therefore an intolerance assessment of not sensitive* has been made. For information, disturbance tolerance by birds is species dependant, some species habituating to noise and visual disturbance while other become more nervous. For example brent geese, redshank, bar-tailed godwit and curlew are more 'nervous' than oyster catcher, turnstone and dunlin. Turnstones will often tolerate one person within 5-10m. However, one person on a tidal flat can cause birds to stop feeding or fly off affecting c. 5 ha for gulls, c.13ha for dunlin, and up to 50 ha for curlew (Smit & Visser 1993). Goss-Custard & Verboven (1993) report that 20 evenly spaced people could prevent curlew feeding over 1000 ha of estuary.
Visual Presence
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Disturbance by noise and visual presence of human activities will be considered together. Disturbance causes birds that frequent the biotope to fly away. A reduction in predation pressure may benefit infaunal populations of crustaceans and polychaetes and therefore an intolerance assessment of not sensitive* has been made.
Abrasion & physical disturbance
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Abrasion is unlikely to affect the infaunal species of this biotope. Species such as amphipods and isopods may be small enough to avoid damage. The tops of polychaete burrows may be damaged and repaired subsequently at energetic cost to their inhabitants. In other biotopes represented by this review, the bivalve, Angulus tenuis, may be abundant and is an important food source for young plaice. This brittle bivalve may be damaged by abrasion from objects impacting and dragging through the sand, therefore £LGS.AP£, £LGS.AP.P£, and £LGS.AP.Pon£ may be more intolerant than the LGS.AEur biotope, but intolerance has been assessed to be low. Recovery has been assessed to be very high as a proportion of the tellin population is likely to remain undamaged and it breeds annually.
Displacement
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The important characterizing species, Eurydice pulchra and Bathyporeia pelagica, are both mobile species and leave the protection of the substratum regularly owing to their endogenous swimming rhythm. The polychaete, Scolelepis squamata, lives infaunally in vertical tubes formed from sand and mucus and is associated with the swash and surf zones of high energy sandy beaches (Dauer, 1983). Scolelepis squamata has been observed to swim and significant seasonal changes in its distribution within the swash and surf zones have been reported, indicating that the species is able to re-establish itself within the substratum following displacement. The biotope community has been assessed to be not sensitive to displacement.

Chemical Factors

Synthetic compound contamination
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Areas of sandy intertidal adjacent to industrialised and urbanised estuaries and coastlines may receive effluent discharges which contain a variety of synthetic conservative contaminants, i.e. those with a long half-life are likely to bioaccumulate and thus have a toxic effect (Clark, 1997). In general, crustaceans are widely reported to be intolerant of synthetic chemicals (Cole et al., 1999) and intolerance to some specific chemicals has been observed in amphipods. Powell (1979) inferred from the known susceptibility of Crustacea to synthetic chemicals and other non-lethal effects, that there would probably also be a deleterious effect on isopod fauna as a direct result of chemical application. Smith (1968) found that, at a concentration of 10 ppm, the oil dispersant BP 1002 killed the majority of Eurydice pulchra in 24 hours at 12°C. However, in the field a proportion of the Eurydice pulchra population survived exposure to lethal concentrations of BP 1002, both in the sand and water.
It is apparent that different taxa of the biotope are likely to differ in their susceptibility to different synthetic chemicals and that this may be related to differences in their physiology (Powell, 1979). Consequently, in the absence of evidence to the contrary and owing to the diversity of synthetic chemicals to which the biotope may be exposed, intolerance has been assessed to be high. Recovery requires dilution, biodegradation or removal of the contaminant from the sediments which may take several years, and recoverability has therefore been assessed to be moderate.
Heavy metal contamination
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For most metals, toxicity to crustaceans increases with decreased salinity and elevated temperature, therefore marine species living within their normal salinity range may be less susceptible to heavy metal pollution than those living in salinities near the lower limit of their salinity tolerance (McLusky et al., 1986).
Jones (1973; 1975b) found that mercury (Hg) and copper (Cu) reacted synergistically with changes in salinity and increased temperature (10°C) to become increasingly toxic to species of isopod, including Eurydice pulchra. Intolerance has been assessed to be intermediate specifically because alterations in salinity and temperature influence the effect of heavy metals on the community and the entire population may not be destroyed but may experience sublethal effects which may reduce the viability of the population. Recovery requires dilution, biodegradation or removal of the contaminant from the sediments which may take several years. Therefore recoverability has been assessed to be moderate.
Hydrocarbon contamination
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Oil spills result in large scale damage to intertidal communities. Oil smothers sediments preventing oxygen exchange, producing anoxia and death of infauna. Stranded oil penetrates the sediment, especially sands due to wave and tidal action and destabilises the sediment. Microbial degradation of the oil increases the biological oxygen demand and hence anoxia. Amphipods have been reported to be particularly intolerant of oil pollution (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 and the effects of smothering, therefore intolerance has been assessed to be high as amphipods are important characterizing species in all the biotopes represented by this review. Often populations do not return to pre-spill abundances for 5 or more years, which is most likely related to the persistence of oil within sediments (Southward, 1982) and recoverability has therefore been assessed to be moderate.
Radionuclide contamination
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Radionuclides can accumulate within substrata in a similar way to heavy metals. However, there is little information concerning their biological effects (Cole et al., 1999).
Changes in nutrient levels
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The effects of organic enrichment on sedimentary systems and their benthos is well documented and shows a consistent sequence of response - the Pearson-Rosenberg model (Pearson & Rosenberg, 1978). Greater organic inputs, coupled with reduced oxygenation lead to conditions of slow degradation and create anaerobic chemical conditions within the sediment. In turn, microbial activity is enhanced whilst the redox potential of the sediments is reduced which in turn increases the production of hydrogen sulphide and methane (Fenchel & Reidl, 1970). A state of anaerobiosis limits the macroinfauna to species which can form burrows or have other mechanisms to obtain their oxygen from the overlying water. Moderate enrichment provides food which enhances species abundance, whilst a mixing of organisms with different responses initially increases diversity (Elliott, 1994). With greater enrichment, the diversity declines and the community becomes increasingly dominated by a few pollution tolerant, opportunistic species such as the polychaete Capitella capitata.
For instance, prior to the introduction of a sewage treatment scheme in the Firth of Forth, the communities of several sandy beaches were considerably modified by gross sewage pollution (Read et al.,1983). The west end of Seafield beach exhibited extremely reduced diversity with a community dominated by Scolelepis fuliginosa and Capitella capitata, to the almost exclusion of all other species of macrofauna. However, at Portobello beach, a reduction in the number of species was recorded and the presence of a 'dominant' replacement community was less obvious. Furthermore, in 1977, before the introduction of the sewage scheme, meiofauna population counts at Seafield and Portobello were also conspicuously lower than for other Scottish beaches (McIntyre, 1977). Many of the major taxa commonly associated with marine intertidal meiobenthos were scarce or absent. Only nematodes, gastrotriches, harpacticoids and turbellarians were commonly identified from samples, nematodes being the most abundant taxon.
intolerance to nutrient enrichment has been assessed to be high owing to the resultant modification of the faunal community. Following sewage pollution abatement in 1977, dramatic changes in the macrofauna occurred. The Scolelepis / Capitella community declined steadily throughout 1978-1979, so that by spring 1980 species normally associated with 'cleaner' sandy beaches were recorded e.g. Microthalmus sp., Ophiodromus flexuosus, Eulalia viridis, Eurydice pulchra and Monoculodes sp., but not at pre-impact abundances. There was also an increase in meiofaunal diversity and reduction in dominance by certain taxa. Recovery has been reported to be high as full recovery is likely to take several years.
Increase in salinity
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Salinities higher than that of seawater are uncommon, although surface pools may increase in salinity owing to evaporation in hot conditions. However, owing to the relatively well drained nature of the substratum in the LGS.AEur biotope, pooling of surface water is unlikely and the infaunal species may avoid the factor by burrowing. Intolerance has been assessed to be low in light of lack of evidence to the contrary. Recovery has been assessed to be very high because the important characterizing species are abundant and would rapidly repopulate areas of localised reduced abundance.
Decrease in salinity
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Intertidal sands may be exposed to rainfall at low tide, however, freshwater sits on the surface of denser seawater and interstitial water remains close to full salinity. In order to tolerate salinity changes, species may osmoregulate, may stop irrigating their burrow, or may move seaward if mobile or burrow deeper into the sediment (McLusky 1989). Freshwater flowing seaward over sandflats may have a localised effect on species diversity and abundance. Eurydice pulchra was found to be relatively euryhaline (Jones, 1970b), whilst Bathyporeia pelagica migrates seaward in response to reduced salinities, the effect of which is enhanced by higher temperature (Preece, 1970). An intolerance assessment of low has been made, owing to the lack of mortalities arising from reduced salinities in the field. Recovery has been assessed to be very high because the important characterizing species are abundant and would rapidly repopulate areas of localised reduced abundance.
Changes in oxygenation
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Coarse sands may have relatively high oxygen concentration and a lack a black reducing layer. Brafield (1964) concluded that the most significant factor influencing the oxygenation is the drainage of the beach which, in turn, is determined by the slope and particle size. Oxygen depletion becomes a severe problem at all states of the tide on only the finest grained beaches, and as a general rule, if the percentage of particles of less than 0.25 mm in diameter exceeds 10% of a sand, then the oxygen concentration of its interstitial water will be less than 20 % of the air saturation level, and will drop rapidly during low tide periods. As the LGS.AEur biotope community is not normally exposed to conditions of anoxia it has consequently been inferred that the biotope community would have a high intolerance to a decrease in oxygenation at the benchmark level. On return to prior conditions, re-population is likely and has been assessed to be high (see additional information below).

Biological Factors

Introduction of microbial pathogens/parasites
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The most common parasites of sand inhabiting invertebrates belong to the Trematoda, a class of the phylum Platyhelminthes, and to the Copepoda, a group of crustaceans whose free living members are either planktonic or sediment dwelling. Trematodes (flukes) usually have three consecutive hosts, although two to four are known. In the marine environment, the primary hosts are normally fish or birds, and the first secondary host a gastropod or bivalve mollusc. The second intermediate host may belong to a variety of taxonomic hosts including the coelenterates, turbellarians, annelids, crustaceans, molluscs, insects or fish (Eltringham, 1971). However, an intolerance assessment for the biotopes represented by this review cannot be made owing to insufficient information concerning impacts on the population.
Introduction of non-native species
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Insufficient information.
Extraction
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None of the important characterizing species of the LGS.AEur, LGS.AP, LGS.AP.P & LGS.AP.Pon biotopes are targeted for extraction. However, Arenicola marina occurs in the biotopes LGS.AP and LGS.AP.P, which have a more diverse polychaete community than LGS.AEur. Arenicola marina is targeted by bait diggers who extract the species both manually and mechanically. Mechanical lugworm dredging is more severe and can result in the complete removal of Arenicola marina (Fowler, 1999). McLusky et al. (1983) examined the effects of bait digging on blow lug populations in the Forth estuary. Dug and infilled areas and unfilled basins left after digging re-populated within 1 month, whereas mounds of dug sediment showed a reduced population. Basins accumulated fine sediment and organic matter and showed increased population levels for about 2-3 months after digging. Overall recovery is generally regarded as rapid. However, Fowler (1999) pointed out that recovery may take longer on a small pocket beach with limited possibility of recolonization from surrounding areas. Therefore, if adjacent populations are available recovery will be rapid and a rank of 'very high' has been given. However where the affected population is isolated or severely reduced (e.g. by long-term mechanical dredging), then the recovery period may be extensive.

Additional information icon Additional information

Recoverability
Little evidence concerning community development was found and consequently information on the important characterizing species recruitment processes and longevity has been used to infer a time period of 1 to 2 years for the community to recover. One of the important characterizing species, Bathyporeia pelagica, produces a sequence of broods throughout the spring and summer which reach maturity within a year to produce subsequent generations. The meiofaunal community produces several generations within a year.

This review can be cited as follows:

Budd, G.C. 2004. Burrowing amphipods and Eurydice pulchra in well-drained clean sand shores. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=344&code=2004>