Biodiversity & Conservation

SS.IMS.FaMS.MacAbr

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Muddy sand communities are highly intolerant of substratum loss because most species are infaunal and so will be removed. A few mobile demersal species like the shrimp Crangon crangon may be able to avoid the factor. However, owing to the loss of the characterizing and important functional infaunal species the biotope would not be recognized so intolerance has been assessed to be high. Recoverability has been assessed to be high (see additional information below).
Smothering
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The biotope is characterized by mostly burrowing bivalve species, polychaete worms and macrofauna such as the heart urchin Echinocardium cordatum and brown shrimp, Crangon crangon. The biotope has been assessed to be not sensitive to smothering by 5 cm of additional sediment as the infauna should be able to burrow upwards (Schafer, 1972; Rees & Dare, 1993) or are sufficiently mobile to avoid the factor. However, a higher intolerance would be expected following smothering by other materials that are very viscous or impermeable.
Increase in suspended sediment
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Deposit feeders are the dominant trophic group in this biotope and therefore are not directly reliant on suspended matter as a food resource, although Macoma balthica, Abra alba and Fabulina fabula are also facultative filter feeders and may switch to suspension feeding should the food supply become more profitable (Lin & Hines, 1994; Salzwedel, 1979). An increase in suspended sediment will increase the rate of siltation at the sediment surface, potentially enhancing the food supply for all deposit feeders in the biotope. The community of the biotope has been assessed to be not sensitive* with the potential for growth and reproduction to be enhanced by the enhanced food supply.
Decrease in suspended sediment
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Deposit feeders are the dominant trophic group in this biotope and therefore are not directly reliant on suspended matter as a food resource. However a decrease in siltation may result in a decreased rate of deposition on the substratum surface and therefore a reduction in food availability for deposit feeders. This would be likely to impair growth and reproduction. The benchmark states that this change would occur for one month and therefore would be unlikely to cause mortality. An intolerance of low is therefore recorded. As soon as suspended sediment levels increase, feeding activity would return to normal and hence recovery is recorded as very high.
Desiccation
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The biotope occurs in the shallow sublittoral where it is continually immersed.
Increase in emergence regime
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The biotope occurs in the shallow sublittoral where it is continually immersed.
Decrease in emergence regime
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The biotope occurs in the shallow sublittoral where it is continually immersed so that a decrease in emergence would not have an effect.
Increase in water flow rate
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The intensive working of the uppermost few centimetres of the sediment by the largely deposit feeding community, especially bivalves, produces a fluid faecal-rich surface that is easily re-suspended by even low velocity tidal currents (Rhoads & Young, 1970). The biotope is found in locations of weak (< 0.5 m/sec) water flow, so the benchmark increase would expose the biotope to strong currents (1.5 -3 m/sec). Over the period of one year loss of the muddy sand surface substratum is likely along with much of the organic matter which the infaunal deposit feeders consume. Whilst infaunal species buried relatively deeply, such as Echinocardium cordatum are unlikely to be washed out, smaller bivalves buried at shallower depths may be periodically displaced. The intolerance of the biotope has been assessed to be high owing to the fact that the biotope may begin to change to another and that benthic food deposits may become limiting. Recoverability has been assessed to be high as a result of recruitment and probable migration from surrounding areas (see additional information below).
Decrease in water flow rate
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The IMS.MacAbr biotope occurs in areas of weak water flow so the benchmark decrease in water flow rate will expose the community to conditions of almost negligible water flow. Whilst a decreased water flow would favour the deposition of particulate organic matter from suspension, the additional food resource is unlikely to be of any particular significance in this already organically enriched environment. More importantly, a decreased water flow rate may limit the dispersion of planktonic larvae, to the extent that larvae settle back into the parent population where larvae in the earliest stages are likely to be preyed upon by deposit feeders, including their parents. An intolerance assessment of low has been made owing to the reduced viability of the population that may result from poor larval recruitment. Recovery has been assessed to be very high as the adults of the important characterizing species will remain and produce again, with the exception of Lagis koreni, which, produces once then dies. However, larval plankton of this species are likely to be transported into the biotope from other locations and re-colonization of the substrata may also occur through re-distribution of adults.
Increase in temperature
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The key functional species Macoma balthica and Abra alba have a geographical distribution that extends to the south of the British Isles, so it is probable that the species would be tolerant of higher temperatures than experienced around Britain and Ireland. Macoma balthica proved to be very tolerant of higher temperatures, for instance it was maintained for six hours at 37.5 °C without death (Ratcliffe et al., 1981) and tolerated temperatures up to 49 °C before thermal numbing of the gill cilia occurred presumably caused death (Oertzen, 1969). The growth of Fabulina fabula (studied as Tellina fabula) correlated positively with water temperature increases up to 16 °C after which temperature increase inhibited growth (Salzwedel, 1979), a similar pattern might be inferred for Abra alba as it is a closely related species. Considering that maximum sea surface temperatures around the British Isles rarely exceed 20 °C (Hiscock, 1998), it is unlikely that the species of this biotope would suffer any mortality as a result of the benchmark increase in temperature. Elevated temperatures may initially enhance growth but later inhibit it as a result of energetic cost associated with sub-optimal metabolic function, therefore intolerance has been assessed to be low. Metabolic activity should return to normal within a few days or weeks at lower temperatures so recoverability has been assessed to be immediate.
Decrease in temperature
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Macoma balthica was apparently unaffected by the severe winter 1962/3 which decimated populations of other bivalves. Arntz & Rumohr (1986) noted the intolerance of Abra alba to extreme low temperatures in Kiel Bay with recovery to former densities taking some two years. Significant mortality of coastal populations of Echinocardium cordatum was reported from around the British Isles and in the German Bight during the severe winter of 1962/63 (Crisp, 1964; Ziegelmeier, 1978). Arntz & Rumohr (1986) reported Lagis koreni to be intolerant of extremely low bottom temperatures. Intolerance has been assessed to be intermediate as the populations of a key/important functional and important characterizing species may be partially destroyed by the factor. Recoverability has been assessed to be high (see additional information below).
Increase in turbidity
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Primary production in the biotope is not significant. An increase in turbidity is therefore not likely to have a significant effect on the biotope directly. The benthic fauna rely on nutrient input from pelagic and coastal fringe production (Barnes & Hughes, 1992). Increased turbidity in these areas may reduce primary production and consequently reduce the food supply to the benthos. The fauna in the IMS.MacAbr biotope may therefore suffer decreased growth and reproduction. However, the nutrient input to the biotope originates from a very wide area and the decrease in food supply is not likely to cause mortality over a year so the biotope intolerance is assessed as low. Primary production would be stimulated as turbidity decreased so recoverability has been assessed to be very high.
Decrease in turbidity
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A decrease in turbidity will mean more light is available for photosynthesis by phytoplankton in the water column and microphytobenthos on the sediment surface. This would increase primary production and may mean greater food availability for facultative suspension feeders and eventually deposit feeders. However, primary production is not a major source of production in the biotope so the turbidity decrease is not likely to have a significant effect. The benthos is probably supported predominantly by detrital materials emanating from the coastal fringe and by pelagic production (Barnes & Hughes, 1992). The biotope has been assessed to be not sensitive to this factor.
Increase in wave exposure
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Where the biotope occurs in the shallow sublittoral e.g. in the organically rich inshore sediments off estuary mouths, the community may be vulnerable to wave-induced bottom disturbance. Increased wave action is likely to affect the community in several ways, for instance, erosion of muddy sand sediments is probable resulting in the reduction of the available habitat. Wave action is likely to cause bivalve species to withdraw their siphons, resulting in loss of feeding opportunities and compromised growth. The infauna may be dislodged. For instance, Rees et al (1977) recorded strandings of Lagis koreni and mass stranding of Echinocardium cordatum following storms on the North Wales coast. Intolerance has been assessed to be intermediate as populations within the biotope are likely to be reduced by the factor and that the habitat may be partially destroyed. Recoverability has been assessed to be high (see additional information below).
Decrease in wave exposure
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The biotope occurs in locations sheltered from wave exposure so is likely to be intolerant of a further decrease this factor.
Noise
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Macoma balthica was able to detect shear-wave vibrations that propagate along the sediment surface in the frequency range 50-200 Hz. Its response consisted of frequent and intense digging attempts (Franzen, 1995). However, no other information concerning noise detection amongst other species of this biotope was found. Macoma balthica is likely to remain buried or take immediate avoidance action in response to this factor, probably without detectable effect upon its viability. Therefore the biotope has been assessed to be not sensitive to this factor.
Visual Presence
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The majority of the species particularly characteristic of this biotope are infaunal and have little or no visual acuity. Epibenthic predators such as Crangon crangon and fish have visual acuity and may be temporarily scared away or cease hunting in response to the visual presence of objects not normally found in the marine environment (see benchmark). However, the biotope is unlikely to be affected as the infauna will remain in situ. Therefore an assessment of not sensitive has been made.
Abrasion & physical disturbance
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The relatively delicate shells of the bivalves that characterize this biotope are vulnerable to physical damage. The biotope community may be subjected to more intense abrasive / physical disturbance from otter and beam trawls used to capture the brown shrimp, Crangon crangon.

Bergman & van Santbrink (2000) suggested that the megafauna such as Echinocardium cordatum, Corystes cassivelaunus, and bivalves such as Phaxas pellucidus, Dosinia lupinus, Mactra corallina, Abra alba, Spisula solida and Spisula subtruncata were amongst the species most vulnerable to direct mortality due to bottom trawling in sandy sediments. Bivalves such as Ensis spp.,
Corbula gibba and Chamelea gallina together with starfish were relatively resistant (Bergman & van Santbrink, 2000). Bradshaw et al. (2000) suggested that fragile species such a urchins (e.g. Spatangus purpureus and Echinus esculentus), the brittlestar Ophiocomina nigra, starfish Anseropoda placenta and the edible crab Cancer pagurus suffered badly from impact with a passing scallop dredge. More robust bodied or thick shells species were less sensitive. Overall, species with brittle, hard tests are regarded to be sensitive to impact with scallop dredges (Kaiser & Spencer, 1995; Bradshaw et al., 2000). However, the small size of Macoma balthica and Abra alba relative to the gear and meshes of commercial trawls may ensure survival of at least a moderate proportion of disturbed individuals which pass through.

Abra alba and Macoma balthica demonstrate an 'r' type life-cycle strategy and are able to rapidly exploit any new or disturbed substratum available for colonization through larval recruitment, secondary settlement of post-metamorphosis juveniles or re-distribution of adults. Bonsdorff (1984) studied the recovery of a Macoma balthica population in a shallow, brackish bay in SW Finland following removal of the substratum by dredging in the summer of 1976. Recolonization of the dredged area by Macoma balthica began immediately after the disturbance to the sediment and by November 1976 the Macoma balthica population had recovered to 51 individuals/mē. One year later, there was no detectable difference in the Macoma balthica population between the recently dredged area and a reference area elsewhere in the bay. In 1976, 2 generations could be detected in the newly established population indicating that active immigration of adults was occurring in parallel to larval settlement. In 1977, up to 6 generations were identified, giving further evidence of active immigration to the dredged area. Abra alba recovered to former densities following loss of a population from Keil Bay owing to deoxygenation within 1.5 years (Arntz & Rumohr, 1986).

Effects on other infauna would depend upon the depth penetration of the gear, relative to the distribution of animals in the sediments but significant trawl-induced mortality has been reported for Echinocardium cordatum (De Groot & Apeldoorn 1971; Rauck, 1988). Furthermore, Lagis koreni is incapable of reconstructing its delicate sand-tube once removed from it (Schafer, 1972), and hence mortality following physical disturbance would be expected to be high for this species in particular. Therefore, an overall biotope intolerance of intermediate has been recorded. Recoverability has been assessed to be high (see additional information below).

Displacement
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The bivalve species of this biotope are likely to be tolerant of displacement owing to their burrowing ability. For example, Macoma balthica is able to rebury itself within 17 minutes when placed on the surface of a suitable substratum (McGreer, 1979), the other bivalves would be expected to behave in a similar manner, as would Echinocardium cordatum. However, the polychaete Lagis koreni is incapable of reconstructing its delicate sand-tube once removed from it (Schafer, 1972), and hence mortality following displacement would be expected to be high for this species in particular. The intolerance of this biotope has been assessed to be intermediate owing to mortality of an important characterizing species and the fact that normally infaunal species displaced to the surface will be prone to predation by fish and the shrimp Crangon crangon. On balance recoverability is likely to be immediate as the species would seek protection and any that were lost to predators would be replaced by new recruits within the year.

Chemical Factors

Synthetic compound contamination
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Deposit feeding may be a particularly important route for exposure to toxins within this biotope. Beaumont et al. (1989) concluded that bivalves were particularly sensitive to tri-butyl tin (TBT), the toxic component of many antifouling paints. 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 caused recruitment failure in bivalves, either due to reproductive failure or larval mortality (Bryan & Gibbs, 1991). Abra alba failed to burrow into sediment contaminated with pesticides (6000 ppm parathion, 200 ppm methyl parathion and 200 ppm malathion) (Møhlenberg & Kiørboe, 1983), such behaviour would make it prone to predation.
Detergents used to disperse oil from the Torrey Canyon oil spill caused mass mortalities of Echinocardium cordatum (Smith, 1968) and its intolerance to TBT was similar to that of other benthic organisms with LC50 values of 222 ng Sn/l in pore water and 1594 ng Sn/g dry weight of sediment (Stronkhorst et al., 1999). Owing to evidence of mortalities, recruitment failure and disrupted behaviour experienced by key and important functional species of the biotope, intolerance has been assessed to be high. Recovery would be expected following degradation of the contaminants and recoverability has been assessed to be high (see additional information below).
Heavy metal contamination
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There is evidence of both lethal and sub-lethal effects upon Macoma balthica as a result of exposure to heavy metal pollution (McGreer, 1979; Luoma et al., 1983; Boisson et al., 1998). Other bivalves in the biotope are also likely to be intolerant of heavy metal pollution as bivalves tend to accumulate heavy metals in their tissues far in excess of environmental levels. Reactions to sub-lethal levels of heavy metal stressors include siphon retraction, valve closure, inhibition of byssal thread production, disruption of burrowing behaviour, inhibition of respiration, inhibition of filtration rate, inhibition of protein synthesis and suppressed growth (see review by Aberkali & Trueman, 1985). Bryan (1984) stated that Hg was the most toxic metal to bivalve molluscs while Cu, Cd and Zn seemed 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). Owing to evidence in the literature of sub-lethal effects and mortality of bivalves, the intolerance of the characteristic bivalve community inhabiting this biotope to heavy metal contamination has been assessed to be intermediate and species richness is expected to decline. In the absence the biotope may begin to change to another. Furthermore, echinoderms are also regarded as being intolerant of heavy metals (e.g. Bryan, 1984; Kinne, 1984) while polychaetes are often more tolerant (Bryan, 1984). Recovery is likely to be high but would be dependent on the removal of the contaminant.
Hydrocarbon contamination
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Stekoll et al. (1980) reported a range of behavioural, physical, physiological and biochemical changes prior to death following exposure to Prudhoe Bay crude oil at varying concentrations (0.03; 0.3 and 3.0 mg /l). Effects included inhibition of growth, reabsorption and abnormalities of the gonads, emergence from the substratum and poor orientation in addition to increased mortality at the highest concentration. Stekoll et al. (1980) concluded that chronic exposure of Macoma balthica to oil-in-seawater concentrations even as low as 0.03 mg/l would in time lead to population decreases. The specimens used by Stekoll et al., (1980) were not subjected to any of the stresses that normally occur in their natural environments so intolerance would be expected to be higher in field conditions. Macoma balthica was considered to be a key functional species of this biotope and is also characteristic. If Macoma balthica was lost from the biotope as a result of hydrocarbon pollution, the biotope would not be recognized so intolerance has been assessed to be high. Recoverability has been assessed to be high assuming contamination is removed (see additional information below).
Radionuclide contamination
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There is insufficient information concerning the biological effects of radionuclide contamination to assess the intolerance of this biotope.
Changes in nutrient levels
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Macoma balthica and Abra alba are reported to favour organic enrichment. Madsen & Jensen (1987) reported increased shell growth, productivity : biomass radio and improvement in 'condition index' of Macoma balthica in organically enriched areas of the Dutch Wadden Sea, which was presumably due to the increased food supply. Furthermore, as Macoma balthica is relatively tolerant to periodic deoxygenation (an associated consequence of nutrient enrichment) it is likely that it will benefit from nutrient enrichment at the benchmark level. Abra alba increased its reproductive output to three spawning as opposed to its normally occurring twice yearly recruitment, as an adaptive response to eutrophic conditions that followed the Amoco Cadiz oil spill (Dauvin & Gentil, 1989). Lagis koreni may favour moderate organic enrichment, but it is displaced in anoxic sediments (Pearson & Rosenberg, 1978). Growth levels of Echinocardium cordatum have been observed to be lower in sediments with high organic content although it is suggested that this may be due to higher levels of intraspecific competition (Duineveld and Jenness, 1984). Owing to the evidence of improved condition, growth and reproductive output in the bivalve species that are key functional species, the biotope has been assessed to be not sensitive* to nutrient enrichment at the benchmark level.
Increase in salinity
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The IMS.MacAbr biotope occurs in 'full' salinity conditions (Connor et al., 1997a) and therefore an increase in salinity was considered not to be a relevant factor.
Decrease in salinity
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IMS.MacAbr occurs in 'full' salinity conditions (Connor et al., 1997a) and therefore is likely to be intolerant of salinity decreases in some way. The benchmark decrease in salinity would place the biotope in areas of variable salinity for one year or reduced salinity for one week. Biotope intolerance is dependent on the intolerance of the characterizing species. For example, although Macoma balthica is found in brackish and fully saline waters (Clay, 1967b) survival times of Macoma balthica declined with decreasing salinity (McLusky & Allan, 1976). Abra alba and Fabulina fabula are typically found in full salinity conditions and are therefore likely to be intolerant of reductions in salinity in some way. Salzwedel (1979) reported Fabulina fabula to occur in variable salinity conditions (down to 20 psu) but that growth was inhibited. Echinoderms are considered to be stenohaline animals that lack the ability to osmo- and ion-regulate (Stickle & Diehl, 1987). However, Echinocardium cordatum was recorded from brackish waters in the Delta region of the Netherlands to about the 15 psu isohaline (Wolff, 1968), so may be able to tolerate the stress for the given time period. Decreased salinity is likely to cause inhibition of growth and reproduction and hence reduce viability therefore intolerance has been assessed to be low. Recoverability has been assessed to be high as on return to prior conditions growth and reproduction would probably return rapidly to normal and recruitment would compensate for any vulnerable individuals lost.
Changes in oxygenation
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Jorgensen (1980) observed the response of macrofauna to reduced dissolved oxygen levels of 0.2 to 1 mg/l for a period of 3 to 4 weeks in an estuarine/marine area in Sweden by diving. The shrimp Crangon crangon was amongst the first to die from lack of oxygen. Polychaetes were observed to come to the surface, small specimens first. Lagis koreni was observed limp and motionless on the surface but could be revived in 30 minutes by placing in oxygenated water. Nichols (1977) reported high mortality of Lagis koreni in association with periodic oxygen deficiency of the bottom waters of Kiel Bay, however it was capable of reaching former densities within a year following larval recruitment. During periods of hypoxia, burrowing bivalves were first observed to extend their siphons further into the water column but, as oxygen depletion continued, they emerged and laid on the sediment surface. For instance, Macoma balthica lay upon its side with the foot and siphons retracted but with valves gaping slightly allowing the mantle edge to be brought into full contact with more oxygenated water (Brafield & Newell, 1961). Furthermore, Macoma balthica proved to be resistant to anoxia for periods of up to 70 days at 5 °C and 11 days at 20 °C (Dries & Theede, 1984). Abra alba became inefficient in its use of available organic matter over a period of prolonged hypoxia (93 days) in an experiment to examine the interaction between eutrophication and oxygen deficiency (Hylland et al., 1996). Abra alba was also reported to be intolerant of lowered oxygen concentrations arising from eutrophication off the Swedish west coast (Rosenberg & Loo, 1988), whilst lethal effects were noted by Weigelt & Rumohr (1986) and Arntz & Rumohr (1986) in the western Baltic Sea. However, the benchmark assesses intolerance to hypoxia for one week whilst evidence of significantly reduced viability or death are reported after much longer periods. Therefore intolerance at the benchmark level has been assessed to be low. However, as the evidence suggests, prolonged exposure to oxygen concentrations below 2 mg O2 /l may severely impact upon species growth and survival and intolerance would be reported to be higher.

Biological Factors

Introduction of microbial pathogens/parasites
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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). Therefore mortality of some of the bivalves that characterize the biotope is likely following the introduction of pathogens or parasites and intolerance has been assessed to be intermediate. Recovery of the population is probable
Introduction of non-native species
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No particular non-native species was identified as posing a current threat to this biotope.
Extraction
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The brown shrimp, Crangon crangon, one of the species indicative of sensitivity, is the target of a commercial fishery. Aside from the effects on the shrimp, however, the otter and/or beam trawls used to capture Crangon crangon tend to disrupt the habitat and dislodge inhabitants from the substratum.

Bergman & van Santbrink (2000) suggested that the megafauna including Echinocardium cordatum and Abra alba were amongst the species most vulnerable to direct mortality due to bottom trawling in sandy sediments. Bivalves such as Ensis spp.,
Corbula gibba and Chamelea gallina together with starfish were relatively resistant (Bergman & van Santbrink, 2000). Bradshaw et al. (2000) suggested that fragile species such a urchins (e.g. Spatangus purpureus and Echinus esculentus), the brittlestar Ophiocomina nigra, starfish Anseropoda placenta and the edible crab Cancer pagurus suffered badly from impact with a passing scallop dredge. More robust bodied or thick shells species were less sensitive. Overall, species with brittle, hard tests are regarded to be sensitive to impact with scallop dredges (Kaiser & Spencer, 1995; Bradshaw et al., 2000). However, the small size of Macoma balthica and Abra alba relative to the gear and meshes of commercial trawls may ensure survival of at least a moderate proportion of disturbed individuals which pass through.

Abra alba and Macoma balthica demonstrate an 'r' type life-cycle strategy and are able to rapidly exploit any new or disturbed substratum available for colonization through larval recruitment, secondary settlement of post-metamorphosis juveniles or re-distribution of adults. Bonsdorff (1984) studied the recovery of a Macoma balthica population in a shallow, brackish bay in SW Finland following removal of the substratum by dredging in the summer of 1976. Recolonization of the dredged area by Macoma balthica began immediately after the disturbance to the sediment and by November 1976 the Macoma balthica population had recovered to 51 individuals/mē. One year later, there was no detectable difference in the Macoma balthica population between the recently dredged area and a reference area elsewhere in the bay. In 1976, 2 generations could be detected in the newly established population indicating that active immigration of adults was occurring in parallel to larval settlement. In 1977, up to 6 generations were identified, giving further evidence of active immigration to the dredged area. Abra alba recovered to former densities following loss of a population from Keil Bay owing to deoxygenation within 1.5 years (Arntz & Rumohr, 1986).

Effects on other infauna would depend upon the depth penetration of the gear, relative to the distribution of animals in the sediments but significant trawl-induced mortality has been reported for Echinocardium cordatum (De Groot & Apeldoorn 1971; Rauck, 1988). Furthermore, Lagis koreni is incapable of reconstructing its delicate sand-tube once removed from it (Schafer, 1972), and hence mortality following physical disturbance would be expected to be high for this species in particular. Therefore, an overall biotope intolerance of intermediate has been recorded. Recoverability has been assessed to be high (see additional information below).

Additional information icon Additional information

Recoverability
The life history characteristics of the species which characterize the biotope suggest that the biotope would recover from major perturbations within 5 years. For instance, Abra alba and Macoma balthica demonstrate an 'r' type life-cycle strategy and are able to rapidly exploit any new or disturbed substratum available for colonization through larval recruitment, secondary settlement of post-metamorphosis juveniles or re-distribution of adults. Bonsdorff (1984) studied the recovery of a Macoma balthica population in a shallow, brackish bay in SW Finland following removal of the substratum by dredging in the summer of 1976. Recolonization of the dredged area by Macoma balthica began immediately after the disturbance to the sediment and by November 1976 the Macoma balthica population had recovered to 51 individuals/mē. One year later there was no detectable difference in the Macoma balthica population between the recently dredged area and a reference area elsewhere in the bay. In 1976, 2 generations could be detected in the newly established population indicating that active immigration of adults was occurring in parallel to larval settlement. In 1977, up to 6 generations were identified, giving further evidence of active immigration to the dredged area. Abra alba recovered to former densities following loss of a population from Keil Bay owing to deoxygenation within 1.5 years as did Lagis koreni, taking only one year (Arntz & Rumohr, 1986). Such evidence suggests that recoverability of the key functional and important characterizing species of the IMS.MacAbr biotope would be typically be high. However, the recovery of Echinocardium cordatum may take longer owing to recruitment that is frequently unsuccessful (Rees & Dare, 1993).

This review can be cited as follows:

Budd, G.C. 2007. Macoma balthica and Abra alba in infralittoral muddy sand or mud. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 01/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=173&code=1997>