Biodiversity & Conservation

SS.IMX.FaMx.Lim

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum would result in removal of the Limaria hians byssal carpet and the associated community. Therefore, an intolerance of high has been recorded. Recoverability would depend on recruitment from the surrounding area and subsequent growth of the Limaria hians population and its associated community, and has been assessed as low (see additional information below).
Smothering
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Minchin (1995) reported that degradation of the Limaria hians bed resulted in patches of exposed shell-sand, destabilization of the sea bed and subsequent burial of surviving Limaria hians, which contributed to the decline of the bed. Smothering by 5 cm of sediment will probably prevent water flow through the intricate byssal nests of Limaria hians, preventing feeding and resulting in local hypoxia. Limaria hians is capable of swimming, and some individuals may be able to evacuate their nests. However, a proportion of the Limaria hians may be lost and an intolerance of intermediate has been recorded.

Interstitial or infaunal species are unlikely to be adversely affected, although feeding may be interrupted and mobile species will avoid the effects. Loss of a proportion of the gaping file shell population and resultant degradation of the byssal carpet and loss of some associated epifauna, will result in the loss of species richness. Therefore, an intolerance of intermediate has been recorded. Recovery of the Limaria hians bed will depend on recruitment from outside the population and from survivors and is likely to be high (see additional information below).

Increase in suspended sediment
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An increase in suspended sediment levels may adversely affect suspension feeding species by clogging feeding and respiratory structures, and may result in increased siltation depending on water movement. Minchin (1995) suggested that Limaria hians was common in areas free of silt and mud. But Limaria hians beds have been recorded on muddy sand and gravel in wave sheltered areas with weak tidal streams such as lochs, and presumably subject to suspended sediment and siltation. The byssal nest probably protects the residents from the direct effects of siltation. Therefore, Limaria hians beds are probably tolerant of a variety of suspended sediment and siltation regimes. However, an increase in suspended sediment loads is likely to reduce feeding efficiency of suspension feeders including Limaria hians and increase energetic costs in the form of sediment rejection currents, mucus and pseudofaeces in the Limaria hians. The diversity of hydroids and bryozoans is likely to be reduced by siltation and the species composition of the biotope is likely to vary with suspended sediment loads.
Overall, an intolerance of low has been recorded with a recoverability of very high.
Decrease in suspended sediment
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A decrease in suspended sediment may reduce the food availability for suspension feeding invertebrates. The species composition of associated epifaunal species is likely to vary with suspended sediment concentration, with sediment tolerant species being out-competed by fast growing but less sediment tolerant species as the suspended sediment concentration decreases. Overall, although the associated epifaunal species may change, and species richness decline temporarily, the Limaria hians carpet is unlikely to be adversely affected. Therefore, an intolerance of low has been recorded with a recoverability of very high.
Desiccation
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Limaria hians bears numerous fleshy, hydrostatic tentacles that can not be withdrawn into the shell, together with a wide gaping shell (Gilmour, 1967; Tebble, 1976). Therefore, it is probably highly intolerant of desiccation and any specimen washed ashore will probably die. However, this biotope is subtidal, and unlikely to be exposed to the air.
Increase in emergence regime
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An increase or decrease in tidal emergence is unlikely to affect subtidal habitats, except that the influence of wave action and tidal streams may be increased (see water flow rate below).
Decrease in emergence regime
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An increase or decrease in tidal emergence is unlikely to affect subtidal habitats, except that the influence of wave action and tidal streams may be increased (see water flow rate below).
Increase in water flow rate
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This biotope occurs in weak to moderately strong tidal streams. An increase in water flow rate to strong or very strong is likely to physically damage the bed due to drag and modify the substratum in favour of coarser sediments, boulders and bedrock. The additional drag caused by emergent epifauna attached to the carpet, especially if kelps are present, is likely to cause the carpet to be removed in lumps. Holes in the carpet, may then allow mobilization of the sediment, resulting in further damage (see Minchin, 1995). Loss of the carpet will entail loss of the byssal carpet and its associated community, although individual gaping file shells will probably survive and be transported elsewhere (see displacement). Therefore, an intolerance of high has been recorded. Recoverability is likely to be low (see additional information below).
Decrease in water flow rate
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This biotope occurs in weak to moderately strong tidal streams. Decreases in water flow will favour epifaunal species tolerant of reduced water flow over species that prefer high water flow rates, so that the composition of the epifaunal species will change. A decrease in water flow to negligible in the absence of wave induced water movement may result in a stagnant deoxygenated water (see deoxygenation) and increased siltation (see above). Although, Limaria hians probably produces a strong ventilation current for feeding it require water flow to remove waste products and provide adequate food. Therefore, a proportion of the population, and the associated species may be lost and an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).
Increase in temperature
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Limaria hians has been recorded from the Lofoten Isles, Norway south to the Canary Isles and the Azores. Therefore, it is unlikely to be affected by long term changes in temperature at the benchmark level in British waters.

Other members of the community may be adversely affected, for example boreal species (e.g. Balanus crenatus and Modiolus modiolus) may be replaced in the community by more southern species. In addition, reproduction and recruitment in echinoderms, and reproduction in hydroids and bryozoans are probably influenced by temperature (refer to species reviews).

Overall, the species composition may vary but the gaping file shell carpet and hence the biotope will probably survive. The biotope is protected from extremes of temperature change by its subtidal habit. Therefore, an intolerance of low has been recorded to represent changes in species composition.
Decrease in temperature
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Limaria hians has been recorded from the Lofoten Isles, Norway south to the Canary Isles and the Azores. Therefore, it is unlikely to be affected by long term changes in temperature at the benchmark level in British waters.

Other members of the community may be affected, for example boreal species (e.g. Balanus crenatus and Modiolus modiolus) may increase in abundance. In addition, reproduction and recruitment in echinoderms, and reproduction in hydroids and bryozoans are probably influenced by temperature (refer to species reviews).

Overall, the species composition may vary but the gaping file shell carpet and hence the biotope will probably survive. The biotope is protected from extremes of temperature change by its subtidal habit. Therefore, an intolerance of low has been recorded to represent changes in species composition.
Increase in turbidity
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Increased turbidity will reduce phytoplankton productivity and may reduce food availability for Limaria hians and other suspension feeders, however, most are probably capable of utilizing other organic particulates so that the effects would probably be sub-lethal. Increased turbidity will also decrease the depth to which kelps and other macroalgae can grow. Therefore, increased turbidity may decrease the occurrence of kelp and other macroalgae in examples of the biotope in which they occur, reducing species richness and the diversity of the habitat. However, the byssal carpet is unlikely to be affected, and an intolerance of low has been recorded. Recovery will depend on recolonization of available space by macroalgae and may be rapid in the case of red algae or take many years in the case of kelps (e.g. see Laminaria hyperborea).
Decrease in turbidity
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Decreased turbidity will result in increased light penetration, macroalgal growth and phytoplankton productivity, both of which may benefit Limaria hians and other suspension feeders by providing additional food. Increased macroalgal growth, especially red algae, may compete for space with epifaunal hydroids and bryozoans, resulting in a change in epifaunal species composition and increased abundance of algae, and potentially increased species richness. Where kelps are able to grow, the increased drag on the carpet may increase the biotopes intolerance to damage by increase in water flow or wave exposure. Nevertheless, the biotope would be little affected and an intolerance of low has been recorded. Recoverability is likely to be very high (see additional information below).
Increase in wave exposure
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This biotope has been recorded from extremely wave sheltered to wave exposed sites (JNCC, 1999). However, it probably occurs at greater depth with increasing wave exposure, since the effect of wave action on water movement decreases with depth (see Hiscock, 1983). The oscillatory nature of wave induced water movement is probably potentially damaging, especially where foliose macroalgae (e.g. kelps) attached to the carpet increase drag. The associated species will probably vary, favouring species more tolerant of wave exposure. However, an increase in wave exposure from e.g. moderately exposed to very exposed will probably result in disruption of the byssal carpet and mobilization of the substratum, especially in shallow representatives of the biotope. Therefore, the byssal carpet, its associated community and, hence the biotope, will probably be lost and an intolerance of high has been recorded. Recoverability would probably be low (see additional information below).
Decrease in wave exposure
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This biotope has been recorded from extremely wave sheltered to wave exposed sites (JNCC, 1999). Any further decrease in wave exposure is unlikely. The biotope would probably not be adversely affected as long as there was at least weak water flow (see above).
Noise
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Limaria hians, other bivalve molluscs, mobile or sessile epifauna or infauna are unlikely to be intolerance of noise or vibration at the benchmark level. Mobile fish species may be temporarily scared away from the areas but few if any adverse effects on the biotope are likely to result.
Visual Presence
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Limaria hians, other bivalve molluscs, mobile or sessile epifauna or infauna are unlikely to be sensitive to visual presence at the benchmark level. Mobile fish species may be temporarily scared away from the areas but few if any adverse effects on the biotope are likely to result.
Abrasion & physical disturbance
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Hall-Spencer & Moore (2000b) concluded that Limaria hians beds were intolerant to physical disturbance by mooring chains, hydraulic dredges or towed demersal fishing gear. Hall-Spencer & Moore (2000b) reported that a single pass of a scallop dredge at Creag Gobhainn, Loch Fyne ripped apart and mostly removed the Limaria hians reef. Damaged file shells were consumed by scavengers (e.g. juvenile cod Gadus morhua, whelks Buccinum undatum, hermit crabs Pagurus bernhardus and other crabs) within 24 hrs. Hall-Spencer & Moore (2000b) noted that although Limaria hians was able to swim, the shell was thin and likely to damaged by mechanical impact. Damage of the Limaria hians carpet would probably result in exposure of the underlying sediment and exacerbate the damage resulting in the marked loss of associated species (Hall-Spencer & Moore, 2000b). Species with fragile tests such as Echinus esculentus and the brittlestar Ophiocomina nigra and edible crab Cancer pagurus were reported to suffer badly from the impact of a passing scallop dredge (Bradshaw et al., 2000). Scavenging species would probably benefit in the short term, while epifauna would be removed or damaged with the byssal carpet. Therefore an intolerance of high has been recorded. Severe physical disturbance would be similar to substratum removal in effect. Recoverability would probably be low (see additional information below).
Displacement
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Individual Limaria hians removed from their nests, e.g. by physical disturbance but not damaged are capable of swimming. Limaria hians exudes a irritating, sticky mucus which renders it distasteful to most predators (see ecological relationships). On settling onto suitable substratum the gaping file shell burrows and constructs a nest (see Gilmour, 1967 for details). Merrill & Turner (1963) noted that Limaria hians was able to build a protective nest more rapidly than Musculus discors because the file shell utilized the surrounding substrata. Therefore, an intolerance of low has been recorded to represent the energetic costs of displacement.

Chemical Factors

Synthetic compound contamination
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In the Moross Channel, Mulroy Bay, an intensive settlement of Limaria hians spat occurred in 1982 followed by five years of failed settlement, which coincided with the use of TBT in fish farms in the area. Limaria hians samples in 1985 contained 0.2 µg/g tri-butyl tin oxide and similar levels were found in the Pacific oyster, scallops and mussels in the same area. Limaria hians larvae were detected again after the use of TBT was discontinued in 1985 (Minchin et al., 1987; Minchin, 1995). Minchin (1995) suggested that TBT contamination was the most likely cause of the disappearance of larvae from the plankton. Mytilus edulis continued to settle during the impacted period suggesting that Limaria hians was more intolerant.

Minchin (1995) noted that good recruitment was necessary to maintain the byssal carpet. Poor recruitment resulted in weakening of the byssal carpet, which was pulled away in tufts due to drag by kelps in the strong currents, mobilization of the sediment and resultant smothering, and loss of the carpet, its attached kelps and associated community and the population was reduced to 1.6% of its 1980 abundance. Therefore, while numerous species have been shown to be intolerance of TBT contamination to varying degrees, loss of the Limaria hians population and its associated community would result in loss of the biotope and an intolerance of high has been recorded. A recoverability of low has been recorded (see additional information below).

Heavy metal contamination
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No information concerning the effects of heavy metals on Limaria hians was found. However, 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, 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). Crompton (1997) reported that adult bivalve mortalities occurred after 4-14 day exposure to 0.1-1 µg/l Hg, 1-10 µg/l Cu and Cd, 10-100 µg/l Zn but 1-10 mg/l for Pb and Ni.

Various heavy metals have been show to have sublethal effects on growth in the few hydroids studied experimentally (Stebbing, 1981; Bryan, 1984; Ringelband, 2001). Bryozoans are common members of the fouling community and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints. Bryozoans were also shown to bioaccumulate heavy metals to a certain extent (Soule & Soule, 1979; Holt et al., 1995).

The sea urchin Echinus esculentus and starfish Asterias rubens were reported to show developmental or reproductive abnormalities in response to heavy metal contamination. In addition, sea urchin larvae are used a sensitive assay for water quality so that echinoderms are probably intolerance of a heavy metal contamination.

Gastropod molluscs have been reported to relatively tolerant of heavy metals while a wide range of sublethal and lethal effects have been observed in larval and adult crustaceans (Bryan, 1984). Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes.

Overall, there was insufficient information to assess intolerance to heavy metals in Limaria hians. However, the above evidence suggests that echinoderms are probably intolerant while other epifaunal species will probably exhibit at least sub-lethal effects. Therefore, an intolerance of low has been recorded at very low confidence to represent the likely decrease in abundance of some species in the biotope.

Hydrocarbon contamination
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Subtidal populations are protected from the direct effects of oil spills by their depth but are likely to be exposed to the water soluble fraction of oils and hydrocarbons, or hydrocarbons adsorbed onto particulates.
  • Suchanek (1993) noted that sub-lethal levels of oil or oil fractions reduce feeding rates, reduce respiration and hence growth, and may disrupt gametogenesis in bivalve molluscs. Widdows et al. (1995) noted that the accumulation of PAHs contributed to a reduced scope for growth in Mytilus edulis. However, no information on the responses of Limaria hians to hydrocarbons was found.
  • The hydroid Tubularia sp. experienced significant mortality when exposed to low concentrations of crude oil (Suchanek, 1993).
  • Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy, 1984 cited in Holt et al., 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination.
The intolerance of the epifaunal species within the community is probably variable, so that some species may be lost while others survive, so that species richness is likely to be reduced. However, in the absence of specific information on Limaria hians an assessment has not been made.
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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Moderate increases in nutrient levels may benefit Limaria hians by increasing macroalgal and phytoplankton productivity, increasing the proportion of organic particulates and hence increasing the food supply. Similarly, increased availability of organic particulates may benefit the other suspension feeding members of the community, e.g. hydroids, bryozoans, sponges and ascidians. Nutrient enrichment may also lead to increased turbidity (see above) and decreased oxygen levels due to bacterial decomposition of organic material (see below).

However, Shumway (1990) reported the toxic effects of algal blooms on commercially important bivalves. This would suggest that prolonged or acute nutrient enrichment may have adverse effects on suspension feeding bivalves such as Limaria hians. A bloom of the toxic flagellate Chrysochromulina polypedis in the Skagerrak resulted in death or damage of numerous benthic animals, depending on depth. The red algae Delesseria sanguinea lost pigmentation, and ascidians exhibited high mortalities even at 17 m depth, while in shallow water all dominant species (including Ciona intestinalis, Halichondria panicea and Asterias rubens) were killed. The toxic effects of the algal bloom resulted in a marked change in the community structure (Lundälv, 1990). The species composition of the epifaunal community may also change as a result.

Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).
Increase in salinity
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This biotope occurs in full salinity and is unlikely to encounter increases in salinity.
Decrease in salinity
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This biotope has only been reported from sites with full salinity. However, shallow sites may be vulnerable to reductions in salinity due to extreme freshwater runoff during heavy rainfall, e.g. in enclosed water such as lochs (see £MCR.ModT£ for example).

Several bivalves have been shown to be able to increase the concentration of free amino acids in their cytoplasm to compensate for decreases in salinity. As salinity falls most bivalves close their shells to isolate themselves from the surrounding environment. Limaria hians has a gaping shell that cannot be fully closed, and numerous, hydrostatic tentacles that cannot be withdrawn. Therefore, although it may exhibit an unknown degree of physiological tolerance, it is unlikely to be able to tolerate reduced or prolonged periods of variable salinity.

The majority of hydroids are subtidal and, although some brackish water species exist (Gili & Hughes, 1995), they are probably intolerance of prolonged decreases in salinity. Similarly, echinoderms are generally unable to tolerate low salinity (i.e. they are stenohaline) and possess no osmoregulatory organ (Boolootian, 1966). At low salinity e.g. sea urchins gain weight, and the epidermis loses its pigment as patches are destroyed; prolonged exposure is fatal. Although, local adaptation to reduced salinity may occur (see Stickle & Diehl, 1987), the inability of echinoderms to osmoregulate makes them sensitive short term acute or chronic long term reductions in salinity, e.g., a sudden inflow of river water into an inshore coastal area caused mass mortality of the Asterias vulgaris at Prince Edward Island, Canada (Smith, 1940, in Lawrence, 1995).

A short term decrease in salinity e.g. to reduced may result in death of intolerant sessile species, or migration mobile echinoderms and some individual Limaria hians to deeper waters. The species richness is likely to decline as a result. Therefore, a proportion of the population may be lost and the byssal carpet and its associated community degraded and an intolerance of intermediate has been recorded. A recoverably of high has been suggested (see additional information below).

Changes in oxygenation
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No information on the tolerance of hypoxia by Limaria hians was found. Most hydroids and bryozoans require adequate water flow and would probably be adversely affected by low oxygen concentration but may survive as dormant stages. Echinoderms appear to be intolerant (see reviews of Asterias rubens and Echinus esculentus) and would probably be killed or excluded by low oxygen concentrations. Similarly, some red algae may be intolerant (e.g. Delesseria sanguinea). However, while sessile and mobile epifauna may be killed, or lost by migration, the survival of the biotope is primarily dependant on the survival of Limaria hians. Therefore, in the absence of further evidence no assessment has been made.

Biological Factors

Introduction of microbial pathogens/parasites
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Limaria hians may be infested with 'oyster gill worms', trematodes of the genus Urastoma but they are considered to be harmless facultative commensals (Lauckner, 1983). Limaria hians may also act a secondary hosts for the metacercariae of digenean trematodes, which may cause sublethal effects or in extreme cases parasitic castration (Lauckner, 1983). Therefore, an intolerance of low has been recorded. Infected individuals may not recover although the population will probably recover rapidly.
Introduction of non-native species
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No information found
Extraction
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Limaria hians is not directly subject to extraction. However, Hall-Spencer & Moore (2000b) reported that a passing scallop dredge significantly damaged a Limaria hians bed in Loch Fyne due to physical disturbance (see above). Hall-Spencer & Moore (2000b) suggested that scallop dredging over the past 30 years was a likely cause of the decline in Limaria hians in the Clyde Sea, off the Isle of Man and other areas of the British coast. Therefore, an intolerance of low has been recorded. Recoverability is probably low (see additional information below).

Additional information icon Additional information

Recoverability
The veliger larvae of Limaria hians may spend a few weeks in the plankton (Lebour, 1937b) and could potentially disperse over a wide area, depending on local currents. Minchin (1995) studied the recovery of a population of Limaria hians in Mulroy Bay that had been reduced to only <2% of its 1980 abundance by 1986 due to unsuccessful recruitment associated with TBT contamination in the area. Minchin (1995) reported that once recruitment began again in 1989, recovery was rapid, so that by 1994 the population and an extensive carpet of byssal nests indicated recovery to the earlier 1980 state. Young saithe were again present sheltering in an re-established kelp cover, suggesting that the community as a whole had also recovered. Therefore, where individuals survive and in the presence of good recruitment, a population may be able to regain its prior abundance within 5 years.

However, wide scale declines of this species have been recorded, for example in the Clyde Sea and off the Isle of Man, and it has disappeared from prior strongholds such as the Skelmorlie Bank, Stravanan Bay and Tan Buoy, Great Cumbrae (Hall-Spencer & Moore, 2000). Hall-Spencer (pers comm.) suggested that the recovery observed in Mulroy Bay was probably was an exception to the rule, since Limaria hians beds have not recovered in other areas. Therefore, the recoverability of this biotope is probably low. In heavily fished areas recovery is unlikely (Jason Hall-Spencer pers comm.).


This review can be cited as follows:

Tyler-Walters, H. 2003. Limaria hians beds in tide-swept sublittoral muddy mixed sediment. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 23/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=112&code=1997>