Foraminiferans and Thyasira sp. in deep circalittoral fine mud

18-10-2002
Researched byDr Heidi Tillin & Karen Riley Refereed byThis information is not refereed.
EUNIS CodeA5.372 EUNIS NameForaminiferans and Thyasira spp. in deep circalittoral soft mud

Summary

UK and Ireland classification

EUNIS 2008A5.372Foraminiferans and Thyasira spp. in deep circalittoral soft mud
EUNIS 2006A5.372Foraminiferans and Thyasira spp. in deep circalittoral soft mud
JNCC 2004SS.SMu.OMu.ForThyForaminiferans and Thyasira sp. in deep circalittoral fine mud
1997 BiotopeCOS.COS.ForThyForamaniferans and Thyasira sp. in deep circalittoral soft mud

Description

In deep water and soft muds of Boreal and Arctic areas, a community dominated by foraminiferans and the bivalve Thyasira sp. (e.g. Thyasira croulinensis and Thyasira pygmaea) may occur (Thorson, 1957; Knitzer et al., 1992). Foraminiferans such as Saccammina, Psammosphaera, Haplophragmoides, Crithionina and Astorhiza are important components of this community with dead tests numbering thousands per m2 (see Stephen 1923; McIntyre 1961) and sometimes visible from benthic photography (Mackie et al., 1995). It is likely that a community dominated by Astorhiza in fine sands in the Irish Sea may be another distinct biotope (E.I.S. Rees pers. comm. 2002). Polychaetes, e.g. Paraonis gracilis, Myriochele heeri, Spiophanes kroyeri, Tharyx sp., Lumbrineris tetraura, are also important components of this biotope. These communities appear to have no equivalent on the continental plateau further south (Glemarec, 1973) but are known from the edge of the Celtic Deep in the Irish Sea (Mackie et al., 1995). The benthos in these offshore areas has been shown to be principally Foraminifera and similar, rich communities may exist in Scottish sealochs (McIntyre 1961). Communities from yet deeper (northern) waters at the extremes of the North Sea may be reminiscent, although dissimilar to ForThy (see Pearson et al., 1996) reflecting a higher proportion of silt/clay. A fully Arctic version of this biotope has also been described (Thorson 1934, 1957) although it should be noted that Jones (1950) considered this Boreal foraminiferan community to be part of a 'Boreal Deep Mud Association' (JNCC, 2015).

Recorded distribution in Britain and Ireland

Recorded from a few isolated sites in the northern North Sea, the Celtic Deep and Scottish lochs on the Atlantic coast.

Depth range

50-100 m

Additional information

None entered

Listed By

Further information sources

Search on:

JNCC

Habitat review

Ecology

Ecological and functional relationships

Community structure
The presence of the characterizing and other species in this biotope is primarily determined by the occurrence of a suitable substratum rather than by interspecific interactions. However, the component species modify the habitat and, in that way, affect each other. The following points may be relevant to this biotope.
  • Deposit feeders sort and process sediment particles and may result in destabilization of the sediment, which inhibits survival of suspension feeders. This can result in a change in the vertical distribution of particles in the sediment that may facilitate vertical stratification of some species with particle size preferences. Vertical stratification of species according to sediment particle size has been observed in some soft-sediment habitats (Petersen, 1977). Polychaetes also significantly influence nutrient fluxes of nitrogen and phosphorus at the sediment-water interface, owing to their burrowing activity promoting oxygenation of the substrata. The burrowing and feeding activities of the macrofauna are likely to modify the fabric and increase the mean particle size of the upper layers of the substrata by aggregation of fine particles into faecal pellets. Such actions create a more open sediment fabric with a higher water content which affects the rigidity of the seabed (Rowden et al., 1998). Such alteration of the substratum surface can affect rates of particle resuspension.
  • Bioturbation is particularly important in controlling chemical, physical and biological processes in marine sediments, especially when the influences of physical disturbances such as wave action or strong currents are minimized (Widdicombe & Austen, 1999).
Another factor determining the distribution of assemblages is the annual variation of temperature in bottom layers, influenced by the amount of stratification in the water column. COS.ForThy occurs in water depth greater than 100 m in the North Sea and Celtic Sea, i.e. deeper than the seasonally stratified water.
  • Differences in stratification north and south of the Dogger Bank might explain why cold water species do not go further south than the Dogger Bank (Kunitzer et al., 1992).
  • In Loch Nevis there is greater vertical mixing and primary production, therefore a higher rate of deposition of organic material would be present and able to support greater populations of benthic animals (McIntyre, 1961).
Predator-prey relationships
Most of the species living in deep mud biotopes are generally cryptic so are protected to some extent from visual surface predators. However, some species of foraminifera, such as Astrorhiza sp. usually live on the substratum surface. The arm tips of Amphiura chiajei, which is often present in this biotope, are also an important food source for demersal species.
  • Foraminifera are able to move along the sediment surface. Feeding takes place when the animal is stationary, by developing a network of numerous thin extensions of cytoplasm called reticulopodia or pseudopodia (Buchanan & Hedley, 1960; Wetmore,1995). Buchanan & Hedley (1960) noted that the pseudopodia of Astrorhiza lamicola ramify over the sediment surface and through the interstitial spaces to a depth of 2-3mm, extending to a distance of ~7cm from the animal.
  • Depending on size and available food, foraminifera, prey on dissolved organic molecules; bacteria, diatoms and other single-celled phytoplankton; small crustacea and recently metamorphosed Echinocardium flavesens (Buchanan & Hedley, 1960; Wetmore, 1995; Rivkin & DeLaca, 1990).
  • Buzas (1978) suggested that foraminiferans probably also represent an important food source for benthic macrofauna. Predation was thought mainly to be by demersal fish species (McIntyre, 1961).
  • Dando & Southward (1986), Southward (1986), and Spiro et al. (1986) found that different species of Thyasira species show a range of nutritional dependence on bacteria in their gills; from none (heterotrophs) to complete dependence (chemoautotrophs).
  • Seasonal and longer term change

    Large areas of the southern North Sea are not stratified during most of the year and the summer temperature of bottom waters is high (>10°C) (Tomczak & Goedecke, 1964), while in the stratified areas north of the Dogger Bank summer temperatures are <7°C. In winter the southern North Sea is colder (4°C) than the rest of the North Sea (5-7°C). Phytoplankton productivity increases during the summer, which may lead to more available food for macrofauna. However, in the North Sea large stocks of copepods develop, which consume the summer production of phytoplankton (Fransz & Gieskes, 1984). The faecal pellets do not reach the deep water, being recycled higher in the water column (Krause, 1981) so limiting this source of food to benthos in the summer months. This could explain the low biomass of infauna in the northern North Sea (Kunitzer et al., 1992).

    Habitat structure and complexity

    The biotope has very little surface structural complexity as most species are infaunal, however, the bioturbating megafauna can create considerable structural complexity below the surface, relative to sediments that lack such animals.
    • The sediment surface may appear pitted by small burrows of infaunal species, with arm tips of Amphiura chiajei stretching out over the surface but these are not likely to provide a significant habitat for other fauna. Infaunal and epifaunal species colonize the area and foraminifera tests may also be present in large numbers on the surface of the sediment.
    • Most species living within the sediment are restricted to the area above the anoxic layer, the depth of which will vary depending upon sediment particle size and organic content. Some structural complexity is provided by the burrows of macrofauna. Burrows and the bioturbatory activity that creates them allows a much larger volume of sediment to become oxygenated, enhancing the survival and diversity of a considerable variety of smaller infaunal species (Pearson & Rosenberg, 1978).

    Productivity

    Macroalgae are absent from COS.ForThy and consequently productivity is mostly secondarily derived from detritus and organic material. Allochthonous organic material is therefore derived from plankton including dead plankton sinking to the seabed and other animal productivity. Autochthonous organic material is also formed by benthic microalgae (microphytobenthos e.g. diatoms and euglenoids) and heterotrophic micro-organism production. Organic material is degraded by micro-organisms and the nutrients recycled.

    Recruitment processes

    No information is known about the reproduction and recruitment of foraminifera within this biotope.

    Larval development of Thyasira equalis is lecithotrophic and the pelagic stage is very short or quite suppressed. This agrees with the reproduction of other Thyasira sp., and in some cases (Thyasira gouldi) no pelagic stage occurs at all (Thorson, 1946). This means that larval dispersal is limited. No information relating to fecundity of Thyasira species within the biotope was found, however information is available for another Thyasira sp., and it is possible that fecundity is similar in species within the COS.ForThy biotope. Spawning of Thyasira gouldi occurs throughout the year, with up to 750 eggs produced each time. No information is available on the mechanism of spawning or the number of spawnings per year.

    Other species that usually occur in the biotope, such as polychaetes and brittlestars usually have planktonic development, an annual reproductive cycle and are fecund.

    Time for community to reach maturity

    Little is known about the mode of reproduction and recoverability of foraminifera. All other characteristic species within the biotope are fecund and species such as polychaetes and brittlestars are likely to recover fairly quickly. However, the larval development of Thyasira equalis is lecithotrophic and the pelagic stage is very short or quite suppressed. This agrees with the reproduction of other Thyasira sp., and in some cases (Thyasira gouldi) no pelagic stage occurs at all (Thorson, 1946). This means that larval dispersal is limited.
    • Between 1979 and 1980, deoxygenation of bottom waters resulted in the depletion of Thyasira equalis and Thyasira sarsi from 550/m² to almost zero. However, by 1987 200/m² were present (Dando & Spiro, 1993).
    • After a decline in the abundance of Thyasira flexuosa in Penobscot Bay, Maine, after trawler disturbance, populations were reported to recover within 3.5 months (Sparks-McConkey & Watling, 2001).
    Explanations for the high recovery of these populations could be due to high post-settlement survival, or new populations of adults washed in by bedload transport to colonize the area.

    Additional information

    No text entered.

    Preferences & Distribution

    Recorded distribution in Britain and IrelandRecorded from a few isolated sites in the northern North Sea, the Celtic Deep and Scottish lochs on the Atlantic coast.

    Habitat preferences

    Depth Range 50-100 m
    Water clarity preferences
    Limiting Nutrients No information found
    Salinity Full (30-40 psu)
    Physiographic
    Biological Zone Circalittoral
    Substratum Mud
    Tidal Very Weak (negligible)
    Wave
    Other preferences

    Additional Information

    • Differences in the faunal composition between Atlantic (Loch Nevis, Scotland) and northern North Sea sites (Forties oil field & Fladen Ground) have been described.
      • In the northern North Sea high densities of Saccammina sp., Psammosphaera sp., Astrohiza arenaria (Foraminifera), Thyasira equalis (bivalve) and Polychaetes such as Spiophanes kroyeri and Tharyx sp. were present in abundance (McIntyre, 1961; Hartley, 1984; Stephen, 1923). Whereas, in the Atlantic high densities of Crithionina granum (foraminifera), Thyasira flexuosa (bivalve) and Polychaetes were present in abundance McIntyre (1961).
      • Densities of foraminifera varied as follows; Stephen (1923) found 1074/m² of Saccammina sp. and Psammosphaera sp., and 190/m² of Astrorhiza arenaria. McIntyre (1961) found that in the Fladen Grounds dead tests of Saccammina sp. were more abundant (>10,000/m²) and Astrorhiza arenaria was not as common. However, the number of live foraminifera species would probably be much less; McIntyre (1961) estimated the abundance of living Saccammina sp. to be 263/m².
    • At sites in the northern North Sea, communities live in constant Boreal water where the bottom temperature among foraminifera communities has been noted to have a low range (Stephens, 1923), with temperatures and salinities remaining fairly constant, oscillating between 6 and 8°C and salinities of 35.20-35.26ppm (McIntyre, 1961). However, the Atlantic community lives in varying Boreal water (McIntyre, 1961).
    Ockelmann (1958) indicated that records of Thyasira flexuosa in east Greenland and Jan Mayen were thought to actually refer to Thyasira gouldi and Thyasira equalis respectively, as Thyasira flexuosa has a boreal-lusitanian main distribution and is absent from arctic waters.

    Species composition

    Species found especially in this biotope

      Rare or scarce species associated with this biotope

      -

      Additional information

      In addition to species mentioned in the biotope description, polychaetes such as Exogone verugera, Nephtys spp., Aricidea catherinae and Minuspio cirrifera, and brittlestars, Amphiura sp. are also abundant in the biotope (Connor et al., 1997a) and information on these species has been used.

      Sensitivity reviewHow is sensitivity assessed?

      Explanation

      The biotope is characterized by the presence of foraminifera and Thyasira spp. in the absence of either of these species the biotope would not necessarily be recognized. Polychaetes are usually abundant and their burrowing activity is important in controlling species diversity and abundance in the community.

      Species indicative of sensitivity

      Community ImportanceSpecies nameCommon Name
      Important characterizingThyasira sp.A bivalve

      Physical Pressures

       IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
      High Moderate Moderate Major decline High
      The community would be highly intolerant of substratum loss as it is dominated by infaunal and epifaunal species. Removal of the substratum would remove these species. Intolerance has been assessed to be high. Recoverability may be only moderate (see additional information below).
      High Moderate Moderate Minor decline Very low
      Burrowing species are likely to be able to burrow through the extra layer of smothering sediment and resume their usual infaunal positions, although this would involve an energetic cost. Epifaunal foraminifera may not be able to burrow to the surface and at least a proportion of the population may be lost. However, little information on foraminiferans biology was found, and so it the absence of information an intolerance of high has been recorded, albeit with very low confidence. The biotope is likely to be more intolerant of smothering by viscous or impenetrable materials e.g. smothering by sediment of a coarser texture may affect burrowing and feeding. Loss of the characterizing species of foraminifera would mean that the biotope is no longer COS.ForThy and so intolerance is high. Recoverability may only be moderate.
      Low Very high Very Low No change High
      Many species in the biotope are either infaunal or deposit feeders that would probably be able to tolerate an increase in suspended sediment at the level of the benchmark. However, there may be additional cleaning costs for Thyasira sp., but this will not affect survival of animals. Some species may benefit from increased food supply if suspended sediment has a high organic content. The intolerance of the biotope is therefore reported to be low. Recovery is likely to be very high as affected animals clean away sediment particles.
      Low Moderate Low Major decline Moderate
      A decrease in sedimentation is not likely to affect deposit feeders or foraminifera. Food availability for Thyasira sp. may decline, but this will not affect survival of animals. The intolerance of the biotope has been reported to be low. Recoverability is likely to be moderate.
      Not relevant Not relevant Not relevant Not relevant Not relevant
      The COS.ForThy biotope occurs at a depth below 100 m, therefore desiccation is not relevant.
      Not relevant Not relevant Not relevant Not relevant Not relevant
      The COS.ForThy biotope occurs at a depth below 100 m, therefore an increase in emergence is not relevant.
      Not sensitive* Not relevant
      The COS.ForThy biotope occurs at a depth below 100 m, therefore a decrease in emergence is not relevant.
      Intermediate High Low Minor decline Moderate
      The community occurs in fine soft mud that only develops in areas of weak tidal streams. Following an increase in water flow rate the surface sediments and epifaunal foraminifera are likely to be winnowed away. The lower substratum inhabited by mature specimens of Thyasira sp., infaunal foraminifera, polychaetes and Amphiura chiajei is likely to remain unchanged. Therefore, since the majority of characterizing species are likely to persist, intolerance has been assessed to be intermediate. On return to normal water flow rates, recoverability is likely to be high.
      Tolerant Not sensitive* No change Moderate
      The biotope occurs in weak tidal streams. A decrease in water flow rate may reduce the supply of particles to suspension feeders in the biotope. However, effects are only expected to be sub-lethal therefore intolerance has been reported to be low. Normal feeding and tube building will resume on return to normal conditions. Recoverability is likely to be very high.
      High Low High Major decline Moderate
      The distribution of fossilised foraminifera is used to track changes in bottom water temperatures, as each species occurs in a particular temperature range (Archer & Martin, 2001). This suggests that they are intolerant of temperature changes.

      In the northern North Sea, the COS.ForThy biotope containing Thyasira equalis, Saccammina sp., Psammosphaera sp. and Astrohiza arenaria are present in ‘constant Boreal water’ where the bottom temperature among foraminifera communities has been noted to have a low range of variation (Stephen, 1923), with temperatures oscillating between 6 and 8 °C (McIntyre, 1961). Further south, a greater range of bottom temperatures occurs and the biotope is not present. But this could also be due to an increase in sediment particle size with decreasing depth in this area. However, the Atlantic community which contains Thyasira flexuosa and Crithionina granum lives in ‘varying Boreal water’, with temperatures varying between 7 and 13 °C (McIntyre, 1961).

      The above evidence suggests that the community is highly dependent on a relatively constant temperature and that different species of Thyasira sp. and foraminifera thrive in different temperature ranges. Intolerance has been assessed to be high. Recoverability is likely to be extremely slow as characterizing species of foraminifera would be lost over a large area (see additional information below).
      High Low No information Major decline Moderate

      The distribution of fossilised foraminifera is used to track changes in bottom water temperatures, as each species occurs in a particular temperature range (Archer & Martin, 2001). This suggests that they are intolerant of temperature changes.

      In the northern North Sea, the COS.ForThy biotope containing Thyasira equalis, Saccammina sp., Psammosphaera sp. and Astrohiza arenaria is present in ‘constant Boreal water’ where the bottom temperature among foraminifera communities has been noted to have a low temperature range (Stephen, 1923), with temperatures oscillating between 6 and 8 °C (McIntyre, 1961). Further south, a greater range of bottom temperatures occurs and the biotope is not present. But this could also be due to an increase in sediment particle size with decreasing depth in this area. However, the Atlantic community which contains Thyasira flexuosa and Crithionina granum lives in ‘varying Boreal water’, with temperatures varying between 7 and 13 °C (McIntyre, 1961).

      This suggests that the community is highly dependent on a relatively constant temperature and that different species of Thyasira sp. and foraminifera thrive in different temperature ranges. Intolerance has been assessed to be high. Recoverability is likely to be extremely slow as characterizing species of foraminifera would be lost over a large area (see additional information below).
      Low Very high Very Low No change Moderate
      An increase in turbidity, reducing light availability, may reduce primary production by phytoplankton in the water column. However, productivity in the COS.ForThy biotope is secondary (detritus) and is not likely to be significantly affected by changes in turbidity and so intolerance is assessed as low. On return to normal turbidity levels recovery will be very high as food availability returns to normal.
      Low High Low No change Moderate
      A decrease in turbidity, increasing light availability, may increase primary production by phytoplankton in the water column. However, productivity in the COS.ForThy biotope is secondary (detritus) and is not likely to be significantly affected by changes in turbidity and so intolerance is assessed as low. On return to normal turbidity levels recovery will be high as food availability returns to normal.
      Tolerant Not relevant Not relevant No change Moderate
      The effects of wave action are attenuated with depth. At a depth of 100 m or more, where the COS.ForThy biotope is present, the effects of an increase in wave exposure would not be felt (Hiscock, 1983) and would probably not have any effect on the characteristic species.
      Tolerant Not sensitive* No change Moderate
      The depths at which the biotope are found means that the community is rarely, if at all, affected by wave disturbance, therefore a decrease in wave exposure is not likely to affect the species within the biotope.
      Tolerant Not relevant Not relevant No change High
      Some species such as polychaetes may respond to vibrations from predators or excavation, however, it is unlikely that noise at the benchmark level would have a detectable effect on the viability of the community. An assessment of not sensitive has been made.
      Not relevant Not relevant Not relevant No change High
      The biotope occurs in deep water where available light is very low. Most species are likely either to have low visual acuity or no mode for detection of visual presence. Therefore, an assessment of not relevant has been made.
      Intermediate High Low Decline High
      Abrasion is likely to damage or result in death of some individuals of the characteristic species of the biotope. For instance, Thyasira sp. are small bivalves, the shells are thin and fragile and abrasion is likely to cause death. Residing 2 cm below the sediment surface means that they are susceptible to abrasive damage. However, some of the impact of physical disturbance will displace individuals without killing them allowing for recovery. Sparks-McConkey & Watling (2001) found that trawler disturbance resulted in a decline of Thyasira flexuosa in Penobscot Bay, Maine. However, the population recovered after 3.5 months. Brittlestars have fragile arms that are likely to be damaged by abrasion or physical disturbance. Amphiura chiajei burrows in the sediment and extends its arms across the sediment surface to feed. Ramsay et al. (1998) suggested that Amphiura sp. may be less susceptible to beam trawl damage than other species of echinoid or tube dwelling amphipods and polychaetes. Brittlestars can tolerate considerable damage to arms and even the disc without suffering mortality and are capable of disc and arm regeneration.

      Whilst a proportion of Thyasira sp. and some other species would probably die and other species important within the biotope may be damaged, many individuals would be displaced or suffer damage that can be repaired. Intolerance has been assessed to be intermediate. Recoverability is probably high (see additional information below).

      Low High Low No change High
      As long as the characterizing species are displaced onto suitable sediment, bivalves, polychaetes and brittlestars would be able to create new burrows and foraminifera would be able to survive.

      However, exposure to predators would be increased for a short time and there would be an energetic cost in creating new burrows. Intolerance has been assessed to be low. Recoverability is likely to be high (see additional information below).

      Chemical Pressures

       IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
      No information Not relevant No information Not relevant Not relevant

      No information was found concerning the effects of synthetic chemicals on Thyasira sp. or foraminifera, however, other species within the community may be adversely affected. Dahllöf et al. (1999) studied the long term effects of tri-n-butyl-tin (TBT) on the function of a marine sediment system. TBT spiked sediment was added to a sediment that already had a TBT background level of approximately 27ng/g (83 pool TBT per g) and contained the following fauna: Amphiura spp. and several species of polychaete. Within two days of treatment with a TBT concentration above 13.7 µmol / m² all species except the polychaetes had crept up to the surface and after six weeks these fauna had started to decay. Thus contamination from TBT is likely to result in the death of some intolerant species such as brittle stars. Amphiura chiajei is also known to bioaccumulate PCBs, although direct effects of synthetic chemicals on this species are unknown (Gunnardsson & Skold, 1999). However, Walsh et al., (1986) observed inhibition of arm regeneration in another brittle star, Ophioderma brevispina, following exposure to TBT at levels between 10 ng/l and 100 ng/l.

      As no information was found concerning the effects of synthetic chemicals on foraminifera and Thyasira sp., there was insufficient information available to assess intolerance.

      Heavy metal contamination
      No information Not relevant No information Not relevant Not relevant

      No information on the effects of heavy metals on Thyasira sp. or foraminifera were found. There is evidence that polychaetes may be able to adapt to high heavy metal concentrations. For instance, Bryan & Gibbs (1983) presented evidence that Nephtys hombergii from Restronguet Creek possessed increased tolerance to copper contamination. Specimens from the Tamar Estuary had a 96 h LC50 of 250 µg/l, whilst those from Restronguet Creek had a 96 h LC50 of 700 µg/l (35 psu; 13°C). Bryan & Gibbs (1983) suggested that since the area had been heavily contaminated with metals for >200 years, there had been adequate time for metal-resistant populations to develop especially for relatively mobile species. In the short term, however, acute exposure of heavy metals may be deleterious to populations not previously exposed.

      Adult echinoderms, such as Ophiothrix fragilis are known to be efficient concentrators of heavy metals including those that are biologically active and toxic (Hutchins et al., 1996). However, there is no information available regarding the effects of this bioaccumulation.

      As no information was found concerning the effects of heavy metals on foraminifera and Thyasira sp., there was insufficient information available to assess intolerance.

      Hydrocarbon contamination
      No information Not relevant No information Not relevant Not relevant

      No information on the effects of hydrocarbons on Thyasira sp. or foraminifera were found. A decrease in brittlestar burrowing activity was recorded at 4,800 and 1,200 ppm total hydrocarbons in sediment (Newton & McKenzie, 1998). However, Newton & McKenzie (1998) suggested that these were a poor predictor of chronic response. Kelly & McKenzie (1995) detected chronic sub-lethal effects around the Beryl oil platform in the North Sea where the hydrocarbon content of the sediment was very low (<3 ppm total hydrocarbons in sediment), and Amphiura chiajei was excluded from areas nearer the platform with higher sediment hydrocarbon content (> 10 ppm). However, the authors did suggest that deleterious effects may also be related to the non-hydrocarbon element of the cuttings such as metals, physical disturbance or organic enrichment. Amphiura chiajei is also host to symbiotic sub-cuticular bacteria (Kelly & McKenzie, 1995). After exposure to hydrocarbons, loadings of such bacteria were reduced indicating a possible sub-lethal stress to the host (Newton & McKenzie, 1995).

      As no information was found concerning the effects of hydrocarbons on foraminifera and Thyasira sp., there was insufficient information available to assess sensitivity.

      Radionuclide contamination
      No information Not relevant No information Not relevant Not relevant
      No information concerning effects of radionuclides on characteristic species within the biotope was found, although adult echinoderms, such as Ophiothrix fragilis are known to be efficient concentrators of radionuclides (Hutchins et al., 1996). As no information was found concerning the effects of radionuclides on foraminifera and Thyasira sp., there was insufficient information available to assess sensitivity.
      Changes in nutrient levels
      Tolerant Not relevant Not relevant Not relevant Very low
      Organic enrichment from pulp mills is believed to have been the cause of the death of two Thyasira sp. populations in west Scotland sea lochs (Kunitzer et al., 1992). However, other toxins discharged by the pulp mills could also have been responsible. In addition, similar species such as Thyasira flexuosa may be considerably more tolerant of nutrient enrichment, for example densities of up to 4000 per square metre have been recorded in areas or organic enrichment.

      Nilsson (1999) reported a positive response by Amphiura chiajei to increased organic enrichment (27 and 55 g C m², applied four times over eight weeks) demonstrable by an increase in arm tip regeneration rate. In the Skagerrat in the North Sea, Josefson (1990) reported a massive increase in abundance and biomass of Amphiura species between 1972 and 1988 attributable to organic enrichment. Thus increased nutrient availability promoting phytoplankton productivity and an increase in the organic matter reaching the sea bed is likely to be beneficial to Amphiura chiajei. An increase in nutrients in subtidal habitats of this depth will not cause the biotope to become overgrown with ephemeral algae so the smothering effects often associated with eutrophication will not occur. No information regarding the effects of nutrient enrichment were found. But other characterizing species could potentially benefit from nutrient enrichment. Therefore, on balance not sensitive has been recorded, albeit with very low confidence.

      Not relevant Not relevant Not relevant Not relevant Not relevant
      The biotope occurs in fully saline waters, therefore it is unlikely that an increase in salinity will occur.
      High Moderate Intermediate Major decline Moderate
      COS.ForThy is a circalittoral biotope that has not been recorded from locations with brackish waters and so is probably highly intolerant of a decrease in salinity. In the northern North Sea, the COS.ForThy biotope containing Thyasira equalis, Saccammina sp., Psammosphaera sp. and Astrohiza arenaria, is present where salinities remain fairly constant, between 35.20 and 35.26 ppm (McIntyre, 1961). However, the Atlantic community which contains Thyasira flexuosa and Crithionina granum (foraminifera) occurs in waters where salinity varies between 33.86 and 34.33 (McIntyre, 1961). This suggests that the community is highly dependent on a relatively constant salinity. Mobile species would be able to avoid the change in salinity by moving away, but localised densities would decline. Amphiura chiajei taken from an area of 24 psu had an LD50 of >21 days for a 70% dilution (17 psu) and an LD50 of 8.5 days for a 50% dilution (12 psu). In comparison, specimens taken from an area with salinity 28.9 psu, had an LD50 of > 12.5 days for a 70% dilution (20 psu) and an LD50 of 6 days for a 50% dilution (14 psu). As Amphiura chiajei is mobile and burrows it may be able to avoid changes in salinity outside its tolerable range. intolerance has been assessed to be high. Recoverability may be moderate (see additional information below).
      High Moderate Moderate Major decline High

      Dando & Spiro (1993) found that numbers of Thyasira equalis and Thyasira sarsi decreased rapidly following the deoxygenation of bottom water in the deep basin of Gullmar fjord in 1979-80 (from ~550/m² to~0). However, the abundance of the species increased to approximately 200/m² by 1987.

      Polychaetes are burrowing predators in marine sediments that have to survive periods of severe hypoxia and sulphide exposure, while at the same time maintaining agility in order to feed on other invertebrates. Fallesen & Jørgensen (1991) recorded Nephtys hombergii in localities in Århus Bay, Denmark, where oxygen concentrations were permanently or regularly low, but in the late summer of 1982 a severe oxygen deficiency killed populations of Nephtys hombergii and Nephtys ciliata in the lower part of the bay. Such evidence suggests that Nephtys hombergii to be tolerant of short episodes of oxygen deficiency and at the benchmark duration of one week Nephtys hombergii is unlikely to be adversely affected by hypoxic conditions and would revive on return to oxygenated sediment.

      Mass mortality in Amphiura filiformis from the south-east Kattegat has been observed during severe hypoxic events (<0.7 mg/l O2), while the abundance of Amphiura chiajei remained unchanged at the same site and time (Rosenberg & Loo, 1988). In laboratory conditions, Nilsson (1999) maintained specimens of Amphiura chiajei in hypoxic conditions (1.8-2.2 mg O2/l) for eight weeks and recorded no deaths or witnessed specimens escaping to the surface. This evidence suggests the intolerance of Amphiura chiajei to the benchmark level of 2 mg/l for one week to be low.

      Loss of Thyasira sp. would result in loss of the biotope, therefore intolerance has been assessed to be high. Recoverability is likely to be moderate (see additional information below).

      Biological Pressures

       IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
      Low High Low Minor decline Low
      Evidence of the effect of pathogens has only been found for Thyasira gouldi of late. Viral infection of the mutualist bacterium living on the gills of Thyasira gouldi has been suggested as the reason for a major decline in the Loch Etive population. It is likely that similar species of Thyasira sp. would react in the same way. However, it is unlikely that the biotope would be lost entirely. An intolerance of low is suggested but with very low confidence. Recoverability is probably high.
      No information Not relevant No information Not relevant Not relevant
      No alien species are known to compete with species within the biotope.
      Intermediate High Low Decline Moderate
      It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction. However, benthic trawls or dredging for other species may damage or destroy the shells of Thyasira sp. Other species such as brittlestars may constitute a component of demersal fishing trawl by-catch. Whilst some individuals may die, many more may suffer physical injury.

      Thyasira sp. are small bivalves, the shells are thin and fragile and a passing dredge, for example, may cause death. However, some individuals will simply be displaced without killing them. Sparks-McConkey & Watling (2001) found that trawling resulted in the decline of Thyasira flexuosa in Penobscot Bay, Maine. However, the population had recovered within 3.5 months.

      Brittlestars have fragile arms that are likely to be damaged by abrasion or physical disturbance. Amphiura chiajei burrows in the sediment and extends its arms across the sediment surface to feed. However, Ramsay et al. (1998) suggested that Amphiura sp. may be less susceptible to beam trawl damage than other species of echinoid or tube dwelling amphipods and polychaetes. Brittlestars can tolerate considerable damage to arms and even the disc without suffering mortality and are capable of disc and arm regeneration.

      Whilst a proportion of Thyasira sp. and some other species would probably die and other species important within the biotope may be damaged, many individuals would be displaced or suffer damage that can be repaired. Intolerance has been assessed to be intermediate. Recoverability is probably high (see additional information below).

      Intermediate High Low Major decline Moderate

      Additional information

      Recoverability
      Little is known about the mode of reproduction, growth rate and recoverability of foraminifera. In the absence of such information, assessment of recovery potential has to be precautionary and may be more than five years. All other characteristic species within the biotope are fecund and species such as polychaetes and brittlestars are likely to recover fairly quickly.

      However, the larval development of Thyasira equalis is lecithotrophic and the pelagic stage is very short or quite suppressed. This agrees with the reproduction of other Thyasira sp., and in some cases (Thyasira gouldi) no pelagic stage occurs at all (Thorson, 1946). This means that larval dispersal is limited. If mortality of Thyasira sp. occurs, there would have to be nearby populations for recovery to occur. Where some individuals survive, due to the fact that larvae spend little or no time in the water column, post-settlement survival may be higher, and the population may be able to recover. It is also possible that adults could be brought into the area by bedload transport, enabling colonization for example:

      • after a decline in the abundance of Thyasira flexuosa in Penobscot Bay, Maine, after trawler disturbance, populations were reported to recover within 3.5 months (Sparks-McConkey & Watling, 2001);
      • although deoxygenation of bottom waters between 1979 and 1980, resulted in the depletion of Thyasira equalis and Thyasira sarsi from 550/m² to almost zero, by 1987 200/m² were present (Dando & Spiro, 1993).
      Overall, and particularly bearing in mind the lack of information on foraminiferans, recovery of the biotope following catastrophic loss may be only moderate or possibly low.

      Importance review

      Policy/Legislation

      Habitats of Principal ImportanceMud habitats in deep water
      Habitats of Conservation ImportanceMud habitats in deep water
      UK Biodiversity Action Plan PriorityMud habitats in deep water
      Priority Marine Features (Scotland)Offshore deep sea muds

      Exploitation

      No species within the biotope are targeted specifically, however, deep soft bottom sediments are vulnerable to effects from trawling activities.

      Additional information

      -

      Bibliography

      1. Archer, D. & Martin, P., 2001. Thin walls tell the tale. Science (Washington), 5549, 2108-2109.
      2. Bryan, G.W. & Gibbs, P.E., 1983. Heavy metals from the Fal estuary, Cornwall: a study of long-term contamination by mining waste and its effects on estuarine organisms. Plymouth: Marine Biological Association of the United Kingdom. [Occasional Publication, no. 2.]
      3. Buchanan, J.B. & Hedley, R.H., 1960. A contribution to the biology of Astrorhiza limicola (Foraminifera). Journal of the Marine Biological Association of the United Kingdom, 39, 549-60.
      4. Buchanan, J.B., 1964. A comparative study of some of the features of the biology of Amphiura filiformis and Amphiura chiajei (Ophiuroidea) considered in relation to their distribution. Journal of the Marine Biological Association of the United Kingdom, 44, 565-576.
      5. Buzas, M.A., 1978. Foraminifera as prey for benthic deposit feeders: results of predator exclusion experiments. Journal of Marine Research, 36, 617-625
      6. Connor, D.W., Dalkin, M.J., Hill, T.O., Holt, R.H.F. & Sanderson, W.G., 1997a. Marine biotope classification for Britain and Ireland. Vol. 2. Sublittoral biotopes. Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06., Joint Nature Conservation Committee, Peterborough, JNCC Report no. 230, Version 97.06.
      7. Dahllöf, I., Blanck, H., Hall, P.O.J. & Molander, S., 1999. Long term effects of tri-n-butyl-tin on the function of a marine sediment system. Marine Ecology Progress Series, 188, 1-11.
      8. Dando, P.R. & Southward, A.J., 1986. Chemoautotrophy in bivalve molluscs of the Genus Thyasira. Journal of the Marine Biological Association of the United Kingdom, 60, 915-929.
      9. Dando, P.R. & Spiro, B., 1993. Varying nutritional dependence of the thyasirid bivalves Thyasira sarsi and Thyasira equalis on chemoautotrophic symbiotic bacteria, demonstrated by isotope ratios of tissue carbon and shell carbonate. Marine Ecology Progress Series, 92, 151-158.
      10. Davies, C.E. & Moss, D., 1998. European Union Nature Information System (EUNIS) Habitat Classification. Report to European Topic Centre on Nature Conservation from the Institute of Terrestrial Ecology, Monks Wood, Cambridgeshire. [Final draft with further revisions to marine habitats.], Brussels: European Environment Agency.
      11. Fallesen, G. & Jørgensen, H.M., 1991. Distribution of Nephtys hombergii and Nephtys ciliata (Polychaeta: Nephtyidae) in Århus Bay, Denmark, with emphasis on the severe oxygen deficiency. Ophelia, Supplement 5, 443-450.
      12. Fransz, H.G. & Gieskes, W.N.C., 1984. The imbalance of phytoplankton and copepods in the North Sea. Rapports et Procés - Verbaux des réunion du Conseil International pour l'Exploration de la Mer, 183, 218-225.
      13. Glémarec, M., 1973. The benthic communities of the European North Atlantic continental shelf. Oceanography and Marine Biology: an Annual Review, 11, 263-289.
      14. Gunnarsson, J.S. & Skold, M., 1999. Accumulation of polychlorinated biphenyls by the infaunal brittle stars Amphiura filiformis and A. chiajei: effects of eutrophication and selective feeding. Marine Ecology Progress Series, 186, 173-185.
      15. Hartley, J.P., 1984. The benthic ecology of the Forties Oilfield (North Sea). Journal of Experimental Marine Biology and Ecology, 80, 161-195.
      16. Hiscock, K., 1983. Water movement. In Sublittoral ecology. The ecology of shallow sublittoral benthos (ed. R. Earll & D.G. Erwin), pp. 58-96. Oxford: Clarendon Press.
      17. Hutchins, D.A., Teyssié, J-L., Boisson, F., Fowler, S.W., & Fisher, N.S., 1996. Temperature effects on uptake and retention of contaminant radionuclides and trace metals by the brittle star Ophiothrix fragilis. Marine Environmental Research, 41, 363-378.
      18. Jones, N.S., 1950. Marine bottom communities. Biological Reviews, 25, 283-313.
      19. Künitzer, A., Basford, D., Craeymeersch, J.A., Dewarumez, J.M., Derjes, J., Duinevald, G.C.A., Eleftheriou, A., Heip, C, Herman, P., Kingston, P., Neirmann, U., Rachor, E., Rumohr, H. & Wilde, P.A.J. de, 1992. The benthic infauna of the North Sea: species distribution and assemblages. ICES Journal of Marine Science, 49, 127-143.

      20. Kelly, M.S. & McKenzie, J.D., 1995. A survey of the occurrence and morphology of sub-cuticular bacteria in shelf echinoderms from the north-east Atlantic. Marine Biology, 123, 741-756.
      21. Krause, M., 1981. Vartical distribution of faecal pellets during FLEX '76. Helgoländer Meeresuntersuchungen, 34, 313-337.
      22. Mackie, A.S.Y., Oliver, P.G. & Rees, E.I.S., 1995. Benthic biodiversity in the southern Irish Sea. Studies in Marine Biodiversity and Systematics from the National Museum of Wales. BIOMOR Reports, no. 1.
      23. McIntyre, A.D., 1961. Quantitative differences in the fauna of boreal mud associations. Journal of the Marine Biological Association of the United Kingdom, 41, 499-616.
      24. Newton, L.C. & McKenzie, J.D., 1995. Echinoderms and oil pollution: a potential stress assay using bacterial symbionts. Marine Pollution Bulletin, 31, 453-456.
      25. Newton, L.C. & McKenzie, J.D., 1998. Brittlestars, biomarkers and Beryl: Assessing the toxicity of oil-based drill cuttings using laboratory, mesocosm and field studies. Chemistry and Ecology, 15, 143-155.
      26. Nilsson, H.C., 1999. Effects of hypoxia and organic enrichment on growth of the brittle star Amphiura filiformis (O.F. Müller) and Amphiura chaijei Forbes. Journal of Experimental Marine Biology and Ecology, 237, 11-30.
      27. Ockelmann, W.K., 1958. The zoology of east Greenland. Marine Lamellibranchiata. Meddelelser om Grønland, 122, 1-256.
      28. Pearson, T.H. & Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology: an Annual Review, 16, 229-311.
      29. Pearson, T.H., Mannvik, Hans-Petter, Evans, R. & Falk-Petersen, Falk. 1996. The benthic communities of the Snorre Field in the Northern North Sea. 1. The distribution and structure of communities in undisturbed sediments. Journal of Sea Research, 35, 301-314.
      30. Peterson, C.H., 1977. Competitive organisation of the soft bottom macrobenthic communities of southern California lagoons. Marine Biology, 43, 343-359.
      31. Ramsay, K., Kaiser, M.J. & Hughes, R.N. 1998. The responses of benthic scavengers to fishing disturbance by towed gears in different habitats. Journal of Experimental Marine Biology and Ecology, 224, 73-89.
      32. Rivkin, R.B. & DeLaca, T.E., 1990. Trophic dynamics in Antarctic benthic communities. I. In situ ingestion of macroalgae by foraminifera and metazoan meiofauna. Marine Ecology Progress Series, 64, 129-136.
      33. Rosenberg, R. & Loo, L., 1988. Marine eutrophication induced oxygen deficiency: effects on soft bottom fauna, western Sweden. Ophelia, 29, 213-225.
      34. Rowden, A.A., Jago, C.F. & Jones, S.E., 1998b. Influence of benthic macrofauna on the geotechnical and geophysical properties of surficial sediment, North Sea. Continental Shelf Research, 18, 1347-1363.
      35. Southward, E.C., 1986. Gill symbionts in the Thyasirids and other bivalve molluscs. Journal of the Marine Biological Association of the United Kingdom, 66, 889-914.
      36. Sparks-McConkey, P.J. & Watling, L., 2001. Effects on the ecological integrity of a soft-bottom habitat from a trawling disturbance. Hydrobiologia, 456, 73-85.
      37. Spiro, B., Greenwood, P.B., Southward, A.J. & Dando, P.R., 1986. 13C/12C ratios in marine invertebrates from reducing sediments: confirmation of nutritional importance of chemoautotrophic endosymbiotic bacteria. Marine Ecology Progress Series, 28, 233-240.
      38. Stephen, A.C., 1923. Preliminary survey of the Scottish waters of the North Sea by the Petersen grab. Scientific Investigations of the Fisheries Division of the Scottish Home Department, 11.
      39. Suchanek, T.H., 1993. Oil impacts on marine invertebrate populations and communities. American Zoologist, 33, 510-523.
      40. Thorson, G., 1934. Contributions to the animal ecology of the Scoresby Sound Fjord complex (east Greenland). Meddelelser om Grønland. Kommissionen for Videnskabelige Undersøgelser I Grønland, 100, 1-67.
      41. Thorson, G., 1946. Reproduction and larval development of Danish marine bottom invertebrates, with special reference to the planktonic larvae in the Sound (Øresund). Meddelelser fra Kommissionen for Danmarks Fiskeri- Og Havundersögelser, Serie: Plankton, 4, 1-523.
      42. Thorson, G., 1957. Bottom communities (sublittoral or shallow shelf). Memoirs of the Geological Society of America, 67, 461-534.
      43. Tomczak, G. & Goedecke, E., 1964. Die thermische Schichtung der Nordsee auf Grund des mittleren Jahresgangs der Temperatur in 1/2°- und 1°- Feldern. Deutsche Hydrographische Zeitschrift, Ergänzungsheft B, 8
      44. Walsh, G.E., McLaughlin, L.L., Louie, M.K., Deans, C.H. & Lores, E.M., 1986. Inhibition of arm regeneration by Ophioderma brevispina (Echinodermata: Ophiuroidea) by tributyltin oxide and triphenyltin oxide. Ecotoxicology and Environmental Safety, 12, 95-100.
      45. Wetmore, K., 1995. Learning from the fossil record: Foram facts - an introduction to foraminifera [On-line]. http://www.ucmp.berkeley.edu/fosrec/Wetmore.html, 2002-08-15
      46. Widdicombe, S. & Austen, M.C., 1999. Mesocosm investigation into the effects of bioturbation on the diversity and structure of a subtidal macrobenthic community. Marine Ecology Progress Series, 189, 181-193.

      Citation

      This review can be cited as:

      Tillin, H.M. & Riley, K., 2016. Foraminiferans and Thyasira sp. in deep circalittoral fine mud. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/215

      Last Updated: 01/06/2016