Biodiversity & Conservation

SS.SMu.SMuVS.AphTubi

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum would remove the entire benthic population. Significant recolonization by many species in the biotope might occur within a few months but the biotope would be unlikely to be recognised until after six months. Recoverability is therefore recorded as high (see additional information below).
Smothering
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The characterizing species are all mobile and capable of burrowing through 5 cm of smothering sediment. Some mortality of the population may, however occur. Tube building polychaetes, including Polydora ciliata, would be covered and the population would have to build new tubes at the new sediment surface, with some energetic cost. Hydrobia ulvae may not be able to reach the sediment surface. The infaunal burrowing polychaetes would probably be able to relocate to their preferred depth and hence are unlikely to be sensitive. Based on the likelihood that some individuals of some species would perish, the biotope intolerance is assessed as intermediate but there is unlikely to be a decline in species richness. Recoverability is recorded as very high (see additional information below).
Increase in suspended sediment
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The biotope occurs in estuarine waters that are subject to occasional very high suspended sediment loads. Most of the species in this biotope are deposit feeders and may benefit from increased settlement of detritus from increased siltation. Tube building polychaetes are likely to tolerate high suspended sediment as they normally inhabit waters with high levels of suspended sediment which they actively fix in the process of tube making. For example, in the Firth of Forth, Polydora ciliata formed extensive mats in areas that had an average of 68 mg/l suspended solids and a maximum of approximately 680 mg/l indicating the species is able to tolerate different levels of suspended solids (Read et al., 1982; Read et al., 1983). The biotope may benefit from an increase in suspended sediment.
Decrease in suspended sediment
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Deposit feeders and tube builders rely on siltation of suspended sediment. A decrease in suspended sediment will reduce this supply and therefore may compromise growth and reproduction. The benchmark change only lasts for a month and so mortality is unlikely. Intolerance is therefore assessed as low. Growth would quickly return to normal when suspended sediment returns to original levels so recoverability is recorded as very high.
Desiccation
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The biotope occurs from the lowest shore downwards and may be subject to desiccation. However, all of the characterizing species are burrowing and other frequently occurring species that are surface dwellers may be able to migrate (for instance: Crangon crangon, Hydrobia ulvae, Carcinus maenas). Therefore, desiccation, where the biotope occurs on the lower shore upward extent of its range, is considered not relevant.
Increase in emergence regime
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The biotope occurs from the lowest shore downwards and may be subject to significant desiccation if emergence increased. Also, during heavy rain, low salinity is a consideration. However, all of the characterizing species are burrowing and other frequently occurring species that are surface dwellers may be able to migrate (for instance: Crangon crangon, Hydrobia ulvae, Carcinus maenas). The biotope occurs in situations subject to variable salinity and species are protected within the sediment and fairly stable interstitial water salinity and not expected to be intolerant of occasional downpours. Therefore, a minority of the community would be expected to be affected by increased emergence and no great alteration to the abundance of dominant or characterizing species so that an intolerance of low is suggested but with low confidence. Overall, the biotope would not be changed and so a recoverability of very high is suggested (see additional information below).
Decrease in emergence regime
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The biotope is predominantly subtidal and a decrease in emergence would be unlikely to have any adverse effect and would increase the habitat available for development of the biotope.
Increase in water flow rate
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The biotope occurs in areas of 'weak' to 'moderately strong' tidal streams (Connor et al., 1997b) and is therefore likely to be intolerant of increases in water flow to some degree. An increase in water flow of 2 categories could place the biotope in areas of 'very strong' flow. Although muddy sediments are cohesive and may resist winnowing by strong currents, the turbulence involved in tidal flows of 3 knots and more will most likely alter the substratum. The increase would change the sediment characteristics in which the biotope occurs, primarily by re-suspending and preventing deposition of finer particles (Hiscock, 1983). There would be a decrease in tube building material and the lack of deposition of particulate matter at the sediment surface would reduce food availability for the deposit feeders in the biotope. The resultant energetic cost over one year would be likely to result in some mortality of tube builders and infauna. Overall, the biotope is likely to change to one that is characteristic of coarser sediments. A biotope intolerance of high is therefore recorded and species richness is expected to decline. Recoverability is assessed as high (see additional information below) especially as silt, from typically high turbidity estuarine conditions, is likely to redeposit rapidly.
Decrease in water flow rate
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The biotope occurs in areas of 'weak' tidal streams (Connor et al., 1997b), the characterizing species are adapted to low flow conditions and hence the biotope is unlikely to be intolerant of a further reduction in water flow. (The possibility of water becoming stagnant and, because wave action is typically very low in this biotope, de-oxygenated is considered later in 'Changes in oxygenation'.)
Increase in temperature
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Bamber & Spencer (1984) observed that Tubificoides and Caulleriella species, common species in the biotope, were dominant in the area affected by thermal discharge in the River Medway estuary. Murina (1997) categorised Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9° C. Increased temperature may have indirect effects. For instance, higher temperatures have been implicated in the proliferation of trematode parasites which have caused mass mortalities in the snail Hydrobia ulvae (Jensen & Mouritsen, 1992). No other information has been found on tolerance of component species to increased temperature although it would be expected that the infauna in the biotope will be insulated from extreme changes of temperature. Nevertheless, an increase in temperature may indirectly affect some species as microbial activity within the sediments will be stimulated increasing oxygen consumption and promoting hypoxia (see 'Change in oxygenation' below). An intolerance of low is suggested but with a low confidence. Recoverability is likely to be rapid.
Decrease in temperature
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Very little information has been found describing the tolerance of component species in the biotope to low temperatures. Beukema et al. (1988) observed that Nephtys hombergi showed a lower survival in the (colder) north-east part of the Wadden Sea compared to the south-west. Polydora ciliata survived a drop in temperature from 11.5 to 7.5°C over the course of 15 hours (Gulliksen, 1977) and so it appears the species is tolerant of acute temperature decreases. During the extremely cold winter of 1962/63 when temperatures dropped below freezing point for several weeks, Polydora ciliata was apparently unaffected (Crisp, 1964). Observations in Crisp (1964) described mortality of Lanice conchilega between the tidemarks but not at lower levels. However, species dwelling in the sediments (at the upper intertidal limits of this biotope) are likely to be protected from the direct effects of temperature change at the surface. For instance, Hediste diversicolor burrows deeper in very cold and frosty weather (Linke, 1939). Overall, although mortality seems unlikely, especially as the biotope is mainly subtidal, some reduction in feeding and loss of condition may occur and an intolerance of low has been reported. Recovery would be likely to be immediate.
Increase in turbidity
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The biotope occurs in relatively turbid waters and therefore the species in the biotope are likely to be well adapted to turbid conditions. An increase in turbidity may affect primary production in the water column and therefore reduce the availability of diatom food, both for suspension feeders and deposit feeders. In addition, primary production by the microphytobenthos on the sediment surface may be reduced, further decreasing food availability for deposit feeders. However, primary production is probably not a major source of nutrient input into the system and, furthermore, phytoplankton will also immigrate from distant areas so the effect may be decreased. As the benchmark turbidity increase only persists for a year, decreased food availability would probably only affect growth and fecundity of the intolerant species so a biotope intolerance of low is recorded. As soon as light levels return to normal, primary production will increase and hence recoverability is recorded as 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 the primary production in the biotope and may mean greater food availability for deposit feeders and suspension feeders. However, primary production is probably not a major source of production in the biotope so the turbidity decrease is not likely to have a significant effect.
Increase in wave exposure
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The biotope occurs in 'sheltered' and 'very sheltered' areas (Connor et al., 1997a). This suggests that the biotope would be intolerant of wave exposure to some degree. An increase in wave exposure by two categories for one year would be likely to affect the biotope in several ways. Fine sediments would be eroded (Hiscock, 1983) resulting in the likely reduction of the habitat of the infaunal species, a decreased supply of tube building material and a decrease in food availability for deposit feeders. Furthermore, strong wave action is likely to cause damage or withdrawal of delicate feeding and respiration structures of species within the biotope resulting in loss of feeding opportunities and compromised growth. It is likely that high mortality would result and therefore an intolerance of high is recorded and species richness is expected to decline. Recoverability is recorded as high (see additional information below).
Decrease in wave exposure
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The biotope occurs in 'sheltered' and 'very sheltered' areas (Connor et al., 1997b). For a subtidal biotope, there is therefore likely to be very little oscillatory water movement and the predominant water movement will be tidal flow. A decrease in wave exposure by 2 categories for a year would place a portion of the biotope in 'ultra sheltered' areas. The characterizing species are adapted to low flow conditions and are likely to tolerate this change.
Noise
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There is no evidence to suggest that any of the species which characterize the biotope are sensitive to noise or vibration at the level of the benchmark.
Visual Presence
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Some of the species in the biotope may be intolerant of shading but would not 'see' predators. Farke (1979) noted their intolerance of Aphelochaeta marioni to disturbance by light in a microsystem in the laboratory. Polydora ciliata responds to shading by withdrawing its palps into its burrow, believed to be a defence against predation (Kinne, 1970). Although not strictly "visual presence", the withdrawal of feeding structures means that growth may be compromised by the interruption of feeding and so intolerance is assessed as low. Growth should quickly return to normal when the disturbance is over so recoverability is recorded as very high.
Abrasion & physical disturbance
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Many species in the biotope are vulnerable to physical abrasion. The tubes of the polychaetes are bound only with mucous and are therefore likely to damaged by a passing scallop dredge. The infaunal annelids are predominantly soft bodied, live within a few centimetres of the sediment surface and may expose feeding or respiration structures where they could easily be damaged by a physical disturbance. Biotope intolerance is therefore recorded as intermediate. Recoverability is recorded as very high as damage at the benchmark level will be restricted in extent (see additional information below). For large scale physical disturbance, sensitivity will be more similar to 'substratum removal' above.
Displacement
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The species in the biotope are either mobile and capable of re-burrowing or, mainly, capable of re-building tubes. However, following displacement of key or characterizing species, the biotope would have to be structurally re-established - there may be a succession of species before IMU.AphTub is recognised. Intolerance is identified as high and recoverability moderate but with low confidence.

Chemical Factors

Synthetic compound contamination
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Some species in the biotope are known to be adversely affected by synthetic chemicals. For instance, Scoloplos armiger (frequently found in the biotope) exhibited 'moderate' intolerance to tri-butyl tin antifoulants (Bryan & Gibbs, 1991). Collier & Pinn (1998) investigated the effect on the benthos of Ivermectin, a feed additive treatment for infestations of sea-lice on farmed salmonids. The polychaete Hediste diversicolor (frequently found in the biotope) was particularly susceptible, exhibiting 100% mortality within 14 days when exposed to 8 mg/m² of Ivermectin in a microcosm. On the other hand, Beaumont et al. (1989) investigating the effects of tri-butyl tin (TBT) on benthic organisms found that at concentrations of 1-3 µg/l there was no significant effect on the abundance of Hediste diversicolor or Cirratulus cirratus (an infrequent component of the biotope) after 9 weeks in a microcosm. However, no juvenile polychaetes were retrieved from the substratum and hence there is some evidence that TBT had an effect on the larval and/or juvenile stages of these polychaetes. Polydora ciliata was abundant at polluted sites close to acidified, halogenated effluent discharge from a bromide-extraction plant in Amlwch, Anglesey (Hoare & Hiscock, 1974). Spionid polychaetes, oligochaetes (principally Tubificoides benedeni) and Hydrobia ulvae were found by McLusky (1982) to be amongst the most tolerant species in the vicinity of a of a petrochemical industrial waste in the Firth of Forth, Scotland. The biotope occurs in polluted conditions and overall, an intolerance of intermediate is suggested reflecting the likelihood that some chemicals might adversely affect some species reducing abundance and viability but the biotope would persist. For recoverability, see additional information. Recovery would require synthetic chemicals to have depurated from the sediment.
Heavy metal contamination
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The majority of species in this biotope are polychaetes and evidence suggests that they are "fairy resistant" to the effects of heavy metals (Bryan, 1984). However, Hall & Frid (1995) found that the four dominant taxa in their study (species typically found in this biotope including Tubificoides spp. and Capitella capitata) were reduced in abundance in copper-contaminated sediments and that recovery took up to one year after the source of contamination ceased. Some other species (for instance Carcinus maenas) , may adapt to high metal concentrations (Bryan, 1984). Polydora ciliata, one of the species that occurs frequently in the biotope, occurs in an area of the southern North Sea polluted by heavy metals but was absent from sediments with very high heavy metal levels (Diaz-Castaneda et al., 1989). However, Hediste diversicolor has been found successfully living in estuarine sediments contaminated with copper ranging from 20 µm Cu/g in low copper areas to >4000 µm Cu/g where mining pollution is encountered e.g. Restronguet Creek in the Fal Estuary, Cornwall (Bryan & Hummerstone, 1971). Taking account of the low salinity conditions that affect this biotope (in general, for estuarine animals, heavy metal toxicity increases as salinity decreases and temperature increases: McLusky et al., 1986), it seems possible that some species at least in the biotope might be adversely affected by high contamination by heavy metals. The assessment of intermediate intolerance is 'precautionary' and the specific levels at a location would need to be matched to experimental or field studies to assign a more accurate rank. For recoverability, see additional information below. Recovery of species in the biotope would be influenced by the length of time it would take for the habitat to return to a suitable state (e.g. factors such as the decline of bioavailable metals within the marine environment), recolonization by adult and juvenile specimens from adjacent habitats, and the establishment of a breeding population.
Hydrocarbon contamination
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The biotope is predominantly subtidal and component species 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. Some of the polychaetes in this biotope proliferate after oil spills: for instance Capitella capitata (Suchanek, 1993) and Aphelochaeta marioni (Dauvin, 1982, 2000). Cirratulids seem mostly immune probably because their feeding tentacles are protected by mucus (Suchanek, 1993). Nevertheless it might be expected that some of the species in the biotope may be affected and the increase in abundance of some species suggests reduced competition with others. However, because some species in the biotope may increase in abundance following a spill, and because of the subtidal character of the biotope, it is expected that adverse effects from hydrocarbons may reduce abundance and viability of some species but the biotope would persist. An intolerance of intermediate is therefore suggested but with a high recoverability (see additional information below).
Radionuclide contamination
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No information has been found.
Changes in nutrient levels
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It would be expected that some increase in nutrients would favour the expansion of food resources for deposit feeders. Increased nutrients often derive from sewage inputs and presence of species such as Aphelochaeta marioni in such situations (for instance Broom et al., 1991) may reflect tolerance to high nutrients or to deoxygenated conditions or both. Overall, the benefits (higher food resources) and disbenefits (possible hypoxia) make it difficult to determine intolerance but, considering the often eutrophic situations the biotope occurs in, an intolerance of low is suggested but with very low confidence.
Increase in salinity
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The biotope occurs in reduced to full salinity and so increase in salinity is considered not relevant.
Decrease in salinity
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The biotope occurs in reduced salinity. One of the characterizing species, Aphelochaeta marioni , has been recorded from brackish inland waters in the Southern Netherlands with a salinity of 16 psu, but not in areas permanently exposed to lower salinities (Wolff, 1973). However, it also penetrates into areas exposed to salinities as low as 4 psu for short periods at low tide when fresh water discharge from rivers is high (Farke, 1979). The distribution of Aphelochaeta marioni, therefore, suggests that it is very tolerant of low salinity conditions and would be tolerant of reduced salinity especially for short periods. However, a long term reduction from reduced to low salinity may affect some of the species in the biotope with possible losses and reduced viability. The biotope would probably change to one more tolerant of very low salinity conditions. An intolerance of high is therefore suggested but recovery would be rapid on return to previous conditions (see additional information below).
Changes in oxygenation
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Some of the species frequently found in the biotope (Malacoceros fuliginosus, Nephtys hombergi, Heteromastus filiformis) are noted by Diaz & Rosenberg (1995) as resistant to severe hypoxia or (Capitella capitata, Hediste diversicolor) to moderate hypoxia. Tubificoides benedii has a high capacity to tolerate anoxic conditions (see Giere et al., 1999). Broom et al. (1991) found communities with species characteristic of this biotope in the Severn Estuary where the oxygenated layer was very thin probably as a result of sewage input and suggested that Aphelochaeta marioni was characteristic of faunal assemblages in the Severn Estuary with very poorly oxygenated mud. The successful survival of Hediste diversicolor under prolonged hypoxia was confirmed by the resistance experiments of Vismann (1990), which resulted in a mortality of only 15% during a 22 day exposure of Hediste diversicolor at 10% oxygen (ca. 2.8 mg O2 per litre). Whilst the biotope might thrive in conditions of hypoxia, some species might suffer, reducing species richness. Following a hypoxia event in summer 1994 in the southern Baltic, species (some of which occur in the biotope) took at least two years to recolonize but by summer 1996 had returned to pre-event community structure (Powilleit & Kube, 1999). Since species richness may be reduced by reduction in oxygen, an intolerance of intermediate is suggested reflecting the likelihood that the biotope will not be lost.

Biological Factors

Introduction of microbial pathogens/parasites
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No information was found concerning the infection of most of the characterizing species by microbial pathogens. However, there are records of mass mortalities of Hydrobia ulvae caused by high temperatures triggering mass development of larval digenean trematodes within the snails (Jensen & Mouritsen, 1992). The effect on the biotope is likely to be low and recovery high.
Introduction of non-native species
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Invasion by the slipper limpet Crepidula fornicata may switch the biotope to £IMU.CreAph£ suggesting high intolerance as the original biotope would be lost. Species richness might decline as Crepidula may dominate the seabed. On the other hand, low densities of Crepidula might have no effect on species richness and add one species (Crepidula) to the community.
Extraction
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It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

Recoverability
The biotope typically consists of fast growing opportunistic species so that recoverability is expected to be very high or high. However, recovery to full species richness may take longer than one year. The following information has informed the recoverability assessment. Ferns et al. (2000) found that, following significant depletion of Nephtys hombergi by cockle dredging recovery took more than 50 days (but not more than 100 days). Hall & Frid (1998) found that colonization by many of the polychaetes associated with this biotope did not vary significantly with season although recruitment of Tubificoides benedii and Ophyrotrocha hartmanni did vary significantly with season. Also, there may be spawning failure in some years, for instance in Nephtys hombergi (Olive et al. 1997). Following a hypoxia event in summer 1994 in the southern Baltic, species (some of which occur in the biotope) took at least two years to recolonize but by summer 1996 had returned to pre-event community structure (Powilleit & Kube, 1999).

This review can be cited as follows:

Hiscock, K. 2002. Aphelochaeta marioni and Tubificoides spp. in variable salinity infralittoral mud. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 20/04/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=201&code=2004>