Biodiversity & Conservation

SS.IGS.FaS.NcirBat

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Biotopes occurring within sandy substrata risk the loss of substratum through both physical (hydrodynamic regime) and anthropogenic activity, e.g. aggregate extraction.
Under normal circumstances the sediment is subject to a high level of physical disturbance as a consequence of the hydrodynamic regime, and during storms the upper most layers of sand may be removed, retained in suspension and deposited later. At the benchmark level, intolerance to substratum loss has been assessed to be intermediate as, whilst the species are mobile and would survive displacement, they would lack a substratum within which to seek protection from predators and within which to feed for the duration of the disturbance event. However, such disturbance is normal and the sand is retained within the system, although the spatial extent and surface form of the substratum may change. Recoverability would be expected to be very high on return to prior conditions as displaced infauna would re-enter the sand.
In contrast, aggregate extraction may be responsible for degradation of the biotope, as sand with associated fauna is lost from the system. Intolerance would be expected to be higher because a proportion of the population would die and displaced fauna suffer a reduction in habitat.
Smothering
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Smothering by 5 cm of sand is unlikely to adversely affect the important characterizing species which are able to burrow. At the benchmark level intolerance has been assessed to be low as the mobile polychaetes and crustaceans would burrow through the sediment and recoverability has been assessed to be immediate. However, biotope intolerance is likely to be higher if the smothering sediment is atypical for the biotope e.g. fine silt or shingle (arising from dredging spoil), and assuming that the smothering materials were not rapidly removed or dispersed by the hydrographic regime, the atypical substrata would dramatically change the nature of the surface substratum. Over the duration of one month species not normally found within the biotope may find conditions favourable for colonization and a transitional community may result and the biotope begin to change to another.
Increase in suspended sediment
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Owing to the high energy environment, elevated concentrations of suspended sediment are a normal feature of the biotope, especially during and following storm events. Species within the biotope are infaunal and so are offered protection from scour and characterizing species do not suspension feed. Effects of increased turbidity are addressed elsewhere and the biotope has been assessed to be not sensitive to increased suspended sediment.
Decrease in suspended sediment
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Fluctuations of suspended sediment are experienced within the biotope and are a characteristic feature owing to the high energy hydrographic regime. It is unlikely that the community would be adversely affected by a reduction in the amount of suspended sediment for a period of one month. An assessment of not sensitive has been made.
Desiccation
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The biotope is subtidal so populations inhabiting the sandbanks do not experience desiccation. However, many of the important characterizing species are also found in the intertidal so are likely to be tolerant of continuous exposure to sunshine and air for one hour or will demonstrate an avoidance behaviour or habit. For instance, Nephtys species live infaunally so that the substratum offers the polychaete protection from desiccation and if displaced to the surface will immediately attempt to bury itself. Mobile crustacean species such as Bathyporeia pelagica will avoid desiccation by moving away or burrowing in to the sediment. An assessment of not relevant has been made.
Increase in emergence regime
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The biotope is subtidal so is not normally subjected to emergence. However, coastal developments such as tidal and storm-surge barriers restrict tidal amplitude and may cause a lowering of the low water mark, so that in some locations the biotope in the shallow sublittoral is subjected to emergence. In such instances, factors such as desiccation and temperature become more important factors of stress, but owing to the infaunal habit and/or mobility, the characterizing species are likely to be offered considerable protection or would move away to seek more favourable conditions. Therefore an assessment of not relevant has been made.
Decrease in emergence regime
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The biotope is subtidal and a decrease in emergence is unlikely to have any detectable effect on the survival of characterizing species. An assessment of not sensitive has been made.
Increase in water flow rate
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The type of sediment present is determined by the type of substratum available and strength of water movement, so that sediments within an area probably reflect the average energy conditions of that area (Hiscock, 1983). In the IGS.NcirBat biotope water flow may fluctuate between weak to strong and well sorted medium and fine grained sands are typical of the biotope.
A velocity of >0.3 m/s is the minimum required to transport fine sand in suspension and higher currents will move larger grades of sediment via bedload transport (see Figure 3.11, Hiscock, 1983). Water flow in the biotope may under normal conditions fluctuate between weak and strong. However, if water flow changed from weak to very strong for a period of year, it would probably bring about concomitant changes in the grade of the sediment owing to the winnowing away of the sediment with consequences for the infauna. For instance, Bathyporeia pilosa avoided burrowing into substrata with particles >500µm median diameter (Khayrallah & Jones, 1978a). Thus it is likely that some important characterizing species would become exposed to conditions outside of their habitat preference and would probably no longer be found at such a location. Polychaetes characteristic of the biotope are less likely to be affected by increased water flow rate as they burrow deeper and hunt infaunally. Intolerance to increased water flow has been assessed to be intermediate as over a year the biotope may become impoverished as species intolerant of a coarser substratum move elsewhere and the biotope begin to change to another. On return to prior conditions recoverability has been assessed to be very high (see additional information below).
Decrease in water flow rate
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The type of sediment present is determined by the type of substratum available and strength of water movement, so that sediments within an area reflect the average energy conditions of that area (Hiscock, 1983). In the IGS.NcirBat biotope water flow may fluctuate between weak to strong and well sorted medium and fine grained sands are typical of the biotope. A reduction in the water flow rate for a period of one year would probably reduce the degree of sorting of grain size as current velocity within the close proximity of the sea bed drops below the critical erosion velocity causing bedload transport of medium and coarse grained sands to cease. During periods of low wave action, deposition of finer sediments from suspension may occur so that the composition of the substratum begins to change. Finer sediments and increased stability may enhance the survival of more sedentary forms of polychaete and bivalves and the biotope begin to change to another. Species richness is likely to rise. Intolerance has been assessed to be high as considerable changes in community composition may occur and the biotope no longer be recognized. On return to prior conditions recoverability has been assessed to be very high (see additional information below).
Increase in temperature
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The geographic distribution of polychaete and crustacean species characteristic of this biotope extend south of the British Isles, so are likely to be tolerant of a long-term chronic temperature increase of 2°C. Infaunal species are likely to be protected to some extent from direct effects of acute increases in temperature, although increased temperatures may affect infauna indirectly, by stimulating increased bacterial activity and increased oxygen consumption.
Emery & Stevensen (1957) reported that Nephtys hombergii could withstand summer temperatures of 30-35 °C so is likely to withstand the benchmark acute temperature increase. An acute increase in temperature at the benchmark level may result in physiological stress endured by the infaunal species but is unlikely to lead to mortality as the biotope is subtidal and probably protected from extremes of temperature by the depth of overlying water. Therefore, an intolerance of low has been recorded to represent sub-lethal effects on growth and reproduction. A recoverability of very high has been suggested.
Decrease in temperature
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Olive and Morgan (1991) concluded that patterns of reproduction in the Nephtyidae were related to environmental conditions in central parts of the range of each species and that marginal populations exhibited occasional reproductive failures. Nephtys cirrosa is a temperate species, reaching the northern limit of its range in northern Britain where it breeds unpredictably. Over a three year period, Olive and Morgan (1991) failed to observe spawning in a population of Nephtys cirrosa from the Northumbrian coast. The observations of Olive and Morgan (1991) suggested that a long-term chronic decrease in temperature may be responsible for recruitment failure amongst Nephtys populations in northern Britain. Crisp (1964) reported that the polychaetes Nephtys hombergii, Scoloplos armiger to be unaffected by the unusually severe winter of 1962/63, their infaunal position may have offered protection from extreme temperature change.
intolerance to decreased temperature for the period of a year has been assessed to be low as the viability of an important characterizing species may be affected as a result of recruitment failure. On return to prior conditions, recovery of the polychaete would be expected owing to adult migration and eventual reproduction and has been assessed to be high.
Increase in turbidity
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Owing to the lack of stable substrata, primary production in the biotope is restricted to the microphytobenthos (see 'general biology - productivity) and the biotope is heavily subsidised with organic matter from external sources, e.g. plankton. Increased turbidity would further limit primary production within the biotope, over the period of a year a loss of condition might be detectable amongst the infauna, but more severe effects are unlikely as long as an adequate amount of organic matter continues to be supplied to the biotope from more productive biotopes and environments elsewhere. Intolerance has been assessed to be low and recovery very high as on return to prior conditions optimal feeding would be expected to recommence.
Decrease in turbidity
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Owing to the lack of stable substrata, primary production in the biotope is restricted to the microphytobenthos (see 'general biology - productivity). A concomitant increase in primary productivity of the microphytobenthos might be expected with a reduction in turbidity which, although beneficial to the community may be difficult to detect unless organic matter produced from external sources became limiting. An intolerance assessment of not sensitive* has been suggested.
Increase in wave exposure
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The biotope typically occurs in locations with a range of wave exposures. Wave action is a particularly important physical factor in the shallow subtidal as oscillatory wave action disturbs the sand and can cause large scale sediment transport. Although, the biotope is dominated by errant polychaetes and small crustacean species tolerant of abrupt changes in wave exposure, over the period of one year it is likely that the sand would be disrupted to a greater degree and the finest grades lost. Consequently, some species may begin to experience conditions outside of their habitat preferences e.g. Bathyporeia pelagica, and decline in abundance. Intolerance has been assessed to be intermediate and recoverability high as, on return to prior conditions adults are likely to migrate into the biotope.
Decrease in wave exposure
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A decrease in wave exposure would be expected to bring about significant changes in the physical composition of the biotope and the colonizing fauna. Over a year the composition of the substratum would be expected to change owing to poorer sorting and elevated sedimentation of silt and organic matter bringing about changes of the chemical environment of the substratum. The substratum would be disturbed less frequently and would allow less mobile and sessile species, e.g. tube building polychaetes and bivalves, to colonize the biotope. A transitional community would develop. Important characterizing species of the IGS.NcirBat biotope would probably remain but may no longer be numerically dominant. Intolerance has been assessed to be high as the biotope may no longer be recognized. On return to prior conditions recoverability has been assessed to be very high (see additional information below).
Noise
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Species within the biotope may be able to detect vibration but noise at the benchmark level is unlikely to have a detectable effect on the survival of the species.
Visual Presence
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Species within the biotope may have the visual acuity to detect predators and/or changes in light intensity, but are unlikely to be adversely affected by the visual presence of e.g. boats, machinery and humans moving about on the surface of overlying water owing to their infaunal habit. An assessment of not relevant has been suggested.
Abrasion & physical disturbance
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Amphipod crustaceans such as Bathyporeia pelagica are not of a growth form likely to be damaged by abrasion caused by a passing scallop dredge or the dragging of an anchor and are sufficiently mobile to avoid the disturbance.

Important characterizing polychaete worms, such as the Nephtyidae, live in the sediment between a depth of 5-15 cm and are therefore protected from most sources of abrasion and disturbance caused by surface action. However, Ferns et al. (2000) recorded significant losses of infaunal polychaetes from areas of muddy sand worked with a tractor-towed cockle harvester. For example, 31% of Scoloplos armiger and 83% of Pygospio elegans were lost in dense populations. Their populations remained depleted for between 50 and 100 days indicating that abrasion and physical disturbance can be responsible for the deterioration of infaunal polychaete populations. However, such disturbance is probably greater than that caused by a passing scallop dredge.

Most importantly, this biotope is characteristic of infralittoral sands subject to physical disturbance due to wave exposure and tidal streams, so that frequent displacement of shallow infauna is to be expected. Therefore, intolerance has been assessed to be low with a very high recoverability.

Displacement
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Owing to the high energy environment, species that characterize the biotope are predominantly mobile forms (swimming and burrowing) that are able to re-enter the substratum following disturbance. Intolerance has been assessed to be low as displacement itself is unlikely to have a detectable effect on the infauna. Recoverability has been assessed to be immediate (see additional information below) However, whilst briefly exposed at the surface the infauna would be potentially predated upon by the epibenthos and fish.

Chemical Factors

Synthetic compound contamination
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Sedimentary biotopes in sheltered, low energy areas, such as those in the intertidal zones of estuaries and bays are more susceptible to chemical pollution than high energy sedimentary biotopes such as this. The coarser sediments and hydrodynamic regime, including high dispersion, serves to hinder cases of severe pollution (Elliott et al., 1998).
No evidence concerning the specific effects of chemical contaminants on Nephtys species was found. Boon et al. (1985) reported that Nephtys species in the North Sea accumulated organochlorines but, based on total sediment analyses, organochlorine concentrations in Nephtys species were not correlated with the concentrations in the (type of) sediment which they inhabited. Specific effects of synthetic chemicals have been reported for other species of polychaete. Exposure of Hediste diversicolor and Arenicola marina to Ivermecten resulted in significant mortality (see MarLIN reviews; Collier & Pinn, 1998). Beaumont et al. (1989) investigated the effects of tri-butyl tin (TBT) on benthic organisms. At concentrations of 1-3 µg/l there was no significant effect on the abundance of Hediste diversicolor or Cirratulus cirratus after 9 weeks in a microcosm. However, no juvenile polychaetes were retrieved from the substratum suggesting that TBT had an effect on the larval and/or juvenile stages of these polychaetes. Bryan & Gibbs (1991) reported that Arenicola costata larvae were unaffected by 168 hr exposure to 2000 ng TBT/ l seawater and were probably relatively tolerant, but in another study, Scoloplos armiger exhibited a dose related decline in numbers when exposed to TBT paint particles in the sediment.
In general, crustaceans are widely reported to be intolerant of synthetic chemicals (Cole et al., 1999) and intolerance to some specific chemicals has been observed in amphipods. Gammarid amphipods have been reported to be sensitive to TBT with 10 day LC50 values of 1-48ng/l (Meador et al., 1993). Intolerance has been assessed to be intermediate owing to the fact that different chemicals are likely to have different modes of action and effect on different species of polychaete and crustacean. Important characterizing species may demonstrate similar sensitivities as the species mentioned above but little evidence was found and a low confidence is recorded. Assessment of recovery assumes deterioration of contaminants (likely in a high energy environment) and recoverability has been assessed to be high as recolonization is likely via adult migration and larval settlement.
Heavy metal contamination
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Higher energy sedimentary biotopes such as IGS.NcirBat are less likely to concentrate heavy metal contaminants. The coarser sediment grade and the hydrographic conditions are responsible for a high dispersion, so that instances of severe pollution are less in comparison to sheltered sand and mudflats, e.g. Bryan & Gibbs (1983; table 5) reported lower sediment-metal concentrations in sandy areas than mud near the mouth of Restronguet Creek, a branch of the Fal Estuary system which is heavily contaminated with metals.
Although heavy metals may not accumulate in the substratum to the extent that they would in muddy substrata, characterizing infauna are likely to be susceptible.
Bryan & Gibbs (1983) suggested that in populations of polychaetes exposed to heavy metal contamination for a long period, metal resistance could be acquired. For example Nephtys hombergii from Restronguet Creek seemed able to regulate copper. The head end of the worm became blackened and x-ray microanalysis by Bryan & Gibbs (1983) indicated that this was caused by the deposition of copper sulphide in the body wall. In the same study, 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).
For most metals, toxicity to crustaceans increases with decreased salinity and elevated temperature. Consequently amphipod species living within their normal salinity range may be less susceptible to heavy metal pollution than those living in salinities near the lower limit of their salinity tolerance (McLusky et al., 1986).
intolerance of the IGS.NcirBat community has been assessed to be intermediate. Infaunal population of polychaetes may be intolerance of pulses of heavy metals in solution entering the biotope, as in the absence of mud and silts in combination with the highly dispersive hydrographic regime, concentrations in the substratum are likely to be low and populations not develop resistance. Whilst many individuals may survive by escaping from the vicinity, some mortality would be expected and defaunation of the sediment occur. However, a low confidence is reported owing to limited evidence. On return to prior conditions (which assumes deterioration of the contaminant) recolonization of polychaetes and amphipod crustaceans would be expected to be rapid via adult migration and juvenile recruitment.
Hydrocarbon contamination
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Oil spills resulting from tanker accidents have caused deterioration of sandy communities in the intertidal and shallow sublittoral. Subtidal sediments, however, may be at less risk from oil spills unless oil dispersants are used, or if wave action causes dispersion of oil into the water column and sediment mobility drives oil in to the sediment (Elliott et al., 1998). Microbial degradation of the oil within the sediment would increase the biological oxygen demand and oxygen within the sediment may become significantly reduced.
Species within the biotope have been reported to be intolerant of oil pollution, e.g. amphipods (Suchanek, 1993). After the Amoco Cadiz oil spill there was a reduction in both the number of amphipod species and the number of individuals (Cabioch et al., 1978). Initially, significant mortality would be expected, attributable to toxicity. Amphipod populations have been reported not return to pre-spill abundances for five or more years, which is most likely related to the persistence of oil within sediments (Southward, 1982). Nephtys species were amongst the fauna that was eradicated from sediments following the 1969 West Falmouth spill of Grade 2 diesel fuel documented by Saunders (1978). Intolerance to hydrocarbon contamination has been assessed to be high even though in the sublittoral oil may not reach the benthos as readily. Recoverability has been assessed to be moderate owing to evidence that following oil spills amphipod communities have not rapidly recovered.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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The effect of organic enrichment on sedimentary systems and their benthos is well documented, as a consistent sequence of response is observed, see Pearson & Rosenberg (1978).
The substratum has a characteristically low level of organic matter. Moderately enhanced levels of organic matter would be used as a food resource by meiofauna and macrofauna, secondary production would increase and a mixing of organisms with different responses increases diversity (although they would need to be tolerant of the prevailing hydrodynamic regime). In extreme instances of enrichment, diversity would be expected to decline and the fauna become dominated by fewer pollution tolerant species, such as the polychaete Capitella capitata. Excessive nutrient enrichment leading to anoxia in the sediment is likely to result in defaunation. Such a sequence has been observed in sand biotopes as the result of hydrocarbon pollution (Majeed, 1987).
At the benchmark level the intolerance of the biotope to nutrient enrichment has been suggested to be not sensitive* owing to evidence suggesting that nutrients within the biotope are often limiting and that the biotope is heavily subsidised with organic matter produced outside the biotope.
Increase in salinity
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IGS.NcirBat occurs in locations of full salinity (Connor et al., 1997a). No information was found concerning the intolerance of the benthic community to hypersaline conditions.
Decrease in salinity
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IGS.NcirBat occurs in locations of full salinity (Connor et al., 1997a) and therefore is likely to be intolerant of decreased salinity in some way. The benchmark decrease in salinity would place the biotope in areas of variable salinity for one year or reduced salinity for one week.
Nephtys species are tolerant of brackish waters and penetrate in to the mouths of estuaries and estuarine lagoons where salinity may fall below 20 psu (Barnes, 1994), so are unlikely to be especially affected by a reduction in salinity. Bathyporeia pelagica is found in the intertidal but is restricted to the lower half of the tidal range by its intolerance to reduced salinity (Preece, 1970). Salvat (1967), Fish & Preece (1970), Ladle (1975) and Fish & Fish (1978) have reported both the re-distribution of Bathyporeia pelagica populations down the shore during spring and summer on open coasts, and the migration of Bathyporeia pelagica from sandy estuarine beaches to sites on the open coast. Thus it is probable that in the shallow sublittoral where reduced salinity is most likely to occur, the species would migrate offshore. Other species of amphipod crustaceans appear more tolerant of reduced salinity than Bathyporeia pelagica, e.g. Haustorius arenarius will tolerate salinities <10 psu and Bathyporeia pilosa tolerates salinities as low as 4 psu (Barnes, 1994). The intolerance of the biotope is suggested to be low. Reduced salinities may cause the fauna to become impoverished as, species intolerant of reduced salinity are sufficiently mobile to avoid the factor and move away. On return to prior conditions recovery is likely to be immediate as species temporarily displaced return. an intolerance assessment of high would have been given except for the fact that as a mobile species Bathyporeia pelagica is able to migrate and avoid conditions of depressed salinity.
Changes in oxygenation
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Subtidal sands in wave exposed locations are well-oxygenated owing to the mobile nature of the substratum and tidal pumping of overlying water which ensures a deep anaerobic layer (>15 cm). Any organic matter incorporated in to the substratum is rapidly degraded (Elliott et al., 1998). Oxygen within the substratum is unlikely to become limiting under normal conditions, but may do so in the event of an influx of excessive organic matter (see nutrients above). Laboratory studies by Khayrallah (1977) on Bathyporeia pilosa revealed it to have a relatively poor resistance to conditions of hypoxia in comparison to other interstitial animals. It was also susceptible to hydrogen sulphide, supporting the conclusion that aerated deposits are a fundamental requirement of Bathyporeia pilosa and also probably other Bathyporeia species. It is likely, therefore, that some crustacean species would be unable to endure hypoxic conditions for a week and would move away.
Information concerning the reduced oxygen tolerance of Nephtys cirrosa was not found but evidence (Alheit, 1978; Arndt & Schiedek, 1997; Fallesen & Jørgensen, 1991) indicated a similar species, Nephtys hombergii, to be very tolerant of episodic oxygen deficiency and at the benchmark duration of one week. At the benchmark level intolerance has been assessed to be low as some important characterizing species may move away from the biotope for the duration of the factor but populations are likely to recover rapidly on return to prior conditions.

Biological Factors

Introduction of microbial pathogens/parasites
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The most common parasites of sand inhabiting invertebrates belong to the Trematoda, a class of the phylum Platyhelminthes, and to the Copepoda, a group of crustaceans whose free living members are either planktonic or sediment dwelling. Trematodes (flukes) usually have three consecutive hosts, although two to four are known. In the marine environment, the primary hosts are normally fish or birds, and the first secondary host a gastropod or bivalve mollusc. The second intermediate host may belong to a variety of taxonomic hosts including the coelenterates, turbellarians, annelids, crustaceans, molluscs, insects or even fish (Eltringham, 1971). However, an intolerance assessment for the biotopes represented by this review cannot be made owing to insufficient information concerning impacts on populations.
Introduction of non-native species
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No evidence was found to suggest that important characterizing species of the biotope are threatened by alien species.
Extraction
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Whilst species characteristic of the biotope may be targeted for extraction when they are present in the intertidal, e.g. bait digging for Nephtys cirrosa, the species is unlikely to be targeted in the sublittoral. We have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

Recoverability
Subtidal sandbanks are the result of relatively high energy conditions and experience regular episodes of natural disturbance by disruption of the prevailing hydrographic regime.
The ability of the community to recover from physical disturbance is likely to be very high or immediate in some instances, because the component species, errant polychaetes and small crustaceans, are highly mobile, tolerant of sediment movement and would accompany the influx/re-settlement of disturbed material. Sherman & Coull (1980) observed that meiofaunal recolonization occurred within a few days owing to recruitment from hyperbenthic populations. The attainment of typical densities of macrofauna would also be dependant to some extent on the timing of disturbance in relation to reproductive period, which for many of the macrobenthos occurs over a discrete period of the year.

This review can be cited as follows:

Budd, G.C. 2006. Nephtys cirrosa and Bathyporeia spp. in infralittoral sand. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 25/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=154&code=1997>