Biodiversity & Conservation

SS.SMu.SMuVS.PolCvol

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum, perhaps by dredging, would result in the loss of Polydora ciliata tubes and hence the loss of the animals so intolerance is assessed as high. However, if some individuals remain, rapid recolonization of the remaining substratum is possible because the species is capable of tube building throughout its life. For example when Daro & Polk (1973) removed Polydora ciliata individuals of all ages on several occasions, all built new tubes. Recovery is likely to be high because the larvae of Polydora ciliata are planktonic and capable of dispersal over long distances and the reproductive period is of several months duration. In colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring.
Smothering
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Polydora ciliata is probably relatively tolerant smothering by 5 cm of sediment because the species inhabits a range of habitats including muddy sediment, larvae settle preferentially on substrates covered with mud (Lagadeuc, 1991) and worms can rebuild tubes close to the surface. The species also plays an important part in the process of temporary sedimentation of muds in some estuaries, harbours or coastal areas (Daro & Polk, 1973). Adults of Polydora ciliata produce a 'mud' resulting from the burrowing and tube building activities in mud, clay and soft rock substrata (Lagadeuc, 1991). A Polydora mud can be up to 50cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes, or leave them to rebuild tubes close to the surface.
Increase in suspended sediment
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Polydora ciliata is able to inhabit a wide range of habitats from muddy sediments to soft rock. For example, the species is found in turbid waters with high levels of suspended sediment which it actively fixes in the process of tube making. Daro & Polk (1973) report that the success of Polydora is directly related to the quantities of muds of any origin carried along by rivers or coastal current. In the Firth of Forth Polydora ciliata formed extensive mats in areas that had an average of 68mg/l suspended solids and a maximum of approximately 680mg/l indicating the species is able to tolerate a huge range of quantities of suspended solids (Read et al., 1982; Read et al., 1983). Occasionally, in certain places siltation is speeded up when Polydora ciliata is present because the species actually produces a 'mud' as it perforates soft rock and chalk habitats and larvae settle preferentially on substrates covered with mud (Lagadeuc, 1991). Therefore, it seems likely that the biotope will be relatively tolerant of increases in suspended sediment and siltation.
Decrease in suspended sediment
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Polydora ciliata is able to inhabit a wide range of habitats from muddy sediments to soft rock. Occasionally, in certain places siltation is speeded up when Polydora ciliata is present. Suspended sediment and siltation of those particles is important for tube building in Polydora ciliata so a decrease may reduce tube building or the thickness of the mud surrounding the 'colonies'. Daro & Polk (1973) report that the success of Polydora is directly related to the quantities of muds of any origin carried along by rivers or coastal currents. However, at the level of the benchmark the effects are not likely to be significant and an intolerance rank of low is recorded.
Desiccation
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The biotope only occurs in the infralittoral zone and so is not subject to desiccation. Therefore, the factor is not relevant.
Increase in emergence regime
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The biotope only occurs in the infralittoral zone and so will not be subject to an increase in emergence. Therefore, the factor is not relevant.
Decrease in emergence regime
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The biotope only occurs in the infralittoral zone and so is not subject to a decrease in emergence. Therefore, the factor is not relevant.
Increase in water flow rate
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Polydora ciliata was present and colonized test panels in Helgoland in three areas, two exposed to strong tidal currents and one site sheltered from currents (Harms & Anger, 1983) so the species appears to tolerate a wide range of water flow regimes. However, in very strong tidal currents little sediment deposition will take place resulting in coarse sediments retaining little organic matter and may become unsuitable for the deposit feeding and tube building activities of Polydora ciliata. Nevertheless, where suspended sediment levels are high, deposition of fine sediment may occur even in strong flows providing suitable conditions for the species. Very strong water flows may sweep away Polydora colonies, often in a thick layer of mud on a hard substratum. If the species tube is embedded in a burrow excavated in limestone rock, shells or calcareous algae the animals may be protected from being washed away in increased flow. However, a change in water flow of 2 categories (see benchmark) for a period of a year is likely to interfere with feeding and tube building by removing sediments and may wash some individuals away. The viability of the biotope is likely to be reduced and so intolerance is set at intermediate. Recovery is very high because the larvae of Polydora ciliata are planktonic and capable of dispersal over long distances and the reproductive period is of several months duration. In colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring.
Decrease in water flow rate
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Polydora ciliata was present and colonized test panels in Helgoland in three areas, two exposed to strong tidal currents and one site sheltered from currents (Harms & Anger, 1983) so the species appears to tolerate a wide range of water flow regimes. A decrease in water flow rate may reduce the suspended particulate material carried in the water column important for Polydora ciliata tube building and feeding. Thus effects will be sub-lethal so intolerance is assessed as low. On return to normal conditions recovery will be very high because Polydora ciliata is able to rapidly recolonize suitable substrata.
Increase in temperature
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Murina (1997) categorised Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe which extends into the warmer waters of Portugal and Italy (Pardal et al., 1993; Sordino et al., 1989). In the western Baltic Sea Gulliksen (1977) recorded high abundances of Polydora ciliata in temperatures of 7.5 to 11.5°C and in Whitstable in Kent sea temperatures varied between 0.5 and 17°C (Dorsett, 1961). Although there was no information found on the maximum temperature tolerated by Polydora ciliata it does seem likely that the species is able to tolerate a long term increase in temperature of 2°C and may tolerate a short term increase of 5°C. However, growth rates may increase if temperature rises. For example, at Whitstable in Kent, Dorsett (1961) found that a rapid increase in growth coincided with the rising temperature of the sea water during March. However, since effects are likely to be sub-lethal, the intolerance of the biotope is assessed as low. Recovery of the species will be very high because growth and fecundity will return to normal when conditions become more favourable.
Decrease in temperature
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Murina (1997) categorised Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe. In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata in temperatures of 7.5 to 11.5°C and in Whitstable in Kent abundance was high when winter water temperatures dropped to 0.5°C (Dorsett, 1961). Rapid changes in hydrographical conditions occurred when temperatures dropped from 11.5°C to 7.5°C in the course of 15 hours (Gulliksen, 1977) and so it appears the species is tolerant of short term changes in temperature. During the extremely cold winter of 1962/63 Polydora ciliata was apparently unaffected (Crisp (ed.), 1964). However, it is likely that growth and fecundity may be affected. The intolerance of the biotope is therefore assessed as low because Polydora ciliata appears to be tolerant of both long and short term decreases in temperature. The high fecundity, short generation times and large dispersal distances achieved by Polydora ciliata means the species, and hence the biotope, will probably recover very rapidly on return to normal conditions.
Increase in turbidity
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An increase in turbidity, reducing light availability, may reduce primary production by phytoplankton in the water column. However, productivity in the MCR.Pol biotope is secondary because Polydora ciliata deposit feeds on detritus or suspended particles in the water column. Therefore, the biotope is not likely to be significantly affected by changes in turbidity and so intolerance is assessed as low. In estuaries and surf zones on the lower shore, turbidity can be measured in g/l so the benchmark level is low in comparison. Nevertheless, primary production by pelagic phytoplankton and microphytobenthos do contribute to benthic communities and so long term increases in turbidity may reduce the overall organic input to the detritus. Reduced food supply may affect growth rates and fecundity of some species in the biotope. However, at the level of the benchmark effects are not likely to be significant and a rank of low intolerance is reported. On return to normal turbidity levels recovery will be very high as food availability returns to normal.
Decrease in turbidity
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A decrease in turbidity, increasing light availability may increase primary production by phytoplankton in the water column. However, productivity in the MCR.Pol biotope is secondary because Polydora ciliata deposit feeds on detritus or suspended particles in the water column. Therefore, the biotope is not likely to be significantly affected by changes in turbidity and so intolerance is assessed as low. Nevertheless, primary production by pelagic phytoplankton and microphytobenthos do contribute to benthic communities and long term decreases in turbidity may increase the overall organic input to the detritus. Increased food supply may increase growth rates and fecundity of some species in the biotope.
Increase in wave exposure
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The biotope is found in a range of wave exposures from very sheltered to moderately exposed. Feeding may be impaired in strong wave action and changes in wave exposure may also influence the supply of particulate matter. Polydora tubes normally form into 'mats' which are likely to be washed away if exposure were to increase by two exposure scales for a year and so intolerance is reported to be high.
Decrease in wave exposure
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The biotope is found in moderately wave exposed to very wave sheltered sites. A decrease in wave exposure may influence the supply of particulate matter for suspension feeding because wave action may have an important role in re-suspending the sediment that is required by the species to build its tubes. Food supplies may also be reduced affecting growth and fecundity of the species. Abundance of the species may decline if wave exposure decreases. However, since the benchmark level is likely to result in sub-lethal changes only the intolerance of the biotope is regarded to be low.
Noise
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Polydora ciliata may respond to vibrations from predators or bait diggers by retracting their palps into their tubes. However, the species is unlikely to sensitive to noise at the benchmark levels and so the biotope is assessed as not sensitive.
Visual Presence
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Polydora ciliata exhibits shadow responses withdrawing its palps into its burrow, believed to be a defence against predation. However, since the withdrawal of the palps interrupts feeding and possibly respiration the species also shows habituation of the response (Kinne, 1970). The species is, therefore, likely to have very low intolerance to visual disturbance and the biotope will be little affected by the presence of boats, humans or other visual factors not normally present in the marine environment.
Abrasion & physical disturbance
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A passing scallop dredge (or other mobile fishing gear) is likely to remove or break up the tubicolous mat of Polydora ciliata. Individuals are likely to be crushed and killed. However, some individuals are likely to survive, as individuals are small and can withdraw into burrows. Therefore, intolerance has been assessed as intermediate. Recovery is good because Polydora ciliata has planktonic larvae that are capable of dispersal over long distances and the reproductive period is of several months duration. In colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring.
Displacement
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Polydora ciliata is capable of tube building throughout its life and so is able to re-establish attachment on displacement. For example, in removal experiments, Polydora ciliata individuals of all ages that were removed from their tubes on many occasions built new tubes (Daro & Polk, 1973). Recovery is likely to be high because Polydora ciliata has planktonic larvae that are capable of dispersal over long distances and the reproductive period is of several months duration. In colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring.

Chemical Factors

Synthetic compound contamination
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The biotope occurs in polluted sites and so has a low intolerance to the factor. For example, Polydora ciliata was abundant at polluted sites close to acidified, halogenated effluent discharge from a bromine-extraction plant in Amlwch, Anglesey (Hoare & Hiscock, 1974). Spionid polychaetes were found by McLusky (1982) to be relatively tolerant of distilling and petrochemical industrial waste in Scotland.
Heavy metal contamination
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Experimental studies with various species suggests that polychaete worms are quite tolerant to heavy metals (Bryan, 1984). Polydora ciliata 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). Intolerance has thus been assessed to be intermediate. Recovery is likely to be very high - see additional information below.
Hydrocarbon contamination
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In analysis of kelp holdfast fauna following the Sea Empress oil spill in Milford Haven the fauna present, including Polydora ciliata, showed a strong negative correlation between numbers of species and distance from the spill (SEEEC, 1998). After the extensive oil spill in West Falmouth, Massachusetts, Grassle & Grassle (1974) followed the settlement of polychaetes in this environmental disturbed area. Species with the most opportunistic life histories, including Polydora ligni, were able to settle in the area. Intolerance has therefore, been assessed as intermediate. This species has some brood protection which enables larvae to settle almost immediately in the nearby area (Reish, 1979) and so recovery is expected to be very high - see below for additional information.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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Polydora ciliata is often found in environments subject to high levels of nutrients. For example, the species was abundant in areas of the Firth of Forth exposed to high levels of sewage pollution (Smyth, 1968) and in nutrient rich sediments in the Mondego estuary, Portugal (Pardal et al., 1993) and the coastal lagoon Lago Fusaro in Naples (Sordino et al., 1989). Extensive growths of Polydora ciliata in mat formations were recorded at West Ganton, in the Firth of Forth, prior to the introduction of a sewage treatment scheme (Read et al., 1983). The abundance of the species was probably associated with their ability to use the increased availability of organic matter as a food source and silt for tube building. As water quality improved following introduction of the scheme these 'pollution tolerant' species disappeared providing space for colonization by other fauna (Read et al., 1983). Polydora ciliata can also occur in organically poor areas (Pearson & Rosenberg, 1978). The species and hence the biotope is likely to benefit from increased nutrients and so a rank of 'not sensitive*' is recorded. This response is likely to be very rapid. For example, in colonization experiments in an organically polluted fjord receiving effluent discharge from Oslo, Polydora ciliata had settled in large numbers within the first month (Green, 1983, Pardal et al., 1993) and in colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring.
Increase in salinity
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Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. However, there are no records of the species or the biotope occurring in hypersaline waters and an increase for a period of a year is likely to result in the death of many individuals and so intolerance is reported to be high.
Decrease in salinity
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Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. In an area of the western Baltic Sea, where bottom salinity was between 11.1 and 15.0psu Polydora ciliata was the second most abundant species with over 1000 individuals per m2 (Gulliksen, 1977). Intolerance to a decrease in salinity is therefore, expected to be low.
Changes in oxygenation
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Polydora ciliata has low intolerance to reduced oxygenation because the species is repeatedly found at localities with oxygen deficiency (Pearson & Rosenberg, 1978). For example, in polluted waters in Los Angeles and Long Beach harbours Polydora ciliata was present in the oxygen range 0.0-3.9 mg/l and the species was abundant in hypoxic fjord habitats (Rosenberg, 1977). Only in very hypoxic and anoxic conditions can Polydora ciliata not survive. Therefore, at the benchmark level of deoxygenation the biotope may establish or expand as a result of reduced oxygen adversely affecting other species and so a rank of 'not sensitive* is indicated.

Biological Factors

Introduction of microbial pathogens/parasites
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No information on diseases affecting Polydora ciliata or the biotope was found.
Introduction of non-native species
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No known non-native species compete with Polydora ciliata and so the biotope is assessed as not sensitive.
Extraction
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The biotope consists of Polydora ciliata to the exclusion of almost all other species. Extraction of Polydora ciliata is unlikely and we have no evidence for the indirect effects of extraction of other species on this biotope. However, if dredging occurred, populations may be removed in some habitats (see Physical Disturbance above). Overall this factor is not considered to be relevant.

Additional information icon Additional information

Recoverability
Effects on the biotope, even significant effects, will not change the species diversity because the biotope is defined as a single species community.

This review can be cited as follows:

Hill, J.M. 2002. Polydora ciliata in variable salinity infralittoral firm mud or clay. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 23/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=193&code=2004>