Aphelochaeta spp. and Polydora spp. in variable salinity infralittoral mixed sediment

15-11-2002
Researched byDr Harvey Tyler-Walters Refereed byThis information is not refereed.
EUNIS CodeA5.421 EUNIS NameAphelochaeta spp. and Polydora spp. in variable salinity infralittoral mixed sediment

Summary

UK and Ireland classification

EUNIS 2008A5.421Aphelochaeta spp. and Polydora spp. in variable salinity infralittoral mixed sediment
EUNIS 2006A5.421Aphelochaeta spp. and Polydora spp. in variable salinity infralittoral mixed sediment
JNCC 2004SS.SMx.SMxVS.AphPolAphelochaeta spp. and Polydora spp. in variable salinity infralittoral mixed sediment
1997 BiotopeSS.IMX.EstMx.PolMtruPolydora ciliata, Mya truncata and solitary ascidians in variable salinity infralittoral mixed sediment

Description

Variable salinity mixed muddy sediment characterized by the polychaetes Polydora ciliata, Aphelochaeta marioni, the bivalve molluscs Abra nitida and Mya truncata and the ascidians Ascidiella aspersa, Ascidiella scabra, Molgula sp. and Dendrodoa grossularia (the ascidians may not be recorded adequately by remote infaunal surveys). This biotope occurs in lower estuary mixed muddy sediments which are relatively stable, even though subject to moderate tidal streams. It may be found adjacent to IMU.AphTub, IMX.CreAph, IMX.Ost and IMX.MytV. It may also (as yet unproven) represent the infaunal component of SCR.Aasp. It is similar to IMU.AphTub, separated by a combination of sediment characteristics and the abundance of Aphelochaeta marioni. Some difficulty may arise in distinguishing this biotope from reduced versions of IMX.CreAph, IMX.Ost and IMX.MytV as it is unclear at what density the characterizing molluscs have to occur to divide a 'bed' from shell debris. This biotope may be associated with IMX.VsenMtru. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

Found off Hartlepool on the north east coast, in several river channels of the south coast of Britain and Milford Haven, Wales.

Depth range

-

Additional information

None entered

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Habitat review

Ecology

Ecological and functional relationships

This biotope occurs in the lower estuary where the hydrodynamic regime allows a suitable environment to develop. The presence of a suitable substratum is probably the primary structuring force, rather than the interspecific relationships. Mixed sediment provides a stable substratum for the epifauna such as solitary and colonial ascidians while the soft sediment supports infaunal annelids, crustaceans and bivalves. Sediment is the most extensive sub-habitat within the biotope and hence infauna dominate.
  • In areas of mud, the tubes built by Polydora ciliata can agglomerate and form layers of mud up to an average of 20cm thick, occasionally to 50cm. These layers can eliminate the original fauna and flora. Daro & Polk (1973) state that the formation of layers of Polydora ciliata tend to eliminate original flora and fauna. The species readily overgrows other species with a flat morphology and feeds by scraping its palps outside its tubes, which would inhibit the development of settling larvae of other species.
  • Burrowing deposit feeding species potentially disturb and mobilize the sediment, but the presence of mats of Polydora ciliata and the burrowing piddock Petricola pholadiformis suggests that the sediment is relatively stable. Tube building, e.g. by Lanice conchilega and Lagis koreni, probably stabilizes the sediment and arrests the shift towards a community dominated by deposit feeders. Many of the infaunal polychaetes within the biotope are surface deposit feeders (e.g. the terebellids and cirratulids).
  • Amphipods, e.g. Corophium sp., and the infaunal annelid species in this biotope probably interfere strongly with each other. Adult worms probably reduce amphipod numbers by disturbing their burrows, while high densities of amphipods can prevent establishment of worms by consuming larvae and juveniles (Olafsson & Persson, 1986). For example, Arenicola marina was shown to have a strong negative effect on Corophium volutator due to reworking of sediment causing the amphipod to emigrate (Flach, 1992).
  • Hard substrata support suspension feeding ascidians such as Ascidiella scabra, Ascidiella aspera, Molgula spp. and Dendrodoa grossularia and tubeworms e.g. Pomatoceros triqueter, while infaunal suspension feeders include the bivalves Abra alba and Mya truncata and Mya arenaria and tubeworms e.g. Lanice conchilega.
  • Carcinus maenas is a significant predator in the biotope. It has been shown to reduce the density of Mya arenaria, Cerastoderma edule, Abra alba, Tubificoides benedii, Aphelochaeta marioni and Corophium volutator (Reise, 1985). A population of Carcinus maenas from a Scottish sea-loch preyed predominantly on annelids (85% frequency of occurrence in captured crabs) and less so on molluscs (18%) and crustaceans (18%) (Feder & Pearson, 1988).
  • Carnivorous annelids such as Nephtys hombergi, Eteone longa, Glycera spp. and Harmothoe spp. operate at the trophic level below Carcinus maenas (Reise, 1985). They predate the smaller annelids, such as Exogone naidina, and crustaceans, such as Corophium volutator and Cumacea sp.
  • Seasonal and longer term change

    Seasonal changes occur in the abundance of the fauna due to seasonal recruitment processes. Variation in abundance is very pronounced in the polychaete Aphelochaeta marioni. In the Wadden Sea, peak abundance occurred in January (71,200 individuals per m²) and minimum abundance occurred in July (22,500 individuals per m²) following maximum spawning activity between May and July (Farke, 1979). However, the spawning period varies according to environmental conditions and so peak abundances will not necessarily occur at the same time each year. Adult densities of the bivalve, Abra alba, may exceed 1000 per m² in favourable conditions but typically fluctuate widely from year to year due to variation in recruitment success or adult mortality (see review by Rees & Dare, 1993). However, the sea squirt Ascidiella scabra showed regular annual recruitment onto artificial and scraped natural substrata and was described as an 'annual ascidian' by Svane (1988).

    One of the key factors affecting benthic habitats is disturbance which, in shallow subtidal habitats increases in winter due to weather conditions. Storms may cause dramatic changes in distribution of macro-infauna by washing out dominant species, opening the sediment to recolonization by adults and/or available spat/larvae (Eagle, 1975; Rees et al., 1977; Hall, 1994) and by reducing success of recruitment by newly settled spat or larvae (see Hall, 1994 for review). For example, during winter gales along the North Wales coast large numbers of Abra alba were cast ashore and over winter survival rate was as low as 7% in the more exposed locations, whilst the survival rates of the polychaetes Eteone longa and Nephtys hombergi were 29% and 22% respectively (Rees et al., 1976). Soft bodied epifauna, such as ascidians, are likely to be very sensitive to storm damage and will probably suffer high mortality during winter storms. Rapid recolonization occurs in summer and therefore abundances are likely to vary considerably due to physical disturbance. Sediment transport and the risk of smothering also occurs. A storm event at a silt/sand substratum site in Long Island Sound resulted in the deposition of a 1cm layer of shell fragments and quartz grains (McCall, 1977).

    Habitat structure and complexity

    The biotope consists of hard substrata such as cobbles and pebbles or shell debris sitting in or on consolidated sediments. The mixed substrata provides habitats for a diverse assemblage of epifaunal and infaunal species. Most of the species that occur in the biotope are not closely associated with the community and it is probably transitional between other biotopes such as Aphelochaeta marioni (e.g. IMU.AphTub), or bivalves (e.g. IMX.VsenMtru).
    • The mixed sediment in this biotope is the important structural component, providing the complexity required by the associated community. Epifauna attached to the gravel and pebbles and infauna burrow in the soft underlying sediment. Sediment deposition, and therefore the spatial extent of the biotope, is dictated by the physiography and underlying geology coupled with the hydrodynamic regime (Elliot et al., 1998).
    • The presence of both sediment and hard substrata increases the range of substrata available for settlement by organism with different habitat requirements; both infaunal and epifaunal species may be abundant . Attrill et al. (1996) described a "biodiversity hot spot" in similar situations of mixed substrata in the Thames estuary.
    • There is a traditional view that the distribution of infaunal invertebrates is correlated solely with sediment grain size. In reality, and in this biotope, it is likely that a number of additional factors, including organic content, microbial content, food supply and trophic interactions, interact to determine the distribution of the infauna (Snelgrove & Butman, 1994).
    • Structural complexity is provided by the many tube building species in the biotope. The tubes built by Polydora ciliata for example are embedded in the sediment and the ends extend a few millimetres above the substratum surface. The resultant mats of agglomerated sediment may be up to 50 cm thick.
    • Reworking of sediments by deposit feeders increases bioturbation and potentially causes a change in the substratum characteristics and the associated community (e.g. Rhoads & Young, 1970). The presence of tube builders, such as Lanice conchilega, stabilizes the sediment and provides additional structural complexity.
    • The burrows of large bivalves (e.g. Mya spp.) and piddocks provide additional complexity to the biotope and probably increase the depth to which the sediment is oxygenated.

    Productivity

    The majority of the productivity in the biotope is secondary, derived from detritus and organic particulates. Primary production is derived from phytoplankton and converted into secondary productivity by the suspension feeders. The benthos is supported predominantly by pelagic production and by detrital materials emanating from the coastal fringe (Barnes & Hughes, 1992). Secondary productivity is probably high given the high densities attained by some species and the diversity of species within the biotope, however no specific information was found.

    Recruitment processes

    The recruitment processes exhibited by the major groups within the biotope are demonstrated by the examples below.
    • The lifecycle of Aphelochaeta marionivaries according to environmental conditions. In Stonehouse Pool, Plymouth, Aphelochaeta marioni (studied as Tharyx marioni) spawned in October and November (Gibbs, 1971) whereas in the Wadden Sea, Netherlands, spawning occurred from May to July (Farke, 1979). The embryos developed lecithotrophically and hatched in about 10 days (Farke, 1979). Under stable conditions, adult and juvenile Aphelochaeta marioni will disperse by burrowing (Farke, 1979).
    • The spawning period for Polydora ciliata in northern England is from February until June and three or four generations succeed one another during the spawning period (Gudmundsson, 1985). After a week, the larvae emerge and are believed to have a pelagic life from two to six weeks before settling (Fish & Fish, 1996). The larvae settle preferentially on substrata covered with mud (Lagadeuc, 1991).
    • Nephtys hombergi exhibits variable spawning success with failures in some years (Olive et al., 1997).
    • The mating system of amphipods is polygynous and several broods of offspring are produced, each potentially fertilized by a different male. There is no larval stage and embryos are brooded in a marsupium, beneath the thorax. Embryos are released as sub-juveniles with incompletely developed eighth thoracopods and certain differences in body proportions and pigmentation. Dispersal is limited to local movements of these sub-juveniles and migration of the adults and hence recruitment is limited by the presence of local, unperturbed source populations (Poggiale & Dauvin, 2001). Dispersal of sub-juveniles may be enhanced by the brooding females leaving their tubes and swimming to un-colonized areas of substratum before the eggs hatch (Mills, 1967).
    • The tube building polychaetes, e.g. Pygospio elegans, generally disperse via a pelagic larval stage (Fish & Fish, 1996) and therefore recruitment may occur from distant populations, aided by bed load transport of juveniles (Boström & Bonsdorff, 2000). However, dispersal of some of the infaunal deposit feeders, such as Scoloplos armiger, occurs through burrowing of the benthic larvae and adults (Beukema & de Vlas, 1979; Fish & Fish, 1996). Recruitment must therefore occur from local populations or by longer distance dispersal during periods of bedload transport. Recruitment is therefore likely to be predictable if local populations exist but patchy and sporadic otherwise.
    • Mya arenaria demonstrates high fecundity, increasing with female size, with long life and hence high reproductive potential. The high potential population increase is offset by high larval and juvenile mortality. Juvenile mortality reduces rapidly with age (Brousseau, 1978b; Strasser, 1999). Strasser et al. (1999) noted that population densities in the Wadden Sea were patchy and dominated by particular year classes. Therefore, although large numbers of spat may settle annually, successful recruitment and hence recovery may take longer than a year. Recruitment of shallow burrowing infaunal species can depend on adult movement by bedload sediment transport and not just spat settlement. Emerson & Grant (1991) investigated recruitment in Mya arenaria and found that bedload transport was positively correlated with clam transport. They concluded that clam transport at a high energy site accounted for large changes in clam density. Furthermore, clam transport was not restricted to storm events and the significance is not restricted to Mya arenaria recruitment. Many infauna, e.g. polychaetes, gastropods, nematodes and other bivalves, will be susceptible to movement of their substratum.
    • Ascidians such as Ascidiella scabra and Molgula manhattensis have external fertilization but short lived larvae (swimming for only a few hours), so that dispersal is probably limited (see MarLIN reviews). Ascidiella scabra has a high fecundity and settles readily, probably for an extended period from spring to autumn. Svane (1988) describes it as "an annual ascidian" and demonstrated recruitment onto artificial and scraped natural substrata. Eggs and larvae are free-living for only a few hours and so recolonization would have to be from existing individuals no more than a few km away. It is also likely that Ascidiella scabra larvae are attracted by existing populations and settle near to adults (Svane et al., 1987) . Fast growth means that a dense cover could be established within about 2 months. Where neighbouring populations are present recruitment may be rapid but recruitment from distant populations may take a long time.
    Most other macrofauna in the biotope breed several times in their life history (iteroparous) and are planktonic spawners producing large numbers of gametes. Dispersal potential is high. Overall recruitment is likely to be patchy and sporadic, with high spat fall occurring in areas devoid of adults, perhaps lost due to predation or storms. The presence of fast growing space occupying species, e.g. Polydora ciliata and Ascidiella scabra suggests that competition for space for settling larvae is probably intense, with recruitment dependant on the coincidence of factors that free space (e.g. death of short-lived species or storm related physical disturbance) with larval supply. The presence of numerous suspension feeders an surface deposit feeders suggests that post-settlement mortality of larvae would be high.

    Time for community to reach maturity

    The community is dominated by fast growing opportunistic polychaete and ascidian species and the community most likely reaches maturity within one year of space becoming available. In an experimental study investigating recovery of a range of species characteristically found in this biotope after copper contamination, Hall & Frid (1995) found that recovery took up to a year. 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. Polydora ciliata is another short-lived species that reaches maturity within a few months and has three or four spawnings during a breeding season of several months. For example, in colonization experiments in Helgoland (Harms & Anger, 1983), Polydora ciliata settled on panels within one month in the spring. The bivalve Abra alba demonstrates an 'r' type life-cycle strategy and is able to rapidly exploit any new or disturbed substratum available for colonization through larval recruitment, secondary settlement of post-metamorphosis juveniles or re-distribution of adults. For example, Abra alba recovered to former densities following loss of a population from Keil Bay owing to deoxygenation within 1.5 years, as did Lagis koreni, taking only one year (Arntz & Rumohr, 1986). Mya arenaria has a high fecundity and reproductive potential but larval supply is sporadic and juvenile mortality is high, so that although, large numbers of spat may settle annually, successful recruitment and hence recovery may take longer than a year. For example, Beukema (1995) reported that a population of Mya arenaria in the Wadden Sea, drastically reduced by lugworm dredging took about 5 years to recover. Therefore, the polychaete infauna, ascidian and tube worm epifauna would probably colonize the habitat rapidly, producing a recognizeable biotope within 1-2 years, while the abundance of some species, e.g. Mya sp. would take up to 5 years to develop.

    Additional information

    None.

Preferences & Distribution

Recorded distribution in Britain and IrelandFound off Hartlepool on the north east coast, in several river channels of the south coast of Britain and Milford Haven, Wales.

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients Data deficient
Salinity
Physiographic
Biological Zone
Substratum
Tidal
Wave
Other preferences None known

Additional Information

The full development of this biotope requires relatively stable mixed muddy sediments. For example, Polydora ciliata is only found in areas of soft rock, such as limestone and chalk, and firm muds and clay where it can make its burrows.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

-

Additional information

The MNCR recorded 398 species within records of this biotope, although not all species occurred in all records (JNCC, 1999).

Sensitivity reviewHow is sensitivity assessed?

Explanation

This biotope is distinguished from other similar biotopes by the relative abundance of Polydora ciliata, Aphelochaeta marioni and the presence of Mya arenaria or Mya truncata. Therefore, these species have been included as important characterizing. Solitary ascidians are another characterizing feature of the biotope, so Ascidiella scabra and Molgula manhattensis have been included to represent their sensitivity. Reference has also been made to reviews of other representative species of polychaetes, ascidians, and bivalves in the assessment of sensitivity.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingAphelochaeta marioniA bristleworm
Important otherAscidiella scabraA sea squirt
Important otherMolgula manhattensisSea grapes
Important characterizingMya arenariaSand gaper
Important characterizingMya truncataBlunt gaper
Important characterizingPolydora ciliataA bristleworm

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High High Moderate Major decline Moderate
Removal of the substratum would result in loss of its associated community and hence the biotope and an intolerance of high has been recorded. Recoverability is likely to be high (see additional information below).
Intermediate High Low Minor decline Low
The more mobile burrowing infauna, such as polychaetes, are likely to be able to relocate to their preferred depth following smothering with little or no loss of fitness, as long as the deposited sediment is similar to that already present.

Polydora ciliata is likely to tolerate smothering by 5 cm of sediment because the species inhabits a range of habitats including muddy sediment, larvae settle preferentially on substrata covered with mud (Lagadeuc, 1991) and worms can rebuild tubes close to the surface.

Emerson et al. (1990) examined smothering and burrowing of Mya arenaria after clam harvesting. Significant mortality (2 -60%) in small and large clams occurred only at burial depths of 50 cm or more in sandy substrata. However, they suggested that in mud, clams buried under 25 cm of sediment would almost certainly die. Dow & Wallace (1961) noted that large mortalities in clam beds resulted from smothering by blankets of algae (Ulva sp.) or mussels (Mytilus edulis). In addition, clam beds have been lost due to smothering by 6 cm of sawdust, thin layers of eroded clay material, and shifting sand (moved by water flow or storms) in the intertidal.

The siphons of epifaunal ascidians such as Ascidiella scabra would probably extend above 5cm of sediment, and together with Molgula manhattensis (see MarLIN reviews) could probably survive under sediment for a month (see benchmark). Therefore, most of the species within the biotope are likely to survive smothering by 5cm of sediment suggesting low intolerance. Nevertheless, deep burrowing bivalves such as Mya species may be adversely affected and experience a reduction in abundance, so that an overall intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).

Low Very high Very Low No change Low
This biotope is probably exposed to the high levels of suspended sediment characteristic of estuarine conditions. Therefore, the resident species are probably adapted to high suspended sediment levels and an increase at the benchmark level are probably insignificant. An increase in suspended sediment may increase food availability to deposit feeders but increase the energy expenditure of suspension feeders (on clearance mechanism). Therefore, an intolerance of low has been recorded.
Low Immediate Moderate Minor decline Low
This biotope is probably exposed to the high levels of suspended sediment characteristic of estuarine conditions and decrease at the benchmark level is probably insignificant. But food supply is probably important for rapid growing species such as ascidians and suspension feeding polychaetes (e.g. Polydora ciliata), and a reduction in food availability in the form of organic particulates may adversely affect the growth and reproduction of members of the biotope. Hence an intolerance of low has been recorded.
Low Very high Very Low No change Low
This biotope occurs in the infralittoral so that only the upper extent of shallow examples of the biotope are likely to be emersed on extreme low tides. Most of the infaunal and burrowing species are likely to be protected from desiccation by their water logged habitat. However, epifauna such as Ascidiella scabra and Molgula manhattensis may be adversely affected. Other species such as Dendrodoa grossularia occurs in damp areas of the intertidal and can tolerant some desiccation. Similarly, the characteristic species Polydora ciliata and Mya arenaria occur in the mid to low intertidal, and would probably survive an increase in desiccation at the benchmark level. Therefore, an intolerance of low has been recorded.
Intermediate High Low Minor decline Low
Shallow records of this biotope may be subject to emergence during extreme low water. An increase in emergence is likely to increase the risk of desiccation (see above) but also allow more intertidal species, e.g. barnacles and macroalgae (e.g. fucoids) to invade the biotope. The upper extent of the biotope may come to more closely resemble a typical intertidal mixed sediment community, and hence the upper extent of the biotope would be 'effectively' lost. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).
Tolerant* Not sensitive Not relevant
A decrease in emergence is likely to allow the biotope to extend its upper limit, where suitable substrata exist. Therefore, not sensitive* has been recorded.
High High Moderate Major decline Low
This biotope occurs in moderately strong tidal streams. The hydrographic regime is an important structuring factor in sedimentary habitats. Therefore, an increase in water flow from moderately strong to very strong (see benchmark) may have significant effects on the community due to changes in the sediment characteristics. An increase in water flow to very strong, is likely to mobilize the sediment, removing fine muds and muddy sands, increasing sediment scour and rolling the smaller pebbles and cobbles. Therefore, the biotope is likely to be replaced by a coarse sediment, gravel or cobble biotope, and an intolerance of high has been recorded.
Tolerant Not sensitive* Not relevant Low
The hydrographic regime is an important structuring factor in sedimentary habitats. This biotope has only been recorded from moderately strong tidal streams suggesting that water flow is an important habitat preference. In the highly turbid waters of estuaries, a reduction in water flow is likely to result in a significant increase in siltation, resulting in long-term smothering of epifauna and coarse substrata and leading to a change in the dominant substratum to muds or muddy gravel and increased dominance by infaunal polychaetes or bivalves (e.g. see A5.433 or A5.322). Therefore, the biotope as described would be lost and an intolerance of high has been recorded. Recoverability is likely to be high (see additional information below).
Tolerant Not relevant Not relevant Not relevant Low
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) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9° C. Mya arenaria is reported from the White Sea, south to Portugal, while Mya truncata has a wider distribution. But the southern distribution of Mya arenaria may be restricted by a limit of 28 °C for both adults and larvae (Newell & Hidu, 1986; Strasser, 1999). Most organisms in the biotope are distributed to the north and south of Britain and Ireland and unlikely to be adversely affected by long term temperature change. In addition, subtidal and especially infaunal species are likely to be protected from acute temperature change. Therefore, not sensitive has been recorded at the benchmark level. 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.
Tolerant Not sensitive* Not relevant Low
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). Over-wintering Mya arenaria survived temperatures as low as -2 °C in Alaska, persisted in the St. Lawrence estuary exposed to freezing winter air temperatures, and survived 60 days of ice in the severe 1995/1996 winter in the Wadden Sea (Strasser, 1999). However, severe winters have been known to cause mortality (Rasmussen, 1973; Strasser, 1999). This biotope is probably protected from freezing events and extremely low temperatures by its depth. Most of the characterizing species are distributed to the north and south of Britain and Ireland, and unlikely to affected by long-term temperature change. Therefore not sensitive has been recorded.
Low Very high Very Low No change Low
The absence of macroalgae in records of this biotope suggests that it exists in areas of high turbidity and hence very low light intensity. An increase in turbidity will probably reduce primary production in the water column and therefore reduce the availability of food to suspension feeders. In addition, primary production by the micro-phyto benthos on the sediment surface may be reduced, further decreasing food availability. However, phytoplankton will also immigrate from distant areas and so the effect may be decreased. As the turbidity increase only persists for a year (see benchmark), decreased food availability would probably only affect growth and fecundity and an intolerance of low is recorded.
Intermediate Very high Low Rise Low
A decrease in turbidity is likely to allow subtidal algae such as Fucus spp. and Saccharina latissima, Chorda filum and red algae to colonize the hard substrata within shallower records of the biotope. The macroalgae would compete for space with epifauna, possibly reducing the abundance of ascidians. Few other species would be directly affected and the increased primary productivity and plant debris may benefit suspension feeders and detritivores. However, the biotope would probably come to resemble a macroalgal dominated mixed substrata biotope, e.g. A5.521 and the shallow extent of the described biotope would be lost. Therefore, an intolerance of intermediate has been recorded.
High High Moderate Major decline Low
This biotope was recorded from wave sheltered to very sheltered habitats. The hydrographic regimes is an important structuring factor in sedimentary habitats. An increase in wave action from wave sheltered to wave exposed (see benchmark) is likely to significantly alter the community by removing the finer sediments, increasing erosion of consolidated sediment and mobilizing the large coarser sediments increasing scour. Therefore, the biotope is likely to be lost, and replaced with a coarser sediment biotope. An intolerance of high has been recorded although recoverability is likely to be high (see additional information below).
Tolerant Not sensitive* Not relevant Low
This biotope was recorded from wave sheltered to very sheltered habitats. A decrease in wave exposure from very sheltered to extremely sheltered may increase the siltation rate although in the moderately strong tidal streams encountered in this habitat the effects are likely to be marginal. Therefore, not sensitive has been recorded.
Tolerant Not relevant Not relevant No change High
None of the species in the biotope are likely to be sensitive to noise or vibration at the benchmark level.
Tolerant Not relevant Not relevant No change Low
Most species will respond to the shading caused by the approach of a predator, however, their visual acuity is probably very low and none of the component species are likely to respond to visual presence at the benchmark level.
Intermediate High Low Decline Low
Both the epifaunal and the infaunal species in the biotope are likely to be sensitive to physical disturbance, such as a passing scallop dredge. Soft bodied epifauna, such as ascidians, are most vulnerable, and are likely to suffer high mortality. Erect epifaunal species are particularly vulnerable to physical disturbance. Veale et al.(2000) reported that the abundance, biomass and production of epifaunal assemblages decreased with increasing fishing effort. Mobile gears also result in modification of the substratum, including removal of shell debris, cobbles and rocks, and the movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998). The removal of rocks or boulders to which species are attached results in substratum loss (see above). Despite their robust body form, bivalves are also vulnerable. For example, as a result of dredging activity, mortality and shell damage have been reported in Mya arenaria and Cerastoderma edule (Cotter et al., 1997). Overall, physical disturbance by passing scallop dredge, or mobile fishing gear is likely to result in loss of epifauna and hard substrata and a reduction in the abundance of infaunal species. Therefore, an intolerance of intermediate has been recorded. Recovery is likely to be rapid.
High High Moderate Major decline Low
The infaunal species are active burrowers, unlikely to be adversely affect by displacement. Mya arenaria is a slow burrowing species: for example, Pfitzenmeyer & Droebeck (1967) reported that 62% of small clams (35-50mm), 39% of medium sized (51-65mm) and only 21% of large clams (66-75mm) had reburrowed within 48 hours, so that some individuals my be lost due to predation. But epifaunal ascidians and tubeworms are permanently attached to their substratum and cannot reattach and would probably be lost, unless transported with their substrata. While the characterizing species would probably survive displacement, overall the biotope would effectively be removed from its recorded location so an intolerance of high has been recorded. Recoverability is likely to be high (see additional information below).

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Intermediate High Low Decline Low
The component species within the biotope vary in their tolerance to synthetic chemical contamination. For example:
  • 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 were found by McLusky (1982) to be relatively tolerant of distilling and petrochemical industrial waste in Scotland.
  • Scoloplos armiger exhibited 'moderate' intolerance to tributyl tin (TBT) anti-foulants (Bryan & Gibbs, 1991).
  • The polychaete Hediste diversicolor exhibited 100% mortality within 14 days when exposed to 8 mg/m² of the insecticide Ivermectin in a microcosm (Collier & Pinn, 1998). Ivermectin was found to produce a 10 day LC50 of 18µg ivermectin /kg of wet sediment in Arenicola marina and sub-lethal effects were apparent between 5 - 105 µg/kg (Cole et al., 1999). Cole et al. (1999) suggested that this indicated a high intolerance. Arenicola marina was also intolerant of ivermectin through the ingestion of contaminated sediment (Thain et al., 1998; cited in Collier & Pinn, 1998).
  • Beaumont et al. (1989) concluded that bivalves are particularly sensitive to tri-butyl tin (TBT), the toxic component of many antifouling paints. For example, when exposed to 1-3 µg TBT/l, Cerastoderma edule and Scrobicularia plana suffered 100% mortality after 2 weeks and 10 weeks respectively. Furthermore, there is evidence that TBT causes recruitment failure in bivalves, either due to reproductive failure or larval mortality (Bryan & Gibbs, 1991). Beaumont et al. (1989) also concluded that TBT had a detrimental effect on the larval and/or juvenile stages of infaunal polychaetes.
  • Waldock et al. (1999) reported that the species diversity of polychaete infauna, including Aphelochaeta marioni, Scoloplos armiger and Nephtys hombergii and the bivalve infauna (e.g. Mysella bidentata, Cerastoderma edule, and Abra alba) in the Crouch estuary increased in the three years after the use of TBT was banned within the estuary, suggesting that TBT had suppressed their abundance previously.
  • Rees et al. (2001) reported that the abundance of epifauna, including Ascidiella aspersa and Ciona intestinalis, had increased in the Crouch estuary in the five years since TBT was banned from use on small vessels. Rees et al. (2001) suggested that TBT inhibited settlement in ascidian larvae. This report suggested that epifaunal species (including, bryozoan, hydroids and ascidians) may be at least inhibited by the presence of TBT.
Overall, some polychaetes, ascidians and bivalves are probably intolerant of TBT contamination, while polychaetes and crustaceans are likely to be intolerant of ivermectin contamination. Therefore, synthetic contaminants are likely to at least reduce the abundance and probably recruitment in several members of the community and an intolerance of intermediate has been recorded. Recoverability is likely to be rapid.
Heavy metal contamination
High High Moderate Decline Low
Evidence suggests that polychaetes are "fairy resistant" to the effects of heavy metals (Bryan, 1984). But Hall & Frid (1995) found that the four dominant taxa in their study ( 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. Aphelochaeta marioni is tolerant of heavy metal contamination occurring in the heavily polluted Restronguet Creek (Bryan & Gibbs, 1983) and it is also an accumulator of arsenic (Gibbs et al., 1983). 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). 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 variable 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 polychaete species at least in the biotope might be adversely affected by high contamination by heavy metals.

Eisler (1977) exposed Mya arenaria to a mixture of heavy metals in solution at concentrations equivalent to the highest recorded concentrations in interstitial waters in the study area. At 0°C and 11°C (winter temperatures) 100% mortality occurred after 4-10 weeks. At 16-22°C (summer temperatures) 100% mortality occurred after 6-14 days, indicating greater intolerance at higher temperatures.

Overall, the dominant polychaetes within the biotope are probably tolerant of heavy metal contamination, while Mya arenaria (and by inference Mya truncata) is probably intolerant. Other component species probably vary in their heavy metal tolerance and species richness would probably decline. Therefore, an intolerance of high has been recorded to represent loss of an important characterizing species. Recoverability is probably high (see additional information below).
Hydrocarbon contamination
Intermediate High Low Major decline Low
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. Suchanek (1993) reported that infaunal polychaetes were vulnerable to hydrocarbon contamination e.g. high mortality has been demonstrated in Arenicola marina (Levell, 1976). But 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).

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. This species has some brood protection which enables larvae to settle almost immediately in the nearby area (Reish, 1979).

Suchanek (1993) reported that sublethal concentrations may produce substantially reduced feeding rates and/or food detection ability in bivalves, probably due to ciliary inhibition. Respiration rates increased at low concentrations and decreased at high concentrations. Generally, contact with oil causes an increase in energy expenditure and a decrease in feeding rate, resulting in less energy available for growth and reproduction. Sublethal concentrations of hydrocarbons also reduce byssal thread production (thus weakening attachment) and infaunal burrowing rates. Mortality following oil spills has been recorded in Mya arenaria (Dow, 1978; Johnston, 1984), Ensis sp. (SEEEC, 1998) and Cerastoderma edule (SEEEC, 1998). However, the Abra alba population affected by the 1978 Amoco Cadiz benefited from the nutrient enrichment caused by the oil pollution (see nutrient enrichment, below).

Overall, hydrocarbon contamination is likely to adversely affect some members of the community, and low more tolerant or opportunistic species to increase in abundance, resulting in a reduction in species richness. Nevertheless, the biotope would probably survive and an intolerance of intermediate has been recorded to represent loss of some characterizing species.

Radionuclide contamination
No information Not relevant No information Insufficient
information
Not relevant
No information found.
Changes in nutrient levels
High High Moderate Decline Low
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). 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. A 'Sewage Scheme' was introduced in the Firth of Forth (Read et al., 1983). Extensive growths of Polydora ciliata were recorded at West Ganton, in the Firth of Forth, but 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). However, Polydora ciliata can also occur in organically poor areas (Pearson & Rosenberg, 1978) and so is likely to have low intolerance to changes in nutrient concentrations.

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. Similarly, an Abra alba population affected by the 1978 Amoco Cadiz oil spill benefited from the nutrient enrichment caused by the oil pollution.

Increased levels of nutrient may result in eutrophication, algal blooms and reductions in oxygen concentrations (see Rosenberg & Loo, 1988). Rosenberg & Loo (1988) reported mass mortalities of Mya arenaria and Cerastoderma edule following a eutrophication event in Sweden, although no direct causal link was established.

Overall, an increase in nutrient levels is likely to favour deposit feeding species, tolerant of increased hypoxia, and exclude suspension feeding invertebrates such as bivalves, resulting in a decline in species richness. The biotope is likely to come to resemble polychaete dominated biotopes (e.g. A5.322) and biotope as described will be lost. Therefore, an intolerance of high has been reported. Recoverability is likely to be high (see additional information below).

Not relevant Not relevant Not relevant Not relevant Not relevant
This biotope occurs in variable salinity conditions but is unlikely to experience hypersaline conditions.
Low Immediate Not relevant Minor decline Low
This biotope occurs in variable salinity. 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/m² (Gulliksen, 1977). Its intolerance to a decrease in salinity is therefore, expected to be low. 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 but a long term reduction from reduced to low salinity may affect some of the species in the biotope with possible losses and reduced viability. Mya arenaria is a euryhaline osmoconformer and has been reported from the west Atlantic coast in salinities of 4 psu (Strasser, 1999). However, Abra alba is typically found in full salinity conditions and is therefore likely to be intolerant of reductions in salinity in some way. The ascidian Ascidiella scabra occurs in reduced salinity conditions. Van Name (1945; quoted in Kott, 1985), noted that Molgula manhattensis occurred in salinities equivalent to 20 to 36 psu whilst Hartmeyer (1923; quoted in Tokioka & Kado, 1972) recorded Molgula manhattensis in brackish (16-30 psu) water of the Belt Sea. A fall in salinity from full to reduced would not therefore be expected to have an adverse effect on or Ascidiella scabra or Molgula manhattensis

Overall, the important characterizing species are likely to tolerate a short term change in salinity from e.g. variable to low salinity and a long term change from variable to reduced salinity. The species richness of the biotope may decline but the biotope will probably not be adversely affected. Therefore, an intolerance of low has been recorded.

Low Immediate Not sensitive Minor decline Moderate
Sagasti et al. (2000) reported that epifaunal communities, especially tunicates, hydroids and anemones were equally abundant in the York River estuary exposed to brief hypoxic episodes and moderate hypoxia (0.5-2mg O2/l). The communities studied included the tunicate Molgula manhattensis and the polychaete Polydora cornuta. Their study suggests that estuarine epifaunal communities are relatively tolerant of hypoxia. 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). Other polychaetes may also tolerate hypoxia and many are facultative anaerobes (Diaz & Rosenberg, 1995). For example, Nephtys hombergi and Heteromastis filiformis) are noted by Diaz & Rosenberg (1995) as resistant to severe hypoxia, while Capitella capitata, Hediste diversicolor, Scoloplos armiger and Lagis koreni were considered to be resistant 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 polychaete 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.

Mya arenaria tolerates low oxygen concentration and the presence of hydrogen sulphide for several days or weeks. Fifty percent mortality was observed after 21 days at 10 °C exposed to 0.15 ml O2/l (0.21 mg/l) in the presence of H2S (Theede et al., 1969). At 0.5-1.0 ml O2/l(0.7-1.4mg/l), 8% survived in sediment for 32 days and 54% survived for 43 days (Rosenberg et al., 1991). Rosenberg & Loo (1988) reported mass mortalities of Mya arenaria and Cerastoderma edule in the 1980s in the Kattegat, which were associated with eutrophication and resultant low oxygen concentrations over several years (often <1 ml O2/l). However, Mya arenaria is probably tolerant of 2mg/l for a week (see benchmark).

Overall, most of the characterizing species are probably tolerant of hypoxia at the benchmark level and the biotope would probably not be adversely affected, although species richness may decline. Physiological tolerance and anaerobic metabolism incur extra energy demands, therefore, an intolerance of low has been recorded.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Intermediate High Low Minor decline Low
Several parasites occur in Mya arenaria, e.g. cercaria of Himasthla leptosoma, the nemertean parasite Malacobdella sp. and the copepod Myicola metisciensis may be commensal (Clay, 1966). The protozoan, Perkinsus sp. has recently been isolated from Mya arenaria in Chesapeake Bay, USA (McLaughlin & Faisal, 2000). Mya arenaria is also known to suffer from cancers, disseminated neoplasia and gonadal tumours. Disseminated neoplasia, for example, has been reported to occur in 20% of the population in north eastern United States and Canada, and caused up to 78% mortalities in New England (Brousseau & Baglivo, 1991; Landsberg, 1996).
Little information was found regarding microbial infection of polychaetes, although Gibbs (1971) recorded that nearly all of the population of Aphelochaeta marioni in Stonehouse Pool, Plymouth Sound, was infected with a sporozoan parasite belonging to the acephaline gregarine genus Gonospora, which inhabits the coelom of the host. No evidence was found to suggest that gametogenesis was affected by Gonospora infection and there was no apparent reduction in fecundity.
The parasite loads of the bivalves discussed above have been proven to cause mortality and therefore a biotope intolerance of intermediate is recorded and there may be a minor decline in species richness in the biotope. Recoverability is recorded as high (see additional information below).
High High Moderate Minor decline Low
The American hard-shelled clam, Mercenaria mercenaria, colonized the niche left by Mya arenaria killed after the cold winters of 1947 and 1962/63 in Southampton Water (Eno et al. 1997). The Mya arenaria populations had not recovered in this area by 1997 (Eno et al., 1997). Mya arenaria often occurs in the IMX.PolMtru biotope and therefore Mercenaria mercenaria may pose a threat of invasion.

Invasion by the slipper limpet Crepidula fornicatamay switch the biotope to IMU.CreAph, as this IMX.PolMtru is often difficult to distinguish from reduced versions of IMU.CreAph (Connor et al., 1997b), 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. Once established Crepidula fornicata is difficult to remove but should its numbers decrease then recoverability of IMX.PolMtru would probably be rapid.

Not relevant Not relevant Not relevant Not relevant Not relevant
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.
Not relevant Not relevant Not relevant Not relevant Not relevant

Additional information

Recoverability
The community is dominated by fast growing opportunistic polychaete and ascidian species and the community most likely reaches maturity within one year of space becoming available. In an experimental study investigating recovery of a range of species characteristically found in this biotope after copper contamination, Hall & Frid (1995) found that recovery took up to a year. However, 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. Similarly Polydora ciliata is a short lived species that reaches maturity within a few months and has three or four spawnings during a breeding season of several months. For example, in colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring. The bivalve Abra alba demonstrates an 'r' type life-cycle strategy and is able to rapidly exploit any new or disturbed substratum available for colonization through larval recruitment, secondary settlement of post-metamorphosis juveniles or re-distribution of adults. For example, Abra alba recovered to former densities following loss of a population from Keil Bay owing to deoxygenation within 1.5 years, as did Lagis koreni, taking only one year (Arntz & Rumohr, 1986).

Mya arenaria has a high fecundity and reproductive potential but larval supply is sporadic and juvenile mortality is high so that, although large numbers of spat may settle annually, successful recruitment and hence recovery may take longer than a year. For example, Beukema (1995) reported that a population of Mya arenaria in the Wadden Sea, drastically reduced by lugworm dredging took about 5 years to recover.

Therefore, the polychaete infauna, ascidian and tube worm epifauna would probably colonize the habitat rapidly, producing a recognizable biotope within 1-2 year, while the abundance of some species, e.g. Mya sp. may take up to 5 years to recover.

Importance review

Policy/Legislation

UK Biodiversity Action Plan Priority

Exploitation

No species within this biotope are known to be subject to exploitation in the British Isles.

Additional information

-

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Citation

This review can be cited as:

Tyler-Walters, H., 2002. Aphelochaeta spp. and Polydora spp. in variable salinity infralittoral mixed sediment. 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/114

Last Updated: 15/11/2002