Ceramium sp. and piddocks on eulittoral fossilised peat

03-04-2008
Researched byGeorgina Budd Refereed byDr Eunice Pinn
EUNIS CodeA1.127 EUNIS NameCeramium sp. and piddocks on eulittoral fossilised peat

Summary

UK and Ireland classification

EUNIS 2008A1.127Ceramium sp. and piddocks on eulittoral fossilised peat
EUNIS 2006A1.127Ceramium sp. and piddocks on eulittoral fossilised peat
JNCC 2004LR.HLR.FR.RPidCeramium sp. and piddocks on eulittoral fossilised peat
1997 BiotopeLR.MLR.R.RPidCeramium sp. and piddocks on eulittoral fossilised peat

Description

Outcrops of fossilized peat in the eulittoral are soft enough to allow a variety of piddocks (such as Barnea candida and Petricola pholadiformis) to bore into them. The surface of the peat is characterized by a dense algal mat, predominantly Ceramium spp. but also with Ulva spp. and Polysiphonia spp. Damp areas amongst the algal mat are covered by aggregations of the sand mason worm Lanice conchilega and the fan worm Sabella pavonina. The anemone Sagartia troglodytes and the crabs Carcinus maenas and Cancer pagurus occur in crevices in the peat. Small pools on the peat may contain hydroids, such as Obelia longissima and Kirchenpaueria pinnata, the brown alga Dictyota dichotoma and the prawn Crangon crangon. [Description derived largely from sites in north Norfolk. Further records of this biotope required]. (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

Few records of the biotope exist; its description is derived from sites in north Norfolk (Tichwell Marsh, Brancaster) and Cardigan Bay (Borth, north of Aberystwyth).

Depth range

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Additional information

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Habitat review

Ecology

Ecological and functional relationships

  • Little information was found concerning the community of this biotope.
  • All boring piddocks begin excavation following settling of the larva and slowly enlarge and deepen the burrow with growth (Pinn et al., 2005). They are forever locked within their burrows, and only the siphons project to the surface opening (Barnes, 1980). A relationship exists between the distribution of piddock species and substratum type. Duval (1963a) examined the penetrability of a variety of substrata by Petricola pholadiformis. It may bore into London Clay, Thanet Sandstone, softer chalk and peaty substrata. It was unable to bore into abnormally hard clays, soft loose mud, shifting sand, gritty and Lower Greensand Gault clay, hard chalk and Blue Lower Lias. Thus its distribution is determined by changes in the substratum of the shore rather than by tidal level (the piddock may flourish from extreme low water to mid-tide level).
  • Hydroids living in pools in the peat are opportunistic carnivores mainly catching suspended plankton as food.
  • Filter / suspension feeding organisms such as the piddocks, Barnea candida and Petricola pholadiformis; the peacock worm, Sabella pavonina and sand mason worm, Lanice conchilega, are the dominant trophic group in the biotope, indicating the importance of planktonic inputs to the community. Piddocks probably contribute to the creation of a relatively high silt environment through burrowing activities.
  • Crabs, such as Carcinus maenas and Cancer pagurus, are the predominant mobile species in the biotope, travelling through as they scavenge for food.
  • The anemone, Sagartia troglodytes, which may occur in crevices of the peat, uses 'catch tentacles to prey upon small shrimps and crabs. In turn, Sagartia troglodytes is preyed upon by the grey sea slug, Aeolidia papillosa, and attacked by the tompot blenny, Parablennius gattorugine (BMLSS, 2002c) that may frequent the biotope
  • Algae that grows on the surface of the peat may provide shelter for small crustaceans and possibly a source of food for grazing prosobranchs, such as Littorina littorea, which may occasionally occur in the biotope but is not characteristic.
  • Species of isopod and amphipod may also feed on detrital matter within the dense algal mat and prey upon each other.

Seasonal and longer term change

  • One of the characteristic species of this biotope, Petricola pholadiformis, has a longevity of up to 10 years (Duval, 1963a) and whose established populations may not exhibit significant seasonal changes, besides spawning in the summer. Variations in the abundance and seaweed species present would be expected to vary between and within locations according to the season. For instance, following storms, the peat may be covered by a layer of sand which could adversely affect the surface of algal species, especially propagules.

    Habitat structure and complexity

    Outcrops of fossilized peat in the eulittoral may project above sand level by > 15 cm and form extensive platforms up to 100 m in length across the shore. Fossilized peat tends to be firm and relatively erosion resistant (Murphy, 1981), and occur in localities backed by extensive beach and dune systems, so that the patches of peat exposed varies according to sand movement. The peat is likely to have pits, crevices and undulations in surface level in addition to vacant piddock burrows. Empty piddock burrows can influence the abundance of other species by providing additional habitats and refuges. For instance, Pinn et al. (in press) found a statistically significant increase in species diversity in areas where old piddock burrows were present compared to where they were absent. Pools of water may accumulate in surface depressions which favour hydroids (e.g. Obelia longissima and prawns such as Crangon crangon). The covering of red and ephemeral green algae probably provide cover for cryptic fauna.

    Productivity

    Algal species, Ceramium, Ulva, form a characteristic mat over the surface of the peat substratum so primary production is a component of productivity. Many of the characterizing species that are present in the biotope are suspension/filter feeders, so productivity of the biotope would probably be largely dependent on detrital input. However, specific information about the productivity of characterizing species or about the biotope in general was not found.

    Recruitment processes

    Most of the characterizing species in the biotope are sessile or sedentary. Consequently, recruitment must occur primarily through dispersive larval or spore stages. Examples of characterizing species are given below.
    • Duval (1963a) reviewed the biology of Petricola pholadiformis. The sexes of Petricola pholadiformis are separate. Females are estimated to produce between 3,000,000 and 3,500,000 eggs annually. Gametogenesis takes place between April and early June and a waiting period ensues before spawning occurs towards late July and during August, lasting just over six weeks in total. The juvenile trochophore stage is reached within 28 hours, and the veliger stage in 44 hours. Length of planktonic life was estimated to be in the region of only one and a half to two weeks in duration, after which the young Petricola pholadiformis assume a benthic lifestyle, but remain extremely active. Juveniles of 0.4 cm length possess a very strongly ciliated and mobile foot and large amounts of mucus aid adherence to the substratum. Shell growth may begin in April or during May and continues until after June. Thereafter, growth rings are laid down annually, and annual growth in younger specimens is in the region of 0.7 - 0.9 cm.
      Similarly, the white piddock, Barnea candida, has separate sexes and fertilization occurs externally (Duval, 1963b). Many bivalves spawn during the part of the year when sea temperatures are rising. No information was found concerning length of planktonic life in Barnea candida but El-Maghraby (1955) showed that in southern England Barnea candida spawned in September, being unusual that it started to spawn when the temperature fell at the beginning of the autumn. The maximum age estimated for Barnea candida is 4 years with growth rates ranging from 0.1-6.8 mm per year (Pinn et al., 2005).
    • Edwards (1973) reported that the red seaweed, Ceramium virgatum (as Ceramium nodulosum), has a triphasic life history consisting of a sequence of gametophytic, carposporophytic and tetrasporophytic phases in which the first and the third are morphologically similar. Maggs & Hommersand (1993) reported spermatangia in January, March-April, June and August-September; cystocarps in January-February and April-September; tetrasporangia in February-September. Although no information on dispersal has been found directly for Ceramium virgatum, Norton (1992) concluded that dispersal potential is highly variable in seaweeds, but recruitment probably occurs on a local scale, typically within 10m of the parent plant.
    • The green seaweed, Ulva is considered to be opportunistic in its colonization of available substrata, its rapid recruitment made feasible by its life cycle, which consists of both sexual and asexual generations. Reproduction can occur throughout the year, but is maximal in summer. The haploid gametophytes (arising from sexual reproduction) of Ulva produce enormous numbers of motile gametes that fuse and germinate to produce sporophytes. Sporophytes also produce large numbers of motile spores that are released in such great numbers that the water can become green (Little & Kitching, 1996). The dispersal potential of such spores is great (> 10 km) so that the species may recruit from distant populations.
    • Hydroids, such as Obelia longissima, are often the first organisms to colonize available space in settlement experiments (Gili & Hughes, 1995). The hydroid phase of Obelia longissima releases dioecious sexual medusae that swim for up to 21 days (Sommer, 1992) and release sperm or eggs into the sea (fertilization is external). The resultant embryos then develop into planulae larvae that swim for 2-20 days (Sommer, 1992). Therefore, their potential dispersal is much greater than those species that only produce planulae. In addition, few species of hydroids have specific substratum requirements and many are generalists, for example Obelia longissima has been reported from a variety of rock and mud substrata.

    Time for community to reach maturity

    Little information was found concerning community development. However, piddocks, Barnea candida and Petricola pholadiformis are likely to settle readily. These piddocks breed annually and produce a large number of gametes. Once established individuals may live for a considerable length of time; Petricola pholadiformis of length 5-6 cm are likely to be between 6-10 years old (Duval, 1963a). Another characteristic component of the biotope is the algal mat of Ceramium and Ulva that caps the peat and development of this algal mat would be expected to be rapid. For instance, panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001), whilst Ulva spp. Are known to colonize available substrata rapidly. Barnea candida grows rapily to a length of approximately 25-35 mm within 2 to 3 years, living for a maximum of 4 years (Pinn et al., 2005).

    Additional information

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Preferences & Distribution

Recorded distribution in Britain and IrelandFew records of the biotope exist; its description is derived from sites in north Norfolk (Tichwell Marsh, Brancaster) and Cardigan Bay (Borth, north of Aberystwyth).

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients Field unresearched
Salinity Full (30-40 psu)
Physiographic
Biological Zone Eulittoral
Substratum Peat (fossilized)
Tidal
Wave Moderately exposed
Other preferences Fossilized peat.

Additional Information

Further records of this biotope are required.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

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Additional information

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Sensitivity reviewHow is sensitivity assessed?

Explanation

The most significant feature for identification of this biotope is the fossilized peat substratum. In the absence of peat the biotope would not be recognized. All species of the community can occur elsewhere, on and in other substrata. The most faithful species to the MLR.RPid biotope are the piddocks, Barnea candida and Petricola pholadiformis, and these species have been assessed to be important characterizing species. The surface of the peat is covered by a mat of predominantly red seaweed, Ceramium sp., but also ephemeral green seaweeds such as Ulva and Ulva. These species are included as important structural species as they provide a habitat for small invertebrates.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingBarnea candidaWhite piddock
Important structuralCeramium virgatumA red seaweed
Important characterizingPetricola pholadiformisAmerican piddock
Important structuralUlva intestinalisGut weed

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High None Very High Major decline High
The biotope is characterized by a substratum of fossilized peat. Removal of the fossilized peat would therefore mean that the biotope no longer existed. Intolerance has been assessed to be high and recoverability none, as the formation of peat and its fossilization takes many thousands of years and is dependent on appropriate conditions for formation. However, if only a layer of the peat is removed, recolonization of the remaining peat may be fairly rapid and a recovery of moderate likely.
Intermediate Very high Low Decline Moderate
Sometimes the substratum in which piddocks reside is covered by a thin layer of loose sandy material, through which the piddocks maintain contact with the surface via their siphons. It is likely that the piddocks would be able to extend their siphons through loose material, particularly where tidal movements shift the sand around. Continued smothering is likely to lead to death. Species comprising, and living within the dense algal mat are likely to be more intolerant of smothering. Over the period of one month, seaweeds may begin to decompose owing to frond damage and inhibition of photosynthesis. Sporelings would certainly be adversely affected as Vadas et al. (1992) stated that algal spores and propagules are adversely affected by a layer of sediment, which can exclude up to 98% of light. Intolerance has been assessed to be intermediate, as impoverishment of the community would result as a consequence of smothering by an additional covering of 5 cm of sediment.
Seaweeds such as Ceramium virgatum are known to recruit rapidly to cleared surfaces. For instance, experimental panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001). Recoverability has been assessed to be very high.
A higher intolerance would be expected if the biotope were smothered by materials that were impermeable or of a viscous nature.
Tolerant* Not relevant Not sensitive* No change Low
Although increased levels of suspended sediment may require additional clearance of feeding structures, increased levels of suspended sediment may in fact be beneficial to the community. Suspension / filter feeders are the dominant trophic group within the MLR.RPid biotope, and particles in suspension represent a food resource. An assessment of not sensitive* has been made.
Low Very high Not relevant Minor decline Low
A significant decrease in suspended sediment may reduce food input to the biotope resulting in reduced growth and fecundity of suspension feeding animals, e.g. piddocks. Intolerance has been assessed to be low. Normal feeding would resume on return to prior conditions and recovery has been assessed to be immediate.
Intermediate Very high Low Decline Moderate
The adult piddocks are offered significant protection from desiccation by their environmental position within the peat substratum. However, the dense algal mat covering the substratum, predominantly of the red seaweed Ceramium virgatum, may be more intolerant of an increase in desiccation. Ceramium virgatum occurs profusely in rockpools, on the lower shore and in the subtidal but not on the open shore away from damp places suggesting that it is intolerant of desiccation. As a consequence of a change in this factor, the algal cover may become diminished. Intolerance has been assessed to be intermediate to reflect impoverishment of the community. Recovery is expected to be very high as settlement and growth appears to be rapid at least at appropriate times of year. For example, Brown et al. (2001) found that the red seaweed had settled onto panels within four weeks of their placement in Langstone Harbour.
Low Very high Very Low Minor decline Low
The biotope occurs in the eulittoral zone, where it experiences regular immersion and emersion. Species present are therefore tolerant of periods of emergence to some extent. A one hour increase in the period of emergence for one year, may impact on the viability of suspension feeding species, as they have less time for feeding. Furthermore, physiological stresses on both surface flora and fauna are likely to increase as they cope with effects of desiccation. Intolerance to increased emergence has been assessed to be low. On return to prior conditions, recoverability has been assessed to be very high as normal feeding resumes, and species recover form effects of desiccation (see above).
Tolerant Not sensitive* No change Low
The biotope occurs in the eulittoral zone, where it experiences regular immersion and emersion. All species within the biotope are also found in the subtidal, so a decrease in emergence is not likely to be detrimental to the biotope. An assessment of not sensitive has been made.
Intermediate Very high Low Decline Moderate
Established adult piddocks are, to a large extent, protected from effects, direct and indirect, of increased water flow, owing to their environmental position within the substratum. Adult piddocks may become exposed should physical erosion occur at a greater rate than burrowing, and lost from the substratum. This is not nonetheless, not a likely occurrence. However, increased water flow rate may be responsible for a reduction in the recruitment of juvenile piddock species. Duval (1963b) reported that the reduced density of Barnea candida on the 'street' Whitstable (south coast of England) was attributable to the redistribution and deposition of loose material during storms causing smothering, and increased scour during periods of elevated water flow. Similarly, increased scour, as a consequence of increased water flow, would also inhibit settlement of seaweed spores. The fronds of adults and germlings may also be damaged. Furthermore, feeding by suspension feeders within the biotope may be impaired, as delicate structures are withdrawn for protection. Intolerance has been assessed to be intermediate. On return to prior conditions, recoverability has been assessed to be very high. Adult populations capable of reproducing are likely to remain in the vicinity. Piddocks recruit annually and produce many gametes, and the red seaweed, Ceramium recruits rapidly to cleared surfaces. For instance, experimental panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001).
Tolerant Not sensitive* No change Low
Changes in water flow rate affect siltation levels and also probably the feeding of suspension feeders. A decrease in water flow rate may reduce the suspended particulate material carried in the water column important for the feeding of the faunal components of the community. This may result in reduced viability of the population. Intolerance has been assessed to be low. On return to prior conditions, recovery is likely to be rapid as normal feeding would resume.
Tolerant Not relevant Not relevant Not relevant Low
The piddocks, Barnea candida and Petricola pholadiformis both occur to the south of the British Isles, so are likely to be tolerant of a chronic increase in temperature of 2 °C. Lüning (1990) reported that Ceramium virgatum (as Ceramium rubrum) survived temperatures from 0 to 25 °C with optimal growth at about 15 °C. The species is therefore likely to be tolerant of higher temperatures than it experiences in the seas around Britain and Ireland. Ulva intestinalis is considered to be tolerant of elevated temperatures. It is characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days, whilst (Vadas et al., 1976) observed Ulva intestinalis to significantly increase in abundance near a heated effluent outfall.
Spawning of the piddock, Petricola pholadiformis, is initiated by increasing water temperature (> 18 °C) (Duval, 1963a), so elevated temperatures outside of usual seasons may disrupt normal spawning periods. The spawning of Barnea candida was also reported to be disrupted by changes in temperature. The species normally spawns in September when temperatures are dropping (El-Maghraby, 1955), however, a rise in temperature in late June of 1956, induced spawning in some specimens of Barnea candida (Duval, 1963b). Disruption from established spawning periods, caused by temperature changes, may be detrimental to the survival of recruits as other factors influencing their survival may not be optimal, and some mortality may result. Established populations may otherwise remain unaffected by elevated temperatures. On balance, an assessment of not sensitive has been suggested.
High Moderate Intermediate Major decline Moderate
The piddocks, Barnea candida and Petricola pholadiformis both occur to the north of the British Isles, so are likely to be tolerant of a chronic decrease in temperature of 2 °C. During the exceptionally cold winter of 1962-1963, the population of Barnea candida was entirely wiped out in the Whitstable area of the south-east coast of England (Crisp, 1964). Lüning (1990) reported that Ceramium virgatum (as Ceramium rubrum) survived temperatures from 0 to 25 °C with optimal growth at about 15 °C. The species is therefore likely to be tolerant of lower temperatures than it experiences in the seas around Britain and Ireland. Sub-optimal temperatures may delay or slow reproduction. Intolerance has therefore been assessed to be high since acute decreases in temperature may be responsible for the decimation of piddock populations. Recovery would be expected, assuming that a breeding adult population remains in a refuge locally, as the piddocks recruit annually and produce many gametes. However, the occurrence of suitable substrata for piddock species is localized and patchy. Following complete loss of a population, recovery would be reliant on larval recruitment over considerable distances. Evidence suggests that such recolonization is possible for Petricola pholadiformis, as the non-native species has successfully invaded continental Europe from sites in Britain via its pelagic larva. Information concerning length of time in the plankton was not found for Barnea candida and recoverability has been assessed to be moderate.
Tolerant Not relevant Not relevant No change Moderate
Faunal species are unlikely to be affected by the light attenuating effects of an increase in turbidity. Hily et al. (1992) found that, in conditions of high turbidity, Ceramium virgatum (as Ceramium rubrum) (and Ulva sp.) dominated sediments in the Bay of Brest, France. It is most likely that Ceramium virgatum thrived because other species of algae could not. Whilst the field observations in the Bay of Brest suggested that an increase in abundance of Ceramium virgatum might be expected in conditions of increased turbidity, populations where light becomes limiting will be adversely affected. However, in shallow depths, such as in the MLR.RPid biotope, Ceramium virgatum may benefit from increased turbidity. An assessment of not sensitive has been made.
Tolerant Not sensitive* No change Moderate
Faunal species are unlikely to be affected by the increased light penetration of the water column following a decrease in turbidity. A decrease in turbidity would result in greater light availability for algae and potentially potential benefit from the factor. Although, the work of Hily et al. (1992) suggested that other species of algae might out-compete Ceramium virgatum in lower turbidity situations, the situation is unlikely in this biotope, owing to the nature of the fossilized peat substratum. An assessment of not sensitive has been made.
Intermediate Very high Low Decline Moderate
The biotope typically occurs in moderately wave exposed locations. The piddocks are unlikely to be affected by changes in wave exposure, owing to their environmental position within the peat substratum, which protects them. On clay substrates, it is possible however, that wave action actively erodes the substratum at a faster rate than the piddocks leaving them vulnerable and exposed. The surface of fossilized peat covered by a dense mat of predominantly red algae Ceramium virgatum is reported to thrive in wave sheltered environments (see full MarLIN review). Strong wave action is likely to cause some damage to fronds resulting in reduced photosynthesis and compromised growth. Furthermore, individuals may be damaged or dislodged by scouring from sand and gravel mobilized by increased wave action (Hiscock, 1983). Damage to at least a part of the seaweed stand is likely due to increased wave exposure and intolerance has been assessed to be intermediate. Recovery of the red seaweed Ceramium virgatum would be expected to be expected to be very high. For instance, experimental panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001).
Tolerant Not sensitive* No change Low
The biotope typically occurs in moderately wave exposed locations. The piddocks are unlikely to be affected by changes in wave exposure, owing to their environmental position within the peat substratum. Ceramium virgatum is reported to thrive in wave sheltered locations (see full MarLIN review). For instance, it is recorded in some of the most sheltered parts of Hardangerfjord in Norway (Jorde & Klavestad, 1963). A decrease in wave exposure is therefore unlikely to be an adverse factor for this biotope and assessment of not sensitive has been made.
Tolerant Not relevant Not relevant Not relevant Low
Although some species may respond to vibration, the biotope as a whole is not likely to be affected by noise disturbance.
Tolerant Not relevant Not relevant Not relevant Low
Piddocks may react to changes in light intensity. For instance, the common piddock Pholas dactylus reacts to changes in light intensity by withdrawing its siphon which may be an adaptive response to avoid predation by shore birds and fish (Knight, 1984). Such responses are not documented in either Barnea candida or Petricola pholadiformis, but the behaviour of other piddocks suggests that the visual presence of boats or humans is not likely to be detrimental to the MLR.RPid community. On removal of visual disturbance normal behaviour will resume.
Intermediate Very high Low Decline Moderate
Piddocks are the most important characterizing species of the MLR.Rpid biotope and, owing to their position within the fossilized peat, they are protected from physical disturbance and abrasion. However, the biotope is also characterized by a dense algal mat of red and green seaweed that would be susceptible to physical disturbance. Some species protruding from the surface, e.g. Lanice conchilega, Sabella pavonina may also be removed. Intolerance has been assessed to be intermediate. Recovery of the algal mat would be expected to be rapid. For instance, experimental panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001). Recoverability has been assessed to be very high.
High High Moderate Major decline Moderate
Adult piddocks are confined to their cavities for life. If removed from the substratum death of adults is likely as no displaced specimens of Petricola pholadiformis were ever observed to make a second boring in a consolidated substratum (Duval, 1963a). Intolerance has been assessed to be high. Recovery would be expected, assuming that a breeding adult population remains in a refuge locally, as the species recruit annually and produce many gametes. However, the occurrence of suitable substrata for piddock species is localized and patchy. Following complete loss of a population, recovery would be reliant on larval recruitment over considerable distances. Evidence suggests that such recolonization is possible for Petricola pholadiformis as the non-native species has successfully invaded continental Europe from sites in Britain via its pelagic larva. Barnea candida also bores into wood, so the beaching of driftwood is also a route of recolonization for the species (e.g. adults arrive and spawn). Recoverability has therefore been assessed to be high.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
High High Moderate Major decline Low
No information on the specific effects of chemicals on the piddocks, Barnea candida and Petricola pholadiformis was found. However the toxicity of some synthetic chemicals, e.g. TBT, to bivalves has been widely reported. For instance, reports of reductions in the numbers of bivalves in estuaries with high pleasure craft activity have provided evidence of the high toxicity of TBT to bivalves (Beaumont et al., 1989).
Ceramium virgatum seems to be intolerant of at least some synthetic chemicals. In studies of the effect of chromated copper arsenate wood preservative, Brown et al. (2001) found that a significantly higher coverage of Ceramium virgatum (as Ceramium nodulosum) occurred on untreated wood after four weeks. Hardy (1993) observed that Ceramium virgatum (as Ceramium rubrum) was lost between 1923 and 1991 from the mouth of the (polluted) Tees Estuary. Inferences may also be drawn from the sensitivities of red algal species generally. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. They also reported that red algae are effective indicators of detergent damage since they undergo colour changes when exposed to relatively low concentration of detergent. Smith (1968) reported that 10 ppm of the detergent BP 1002 killed the majority of specimens of Ceramium vergatum (as Ceramium rubrum) in 24 hour toxicity tests. Evidence suggests that this community would probably have a high intolerance to synthetic chemical contamination. Recovery would be expected assuming deterioration of contaminants. Piddock species recruit annually and produce many gametes. However, the occurrence of suitable substrata for piddock species is localized and patchy. Following complete loss of a population, recovery would be reliant on larval recruitment over considerable distances. Evidence suggests that such recolonization is possible for Petricola pholadiformis as the non-native species has successfully invaded continental Europe from sites in Britain via its pelagic larva. Barnea candida also bores into wood, so the beaching of driftwood is also a route of recolonization for the species (e.g. adults arrive and spawn). Recovery of the algal mat would be expected to be rapid. For instance, experimental panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001). Overall recoverability has therefore been assessed to be high.
Heavy metal contamination
No information Not relevant No information Not relevant Not relevant
Specific information concerning heavy metal pollution and this piddock community was not found. Bryan (1984) stated that Hg was the most toxic metal to bivalve molluscs while Cu, Cd and Zn seem to be most problematic in the field. In bivalve molluscs Hg was reported to have the highest toxicity, mortalities occurring above 0.1-1 µg/l after 4-14 days exposure (Crompton, 1997), toxicity decreasing from Hg> Cu and Cd > Zn > Pb and As > Cr ( in bivalve larvae, Hg and Cu > Zn> Cd, Pb, As, and Ni > Cr). Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds to be: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. In the absence of evidence from which to derive an intolerance assessment for this community, insufficient information has been recorded.
Hydrocarbon contamination
High Moderate Moderate Major decline Moderate
Specific information concerning effects of hydrocarbon contamination on piddocks was not found. However, should oil be washed ashore and coat the peat substratum in which piddocks reside, smothering and suffocation may occur as siphons in contact with the surface are coated and withdrawn in to the cavity for a prolonged period of time. Mortalities may also in the longer term be attributable to toxic effects of oil.
Smith (1968) reported that Ceramium virgatum (as Ceramium rubrum) was killed during the Torrey Canyon oil spill. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/ dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984). Intolerance has been assessed to be high. Until oil that had covered the substratum becomes sufficiently weathered, it may serve to deter the settlement of planktonic larvae and spores, otherwise recovery of the community would be expected, although not to previous levels of abundance for some time. Piddock species recruit annually and produce many gametes. However, the occurrence of suitable substrata for piddock species is localized and patchy. Following complete loss of a population, recovery would be reliant on larval recruitment over considerable distances. Evidence suggests that such recolonization is possible for Petricola pholadiformis as the non-native species has successfully invaded continental Europe from sites in Britain via its pelagic larva but the potential for Barnea candida to recolonize over considerable distances is not known. Recovery of the algal mat would be expected to be rapid. For instance, experimental panels were colonized by Ceramium virgatum (as Ceramium nodulosum) within a month of being placed in Langstone Harbour (Brown et al., 2001). Overall recoverability has therefore been assessed to be moderate.
Radionuclide contamination
No information Not relevant No information Not relevant Not relevant
Insufficient
information.
Changes in nutrient levels
Tolerant* Not relevant Not sensitive* No change Low
Specific information concerning effects of nutrient enrichment on the community was not found. Hily et al. (1992) found that, in conditions of high nutrients, Ceramium virgatum (as Ceramium rubrum) and Ulva sp. dominated substrata in the Bay of Brest, France. Ceramium spp. are also mentioned by Holt et al. (1995) as likely to smother other species of macroalgae in nutrient enriched waters. Fletcher (1996) quoted Ceramium virgatum (as Ceramium rubrum) to be associated with nutrient enriched waters. It therefore seems that algal stands of Ceramium virgatum are likely to benefit from elevated levels of nutrients. Furthermore, nutrient enrichment that enhances productivity of phytoplankton may indirectly benefit the faunal community. The dominant trophic group are filter/suspension feeders and abundant phytoplankton represent a food resource. An assessment of not sensitive* has been made.
Not relevant Not relevant Not relevant Not relevant Not relevant
The salinity tolerances of the piddocks, Barnea candida and Petricola pholadiformis, and other important characterizing species of the biotope are not known. However, the biotope occurs in the eulittoral zone under conditions of full salinity and where conditions of hyper salinity are not likely to be encountered. An assessment of not relevant has been made.
Low Very high Moderate Minor decline Low
The biotope will experience periods of reduced salinity, for example when the tide is out and rain occurs. Barnea candida is reported to extend in to estuarine environments in salinities down to 20 psu (Fish & Fish, 1996). Petricola pholadiformis is particularly common off the Essex and Thames estuary, e.g. the River Medway (Bamber, 1985) suggesting tolerance of brackish waters. Ceramium virgatum occurs over a very wide range of salinities. The species penetrates almost to the innermost part of Hardanger Fjord in Norway where it experiences very low salinity values and large salinity fluctuations due to the influence of snowmelt in spring (Jorde & Klavestad, 1963). It is likely therefore that the benchmark decrease in salinity would not result in mortality. Seaweed photosynthesis by seaweed may be impaired and also growth and reproduction of both fauna and flora may be compromised. Intolerance has been assessed to be low. Physiological processes should quickly return to normal when salinity returns to original levels, so recoverability is recorded as very high.
No information Not relevant No information Not relevant Not relevant
Specific information concerning oxygen consumption and reduced oxygen tolerances were not found for important characterizing species within the biotope. Cole et al. (1999) suggested possible adverse effects on marine species below 4 mg O2/l and probable adverse effects below 2mg O2/l. Duval (1963a) observed that conditions within the borings of Petricola pholadiformis were anaerobic and lined with a loose blue/black sludge, suggesting that the species may be relatively tolerant to conditions of reduced oxygen. However, insufficient information has been recorded.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information Not relevant No information Not relevant Not relevant
More than 20 viruses have been described for marine bivalves (Sinderman, 1990). Bacterial diseases are more significant in the larval stages and protozoans are the most common cause of epizootic outbreaks that may result in mass mortalities of bivalve populations. Parasitic worms, trematodes, cestodes and nematodes can reduce growth and fecundity within bivalves and may in some instances cause death (Dame, 1996). However, no information concerning the effects of microbial pathogens upon the community of this biotope was found and insufficient information has been recorded.
Tolerant Not relevant Not relevant Not relevant Low
The American piddock, Petricola pholadiformis is a non-native, boring piddock that was unintentionally introduced from America with the American oyster, Crassostrea virginica, not later than 1890 (Naylor, 1957). Rosenthal (1980) suggested that from the British Isles, the species has colonized several northern European countries by means of its pelagic larva and may also spread via driftwood, although it usually bores into clay, peat or soft rock shores. In Belgium and The Netherlands Petricola pholadiformis has almost completely displaced the native piddock, Barnea candida (ICES, 1972). However, there is no documentary evidence to suggest that Barnea candida has been displaced in the British Isles (J. Light & I. Kileen pers. comm. to Eno et al., 1997). The two species co-occur in this biotope and an assessment of not sensitive has been made.
Intermediate Moderate Moderate Not relevant Not relevant
Pholas dactylus is known to be harvested in Britain but not to the same extent. In Italy, harvesting of piddocks has had a destructive impact on habitats and has now been banned (E. Pinn, pers. Comm. To MarLIN). In Britain, collection of piddocks is thought to have a similarly destructive effect. People have been known to go out onto the shore and, with the use of a hammer and chisel, excavate the piddocks from the soft rock (K. Hiscock, pers. Comm.). This would be catastrophic for the biotope. The stability of the peat would be reduced and potentially lead to the loss of the vast majority of piddocks that inhabit the top few centimetres (up to about 10 cm depth) of the substratum. Farming methods are being investigated as an alternative and it is therefore possible that further targeted extraction could be a future possibility. Even a small amount of piddock exploitation would lead to the loss of a proportion of the biotope and accordingly, intolerance has been assessed as intermediate. Formation of peat and its fossilization takes many thousands of years and is dependent on appropriate conditions for formation. If only a layer of the peat is removed, recolonization of the remaining peat may be fairly rapid and a recovery of moderate likely.
Not relevant Not relevant Not relevant Not relevant Not relevant

Additional information

No text entered.

Importance review

Policy/Legislation

Habitats of Principal ImportancePeat and clay exposures [N. Ireland, England, Wales]
Habitats of Conservation ImportancePeat and clay exposures
Habitats Directive Annex 1Reefs
UK Biodiversity Action Plan PriorityPeat and clay exposures

Exploitation

Piddocks may be consumed and there has been concern about collection (that involves habitat destruction) in chalk areas of Kent (K. Hiscock, pers. comm.).

Additional information

-

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Citation

This review can be cited as:

Budd, G.C. 2008. Ceramium sp. and piddocks on eulittoral fossilised peat. 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/369

Last Updated: 03/04/2008