Seapens and burrowing megafauna in circalittoral fine mud

08-07-2004
Researched byJacqueline Hill Refereed byDr David Hughes
EUNIS CodeA5.361 EUNIS NameSeapens and burrowing megafauna in circalittoral fine mud

Summary

UK and Ireland classification

EUNIS 2008A5.361Seapens and burrowing megafauna in circalittoral fine mud
EUNIS 2006A5.361Seapens and burrowing megafauna in circalittoral fine mud
JNCC 2004SS.SMu.CFiMu.SpnMegSeapens and burrowing megafauna in circalittoral fine mud
1997 BiotopeSS.CMU._.SpMegSeapens and burrowing megafauna in circalittoral soft mud

Description

Plains of fine mud at depths greater than about 15 m may be heavily bioturbated by burrowing megafauna; burrows and mounds may form a prominent feature of the sediment surface with conspicuous populations of sea pens, typically Virgularia mirabilis and Pennatula phosphorea. These soft mud habitats occur extensively throughout the more sheltered basins of sea lochs and voes and are present in quite shallow depths (as shallow as 15 m) in these areas probably because they are very sheltered from wave action. This biotope also seems to occur in deep offshore waters in the North Sea, where densities of Nephrops norvegicus may reach 68 per 10 m-2 (see Dyer et al., 1982, 1983), and the Irish Sea. The burrowing crustaceans present may include Nephrops norvegicus, Calocaris macandreae or Callianassa subterranea. The former of these species is the only one frequently recorded from surface observations, whilst grab sampling may fail to sample any of these species. Indeed, some forms of sampling may fail to indicate sea pens as characterizing. The crab Goneplax rhomboides may sometimes be recorded, again rarely, in this habitat. Large mounds formed by the echiuran Maxmuelleria lankesteri are also present in some sea loch sites. It is unclear from the data examined whether differences in the balance of species composition from site to site represent additional biotopes within this assemblage. Pachycerianthus multiplicatus is quite specific to this habitat and is scarce in Great Britain (Plaza & Sanderson, 1997). The ubiquitous epibenthic scavengers Asterias rubens, Pagurus bernhardus and Liocarcinus depurator are present in low numbers. The brittlestars Ophiura albida and Ophiura ophiura are sometimes present, but are much more common in slightly coarser sediments. In the deeper fjordic lochs which are protected by an entrance sill, the tall sea pen Funiculina quadrangularis may also be present (CMU.SpMeg.Fun). The brittlestars Amphiura chiajei and Amphiura filiformis may be present in large numbers, although there may be some sites where these species are absent. The infauna may contain significant populations of the polychaetes Pholoe spp., Glycera spp., Nephtys spp., spionids, Pectinaria belgica and Terebellides stroemi, the bivalves Nucula sulcata, Corbula gibba and Thyasira flexuosa and the echinoderm Brissopsis lyrifera, although the latter may not be frequently found in remote samples. Overall, CMU.SpMeg is closely allied to CMU.BriAchi and COS.ForThy and shows strong similarities in infaunal species composition. It may differ from these biotopes as a result of a lack of disturbance or linkage to productive overlying waters. IMU.PhiVir is superficially similar to CMU.SpMeg but is found in shallower, less thermally stable waters and lacks the large burrowing species. (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

CMU.SpMeg, and the sub-biotope CMU.SpMeg.Fun are typical of the deep mud habitats of the Scottish sea lochs. The biotope CMU.SpMeg has been recorded in most of the Scottish sea lochs (Howson et al., 1994) and in the Shetland voes (Howson, 1988). It has also been observed in the north-eastern Irish Sea (Hughes & Atkinson, 1997) and in the deep offshore waters of the North Sea (Dyer et al., 1982).

Depth range

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Additional information

The biotope does occur in shallower water, at 10-12m in Loch Sween for example (D. Hughes pers. comm.). In some instances of this biotope Asterias rubens, Pagurus bernhardus and Liocarcinus depurator may be present in high numbers (D. Hughes pers. comm.).

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Further information sources

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JNCC

Habitat review

Ecology

Ecological and functional relationships

  • The characterizing and other species in this biotope occupy space in the habitat but their presence is most likely primarily determined by the occurrence of a suitable substratum rather by interspecific interactions. Sea pens and burrowing megafauna are functionally and ecologically dissimilar and are not necessarily associated with each other but occur in the same muddy sediment habitats. For example, some sites with abundant burrowing megafauna have no sea pens (and vice versa). It is possible that sea pens might be adversely affected by high levels of megafaunal bioturbation, perhaps by preventing the survival of newly settled colonies. No single species can be considered a keystone species whose activity is essential to the structure of the community. In addition to sea pens and burrowing megafauna, the biotope often supports a rich fauna of smaller less conspicuous species, such as polychaetes, nematodes and bivalves, living within the sediment.
  • There are however, some interspecific relationships within the biotope. For instance, the shrimp Jaxea nocturna, which often lives in association with the echiuran worm Maxmuelleria lankesteri (Nickell et al., 1995), may benefit from the organic-rich mud pulled into its burrows by the worm. Nickell et al. (1995) found that numerous small bivalves and polychaete worms colonized the walls of Maxmuelleria lankesteri burrows. Mobile polychaetes such as Ophiodromus flexuosus, which normally live out on the sediment surface were also seen to enter burrows. The body of shrimps may offer a substratum for colonization. The ctenostome bryozoan Triticella flava, for example, grows a dense 'furry' covering on the antennae, mouthparts and legs of burrowing crustaceans. It is most commonly found on Calocaris macandreae but has also been found on several of the other crustacean burrowers present in the biotope (Hughes, 1998b). The mouthparts of Nephrops norvegicus harbour a small commensal sessile animal, the newly described Symbion pandora (Conway Morris, 1995). A few organisms have also been recorded in association with British sea pens. Funiculina quadrangularis is often host to the isopod Astacilla longicornis, which clings to the rachis, and the brittlestar Asteronyx loveni, which clings to the sea pen maintaining an elevated position above the seabed. However, Asteronyx is only found in deeper waters, usually below 100 m depth. There are also a few specialist predators of sea pens (see below). Although rare, the tube of the large sea anemone Pachycerianthus multiplicatus, which is only found in this biotope, creates a habitat for attached species (O'Connor et al., 1977).
  • The species living in deep mud biotopes are generally cryptic in nature. Predation is probably low because many species will be sheltered to some extent from visual surface predators such as fish. Evidence of predation on Virgularia mirabilis by fish seems limited to a report by Marshall & Marshall (1882 in Hoare & Wilson, 1977) where the species was found in the stomach of haddock. Observations by Hoare & Wilson (1977) suggest however, that predation pressure on this species is low. Many specimens of Virgularia mirabilis lack the uppermost part of the colony which has been attributed to nibbling by fish. The sea slug Armina loveni is a specialist predator of Virgularia mirabilis. Nephrops norvegicus is eaten by a variety of bottom-feeding fish, including cod, haddock, skate and dogfish. There are also numerous records of fish predation on thalassinidean mud shrimps such as Calocaris macandreae which has been found in the stomachs of cod and haddock. Maxmuelleria lankesteri has also been recorded in the stomachs of Irish sea cod (Hughes, 1998b). Nephrops norvegicus is carnivorous, feeding on brittle stars, polychaetes, bivalves and other crustaceans such as Calocaris macandreae.
  • The bioturbatory activities of thalassinidean mud-shrimps such as Callianassa subterranea have important consequences for the structural characteristics of the sediment they inhabit. An important aspect of bioturbatory activity was emphasised by Johnston (1974) who showed that the activity of deposit-feeders results in the production of organic-mineral aggregates which may comprise as much as 70% of the sediment particle total. Such aggregation of particles must greatly increase the porosity of the sediments and so have a considerable influence on the transfer of chemicals by diffusion or other physical processes, as well as critically affecting environmental space for meio- and macrofauna and the bacterial flora. Such influences affect a variety of important ecosystem functions, including nutrient exchange (Nickell et al., 1995), faunal community structure and biogeochemical cycling (e.g. Koike & Mukai, 1983; Waslenchuk et al., 1983; Posey, 1986). Several studies have examined the effects of thalassinidean shrimp bioturbation on sedentary and mobile infaunal species. Tamaki (1988) found that Callianassa japonica had a positive effect on colonization by other mobile taxa, possibly by irrigating and fertilizing the sediment that stimulated the growth of microalgae and bacteria or by loosening up the sediment that eased burrowing and penetration. The abundance of sedentary species such as spionid polychaetes and some bivalves have been observed to be negatively correlated with abundance of Callianassid shrimps (e.g. Posey, 1986). The redistribution of organic matter within the sediment by effective bioturbating species, such as the deep burrowing mud shrimp Callianassa subterranea and the shallower burrowing Nephrops norvegicus, will influence depth distribution and community structure as well. However, the activities of the larger burrowers can either enhance or reduce the overall abundance of sediment macrofauna, depending on the species involved. Megafaunal activity creates a mosaic of disturbance patches which may be important to the maintenance of biodiversity in the sediment community (Hughes, 1998(b)). The presence and activity of Callianassa species has been shown to be linked to significant sediment and radioactive particulate resuspension (Roberts et al., 1981; Colin et al., 1986). Bioturbatory activities of deposit feeding genera such as Nucula and Pectinaria will also actively increase the rate of oxygen diffusion through finer sediments (Pearson & Rosenberg, 1978).
  • Where several species of burrowing megafauna occur together in the same biotope it is not unusual for burrows to interconnect. Tuck et al. (1994) found that 34% of Nephrops burrows at a site in Loch Sween showed evidence of interactions with other species, including Maxmuelleria lankesteri, Jaxea nocturna and Leseurigobius friesii. These interconnections are probably accidental and not indicative of any close symbiotic relationship between different burrowers. Such interconnections may improve ventilation and nutritional content of the burrows.
  • Mobile adults, such as Nephrops norvegicus and Callianassa subterranea, often show spacing out phenomena. Such behaviour is usually linked to territorial aggression (Gray, 1974).
  • The opening of the burrows of Callianassa subterranea provide temporary refuge for fish such as the black goby Gobius niger and Pomatoschistus minutus. Occasional errant polychaetes, particularly polynoid worms, inhabit the burrows (Nickell & Atkinson, 1995).
  • The burrowing and feeding activities of Amphiura filiformis, if present in high abundance, can modify the fabric and increase the mean particle size of the upper layers of the substrata by aggregation of fine particles into faecal pellets. Such actions create a more open fabric with a higher water content which affects the rigidity of the seabed (Rowden et al., 1998). Such destabilisation of the seabed can affect rates of particle resuspension.
  • The arms of Amphiura filiformis are an important food source for demersal fish and Nephrops norvegicus providing significant energy transfer to higher trophic levels including to humans. Increased nutrients and eutrophication processes may contribute to increase the accumulation of hydrophobic contaminants in Amphiura filiformis and their transfer to higher trophic levels (Gunnarsson & Skold, 1999).
  • In their investigation of density dependent migration in Amphiura filiformis Rosenberg et al. (1997) calculated that in areas of high density of the species (3000 individuals per m2), the area of sediment at about 3 to 4cm depth covered by disks of Amphiura filiformis can be estimated as 22%. The capacity of such a density of brittle stars to displace sediment can be calculated at 0.18m2 per hour. Thus, movement of Amphiura filiformis should generate a more or less continuous displacement of sediment and be of great significance to the biogeochemical processes in the sediment.
  • The hydrodynamic regime determines whether a biotope, such as CMU.SpMeg, exists in a particular place by allowing deposition of fine sediment. The hydrography also affects the water characteristics in terms of salinity, temperature and dissolved oxygen. It is also widely accepted that food availability (see Rosenberg, 1995) and disturbance, such as that created by storms, (see Hall, 1994) are also important factors determining the distribution of species in benthic habitats.

Seasonal and longer term change

  • Seapen and burrowing megafaunal communities appear to persist over long periods at the same location. Species such as the sea pen Virgularia mirabilis, the brittle star Amphiura filiformis and the mud shrimp Calocaris macandreae appear to be long-lived and are unlikely to show any significant seasonal changes in abundance or biomass. The numbers of some of the other species in the biotope may show peak abundances at certain times of the year due to seasonality of breeding and larval recruitment. Immature individuals of Liocarcinus depurator, for example, are more frequent in the periods May - September.
  • There are daily patterns of activity in some species. Nephrops norvegicus, for example, forages for food at night, returning to their burrows at sunrise. However, in deeper water (> 100m) this activity is reversed suggesting that activity is determined by light intensity. The echiuran Maxmuelleria lankesteri has been observed to feed only at night and so activity may also be related to light intensity. Movement of the sea pen Virgularia mirabilis in and out of the sediment may be influenced by tidal conditions (Hoare & Wilson, 1977).
  • Burrowing activity of the mud shrimp Callianassa subterranea in the North Sea appears to be seasonal (Rowden & Jones, 1997). Relatively little activity was observed in the period January - April, before a steady increase through spring and early summer, reaching a maximum in at the end of the summer and a decline in autumn and winter. In January, when bioturbatory activity was low the seabed appeared essentially flat and smooth, whilst in September the bed was littered with numerous mounds and depressions. Tunberg (1986) found that Upogebia deltaura remained inactive in the deepest parts of its burrow during the winter. Maxmuelleria lankesteri is active all year round but seem to show peaks of activity in December and April when the proportion of easily-degradable organic matter at the sediment surface is at its highest (Hughes, 1998b).
  • The behaviour of Nephrops norvegicus may be seasonal. In Loch Sween, Nephrops burrows were aggregated in groups during the late summer, which then broke up into a random distribution during the winter (Tuck et al., 1994). Such aggregations may result when burrow complexes formed when juvenile animals settle in pre-existing adult systems, then break up as the juveniles gradually extend their own burrows and lose contact with those of the adults.

Habitat structure and complexity

  • The biotope has little structural complexity above the sediment surface. Burrows and mounds of burrowing megafauna may form a prominent feature of the sediment surface with conspicuous populations of sea pens, typically Virgularia mirabilis and Pennatula phosphorea. However, apart from a couple of species of nudibranch the sea pens do not provide significant habitat for other fauna. Where present, the tube of the rare sea anemone Pachycerianthus multiplicatus, creates a habitat for attached species.
  • However, dense populations of burrowers create considerable structural complexity, below the surface, relative to sediments lacking these animals. For example, Callianassa subterranea creates complex burrow systems in sandy mud sediments. The burrows consist of a multi-branched network of tunnels connected to several inhalent shafts, each terminating in a funnel shaped opening to the surface. These burrows allow a much larger surface area of sediment to become oxygenated, and thus enhance the survival of a considerable variety of small species (Pearson & Rosenberg, 1978). Burrows also create habitats for other animals such as clams and polychaetes. Burrows are also created by other crustacean species such as Nephrops norvegicus and Calocaris macandreae although these are not as complex as those of Callianassa. The echiuran worm Maxmuelleria lankesteri produces long-lasting burrows that provide a habitat for a variety of small polychaetes and bivalves but none of these appear to be obligate relationships (Jones et al., 2000). In Scottish sea lochs the black goby Gobius niger will take up residence in burrows belonging to Maxmuelleria lankesteri and other species, frequently extending or changing the shape of the burrow opening. The squat lobster Munida rugosa is frequently found inhabiting burrows on the periphery of megafaunally-burrowed muds, close to coarser sediments. The sediment expelled by Callianassa subterranea forms unconsolidated volcano-like mounds, which significantly modify seabed surface topography (Rowden et al., 1998).
  • The bioturbatory activities of callianassids such as Callianassa subterranea has important consequences for the structural characteristics of the sediment. Many infauna are limited to the upper oxygenated layer, however others penetrate deeper in irrigated burrows or possess long siphons capable of transporting oxygenated water into the sediment, which may result in an oxygenated layer around their burrows.

Productivity

Productivity in subtidal sediments is often quite low. Macroalgae are absent from CMU.SpMeg and so productivity is mostly secondary, derived from detritus and organic material. However, some shallower sites can have an extensive growth of benthic diatoms in the summer. Allochthonous organic material is derived from anthropogenic activity (e.g. sewerage) and natural sources (e.g. plankton, detritus). Autochthonous organic material is formed by benthic microalgae (microphytobenthos e.g. diatoms and euglenoids) and heterotrophic micro-organism production. Organic material is degraded by micro-organisms and the nutrients are recycled. The high surface area of fine particles provides surface for microflora.

Recruitment processes

The reproductive biology of British sea pens has not been studied, but in other species, for instance Ptilosarcus guerneyi from Washington State in the USA, the eggs and sperm are released from the polyps and fertilization takes place externally. The free-swimming larvae do not feed and settle within seven days if a suitable substratum is available (Chia & Crawford, 1973). Thus, the limited data available from these other species would suggest a similar pattern of patchy recruitment, slow growth and long life-span. As is typical of decapod crustaceans the female thalassindean burrowers in the biotope carry fertilized eggs on the abdomen before hatching into planktonic larvae. The length of time the larvae spends in the plankton appears to vary between species. The larval stages of Nephrops norvegicus spend about 50 days in the plankton before settlement and it is thought to be about 28 days for Callianassa subterrranea. In Northumberland the life-history of Calocaris macandreae was found to be rather different. Animals produced eggs in January-February which hatched in September-October. Only about 100 eggs were produced in each batch and the large larvae had no free-swimming phase before settling. The larval stage of the echiuran Maxmuelleria lankesteri is completely unknown but the large, yolky eggs suggest that the planktonic stage is brief or absent. However, many of the species in the biotope appear to have planktonic larvae so recruitment to the biotope may often be from distant sources.

Time for community to reach maturity

There is very little known about community development for this biotope. Almost nothing is known about the life cycle and population dynamics of British sea pens, but data from other species suggest that they are likely to be long-lived and slow growing with patchy and intermittent recruitment. The burrowing decapods that characterise the biotope vary in their reproductive strategies and longevity. In the North Sea the life span of Callianassa subterranea appears to be 2-3 years (Rowden & Jones, 1994) and individuals become sexually mature in their first year. Time to sexual maturity is longer in Nephrops norvegicus, about 2.5 - 3 years, and for the very long-lived Calocaris macandreae individuals off the coast of Northumberland did not become sexually mature until five years of age, and produced only two or three batches of eggs in their lifetime. Although little is known of the life cycle of the echiuran worm Maxmuelleria lankesteri long term observations of populations in situ have provided no evidence of any major fluctuations in population size, and it has been suggested that the species is long-lived with stable populations and low recruitment rates. Many of the other species in the biotope, such as polychaetes and bivalves, are likely to reproduce annually, be shorter lived and reach maturity much more rapidly. Since most key species reproduce regularly but take a while to grow, recruitment will be rapid but it will take several years to reach maturity and so it will probably take at least five years for the overall community to reach maturity.

Additional information

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Preferences & Distribution

Recorded distribution in Britain and IrelandCMU.SpMeg, and the sub-biotope CMU.SpMeg.Fun are typical of the deep mud habitats of the Scottish sea lochs. The biotope CMU.SpMeg has been recorded in most of the Scottish sea lochs (Howson et al., 1994) and in the Shetland voes (Howson, 1988). It has also been observed in the north-eastern Irish Sea (Hughes & Atkinson, 1997) and in the deep offshore waters of the North Sea (Dyer et al., 1982).

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients Not relevant
Salinity
Physiographic
Biological Zone
Substratum
Tidal
Wave
Other preferences Muddy sediment

Additional Information

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

Additional information

Sensitivity reviewHow is sensitivity assessed?

Explanation

Sea pens characterise the biotope and the several sea pen species that are found within the biotope are represented by Virgularia mirabilis. Of the burrowing megafauna the burrowing crustaceans are probably the most important because they affect habitat complexity and bioturbation of the sediment and can influence the overall biotope species composition. The burrows of Callianassa subterranea, for example, allow a much larger surface area of sediment to become oxygenated, and thus enhance the survival of a considerable variety of small species (Pearson & Rosenberg, 1978). Brittle stars such as Amphiura filiformis can be present in large numbers. There are often scavengers in the biotope and although generally present in low numbers can be important to the biotope and are represented here by Liocarcinus depurator.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important functionalAmphiura filiformisA brittlestar
Key functionalCallianassa subterraneaBurrowing mud shrimp
Important functionalLiocarcinus depuratorHarbour crab
Important characterizingVirgularia mirabilisA sea pen

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Moderate Moderate Major decline High
Most species are infaunal or epifaunal and will be lost if the substratum is removed so the overall intolerance of the biotope is high. Although some of the mobile species in the biotope may be able to escape, most, such as the harbour swimming crab Liocarcinus depurator and the starfish Asterias rubens are not very fast moving and so are also likely to be removed. Nothing is known about the life cycle and population dynamics of British sea pens, but data from other species suggest that they are likely to be long-lived and slow growing with patchy and intermittent recruitment. The burrowing megafauna in the biotope vary in their longevity and reproductive strategies and some species do not reach sexual maturity for several years. Calocaris macandreae, for example, does not reproduce until five years old. Therefore, it seems likely that a community of sea pens and burrowing megafauna may take longer than five years to recover and so a recoverability rank of moderate is reported (see additional information).
Low Immediate Not sensitive No change High
The biotope will have low intolerance to smothering by 5 cm of sediment because most species are burrowing and live within the sediment anyway. The burrowing thalassindean crustaceans, the echiuran worm Maxmuelleria lankesteri, infaunal polychaetes, brittlestars and bivalves are not likely to be affected by smothering by 5 cm of sediment. There may be an energetic cost expended to either re-establish burrow openings or to move up through the sediment though this is not likely to be significant. The sea pens Virgularia mirabilis and Pennatula phosphorea are able to withdraw rapidly into the sediment and appear to be able to recover from smothering. Although the sea pen Funiculina quadrangularis is not able to withdraw into the sediment its height, up to 2m, means that it is unlikely to be affected by smothering of 5cm of sediment. Most animals will be able to reburrow or move up through the sediment within hours or days so recovery is set at immediate (see additional information). Intolerance to smothering by other factors such as oil may be higher.
Low Immediate Not sensitive No change Moderate
Most species in the biotope are burrowing infauna so will not be affected by an increase in suspended sediment. There may be possible clogging of the feeding organs of the suspension feeding sea pens although since these animals are able to self-clean this is not likely to be very energetically costly, particularly at the level of the benchmark. Some species may benefit from increased food supply if suspended sediment has a high organic content. However, since most species in the biotope have low intolerance to an increase in suspended sediment at the benchmark level an overall rank of low is also reported for the biotope. Overall species composition and richness is not expected to be affected. On return to normal, suspended sediment levels recovery will be immediate as affected species will be able to self-clean within a few days.
Low Moderate Moderate Major decline Moderate
A decrease in suspended sediment and siltation will reduce the flux of particulate material to the seabed. Since this includes organic matter the supply of food to the biotope would probably also be reduced. However, the benchmark is a reduction in suspended sediment of 100 mg/l for a month which is unlikely to have a significant effect on the biotope and would not alter species composition. Intolerance is therefore, assessed as low. On return to normal conditions, recovery will be rapid and a rank of very high is recorded.
Not relevant Not relevant Not relevant Not relevant High
The biotope only occurs in the circalittoral zone (below 15 m) and is not subject to desiccation.
Not relevant Not relevant Not relevant Not relevant High
The biotope only occurs in the circalittoral zone (below 15 m) and is not subject to emergence.
Not sensitive* High
The biotope only occurs in the circalittoral zone (below 15 m) and is not subject to emergence.
High High Moderate Minor decline Moderate
The biotope is found in areas of weak or very weak tidal streams and so is likely to be intolerant of increases in water flow. Strong tidal currents keep most of the organic particles in the sediment in suspension which can support suspension feeders even in low organic content sediments. The horizontal supply of small and light nutritious particles by resuspension and advective transport has been shown to influence the growth rate of suspension-feeding benthos (Dauwe, 1998). However, some suspension feeders in the biotope will be unable to feed if the water flow rate increases by two categories in the water flow scale (see benchmarks). The sea pen Virgularia mirabilis for example, will retract into the sediment at water currents speeds greater than 0.5m/s (i.e. 1 knot). If water speeds remain at this level or above, the sea-pen will be unable to extend above the sediment, unable to feed and will die. Increases in flow rate will change the surface layer of the sediment structure, removing the fine mud element to leave the coarser particles behind. A long term increase (i.e. the benchmark level of one year) will change the nature of the top layers of sediment, becoming coarser and possibly unsuitable for some shallow burrowing species such as the brittle stars Amphiura. Deeper burrowing species such as the thalassinidean crustaceans Callianassa subterranea and Nephrops norvegicus are not likely to be affected by sediment changes at the surface. The overall impact of an increase in water flow rate on the biotope may be the loss of some key species, such as sea pens, which changes the biotope, and some other species such as brittle stars and so intolerance is assessed as high. In slightly more energetic conditions and coarser sediment the biotope CMS.AfilEcor which includes Callianassa subterranea and sparse Virgularia mirabilis is more likely to be present. Recovery has been assessed as high (see additional information).
Not sensitive* High
The biotope exists in habitats where tidal streams are already very weak so a decrease in flow rate would result in almost non-moving water. Tidal currents keep most of the organic particles in the sediment in suspension which can support suspension feeders even in low organic content sediments. Therefore, if water movement becomes negligible suspended organic particles available to filter feeders such as the sea pens will decline. Growth and fecundity will be affected and over a period of a year may result in the death of sea pens. In enclosed or semi-enclosed water bodies, such as sea lochs, negligible water flow may result in some deoxygenation of the overlying water and the loss of some intolerant species. The sea pen Virgularia mirabilis for example, has high intolerance to deoxygenation and may die. However, other species such as Callianassa subterranea and many other thalassinidean crustaceans are tolerant of reduced oxygenation and are not likely to die. The overall impact on the biotope is likely to be the loss of a few key species such as sea pens and so intolerance is assessed as high. Recovery has been assessed as high (see additional information).
Intermediate High Low Minor decline Low
In shallow sea lochs, sedimentary biotopes typically experience seasonal changes in temperature of about 10 °C and so CMU.SpMeg may be tolerant of long term increases although growth and fecundity of some species may be affected. No information was found on the upper limit of sea pens tolerance to temperature increases. However, the distribution of the sea pens typically found in the biotope, Virgularia mirabilis, Pennatula phosphorea and Funiculina quadrangularis, extends south into the warmer waters of the Mediterranean suggesting they may be able to tolerate a long term increase in temperature of 2 °C. However, sea pens are subtidal animals where wide and rapid variations in temperature, such as experienced in the intertidal, are not so common and so may be more intolerant of a short term increase of 5 °C. The reported intolerance to changes in temperature for Virgularia mirabilis is intermediate. Since the loss of sea pens changes the biotope the intolerance of the biotope to increased temperature is also recorded as intermediate. For most deep burrowing species temperature changes in the water column are likely to be buffered to some extent by the sediment and so many individuals will not be affected. See additional information for details of recovery.
Intermediate High Low Minor decline Low
In shallow sea lochs, sedimentary biotopes typically experience seasonal changes in temperature of about 10 °C and so CMU.SpMeg may be tolerant of long term decreases although growth and fecundity of some species may be affected. No information was found on the lower limit of sea pens tolerance to temperature decreases. However, the distribution of the sea pens typically found in the biotope, Virgularia mirabilis, Pennatula phosphorea and Funiculina quadrangularis, extends into the northern North Atlantic where waters are colder than in the UK suggesting they may be able to tolerate a long term decrease in temperature of 2°C. However, sea pens and other species in the biotope are subtidal where wide and rapid variations in temperature, such as experienced in the intertidal, are not so common and so may be more intolerant of a short term decrease in temperature of 5°C. For most deep burrowing species temperature changes in the water column are likely to be buffered to some extent by the sediment and so many individuals will not be affected. During the very cold winter of 1962-63 a few dead Nephrops norvegicus were caught in the North Sea although the majority were caught alive (Crisp, 1964) therefore it seems likely that burrowing species will probably be not sensitive to the factor. Since one of the key faunal groups, the sea pens may be intolerant of a short term decrease and the viability of populations may be threatened the intolerance of the biotope to decreased temperature is recorded as intermediate. See additional information for details of recovery.
Low Very high Very Low No change Moderate
An increase in turbidity, reducing light availability may reduce primary production by phytoplankton in the water column. However, productivity in the CMU.SpMeg biotope is secondary (detritus) and is not likely to be significantly affected by changes in turbidity and so intolerance is assessed as low. In estuaries and surf zones on the lower shore turbidity can be measured in g/l so the benchmark level is low in comparison. Nevertheless, primary production by pelagic phytoplankton and microphytobenthos do contribute to benthic communities and so long term increases in turbidity may reduce the overall organic content of the detritus. Reduced food supply may affect growth rates and fecundity of some species in the biotope so intolerance is assessed as low. On return to normal turbidity levels recovery will be high as food availability returns to normal.
Low Very high Moderate No change Moderate
A decrease in turbidity, increasing light availability may increase primary production by phytoplankton in the water column. However, productivity in the CMU.SpMeg biotope is secondary (detritus) and is not likely to be significantly affected by changes in turbidity and so intolerance is assessed as low. In estuaries and surf zones on the lower shore turbidity can be measured in g/l so the benchmark level is low in comparison. Nevertheless, primary production by pelagic phytoplankton and microphytobenthos do contribute to benthic communities and long term decreases in turbidity may increase the overall organic input to the detritus. Increased food supply may increase growth rates and fecundity of some species in the biotope. Nephrops norvegicus avoid bright light and exposure to high intensities causes blindness (Loew, 1976) and so a decrease in light attenuation resulting from decreased turbidity may affect the depth at which the species is present or more likely that Nephrops will only feed at night. See additional information for details of recovery.
High Moderate Moderate Major decline Moderate
The biotope exists in areas with physically-sheltered conditions of low wave exposure and weak tidal currents. An increase in wave exposure is likely to change the composition of species present in the biotope because it is likely to disrupt feeding and burrowing and may also have an impact on reproduction and recruitment. An increase in the factor can also change the sediment characteristics which may result in a change in the proportion of suspension to deposit feeders within it. Sea pens, for example, may be unable to feed and may be damaged or broken by increased wave exposure. Virgularia mirabilis is able to withdraw into the sediment to avoid the factor but will be unable to feed if wave exposure increases are long term and will be likely to die. Coarser material is more difficult to burrow through, and organisms need to be robust the survive and so a major decline in the number of species able to inhabit the biotope is likely to result. Even very deep burrowing species like Callianassa subterranea are likely to be affected because increased wave exposure will probably disturb burrow openings and water flow through the burrows making feeding difficult. With the loss of key species, in particular the sea pens, the biotope will change so intolerance is assessed as high. See additional information for details of recovery.
Not sensitive* High
The biotope occurs in areas of very low or no wave exposure so a decrease is not relevant.
Tolerant Not relevant Not relevant Not relevant High
Some of the important characterizing species associated with this biotope, in particular the sea pens, may respond to sound vibrations and can withdraw into the sediment. Feeding will resume once the disturbing factor has passed. However, most of the species are infaunal and likely to be not sensitive to noise disturbance at the benchmark level. It is possible that predator avoidance behaviour in Liocarcinus depurator and other species may be triggered by noise vibrations although this has not been recorded. Therefore, unless predation pressure is reduced increased noise disturbance is not likely to have an impact on the nature and function of the biotope and a rank of not sensitive is recorded.
Tolerant Not relevant Not relevant Not relevant High
Most species within the biotope are burrowing and have no or poor visual perception and are unlikely to be affected by visual disturbance such as shading. Epifauna such as crabs have well developed visual acuity and are likely to respond to movement in order to avoid predators. However, it is unlikely that the species will be affected by visual disturbance at the benchmark level. The biotope is therefore, not sensitive to the factor.
Intermediate High Low Decline Moderate
The biotope is subject to physical disturbance because it supports a major fishery for one of its characteristic species, Nephrops norvegicus. Information on the effects of trawling on the other fauna in the biotope is limited but it is likely that the deep burrowing species such as the crustaceans Callianassa subterranea and Jaxea nocturna and the echiuran worm Maxmuelleria lankesteri and some burrowing fish will be little affected by this type of disturbance. Individual burrowing crustaceans may occasionally be displaced from burrow openings by towed gear (Atkinson, 1989). However, the animals will be able to re-establish burrow openings if these become blocked so recovery would be immediate.

Of the three sea pen species Funiculina quadrangularis is likely to be the most sensitive to abrasion and disturbance because it has a long brittle stalk and is unable to retract into the sediment. However, experimental studies have shown that all three species of seapen can re-anchor themselves in the sediment if dislodged by fishing gear (Eno et al., 1996). Eno et al. (1996) found that even if damaged Funiculina quadrangularis appeared to remain functional and this could also be true of the other sea pens. However, the apparent absence of Funiculina from open-coast Nephrops grounds may be a consequence of its susceptibility to trawl damage (D.W. Connor, pers. comm. in Hughes, 1998b).

In long term experimental trawling Tuck et al. (1998) found no effect on Virgularia mirabilis populations and Kinnear et al. (1996) found that sea pens were quite resilient to being smothered, dragged or uprooted by creels. The investigation by Tuck et al. (1998) examined the effects of extensive and repeated experimental trawl disturbance on whole benthic communities over an 18 month period in a Scottish loch that had previously been un-fished for 25 years. The subsequent patterns of recovery over a further 18 month period were also investigated. Trawling disturbance resulted in reduced species diversity and a disproportionate increase in the abundance of a few dominant species, in particular the opportunistic polychaetes Chaetozone setosa and Caulleriella zetlandica. Other species, also found in this biotope, that were observed to be sensitive include the bivalves Nucula nitidosa and Corbula gibba and the polychaetes Nephtys sp. and Terebellides stroemi. For epifaunal species, no long-term effects on the total number of species or individuals were detected, but individual species did show effects, notably an increase in the density of Ophiura sp. and a decrease in numbers of the fish Hippoglossoides platessoides and the whelk Buccinum undatum.

Other authors have also suggested that increases in echinoderm populations in the North Sea are associated with fishing disturbance (Aronson, 1990; Lindley et al., 1995).

Scavenging species such as Liocarcinus depurator, Pagurus bernhardus and Asterias rubens might be expected to benefit from fishing disturbance, through increased food availability. Kaiser & Spencer (1994) found that benthic disturbance by fishing gear caused an increase in the density of epifaunal scavengers, in response to an increase in food availability in the form of damaged and disturbed organisms. The long term effects on infauna were still noticeable after 18 months and short term effects on epifauna recovered 6 months after fishing ceased. During long term monitoring of fishing disturbance on the Northumberland coast Frid et al. (1999) observed a decrease in numbers of sedentary polychaetes, echinoid echinoderms and large (>5 cm) brittlestars. Observations of the effects of Nephrops trawl fishing in the Irish Sea led Ball et al. (2000a) to suggest that the bivalves Corbula gibba and Thyasira flexusa were sensitive to fishing disturbance.

Thus, it appears that abrasion and physical disturbance, such as that caused by fish trawling or scallop dredging, is likely to affect the species composition of the biotope and so intolerance is assessed as intermediate. Recovery is expected to be high (see additional information).

Low Immediate Not sensitive No change Moderate
Most species in the biotope are burrowing and have low intolerance to displacement, such as that caused by a passing trawl that does not kill species but throws them into suspension, because animals can reburrow into suitable substrata. Displaced individuals of Virgularia mirabilis, which are not damaged (see Abrasion above for damage), will re-burrow (Jones et al., 2000) and recover completely within 72 hours, provided the basal peduncle remains in contact with the sediment surface. Eno et al. (1996) found that even when damaged Funiculina quadrangularis appeared to remain functional. Recovery will be immediate because burrowing species can rapidly reburrow into the sediment, thereby avoiding predation. Full burrow construction for some species may take longer however.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
High Moderate Moderate Decline Low
There was no information found on the effect of chemical pollutants on the biotope, probably because burrowing megafauna are generally too difficult to sample to be included in standard pollution monitoring studies. However, effects on some of the individual species in the biotope have been reported. Dahllöf et al. (1999) studied the long term effects of tri-n-butyl-tin (TBT) on the function of a marine sediment system. TBT spiked sediment was added to a sediment that already had a TBT background level of approximately 27ng g-1 (83 pmol TBT g-1) and contained the following fauna: Amphiura spp., Brissopsis lyrifera, the bivalve Abra alba and several species of polychaete. Within two days of treatment with a TBT concentration above 13.7 µmol / m² all species except the polychaetes had crept up to the surface and after six weeks these fauna had started to decay. Thus, increased contamination from TBT is likely to result in the death of some intolerant species such as brittle stars and heart urchins. Bryan & Gibbs (1991) report that crabs appear to be relatively resistant to TBT although some deformity of regenerated limbs has been observed. However, arthropods are very intolerant of the insecticide carbaryl (1-napthol n-methyl carbamate; sold under the trade name Sevin®) which has been used to control burrowing shrimp in oyster farms (Feldman et al., 2000). There is no information available on the possible consequences of chemicals to British sea pens. Different species will be affected by different chemicals but a general trend in areas of increasing pollution is a reduction in species diversity with habitats becoming dominated by pollution tolerant polychaete worms. However, Ivermectin, an anti-louse treatment coming into use in the salmon fish farming industry, has been shown to be highly toxic to sediment dwelling polychaetes (Hughes, 1998b).

Overall the biotope has been recorded as highly intolerant to synthetic chemicals. Recovery is likely to take longer than five years and has been recorded as moderate (see additional information).

Heavy metal contamination
Intermediate High Low Decline High
In Norwegian fjords Rygg (1985) found a relationship between species diversity in benthic fauna communities and sediment concentrations of heavy metals Cu, Pb and Zn. Cu in particular showed a strong negative correlation and the author suggested a cause-effect relationship. Those species not present at sites where Cu concentrations were greater than ten times higher than the background level, such as Calocaris macandreae, Amphiura filiformis and several bivalves including Nucula sulcata and Thyasira equalis, were assessed as non-tolerant species. The tolerant species were all polychaete worms. Therefore, increased heavy metal contamination in sediments may change the faunal composition of the community and decrease overall species diversity and intolerance has been assessed intermediate. Some burrowing crustaceans, brittle stars and bivalves may disappear from the biotope and lead to an increasing dominance of polychaetes. There was no information found on the effect of heavy metals on sea pens. Recovery is likely to be high.
Hydrocarbon contamination
High Moderate Moderate Major decline High
There was no information found on the effect of hydrocarbon pollution on the biotope. The best documented oil spill for protected habitats with soft mud/sand substrates is the West Falmouth, Florida spill of 1969. Immediately after the spill virtually the entire benthic fauna was eradicated immediately following the incident and populations of the opportunistic polychaete Capitella capitata increased to abundances of over 200,000/m² (Sanders, 1978). Persistent toxicity of Amoco Cadiz oil in sediment prevented the start of the recovery period (Clark, 1997). Callinanassa subterranea appears to be highly intolerant of sediment contaminated by oil-based drilling muds (Daan et al., 1992). Oil from spills would have to be dispersed deep into the water column to affect the biotope and since the biotope occurs in very sheltered conditions this is unlikely to occur. However, should the sediment become contaminated with oil there is likely to be the loss of many species and so intolerance is assessed as high. Nothing is known about the life cycle and population dynamics of British sea pens, but data from other species suggest that they are likely to be long-lived and slow growing with patchy and intermittent recruitment. The burrowing megafauna in the biotope vary in their longevity and reproductive strategies and some species do not reach sexual maturity for several years. Calocaris macandreae, for example, does not reproduce until five years old. Therefore, it seems likely that a community of sea pens and burrowing megafauna may take longer than five years to recover and so a recoverability rank of moderate is reported.
Radionuclide contamination
Low High Low Minor decline Moderate
In an investigation of bioturbation in the north-eastern Irish Sea Hughes & Atkinson (1997) surveyed several sites close to the Sellafield nuclear reprocessing plant. At a station immediately offshore from the Sellafield outfall pipeline a community similar to the CMU.SpMeg biotope was present. Burrow openings and shafts indicated the presence of the burrowing crustaceans Callianassa subterranea, Goneplax rhomboides and Upogobia deltaura. Epifauna were abundant, particularly Ophiura ophiura and Asterias rubens. The sea pen Virgularia mirabilis occurred at high density. Dragonets and small gobies were also common. Other species in the biotope such as Nephrops norvegicus and the echiuran worm Maxmuelleria lankesteri were also present at sites close to the outfall pipeline. Thus, the biotope occurs in bottom sediments that contain particles of long half-life radionuclides derived from the liquid effluent released from the reprocessing plant at Sellafield and so intolerance is assessed as low. However, species diversity may be slightly reduced compared to unpolluted sites. Recovery is likely to take less than five years and has been recorded as high (see additional information).
Changes in nutrient levels
Intermediate High Low Minor decline Moderate
Most species in the biotope appear to tolerate sediments relatively high in organic content. In Loch Sween in Scotland, for example, where the organic content is about 5% and as high as 9% in some areas burrowing species such as the crustaceans Callianassa subterranea, Calocaris macandreae and Nephrops norvegicus and the echiuran worm Maxmuelleria lankesteri are present in high densities. Although absent from the most enriched areas the sea pen Virgularia mirabilis was present at organic contents of 4.5% (Atkinson, 1989). Very large increases in organic content can result in significant changes in community composition of sedimentary habitats and sometimes defaunation. Typically an increasing gradient of organic enrichment results in a decline in the suspension feeding fauna and an increase in the number of deposit feeders, in particular polychaete worms (Pearson & Rosenberg, 1978). For example, in areas under fish farm cages gross organic pollution has been observed to result in the loss of megafaunal burrowers. However, these changes generally refer to gross nutrient enrichment. At the level of the benchmark, a 50% increase in nutrients is likely to impact only the most intolerant species and may result in a reduction in the number of sea pens so intolerance is assessed as intermediate. A high recovery is expected (see additional information).
High Moderate Moderate Major decline Moderate
The biotope is found in fully marine conditions so is likely to be intolerant of increases in salinity. The overall effect on the biotope of a chronic decrease in salinity for a period of a year is likely to be the loss of most species and so intolerance is reported as high. Recovery is likely to take longer than five years and has been recorded as moderate (see additional information).
High Moderate Intermediate Major decline Moderate
The biotope is found in fully marine conditions and does not extend into estuaries so is likely to be intolerant of decreases in salinity. The key species are highly intolerant of salinity changes although Jones et al. (2000) suggest that Virgularia mirabilis appears to be somewhat tolerant of occasional lowering of salinity. However, the species is found only in fully marine environments and so is likely to be intolerant of a long term, chronic decrease; e.g., a change of one category from the MNCR salinity scale for one year. The overall effect on the biotope of a chronic decrease in salinity for a period of a year is likely to be the loss of most species and so intolerance is reported as high. Recovery is likely to take longer than five years and has been recorded as moderate (see additional information).
Low Immediate Not sensitive Minor decline Moderate
Large active animals with high respiratory demands will be most affected by oxygen depletion. In moderately hypoxic conditions (1mg l-1) Nephrops norvegicus compensates by increasing production of haemocyanin (Baden et al., 1990). In the laboratory this compensation lasted one week so at the level of the benchmark the species will not be killed. However, at levels of about 0.6 mg l-1 the species died within 4 days. Catches of Nephrops norvegicus have been observed to be high when oxygenation in the water is low, probably because animals are forced out their burrows. Thalassinidean mud-shrimps are very resistant to oxygen depletion and enriched sulphide levels. Callianassa subterranea, for example, often lives in hypoxic or even anoxic conditions. Virgularia mirabilis is often found in sea lochs so may be able to tolerate some reduction in oxygenation. However, Jones et al., (2000) found sea pen communities to be absent from areas which are deoxygenated and characterized by a distinctive bacterial community and Hoare & Wilson (1977) reported Virgularia mirabilis absent from sewage related anoxic areas of Holyhead harbour. Therefore, the benchmark level of 2 mg/l of oxygenation for one week will result in the death of only the most intolerant species and maybe some individual sea pens. The total loss of populations of the key is not likely to occur at the benchmark level and since the faunal composition of the overall biotope is unlikely to change to any great extent intolerance is assessed as low. On return to normal oxygenation recovery will be immediate as respiratory rates return to normal. However, recruitment of intolerant species that are killed will be required to return the biotope to pre-impact species diversity.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Intermediate High Low No change High
The only major disease causing organism found in the biotope is the dinoflagellate parasite, Hematodinium sp. found in Nephrops populations from the west of Scotland, Irish Sea and North Sea (Hughes, 1998b). The parasite occurs in the blood and connective tissue spaces and appears to cause death by blocking the delivery of oxygen to the host's tissues (Taylor et al., 1996). Infection is at its highest in the spring and early summer when a dense concentration of parasite cells in the blood give Nephrops an abnormal bright orange body and milky white ventral abdomen. Heavily infected animals become moribund, spend more time out of their burrows than healthy individuals making them more vulnerable to predation and fishing gear. Heavy infestation is fatal. The ecological consequences of Hematodinium infection and host mortality in Nephrops populations are unknown, but there are potential economic implications, since the disease adversely affects meat quality. Since the parasite can cause mortality of a species within the biotope intolerance is assessed as intermediate. However, so far the Nephrops fishery has not suffered any serious decline. The infection appears to be cyclical. In the Clyde Sea infection peaked in 1991-92 at 70% and had declined to 10 - 20% by 1996-7 so recovery appears to be possible within five years and so a rank of high is reported.
Tolerant Not relevant Not relevant Not relevant Moderate
There are no records of any non-native species invading the biotope and so is assessed as not sensitive. However, as several species have become established in British waters there is always the potential for new introduced non-native species to have an effect on the biotope.
Intermediate High Low Minor decline Moderate
Nephrops norvegicus is a characterizing species and Nephrops fisheries are of major economic importance. The species is fished throughout most of the geographic range of the biotopes in which it occurs including CMU.SpMeg. In trawled areas it is likely that the density of Nephrops norvegicus has been reduced but Hughes (1998b) reports that most stocks have the potential to recover even after heavy fishing pressure. Atkinson (1989) concluded that trawling for Nephrops was unlikely to affect other megafaunal burrowers to any great extent. The upper section of burrows will be disrupted by trawling but observations in Loch Sween have shown that surface openings are soon re-established (Hughes, 1998b). Some sea pens are likely to be uprooted by trawling activities although in observations of the impact of creeling activities all three British species proved able to re-anchor themselves provided the basal peduncle remained in contact with the sediment surface. Crabs such as Liocarcinus depurator are often extracted as a by-catch species in benthic trawling. A reduction in the density of predators may affect species abundance but is not likely to have a significant effect on overall species diversity. Removal of Nephrops norvegicus would probably not change the nature of the biotope because there are likely to be other megafaunal burrowers present. None of the key or important species in the biotope are targeted for collection or harvesting. An intolerance of intermediate has been suggested to reflect likely loss of Nephrops norvegicus. Recovery is likely to be high.
Intermediate High Low Minor decline Low

Additional information

Recoverability
There is very little known about community development for this biotope. Almost nothing is known about the life cycle and population dynamics of British sea pens, but data from other species suggest that they are likely to be long-lived and slow growing with patchy and intermittent recruitment. The burrowing decapods that characterise the biotope vary in their reproductive strategies and longevity. In the North Sea the life span of Callianassa subterranea appears to be 2-3 years (Rowden & Jones, 1994) and individuals become sexually mature in their first year. Time to sexual maturity is longer in Nephrops norvegicus, about 2.5 - 3 years, and for the very long-lived Calocaris macandreae individuals off the coast of Northumberland did not become sexually mature until five years of age, and produced only two or three batches of eggs in their lifetime. Although little is known of the life cycle of the echiuran worm Maxmuelleria lankesteri long term observations of populations in situ have provided no evidence of any major fluctuations in population size, and it has been suggested that the species is long-lived with stable populations and low recruitment rates. Many of the other species in the biotope, such as polychaetes and bivalves, are likely to reproduce annually, be shorter lived and reach maturity much more rapidly. Since most key species reproduce regularly but take a while to grow, recruitment will be rapid but it will take several years to reach maturity and so it will probably take at least five years for the overall community to reach maturity. Therefore, recovery will probably be moderate from factors to which the biotope is highly intolerant.

Importance review

Policy/Legislation

Habitats of Principal ImportanceMud habitats in deep water
Habitats of Conservation ImportanceMud habitats in deep water / Sea-pen and burrowing megafauna communities
UK Biodiversity Action Plan PriorityMud habitats in deep water
OSPAR Annex VSea-pen and burrowing megafauna communities
Priority Marine Features (Scotland)Burrowed mud

Exploitation

  • Nephrops norvegicus is the only species within the biotope that is of any commercial importance. Nephrops fisheries are of major economic importance and the species is fished throughout most of the geographic range of the biotopes in which it occurs including CMU.SpMeg. This includes both shallow, semi-enclosed sea loch areas, and open-coast grounds in deeper water such as the Irish and North Seas. In British waters the Nephrops fishery has grown rapidly since its inception in the 1950s. Nephrops is now one of the most valuable shellfish resources in the north-eastern Atlantic (Hughes, 1998b). None of the other species in the biotope are collected or harvested.
  • Thalassinidean shrimps such as Callianassa subterranea can be a pest of oyster fisheries. Oyster survival and growth is affected indirectly through sediment disturbance. As the shrimps burrow through the mud constructing their extensive burrows, sediment compaction is reduced to the point that oysters growing directly on the benthos sink into the unconsolidated mud and settling larvae and spat are particularly vulnerable (Feldman et al., 2000).

Additional information

EC Habitats Directive: Sea pen faunal communities can be found in some very sheltered examples of Annex 1 type Large shallow inlets and bays, and in Scandinavian fjords. UK Biodiversity Action Plan: Mud in deep water (Habitat Action Plan).

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Citation

This review can be cited as:

Hill, J.M. 2004. Seapens and burrowing megafauna in circalittoral fine mud. 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/131

Last Updated: 08/07/2004

Tags: Seapen sea pen sea-pen mud burrow spoon worm mud shrimp