Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand

Researched byAngus Jackson Refereed byDr Jason Hall-Spencer
EUNIS CodeA5.5112 EUNIS NamePhymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand

Summary

UK and Ireland classification

EUNIS 2008A5.5112Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand
EUNIS 2006A5.5112Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand
JNCC 2004SS.SMp.Mrl.Pcal.NmixPhymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand
1997 BiotopeSS.IGS.Mrl.Phy.HEcPhymatolithon calcareum maerl beds with hydroids and echinoderms in deeper infralittoral clean gravel or coarse sand

Description

Lower infralittoral maerl beds characterized by Phymatolithon calcareum in gravels and sand with a variety of associated hydroids and echinoderms. Hydroids present are typically erect colonies such as Nemertesia spp. and often occur on the maerl or attached to dead shells within the maerl. Echinoderms such as Antedon bifida, Ophiothrix fragilis, Ophiocomina nigra, Ophiura albida and Neopentadactyla mixta are occasional or frequent in IGS.Phy.HEc but do not often occur in IGS.Phy.R. Other, more ubiquitous echinoderms such as Marthasterias glacialis are found throughout IGS.Phy biotopes. (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

Present at locations within the photic zone all along the west coast of Scotland, including the Western Isles, Orkney, and Shetland. The biotope is almost certainly present round the Isle of Man. Localised occurrences in southern England. Also Strangford Lough in Northern Ireland. The biotope has not yet been officially recorded from Ireland but is expected to be widespread but patchily distributed around the south and west.

Depth range

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Additional information

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Listed By

Further information sources

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JNCC

Habitat review

Ecology

Ecological and functional relationships

The ecological relationships of maerl beds can be very complex. The maerl thalli provide considerable surface area to which both flora and fauna can attach. The maerl nodules themselves may be directly grazed by species like Tectura virginea. The surface film of microalgae and detritus can also be grazed. The loose structure permits water circulation and oxygenation to considerable depth. As a consequence of this loose structure, maerl provides shelter for an astonishing variety of fauna e.g. molluscs (Hall-Spencer, 1998) and amphipods (Grave De, 1999). The loose structure also permits animals to burrow to considerable depths (at least 60 cm) within the gravel.

Seasonal and longer term change

Cabioch (1969) suggested Phymatolithon calcareum may have phasic reproduction with peaks every six years. This may account for observed changes in the relative proportions of live Lithothamnion corallioides and Phymatolithon calcareum nodules in some maerl beds. Dominance cycles with periods of about thirty years have been recorded on some of the maerl beds of northern Brittany.

Habitat structure and complexity

The habitat of this biotope is extremely complex. The maerl nodules are frequently loose and mobile preventing colonization by many species. However, deep burrowing fauna (to 68 cm) are a notable feature of this biotope (Hall-Spencer & Atkinson, 1999). Some surveys record as few as 10 species in the biotope, primarily because the vast majority of species live below the maerl surface. Maerl in general is known as a particularly diverse habitat with over 150 macro algal species and 500 benthic faunal species recorded (Birkett et al., 1998(a)).

Productivity

Maerl beds may contain dead as well as live nodules. Productivity will depend on the relative proportions of dead and alive nodules. Primary productivity may be less than in maerl biotopes found in shallower waters (e.g. IGS.Phy.R) where there are more epiphytic algae. Secondary production may be very high in situations where there are dense aggregations of consumers. The sea cucumber Neopentadactyla mixta can reach densities of up to 400 per square metre in loose gravels such as maerl (Smith and Keegan, 1984).

Recruitment processes

Recruitment of Phymatolithon calcareum is mainly through vegetative propagation. Although spore bearing individuals of Phymatolithon calcareum thalli have been found in the British Isles, the crustose individuals that would result from sexual reproduction have yet to be recorded in the British Isles. Recruitment may occur from distant populations that exhibit sexual reproduction and have crustose individuals (e.g. Brittany). Hall-Spencer (pers. comm.) has observed that colonization of new locations by maerl can be mediated by a 'rafting' process where maerl thalli are bound up with other sessile organisms that are displaced and carried by currents (e.g. Saccharina latissima holdfasts after storms).

Time for community to reach maturity

Phymatolithon calcareum is extremely slow growing (c. 1mm per year) (Potin et al., 1990 and Birkett et al., 1998a). Development of a new maerl bed would take a long time. Maerl beds are also extremely long lived with life-span of the habitat being 6000 years or more (Birkett et al., 1998a) Within the biotope, the community is dependent on the growth of a surface veneer of photosynthetically active maerl thalli.

Additional information

Although Phymatolithon calcareum has a patchy distribution around the British Isles, it is the most widespread maerl-forming species in European waters (BIOMAERL team, 1999). "Maerl is a 'living sediment'; it is slow to recover from disturbance due to infrequent recruitment and extremely slow growth rates (Hall-Spencer & Moore, 2000(a))". Although from outward appearances suspension feeders may appear to be dominant, Grall & Glemarec (1997) found that dominant trophic groups varied according to the assessment criteria used. In terms of species richness carnivores were most dominant, for abundance it was detritivores and for biomass it was surface deposit feeders. Detrital input is important in enclosed areas such as the Firth of Clyde and the Fal estuary.

Preferences & Distribution

Recorded distribution in Britain and IrelandPresent at locations within the photic zone all along the west coast of Scotland, including the Western Isles, Orkney, and Shetland. The biotope is almost certainly present round the Isle of Man. Localised occurrences in southern England. Also Strangford Lough in Northern Ireland. The biotope has not yet been officially recorded from Ireland but is expected to be widespread but patchily distributed around the south and west.

Habitat preferences

Depth Range
Water clarity preferences
Limiting Nutrients Calcium
Salinity
Physiographic
Biological Zone
Substratum
Tidal
Wave
Other preferences See additional information.

Additional Information

Growth of Phymatolithon calcareum ceases at 5 degrees C and is optimal at 15 degrees C (typically higher than water temperatures found around the British Isles). Growth of Phymatolithon calcareum is impaired at salinities below 24 psu (King & Schramm, 1976) so the species is absent from areas with variable or reduced salinity. Distribution of maerl is dependent on several factors. Living maerl has poor tolerance of desiccation and so is typically found subtidally (Hall-Spencer, 1998). As a photosynthesising organism there is a requirement for light which restricts the species to depths shallower than 32m in the relatively turbid waters of northern Europe (Hall-Spencer, 1998). Some shelter from wave action is required to prevent physical damage, dispersal or burial although some degree of water movement is important to ensure that silt does not smother the maerl bed. King & Schramm, (1982) report that ionic calcium concentration is the main factor affecting growth of maerl in culture experiments rather than salinity per se (although this has not been shown in the field). Uptake of calcium carbonate occurs optimally at 30 psu.

Species composition

Species found especially in this biotope

  • Cruoria cruoriaeformis
  • Gelidiella calcicola
  • Gelidium maggsiae
  • Halymenia latifolia
  • Scinaia turgida
  • Tectura virginea

Rare or scarce species associated with this biotope

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Additional information

  • Maerl biotopes are well recognised as having particularly rich and diverse communities. The MNCR survey recorded a maximum of 88 species but the BIOMAERL team (1999) recorded a maximum species richness of 490 at one Scottish site. From maerl biotopes in general, over 150 macroalgal species and 500 benthic faunal species have been recorded (Birkett et al., 1998a).
  • Species richness can vary considerably in maerl beds, even within the same geographical area. There are also seasonal changes in species richness although this applies particularly to epiphytic algae.
  • Maerl beds that are or have been dredged for scallops have modified species compositions, reduced species richness and abundance (Hall-Spencer & Moore, 2000).
  • There are several species of algae that are apparently restricted to calcareous habitats and may be characteristically found in maerl beds (e.g. Halymenia latifolia, Scinaia turgida, Gelidiella calcicola, Gelidium maggsiae & Cruoria cruoriaeformis)(Birkett et al., 1998(a)). Since the biotope occurs in deeper waters, then the number of algal species present will be reduced in comparison to other biotopes such as IGS.Phy.R.
  • Tectura virginea can be considered to be associated with maerl although is most common on encrusting coralline algal species. There are several species of mollusc that are common in maerl beds (e.g. Gibbula cineraria, Rissoa interrupta, Modiolarca tumida, Hinia incrassata, Tricolia pullus & Hiatella arctica) but these are also common in other habitats and probably either reflect the nature of the substratum or are widespread in lower shore and sublittoral environments
  • Neither the MNCR surveys (JNCC, 1999) nor Birkett et al., 1998(a) specifically record any species recorded from maerl beds as being rare or scarce. However, this is likely to be caused by non-recognition or under-recording of rare or scarce species.

Sensitivity reviewHow is sensitivity assessed?

Explanation

The biotope IGS.Phy.Hec occurs at greater depths than other maerl biotopes and consequently has fewer algal species. The community within the maerl bed is dominated by infaunal molluscs (Hall-Spencer & Atkinson, 1998) although hydroids and echinoderms may be the most apparent on the surface. The biotope is partly named after these more obvious groups of organisms (hydroids and echinoderms). Two species typical of the biotope that represent these groups are Nemertesia ramosa and Neopentadactyla mixta and these species have been selected to represent the sensitivity of their relevant group. N.B. These two species are often but not necessarily always present in this biotope. Other similar species may be present in addition to or in place of these two species. In order to try and give an idea of the sensitivity of the biotope, Nemertesia ramosa and Neopentadactyla mixta have been used as species indicative of sensitivity for these obvious groups. Even if these species are not present or other species within the group (e.g. Nemertesia antennina, Ophiothrix fragilis are more faithful or abundant, the sensitivity assessments can give a broad impression of the sensitivity of the biotope. In undertaking an assessment of sensitivity of this biotope, account is taken of knowledge of the biology of all characterizing species in the biotope. However, the selected 'indicative species' are particularly important in undertaking the assessment because they have been subject to detailed research.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important characterizingNemertesia ramosaA hydroid
Important characterizingNeopentadactyla mixtaGravel sea cucumber
Key structuralPhymatolithon calcareumMaerl

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Very low / none Very High Major decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is highly intolerant of substratum loss. Other obvious characterizing species in the biotope such as (Neopentadactyla mixta and Nemertesia ramosa) are also likely to be highly intolerant of substratum loss as will the more abundant but less obvious infaunal species. Phymatolithon calcareum has a very low recoverability from substratum loss. Loss of the substratum as well as the structural and characterizing species in the biotope will probably result in a major decline in species richness for the area.
High Very low / none Very High Major decline High
Phymatolithon calcareum is the key structural species within the biotope and is highly intolerant of smothering. Scallop dredging is one of the main causes of smothering in maerl beds. A single passage of a dredge may bury and kill 70 percent of living maerl in their path. Phymatolithon calcareum has a very low recoverability from smothering. The loose and complex consistency of this biotope provides considerable structural diversity utilized by a wide range of species. Smothering of the main structural species, Phymatolithon calcareum, will probably result in a major decline in species richness for the area
High Very low / none Very High Decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is highly intolerant of changes in siltation. Phymatolithon calcareum has a very low recoverability from changes in siltation. Many of the species in this biotope live between the maerl nodules. Some of these species will benefit whilst others will decline due to changes in siltation and subsequent changes in granulometry of the habitat.
High Very low / none Very High Major decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is highly intolerant of desiccation. Phymatolithon calcareum has a very low recoverability from desiccation. Most of the species associated with this deeper water maerl biotope are intolerant of desiccation. Exposure to desiccating influences for an hour is likely to cause many species to die.
High Very low / none Very High Major decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is highly intolerant of changes in emergence regime. Phymatolithon calcareum has a very low recoverability from changes in emergence regime.
High Moderate Moderate Minor decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is intermediately intolerant of decreases in water flow rate. Neopentadactyla mixta, a species that has been chosen as representative of the intolerance of the echinoderms in the biotope (although not necessarily always present itself), is highly intolerant of changes in water flow rate. Phymatolithon calcareum has a moderate recoverability from changes in water flow rate. Many of the species in this biotope live within the structure provided by Phymatolithon calcareum, where there is protection from changes in water flow rate.
Intermediate Moderate Moderate Decline High
Phymatolithon calcareum is the key structural species within the biotope and is intermediately intolerant of changes in temperature This maerl species dies below 2 degrees C and above 22 degrees C. Neopentadactyla mixta, a species that has been chosen as representative of the intolerance of the echinoderms in the biotope (although not necessarily always present itself), is also intermediately intolerant. Phymatolithon calcareum has a moderate recoverability from changes in temperature. This biotope potentially contains a wide variety of species, only some of which will be intolerant of changes in temperature.
Intermediate Very low / none High Minor decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is intermediately intolerant of changes in turbidity. Being photosynthetic, this species is reliant on light availability. Consequently, increases in turbidity drastically reduce the lower depth limits of this species. It occurs to 105 m depth off Malta, to 32 m depth off western Ireland and to 18 m in the Clyde. Phymatolithon calcareum has a moderate recoverability from changes in turbidity. This biotope contains fewer algal species than other maerl biotopes. Faunal species tend to be less intolerant of changes in water clarity.
High Moderate Moderate Decline Moderate
Phymatolithon calcareum is the key structural species within the biotope and is likely to be intermediately intolerant of changes in wave exposure. Strong wave action can cause live maerl thalli to be buried, broken into smaller pieces or dispersed. Neopentadactyla mixta, a species that has been chosen as representative of the intolerance of the echinoderms in the biotope (although not necessarily always present itself), is highly intolerant of changes in wave exposure. Both Phymatolithon calcareum and Neopentadactyla mixta have moderate recoverability from changes in wave exposure. Maerl biotopes can be highly mobile making it difficult for many species to establish themselves, increases in wave exposure may increase this mobility.
Low Very high Very Low No change Moderate
Neopentadactyla mixta, a species that has been chosen as representative of the intolerance of the echinoderms in the biotope (although not necessarily always present itself), shows low intolerance to disturbance by noise. Few benthic species are highly intolerant of noise disturbance.
Tolerant Not relevant Not relevant No change High
None of the key or important species in this biotope are sensitive to visual disturbance. It is unlikely that any of the infaunal and epifaunal species associated with this biotope are sensitive to visual disturbance.
High Very low / none Very High Major decline Moderate
In experimental studies, Hall-Spencer & Moore (2000a, c) reported that the passage of a single scallop dredge through a maerl bed could bury and kill 70% of living maerl in its path. The passing dredge also re-suspended sand and silt that settled over a wide area (up to 15 m from the dredged track), and smothered the living maerl. Evidence from historic specimens of Phymatolithon calcareum collected between 1885 and 1891, before the onset of scallop fishing, showed that specimens collected from a scallop dredged area were smaller than those collected in the late 19th century (Hall-Spencer & Moore, 2000a, c). Abrasion may break up maerl nodules into smaller pieces resulting in easier displacement by wave action. Abrasion may also disrupt the physical integrity of accreted maerl beds. The dredge left a ca 2.5 m track and damaged or removed most megafauna within the top 10 cm of maerl. The tracks remained visible for up to 2.5 years. In pristine beds experimental scallop dredging reduced the population densities of epibenthic species for over 4 years, while the maerl species themselves may take decades to recover. In previously dredged maerl beds, the benthic communities recovered in 1-2 years. Maerl habitats are dependant on survival of slow-growing algae e.g. Phymatolithon calcareumand other maerl species, which cannot withstand prolonged burial, due to the lack of light, and die (Hall-Spencer & Moore, 2000a, c). Hall-Spencer & Moore, (2000a, c) concluded that maerl beds were particularly sensitive to the impacts of towed fishing gears. Boat moorings and dragging anchor chains have been noted to damage the surface of maerl beds, as has demersal fishing gear. Therefore, intolerance has been assessed as high.

However, megafauna on or in the top 10 cm of maerl were either removed or damaged and left on the dredge tracks, susceptible to subsequent predation (Hall-Spencer & Moore, 2000a). For example; crabs, Ensis species, the bivalve Laevicardium crassum, and sea urchins. Deep burrowing species such as the sea anemone Cerianthus lloydii and the crustacean Upogebia deltaura were protected by depth, although torn tubes of Cerianthus lloydii were present in the scallop dredge tracks (Hall-Spencer & Moore, 2000a). Neopentadactyla mixta may also escape damage due to the depth of its burrow, especially during winter torpor.

Hall-Spencer & Moore, (2000a) reported that sessile epifauna or shallow infauna such as Modiolus modiolus or Limaria hians, sponges and the anemone Metridium senile where present, were significantly reduced in abundance in dredged areas for 4 years post-dredging. Other epifaunal species, such as hydroids (e.g. Nemertesia species) and red seaweeds are likely to be removed by a passing dredge.

Overall, the key structural species, Phymatolithon calcareum, is recorded as being highly intolerant of physical disturbance, and an overall biotope intolerance of high has been recorded. Propagation of Phymatolithon calcareum in the British Isles is almost entirely vegetative so recruitment of new individuals to the population will not aid recovery. The very slow growth rate of Phymatolithon calcareum means that vegetative regeneration will take a long time. Therefore, recoverability has been assessed as very low.

High Moderate Moderate Minor decline Low
The important characterizing species Nemertesia ramosa a species selected as being representative of the intolerance of hydroids (although not necessarily always present itself), is highly intolerant of and has a moderate recoverability from displacement. Many of the species in the biotope have an active, infaunal burying habit. Displacement of the key or important species in the biotope is not likely to cause many of the other species living within the biotope to die.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information No information No information Insufficient
information
Not relevant
Insufficient
information is available about the key and important species in this biotope to be able to make an assessment of intolerance to synthetic chemical contamination.
Heavy metal contamination
No information No information No information Insufficient
information
Not relevant
Insufficient
information is available about the key and important species in this biotope to be able to make an assessment of intolerance to heavy metal contamination.
Hydrocarbon contamination
No information No information No information Insufficient
information
Not relevant
Insufficient
information is available about the key and important species in this biotope to be able to make an assessment of intolerance to hydrocarbon contamination.
Radionuclide contamination
No information No information No information Insufficient
information
Not relevant
Insufficient
information is available about the key and important species in this biotope to be able to make an assessment of intolerance to radionuclide contamination.
Changes in nutrient levels
Low Very high Very Low No change Low
The key structural species (Phymatolithon calcareum) in this biotope has a low intolerance to changes in nutrient concentration. King & Schramm, (1982) report that ionic calcium concentration is the main factor affecting growth of maerl in culture experiments rather than salinity per se (although this has not been shown in the field). Uptake of calcium carbonate occurs optimally at 30 psu. Increases in nutrient concentration can indirectly cause intermediate or high intolerance through smothering by fast growing algae that block light and cause anoxia (e.g. Rade de Brest, France, J. Hall-Spencer pers. comm.) This aspect is better covered under smothering.
High Very low / none Very High Major decline Low
The key structural species, Phymatolithon calcareum, has a high intolerance to decreases in salinity (King & Schramm, 1976). Neopentadactyla mixta, a species selected as being representative of the intolerance of echinoderms in the biotope (although not necessarily always present itself) is also highly intolerant of decreases in salinity (Smith 1983). Phymatolithon calcareum has a very low recoverability from changes in salinity. This biotope is found deeper than shallow waters where salinity reductions from freshwater run-off occur. The biotope occurs in the more open parts of inlets where open coast salinity waters prevail. Changes from full salinity will probably cause a major decline in species richness.
High Very low / none Very High Major decline Low
The important characterizing species Nemertesia ramosa is intermediately intolerant of and has a high recoverability from changes in oxygenation. Anoxia will kill live maerl (J. Hall-Spencer, pers. comm.). The loose structure of the maerl bed allows oxygenation to occur to considerable depth and this fact is exploited by many burrowing species. Changes in oxygenation are likely to cause a major decline in species richness.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
Intermediate Moderate Moderate Minor decline Moderate
The key structural species of this biotope (Phymatolithon calcareum) has intermediate intolerance to the introduction of microbial pathogens. This refers to the potential effects of the western pacific disease 'coralline lethal orange disease'. Phymatolithon calcareum has a moderate recoverability from disease. This disease is specific to coralline algae and will not affect other taxa.
Intermediate No information High Decline Moderate
The introduced species Crepidula fornicata has radically altered the ecology of maerl beds in the Rade de Brest, France through increasing siltation and provision of substrata (J. Hall-Spencer pers. comm.).
High Very low / none Very High Major decline High
Phymatolithon calcareum, the only key structuring species for the biotope, is subject to commercial extraction although it is highly unlikely that either of the important characterizing species (Nemertesia ramosa or Neopentadactyla mixta) would be. The actual removal of Phymatolithon calcareum (usually by dredging) would also result in the removal of many other species associated with the biotope. Maerl beds are dredged to extract scallops and other molluscs which causes considerable structural damage. Dredging causes loss of sessile species such as Limaria hians and Modiolus modiolus and this can alter the stability and structural properties of the bed (Hall-Spencer & Moore, 2000(a)). These two species support their own suite of encrusting and epilithic species which will also be lost (see Physical Disturbance for further details). Limaria hians remains at significantly reduced levels for at least 4 years so recoverability will be moderate or worse (Hall-Spencer & Moore, 2000(a)). In experimental studies, Hall-Spencer & Moore (2000a, c) reported that the passage of a single scallop dredge through a maerl bed could bury and kill 70% of living maerl in its path. The passing dredge also re-suspended sand and silt that settled over a wide area (up to 15 m from the dredged track), and smothered the living maerl. Evidence from historic specimens of Phymatolithon calcareum collected between 1885 and 1891, before the onset of scallop fishing, showed that specimens collected from a scallop dredged area were smaller than those collected in the late 19th century (Hall-Spencer & Moore, 2000a, c). The dredging may break up maerl nodules into smaller pieces resulting in easier displacement by wave action. Furthermore, the physical integrity of accreted maerl beds may be disrupted. The dredge left a ca 2.5 m track and damaged or removed most megafauna within the top 10 cm of maerl. The tracks remained visible for up to 2.5 years. In pristine beds experimental scallop dredging reduced the population densities of epibenthic species for over 4 years, while the maerl species themselves may take decades to recover. In previously dredged maerl beds, the benthic communities recovered in 1-2 years. Maerl habitats are dependant on survival of slow-growing algae e.g. Phymatolithon calcareumand other maerl species, which cannot withstand prolonged burial, due to the lack of light, and die (Hall-Spencer & Moore, 2000a, c). Hall-Spencer & Moore, (2000a, c) concluded that maerl beds were particularly sensitive to the impacts of towed fishing gears and, therefore, intolerance has been assessed as high.

Propagation of Phymatolithon calcareum in the British Isles is almost entirely vegetative so recruitment of new individuals to the population will not aid recovery. The very slow growth rate of Phymatolithon calcareum means that vegetative regeneration will take a long time. Therefore, recoverability has been assessed as very low.

Intermediate Moderate Moderate Decline High

Additional information

No text entered

Importance review

Policy/Legislation

Habitats of Principal ImportanceMaerl beds
Habitats of Conservation ImportanceMaerl beds
Habitats Directive Annex 1Sandbanks which are slightly covered by sea water all the time
UK Biodiversity Action Plan PriorityMaerl beds
OSPAR Annex VMaerl beds
Priority Marine Features (Scotland)Maerl beds

Exploitation

Maerl is mainly sold dried as a soil additive but is also used in animal feed, water filtration systems, pharmaceuticals, cosmetics and bone surgery. Maerl beds are dredged for scallops (found in high densities compared with other scallop habitats) where extraction efficiency is very high. This harvesting has serious detrimental effects on the diversity, species richness and abundance of maerl beds (BIOMAERL team, 1999).

Additional information

Maerl extraction from the Fal estuary and from Wyre Sound in Orkney is regulated by quota.

Maerl beds are included within the marine habitat 'sand banks which are slightly covered by seawater at all times' listed in Annex I of the EC Habitats Directive. Phymatolithon calcareum, the key structural species of the biotope is included within Annex V(b) of the EC Habitats Directive. Annex V(b) indicates plant species that are of community interest whose taking in the wild and exploitation may be subject to management measures. This species is also on the UK Biodiversity Action Plan long list.

Bibliography

  1. Adey, W.H. & McKibbin, D.L., 1970. Studies on the maerl species Phymatolithon calcareum (Pallas) nov. comb. and Lithothamnion corallioides (Crouan) in the Ria de Vigo. Botanica Marina, 13, 100-106.
  2. Anonymous, 1999q. Maerl beds. Habitat Action Plan. In UK Biodiversity Group. Tranche 2 Action Plans. English Nature for the UK Biodiversity Group, Peterborough., English Nature for the UK Biodiversity Group, Peterborough.
  3. BIOMAERL team, 1999. Biomaerl: maerl biodiversity; functional structure and anthropogenic impacts. EC Contract no. MAS3-CT95-0020, 973 pp.
  4. Birkett, D.A., Maggs, C.A. & Dring, M.J., 1998a. Maerl. an overview of dynamic and sensitivity characteristics for conservation management of marine SACs. Natura 2000 report prepared by Scottish Association of Marine Science (SAMS) for the UK Marine SACs Project., Scottish Association for Marine Science. (UK Marine SACs Project, vol V.)., http://www.ukmarinesac.org.uk/publications.htm

  5. Bosence, D.W.J., 1979. Live and dead faunas from coralline algal gravels, Co. Galway. Palaeontology, 22, 449-478.
  6. Cabioch, J., 1969. Les fonds de maerl de la baie de Morlaix et leur peuplement vegetale. Cahiers de Biologie Marine, 10, 139-161.
  7. Donnan, D.W. & Davies, J., 1996. Assessing the Natural Heritage Importance of Scotland's Maerl Resource. In Partnership in Coastal Zone Management, (ed. J. Taussik & J. Mitchel), 533-540.
  8. Gili, J-M. & Hughes, R.G., 1995. The ecology of marine benthic hydroids. Oceanography and Marine Biology: an Annual Review, 33, 351-426.
  9. Grall, J. & Glemarec, J., 1997. Biodiversity des fonds de maerl en Bretagne: approche fonctionelle et impacts anthropiques. Vie et Milieu, 47, 339-349.
  10. Grave De, S. & Whitaker, A., 1999a. Benthic community re-adjustment following dredging of a muddy-maerl matrix. Marine Pollution Bulletin, 38, 102-8
  11. Grave De, S., 1999. The influence of sediment heterogeneity on within maerl bed differences in infaunal crustacean community. Estuarine, Coastal and Shelf Science, 49, 153-163.
  12. Grave De, S., & Whitaker, A., 1999b. A census of maerl beds in Irish waters. Aquatic Conservation: Marine and Freshwater Ecosystems, 9, 303-311.
  13. Hall-Spencer, J.M. & Atkinson, R.J.A., 1999. Upogebia deltaura (Crustacea: Thalassinidea) in Clyde Sea maerl beds, Scotland. Journal of the Marine Biological Association of the United Kingdom, 79, 871-880.
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Citation

This review can be cited as:

Jackson, A. 2006. Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand. 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/64

Last Updated: 26/04/2006