Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel

26-04-2006
Researched byAngus Jackson Refereed byThis information is not refereed.
EUNIS CodeA5.512 EUNIS NameLithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel

Summary

UK and Ireland classification

EUNIS 2008A5.512Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel
EUNIS 2006A5.512Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel
JNCC 2004SS.SMp.Mrl.LglaLithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel
1997 BiotopeSS.IGS.Mrl.LglaLithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel

Description

Upper infralittoral tide-swept channels of coarse sediment subject to variable or reduced salinity which support distinctive beds of Lithothamnion glaciale maerl 'rhodoliths'. Phymatolithon calcareum may also be present as a more minor maerl component. This biotope can often be found at the upper end of Scottish sea lochs where the variable salinity of the habitat may not be immediately obvious. Associated fauna and flora may include species found in other types of maerl beds (and elsewhere), e.g. Chaetopterus variopedatus, Lanice conchilega, Mya truncata, Plocamium cartilagineum and Phycodrys rubens. IGS.Lgla, however, also has a fauna that reflects the slightly reduced salinity conditions, e.g. Psammechinus miliaris is often present in high numbers along with other grazers such as chitons and Tectura spp. Hyas araneus, Ophiothrix fragilis and Henricia oculata are also fairly typically present at sites. In Scottish lagoons (obs) this biotope may show considerable variation but the community falls within the broad description defined here. (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

The distribution of Lithothamnion glaciale extends to the southern British Isles and is most abundant off the western coast of Scotland, Orkney and the Shetland Isles. This biotope has been recorded in only a few locations on the west coast of Scotland and in the Shetland Isles.

Depth range

0-5 m, 5-10 m

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 by animals such as Psammechinus miliaris. The loose structure permits water circulation and oxygenation to considerable depth. As a consequence of this loose structure, maerl provides shelter for a wide 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

Seasonal changes in the biotope potentially include variations in the amount of ephemeral algae growing on and over the maerl. Temperature controls the development of reproductive conceptacles in Lithothamnion glaciale (Adey, 1970).

Habitat structure and complexity

Habitat complexity is bought about by the branching nature of the maerl and the open spaces between nodules that occur. However, the maerl nodules are frequently loose and mobile preventing colonization by many species. In some instances, the branched nodules can also interlock creating a more stable environment. Species such as Saccharina latissima and Lanice conchilega may also help to bind the maerl together. The highly branching nature of the maerl thalli permits oxygenation and circulation of water deep within the sediment. This is exploited by many burrowing animals and deep burrowing (to 68 cm) fauna are a notable feature of maerl beds (Hall-Spencer & Atkinson, 1999). Most surveys under-record the 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 live nodules. In the British Isles this biotope tends to occur in shallow waters down to 10 metres in depth where algal primary productivity may be boosted by the occurrence of epiphytic algae. Some maerl beds may have very high faunal densities and in these, secondary production may be very high.

Recruitment processes

The main recruitment mechanism of Lithothamnion glaciale is uncertain. Individual plants have reproductive conceptacles (whether sexual or asexual is unclear) during the winter months and are sterile in summer (Hall-Spencer, 1994 cited in Birkett et al., 1998). Recruitment may occur via planktonic dispersal of sexual or asexual propagules. Vegetative growth and division of maerl nodules also forms a propagation mechanism in the biotope. In fact, in the British Isles this may be the only form of propagation in the species Phymatolithon calcareum (also a minor component of this biotope) and Lithothamnion corallioides. 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 (studied as Laminaria saccharina) holdfasts after storms). Of the other species typically found in this biotope , Psammechinus miliaris is highly fecund with relatively long lived planktonic larva that may disperse and colonize from long distances. Ophiothrix fragilis also has a long-lived planktonic larva that can disperse over distance.

Time for community to reach maturity

Lithothamnium glaciale is very slow growing (although faster than other maerl species (Irvine & Chamberlain, 1994). Individual plants are estimated to live from between 10-50 years (Adey, 1970) and would need a long period for populations to expand into a 'bed'. Development into a thick bed with the associated interstices and open structure important for the development of the associated community would take even longer. Maerl beds are known to be extremely long lived with life-span of the habitat being 6000 years or more (Birkett et al., 1998(a)). Within the biotope, the community is dependent on the growth of a surface veneer of photosynthetically active maerl thalli.

Additional information

Outward appearances of the biotope may be misleading with respect to dominant trophic groups. Grall & Glémarec (1997) found that dominant trophic groups in maerl beds varied according to the assessment criteria used. In terms of species richness, carnivores were most dominant, while detritivores were the most abundant and surface deposit feeders had the highest biomass.

Preferences & Distribution

Recorded distribution in Britain and IrelandThe distribution of Lithothamnion glaciale extends to the southern British Isles and is most abundant off the western coast of Scotland, Orkney and the Shetland Isles. This biotope has been recorded in only a few locations on the west coast of Scotland and in the Shetland Isles.

Habitat preferences

Depth Range 0-5 m, 5-10 m
Water clarity preferencesPoor clarity / Extreme turbidity, Very high clarity / Very low turbidity, Medium clarity / Medium turbidity, No preference, High clarity / Low turbidity, No information found
Limiting Nutrients Calcium
Salinity Variable (18-40 psu)
Physiographic
Biological Zone Infralittoral
Substratum Maerl, Coarse sediments, Gravel / shingle
Tidal Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.)
Wave Extremely sheltered, Sheltered, Very sheltered
Other preferences

Additional Information

Growth of Lithothamnion glaciale is maximal at 10-12 °C (Adey, 1970). Growth of Lithothamnion glaciale is impaired at reduced salinities (Adey, 1970). 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 photosynthetic organism there is a requirement for light which restricts the species to depths shallower than 32 m 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
  • Halymenia latifolia
  • Scinaia turgida
  • Tectura virginea

Rare or scarce species associated with this biotope

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Additional information

  • Maerl biotopes are recognised as having particularly rich and diverse communities.
  • The BIOMAERL team (1999) recorded a maximum species richness of 490 from a maerl bed at one Scottish site. From maerl biotopes in general, over 150 macroalgal species and 500 benthic faunal species have been recorded (Birkett et al., 1998(a)).
  • Species richness can vary considerably in maerl beds, even within the same geographical area. There are also potential 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, 2000a).
  • 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., 1998a). These species are found in maerl beds in general, whether or not they are found in conditions of reduced salinity is uncertain.Tectura virginea can be considered to be associated with maerl although it 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 and 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.(1998a) specifically record any species recorded from maerl beds as being rare or scarce. However, this is likely to be caused by under-recording or difficulties of identification of rare or scarce species.

Sensitivity reviewHow is sensitivity assessed?

Explanation

The biotope is named after the key structural species Lithothamnion glaciale. Two other species have been selected as being representative of this biotope (Ophiothrix fragilis, and Psammechinus miliaris ). Ophiothrix fragilis has a potentially important functional role in the biotope as a suspension feeder. Benthic suspension feeders such as Ophiothrix fragilis can occur in very high densities and can have a dominant role in the main nutrient exchanges in estuarine and coastal ecosystems (Dame, 1993 cited in Smaal, 1994; Lefebvre & Davoult, 1997). Suspension feeders are important in coastal ecosystems because they can remove large amounts of suspended particulate matter (Davoult & Gounin, 1995). Psammechinus miliaris is an active grazing omnivore that may have a functional role in modifying densities of other species. N.B. These three 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. Even if the three selected species are not present, or other similar species 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
Key structuralLithothamnion glacialeMaerl
Important functionalOphiothrix fragilisCommon brittlestar
Important functionalPsammechinus miliarisGreen sea urchin

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Very low / none Very High Major decline High
Lithothamnion glaciale is the key structural species within the biotope and is highly intolerant of substratum loss. The selected important, functional or characterizing species in the biotope such as (Ophiothrix fragilis, Psammechinus miliaris and Hyas araneus) are also likely to be highly intolerant of substratum loss, as will the many abundant but less obvious infaunal species. Lithothamnion glaciale has a very low recoverability from substratum loss. Without this species the biotope would not exist. The species selected as representative of biotope intolerance (e.g. Ophiothrix fragilis, Psammechinus miliaris) are likely to return within a few years given the presence of a suitable substratum. Loss of the substratum as well as the structural, functional and characterizing species in the biotope will result in a major decline in species richness for the biotope. Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. J. 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 (studied as Laminaria saccharina) holdfasts after storms). Growth and development of unattached maerl thalli from crustose individuals is very slow and likely to take a long time.
High Very low / none Very High Major decline High
Lithothamnion glaciale is the key structural species within the biotope and is highly intolerant of smothering. The selected important, functional or characterizing species in the biotope such as Ophiothrix fragilis, Psammechinus miliaris and Hyas araneus are also likely to be highly intolerant of smothering as will the many, abundant but less obvious infaunal species. Lithothamnion glaciale has a very low recoverability from smothering. Without this species the biotope would cease to exist and so intolerance is set to high. Loss of the substratum as well as the structural, functional and characterizing species in the biotope will result in a major decline in species richness for the biotope.
Intermediate Low High Decline High
Lithothamnion glaciale is the key structural species within the biotope and is likely to be intolerant of increases in suspended sediment due to restriction of photosynthesis (Birkett et al., 1998) - see section on turbidity below. Recoverability for this key structural species is recorded as very low. Many of the species in this biotope live between the maerl nodules. Some of these species may benefit by increases in siltation (e.g. suspension feeders, species that use particles in construction (e.g. Lanice conchilega) whilst others will decline due to subsequent changes in granulometry of the habitat. Decreases in siltation may have the reverse effects.
High Very low / none Very High Major decline High
Maerl species such as Lithothamnion glaciale are highly intolerant of desiccation (Birkett et al., 1998). As the key structural species within the biotope, loss of this species will mean the biotope ceases to exist. Recoverability of Lithothamnion glaciale from total loss is very low. Many of the species associated with maerl biotopes (always subtidal) are likely to be intolerant of desiccation. Although some of the species selected as being representative of the biotope are also found in the intertidal, they are typically found sheltering under boulders or weed (e.g. Psammechinus miliaris and Ophiothrix fragilis). Exposure to desiccating influences for an hour is likely to cause many species to die. See additional information for recovery.
High Very low / none Very High Major decline High
Maerl species such as Lithothamnion glaciale are highly intolerant of desiccation, a consequence of emersion (Birkett et al., 1998). As the key structural species within the biotope, loss of this species will mean the biotope ceases to exist. Recoverability of Lithothamnion glaciale from total loss is very low. Although some species associated with this biotope are also found in the intertidal, live maerl beds are entirely sub-tidal (with one exception, Birkett et al., (1998)). Species in sub-tidal biotopes will tend to be intolerant of emergence. See additional information below for recovery.
Intermediate Low High Decline Moderate
Lithothamnion glaciale is the key structural species within the biotope and is intermediately intolerant of decreases in water flow rate. Lithothamnion glaciale has a low recoverability from changes in water flow rate. Many of the species in this biotope live within the structure provided by the maerl nodules, where there is protection from changes in water flow rate. Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. Vegetative propagation by growth and division of unattached maerl thalli is very slow and likely to take a considerable time.
Intermediate Low High Minor decline Low
Lithothamnion glacialeis a northern species so may be intolerant of increases in temperature. Adey (1970) found optimal growth rates at between 10-12 °C. Development of reproductive conceptacles in Lithothamnion glaciale requires winter temperatures of between 1-5 °C (Adey, 1970). Long term chronic increases in temperature may prevent sexual or asexual reproduction from occurring. Other species selected as being representative of the intolerance of the biotope (Psammechinus miliaris and Ophiothrix fragilis) also have intermediate intolerance to short term acute changes in temperature. Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. Vegetative propagation by growth and division of unattached maerl thalli is very slow and likely to take a considerable time.
Low Very high Very Low Decline Moderate
Depth distribution of photosynthesising coralline algae is strongly affected by available light. The low clarity of coastal waters of the British Isles restricts the distribution of maerl beds to shallow waters - typically less than 10 m but occasionally down to around 30 m. An increase in turbidity would reduce photosynthesis but is unlikely to result in mortality, the maerl regaining photosynthetic vigour immediately after water clarity returned to previous conditions. Decreases in turbidity would facilitate photosynthesis and benefit the biotope. Faunal species tend to be less directly intolerant of changes in water clarity although reductions in light penetration may restrict the amount of food (phytoplankton) available to suspension feeders such as Ophiothrix fragilis. See additional information for recovery.
Intermediate Very low / none High Decline Moderate
Maerl beds with loose-lying nodules are restricted to less wave exposed areas (e.g. sea lochs for Lithothamnion glaciale beds). Some wave action may be beneficial in creating the 'streaming water' flow that this biotope requires. Strong wave action can break up the nodules into smaller pieces and scatter them from the maerl bed. Wave action during storms can be very important in determining the loss rates of thalli from maerl beds (Birkett et al., 1998). Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. Vegetative propagation by growth and division of unattached maerl thalli is very slow and likely to take a considerable time.
Tolerant Not relevant Not relevant No change High
Noise vibrations may possibly elicit escape responses in Ophiothrix fragilis (mechanical disturbance causes predator avoidance behaviour) but this will not have any effect on the biotope as a whole.
Tolerant Not relevant Not relevant No change High
None of the selected key or important species in this biotope are intolerant of visual disturbance. It is also 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 High
Abrasion and physical disturbance may break up loose-lying maerl nodules or highly branching crustose plants into smaller pieces resulting in easier displacement by wave action. Abrasion may also disrupt the physical integrity of accreted maerl beds. Boat moorings and dragging anchor chains have been noted to damage the surface of maerl beds, as has demersal fishing gear (BIOMAERL team, 1999). Hall-Spencer & Moore (2000a, c) reported that a single pass of a scallop dredge could bury and kill 70% of the living maerl (usually found at the surface), redistributed coarse sediment and affected the associated community. Dredge tracks remained visible for 2.5 years. Hall-Spencer & Moore (2000a, c) suggested that repeated anchorage could create impacts similar to towed fishing gear. Overall, Hall-Spencer & Moore (2000a, c) concluded that maerl beds were particularly vulnerable to damage from scallop dredging activities.

Other species in the biotope, including those selected as being representative of the sensitivity of the biotope also have intermediate intolerance to abrasion (e.g. the brittle test of Psammechinus miliaris and the fragile arms of Ophiothrix fragilis are easily damaged by impact). Many of the species in the biotope live buried within the maerl bed and will receive some protection from abrasion. 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, 200a). 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). Hall-Spencer & Moore, (2000a) reported that sessile epifauna 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.

Overall, an intolerance of high has been recorded. See additional information for recovery.

Tolerant Not relevant Not relevant No change Low
Lithothamnion glaciale nodules in maerl beds are unattached and generally loose-lying (although may be interlinked and bound together by other species). 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
High High Moderate Decline Very low
There is insufficient information available to assess the intolerance of Lithothamnion glaciale to synthetic chemical contamination. However, red algae are known to be sensitive to contamination (for instance Hoare & Hiscock, 1974). Other species in the biotope such as Psammechinus miliaris and Ophiothrix fragilis are likely to highly intolerant of this factor. Contamination by synthetic chemicals will probably reduce the species diversity within the maerl beds resulting in at least intermediate intolerance. Many of the infaunal species in maerl beds are molluscs which tend to have high intolerance to chemical contamination. Overall, an intolerance of high is recorded by with very low confidence.
Heavy metal contamination
No information Not relevant No information Not relevant Not relevant
There is insufficient information available to assess the intolerance of Lithothamnion glaciale to synthetic chemical contamination. Some species in the biotope such as Psammechinus miliaris are recorded as highly intolerant of heavy metal contamination.
Hydrocarbon contamination
Intermediate High Low Decline Very low
There is insufficient information available to assess the intolerance of Lithothamnion glaciale to hydrocarbon contamination. However, red algae are known to be sensitive to oil spills. For example, Crump et al. (1999) describe "dramatic and extensive bleaching" of 'Lithothamnia' following the Sea Empress oil spill. Other species in the biotope such as Psammechinus miliaris and Ophiothrix fragilis are likely to highly intolerant of this factor. Many of the infaunal species in maerl beds are molluscs which tend to have high intolerance to hydrocarbons. For recovery see additional information below.
Radionuclide contamination
No information No information No information Insufficient
information
Not relevant
Insufficient
information
Changes in nutrient levels
Intermediate Low High Decline Low
Cabioch (1969) has suggested that maerl is tolerant to increases in nutrients. However, in shallower waters, growth of ephemeral algae may be increased, smothering the maerl beds and restricting photosynthesis. 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). Reductions in calcium concentration may theoretically limit growth of maerl nodules. Reductions in nutrient availability may also limit growth of phytoplankton or algal species which are fed on by Ophiothrix fragilis and Psammechinus miliaris respectively.
Low High Low Minor decline Low
Unlike Lithothamnion corallioides and Phymatolithon calcareum, Lithothamnion glaciale is tolerant to some variation in salinity. The biotope is found at the head of sea lochs on the west coast of Scotland where riverine in-put and precipitation run-off cause variable salinity. Growth rates are decreased by reduced salinity (Adey, 1970).
Intermediate Moderate Moderate Major decline Very low
Anoxia will kill live maerl (Jason Hall-Spencer, pers. comm.) but reduced oxygen levels for a week are unlikely to kill the algal nodules. Respiration, growth and reproduction may be affected by hypoxia. 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 Very low / none High Decline Low
No diseases of European maerl species are known. However, the bacterial pathogen 'coralline lethal orange disease' from the Pacific is highly virulent (Littler & Littler, 1985). If this species was introduced to the region then maerl beds could potentially be significantly affected.
Intermediate Very low / none 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.). If this alien species was to extend its distribution to overlap with Lithothamnion glaciale maerl beds, similar alterations may occur.
High Very low / none Very High Major decline Moderate
Maerl beds, of which Lithothamnion glaciale can form an important component, particularly in Scotland, may be subject to exploitation (Flora Celtica Database, 2000). Harvesting of maerl beds is one of the greatest threats. In England only dead maerl is extracted. However, even this can have detrimental effects, resuspending sediments that resettle and cover the algae reducing photosynthesis. In live beds the living nodules are typically on the surface so these are the first to be removed. Lithothamnion glaciale can also be adversely affected indirectly through the removal of other species. Extraction of other organisms such as scallops using dredges can cause great damage through physical disruption, crushing, burial and the loss of stabilizing algae (Hall-Spencer & Moore, 2000(a)). Other large burrowing bivalves such as Ensis sp. and Venerupis sp. are harvested using suction dredging which causes structural damage and resuspends sediment that resettles, covering the algae and reducing photosynthesis (Hall-Spencer & Moore, 2000(a)). These effects are best addressed using the relevant physical factors (see Physical Disturbance) but overall, intolerance has been assessed as high. Recovery is expected to be very low (see additional information).
High Very low / none Very High Major decline High

Additional information

Recoverability
Little information is available regarding sexual and asexual recruitment mechanisms in Lithothamnion glaciale. J. 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 (studied as Laminaria saccharina) holdfasts after storms). Growth and development of unattached maerl thalli from crustose individuals is very slow and likely to take in the order of several decades for a bed to form.

Most of the intolerance assessments are based mainly on Lithothamnion glaciale as this is the key structural species in the biotope. Other species selected to represent the biotope intolerance are not necessarily always present and do not represent particular taxa or groups that feature in the biotope.

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

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Bibliography

  1. Adey, W.H., 1970. The effects of light and temperature on growth rates in boreal-subarctic crustose corallines. Journal of Phycology, 6, 269-276.
  2. BIOMAERL team, 1999. Biomaerl: maerl biodiversity; functional structure and anthropogenic impacts. EC Contract no. MAS3-CT95-0020, 973 pp.
  3. 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
  4. Cabioch, J., 1969. Les fonds de maerl de la baie de Morlaix et leur peuplement vegetale. Cahiers de Biologie Marine, 10, 139-161.
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  6. Davoult, D., & Gounin, F., 1995. Suspension feeding activity of a dense Ophiothrix fragilis (Abildgaard) population at the water-sediment interface: Time coupling of food availability and feeding behaviour of the species. Estuarine, Coastal and Shelf Science, 41, 567-577.
  7. Flora Celtica Database, 2000. Flora Celtic Database.[on-line] http://www.rbge.org.uk/research/celtica/dbase/searchform.html, 2001-05-03
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  9. 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.
  10. 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. Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel. 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/7

Last Updated: 26/04/2006