BIOTIC Species Information for Phymatolithon calcareum
Researched byAngus Jackson Data supplied byMarLIN
Refereed byDr Christine Maggs
Scientific namePhymatolithon calcareum Common nameMaerl
MCS CodeZM255 Recent SynonymsNone

PhylumRhodophycota Subphylum
Superclass ClassRhodophyceae
SubclassFlorideophycidae OrderCorallinales
Suborder FamilyCorallinaceae
GenusPhymatolithon Speciescalcareum

Additional InformationMaerl is a generic name for certain coralline algae that grow unattached on the sea bed. No crustose plants of Phymatolithon calcareum have been recorded from the British Isles.
Taxonomy References Howson & Picton, 1997, Campbell, 1994, Irvine & Chamberlain, 1994, Adey & McKibbin, 1970, Birkett et al., 1998(a),
General Biology
Growth formAlgal gravel
Feeding methodPhotoautotroph
Mobility/MovementSee additional information
Environmental positionEpifloral
Typical food typesNot relevant HabitBed forming
BioturbatorNot relevant FlexibilityNone (< 10 degrees)
FragilityFragile SizeSmall-medium(3-10cm)
HeightInsufficient information Growth Rate1-2 mm/year
Adult dispersal potential10-100m DependencyIndependent
General Biology Additional InformationMobility is recorded as not relevant here since Phymatolithon calcareum does not fall into the available categories. It does have a crustose permanently attached form but this has not been recorded in the British Isles. It is typically found as an unattached plant. Coralline algal thalli that form maerl beds have been found in densities of up to 22,000 thalli per square metre. The proportion of live to dead nodules varies considerably. As far as is known maerl continues to grow throughout its life but fragmentation limits the size of the nodules. There are no sexes and individual plants may reach up to 5 cm across. Maerl beds are highly species rich with 150 macroalgal species and over five hundred faunal species (of which 120 are molluscs) recorded as living on or in maerl beds (Birkett et al., 1998(a)); see the maerl biotope £IGS.Phy.HEc£ for further information. As far as is known, the maerl does not host any commensal or parasitic species. However, a few algae are almost entirely restricted to maerl communities e.g. the red algae Gelidiella calcicola, Gelidium maggsiae and the crustose Cruoria cruoriaeformis (Birkett et al., 1998(a)).
Biology References Adey & McKibbin, 1970, Donnan & Davies, 1996, Birkett et al., 1998(a), Potin et al., 1990, Grall & Glémarec, 1997, Hall-Spencer & Moore, 2000a,
Distribution and Habitat
Distribution in Britain & IrelandRecorded around the Shetland Orkney Islands and along the east coast of Scotland, south coast of England with isolated records at Bideford Bay, Pembrokeshire and Caernarfon Bay. Abundant around the west coasts of Ireland and Scotland
Global distributionFrom Norway down to northern Spain. Includes the western Baltic and the Mediterranean
Biogeographic rangeNot researched Depth range1-30m
MigratoryNot relevant   
Distribution Additional InformationMost frequent at depths between 1-10 m. May be found deeper in clear waters, e.g. found at depths of up to 30 m in outer Galway Bay.
%Phymatolithon calcareum% has been reported recently from 13-20m off Swange to Old Harry and off Bembridge, the Isle of Wight (Collins pers. comm.; Collins et al., 1990).

Substratum preferencesPebbles
Gravel / shingle
Muddy gravel
Coarse clean sand
Fine clean sand
Sandy mud
Muddy sand
Physiographic preferencesOpen coast
Strait / sound
Ria / Voe
Biological zoneSublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Wave exposureModerately Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Campbell, 1994, Irvine & Chamberlain, 1994, Donnan & Davies, 1996, Birkett et al., 1998(a), Grall & Glémarec, 1997, Hall-Spencer & Moore, 2000a, Veale et al., 1999, Collins et al., 1990, Hardy & Guiry, 2003, Hardy & Guiry, 2003,
Reproduction/Life History
Reproductive typeVegetative
Developmental mechanismInsufficient information
Reproductive SeasonInsufficient information Reproductive LocationInsufficient information
Reproductive frequencyInsufficient information Regeneration potential No
Life span51-100 years Age at reproductive maturityNot relevant
Generation timeInsufficient information FecundityInsufficient information
Egg/propagule sizeInsufficient information Fertilization typeInsufficient information
Larval/Juvenile dispersal potential<10m Larval settlement periodInsufficient information
Duration of larval stageInsufficient information   
Reproduction Preferences Additional InformationRecruitment in France is believed to be primarily through fragmentation from crustose forms. No crustose forms are known from the British Isles so propagation must be virtually entirely vegetative. Maerl beds in the Sound of Iona are recorded as containing dead nodules up to 4,000 years old (Farrow, 1983, cited in Maggs et al., 1998). Insufficient information is available on reproductive frequency, fecundity and developmental mechanism. In the British Isles there are a few records of fertile plants but no records of the crustose forms that this reproduction would produce. Plants may be fertile and develop conceptacles throughout the year. Plants from Brittany are mostly fertile in winter. Cabioch (1969) suggested that 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 maerl beds. Dominance cycles with periods of about thirty years have been recorded on some of the maerl beds of northern Brittany. Adey & McKibbon (1970) undertook growth studies of Phymatolithon calcareum in the field and under laboratory conditions. Their results for field studies in the Ria de Vigo, expressed as µ/day, show that growth occurs predominantly in the summer and suggests an annual growth of about 0.55 mm/year for branch tips of Phymatolithon calcareum according to Maggs et al. (1998).
Reproduction References Irvine & Chamberlain, 1994, Birkett et al., 1998(a), Cabioch, 1969, Franz et al. 2000, Halfar et al., 2000, Farrow (1983),
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