Phymatolithon calcareum

Researched By	Angus Jackson	Data Supplied By	MarLIN
Refereed by	Dr Christine Maggs
Taxonomy
Scientific name	Phymatolithon calcareum	Common name	Maerl
MCS Code	ZM255	Recent Synonyms	None
Phylum	Rhodophycota	Subphylum
Superclass		Class	Rhodophyceae
Subclass	Florideophycidae	Order	Corallinales
Suborder		Family	Corallinaceae
Genus	Phymatolithon	Species	calcareum
Subspecies
Additional Information	Maerl 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 form	Algal gravel	Feeding method	Photoautotroph
Mobility/Movement	See additional information	Environmental position	Epifloral
Typical food types	Not relevant	Habit	Bed forming
Bioturbator	Not relevant	Flexibility	None (< 10 degrees)
Fragility	Fragile	Size	Small-medium(3-10cm)
Height	Insufficient information	Growth Rate	1-2 mm/year
Adult dispersal potential	10-100m	Dependency	Independent
Sociability	Gregarious
Toxic/Poisonous?	No
Additional Information	Mobility 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 & Ireland	Recorded 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 distribution	From Norway down to northern Spain. Includes the western Baltic and the Mediterranean
Biogeographic range	Not researched	Depth range	1-30m
Migratory	Not relevant
Distribution Additional Information	Most 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 preferences	Pebbles, Gravel / shingle, Maerl, Muddy gravel, Coarse clean sand, Fine clean sand, Sandy mud, Muddy sand, Mud, Mixed	Physiographic preferences	Open coast, Strait / sound, Sealoch, Ria / Voe, Estuary
Biological zone	Sublittoral Fringe, Upper Infralittoral, Lower Infralittoral	Wave exposure	Moderately Exposed, Sheltered
Tidal stream strength/Water flow	Strong (3-6 kn), Moderately Strong (1-3 kn)	Salinity	Full (30-40 psu)
Habitat 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 type	Vegetative	Developmental mechanism	Insufficient information
Reproductive Season	Insufficient information	Reproductive Location	Insufficient information
Reproductive frequency	Insufficient information	Regeneration potential	No
Life span	51-100 years	Age at reproductive maturity	Not relevant
Generation time	Insufficient information	Fecundity	Insufficient information
Egg/propagule size	Insufficient information	Fertilization type	Insufficient information
Larvae/Juveniles Larval/Juvenile dispersal potential <10m Larval settlement period Insufficient information Duration of larval stage Insufficient information
Additional Information	Recruitment 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)