Maerl-forming species in European waters (Irvine & Chamberlain, 1994; J. Hall-Spencer, pers. comm.).

See Appendix for further details.


Geographical range within Europe

Major maerl-forming species
Lithothamnion corallioides (P. & H. Crouan) P. & H. Crouan Forms maerl from Ireland and the southern British Isles to the Mediterranean
Lithothamnion glaciale Kjellman Forms maerl from Arctic Russia, N. Norway and W. Baltic to northern British Isles
Phymatolithon calcareum (Pallas) W. Adey & McKibbin Forms maerl from S. Norway and W. Baltic to the Mediterranean
Minor maerl-forming species
Corallina officinalis L. Attached thalli from Mediterranean to Norway (Finnmark); records as maerl in Brittany, Scotland and Norway
Lithophyllum dentatum (Kützing) Foslie Species status and limits uncertain; records from Ireland
Lithophyllum racemus (Lamarck) Foslie

(including British records of L. duckeri Woelkerling)

Limits uncertain; now thought to be a Mediterranean endemic with erroneous records from S. England and Ireland
Lithophyllum fasciculatum (Lamarck) Foslie Ireland, UK and Brittany
Lithophyllum hibernicum Foslie Species status uncertain; Ireland
Lithothamnion lemoineae Adey Distribution unclear; encrusting plants reported from Northumberland but known as maerl only from Orkney
Lithothamnion sonderi Hauck Encrusting thalli from Mediterranean to W. Baltic and Norway (Nordland) but reported as maerl only in Scotland
Phymatolithon purpureum (P. & H. Crouan) Woelkerling & L. Irvine Encrusting thalli from Arctic Russia, N. Norway and W. Baltic to S. Spain; records as maerl in Brittany, Scotland and Norway

Notes (by J. Hall-Spencer) on the distribution of Maerl species, supplementary to the table

Numerous encrusting species of non-geniculate Corallinaceae can continue to grow from pieces that break off the attached part of the thallus. I have done this in aquaria with Mesophyllum lichenoides, which is a southern species in the UK but is common as part of Mediterranean maerl beds. It is likely that the number of species that contribute to maerl deposits around the UK is greater than that listed in Table 1.

Free-living Lithophyllum spp. form a minor component of many maerl beds on Atlantic coasts of Europe and can be common in the Mediterranean. The taxonomic status of Lithophyllum specimens is confused and hampered by a lack of fertile material. Old names refer to the overall shape of specimens which can be as much a product of the environment in which they grew as a reflection of their taxonomic status. For example, Lemoine (1913) and Irvine & Chamberlain (1994) suggest that L. dentatum could be a free-living form of L. incrustans Phillippi which is a common encrusting species reported from the Mediterranean to Trondheimsfjord in Norway. Basso et al. (1996) found that Lithophyllum duckeri Woelkerling (listed as part of the British flora in Irvine & Chamberlain, 1994) should be considered conspecific with Lithophyllum racemus which has nomenclatural priority. Irvine & Chamberlain (1994) recorded one UK specimen that was similar to descriptions of Lithophyllum duckeri Woelkerling but suggested that it could also be a free-living form of L. incrustans based on the internal structure of its conceptacles. Thus the European range of Lithophyllum racemus (= duckeri in Irvine & Chamberlain, 1994) is uncertain, and Basso et al. (1996) consider it to be a Mediterranean endemic. The validity of >Lithophyllum hibernicum' is also uncertain as it is only known from three records of sterile specimens made in Galway in the 19th century.