The maerl beds of Brittany and of the Mediterranean have long been recognized as communities with a particularly high diversity of plant and animal species. In the British Isles, there may be somewhere in the range of 150 macroalgal species found on maerl (summary table), and 500 benthic faunal species (over 400 were found in Scotland alone; Scott & Moore, 1996; mollusc table). Numbers and identities of microflora and microfauna and protozoan and fungal species on maerl are almost entirely unknown. Attempts have been made to document as far as possible the entire flora and fauna of maerl beds within a given area. Hall-Spencer (unpublished) has produced a preliminary species list for the flora and fauna of the Clyde, while knowledge of animals and algae living on maerl on the west coast of Ireland has been accumulating for the last three decades (Keegan, 1974; Maggs, 1983a; Maggs & Guiry, 1987; O'Connor et al., 1993; O'Connor & McGrath, 1997).

Biodiversity of maerl beds has been examined in Europe and the British Isles in regard to:

• comparisons with other biotopes in the same geographical area;
• comparisons between maerl beds in different geographical areas;
• seasonal changes in biodiversity; and
• Local differences (e.g. proportion of live thalli).

Taxonomic considerations

Comparisons with other biotopes

Geographical comparisons between Maerl Beds

Seasonal and other temporal changes in biodiversity

Local variations in Maerl biotope biodiversity

Rare species and species confined to Maerl biotopes

References