This Natural England research report introduces a new national categorisation system for maerl habitats in England.
Whilst there are several definitions of maerl beds and habitats (e.g. Marine Habitat Classification system, MHC), there is currently no categorisation system and some records of maerl may therefore be lost during the survey and analysis stages, or not recorded at all.
Maerl is the common and collective term used for several free-living, unattached coralline red algae species (Riosmena-Rodriguez et al., 2016) including Phymatolithon calcareum, Lithothamnion corallioides, Lithothamnion glaciale and Lithophyllum fasciculatum
A maerl habitat categorisation system will help classifying different maerl bed habitats, better inform analysts of habitat maps, aid assessments during field work (for Seasearch, commercial entities and government agency scientists) and improve the analysis and reporting processes.
A categorisation system is particularly important to identify the various maerl bed habitats to improve distribution and mapping data but also allow further consideration around the differing sensitivities and therefore levels of protection and management needed by different maerl habitats along the English coastline.
The main factors being considered when developing a categorising system include physical size, percentage cover, the live versus dead maerl ratio and the physical structure (3D versus 2D).
Considering the large variation in condition and size of maerl bed habitats in England, five main categories have been created with specific terms for each: Dense Maerl, Maerl Sediment, Sparse Maerl, Maerl Veneer and Potential Maerl. Within these five categories, one, two or three groups have also been created for each category.