The relevance of maerl to the MNCR biotope classification

Relevance to MNCR biotope classification

Introduction

There are at present nine biotopes or sub-biotopes with maerl listed in the MNCR habitat classification (Connor et al., 1997), as follows:

Code	Description
IGS.Phy	Phymatolithon calcareum maerl beds in infralittoral clean gravel or coarse sand
IGS.Phy.R	Phymatolithon calcareum maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand
IGS.Phy.HEc	Phymatolithon calcareum maerl beds with hydroids and echinoderms in deeper infralittoral clean gravel or coarse sand
IGS.Lgla	Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel
IGS.HalEdw	Halcampa chrysanthellum and Edwardsia timida on sublittoral clean stone gravel
CGS.Ven.Neo	Neopentadactyla mixta and venerid bivalves in circalittoral shell gravel or coarse sand
IMX.Lcor	Lithothamnion corallioides maerl beds on infralittoral muddy gravel
IMX.Lfas	Lithophyllum fasciculatum maerl beds with Chlamys varia on infralittoral sandy mud or mud
IMX.Lden	Lithophyllum dentatum maerl beds on infralittoral muddy sediment.

All of these biotopes except for CGS.Ven.Neo (which is common) are regarded as uncommon or scarce in Britain. In Ireland, five additional biotopes with maerl have been recorded by the Biomar survey (Costello et al., 1997). They also occur in the MNCR classification but maerl is not a key component in them. These are:

Code	Description
IMS.Zmar.Bv	Zostera marina and bivalves in sheltered infralittoral fine sand and mud
CGS.NcoBv	Neopentadactyla mixta and venerid bivalves in circalittoral gravel and coarse sand
IMX.An	Burrowing anemones in sublitoral muddy gravel
IMX.Ost	Ostrea edulis beds in shallow sublittoral muddy fine sand and shell
IGS.Lhia	Limaria hians nests on infralittoral medium to muddy sand

As more maerl beds are described in biological detail, spatial and temporal patchiness is increasingly being recognized. Although it is possible that more maerl biotopes will be recognized, because there are relatively few species >faithful= to (i.e. found almost exclusively in) maerl biotopes it is probable that the species present at a particular location are a reflection of the unique environmental conditions at that site.

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