The Marine Conservation Review (MNCR) biotope classification provides a hierarchical framework for differentiating and classifying the shallow-water benthic habitats and biological communities of the British Isles (Connor et al, 1997). The basic unit of classification is the Biotope, a recognisable Community of conspicuous species occurring in a Habitat, defined according to parameters of the physical environment such as substratum type or degree of wave exposure. Groups of biotopes with similar overall character, suitable for local mapping where biotopes consistently occur together and are relatively restricted in their extent, are termed Biotope complexes.

Intertidal Sand and mudflats and Subtidal sandbanks are characterised by a restricted number of biotopes due to the biological and physical homogeneity of these areas and the limited availability of niches (Connor et al, 1997). The relevant biotopes typical of ‘intertidal mud and sandflats’ and ‘subtidal mobile sandbanks’ from the MNCR classification are summarised in Tables 1 and 2 respectively. A working classification and full descriptions are given in Connor et al (1997).

For the purposes of this report, the ‘Intertidal mud and sandflats’ biotope complex is taken to include all biotopes that can be found in sheltered (low energy) areas, in the case of mudflats, and all biotopes that can be found in areas along the exposure gradient (low and high energy) in the case of intertidal sandflats. The intertidal biotopes covered in the present report do not include those that consist of either eelgrass (Zostera spp.) or pioneering saltmarsh plants (Salicornia spp.). The ‘Subtidal mobile sandbanks’ biotope complex includes all biotopes likely to be found in subtidal non-vegetated mobile sands. The biotopes are also discussed in terms of change along a gradient of particle sizes or salinity, with biological communities changing as a result of the differing environmental requirements of the characterising species (Conner et al, 1997). The latter is particularly apparent in estuarine habitats.

These biotope complexes, especially mudflats, are of particular importance as feeding grounds for wildfowl and waders (Davidson et al, 1991). The intertidal communities of invertebrates and algae that occupy this biotope complex can be used to define subdivisions of other habitats such as estuaries and large shallow inlets and bays, eelgrass communities that may be exposed for a few hours in the course of every tide (CORINE European classification of communities), and brackish water and vegetation of permanent pools. This review excludes macroalgal dominated areas although their features are mentioned if appropriate. The biotope complex ‘seagrass communities’ are included in another Marine SAC review and thus are not considered here.

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