The MNCR biotope classification

The Marine Nature Conservation Review (MNCR) has developed a system of classification of shallow-water benthic marine communities based on surveys of a very wide range of subtidal and intertidal sites and the relevant literature. The MNCR biotope scheme (Connor et al, 1997) allows the classification of areas according to a combination of biological and habitat characteristics. Biotope maps are being produced for areas of conservation importance.

The hierarchical structure of the scheme is designed for classifying areas of seabed based on their physical and biological characteristics (Connor et al., 1997). Larger-scale differences among shores, including intertidal reefs, are effectively represented at the highest level of division by the 28 habitat complexes. Biological communities thereon are recognisable in the 60 biotope complexes into which these habitat complexes are subdivided. Further subdivision of these complexes results in the biotopes themselves (see summary table for biotopes of relevance to rocky shores).

Some rocky shore communities are highly variable in space and time (mussel-barnacle mosaics, Lewis, 1976, Fucus-barnacle mosaics, Hartnoll and Hawkins, 1985; Hawkins et al., 1992) while others are very stable (beds of Ascophyllum spp.; barnacle-limpet communities on verticals). In consequence classification of rocky shores according to the biotope scheme from a single site visit should be attempted with caution. Many of the biotopes listed in the scheme may represent stages on continua in either space or time (see table for biotopes of relevance to rocky shores).

As an aid to the rapid assessment of shores the biotope classification has value for early management decisions. Broader application must account for the known limitations. Many communities on intertidal bedrock, and especially on unstable boulder shores, may suffer high levels of physical disturbance. Biological communities in such habitats may reflect successional stages towards a climax rarely achieved. Topographically heterogeneous shores may contain a mosaic of interspersed community types, leading to major problems of classification to a single biotope. Finally, a single biotope class for a shore community may mask information on individual species with potentially important consequences for conservation. Disappearance of sensitive species, such as the dogwhelk Nucella lapillus in areas of high levels of tributyltin, may not result in a change in biotope class.

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