Rationale and need for a habitat classification

Purpose and scope

Seabed habitats and the communities of species that occupy them are an essential component of the marine ecosystem and our overall understanding of ecosystem function must relate seabed habitats to hydrography, nutrient cycling, plankton changes and the distribution of wide-ranging species (i.e. fish stocks, marine mammals, birds). A greater understanding of the distribution, extent and status or quality of marine habitats is required to facilitate the protection of threatened and rare habitats and, more generally, the assessment of the state of the marine environment. Such information is also needed to improve spatial and strategic planning of human activities, in particular to promote the wiser use of habitats where there are competing demands (e.g. fishing, sand and gravel extraction, wind energy generation, nature conservation). As such, information on marine habitats needs to play a major role in the ecosystem-based approach to management of the marine environment that is now widely advocated at national and international levels (Defra 2002; North Sea Conference 2002).
This habitat classification has, consequently, been developed as a tool to aid the management and conservation of marine habitats. It provides an ecologically-based classification of seashore and seabed features, aimed primarily at classifying benthic communities of invertebrates and seaweeds in a way which is meaningful both to detailed scientific application and to the much broader requirements for management of the marine environment. The classification is relevant to the habitat requirements of more mobile species, such as fish and marine mammals, but these are not its primary focus. Whilst the corresponding European EUNIS classification also includes water column (plankton) habitats, this aspect has not yet been developed here.
The classification aims to provide comprehensive coverage, by including habitats for artificial, polluted or barren areas as well as more natural habitats, which encompass:
1.   Marine, estuarine and brackish-water (lagoon) habitats - It also includes reference to saltmarsh habitats described in the National Vegetation Classification (NVC) (Rodwell 2000; Doody, Johnston & Smith 1993) as these are regularly covered by the sea, and NVC types which occur in brackish lagoons (Rodwell 1995).
2.   Rock and sediment habitats.
3.   Upper shore to coastal waters - From the supralittoral or splash zone and strand-line on the shore out to the 200 nm limit. The habitats beyond the near-shore subtidal zone (about the 3 mile/5 km limit) and below about 50 m depth are less well described here, due to more limited availability of data; more types will be defined as data become available.
4.   Plant and animal communities, including epibiota and infauna - Types are defined using both their fauna and flora. Most benthic marine habitats include sedentary animals and small mobile animals which are an integral part of the community, whilst in many habitats, especially in deeper water, there are no plants (seaweeds or marine angiosperms) to characterise the habitats. Sediment types are defined both by their epibiota (surface-dwelling animals and plants) and their infauna (animals living in the sediment).
5.   Britain and Ireland - It covers habitats throughout Britain and Ireland and, through a widely-accepted broad framework, is readily expandable to include offshore continental shelf habitats and other areas in the north-east Atlantic, Mediterranean and Baltic Seas. This is being achieved through the EUNIS classification.
Requirements of a habitat classification system
To underpin management and conservation of the marine environment, a habitat classification system should:
  • be scientifically sound, adopting a logical structure in which the types are clearly defined on ecological grounds, avoiding overlap in their definition and duplication of types in different parts of the system, and ensuring that ecologically-similar types are placed near to each other and at an appropriate level (within a hierarchical classification);
  • provide a common and easily understood language for the description of marine habitats;
  • be comprehensive, accounting for all the marine habitats within its geographic scope;
  • be practical in format and clear in its presentation;
  • include sufficient detail to be of practical use for conservation managers and field surveyors but be sufficiently broad (through hierarchical structuring) to enable summary habitat information to be presented at national and international levels or its use by non-specialists;
  • be sufficiently flexible to enable modification resulting from the addition of new information, but stable enough to support ongoing uses. Changes should be clearly documented to enable reference back to previous versions (where possible, newly defined types need to be related back to types in earlier versions of the classification).
The following considerations were taken into account in establishing the classification:
  • its intended application by a variety of users and at various scales (environmental managers, marine scientists and field surveyors working at local, national and international levels);
  • the variety of intended applications;
  • the variation in the scale of physical and biological features (recognising that marine ecosystems operate at a wide variety of scales, e.g. whole estuaries, individual mussel beds);
  • the different levels of detail in available data;
  • the different skill levels of future users and their different methods of survey.


A number of applications for the habitat classification system have been identified:

  • to provide a practical system for the consistent description of habitat types;
  • to map habitats to assess their geographical distribution;
  • to map habitats to assess their extent;
  • to provide categories for the assessment of the state of marine biological communities;
  • to assess changes in habitat distribution and extent over time, to provide information on quality status, and rate of change in habitat distribution;
  • to assess the relative importance of particular habitats (i.e. which habitats are rare or of national or regional importance) and the implications of this for prioritising management and conservation action. Such assessment can lead to the listing of habitats for conservation action (e.g. Red lists);
  • to enable the nature conservation value of habitats at specific sites to be assessed, such as in the identification of marine protected areas (MPAs);
  • to enable an assessment of the extent of protection afforded to habitats by existing or proposed MPAs and the degree to which this provides sufficient protection;
  • to enable the range and intensity of human activities that occur in particular habitats, and the degree to which such habitats are affected by those activities, to be systematically assessed;
  • to facilitate presentation of habitat information at a scale and level of detail that enables appropriate management action to be taken. Such presentation should be flexible to address a variety of biodiversity and management issues;
  • habitat mapping information needs to be used in conjunction with other spatial information in Geographical Information Systems (GIS), particularly activities, management and conservation areas, and other environmental data sets.