Biotopes and classification systems
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Hierarchical levels of biological organisation (such as ecosystem) are widely used by scientists but also by decision-makers and managers. Limits of ecosystems are usually difficult to define and are often too large to be of a practical value. A relatively new way of defining sub-units in an ecosystem is based on the concept of the biotope. They can be mapped easily and changes in time in their distribution can be recorded. A recent definition of a biotope was used in the framework of the European programme Biomar-Life:
Explaination of terminology
In the definition of a biotope, a habitat is understood to be the place in which a plant or animal lives. It is defined for the marine environment according to geographical location, physiographic features and the physical and chemical environment (including salinity, wave exposure, strength of tidal streams, geology, biological zone, substratum, 'features' (e.g. crevices, overhangs, rockpools) and 'modifiers' (e.g. sand-scour, wave-surge, substratum mobility). The notion of ‘community’ also may vary depending on the authors. Data analysed with clustering and ordination techniques have been employed to define association of species in recognisable assemblages. Despite the fact that such groups are the product of statistical analysis, they are often misinterpreted as biological/ecological entities carrying out a recognised function in the ecosystem. In the working definition of a biotope, a community is identified as a group of organisms occurring in a particular environment, presumably interacting with each other and with the environment, and identifiable by means of ecological survey from other groups. A community is normally considered as a biotic element of a biotope. Biotopes help solve the problem of scale in relying on the definition of boundaries which correspond to physical discontinuities along ecological gradients. They summarise not only the type of underlying habitat, and thus the niche created, but also the dominant and structuring biological elements; hence their description does not need to contain all species in a community.
History of the term
The term “biotope” was introduced by a German scientist, F. Dahl in 1908 as an addition to the concept of ‘biocoenosis” earlier formulated by K. Möbius in 1877. Initially it determined the physical-chemical conditions of existence of a biocoenosis (“the biotope of a biocoenosis”). Further, both biotope and biocoenosis were considered as abiotic and biotic parts of an ecosystem, accordingly. This notion (“ecosystem = biotope + biocoenosis”) became accepted in German, French, Russian and other “continental” ecological literature. The new interpretation of the term (“biotope = habitat + community”) appeared in the United Kingdom in the early 1990s while elaborating the classification of the natural conservation objects of the coastal zone. The term was “re-discovered” in the earlier 1990s, when classification and mapping works of the littoral and upper sub-littoral coastal zone of the Great Britain and Ireland began.
Physical and biological features of biotopes
At a given scale, a habitat encompasses a spatial domain, homogeneous in relation to environmental parameters. The environment’s physical and chemical characteristics are taken to encompass the substratum (rock or sediment) and the particular conditions, which are characteristic of the local environment. For the marine environment such conditions include wave exposure, salinity and tidal currents. Such conditions vary within a range, which is characteristic of the habitat. This means that a habitat is limited in space. The biotope integrates the environmental factors which structure the habitat. With regard to physical parameters, the biotope results from a balance between hydrodynamic parameters, physico-chemical parameters such as salinity and continental inputs (including pollutants and nutrients), the local geomorphology creating sheltered or exposed habitats, regional sedimentary characteristics and regional lithology conditioning the type of deposit or the type of substratum. The habitat is indicated by a limited set of words resuming the local conditions, i.e. muddy sand or rock platform. Such expressions integrate the various parameters which play a role in the habitat of a particular population.
The term ‘habitat’ is more widely (and abusively) used to also include living organisms. Within space, species interact and constitute communities. From a biological point of view, the bio-facies or biotope results from a balance between the regional living environment and the local conditions. The presence of a species will be dependant on access to the ecosystem considered and to other biological requirements, i.e. the recruitment of young stages, trophic conditions.
|Factor||Spatial/temporal scale of variability||Gradient||Biological significance|
|Substrate||years - hundreds of years; meters to few km||1) boulders (tens cm to 2-3 m in diameter)||suitable for establishment of macrophytes and sedentary epifauna|
|2) shingles, pebbles and gravel||too coarse for most infauna, too unstable for sedentary epifauna and macrophytes|
|3) sand and mud||suitable for infauna and (hypothetically) for marine psammophyle vascular plants|
|Hydro-dynamic||days - tens of years;||1) swash zone||casting ashore and further decomposition of macroalgae|
|meters to tens of meters (inshore -offshore direction)||2) surf zone||formation of shallow caves with floating algal mats|
|3) breakers zone||preclude establishment of epifauna and macrophytes|
|4) offshore zone||suitable for epi- and infauna, as well for macrophytes|
|Light||days - years;||1) euphotic zone||sufficient light for photosynthesis|
|tens of cm - meters (by depth)||2) aphotic zone||no light of biological significance|
Biotope approach to marine studies and management
Input to biogeography and resource management
The “new” interpretation of biotope begins to dominate nowadays in the international scientific and normative environmental literature. Biotopes are defined according to their physical and dominant and structuring biological features. Applications to coastal management and the management of natural resources rely on the ease of mapping geographical units which evolve on a time scale compatible with mid-term politics. It is a relevant level to work at. Their value lies also in the realisation that the organisms not only respond to the prevailing physical and chemical factors, in relation to the species’ tolerances, but also animals and plants have the ability to modify the environment. They provide an adequate scale in space and time and lead to an explanation of macroscopic properties of coastal ecosystems (i.e. nutrient cycling). The concept provides a coherent and integrated conceptualisation of ecosystems. Nevertheless, the new meaning of the word biotope should be distinguished from the ecosystem definition, which also includes both the physical environment and community. Strictly speaking (according to its original definition), the new concept of biotope does not take into consideration the energy and other ecosystem linkages between its abiotic and biotic components. The community (particularly one of its parts – the complex of the most distinctive, conspicuous species) is being mentioned only as one of the distinctive characteristics, which allows us to distinguish and classify the biotopes.
Classification and conservation
In the late 1980-1990s, with many European Directives being promulgated, law has become a driving force for ecology. Classifications are the most widely used aspects of biotopes. The term biotope is now commonly used in Europe, for example in the European CORINE biotope classification, the Wadden Sea classification, the Helsinki Commission’s Baltic Sea classification and the Marine Nature Conservation Review. The EU CORINE classification was developed in the 1980s. It was used to derive the “habitats”, meeting the requirements of the Habitats Directive. With the establishment of the European Environment Agency, a rationalised and restructured classification is being proposed: EUNIS ( European Union Nature Identification System) used in coastal zone planning and management. Because of significant shortcomings in its structure the CORINE classification remains very broad and alternatives were proposed. The marine biotope classification was published by the Joint Nature Conservation Committee (JNCC) in the United Kingdom. The MNCR classification was developed in the UK as a contribution to BioMar, a project part-funded by the EU’s Life programme. It relies on the notion of “biotope”, under its new acceptation. In France, the Zones Nationales d'Intérêt Scientifique, Faunistique et Floristique (ZNIEFF) have been developed. Such systems are at the basis to a Europe wide classification system put in palace by the European Union (EU) and the Oslo & Paris Commission (OSPARin the early 2000s. The accuracy level of characterization of biotic features in biotopes varies in different classification systems. Thus in the Red list of marine a coastal biotopes complexes of the Baltic Sea, Belt Sea and Kattegat prepared by HELCOM experts, the hierarchical principle is applied:
- Substratum is the main characteristic;
- Further, its location is considered – if it is located within the euphotic zone or outside it;
- And finally, for the euphotic zone biotopes, the presence and abundance (many, few, none) of macrophytes is determined.
Species composition or even their life form (perennial, annual, filamentous) is not defined more precisely. The presence or absence of animals is not taken into consideration, in exception of special types of biotopes – i.e. the mussel bed. The biotical features, which characterize sea floor structures formed by macrozoobenthos activities, are not applied either. The system needs to be further detailed and elaborated.
Perspectives in the use of biotopes
The use of biotopes may lead to a better interpretation of the heterogeneity of the ecosystem (in terms of the relative abundance of the various structural components) and its complexity (in terms of relationships between components). The biotope concept can be adapted to fit in a system approach to the ecology of coastal marine ecosystems. Such aspects include the consideration of:
- biotopes as components of the ecosystem and structuring aspects of dominant organisms,
- the spatial scale of biotopes in relation to their physical boundaries and their individual characteristics,
- the temporal scale relating to the changes to the distribution of biotopes within the ecosystem over time,
- connections between biotopes within the ecosystem demonstrating processes and functions,
- constraints (natural or anthropogenic disturbances) on the ecosystem behaviour and how biotopes translate such changes.
The concept of the biotope links with other levels of biodiversity in the ecosystem and integrates its various functions. Possible further research at biotope and lower hierarchical levels include the modelling of relationships between biotopes in relation to the overall behaviour of the ecosystem. The quantification of fluxes between various compartments, at biotope level and lower, is another avenue to explore in relation to the use of photography and GIS (Geographical Information System). Applications to management could lead to interesting socio-economic considerations (i.e. the sustainable exploitation of natural resources or the search for new fisheries).
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