Determination of change

In order to manage these biotope complexes, it is necessary to determine change as the result of the action of natural and anthropogenic factors and to determine the significance of that change for the integrity of the biotope complexes. Following from the description of the main features of these biotope complexes, it is possible to create a priority list of Favourable Conditions and attributes. The over-riding influence of the physical environment together with the difficulties and effort required in monitoring dictates that it would be more cost-effective to study the changes in those features rather than in the biology which could not be studied in detail.

The parameters for study can be divided into: primary parameters, as the physical-chemical attributes that will cause habitat disruption, and secondary parameters, the biological attributes, that will reflect changes.

The most appropriate physical features are:

  • Area, as the expected size of the habitat, and in certain cases Shape of the habitat;
  • Substratum, as the underlying nature of the bed material;
  • Depth and/or Tidal Elevation, as indicating either the coverage by water for Subtidal Mobile Sandbanks habitats or the extent to which Intertidal Sand and Mudflats are exposed at Low Water; the depth also influences the light regime available to infralittoral plants;
  • Water Characteristics, as the underlying water chemistry, including salinity, temperature and nutrient regime;
  • Hydrophysical regime, as the summation of tidal, wind-induced and residual currents which influence the bed nature and the delivery of food and dispersive stages to an area; and
  • Habitat Mosaic, as an indication of the complexity of the environment created by the physical attributes and thus leading to biological complexity.
  • The biological attributes to be used include important features which describe community structure and functioning. The most appropriate features are:
  • Community Structure, as the net result of taxa and individuals supported, the diversity of the area and, where necessary, the zonation created by the physical and biological features;
  • Biotopes, as the number and mixture of representative biological-environment entities and including where possible those listed in site notification, including the quality of biotopes and the maintenance of balance between them;
  • Species, especially those that are rare and/or included in any site notification, and the dominant species in terms of functioning and support of predators or as predators. The rare species could decline if their niche is removed, the area decreases or the supplying population declines; and
  • Community Functioning, as an indication of the overall health of the system and its support for important grazer and/or predator populations.

These biological attributes can be divided into qualitative ones (e.g. presence of rare species) and quantitative ones (e.g. the importance of sediment supporting fish and birds), thus there is the need to determine the carrying capacity to support predators. In addition, in the terms of the Directive, the substratum is regarded as having an intrinsic value (e.g. mudflats as mud) as well as being a resource for (ultimately) supporting higher predators, e.g. waterfowl. While the above list gives general attributes, there is the need ultimately to focus on particular site-specific cases with specific features (e.g. species) for use by the manager of a particular site.

The functioning of these habitats indicates the importance of physical processes whereby if these are protected, then the biology will be assured, for example a low-energy area will have a typical muddy-substratum faunal community. Although the species composition may change with geographical area, the biotope functioning will remain similar. Furthermore, there is the need to allow for changes to these most widely-varying environments (e.g. intertidal mudflats in estuaries) as well as those exposed to severe natural events, e.g. the 1 in 50 or 200 year storms on subtidal sand-banks.

Each sedimentary site is likely to consist of a single or very few biotopes although the more complex marine habitats, as far as the Directive is concerned, such as estuaries and coastal waters, may be made up of a certain combination of biotopes to give it its unique features. Similarly, it may be necessary to separate features dominant at a site from those responsible for its functioning, e.g. over-wintering birds on a mudflat. Within a complex site, the biotope mosaic as well as its component parts requires management, thus there is a need to assess each as a structural type which functions in combination with the others.

There are many potentially damaging human activities likely to affect the soft substratum habitats. At present, it is not possible to determine for all sites, key features and all human activities, the quantitative effects of changes to the biological structure and functioning as the result of man-induced changes. The nature of the relationships between the features is well-known, especially for well-defined stressors such as sewage disposal or dredged material relocation (Rees et al, 1990; MAFF, 1993; SOAEFD, 1996) but the relationships have been rarely and not fully quantified nor given in a predictive, statistical manner (Elliott & O’Reilly, 1991). However, it is necessary to presume that large-scale physical changes will affect the integrity of a site.

Because of the nature of the changes, it is suggested that:

  • the degree of monitoring should be dictated by the magnitude of the perceived or actual threats;
  • recording of human activities should be carried out to indicate a threat to the integrity of the system;
  • initial and continued low-level surveillance (using skilled eye surveys and remote sensing) will indicate the possibility of change; and
  • the latter will then act as a trigger and require more detailed and quantitative monitoring to indicate the magnitude of the change.

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