The previous sections describe the main features and characteristics of the biotope complexes Intertidal Sand and Mudflats and Subtidal Mobile Sandbanks as well as the links between those features. The Habitats and Species Directive dictates that SAC’s require to be managed to ensure that those characteristics are protected and that they do not change beyond those levels considered usual for the habitats. Where these characteristics are in an optimal state can be defined as Favourable Conditions for the Biotope Complexes and the natural variation within those characteristics can be defined as being within Change Levels; outside those change levels gives cause for concern (Hiscock, pers. comm.). It is of note that defining the maintenance and recovery of Favourable Conditions for marine habitats creates difficulties not encountered for terrestrial habitats.

Marine habitats by their nature exhibit considerable spatial and temporal variability within the habitat and there is more influence by features and structures outside the habitat than is shown in terrestrial systems, for example the delivery of food and colonising organisms. The understanding of that variability is compounded by the non-availability of long term data sets for defining Favourable Conditions and Change Levels, i.e. the natural spatial and temporal variability has not been established. Thus there is a poor quality and quantity of data on which to base trends and detection of change from favourable status.

The definition of Favourable Conditions depends on the time-scale in which changes may occur: on diurnal, spring-neap, lunar, seasonal, inter-annual and decadal bases. Similarly, the definition also depends on spatial scales which incorporate local patterns, those within a well-defined estuarine or sea-area, those within a coastal area which behaves as a given unit (e.g. sedimentary cells) and other scales up to biogeographic regions. In turn, required actions and monitoring have to be related to such temporal and spatial scales.

The most valid assessment of the features of any marine habitat is to define the prevailing hydrographic regime which will create the substratum type and thus the creation of community structure, i.e. a bottom-up control. Once that basic structure has been created, biological interactions (recruitment, competition and predator-prey relationships) will modify it and thus lead to an effect on top predators and the lower trophic levels, i.e. top-down processes.

The aim in any management of marine systems should be to regulate human-induced impacts and then to let natural processes operate. The major difficulty will be if natural processes, such as storm-induced sediment disturbance, lead to significant changes to the habitat. The Habitats Directive implies the maintenance of stability in the systems of concern although the wide variability within marine soft-substrata habitats dictates that such a stability is difficult to quantify.

Determination of change

Procedure for management

Biodiversity perspectives

Quantitative change levels in the management of intertidal sand and mudflats and subtidal mobile sandbanks

References