What data do you need for habitat mapping?

 
Empirical survey techniques and habitat suitability modelling can be contrasted. For empirical techniques, any data will do as long as it works. The best techniques have high resolution, precise measurements and good powers of discrimination.
 
As soon as some form of habitat suitability modelling is involved, then the more biologically relevant the better. But what is biologically relevant? Species are adapted to live under a particular set of conditions, requiring a substrate suitable to their body form and an environment suitable to their physiological needs and tolerances. The same holds true for communities and their characterising species (leaving aside doubts about the community concept). However, not all species respond to the same factors. Habitat criteria can be divided into, firstly, those that are universally important and, secondly, those that are important for certain biological communities, but not others.
 
The two most universally relevant factors are:
 
  • Depth below datum in the subtidal, or height above datum in the intertidal (measured directly by remote sensing)
  • Substratum (determined from remotely-sensed data directly and inferred from point sample data)

 

A more comprehensive list might also include the following (many of which are not independent variables but interrelated):
 
  • Rock type/features and bed-forms (may be derived from high resolution bathymetry)
  • Selected sediment characteristics, e.g. median particle size, silt content (may be inferred or modelled from point samples and remotely-sensed data)
  • Topography (may be derived from depth)
  • Physiographic form (from depth, coastline and topography)
  • Light (measured at points, detected by satellite imagery and correlated with depth)
  • Salinity (point measurement and may be correlated with physiographic feature)
  • Temperature (at a biogeographic scale) (measured and also detected by satellite sensors)
  • Water energy (derived from measurements and  hydrodynamic modelling)
  • Wave action (coastal areas to 50-70m depth) (wave heights measured and wave base energy modelled)
  • Fetch (from physiographic shape, wind characteristics)
  • Currents and bed stress (measured at points and modelled using topography and bathymetry)

 

Some of these data sets are primary in the sense that they can be collected through commissioned survey. Others are modelled using a variety of measurements and data sources. These factors must be carefully assessed as to the availability of data and information at the appropriate scale and usefulness for the modelling of the full range of habitats or a selected list of habitats. The biological relevance of these factors are not universally applicable and depend upon the habitat types in question.
 
 

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