For terrestrial ecosystems, the approach used in Australia centres on the Interim Biogeographic Regionalisation of Australia (IBRA) which now divides the eight States and Territories into 85 bioregions (Thackway & Cresswell 1995) . More recently, the geomorphic units found within the bioregions have been identified and delineated as sub-regions. In the terrestrial environment, bioregions are identified using a land systems approach, taking into account geology, geomorphology and climate. The existence of broad native vegetation communities can assist in identifying the boundaries of bioregions, and is of increasing importance in delineating sub-regions. Bioregions contain repeating patterns of similar ecosystems, while sub-regions contain smaller arrays of such patterns.
The principle lying behind the selection of IBRA regions is the recognition that terrestrial ecosystems depend largely on geology, landform and climate, mediated by community succession, fire, and of course the impact of human activities107.
The IBRA framework was developed to assist the National Reserves System Program, and State governments, in identifying gaps in the developing system of representative terrestrial reserves. Its target is to develop and categorise biodiversity surrogates at the highest useful level. By necessity, it involves broad-scale amalgamations of information on geomorphology, geology, vegetation, climate and soil type. In its current form it represents extremely useful categorisations of habitat at the landscape and regional level. IBRA regions, for the most part, contain similar assemblages of terrestrial ecosystems. The recognition that geomorphology, to a lesser or greater extent, includes information on drainage formations is vital in understanding the relevance of the IBRA framework in relation to freshwater ecosystems. However, the IBRA framework provides no more than a useful base for categorising freshwater ecosystems, as it does not include information on hydrology, and the scale at which it has been developed is at least an order of magnitude above the scale necessary for categorising rivers, and most lakes and wetlands.
5.6.2 Marine bioregions:
Marine reserves are supported under a different program run by the Commonwealth Oceans Office. Marine areas are targeted for protected area status based on the related Interim Marine and Coastal Regionalisation for Australia (IMCRA) which uses a similar broad-scale ecosystem-based approach, taking into account additional oceanographic variables such as depth, persistent and tidal currents, water temperature, and the distribution of groups of organisms. Where data could support multi-variate analysis techniques, these were used on defining IMCRA regions (R Thackway and I D Cresswell 1998).
At the broadest scale, classifications of marine ecosystems use a three-way division by substrate: rock, unconsolidated sediments, and seagrass. Marine bioregions, like terrestrial bioregions, contain repeating patterns (similar assemblages) of ecosystems. Marine sub-regions may be defined to delineate finer ecosystems of finer detail.
5.6.3 Freshwater bioregions:
Hughes and James (1988) used hydrology as a key determinant regarding the development of a freshwater regionalisation for Victoria. The Land Conservation Council (LCC 1989) – through their consultants - used geomorphology and hydrology to define 39, then 16 Victorian river regions. Included in the LCC’s work was a geomorphic feature related to access by marine life-cycle fishes – whether rivers drained inland, or to the Victorian coast.
One could argue that the existing terrestrial bioregionalisation is adequate to guide freshwater system protection. This would be flawed on two grounds. The biodiversity elements that would underpin a freshwater bioregionalisation would be different from, and would not necessarily have the same boundaries as, terrestrial bioregionalisation. Secondly, freshwater systems are by their nature more connected that terrestrial systems. The connections are largely linear and directional. Terrestrial connections are non-linear and weakly directional. Selecting priority sites for freshwater protected areas needs to accommodate these, and other, unique aspects of freshwater biodiversity, ecology, and system function (Possingham, pers. comm. 12/4/2005)
Wells and Newall (1997) found that the terrestrial Interim Bioregionalisation of Australia (IBRA) was “not effective in representing aquatic ecosystem patterns across Victoria”, and suggested an approach to delineating aquatic bioregions based partly on physical and biological data, and partly on expert knowledge.
More recently Unmack (1999, 2001), Metzeling et al.(2001) and Doeg (2001) have used biological variables as key regionalisation determinants: Unmack used fishes, Metzeling used macro-invertebrates, and Doeg used both. A certain degree of regionalisation is inherent in the AusRivAS macroinvertebrate river condition monitoring approach, which establishes expected benchmarks (the occurrence of suites of macroinvertebrates) for pristine river types in different Australian regions. It should be noted that AusRivAS does not rely solely on pristine benchmarks: it uses 'best available' sites for each river type. In NSW, at least, some of these sites have quite significant human impacts.
According to Unmack: “My greatest concern is how well can a terrestrial biogeographic system (eg IBRA) represent freshwater areas. The factors that influence terrestrial and aquatic organisms are somewhat different, but more importantly the type of movement (or dispersal) each these organisms can make is fundamentally different as many aquatic organism are limited to movement within catchments. I very much doubt there would be more than just a couple of aquatic vertebrates that would be endemic to any of those IBRA regions, but there are many that are endemic to particular watersheds. Overall, to me it seems as if drainage catchments must be the units used, not terrestrial regions.” (Unmack, pers.comm. 4/8/03).
Unmack continues: “ An interesting thing that comes to mind is the suggestion that we should compare the terrestrial biogeographic system to the aquatic one. I think it would be far more interesting to see how well an aquatic reserve system could also provide a suitable coverage of terrestrial reserves. It seems to me that it would be far more likely that an aquatic system could be more representative of terrestrial ecosystems than visa versa.” (pers.comm. 6/8/03).
The distribution of freshwater crayfish has been examined by Whiting et al.; the authors do not propose a regionalisation but use IBRA bioregions (not sub regions) to colour-up crayfish richness and endemicity around Australia. Tait (2002) has reviewed approaches to freshwater regionalisation in Australia, and suggested that, while further development of the concept is long-overdue, there is enough information available to commence programs aimed at identifying gaps in existing systems of representative freshwater reserves.
Abell et.al.(2000) and (2002) have developed freshwater regionalisations for North America.