Main Authors: Vincent Lyne, Donna Hayes Project team: David McDonald, Vincent Lyne, Donna Hayes, Rick Smith, Roger Scott, Brian Griffiths, Scott Condie, Gustaaf Hallegraef, Peter Last, Jeff Dunn. Department of the Environment and Heritage and CSIRO, 2005.

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• Pelagic regionalisation: National Marine Bioregionalisation Integration Project (PDF – 7.49 MB)

About the report

The three-dimensional nature of the marine environment and its temporal variability have posed difficult challenges in understanding and managing the pelagic (water column) component of the oceans.

Other than in satellite-based plankton images, biological information lacks spatial and temporal coverage to adequately regionalise this environment, or to determine surrogate relations between geophysical properties and ecological structures and processes.

Management needs and potential uses of pelagic regionalisation information are consequently also unclear because there are no synergies with terrestrially based studies or with regionalisations of benthic marine systems based on distributions of biota and the geophysical properties of the seafloor.

We describe a hierarchical framework for regionalising the pelagic marine system that relies primarily on physical properties and satellite plankton images.

Three levels of the framework (Levels 1–3) are described by application to Australia’s Marine Jurisdiction.

The first level (Level 0) describes the structure at the scale of the oceans.

The second level (Level 1) describes ocean zones that appear as latitudinal bands at the surface (Level 1a) but also have an underlying three-dimensional structure (Level 1b).

The third level (Level 2) describes the different circulation regimes arising from mixing and transport of water properties.

The fourth level (Level 3) describes the energetics and variability of water masses; we present only the surface characterisation at this level.

Although finer-scale levels (Levels 4a and 4b) are presented in the regionalisation framework, we only present analyses down to Level 3.

The finer-scale levels are dynamic features whose description is left as a subject for future research.

Key conclusions of this project are summarised below:

1. Substantial progress has been made in classifying the pelagic environment through an integrated analysis of the whole water column. A hierarchically nested classification appears possible from the scale of oceans (Level 0) down to at least Level 2 (Circulation Regimes). However, the complications due to seasonal and longer timescale variability are yet to be examined in a systematic way.
2. Biological information is required to guide and inform the analyses; this is currently the main major shortcoming of the regionalisation.
3. This is one of the most comprehensive studies undertaken for a pelagic regionalisation. A valuable collection of data for future extensions of this study now exists in a well documented state (Hayes et al. 2005).
4. A workable pelagic framework has been constructed down to the scale of features (Level 4a) and substructure of features (Level 4b).
5. Beyond Level 2, energetics in the ocean system as characterised by fields of homogeneity and heterogeneity in water masses provide useful qualifiers for Level 2 classes. The rich variety of oceanographic processes that can be identified with such an analysis may have implications for biological productivity and hence for marine resource management. Deciding how best to use the available information at the various Levels and what future information will help refine the analyses and descriptions will require careful consideration.
6. The complexity and richness of the pelagic regionalisation demands innovative methods of visualisation and a dedicated program of education and information dissemination for managers, researchers and stakeholders, including the general public and students.

At this stage, the pelagic regionalisation of Australia is being used mainly to illustrate the complexity of the structure of the marine water column.

It is at an earlier stage of development than the benthic regionalisation. However, as with the benthic regionalisation, the key aim ultimately in using the pelagic regionalisation is to determine linkages between biological and geophysical attributes, which we expect to be much stronger in pelagic than benthic systems.

Our work also suggests that the coupling between pelagic and topographic structures is much tighter than we expected, and that a unified treatment of pelagic and benthic regionalisations should be possible.

A corollary conclusion is that benthic structures may be influenced by the pelagic environment and that past benthic regionalisations should be reviewed to take account of this project’s findings.