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LARGE MARINE DOMAINS OF AUSTRALIA’S EEZ
Vincent Lyne0, Peter Last0, Roger Scott0, Jeff Dunn0, David Peters1, Trevor Ward0
0CSIRO
1Department
Division of Marine Research
of Environment & Land Management, Tasmania
EXPLANATORY NOTES TO MAP SERIES
Methods
Scope and Philosophy of Current Project
The IMCRA-derived provincial regionalisation (CSIRO 1996) of the shelf region
(coast to the shelf-break at the 200m isobath) forms the basis of the current Large
Marine Domain (LMD) regions on the shelf.
The prime focus of the current effort is a derivation of the offshore (offshore of the
200m isobath) LMDs and their integration with those on the shelf.
We make no attempt in this limited project to derive any separate regionalisation of
the slope region. It suffices to note here that preliminary inspection of extensive
research expedition data from the slopes of Western Australia and New South Wales
indicate intricate depthwise structuring that may not be related to surface offshore
water properties or benthic substrate on the shelf. Thus a prime limitation of the
current regionalisation is an assumed continuity of the LMD regions across the slope.
Ideally the philosophy of the current offshore regionalisation should follow that for
the shelf (CSIRO 1996). That philosophy relied on a hierarchical framework with
regionalisations at the provincial level derived from distributional data for endemic
fish species. Whilst datasets on commercial fish species and extensive research
expedition data do exist for the offshore region, the only currently available national
dataset is that of chlorophyl derived from the NOAA CZCS satellite flown from the
late 70 to 1986. Given that numerous oceanographic and geological datasets do
exist, an alternate strategy for the offshore regionalisation was required. The current
IMCRA (Version 3.2) uses a physical oceanographic regionalisation for the water
column from the surface to 50m for the so-called pelagic regionalisation offshore of
the shelf-break. For the demersal regionalisation the AGSO-derived slope analysis
was used. The specification for this project was for one offshore regionalisation that
integrated the water column and demersal regions which was also linked to the
regions derived for the shelf.
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The achievable strategy, given limitations of time and resources, was a multivariate
analysis of the existing oceanographic, geological and chlorophyl datasets for the
offshore region which was then integrated with the demersal regionalisation for the
shelf.
Regionalisation Strategy
Key tasks in implementing the multivariate analysis comprised:
1.
Collation and inspection of datasets. Criteria for selecting appropriate
datasets included:
Relevance to regionalisation
Spatial extent and resolution
Ease of processing
IMCRA-derived datasets were used as far as possible. When this was not practical
alternate datasets were sought and analysed.
2.
Subsetting of suitable datasets onto the analysis grid. The grid extent was:
Latitude:
Longitude
Resolution
-50oS to 0o
100oE to 180oE
0.5 o
Where the resolution of the data was finer than the grid an average was computed
over the grid cell. In the case of the oceanographic data, an optimal interpolation
procedure was used that averaged over a set number of the closest neighbours
(CSIRO, 1996).
3. Gridded datasets were compiled into one column-oriented file that became the
primary input for the multivariate analysis.
Datasets
Datasets collated and examined comprised:
Dataset
Type
Source
Comment
Analysed
Etopo5
0.5o grid
US/CSIRO
Too coarse, inaccurate
No
SIO Bathymetry
2 min. grid
Scripps Inst.
OK
Yes
SIO Bathy Variance 0.5o grid
derived CSIRO
SIO Gravity
Scripps Inst.
SIO Bathymetry preferred No
CSIRO
IMCRA, refined 1998
2 min. grid
Temp,Salinity 0-50m 0.5o grid
Yes
Yes
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N,PO4,O2,Si 150m 0.5o grid
CSIRO
IMCRA, refined 1998
Yes
Seasonal T,S 0-50m 0.5o grid
CSIRO
IMCRA, refined 1998
Yes
Dietmar Mueller
Large undefined age areas Yes
CAMRIS Sediments Polygons
ERIN
No attribute, no projection No
AusSeabed
Points
Chris Jenkins
Coarse offshore
No
CZCS Chl.
0.5o grid
CSIRO
Cloud problems S.West
Yes
Seasonal Chl
0.5o grid
CSIRO
Cloud problems S.West
Yes
AGSO Bathymetry
3sec. arc
ERIN
Could not import to A.Info No
Plate Age
0.1 o grid
Since the datasets were compiled, problems with the AGSO bathymetry are in the
process of being resolved. The Jenkins sediment datasets appears to be reasonably
comprehensive for the shelf region but it is too sparse in the offshore area. The point
data were interpolated but yielded what appear to be artificial patterns that would
have unduly influenced the analysis. It was thus not included. The SIO Gravity
dataset would have been a useful additional dataset but given the limited time
available we had to restrict the number of large datasets that we analysed and
unfortunately it was dropped in favour for the SIO bathymetry data.
A simple average was used to reduce high resolution datasets down to the half-degree
resolution grid used for the analysis. In the case of the oceanographic datasets,
optimal interpolation procedures were used to interpolate the point data onto the grid.
Temporal and spatial variability were examined through the seasonal variability maps
for temperature, salinity and chlorophyl, and through the bathymetry variation
computed from the SIO bathymetry. For the seasonal maps a difference of winter
from summer was used. For the bathymetry variation, maps were computed of
averages taken over a 30min. grid and a 10min grid. The difference between these
two was used to examine bathymetry variation.
Temperature and salinity were computed for the layer from 0-50m. Nutrients in the
surface layers are generally stripped in offshore waters around Australia (possible
exceptions being limited upwelling layers and waters in the Indo-Pacific region). To
obtain a more meaningful signal a cut through the thermocline layer at 125-150m was
taken for nitrate (N), Oxygen (O), Phosphate (P) and Silicate (Si).
Analyses
A number of analyses involving principal components, multivariate clustering and
classifications were conducted. We report here the two main analyses:
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
Principal component analysis of all the project data followed by a clustering and
classification analysis of the first two principal components.

Principal component analysis of the three key benthic datasets (Plate Age,
Topography and Topographic Variation) followed by analysis of the first
principal component.
The first analysis, which was dominated by the oceanographic variables, provided the
large-scale general pattern expected of spatial structuring in the water column
properties - albeit modified by the benthic variables. The second analysis was
designed to reveal details of the seafloor structure. Thus these two analyses provide
between them the major spatial structures in water column and seafloor to be
expected from the variables analysed.
PCA Analysis of all variables
The first principal components analysis used all 13 variables:
1
2
3
4
5
6
7
8
9
10
11
12
13
Nitrate
Oxygen
Phosphate
Silicate
Temperature
Salinity
Temperature
Salinity
Plate Age
Chlorophyl
Chlorophyl
Topography
Topography
Mean from 125-150m
Mean from 125-150m
Mean from 125-150m
Mean from 125-150m
Mean from 1-50m
Mean from 1-50m
Summer - Winter difference, 1-50m
Summer - Winter difference, 1-50m
Mean surface concentration from CZCS satellite
January - June surface concentration from CZCS satellite
Variation from large scale mean minus small scale mean
The first two PCAs, from the full dataset, were passed through an unconstrained
clustering algorithm carried out on a reduced subset of the PCA vectors (every 10th
value) as the full dataset of over 10,000 points taxed the limited memory of the
computer on which the statistical analyses was conducted. This analysis suggested
that 4 classes would adequately describe the parameter space spanned by the first two
PCAs, with two additional classes for outlying points. Plots of this classification
were used to classify (manually) the full dataset. In contrast, no classification was
necessary for the benthic PCA analysis as the pattern emerging from the first PCA
provided clear guidance on the spatial structuring.
A gradient analysis of the first 5 PCA was conducted using the so-called Ecotone
Analysis methodology developed by Peters (1990) (see figures in appendix). This
analysis was visualised by displaying the results of the gradients draped over the
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topography. Surface lighting from the north-west was used to simulate a 3-D effect,
this unfortunately tends to obscure features in the south-east which are behind hilly
regions (eg SE Tasmania).
Interpretation
PCA-based classification of all variables
The manual classification of the first two PCAs (see figures appended as part of this
report) show firstly that the not all points were classified - most noticable in the two
classes intersecting southern Australia. The large area of unclassified points in the
south-western part of the figure is due to cloud contamination in the CZCS images.
With the exception of the North Western part of Australia, 4 classes describe the bulk
of the spatial structuring. These being:
1. In the north-west area encompassing Java, Timor and Sulawesi a band
representing Indo-Pacific structure. Around Australia, this extends from the
eastern Arafura Sea to the southern end of the Sahul Shelf.
2. A band encompassing the Solomon Islands, the Solomon Rise and the
Melanesian Basin which are not part of the Australian EEZ. The same band class
appears as a north-west offshoot extending from the Exmouth Plateau.
3. Broad zonal bands on the lower half of western Australia leaking past into the
Great Australian Bight. The same band-class extending from the north-eastern
tip of Australia down past Sydney.
4. A zonal band of subtropical convergence structure with northern extents
intersecting the lower half of NSW, and another possible intersection just east of
the South Australian gulfs.
5. A scattered outlying class in the south notably around the south Is of New
Zealand and to the south of Tasmania.
Benthic PCA
The benthic PCA class (see appended figures) shows structures dominated by the
Plate Age with modifications due to topography in areas of uniform Plate Age.
Principal features to note are:
1. A dominant southern structure extending from just south of Australia flowing
around Tasmania and up the east coast to about Ulladulla before splitting off to
an eastern extent that terminates at the western edge of the Lord Howe Rise and
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it’s connection with New Zealand. There appears to be a faint indication of
possibly disparity in the structures on the eastern and western slopes of Tasmania.
The south Tasman Rise stands out as a unique structure embedded within the
main band.
2. On the eastern end of the main southern structure, a band confined to the west of
the Lord Howe seamount chain extends up to the southern edge of the Great
Barrier Reef.
3. Between the southern band and the slope off the Great Australian Bight a band
sweeps to the west and around the western edge of the Naturaliste Plateau off
south west of WA.
4. To the north of the Naturaliste Plateau, another less defined band (another
dominant element from the Plate Age data) extends up to the Java Trench.
The gradient/ecotone analysis confirms a number of the boundaries evident in the
PCA classification and the benthic PCA (SA gulf, south-east NSW. South-west WA,
north-west Cape) but in addition suggests boundaries running to the north-west from
about Geraldton and a series of striations running off the north-west coast of WA.
Large Marine Domain Boundaries
The 3 key information sets used in defining the Large Marine Domains (LMD) were:
1. The Demersal regionalisation from IMCRA 3.2
2. The classification of the PCA analyses, and gradient analysis, involving
all the compiled data
3. The spatial pattern in the first PCA of the benthic data
The information sets were used to alter and verify the boundaries in the unofficial
LMD map produced by CSIRO/Uni. of Tasmania for the MS&T working group in
December 1997.
The main changes made were as follows:
1. Addition of an area enclosing the south Tasman Rise labelled as a “SubAntarctic” region (but with an alternate suggestion of a label as a “Southern
Ocean” region). We did not investigate the link between this new region and the
existing Macquarie Island region but note in passing that faunal elements on the
south Tasman Rise have recently been shown to be of Sub-Antarctic origin (Last
per. comm.). Clearly a more focussed effort is required to resolve this in the
future.
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2. Alteration of the boundary Eden/Cape Howe boundary off the NSW/Victoria
border so that its eastern edge is more closely aligned with the clearly defined
benthic structure seen in the benthic PCA analysis.
3. Alteration of the southern WA boundary so that its intersection with the WA
coast was shifted to near Lancelin, about the mid-point of the South West
biotone, and its offshore extension following the structure seen in the benthic
PCA analysis.
4. The North West Cape boundary was well supported by the structure seen in the
all-data classification and was not altered.
5. The north-western boundary was shifted to intersect the coast at about Cape
Londonderry (west of Joseph Bonaparte Gulf) and extending offshore in
sympathy with the alignment of structures seen in both the all-data classification
and the benthic PCA.
6. The Cape York boundary was well supported and left unaltered.
7. The Sandy Cape boundary was well supported by the benthic PCA (with no
suggestions from the all-data classification).
8. The offshore domains were left unaltered but we note here that the Lord Howe
and Norfolk domains may require further investigation as to their similarity.
CAVEATS
1. This is a very rough investigation of the LMD structure of the Australian EEZ
designed to provide no more than an impression of what the structure might look
like. We make no pretence that this is a scientifically rigorous derivation because
it isn’t.
2. The only biological dataset used in the analysis was chlorophyl which by itself is
no better at discriminating biogeographic structuring than other water column
properties. Extensive research information does currently exist (both biological
and geological) which would help substantially refine the analysis, and more
importantly provide the necessary ecological knowledge required to manage the
LMDs.
3. A conceptual hierarchical framework is required for the LMDs which follows the
framework envisaged for IMCRA and which accounts for the offshore areas. In
the current analysis there is a mixture of scales which have been blended (for lack
of other data); for instance the topographic variation map picks out such
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structures as individual seamounts which are more appropriately analysed as part
of “habitat” units rather than as a basis for a provincial structure.
4. The slope region has been almost entirely glossed over in current analyses. There
is very good existing biological information which can be analysed in an RAP
(Rapid Assessment Procedure) manner to provide information on the structuring
on the slope.
5. The Plate Age data dominates many structures seen in the benthic PCA. The
validity and accuracy of this data needs careful assessment as it appears to be a
critical information set for identifying offshore provinces.
6. The half-degree resolution grid was much too coarse in resolving a number of
boundaries, particularly their interaction with the shelf. In future an integrative
analysis (of shelf, slope and offshore) is suggested where spatial resolution is tied
to the intrinsic scales of interest. Thus a polygonal analysis method (finite
elements) is advocated so that a more robust integration of the boundaries can be
achieved.
7. We made no attempt at resolving biotones and core provinces in the offshore
region (as was done for the IMCRA shelf region by CSIRO) as this requires a
careful analysis of the faunal elements of the offshore region (eg using the
extensive sharks and rays information set).
8. Given the half-degree resolution grid, boundaries are no more accurate than this
resolution.
9. We did not examine the Jenkins shelf sediment data. This dataset may be
important in providing part of the basis for a comprehensive habitat scale
information set for the shelf region (along with such datasets as the Kirkman
seagrass and subtrate-type data). The AGSO 30 second arc bathymetry would
likewise be useful in resolving the fine-scale habitat structure in the offshore
region. Here again a much finer resolution analysis is required.
10. Time constraints prevented a full classification of the data and we manually
compiled the final boundaries of the Large Marine Domains from the three
analyses. A more comprehensive and robust classification analysis can be carried
out given more time.. In particular the rich structure off the north-western part of
WA needs careful resolution.
11. The claimable seabed areas were not included in this analysis because of a lack of
available data. Their boundaries are shown on the map for consistency.
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References
CSIRO (1996) Interim marine bioregionalisation for Australia: Towards a national
system of marine protected areas. Report to Department of the Environment, Sport
and Territories. Ocean Rescue 2000 report series on a National Representative
System of Marine Protected Areas.
Peters, D. (1990) Cartographic visualisation and generalisation: representation of
ecological data. Proceedings of Resource Technology 90, Second International
Symposium on Advanced Technology in Natural Resource Management, American
Society for Photogrammetry and Remote Sensing.
David T Sandwell, Walter H F Smith, Stuart M Smith, Christopher Small (1998)
Measured and estimated seafloor topography. (Website at:
http://topex.uscd.edu/marine_topo/mar_topo.html
Data from:
ftp://topex.uscd.edu/pub/global_topo_2min/topo_6.2.img)
Acknowledgements
The following individuals and organisations were instrumental in providing data and
information, or facilitating the data acquisition:
Dr Gordon Anderson (Environment Australia) for negotiating with a number of
organisations and individuals for access to datasets and for facilitating their transfer
to the project.
Dr Dietmar Mueller (University of Sydney) for access to the Plate Age data grid and
helpful information on the interpretation of the data.
Mr Adrian Bugg (Portfolio Marine Group, Environment Australia) for technical
assistance in transferring the AGSO 30 second arc bathymetry, slope analysis and the
EEZ boundaries from the ERIN archive.
Mr Ian McLeod (CSIRO Marine Research) provided the CAMRIS marine sediments
coverage (converted to ArcInfo coverage by ERIN from the CSIRO Wildlife &
Ecology SPANS coverage).
Dr Chris Jenkins (University of Sydney) provided the AusSeaBed point data holding.
Dr Simon Pigot (DELM, Tasmania) processed the PCA data for input to the gradient
analysis.
Mr Randall Gray assisted by writing a program to preprocess the data in preparation
for the statistical analyses.
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