Seascapes of the Australian Margin and Adjacent Sea Floor: Methodology and Results

Abstract

Geoscience Australia has undertaken a classification of biophysical datasets to create seabed
\nhabitat maps (termed ‘seascapes’) for the Australian margin and adjacent sea floor. Seascapes
\ndescribe a layer of ecologically meaningful biophysical properties that spatially represents
\npotential seabed habitats. Each seascape area corresponds to a region of the seabed that
\ncontains similar biophysical properties and, by association, potential habitats and
\ncommunities. The procedure adopted is inspired by the shelf classification applied in eastern
\nCanada where physical properties (sediment type, physiography, bed roughness, wave and
\ncurrent regime) were used to define ecologically meaningful habitats on the Scotian Shelf.
\nCreating seascapes as proxies for benthic marine biological communities using biophysical
\ndata is required because it is impossible to count and map the distribution of every organism
\nin the ocean.
\nThis report describes the iterative methods used to create the seascapes, including a
\ndetailed appendix documenting the different datasets used in each planning zone. Creating
\nthe seascapes is necessarily an iterative process whereby the available datasets are integrated
\nin different combinations, or added as they become available, using the ERMapper™
\nunsupervised, crisp ISOclass classification program. In each classification only biophysical
\nproperties that have consistent and definable relationships with the benthic biota and are
\nknown in sufficient detail across Australia’s entire marine region are used to create the
\nseascapes. An initial validation of the classification technique has been undertaken on a
\nsubset of the data for the shelf surrounding Tasmania using an alternative unsupervised
\nfuzzy classification. Results of this validation indicate that the unsupervised classification
\nmethodology provides consistent and reliable classes for defining the seascapes.
\nFinally, a quantitative method designed to determine where the greatest seabed
\nheterogeneity occurs to assist with the selection of potential sites for Marine Protected Areas
\nwas trialled on the final seascapes. This Focal Variety method conducted in ArcGIS simply
\ncounts up the number of seascape types within a specified radius (in this case 20 km). Focal
\nvariety analyses were conducted separately on the seascapes (which comprise continuous
\nspatial data) and geomorphology (which comprise categorical spatial data) and the results
\ncombined. Areas where many different seascapes occur are considered as potential habitat
\ndiversity hotspots.
\nThe mandate for creating the seascapes comes directly from the United Nations
\nConvention on Biological Diversity (CBD), which Australia ratified in 1994. The CBD
\nrequires Australia to set up a system of marine protected areas for the conservation and
\nsustainable use of threatened species, habitats and living marine resources and ecological
\nprocesses. We believe that the seascapes provide a useful method for assisting in the
\ndevelopment of this system of MPA’s by spatially representing seabed heterogeneity in a
\nconsistent, objective and robust way.
\nThe future of seascapes and surrogacy research is to work collaboratively with marine
\nbiologists and ecologists in the formation of seascapes for marine biodiversity prediction,
\nincluding undertaking targeted marine surveys to collect further physical and biological data
\nand building combined databases that permit direct correlation of data. This research will
\nimprove the accuracy and precision with which we can predict Australia’s marine
\nbiodiversity and thus strengthen confidence in decisions about the conservation and
\nsustainable use of Australia’s marine resources.