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Seabed habitat mapping of the continental shelf of NSW

DECCW scientists have, for the first time, created a seamless map of the bathymetry and the sediments of the seabed in NSW State coastal waters, and used new technology to provide great detail of some areas. The mapping has greatly improved our knowledge about the distribution, extent and structure of seabed habitats on the inner and mid-continental shelf of NSW.

DECCW scientists collated known information about seabed habitats in NSW, and surveyed areas with swath acoustic mapping to fill gaps. The scientists collated and analysed existing information from:

  • broad-scale bathymetric (1:150,000 Australian Hydrographic Charts) and marine sediment data
  • seabed habitat data from previous single-beam (in the Byron Bay, Sydney and Central Coast regions) and swath acoustic surveys
  • aerial photography (of nearshore reefs).

Existing information was combined with around 100 km2 of new swath acoustic data collected with the Department's interferometric side scan sonar system. This information was used to create high resolution maps of the seabed. Approximately 1,500 km2 of swath acoustic coverage from NSW continental shelf waters was collated from various sources.

About 120 km of underwater video surveys were examined to ground-truth the acoustic data and determine the dominant attached floral (seaweed and algae) and faunal (sea squirts, urchins, corals, etc) communities.

The data were used to map the fine-scale distribution and extent of seabed habitats, primarily rocky reef and unconsolidated habitats into shallow (0-25 m depth range), intermediate (25-60 m) and deep (60-200 m) classes. The key results are:

  • Shallow reefs in northern NSW waters were a mosaic of corals, urchin barrens, kelp and communities of mixed algae.
  • Intermediate reefs were dominated by sponges and other attached invertebrates, with some kelp and a mixture of algae.
  • Deep reefs were dominated by various sponges, which were massive, branching and cup-shaped, as well as attached invertebrates including ascidians (sea squirts), gorgonians and seawhips.
  • Reefs in central and southern NSW have a similar composition to sub-tropical northern region except that the coral habitat in the north is replaced mainly with beds of seaweed.
  • Along most of the NSW coast there are prominent rocky reef outcrops seaward of most headlands. There are also significant reef systems on the continental shelf that are not continuous to shore, as well as others which are continuous to shore associated with offshore islands.
  • In most areas which were swath mapped, there were larger areas of rocky reef habitat than can be seen on hydrographic charts (which only show significant shoal areas of larger reef systems).
  • Many reefs extended into Commonwealth waters in the mid-shelf region.
  • Significant reef systems were mapped offshore of Yamba, Solitary Islands, Nambucca region, Black Head, Port Stephens, Terrigal, Batemans Bay and Eden. The reefs are very different in their geomorphic structure (e.g. boulders, gutters, walls, pinnacles) and extent of patchiness, although there was no obvious latitudinal or cross-shelf trend in reef structure.
  • The soft-sediment habitats on the shelf were complex, and were mostly inner-shelf sand, mid-shelf muddy sand and outer-shelf coarse sand (with some local variations).
  • Finer sediments occur in patches offshore of the Yamba, Wooli, Newcastle, Sydney, Wollongong and Batemans Bay regions. Coarser sand occurs on the mid or outer shelf offshore of Byron Bay, Yamba, Nambucca Heads, Crowdy Head, Jervis Bay and Narooma.
  • There were areas of coarse sediment on the inner shelf throughout the Solitary Islands, Port Stephens, Sydney and Wollongong regions.
  • There were sand ripples and waves in the soft-sediments on the inner and mid-shelf, which had various particle sizes and shell content.
  • There were areas with boulders, cobbles and pebbles, particularly near rocky reef.
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Page last updated: 21 March 2011