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The Twofold Marine Bioregion*

The Twofold Shelf Marine Bioregion encompasses the area east of Wilsons Promontory, into New South Wales as far north as Tathra. It extends south to the Kent Group of islands in Bass Strait.

What characteristics distinguish this bioregion?

  • It has an exposed coastline with long sandy beaches broken by rocky headlands and numerous coastal lagoons.
  • There is a moderate tidal range of approximately 2m.
  • Variable wave energy.
  • Ocean water temperatures are influenced by the warmer waters of the East Australian Current that originates in the tropics.
  • Reefs are generally dominated by marine animals from warmer waters that occur commonly in southern New South Wales.
  • The kelps Ecklonia and Phyllospora are the dominant seaweeds.
  • The large black sea urchin Centrostephanus rodgersii is common. This animal removes kelp from shallow reefs, creating bare areas known as 'barrens'.

What are some of the significant natural values of the bioregion?

  • The exceptionally high diversity of reef-life at Point Hicks including the magnificent sponge gardens at Whaleback Rock.
  • Areas of the sandy seafloor off the Ninety Mile Beach have some of the highest levels of diversity of tiny sand animals recorded on earth.
  • Gabo Island in eastern Victoria is home to the world's largest colony of Little Penguins Eudyptula minor.

Marine Protected Areas in the region

Ninety Mile Beach Marine National Park
Beware Reef Marine Sanctuary
Point Hicks Marine National Park
Cape Howe Marine National Park

* What is a marine bioregion?
A marine bioregion is a large area of the sea that, through the complex interaction of ocean currents, wave energy, seawater temperature, seafloor geology and geography, displays a distinct grouping or pattern of marine plant and animal communities and species.
For example, the plant and animal species and the habitats that dominate the warm waters of the Twofold bioregion in eastern Victoria are very different to those found in the cold, open waters of the Otway bioregion in the west.
The map on the home page suggests that marine bioregions appear to be divided into distinct areas with clearly defined boundaries, but the boundaries between them are dynamic and not hard lines.
The ocean waters on Australia's continental shelf have been classified into 60 marine bioregions. Victoria's coastal waters span 5 of these regions.