Coasts and Oceans Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Australian State of the Environment Committee, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06751 5
Habitats and species (continued)
Continental shelf and slope
The inner continental shelf encompasses the waters and seabed from the shore to the midshelf (about 50 metres deep). Beyond this is the outer shelf extending to the 'break' (typically 150 metres). The continental slope encompasses the area beyond the shelf break into water depths of 4000 metres or more.
Australia's continental shelf covers about 2.5 million km2, half of which is less than 50 metres deep. Its width varies from 15 kilometres off the coast of New South Wales to 400 kilometres in the Timor Sea. The North West Shelf is about 350 kilometres wide, and supports Australia's major offshore petroleum production activities.
The continental shelf consists mainly of soft sediments, but in places, may comprise gravel and pavement rock. These form substrate for a large variety of invertebrate species, including sponges and bryozoans. These long-lived communities are of critical importance as habitat and food for fish.
Most of the slope environment is too deep for plants because of the reduced light conditions, and the main living organisms are the animals that live on and in the sediments. The dominant large animals are marine worms, crustaceans, echinoderms (e.g. sea urchins) and shellfish. The epifauna include hydroids, sea-pens, small bryozoans and sponges.
Some studies of this environment have been undertaken in the last five years. Surveys of benthic habitat in the Twofold Shelf region off Victoria yielded over 60 000 individuals from 803 species (Coleman et al. 1997). About half of these species were previously undescribed.