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Compiled by Leon P. Zann
Great Barrier Reef Marine Park Authority, Townsville Queensland
Department of the Environment, Sport and Territories, Canberra (1995)
ISBN 0 642 17391 5
Continental Australia has around 2.5 million square kilometres of geomorphic continental shelf, half of which is less than 50 metres deep. The continental slope which drops from a depth of 150 metres to 4,000 metres, is at least 2 million square kilometres in area. The total area of the continental shelf around Australia, as defined by the 1982 United Nations Convention on the Law of the Sea, is 14.8 million square kilometres. Under the Convention definition, the Continental Shelf can extend beyond the 200 nautical mile EEZ, and in Australia's case it does so in various places.(1),(58)
The communities on the deeper areas of sea floor are almost completely unknown to science(13). Only three qualitative studies have ever been made on Australia's shelf, and only two areas of the slope have ever been visited by scientists. Sites examined on shelves and slopes on the Great Barrier Reef, Bass Strait and North West Shelf had very high biodiversity, and very high proportions of species previously unknown to science(13).
Little is known of human impacts on sea floor communities. The rate of sedimentation on the sea floor has greatly increased since European colonisation of Australia by factors of 10 to 100, and even more in some areas(3). Some shelf and slope fish species have been severely overfished, and trawl nets may dislodge attached species such as sponges and modify the habitat and food chains(32). Dredging and dumping of wastes may also cause localised disturbances around ports(36).
Most of Australia's sea floor is not actively managed(13),(67). However, trawling is prohibited in some areas (e.g. in parts of the Great Barrier Reef Marine Park(69)), and dumping of wastes on the sea floor is controlled under international conventions (e.g. London Convention) and various Commonwealth and State/Territory legislation(36).
Phytoplankton, the minute algae which make up the floating pastures of the sea, is the food base of the oceans.
Most rivers, estuaries and coastal waters near Australia's large population centres show signs of eutrophication. Blooms of toxic plankton are increasingly common in areas such as the Hawkesbury River and Tuggerah Lakes (NSW), Gippsland Lakes and Port Phillip Bay (Vic), Huon and Derwent Rivers (Tas), Port River (SA) and Cockburn Sound (WA).(14),(42)
Blooms of toxic marine algae, which are thought to have been introduced from other countries in ships' ballast waters(14),(42),(48), are now periodic, serious problems in parts of Tasmania(54) and Victoria(53) where they kill marine life and cause the closures of shellfish farms.
Figure 22: The distribution of three distinct marine phytoplankton communities in Australian waters: (a) tropical oceanic species;(b) tropical neritic species; and (c) temperate neritic species. These assemblages support different marine food chains and are likely to have different sensitivities towards nutrient and pollutant stress.