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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
Australia's marine environment extends from the shores and wetlands along the coastline to the abyssal deeps, and from the coral reefs of Torres Strait in the north to the pack ice of the antarctic continent in the south.(1) The following section describes the main types of marine and coastal habitats and ecosystems in Australia, the major issues and threats affecting them, and assesses their environmental health or status.
Estuaries are the meeting place of fresh and salt waters. Naturally rich in nutrients, estuaries are ecologically highly productive, and are important fish habitats. In Australia, estuaries and sheltered bays have also been the focus of urban and industrial development, and are important for recreation.(6)
Australia has 783 major estuaries: 415 in the tropics; 170 in the subtropics; and 198 in temperate areas. The long arid coastlines in the south-west and west have few estuaries.(6)
Table 1: distribution and areas (sq km) of estuarine habitat types
Most river catchments in eastern and southern Australia have been extensively cleared. This has resulted in land erosion, sedimentation of rivers and increased sedimentation and levels of nutrients downstream in estuaries, bays and adjacent coastal waters. High sediment levels in the water reduce light penetration which affects rates of photosynthesis. When sediments settle they can also smother seabed organisms. Sedimentation of estuaries and shipping channels causes shoaling and alters currents. Sedimentation is a major problem in ports and shipping channels, necessitating regular dredging. This resuspends sediments, creating further environmental problems.(6),(42)
The flows of many of Australia's rivers have also been significantly altered by dams and barriers, reclamation of wetlands, irrigation schemes and flood mitigation schemes, affecting the hydrodynamics or flushing characteristics of estuaries.(1),(6),(40)
Table 2: Overview of Australia's estuaries
Where rivers drain disturbed acid soils, such as in northern New South Wales and southern Queensland, estuaries may become periodically acidic. This increases levels of dissolved aluminium and iron which form compounds very toxic to fish. As a result fish diseases such as 'red-spot' disease and fish kills are increasingly common in estuaries.(52)
At least 64% of estuaries in New South Wales and 22% in Victoria are considered to have poor water quality. Catchments in the tropical north are less affected by human activities but may carry heavy sediment loads resulting from soil erosion.(6)
Figure 9: Threatened estuaries and enclosed marine waters of high conservation or fisheries value.
Unnaturally elevated sediments and nutrients have led to an alarming decline in seagrass beds in temperate Australia(10). Poor water quality and loss of habitat have also caused a decline in estuarine fisheries. For example, fisheries are thought to be threatened in 21% of estuaries in New South Wales and 23% in Victoria(6). However, eutrophication of some estuaries has enhanced their value for oyster aquaculture(30).
Of great concern in south-eastern and south-western Australia is the declining water quality and eutrophication of coastal lakes and lagoons, particularly those which are insufficiently flushed by the sea, for example, Tuggerah Lakes and Lake Macquarie (NSW), Gippsland Lakes (Vic) and the Peel-Harvey system (WA)(42),(52),(53),(56). As coastal lakes are largely restricted to the densely inhabited south-eastern coastal strip, a significant proportion of the nation's coastal lakes has been degraded.
The intertidal shores are the meeting place of the land and sea. Shores are periodically immersed by sea and exposed to air, and subject to extremes in salinity. They are often enriched by land nutrients and have a high biological productivity. Shores have a high diversity of very specialised animals and plants, and may require special conservation measures. Australia's shores include open coasts with rocky headlands, cliffs and sandy beaches; and sheltered coasts, bays and estuaries with muddy and sandy tidal flats.(1),(9)
Figure 10: Australian shores are varied and picturesque. (a) Warm-temperate humid coastlines in the south-east are noted for their rocky headlands and long sandy beaches. Cape Byron (NSW). (b) Warm-temperate arid coastline. The spectacular Nullabor Cliffs stretch unbroken for around 180 kilometres of the Great Australian Bight (SA). (c) Arid Shark Bay coast (WA). (d) Tropical arid coastline. Fringing coral reefs of Ningaloo (WA). (e) Tropical humid coastline. The wide, macrotidal shore near Hope Islet (NT).
Table 3: Areas of major coastal landforms and of total coastline
Australian shores are also the meeting place for people. Beaches are the most popular areas for outdoor recreation in Australia, and are popular for recreational fishing, swimming and surfing.(23),(28),(29)
Intertidal rocky shore habitats are often limited in area. They are also potentially vulnerable to human impacts. Threats to shore communities include over -harvesting of molluscs, crustaceans and sea urchins for food and bait, trampling by fishers and other visitors(34), oil slicks and other pollutants which float on the sea surface(39), and loss of habitat(40). In the more populous south-east, south and south-west of Australia, significant areas of shores around coastal cities and towns have been reclaimed or alienated by seawalls, port development, industry, housing and tourism and recreational facilities(40),(51-54).
Despite their great ecological and recreational values, shores are often not well protected. On some coasts they are protected through terrestrial conservation reserves which extend to the low water mark. Management of intertidal areas may be confused by overlapping responsibilities, and lack of coordination amongst management agencies. Effects of human uses are also not well understood or monitored.(9),(67)
Because of serious concerns on the over-harvesting of intertidal invertebrates, in 1993 New South Wales introduced a management plan for its shores which included an extensive system of Intertidal Protected Areas, controls on tools used in collecting, and strict bag limits.(6),(52),(77)