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Australia's marine area is one of the largest in the world, extending over about 16 million square kilometres (including an Exclusive Economic Zone of some 11 square kilometres of ocean beyond the territorial sea), from Antarctica to near-equatorial latitudes - more than double Australia's land area. The length of the coastline of Australia's mainland and islands is about 61,700 km. Australia's marine and coastal regions host a broad variety of habitats ranging from estuaries and mangroves, dunes and beaches, rocky and coral reefs, seagrasses, gulfs and bays, seamounts, and a huge area of continental shelf.
There are two distinct marine biogeographic regions in Australia: the temperate south, and the tropical north, which overlap on the western and eastern coastlines. In the south, which has been geographically and climatically isolated for around 40 million years, about 80-90% of species of most marine groups are endemic (found only in a particular area), or restricted to this area. In the north, which is connected by currents to the Indian and Pacific Ocean tropics, only around 10% of most groups are endemic (Zann 1995).
Land use and other human activities impact on the coastline and marine environment in a number of ways. Pressures can arise from local land-based pollution, poor drainage and effluent management, or can emanate from land disturbance in catchments many hundreds of kilometres away. Activities related to fisheries and aquaculture, the shipping and port industries, and marine tourism and recreation, are all potentially threatening to the health of Australia's coastal and marine environments.
A significant factor causing pressure on some parts of Australia's coastline is high population density in coastal regions, particularly along the east and south-east coasts and along the west coast south of Perth. As at 30 June 1996, 83% of the population lived within 50 km of the coast. All states except the Northern Territory and South Australia are experiencing higher rates of population growth and urban development within 3 km of the coast compared to the rest of Australia (Newton et al. 2001). The coastal strip is an ecologically sensitive zone, and urban sprawl, and pollution of rivers, lakes and seas, were described by the Resource Assessment Commission as the two most important problems faced by the coastal zone (RAC 1993).
This section focuses on two significant marine ecosystems - estuaries and coral reefs. It discusses the significance of these habitats and the processes which threaten them. This is followed by a discussion of marine protected areas in Australia. Further information on the Great Barrier Reef Marine Park can be found in the article Sustainable tourism in the Great Barrier Reef Marine Park, which follows Tourism.
Estuaries are semi-enclosed coastal water bodies occurring where inland freshwaters meet inshore marine waters. These waterways are typically marine or brackish, but occasionally are dominated by freshwater. Estuaries are highly productive and diverse habitats that constitute an important part of Australia's coastal environment. They support fisheries, aquaculture and recreational activities, and are the preferred sites for many settlements, and for industry and ports. Australia has over 1,000 estuaries along its coastline. Of these, 783 are regarded as major estuaries: 415 in the tropics, 170 in the subtropics, and 198 in temperate areas (Zann 1995). The long arid coastlines in the south-west and west have few estuaries.
Australia's estuaries occur over a wide range of geological and climatic conditions and consequently display a great variety of forms. Different types of estuaries are defined by the relative influence of the natural processes that shape them. As part of the National Land and Water Resources Audit (NLWRA), Australia's estuaries were classified based on whether they are dominantly affected by river flows, tidal or wave action. According to the NLWRA, 17% of estuaries are wave-dominated estuaries; 11% are tide-dominated estuaries; 10% are wave-dominated deltas; 9% are tide-dominated deltas; 5% are strand plains, coastal lakes and lagoons; and 35% are tidal creeks and flats. Tide-dominated systems are mainly located in northern tropical Australia. Wave-dominated systems are mainly located in southern temperate regions. Their management needs and ecological processes vary (NLWRA 2002a).
Australia's estuaries face a number of pressures from urban and industrial development in coastal areas, and from disturbance through land use and vegetation clearance in catchments. For example, estuaries are often used for dumping, sand or water extraction, construction of marinas, ports and canal estates, and are susceptible to changes in natural flows caused by the construction of dams and weirs. Such pressures threaten the condition of estuaries by causing excess nutrient concentrations, sedimentation, loss of habitat, weed and pest infestation, and the accumulation of pollutants.
Of the 972 estuaries assessed by NLWRA, 9% were in extensively modified condition, 19% were in modified condition, 22% were in largely unmodified condition and 50% were in near-pristine condition (table 14.24). Most of Australia's near-pristine estuaries are located away from population centres. The majority of estuaries in the Northern Territory are in near-pristine condition, primarily as a result of low population pressure and minimal catchment and estuarine shoreline development (graph 14.25). Conversely, most of the estuaries in New South Wales are under intense urban development pressure, with approximately 80% of the state's population living near an estuary (NLWRA 2002a).
Coral reefs are accumulations of dead corals and other organisms with a limestone skeleton, cemented together by some algal species and by physical processes. The reef builds slowly towards the surface of the water, at the rate of a few millimetres per year. Once the reef reaches sea level, the reef grows horizontally. Reefs build as a result of the growth of corals and other living creatures. The accumulation of sand and rubble formed when organisms are broken down by waves and animals, such as worms and sponges that bore into the coral, also add to reef growth (CRC Reef 2002).
Coral reefs are exceptionally diverse marine systems that thrive in relatively low nutrient tropical waters and can only grow in waters where temperatures rarely fall below 180C. They are among the most productive and complex ecosystems in the world. The Great Barrier Reef is the largest coral reef in the world, consisting of about 3,000 individual reefs covering an area of 345,950 square kilometres. Australia's coral reef systems include:
Australian coral reefs face a variety of pressures. These pressures include: run-off of sediment and nutrients at a number of coastal locations, which is steadily increasing through human activities (primarily from the effects of agriculture and land use practices, as well as increasing industrial and urban development); increased recreational and commercial fishing; increasing pressure from tourism developments; threats from invasive and pest species such as the crown of thorns starfish; and coral bleaching possibly due to global warming (SoE 2001b). The article Sustainable tourism in the Great Barrier Reef Marine Park addresses management of the impacts on the Park from tourism.
A global assessment of reefs found that about 25% of the world's reefs have effectively been lost. The largest single cause has been a massive coral bleaching event in 1998, which destroyed about 16% of the world's coral reefs in nine months (Wilkinson 2000). It is likely that half of these reefs will never recover. The impacts of the bleaching event were equally as damaging on pristine, remote reefs as on reefs already stressed by human causes. Coral bleaching occurs when the sea surface temperature goes over a certain level, usually just over 300C. The symbiotic algae (which provide coral polyps with nutrients) in the coral tissues are then expelled, allowing the white calcium carbonate skeleton to show through the clear animal tissue cover. If the temperature remains high for more than two weeks, the coral dies. In 1998, 3% of reefs were destroyed by coral bleaching in Australia. It is estimated that a further 1% of Australia's coral reefs have been destroyed by other causes, such as sediment and nutrient run-off from the land, increased recreational and commercial fishing, and the mining of sand and rocks (SoE 2001b).
During March-April 2002, the Great Barrier Reef Marine Park Authority and the Cooperative Research Centre for the Great Barrier Reef World Heritage Area conducted aerial surveys to determine the area of bleaching on the Reef (GBRMPA 2002). The surveys studied 641 reefs, representing 22% of all reefs in the Marine Park. They found that bleaching was extremely widespread, extending over 1,450 km, including reefs from near the coast to the outer reefs. About 21% of these reefs showed a high level of bleaching (30% or greater of the reef affected), 36% were moderately bleached (1-30% of reef affected) and 43% had low to negligible levels of bleaching (less than 1% of the reef affected) (table 14.26).
In the Great Barrier Reef, during 2002 the worst affected reefs were those closest to the mainland. Nearly 50% of reefs near the coast (inshore reefs) were bleached to high or very high levels, with only 30% relatively unaffected (table 14.26). Many of the outer reefs (offshore reefs) were also affected, with over 50% of reefs bleached to some extent. Among the bleached reefs, however, the intensity of bleaching was highly variable (GBRMPA 2002).
Marine protected areas
A key response to pressures on marine and coastal environments is the establishment of a National Representative System of Marine Protected Areas. This conservation reserve system formally addresses the management and protection of marine areas while allowing a range of sustainable uses. The preservation of the ecological viability of marine and estuarine systems and the protection of marine biodiversity are integral to the aims of Marine Protected Areas. These areas can be declared under Commonwealth, state or territory legislation in seas within each jurisdiction's waters. In November 2000, there were 190 marine protected areas covering about 60 million hectares (SoE 2001b).
Marine protected areas range from nature reserves to marine parks, and can include reefs, seagrass beds, shipwrecks, archaeological sites, mangroves, underwater areas on the coast and seabeds in deep water. The Commonwealth Government has under its jurisdiction 13 marine protected areas, including the Great Barrier Reef Marine Park (table 14.27). With almost 34 million hectares protected, the Great Barrier Reef Marine Park is the world's largest marine protected area and, given its status as a World Heritage area, it is subject to a special management program administered by the Great Barrier Reef Marine Park Authority.