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)
Coral reefs [CO Indicator 2.3]
Formed from the calcareous skeletons of many species of corals and other organisms, coral reefs support a diversity of fish, invertebrates and plant life.
Coral reefs are exceptionally diverse marine ecosystems that thrive in relatively low nutrient tropical waters. Australia has the largest area of coral reefs in the world, including some of the most diverse and well known internationally.
A global assessment of reefs (Wilkinson 2000) shows continuing decline - about 25% of the world's reefs have been effectively lost. The largest single cause has been the massive climate-related coral bleaching event of 1998, which destroyed about 16% of the world's coral reefs in nine months. Probably half of these reefs will never recover. The bleaching event was indiscriminate: impacts were equally severe on pristine, remote reefs as on reefs already under major human stresses. Coral bleaching occurs when the water temperature exceeds a certain threshold, usually just over 30C, and the symbiotic algae in the coral tissues are expelled, allowing the white calcium carbonate skeleton to show through the clear animal tissue cover. If the temperature remains high for more than a few weeks the coral dies.
Australia was fortunate in 1998 that only 3% of reefs were destroyed from bleaching. It was also estimated that a further 1% of Australia's coral reefs have been destroyed from other causes, including sediment and nutrient runoff from land, increased recreational and commercial fishing, the Crown of Thorns Starfish, mining of sand and rocks.
Australia's coral reef systems include:
- Great Barrier Reef system in Queensland of some 2300 km in length,
- Ningaloo Reef off the Western Australian coast,
- High-latitude coral reefs, e.g. the Solitary Islands off the New South Wales coast; Elizabeth and Middleton Reefs on the Lord Howe Rise; and Flinders Reef off Brisbane,
- Torres Strait reefs,
- Coral Sea reefs, e.g. the Coringa-Herald Reserve system and the Lihou Reef which is the largest reef system in the Coral Sea,
- North West Shelf reefs, e.g. Ashmore Reef off Western Australia, Scott (a pinnacle) and Seringapatam Reefs and Rowley Shoals (marine park), Australia's only ' shelf-edge atolls',
- Houtman-Abrolhos Islands reef system, offshore from Perth are the most southerly reefs in the Indian Ocean, and
- Cocos (Keeling) atoll, Australia's only true atoll.
Australian coral reefs are under pressures in some locations. These pressures include:
- sediment and nutrient runoff at certain coastal locations is increasing steadily through human activities - primarily the effects of agriculture and land use practices, combined with increasing industrial and urban development,
- increasing recreational and commercial fishing at some locations, and
- increasing pressure for tourism developments in some locations.
The Great Barrier Reef is managed by a special-purpose Great Barrier Reef Marine Park Authority. The Authority developed a 25-year strategic plan for the Great Barrier Reef World Heritage Area in 1994.
Zoning plans have been implemented over the whole of the Great Barrier Reef Marine Park, with several detailed management plans for specific areas. These plans closely regulate human use over thousands of square kilometres. A Representative Areas Program now under way aims to protect the biodiversity of the World Heritage Area by developing a network of highly protected areas that represent all 72 bioregions recently mapped across the Great Barrier Reef.
The protection of reefs and their habitats through designation as National Nature Reserves has been used for the Coringa-Herald and the Lihou Reefs, located on the Coral Sea plateau east of Cairns.
Ningaloo Reef is Australia's largest fringing reef, stretching 230 km along a very lightly populated coastline.
Ningaloo Reef has an estimated 300 species of coral, 500 fish species and 600 mollusc species. The Marine Park lies on the migration path of the Humpback Whale, is home to turtles and Dugongs, and regularly hosts migratory birds. It is the only place in the world known to be visited regularly and in significant numbers by the Whale Shark (Rhincodon typus).
It is a marine park under both Western Australian legislation (for the inshore waters) and Commonwealth legislation (for offshore waters). Ningaloo Marine Park is the site of a burgeoning tourism industry.
Recent monitoring surveys of the Ningaloo Marine Park show that, apart from a few localised areas, the benthic communities in the park, including corals and macroalgae, are in excellent condition. The results suggest that the impact of human activity in the park is minimal, compared to natural events. Most evidence of human activity is litter associated with recreational fishing activities, particularly in the vicinity of popular moorings (e.g. Bundegi and Coral Bay) and fishing areas. Coral damage from boat moorings, boats and divers was observed at several locations in the marine park. The most significant damage to coral communities is in the southern Bills Bay area, adjacent to the coastal town of Coral Bay. Coral bleaching has not been extensive and has been observed on relatively few individual colonies.
The Great Barrier Reef Marine Park
The Great Barrier Reef is the largest single reef system in the world, stretching for over 2300 km. It extends from the tropics to the temperate zone, with diverse habitats and reef types. It is the world's largest World Heritage Area, covering about 35 million hectares. The population density is relatively low on the neighbouring lengthy coastline of north-east Australia and shipping activity is moderate compared to other tropical ports like Singapore (Reichelt 2000). The World Heritage Area covers not only coral reefs but also extensive areas of seagrass, mangrove, soft bottom communities and island communities.
The Great Barrier Reef World Heritage Area supports:
- six of the world's seven species of marine turtles,
- the largest Green Turtle breeding areas in the world,
- over 3000 km2 of seagrass meadows,
- 2000 km2 of mangroves, including 54% of the world's mangrove biodiversity,
- 2904 coral reefs, built from 359 species of hard coral,
- more than 1500 species of fish,
- 1500 species of sponges, which is 30% of Australia's diversity of sponges,
- 800 species of echinoderms, which is 13% of the world's diversity,
- over 5000 species of molluscs, and
- over one-third of the world's species of soft coral and sea-pens.
The World Heritage Area is also of cultural importance, containing many middens and other archaeological sites of Aboriginal or Torres Strait Islander origin. Some notable examples occur on Lizard and Hinchinbrook Islands, and on Stanley, Cliff and Clack Islands where there are spectacular galleries of rock paintings.
Research on the Great Barrier Reef habitats and species is published by the Great Barrier Reef Marine Park Authority, the Australian Institute of Marine Science, the CRC for the Great Barrier Reef World Heritage Area and others. For example, populations trends in key groups of organisms in the Great Barrier Reef Marine Park has been monitored since 1985 for management purposes (Sweatman et al. 2000).
The Great Barrier Reef is currently in a near-pristine state over large areas, but there are some provisos:
- runoff of freshwater carrying nutrients, sediments and pollutants is affecting the coastal margins of the Great Barrier Reef region,
- water quality in parts of the coastal margin is likely to be in slow decline from cumulative effects of human activities,
- there are areas of local depletion by fishing (both recreational and commercial) near to human settlements,
- the intensity and frequency of outbreak of the Crown of Thorns Starfish (Acanthaster planci) is causing a major reduction of living coral over very large areas of the Great Barrier Reef, yet the precise triggers for the outbreaks of this boom-and-bust species remain uncertain, although freshwater runoff has been implicated, and
- shipping in the region is increasing and so is the possibility of an increased number of pilotage accidents.