Australia's marine area is one of the largest in
the world, extending over about 16 million square kilometres 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 (ABS 2006). At least
one-third of this coastline borders the tropical savannas
Estuaries | Coral Reefs | References |
North Australian beaches are important nesting
sites for a number of species of marine turtles
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. Some of Australia’s most
spectacular cliff coastlines, mangrove forests, archipelagos,
island groups and coral reef systems are found within the tropical
These include sections of the world famous Great Barrier Reef
and the Bonaparte Archipelago off the Kimberley coast.
These coastal and marine habitats are home to a wealth of fauna
and flora species. On a broader scale these regions contribute to
- The highest levels of biodiversity in the world for a number of
types of marine invertebrates.
- The highest mangrove species diversity.
- The world's largest areas and highest species diversity of
tropical and temperate seagrasses, and
- One of the largest areas of coral reefs (SoE 2001).
Two broad habitat types found within the coastal region of the
tropical savannas are estuaries and coral reefs.
Estuaries are common along the tropical savannas coast.
Estuaries are semi-enclosed coastal water bodies commonly occurring
where freshwater from rivers or creeks meet the sea. Here, a mixing
of salt and fresh water occurs, creating many different habitats,
essential for the survival of the many plants and animals who have
adapted to living here. Estuaries are important as;
- They naturally filter the water keeping the water quality
- They provide habitats for fish, birds and other wildlife to
live, feed and reproduce. Many types of fish, shellfish,
crustaceans and other marine animals rely on the sheltered waters
as protected places to breed and lay their eggs.
- They have high nutrient levels and generally sheltered waters
which provide ideal environments for fish and other animals to lay
eggs and for their young to feed and grow.
Estuaries are important for other reasons too. They are popular
places where people live and recreate, and tourists like to visit.
Fishing, boating, camping, hunting and bird watching are popular
pastimes in tropical savanna estuaries. Estuaries also hold
important cultural significance for many Indigenous people .
Commercial fishing and aquaculture often thrive in estuaries,
which are also the preferred sites for ports and harbours. 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 development in the estuary as
well as upstream in the catchment.
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.
Coral reefs are made up of dead corals and other organisms that
have a limestone skeleton. These are cemented together by some
algal species and by physical processes. The reef builds at a rate
of a few millimetres a year until it reaches the water’s
surface, and then it starts growing 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).
Reefs are among the most complex and diverse ecosystems in the
world. The Great Barrier Reef which lies off the eastern coast of
Australia’s tropical savannas region is the largest coral
reef in the world, consisting of about 3,000 individual reefs
covering an area of 345,950 square kilometres, 2300km in length.
This huge reef system is teeming with wildlife and supports more
than 1500 species of fish, 4000 types of mollusc and more than 200
species of birds. Some of the fauna you can find here include
fluorescently coloured nudibranchs, chameleon-like cuttlefish,
eels, trigger fish, dugong, green turtles and whales.
Australian coral reefs face a number of pressures and threats.
- Sediment and nutrient runoff into coastal areas from
agriculture and land use practices and increasing industrial and
- 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 2001).
A global assessment of reefs found that about 25% of the world's
reefs have effectively been lost. A massive coral bleaching event
in 1998 destroyed about 16% of the world's coral reefs in nine
months (Wilkinson 2000). It is thought that half of these reefs
will never recover.
Coral bleaching occurs when the sea surface temperature goes
over a certain level, usually just over 30 0 C. The
coral appears ‘bleached’ (white) because the algae
which live alongside the coral polyps and provide the coral with
nutrients 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 two weeks, the
Australian Bureau of Statistics (2006)
Australian Yearbook 2006
CRC Reef (Cooperative Research Centre for Reef
Research) 2002, Australia 's Coral Reefs
Great Barrier Marine Park Authority
SoE (Australian State of the Environment
Committee) (2001). Coasts and Oceans , Australia State of
the Environment Report 2001, CSIRO Publishing on behalf of the
Department of the Environment and Heritage, Canberra.
Zann, L.P. (1995). Our Sea, Our Future: Major
findings of the State of the Marine Environment Report for
Department of the Environment, Sport and