The Great Barrier Reef
is the largest coral
reef system in the world,
composed of over 2,900 individual reefs
and 900 islands stretching for 2,600 kilometres
(1,600 mi) over an area of approximately
344,400 square kilometres (133,000 sq mi).
The reef is located in the Coral Sea, off the coast
of Queensland in northeast Australia.
Life on the Great Barrier Reef
Barrier Reef can be seen from outer space and is the
world's biggest single structure made by living
This reef structure is composed of and built by
billions of tiny organisms, known as coral polyps.
The Great Barrier Reef supports a wide diversity of
life, and was selected as a World Heritage Site in
CNN has labelled it one of the 7 natural wonders of
The Queensland National Trust has named it a state
icon of Queensland.
A large part of the reef is protected by the
Great Barrier Reef Marine Park, which helps to limit
the impact of human use, such as overfishing and
tourism. Other environmental pressures to the reef
and its ecosystem include water quality from runoff,
climate change accompanied by mass coral bleaching,
and cyclic outbreaks of the crown-of-thorns
The Great Barrier Reef is a distinct
physiographic province of the larger East Australian
Cordillera division. It encompasses the smaller
Murray Islands physiographic section.
Geology and geography
Australia has moved northwards at a rate of 7 cm
(2.8 in) per year, starting during the Cainozoic.
Eastern Australia experienced a period of tectonic
uplift, leading to the drainage divide in Queensland
moving 400 km (250 mi) inland. Also during this
time, Queensland experienced volcanic eruptions
leading to central and shield volcanoes and basalt
Some of these granitic outcrops have become high
After the Coral Sea Basin was formed, coral reefs
began to grow in the Basin, but until about 25
million years ago, northern Queensland was still in
temperate waters south of the tropics - too cool to
support coral growth.
The history of the development of the Great
Barrier Reef is complex; after Queensland drifted
into tropical waters, the history is largely
influenced by how reefs fluctuate (grow and recede)
as the sea level changes.
They can increase in diameter from 1 to 3
centimetres (0.39 to 1.2 in) per year, and grow
vertically anywhere from 1 to 25 centimetres
(0.4–12 in) per year; however, they are limited to
growing above a depth of 150 metres (490 ft) due to
their need for sunlight, and cannot grow above sea
The land that formed the substrate of the current
Great Barrier Reef was a coastal plain formed from
the eroded sediments of the Great Dividing Range
with some larger hills (some of which were
themselves remnants of older reefs
When Queensland moved into tropical waters 24
million years ago, some coral grew,
but a sedimentation regime quickly developed with
erosion of the Great Dividing Range; creating river
deltas, oozes and turbidites, which would have been
unsuitable conditions for coral growth. 10 million
years ago, the sea level significantly lowered,
which further enabled the sedimentation.
The substrate of the GBR may have needed to build
up from the sediment until the edge of the substrate
was too far away for suspended sediments to have an
inhibiting effect on coral growth. In addition,
approximately 400,000 years ago there was a
particularly warm interglacial period with higher
sea levels and a 4 degree Celsius change in water
The Reef Research Centre, a Cooperative Research
Centre, has found coral 'skeleton' deposits that
date back half a million years.
The GBRMPA considers the earliest evidence to
suggest complete reef structures to have been
600,000 years ago.
According to the Great Barrier Reef Marine Park
Authority, the current, living reef structure is
believed to have begun growing on the older platform
about 20,000 years ago.
The Australian Institute of Marine Science agrees,
which places the beginning of the growth of the
current reef at the time of the Last Glacial
Maximum. At around that time, the sea level was
120 metres (390 ft) lower than it is today.
From 20,000 years ago until 6,000 years ago, the
sea level rose steadily. As it rose, the corals
could then grow higher on the hills of the coastal
plain. By around 13,000 years ago the sea level was
60 metres (200 ft) lower than the present day, and
corals began to grow around the hills of the coastal
plain, which were, by then, continental islands. As
the sea level rose further still, most of the
continental islands were submerged. The corals could
then overgrow the hills, to form the present cays
and reefs. Sea level on the Great Barrier Reef has
not risen significantly in the last 6,000 years.The
CRC Reef Research Centre estimates the age of the
present, living reef structure at 6,000 to 8,000
The remains of an ancient barrier reef similar to
the Great Barrier Reef can be found in The
Kimberley, a northern region of Western Australia.
The Great Barrier Reef World Heritage Area has
been divided into 70 bioregions,
of which 30 are reef bioregions,
and 40 are non-reef bioregions.
In the northern part of the Great Barrier Reef,
ribbon reefs and deltaic reefs have formed; these
structures are not found in the rest of the Great
Barrier Reef system.
There are no atolls in the system,
and reefs attached to the mainland are rare.
Fringing reefs are distributed widely, but are
most common towards the southern part of the Great
Barrier Reef, attached to high islands, for example,
the Whitsunday Islands. Lagoonal reefs are also
found in the southern Great Barrier Reef, but there
are some of these found further north, off the coast
of Princess Charlotte Bay. Cresentic reefs are the
most common shape of reef in the middle of the Great
Barrier Reef system, for example the reefs
surrounding Lizard Island. Cresentic reefs are also
found in the far north of the Great Barrier Reef
Marine Park, and in the Swain Reefs (20-22 degrees
South). Planar reefs are found in the northern and
southern parts of the Great Barrier Reef, near Cape
York, Princess Charlotte Bay, and Cairns. Most of
the islands on the reef are found on planar reefs.
The Great Barrier Reef supports a diversity of
life, including many vulnerable or endangered
species, some of which may be endemic to the reef
Thirty species of whales, dolphins, and porpoises
have been recorded in the Great Barrier Reef,
including the dwarf minke whale, Indo-Pacific
humpback dolphin, and the humpback whale. Large
populations of dugongs live there.
Six species of sea turtles come to the reef to
breed – the green sea turtle, leatherback sea
turtle, hawksbill turtle, loggerhead sea turtle,
flatback turtle, and the olive ridley. The green sea
turtles on the Great Barrier Reef have two
genetically distinct populations, one in the
northern part of the reef and the other in the
Fifteen species of sea grass in beds attract the
dugongs and turtles,
and provide a habitat for fish.
The most common genera of sea grasses are
Halophila and Halodule.
Salt water crocodiles live in mangrove and salt
marshes on the coast near the reef.
Nesting has not been reported, and the salt water
crocodile population in the GBRWHA is wide-ranging
and with a low population density.
Around 125 species of shark, stingray, skates or
chimera live on the reef.
Close to 5,000 species of mollusc have been recorded
on the reef, including the giant clam and various
nudibranchs and cone snails.
Forty-nine species of pipefish and nine species of
seahorse have been recorded.
At least seven species of frog can be found on the
215 species of birds (including 22 species of
seabirds and 32 species of shorebirds) are attracted
to the reef or nest or roost on the islands,
including the white-bellied sea eagle and roseate
Most nesting sites are on islands in the northern
and southern regions of the Great Barrier Reef, with
1.4-1.7 million birds using the sites to breed.
The islands of the Great Barrier Reef also support
2,195 known plant species; three of these are
endemic. The northern islands have 300-350 plant
species which tend to be woody, whereas the southern
islands have 200 which tend to be herbaceous; the
Whitsunday region is the most diverse, supporting
1,141 species. The plant species are spread by
Seventeen species of sea snake live on the Great
Barrier Reef. They take three or four years to reach
sexual maturity and are long-lived but with low
fertility. They are usually benthic, but the species
that live on the soft sediment differ from those
that live on the reefs themselves. They live in warm
waters up to 50 metres (164 ft) deep and are more
common in the southern than in the northern part of
the reef. None of the sea snakes found in the Great
Barrier Reef World Heritage Area are endemic to the
reef, nor are any of them endangered.
More than 1,500 species of fish live on the reef,
including the clownfish, red bass, red-throat
emperor, and several species of snapper and coral
Forty-nine species are known to mass spawn, with
eighty-four other species found on the reef spawning
elsewhere in their range.
There are at least 330 species of ascidians found
on the reef system, ranging in size from 1 mm-10 cm
in diameter. Between 300-500 species of bryozoans
are found on the reef system.
Four hundred species of corals, both hard corals
and soft corals are found on the reef.
The majority of these spawn gametes, breeding in
mass spawning events that are controlled by the
rising sea temperatures of spring and summer, the
lunar cycle, and the diurnal cycle. Reefs in the
inner Great Barrier Reef spawn during the week after
the full moon in October, but the outer reefs spawn
in November and December.
The common soft corals on the Great Barrier Reef
belong to 36 genera.
Five hundred species of marine algae or seaweed live
on the reef,
including thirteen species of the genus Halimeda,
which deposit calcareous mounds up to 100 metres
(110 yd) wide, creating mini-ecosystems on their
surface which have been compared to rainforest
The most significant threat to the Great Barrier
Reef is climate change.
Mass coral bleaching events due to rising ocean
temperatures occurred in of the summers of 1998,
2002 and 2006,
and coral bleaching will likely become an annual
Climate change has implications for other forms of
life on the Great Barrier Reef as well - some fish's
preferred temperature range lead them to seek new
areas to live, thus causing chick mortality in
seabirds that prey on the fish. Climate change will
also affect the population and available habitat of
Another key threat faced by the Great Barrier
Reef is pollution and declining water quality. The
rivers of north eastern Australia provide
significant pollution of the Reef during tropical
flood events with over 90% of this pollution being
sourced from farms.
Farm run-off is polluted as a result of overgrazing
and excessive fertiliser and pesticide use. Due to
the range of human uses made of the water catchment
area adjacent to the Great Barrier Reef, water
quality has declined owing to the sediment and
chemical runoff from farming, and to loss of coastal
wetlands which are a natural filter.
It is thought that the mechanism behind poor water
quality affecting the reefs is due to increased
light and oxygen competition from algae.
The crown-of-thorns starfish is a coral reef
predator which preys on coral polyps. Large
outbreaks of these starfish can devastate reefs. In
2000, an outbreak contributed to a loss of 66% of
live coral cover on sampled reefs in a study by the
CRC Reefs Research Centre.
Outbreaks are believed to occur in natural cycles,
exacerbated by poor water quality and overfishing of
the starfish's predators.
The unsustainable overfishing of keystone
species, such as the Giant Triton, can cause
disruption to food chains vital to life on the reef.
Fishing also impacts the reef through increased
pollution from boats, by-catch of unwanted species
(such as dolphins and turtles) and reef habitat
destruction from trawling, anchors and nets.
As of the middle of 2004, approximately one-third of
the Great Barrier Reef Marine Park is protected from
species removal of any kind, including fishing,
without written permission.
Other threats to the Great Barrier Reef include
shipping accidents, oil spills, and tropical
The Great Barrier Reef has long been known to and
utilised by the Aboriginal Australian and Torres
Strait Islander peoples. Aboriginal Australians have
been living in the area from at least 40,000 years
and Torres Strait Islanders since about 10,000 years
For these 70 or so clan groups, the reef is also an
important part of their culture and spirituality.
The reef first became known to Europeans when the
HM Bark Endeavour, captained by explorer
James Cook, ran aground there on June 11, 1770,
sustaining considerable damage. It was finally saved
after lightening the ship as much as possible and
re-floating it during an incoming tide.
One of the most famous wrecks was that of the HMS
Pandora, which sank on August 29, 1791, killing
35. The Queensland Museum has been leading
archaeological digs to the Pandora since
However, as there were no atolls on the reef system,
it was largely unstudied in the 19th century.
During this time, some of the islands on the Great
Barrier Reef were mined for deposits of guano, and
lighthouses were built as beacons through the
as in Raine Island, the earliest example.
The Great Barrier Reef Committee was set up in 1922
which carried out much of the early research on the
After the Royal Commissions' findings, in 1975
the Government of Australia created the Great
Barrier Reef Marine Park and defined what activities
were prohibited on the Great Barrier Reef.
The park is managed, in partnership with the
Government of Queensland, through the Great Barrier
Reef Marine Park Authority to ensure that it is
widely understood and used in a sustainable manner.
A combination of zoning, management plans, permits,
education and incentives (such as eco-tourism
certification) are used in the effort to conserve
the Great Barrier Reef.
In July 2004, a new zoning plan was brought into
effect for the entire Marine Park, and has been
widely acclaimed as a new global benchmark for the
conservation of marine ecosystems.
The rezoning was based on the application of
systematic conservation planning techniques, using
the MARXAN software.
While protection across the Marine Park was
improved, the highly protected zones increased from
4.5% to over 33.3%.
At the time, it was the largest marine protected
area in the world, although as of 2006, the
North-western Hawaiian Islands National Monument is
In 2006, a review was undertaken of the Great
Barrier Reef Marine Park Act 1975. Some
recommendations of the review are that there should
be no further zoning plan changes until 2013, and
that every five years, a peer-reviewed Outlook
Report should be published, examining the health of
the Great Barrier Reef, the management of the reef,
and environmental pressures.
Due to its vast biodiversity, warm clear waters
and its accessibility from the floating guest
facilities called 'live aboards', the reef is a very
popular destination for tourists, especially scuba
divers. Many cities along the Queensland coast offer
daily boat trips to the reef. Several continental
and coral cay islands have been turned into resorts,
including the pristine resort island of Lady Elliot
Domestic tourism made up most of the tourism in
the region as of 1996, and the most popular visiting
times were in the Australian winter. It was
estimated that tourists to the Great Barrier Reef
contributed $AU 776 million per annum at this time.
As the largest commercial activity in the region,
it was estimated in 2003 that tourism in the Great
Barrier Reef generates over AU$4 billion annually.
(A 2005 estimate puts the figure at AU$5.1 billion.)
Approximately two million people visit the Great
Barrier Reef each year.
Although most of these visits are managed in
partnership with the marine tourism industry, there
are some very popular areas near shore (such as
Green Island) that have suffered damage due to
overfishing and land based run off.
A variety of boat tours and cruises are offered,
from single day trips, to longer voyages. Boat sizes
range from dinghies to super yachts.
Glass-bottomed boats and underwater observatories
are also popular, as are helicopter flights. By far,
the most popular tourist activities on the Great
Barrier Reef are snorkelling and diving, for which
pontoons are often used, and the area is often
enclosed by nets. The outer part of the Great
Barrier Reef is favoured for such activities, due to
Management of tourism in the Great Barrier Reef
is geared towards making tourism ecologically
sustainable. A daily fee is levied that goes towards
research of the Great Barrier Reef.
This fee ends up being 20% of the GBRMPA's income.
Plans of management are also in place for the
popular tourist destinations of Cairns and the
Whitsunday Islands, which account for 85% of the
tourism in the region.
Policies on cruise ships, bareboat charters, and
anchorages limit the traffic on the Great Barrier
The fishing industry in the Great Barrier Reef,
controlled by the Queensland Government, is worth
AU$1 billion annually.
It employs approximately 2000 people, and fishing in
the Great Barrier Reef is pursued commercially, for
recreation, and as a traditional means for feeding
Wonky holes in the reef provide particularly
productive fishing areas.