The Great Barrier Reef is the world

The

Great

Barrier

Reef

is

the

world's

largest

coral

reef

system[1][2]

composed

of

over

2,900

individual reefs[3] and 900 islands stretching for over 2,600 kilometres (1,600 mi) over an area of

approximately 344,400

square

kilometres (133,000 sq mi).[4][5] The reef is located in the Coral

Sea, off the coast of Queensland in north-east Australia.

The Great Barrier Reef can be seen

from

outer space and is the world's biggest single structure

made

by

living

organisms.[6]

This

reef

structure

is

composed

of

and

built

by

billions

of

tiny

organisms,

known

as

coral

polyps.[7]

It

supports

a

wide

diversity

of

life

and

was

selected

as

a

World

Heritage

Site

in

1981.[1][2]

CNN

labeled

it

one

of

the

seven

natural

wonders

of

the

world.[8] The Queensland National Trust named it a state icon of Queensland.[9]

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 fishing and tourism. Other environmental pressures on the reef

and its ecosystem include runoff, climate change accompanied by mass coral bleaching, and cyclic

population outbreaks of the crown-of-thorns starfish.

The Great Barrier Reef has long been known to and used by the Aboriginal Australian and Torres

Strait Islander peoples, and is an important part of local groups' cultures and spirituality. The reef

is a very popular destination for tourists, especially in the Whitsunday Islands and Cairns regions.

Tourism is an important economic activity for the region, generating $$1 billion per year.[10]

The Great Barrier Reef is a distinct feature of the East Australian Cordillera division. It includes the

smaller Murray Islands.[11] It reaches from Torres Strait (between Bramble Cay, its northernmost

island, and the south coast of Papua New Guinea) in the north to the unnamed passage between

Lady

Elliot

Island

(its

southernmost

island)

and

Fraser

Island

in

the

south.

Lady

Elliot

Island

is

located 1,915 km (1,190 mi) southeast of Bramble Cay as the crow flies.[12]

Australia

has

moved

northwards

at

a

rate

of

7

cm

(2.8

in)

per

year,

starting

during

the

Cainozoic.[13]

Eastern

Australia

experienced

a

period

of

tectonic

uplift,

which

moved

the

drainage

divide

in

Queensland

400

km

(250

mi)

inland.

Also

during

this

time,

Queens

land

experienced

volcanic

eruptions

leading

to

central

and

shield

volcanoes

and

basalt

flows.[14]

Some of these granitic outcrops have become high islands.[15] After the Coral Sea Basin 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.[16]

The

Great

Barrier

Reef's

development

history

is

complex;

after

Queensland

drifted

into

tropical

waters, it was largely influenced by reef growth and decline as sea level changed.[17] Reefs can

increase in diameter by 1 to 3 centimetres (0.39 to 1.2 in) per year, and grow vertically anywhere

from 1 to 25 cm (0.39 to 9.8 in) per year; however, they grow only above a depth of 150 metres

(490 ft) due to their

need for sunlight, and cannot grow above

sea level.[18]

When Queensland

edged into tropical waters 24 million years ago, some coral grew,[19] but a sedimentation regime

quickly

developed

with

erosion

of

the

Great

Dividing

Range;

creating

river

deltas,

oozes

and

turbidites, unsuitable conditions for coral growth. 10 million years ago, the sea level significantly

lowered, which further enabled sedimentation. The reef's substrate may have needed to build up

from

the

sediment

until

its

edge

was

too

far

away

for

suspended

sediments

to

inhibit

coral

growth. In addition, approximately 400,000 years ago there was a particularly warm interglacial