Case study - The Great Barrier Reef
Figure 1a. World map showing location of Australia and the Great Barrier
Reef.
Source: http://coralprincess.com.au
Figure 1b. Map of Great Barrier Reef along the NE coast of Australia.
Source: http://www.divefishsnow.co.nz
Figure 2a. The Great Barrier Reef
The Great Barrier Reef is located along Queensland coast, Australia extending over 2,300 km and
covering an area of over 344,400 km2.
It consists of over 3,000 individual coral reefs and 900 islands.
It is the largest living structure on earth.
The majority of the GBR is a UNESCO World Heritage Site.
Figure 2b. Coral reefs.
Coral reefs are comprised of organisms called coral polyps and are found in marine waters.
Stony coral polyps cluster together into colonies and use calcium and bicarbonate ions from the
seawater to build hard exoskeletons of calcium carbonate that support and protect their soft
bodies. This leads to the formation of limestone.
There are over 450 hard coral types of hard coral that contribute to reef building.
The colonies provide a habitat to other species. Coral reefs occupy around 0.1% of the world’s
ocean and provide homes for at least 25% of all marine species.
Coral reefs provide ecosystem services such as tourism, fisheries and shoreline protection.
They are fragile ecosystems and have been compromised by global climate change, oceanic
acidification, unsustainable fishing practices (blast fishing and cyanide fishing) and harmful landuse practices resulting in urban runoff and sedimentation.
Figure 2c. Coral polyps.
Coral polyps have a sac-like body with a mouth surrounded by stinging tentacles with specialised
cells called nematocysts. The stinging tentacles are used to stun prey such as zooplankton.
Coral polyps (animals) exists with zooxanthellae (plants):



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Coral polyps produce CO2 and water from cellular respiration.
The zooxanthellae use these by-products to photosynthesise.
Photosynthesis produces carbohydrates, lipids and oxygen, which the coral polyp then
uses.
This exchange of services drives the productivity of the coral reef.
Polyps reproduce asexually most of the time but once a year in October or November they
reproduce sexually in a mass spawning. The products of the spawning are moved by currents and
tides.
Figure
2d. Coral polyp anatomy.
Figure 2e. Optimal conditions for coral reefs.
Conditions
Reason
Water temperature
of 20-32°C.
This is the tolerance range for most corals though some have greater
tolerance.
Clear water and
sunlight.
The water needs to be sufficiently transparent to allow sunlight to reach
the zooxanthellae for photosynthesis.
Clean water - no
pollution.
Corals are very sensitive to pollution. E.g. wastewater high in nutrients can
boost seaweed growth to the point that it smothers the reef.
Figure 2f. Coral reefs require clear, warm water that allows sunlight to
penetrate through.
Figure 2g. Hard coral cover within the Great Barrier Reef 1986-2012.
Source: De’ath et al. 2012 cited in Great Barrier Reef Marine Park
Authority 2014. Great Barrier Reef Outlook Report 2014. GBRMPA,
Townsville.
Figure 3a. The Great Barrier Reef is rich in biodiversity and supports a
wide array of organisms. Unknown species are still being discovered.
Figure 3b. Dugongs
Dugongs (Dugong dugon) are herbivorous feeding on seagrass.
They are an iconic species with historical cultural value to the indigenous Aboriginal and Torres
Strait Islander people who view the hunting of dugongs as an important aspect of ceremonial,
social and community life.
Dugongs were also commercially harvested for their meat, bones, hide and oil until a ban took
force in 2011.
Numbers of dugongs have continued to decline and are classified as vulnerable by the IUCN Red
List.
Figure 3c. Dugong strandings recorded within the Great Barrier Reef,
2000–2013.
Source: Great Barrier Reef Marine Park Authority 2014. Great Barrier
Reef Outlook Report 2014. GBRMPA, Townsville.
Figure 3d. The number of humpback whales (Megaptera novaeangliae)
recorded within the Great Barrier. Reef has increased since whaling ceased
in the 1960s.
Source: Adapted from Noad et al. 2008, Noad et al. 2011, Great Barrier
Reef Marine Park Authority 2009 cited in Great Barrier Reef Marine Park
Authority 2014. Great Barrier Reef Outlook Report 2014. GBRMPA,
Townsville.
Figure 3e. Dugong and humpback whale.
Figure 4a. Lizard Island.
Lizard Island is located in the north of the Great Barrier Reef and is home to a research station
which attracts many coral reef researchers.
It is surrounded by a shallow lagoon with high biodiversity.
The shore fringes consist of mangroves which link land to the sea and provide breeding and
nursery grounds for a diverse range of species including turtles, sharks, rays and other fish.
The mangroves provide protection against larger predators that are too big to move through the
spaces within the tangled root systems.
The mangroves also provide a protection from storms.
Figure 4b. Role of mangroves.
Source: http://coastvserosion.wikispaces.com/Mangrove
Figure 4c. Raine Island.
Raine Island is located on the outer edges of the north of the Great Barrier Reef.
Raine Island is the most significant breeding ground for seabirds within the Great Barrier Reef.
It is also home to the world’s largest population of nesting green sea turtles (Chelonia mydas).
During the nesting period around 60 000 female turtles can arrive on Raine Island.
The survival of turtle eggs has been in decline due to inundation of the beach by tidal water as a
result of rising sea levels. The eggs are unable to survive these wet conditions.
To improve survival rates of turtle eggs and hatchlings the Rain Island Recovery project aims to
restore and protect these important nesting sites through a number of strategies including beach
engineering and sand replenishment.
Figure
4d. Green sea turtle.
Figure 5a. Economic contributions of selected activities dependent on the Great Barrier Reef,
2006–07 and 2011–12.
Source: Access Economics 2008 and 2012 cited in Great Barrier Reef Marine Park Authority
2014. Great Barrier Reef Outlook Report 2014. GBRMPA, Townsville.
Activity
2006–07 Value added
($million)
2011–12 Value added
($million)
Tourism
$5,117
$5,176
Commercial fishing.
$139
$160
Recreational use (including
fishing).
$153
$244
$5,409
$5,580
Total contribution:
Figure 5b. Reef activities undertaken by tourists departing Cairns, 2008–
2012 (a sample of 4337 people). Source: Prideaux et al. 2013 cited in
Great Barrier Reef Marine Park Authority 2014. Great Barrier Reef
Outlook Report 2014. GBRMPA, Townsville.
Figure 5c. Number of recreational vessels registered in the catchment,
1987–2013.
Source: Department of Transport and Main Roads (Qld) cited in Great
Barrier Reef Marine Park Authority 2014. Great Barrier Reef Outlook
Report 2014. GBRMPA, Townsville.
Figure 6a. Cyclones.
Tropical cyclones cause ecological disturbances to the GBR.
Between 1910 and 1999 170 cyclones passed over the GBR. The severity of clones recorded has
increased in the past 10 years.
The amount of damage depends on the severity of the storms but can include:
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Fragmentation of the reef.
Destruction of the underlying reef structures.
Breakage and displacement of corals, especially the branching species (Acropora
Formosa).
Cyclone Yasi in 2011 caused extensive damage to the GBR:
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
6% of the reef was severely damaged.
Corals were broken across an area exceeding 89,000 km2.
Figure 6b. Change in water temperature and pH.
Increases in water temperature caused by climate change is leading to coral bleaching (when
zooxanthellae which gives coral its colour is expelled). This also makes the coral more
susceptible to disease.
Increasing atmospheric CO2 is causing ocean acidification. The oceans absorb atmospheric
carbon dioxide which lowers the pH of seawater.
Decreasing pH impacts most marine animals that produce calcium carbonate shells or skeletons.
Lower seawater pH:
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Reduces the ability of reef-building corals to produce skeletons.
Compromises the fertilisation, larval settlement and survival of some corals.
Reduces the ability of corals to recover from disturbances.
Figure 6c. Coral bleaching.
Source: NOAA
Figure 7a. The crown of thorns starfish and the giant triton.
The crown of thorns starfish (Acanthaster planci) feeds on coral polyps. An explosions in
populations can have devastating effects on the coral population.
High numbers of crown of thorns may be induced by human activities such as eutrophication and
overfishing of its natural predator e.g. Giant Triton.
The Giant Triton (Charonia tritonis) is a keystone species whose number can also be adversely
affected by damage to its habitat through use of trawling nets and anchors. The Giant Triton is
also collected for its attractive shell which is a popular tourist souvenir.
Figure 7b. Crown of Thorns Starfish and Giant Triton.
Figure 8a. Changes in the extent of supporting terrestrial habitats within the catchment area.
Source: Great Barrier Reef Marine Park Authority 2014. Great Barrier Reef Outlook Report 2014.
GBRMPA, Townsville.
Supporting
terrestrial habitat
Total area before European
settlement (km2)
Total area
remaining (km2)
Proportion
remaining
Saltmarshes
2,146
1,830
85 per cent
Freshwater wetlands
1,431
1,237
86 per cent
Forested floodplain
24,597
12,655
51 per cent
Heath and shrublands
5,351
5,025
94 per cent
Grass and sedgelands
12,364
5,988
48 per cent
Woodlands
105,123
64,592
61 per cent
Forests
239,602
145,379
61 per cent
Rainforests
26,886
16,744
62 per cent
Figure 8b. Fertiliser use in the catchment, 1910–2012.
Source: Great Barrier Reef Marine Park Authority 2014. Great Barrier
Reef Outlook Report 2014. GBRMPA, Townsville.
Figure 8c. Exposure to suspended sediments and dissolved inorganic
nitrogen, 2007–2011.
Source: Brodie et al. 2013 cited in Great Barrier Reef Marine Park
Authority 2014. Great Barrier Reef Outlook Report 2014. GBRMPA,
Townsville.
Questions
1a) With reference to Figure 2g, state the region in which hard coral cover
has most significantly declined since 1986. (1)
1b) Using Figure 2g estimate the overall amount of coral cover lost in the
Great Barrier Reef. (1)
1c) Suggest reasons for the loss of hard coral in the Great Barrier Reef. (3)
2a) Identify the ecological relationship between coral polyps and
zooxanthellae. (1)
2b) Justify your answer to (a). (1)
3) Outline why coral reefs are often referred to as the 'rainforests of the
sea'. (3)
4a) Some people believe Aboriginal and Torres Strait Islander people
should have the right to continue to hunt Dugongs. Justify whether you
think this is an acceptable practice. (2)
4b) Suggest the reasons for the differences between change in populations
of dugongs and the humpback whale. (2)
5a) With reference to Figure 4a and 4b describe two ecological services
provided by the mangroves on Lizard Island. (2)
5b) List two factors why green turtles are classified by the IUCN Red List
as endangered. (1)
5c) Describe the impact of climate change on the wildlife in Raine Island.
(2)
6a) With reference to Figure 5b identify the most popular tourist activity.
(1)
6b) Describe the impacts of the activity named above. (2)
6c) With reference to Figure 5c calculate the mean annual increase in
registered vessels within the GBR from 1987 to 2013. (1)
7) Giant Triton is described as a keystone species. Define the role of a
keystone species. (1)
8) With reference to Figures 8a, 8b and 8c, explain the impact changes
within the catchment has on pollution within the Great Barrier Reef. (4)
9) Evaluate different strategies that could be used to reduce threats to GBR
and manage it more sustainably. (7)