Biodiversity under threat: coral reefs

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G eo Factsheet
September 2001 Number 118
CORAL REEFS ­ Ecosystem in Crisis?
In the year 2000, 10% of the world's coral reefs were either totally dead Many of these uses are conflicting; they are all growing and therefore are
or degraded beyond recovery. Unless action is taken in the next ten years increasingly unsustainable as the coral reef ecosystems are being
this will rise to over 30% - indeed only 10% of all coral reefs are not at damaged or destroyed at a greater rate than they can `self-repair'. Saving
risk. Why is this and does it matter? coral reefs has become just as important as saving the rainforests ­ hence
in 1995 the International Coral Reef Initiative to promote sustainable reef
Table 1 The uses of coral reefs management and in 1997 the International Year of the Coral Reef to
promote public education on the state of the reefs and how best to manage
Coral reefs are of great value in many ways because they: them.
· include some of the most biologically rich ecosystems. Whilst
coral reefs only occupy 0.18% of the world's marine Coral reefs as ecosystems
environments, the reefs are home to over 25% of all known marine Coral reefs are unique amongst marine ecosystems in that they are built
fish. Coral reefs rival rainforests for their biodiversity i.e. the up entirely by biological activity. Reefs are massive deposits of calcium
number of different species found within an area or ecosystem. carbonate (CaCO3) produced primarily by corals (Fig. 1). Their
Also many rare species live on reefs. distribution is controlled by what are known as limiting factors, i.e. if the
· protect adjacent shorelines from wave erosion and the impact of factor is not present the reef does not form.
tropical storms ­ at much lower cost than artificial sea defences.
These natural self-repairing breakwaters could become even Fig. 1 Distribution of coral reefs.
more important if sea levels rise due to global warming. Healthy
reefs will grow with rising sea levels.
· supply the basic food needs of many local communities. 109
Distribution of coral reefs
countries have reef systems and 80% of these countries can be
classified as LEDCs (less economically developed countries). A Reefs under threat
huge variety of fish and other species are caught using spears,
traps and other `native' methods.
Tropic B
· make a major contribution to commercial fishing. Globally 20% of Cancer H E
of animal protein consumed by humans comes from marine D
environments ­ with coral reefs providing 25% of this total Equator X C G
commercial fish catch. G Y A F
· are sources of medicine. Reef species may support new treatments Tropic of Capricorn
for bacterial infections or possibly cancer, and corals are also
used for bone grafts.
· contain resident fish and animals such as seahorses which are Coral reefs - threats
vital for the growing global aquarium trade. In the year 2000, 20 A: East Africa Coral mining for building materials, blast
million seahorses were caught for this trade. fishing, tourist trade and sedimentation.
· are home to reef species which are used as decorative objects, for
B: The Gulf Oil and industrial pollution, sedimentation.
example shells and black corals, which are used for jewellery.
This trade supports many `native' craft industries around the C: Thailand & Malaysia Tourist resorts, bucket dredging for tin,
world. over-fishing.
· provide coral which can be mined as a source of lime for cement. Blast fishing, coral mining, collection for
D: Philippines
Many tropical countries lack alternative basic building materials. tourist trade and use of poisons.
· provide ideal habitats for education and scientific research
because of their high biodiversity combined with their shallow E: Southern Japan Destroyed by coastal development and
water and easy accessibility. Ryukyu Archipelago sedimentation.
· are major magnets to the world's tourists. In the year 2000 over F: Indonesia Destroyed by blast fishing, coral mining,
150 million people took a holiday in a coral reef area. 90% of the tourist trade and coastal development.
109 countries with coral reefs have an established tourist
industry. Many LEDCs such as those in the Caribbean derive over G: South Pacific Tourism, sedimentation from coastal
half the Gross National Product (GNP) directly from tourism. development.
H: Wider Caribbean Collection for tourist trade, coastal
development, mangrove destruction/
sedimentation and damage by boat anchors

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Coral reefs ­ Ecosystem in Crisis? Geo Factsheet
Exam Hint: Many exam questions require candidates to comment
· Temperature: No reefs develop where the mean annual temperature on the structure and functioning of a chosen named/location
of the water is below 18°C. The best conditions for reef development ecosystem.
occur in water temperatures between 23-25°C. Above 27°C causes 1. Be sure to distinguish between the two. Structure is how the
problems for the health of the reef.…read more

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Coral reefs ­ Ecosystem in Crisis? Geo Factsheet
Fig. 4 The impact of development on a coral reef ecosystem and the vicious circle of reef decline.…read more

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Coral reefs ­ Ecosystem in Crisis? Geo Factsheet
Fig. 5 Human impacts on the reef
Dredging for harbours
Boating - anchoring and marinas Fishing (often over-fishing) which
White sand beach
can damage the reef Lagoon upsets the ecological balance
Coral heads in lagoon
Coastal Reef crest
development which
leads to pollution
of the reef
Sea lev
Fore-reef slope
Changing land use, e.g.…read more

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Coral reefs ­ Ecosystem in Crisis? Geo Factsheet
Case study: Management of the Buccoo Reef and Bon Accord Fig. 7 Annotated sketch map of Buccoo Reef
Lagoon Complex in South West Tobago N
Traditionally use: fishing, tourism (since 1930s). Reef flat Buccoo Reef
Reef extent TOBAGO
1973: It was declared a Marine Reserve with restricted access.
Sandy beach
0 6km
1990: Management plans developed. Between 1973 and 1990 Navigational
considerable damage was done to the reef and adjacent seagrass and buoy
mangrove areas.…read more


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