Coral reefs
‘Rainforests of the sea’ at risk
Philip Allan Publishers © 2016
What is coral?
• Corals are ancient marine organisms that
evolved around 540 million years ago.
• Despite being sensitive to light levels and
temperature, corals have survived numerous
mass extinction events in geological history.
• Colourful, branching, tropical corals may
look like plants are but are actually animals
(marine invertebrates).
• The coral animals, called polyps, are
colonial and the familiar coral structures
house them.
• Coral polyps are filter feeders, using
tentacles to trap plankton and even small fish.
• Not all corals are tropical. Some species
exist in cold waters but these tend to have
only soft polyp bodies, not a hard skeleton.
Philip Allan Publishers © 2016
This staghorn coral has a hard
calcium carbonate skeleton,
secreted by the colony of polyp
animals that live within it
What are coral reefs?
• Coral reefs consist of ‘stony’ corals with hard
calcium carbonate skeletons.
• Thousands of corals create a mound-like
structure parallel to the shoreline.
• The mound grows upward, on the ‘rubble’ of
dead coral skeleton
• Often there is a shallow, calm-water lagoon
between the reef and beach.
• Reefs are found in tropical seas which are:
•
Less than 50m deep (polyps contain
zooxanthellae algae that photosynthesise
and produce some of the polyps’ food, so
high light levels are needed)
•
Clear water, i.e. distant from river mouths
which are a source of silt.
•
At temperatures of 23°–29°C
Philip Allan Publishers © 2016
Waves breaking on a reef in
the Maldives, with a lagoon
between reef and beach
Coral-reef ecosystem services
• Coral reefs are said to be
home to 25% of all marine
species, but within an area of
less than 1% of the world’s
oceans.
• This exceptional
biodiversity is mirrored by
very high productivity.
• The Net Primary
Productivity (NPP) of coral
reefs is 2500 g / m2 / year –
higher even than tropical
rainforests.
• Reefs provide a wide range
of crucial ecosystem
services as shown in the
table.
Philip Allan Publishers © 2016
Regulating services
Provisioning services
•Carbon sequestration
•Ocean water filtration
•Fis /shellfish protein for humans
•Fishing industry and jobs.
•Building materials .
•Medical and genetic research and
products.
Cultural services
Supporting services
•Tourism
•Recreation and leisure
•Aesthetic beauty
•Coastal erosion prevention
•A ‘nursery’ for small fish.
maintaining fish populations.
Worldwide, reefs provide about $30 billion
in economic value each year.
Hawaii’s reefs are worth $400 million to its
economy annually.
Local and global threats
• Coral reefs are subject to a wide range of threats.
• These fall into two broad categories:
1.Local threats which result from over-exploitation of resources, affecting some reefs more
than others.
2.Global threats as a result of climate change, affecting all reefs.
Local
•Overfishing.
•Destructive fishing (trawling, dynamite and
cyanide fishing)
•Tourism/diving damage.
•Siltation from onshore sediment flows, often
linked to deforestation and farming erosion.
•Eutrophication from urban, industrial and farm
pollution.
•Coral mining for building materials.
Philip Allan Publishers © 2016
Global
•Alien species invasion, linked to changing ocean
temperatures.
•Coral bleaching due to rising global sea
temperatures and stronger El Niño events.
•Ocean acidification, due to increased ocean
carbon dioxide levels, weakening coral skeleton.
•Rising sea levels ‘drowning ‘ coral in deeper
water.
Coral reef health
• Reefs form part of the wider marine
ecosystem.
• The WWF Living Planet Index (LPI)
is a long-term measure of ecosystem
health.
• The Marine LPI (graph) has
declined by 39% since 1970.
• This suggests coral reefs, and other
marine ecosystems such as sea-grass
beds and mangrove forests, are
slowly being degraded by the wide
range of threats facing them.
• A 2011 Report by the World
Resources Institute found that 75% of
the world’s coral reefs were under
threat.
Philip Allan Publishers © 2016
© WWF International
http://wwf.panda.org/about_our_earth/all_publications/living_p
lanet_report/living_planet_index2/
Changing distribution
• The Reefs at Risk project has mapped reefs
by level of threat worldwide.
• This map of part of the Philippines shows
that reefs fringing the large islands are mostly
in the ‘high’ or ‘very high’ threat category.
• Only more isolated, small island reefs are
less threatened.
• This pattern can be found worldwide, and it
suggests coral reefs will disappear from most
populated coastlines by 2030.
• Rising populations and pressure of marine
resources mean many coral reefs are on the
verge of disappearing for ever.
© 2012 World Resources Institute
http://www.wri.org/sites/default/files/pdf/reefs_
at_risk_revisited_coral_triangle_hi-res.pdf
Philip Allan Publishers © 2016
Management approaches
• It’s not all bad news for coral reefs.
• Over 6,500 Marine Protected Areas help
conserve around 2% of the world’s oceans,
including many reefs.
• There are examples of sustainable
management. Reef-dependent communities
are educated to conserve the reefs through
ecotourism, sustainable fishing and
management.
• Coral-reef restoration is possible,
although costly and challenging to
implement.
• The ever present ‘context threat’ of global
warming makes conservation of reefs a
difficult goal.
© Commonwealth of Australia 2012
Large parts of Australia’s oceans are
Marine Protected Areas and the Great
Barrier Reef is a Marine Park.
http://www.marinereservescoalition.org/resources/marine-reservesaround-the-world/australias-marine-protected-area-network/
Philip Allan Publishers © 2016
This resource is part of GEOGRAPHY REVIEW, a magazine written for
A-level students by subject experts. To subscribe to the full
magazine go
to: http://www.hoddereducation.co.uk/geographyreview
Philip Allan Publishers © 2016