1. ‘Rainforests of the sea’ at risk
Coral reefs
‘Rainforests of the sea’ at risk
Philip Allan Publishers © 2016

2. 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.
This staghorn coral has a hard calcium carbonate skeleton, secreted by the colony of polyp animals that live within it
Philip Allan Publishers © 2016

3. 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
Waves breaking on a reef in the Maldives, with a lagoon between reef and beach
Philip Allan Publishers © 2016

4. 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.
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.
Philip Allan Publishers © 2016

5. Local and global threats
Coral reefs are subject to a wide range of threats.
These fall into two broad categories:
Local threats which result from over-exploitation of resources, affecting some reefs more than others.
Global threats as a result of climate change, affecting all reefs.
Local
Global
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.
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.
Philip Allan Publishers © 2016

6. 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.
© WWF International
Philip Allan Publishers © 2016

7. 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
Philip Allan Publishers © 2016

8. 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.
Philip Allan Publishers © 2016

9. 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:  
Philip Allan Publishers © 2016