Coral Reefs Under Threat


Photo: Grenada Board of Tourism

 Shallow water coral reefs, confined to tropical seas, are the richest of all marine habitats.
Callum Roberts, Ocean of Life

Sailing through the turquoise waters of a tropical lagoon and diving on a colourful coral reef teeming with life is a sailor’s dream. But for how much longer? Coral reefs around the world  are facing unprecedented stresses from human activity and by the end of this century scientists predict that there may be no coral reefs left.

Coral Reefs – Rainforests of the sea

Coral reefs cover about 1% of the ocean surface and yet they provide a habitat for 25% of marine life.

Found in shallow, tropical waters around the world, some of the best known reefs areas are the Great Barrier Reef, the Coral Triangle in South East Asia and the Caribbean Sea, all of which lie on the Blue Planet Odyssey route.

What is a reef?

Photo: Grenada Board of Tourism

Coral reefs are made up of colonies of tiny living  organisms called polyps in the same family as jellyfish and sea anemones.

Coral polyps build the ‘skeleton’ structures of the reef from calcium carbonate which is dissolved in the ocean.

Corals host a type of algae called zooxanthellae which provide most of the polyps’ nutrition as well as the beautiful colours of the reef.

Coral reefs are the largest structures on Earth built by animals and the largest reefs are the only biological structure that can be seen from space.


Threats to reefs


Coral reefs around the world are under threat and as a result the amazing biodiversity they support is diminishing. Around 40% of coral reefs around the world have been lost in the past thirty years.

Global threats to reefs, resulting from human activities affecting the whole planetary system, are principally ocean acidification, increasing sea temperature, and more extreme weather.

Local threats to reefs include:

  • Pollution (from raw sewage, plastic debris and chemicals from sunscreen)
  • Overfishing and destructive fishing practices such as the use of dynamite and poisons
  • Soil and fertilisers from agriculture washing out to sea
  • Tourism and coastal developments
  • Damage to reefs from visitors, boats anchoring on top of corals
  • Coral mining for building materials

The global threats require countries to work together on reducing carbon emissions; but the local threats can be reduced by small scale projects, for example creating marine reserves or educating visitors not to damage reefs.

Warming Seas

Warm water corals have adapted to live in a very small temperature range, and they evolve very slowly to cope with changes. If the temperature rises just a small amount it can have devastating effects.

As sea temperature rises, this can cause the relationship between the polyps and the zooxanthellae to break down, and results in the zooxanthellae being expelled by the corals. Without them, the corals have no colour and are left as white structures which is why the phenomenon is called coral bleaching.

If deprived of the nutrients the zooxanthellae bring for too long, the corals will die. 

With the highest ocean temperatures on record in 2014, some scientists think we are beginning to see what will eventually become a global coral bleaching and die-off event, similar to the one in 1998 which caused the worst coral bleaching in recorded history with 16% of the world’s coral lost.

Ocean Acidification

The ocean naturally absorbs much of the carbon in the atmosphere, and as carbon emissions increase more is absorbed by the seas. In the past ten years scientists have realised this is making the oceans more acidic and is having an effect on marine life.
Reefs are built from calcium carbonate so they are sensitive to ocean acidification. A more acid ocean makes it harder for them to absorb calcium from the sea. Studies show that reefs exposed to higher levels of CO2 have much less biodiversity.

What will be the impact of declining coral?

Reefs are worth billions of dollars to the world’s economy, from tourism to fishing.


Photo: Grenada Board of Tourism

Many countries, especially in the developing world, rely on their beautiful underwater corals and sea life to attract tourists. Billions of people around the world depend on fish for food, and coral reefs provide shelter for young fish. Branching corals, where fish like to take refuge, as especially vulnerable to acidification.

Reefs also protect coastlines from storms and waves.

Important new medicines and treatments are being sourced from coral reefs.

So what can be done?

Action can be taken straight away on local threats to reefs, as many communities are doing around the world.

Oceanwatch is an organisation that brings volunteer sailors and local Pacific Islands
communities together to learn about how to look after the reefs.

Reef Relief  is a nonprofit organization based in Key West, Florida, dedicated to improving and protecting our coral reef ecosystem. They publish various useful guides and posters that advise on the best practice for sailors and divers visiting coral reefs.

And what can I do?

    • Choose sustainable seafood
    • Avoid buying products from coral reefs
    • Choose an eco-friendly sunscreen
    • Recycle your trash
    • Reduce your carbon footprint

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