Watch Robert Piggott's colourful look at coral reef destruction

The two-year study, by the UK-based World Conservation Monitoring Centre, was carried out by researchers in this country, the US and the Philippines.

Many have been turned into fields of rubble

They discovered that 60% of the world's reefs have been damaged by human activity, many beyond recovery.

"The threat seems to be immediate," said Dr Mark Spalding from the World Conservation Monitoring Centre.

25% of the world's fish live on reefs

"We're losing reefs already, some have degraded beyond recovery I think. We need to act now if we are going to save one of the most beautiful and exciting natural heritages on the planet."

The report blames pollution, coastal development and farming, all of which can damage the fragile eco-systems which make up coral reefs.

Scientists believe several species of reef-dwellers still have to be identified

The scientists say changes in land use, such as forest clearance and intensification of agriculture, causes increased erosion. This washes soil into rivers and out to sea, silting up reefs along the coast, making the water murky and stopping sunlight, which is vital for coral growth.

They also say sewage and agricultural fertilisers damage reefs by increasing the nutrient levels in sea water, encouraging seaweed to grow at the expense of corals.

Coastal development alters tidal flows which puts pressure on reefs

Many reefs have also been poisoned by pollution.

In some parts of the world coral reefs have been destroyed by local people who have mined them for building materials, or burned the coral to make lime.

Tourists are also blamed for contributing to the problem, the report says many reefs have been damaged by divers, or by people walking out to them, while other reefs have been stripped of shells, which are sold as souvenirs.

Many of the Maldive Islands would be swamped if their reefs were destroyed

The scientists also warn that coral reefs are being over-fished, and big, commercially valuable species such as groupers have nearly disappeared.

Coral reefs are considered to be vital the the world's environment. More than a quarter of the world's ocean fish live on them.

They also protect thousands of low-lying islands like those in the Maldives.