When a coral reef goes silent, it indicates approaching death.

Research from the Universities of Essex and Exeter shows that coral reefs impacted by human activity become silent compared to their healthier counterparts.

Coral reefs are among the noisiest environments on the planet with the teeming life making noise which can be heard on microphones kilometres away.

The sound plays an important role in the larval stages of reef fish and invertebrates, which spend the first few days of their life away from reefs and use the sound as an orientation cue to find their way back.

Led by Dr Julius Piercy from the University of Essex, the team took acoustic recordings of coral reefs with different levels of protection around islands in the Philippines.

The noise produced by the few remaining resident fish and crustaceans on unprotected reefs was only one-third of the sound produced at bustling, healthy reef communities.

With the loss of sound, the distance over which larvae can detect habitat is ten times less. This has impact on future generations that go to build and maintain healthy population levels.

Sound recordings are a cheap, fast and objective way to get a broad idea of whether a reef is in a good condition or not, say the researchers.

The study also highlights the need to further characterise reef soundscapes when working on marine area conservation.

Corals have been shown to be sensitive to rising seawater temperatures, ocean acidification, water pollution from terrestrial runoff and dredging, destructive fishing, overfishing and coastal development.

The Great Barrier Reef which contains the world's largest collection of coral reefs with 400 types of coral, 1,500 species of fish and 4,000 mollusc varieties has lost half its coral cover in the past three decades due to excessive bleaching and cyclones arising from climatic conditions.

The excessive acidification of the oceans due to increased carbon intake has led to erosion of most coral reefs, and amounts to an estimated trillion dollars worth of damage.