Lack of noise from depopulated coral reefs could lead to loss of fish

Young fish are unable to ‘hear' their way home when damaged coral reefs are too quiet, study shows.

A deathly hush descending on coral reefs damaged by global warming is impairing the ability of young fish to find a home, research suggests.

Coral reefs are noisy places filled with the clicks, pops, chirps and chattering of numerous fish and crustaceans.

But a study conducted on Australia’s Great Barrier Reef shows that the “coral orchestra” has been quietened in areas damaged by cyclones and bleaching.

Scientists found that without the din, fish born outside the reef had a hard time locating a suitable place to live and breed.

Experiments showed that the soundscapes of damaged reefs attracted 40% fewer juvenile fish than those of healthy reefs.

The loss of reef fish could have “devastating” consequences, warn the researchers.

A view of coral on Australia’s Great Barrier Reef that has been decimated by severe bleaching and tropical cyclones. (Tim Gordon, University of Exeter/PA)

Lead scientist Tim Gordon, a marine biologist at the University of Exeter, said: “It’s heart-breaking to hear. The usual pops, chirps, snaps and chatters of countless fish and invertebrates have disappeared. The symphony of the sea is being silenced.”

Bleaching occurs when sea water becomes too warm, causing corals to expel the algae living in their tissues and turning them white.

Under normal conditions the algae provide the coral with nutrients generated by photosynthesis. Without them, the coral can starve.

In some parts of the Great Barrier Reef 80% of corals have been killed by bleaching. Scientists say there is a direct link between more frequent coral bleaching events and global warming.

Working on the Northern Great Barrier Reef, the British-led international team of scientists built experimental reefs from coral rubble on sand flats.

Underwater speakers were then used to broadcast the sounds of healthy or degraded reefs to see how they attracted juvenile fish.

Coral reef animals produce a “dazzling array” of sounds to communicate while hunting, warn of approaching predators, or impress during courtship, said the researchers.

Together the noises combine to form a soundscape that can be hard for miles around. The sounds help young fish to navigate their way to suitable reef habitats after a period of early development in the open ocean.

Co-author Harry Harding, from the University of Bristol, said: “If fish aren’t hearing their way home anymore, that could be bad news for the recovery prospects of reefs.

“Fish play critical roles on coral reefs, grazing away harmful algae and allowing coral to grow. A reef without fish is a reef that’s in trouble.”

Mr Gordon added: “The damage we’ve done to reefs worldwide is horrific, but the fight isn’t over yet. If we can fulfil our international commitments to dramatically reduce carbon emissions, it’s still possible to protect some of the reefs that are left.”

The research is reported in the journal Proceedings of the National Academy of Sciences.

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