Coral Bleaching at Heron Island
© Richard Vevers

Reefs have gone quiet and now fish can’t find them

By: Jack O'Donovan
Date posted: 1 May 2018

The Great Barrier Reef, once filled with the noise of its busy inhabitants, has gone silent. New research reveals how the silence among the corals is causing fewer young fish to make coral reefs their home.

it’s definitely the case that a healthy coral reef can be extremely noisy,

Dr. Jean-Luc Solandt,
Principal Specialist on MPAs
Marine Conservation Society

Silence has fallen over coral reefs after extreme bleaching events and destruction from recent storms. The hustle and bustle of a biodiverse coral reef emits a great array of noises. A cacophony of pops, chirps, clicks and crackles attracts young fish to their new home where they feed and mate. Shrimps, fishes and the corals themselves all contribute to this salt water symphony. However, the volume has been dialled down over the last five years.

New research from the University of Exeter on the Northern Great Barrier Reef has shown how silence has blanketed the clamour of the corals. This noise is how young fish locate reefs in early life and make it their homes. The reduction in this noise has led to a 40% decline in the number of young fish visiting the reef.

If fish are not occupying the coral reefs, the base of a complex food web and set of community interactions is not secure, causing a severe threat to the health and maintenance of a reef ecosystem.

Fish graze on harmful algae that grow on and among the corals, which keeps them clean and allows them to grow. This too allows the algae within the corals cells to photosynthesise and produce much needed sugars to feed the coral.

Senior author Steve Simpson, Associate Professor in Marine Biology & Global Change at the University of Exeter, notes; “if the reefs have gone quiet, then the chances of the next generation of fish recolonising the reefs are much reduced. Without fish, the reefs can’t recover”.

Dr. Jean-Luc Solandt, Principal Specialist on MPAs at the Marine Conservation Society adds; “it’s definitely the case that a healthy coral reef can be extremely noisy. When MCS have had expeditions in the past with Biosphere-Expeditions in Musandam, Oman, there are extremely noisy reefs.

“The habitat is dominated by the coral Pocillopora dammicornis - a bushy coral. It is a natural habitat for the spiny urchin Diadema, and also the snapping shrimp. It’s an incredibly noisy zone, sounding like hundreds of crisp packets being crumpled in a pub.” “The noise must be attractive to fish a long way from the reef, as noise travels six times further in the water than in air.

Coral reef

Lead author Tim Gordon, a marine biologist at the University of Exeter concludes; “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 time for action is now.”

While much of the world have committed to tackling global carbon emissions through the Paris Agreement, the Australian government is now also investing half a billion dollars into building coral reef resilience, in partnership with the Great Barrier Reef Foundation. This investment goes towards on the ground efforts to conserve the reefs.

This entails improving water quality, combatting outbreaks of the destructive crown of thorns starfish and ensuring researchers and reef management teams are adequately equipped. With this recent investment and the continued efforts to globally reduce carbon emissions, reefs of the world may once again boom with the colour and sounds for which they are famous.

To learn more about coral check out our six fun facts you didn’t know about coral.

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