Sick reefs that sound healthy attract back marine wildlife

The world’s largest coral reef is in serious danger — and we’re to blame. Climate change — specifically the warming waters and the increasing acidity of the water from CO2 inputs — is pushing the reefs past the point of no return. Many scientists are experimenting with all sorts of methods meant to help the reef cope and recover in the face of increasing adversity. One such reef recovery technique might just be crazy enough to work — playing underwater sounds typical of a healthy reef from loudspeakers in order to attract marine life.

Researchers in the UK and Australia played audio recordings from speakers positioned underwater at dead patches of the Great Barrier Reef. Over the course of six months, researchers played a range of sounds typical of thriving coral communities, including noises made by shrimp, fish, and other reef-dwellers.

Marine life actually took this cue to start settling down in the sick reef, forming new communities. Up to twice as many fish populated the reefs where sounds were played compared to areas of similar decay that had no speakers installed. The researchers also noted higher biodiversity in areas where sounds were played, with up to 50% more species colonizing the coral.

Australia’s Great Barrier Reef has been hampered by four mass coral bleaching events since 1998, the most recent one lasting from June 2014 to May 2017. The longest, most damaging coral bleaching event on record killed 30% of the reef. Today, experts believe the Great Barrier Reef has declined by more than half in the last 30 years

An estimated half a billion people around the world depend on reefs for income from fishing and tourism. Economic activity derived from the Great Barrier Reef alone is thought to be worth $4.5 billion annually.

Bleaching occurs when the ocean’s waters become too warm and expel the photosynthetic algae, called zooxanthellae, which live in a symbiotic relationship with the coral. Without the algae, the coral dies and seaweeds take over. The main culprit is man-made climate change, which warms and increases the acidity of the waters.

If current trends continue unabated, coral bleaching might affect 99% of the world’s reefs within this century, the United Nations warns. Previously, the U.N. Intergovernmental Panel on Climate Change warned that tropical reefs could decline by 70% to 90% if the planet warms by 1.5ºC compared to preindustrial average temperatures — the upper limit set by the Paris Agreement. At 2ºC of warming, 99% of the world’s reefs could perish.

On this note, bringing back marine life to dead and dying coral won’t actually reverse the damage. Also, what happens to these populations once you turn the speakers off? It seems reasonable to assume that they’ll start evacuating the dead coral.

However, there is value to this approach when combined with coral transplanting. Previously, conservationists have also used other methods to restore the Great Barrier Reef such as “coral gardening”, which involves breaking up healthy coral and sticking healthy branches on the reef. 

The findings were described in the journal Nature Communications.

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