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Reduction of Motorboat Noise Could Significantly Help Breeding of Coral Reef Fishes

A new study has reported that the breeding of coral reef fish is done in a successful manner if motorboat noise is decreased.

Boat driving near coral reefs. Image Credit: University of Exeter.

Researchers initiated a so-called “traffic calming” on three reefs for a complete breeding season—thereby reducing the number of boats inside 100 m, and decreasing the speed of those within that distance.

Further, they tracked the breeding of fish known as the spiny chromis—and discovered that 65% of nests on quieter reefs still consisted of offspring at the end of the season, compared to 40% on reefs with busy motorboat traffic.

Also, offspring were bigger on quieter reefs and every nest consisted of more offspring in the late season.

Aquarium tests performed on the same species display that noise interrupts significant parental behaviors such as “fanning” eggs with their fins for oxygen supply to be guaranteed.

The study, headed by the universities of Exeter and Bristol, was performed at reefs next to Lizard Island Research Station on Australia’s Great Barrier Reef.

With coral reefs worldwide facing multiple threats, the results of our experiment offer a way to help struggling populations. Simply reducing boat noise at reefs provides fish with much-needed relief to allow successful reproduction.

Dr Sophie Nedelec, Study Lead Author, University of Exeter

Nedelec added, “Moving boating channels further away from reefs, driving slowly when approaching reefs, and avoiding anchoring next to reefs provide three simple changes that any boat driver can adopt. These solutions put the power in the hands of local people to protect vulnerable ecosystems.”

Dr. Nedelec remarks, “No one has attempted a field experiment like this before. We monitored six reefs (three with traffic calming and three without) for a whole summer breeding season, swimming every other day along each reef to monitor the survival of 86 spiny chromis broods in their natural habitat.”

Amongst the 46 nests that were observed on reefs where traffic calming was applied, 30 still contained offspring by the end of the breeding season. On control reefs (with no traffic calming), only 16 out of 40 still contained offspring.

Spiny chromis hide their eggs in caves in the reef, the nests are tricky to find before the offspring emerge, so we ran a parallel study in aquariums to study embryonic development.

Dr Laura Velasquez Jimenez, Study Co-Author, James Cook University

In this aquarium study performed, a few spiny chromis parents and eggs were held with playbacks of natural reef sounds, and others were vulnerable to intermittent boat noise playbacks through speakers.

The playbacks of boat noise stopped fanning, but with natural sounds, fanning remained continuous.

The complementary lab study demonstrated that these improvements to breeding really are due to limiting noise pollution, and not other kinds of disturbance from the boats.

Andy Radford, Study Co-Author and Professor, University of Bristol

The joint outcomes indicate that decreasing boat noise could have significant benefits for populations of reef fish. This makes reefs stronger to changes that are being driven by human activity at present.

Cyclones and bleaching are turning out to be increasingly common as a result of climate change, and thereby result in destruction when they strike.

Determining methods to expedite population growth following such destructive events could lead to making the difference between fall or revival.

But the team adds that restricting boat traffic would not be sufficient to safeguard coral reefs completely.

Senior author Professor Steve Simpson, from the University of Bristol, stated, “We know reefs around the world are in trouble. While we try to tackle the biggest threat of climate change, we need simple solutions that reduce local threats. Acoustic sanctuaries can build resilience on coral reefs, and help give reefs more chance of recovery.”

The current study was carried out by an international team including James Cook University. The research received funding from the Natural Environment Research Council.

Journal Reference:

Nedelec, S. L., et al. (2022) Limiting motorboat noise on coral reefs boosts fish reproductive success. Nature Communications.


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