‘Traffic calming’ gives Great Barrier Reef fish better chance of survival, study finds

The perpetually-plagued Great Barrier Reef, off the east coast of Australia, has seen its fair share of troubles in the past few decades, from coral bleaching and acidification because of the climate crisis, to water pollution.

And now, a new worry for the iconic marine ecosystem – too much noise.

A new study has found that fewer fish hatchlings survived the breeding season in noisier areas of the reef than more serene locales. Hatchlings in the quiet areas were also bigger, which could help them avoid getting eaten.

Researchers say that protecting reefs from excess noise could help support these ecosystems in the face of their myriad threats.

“I’d really love to see – if we were able to scale this across multiple marine sanctuaries, create acoustic sanctuaries even – whether this is something that we can use to help marine life to rebound after these inevitable, at the moment, stressful events due to climate change like beaching and destruction due to cyclones,” Sophie Nedelec, a marine ecologist at the University of Exeter and one of the study authors, told The Independent.

The ability to hear may help fish do everything from defending their territory to finding a good place to live, Dr Nedelec said.

But despite all the sounds in the water, boats are much louder, she said. And because sound travels better underwater than in the air, even faraway boats can seem very loud.

For this study, Dr Nedelec and her colleagues set up six zones around a field station in the reef – three where boats around the station could move freely and three where they prohibited boats.

Most of the traffic in the area came from people associated with the research station, she says, so they were able to regulate it pretty well – plus, they drove some extra motorboat laps around the “noisy” sites to make sure those areas were louder.

They studied the nests of a fish called the spiny chromis, checking on hatchlings and measuring them over the course of the breeding season to see how many survived and how they were growing. The results were published on Friday in Nature Communications.

In quiet zones, 65 per cent of the nests still had baby fish by the end of the season – but that number dropped to 40 per cent for noisy zones. Hatchlings in the quieter areas were also larger than those in the noisy zones.

Fish size could be connected to survival. Getting eaten is the biggest threat to a young fish – the larger you get, the fewer predators can eat you, Dr Nedelec says. In previous work, they’ve also found that boat noise can impair a fish’s normal anti-predator manoeuvres, she notes.

In addition to their field work, the team looked at the behaviours of some captive fish in response to boat noise. A lot of reef fish keep their nests in hidden spots to protect their young from predators, Dr Nedelec says. However that also means the nests don’t get a lot of water moving in and out of the nest area, which could reduce oxygen levels.

To counteract this, adult fish will often wave their fins to keep the water flowing and the oxygen coming in. But the study found that boat noises interrupted that fanning activity. Differences in growth rates between hatchlings in noisy and quiet zones could be a result of oxygen availability over the young fish’s lifespans, Dr Nedelec notes.

Previous work by Dr Nedelec and her colleagues has found that boat noises can spike stress hormones in fish – causing a similar reaction to your heart rate going up, she says. And, much like in humans, chronic stress could have long-term effects on a fish’s health.

But despite all the potential negative effects of boat noise on fish, the inverse is also true – keeping areas quiet could help protect fish.

“I was really pleased to find out that reducing the motorboat noise was improving the survival,” Dr Nedelec says.

With that in mind, she says she’d be interested to know if the quiet zones put in place for this study could be implemented in larger protected areas to support reef fish.

“All we need to do is drive further away from reefs, and if we do go near reefs, then just to go a bit slower,” Dr Nedelec says.

Noise is far from the only threat to coral reefs. The excess atmospheric carbon dioxide that is heating the planet is also causing mass “coral bleaching” events – where the algae that give corals their colour disappear, leaving the reef pale and unhealthy-looking.

Carbon dioxide in the atmosphere also makes the oceans more acidic, which might impair coral growth.

While we should be doing “absolutely everything that we can” to address the climate crisis, that’s “not always easy”, Dr Nedelec says. But something like reducing noise could help reefs in the meantime, she adds.

“As soon as you stop making so much noise, there’s less noise, straightaway. It doesn’t linger in the ecosystem in the same way as other types of pollution do,” she says.

“So seeing as we know that making a change to the noise can make a positive difference, it could be one of the first things that we do.”