The noise of motor boats over the Great Barrier Reef can stress its inhabitants, slow the growth of young fish and leave them less likely to live to adulthood


May 20, 2022

One of the breeding grounds for barbed chromis on the Great Barrier Reef

Dr. Sophie Nedelets

Some young fish that live in coral reefs exposed to the sounds of motorboats have stunted growth and may be half as likely to survive as fish on quieter reefs, possibly because noise pollution changes the way their parents take care of them.

prickly chromium (Acanthochromis polyacanthus) are fish that scatter water over their eggs, creating streams of inflowing oxygen that helps embryos grow. But in reefs with the noise of motorboats, parents swing their eggs less and look more excited – they swim more and are more likely to expose their hatchlings to more predator attacks than those who hear little or no engine noise.

“Any kind of unexpected noise can increase the stress response. And I think that’s what’s happening here with parenting, “he said Sophie Nedelets at the University of Exeter in the UK.

She and her colleagues snorkeled during the day on the Great Barrier Reef in Australia to observe and photograph wild nests of prickly chromium throughout the breeding season from October 2017 to January 2018. The team marked 59 nests, with an average of 126 eggs per nest, in six experimental sites off the coast of Lizard Island, Australia, and counts the surviving offspring every four days.

Three of the sites were restricted boating areas, where scientists asked motorboat drivers to stay at least 100 meters from the reefs or, if necessary, approach at least 20 meters without waking up. The other three sites were “loaded boat” areas, where the research team drove aluminum motor boats with an outboard engine – usually at full throttle – within 10 to 30 meters of the reef edge. The team made these boat trips about 180 times a day, for a total of about 75 to 90 minutes, to mimic a port or popular tourist or fishing areas.

They found that breeding pairs in restricted boating areas were twice as likely to have live offspring by the end of the three-month breeding season, she said.

To better understand this finding, the team captured adults with prickly chromium to pair them in a lab where scientists could study their parental behavior. They played recordings of natural coral reef through loudspeakers for 12 hours a day for 13 pairs of fish; for the other nine pairs, the recordings include 100 minutes of boat noise recorded from the reef and equipped with audio interruptions in 20-minute segments.

The noise from the boat did not change the number of eggs the fish lay, says Nedelets. However, in the laboratory, researchers note that adults often stop inflating their eggs when they hear recordings from motorboats, and do not inflate more during quiet periods to compensate. These fish also became more active, swimming longer distances – including away from the nest – during the reproduction of motorboat recordings, compared to adults who heard recordings of normal reef sounds. “It can be a sign of stress,” she said.

Embryos in restricted boating conditions are 1% longer than those in busy boating conditions, and 21-day-old hatchlings are 4% longer. Smaller offspring may be more susceptible to wild predators, Nedelets said.

The change in parental behavior also affected the survival of the pups, she said. In the lab, the chances of young fish surviving to 3 weeks of age almost doubled without the sound of a boat.

These findings suggest that fishermen, tourists, pleasure boats, cruise operators and even researchers could help reef populations recover from hurricanes and heat waves simply by slowing down their boats or, better yet, avoiding reefs altogether. says Nedelec.

“Coral reefs are going through these intense climatic shocks, affected by bleaching or cyclones, for example, and the populations that live there need to regenerate,” she said. “It’s an exciting decision. It cannot replace action against climate change and will not save coral reefs. But it can potentially support their resilience. “

Reference in the magazine: Natural communications, DOI: 10.1038 / s41467-022-30332-5

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