When boats buzz by the Great Barrier Reef, some small fish pause their parenting, lowering their offspring’s chances of survival, a May 20 study in Nature Communications finds. The results add to a growing body of research documenting the myriad ways noise pollution can harm marine organisms.

The research focuses on the breeding behavior of spiny chromis (Acanthochromis polyacanthus)—an abundant fish species on reefs throughout the tropical Pacific that exhibits extensive parental care. Pairs of these palm-sized fish fan their eggs with water to ensure the embryos receive enough oxygen until they hatch. Once that happens, the parents continue to guard the fry for up to four months.

Curious how noise from boats might affect that behavior, University of Exeter marine ecologist Sophie Nedelec and colleagues tagged and monitored 59 nests across six sites near Lizard Island, Australia, from October 2017 to January 2018, during the fish’s breeding season. Since most of the boat traffic in the area was from other researchers, the team asked their colleagues to keep at least 100 meters from three of the sites, or if that wasn’t possible, to stay at least 20 meters away and slow down to the point that they don’t produce a wake behind them while passing the sites. They made no such request at the other three sites, and even ensured that the fish would experience boat noise by passing within 10 to 30 meters of the reef’s edge at full throttle for 75 to 90 minutes per day.

At the end of the season, 65 percent of nests near the quieter sites had surviving young, versus 40 percent of nests in sites with heavy boat traffic, and the offspring raised in quiet sites were larger than the survivors from the noisy sites. The researchers also collected and kept adult fish in pairs in laboratory tanks, giving each a terracotta pot that served as a nesting cave, to observe whether different noise regimes altered their behavior. They found that pairs exposed to audio recordings of boats fanned their eggs less and acted more agitated than those that received ambient reef sounds. For example, they swam away from their nests more often than those in a more peaceful environment.

"Any kind of unexpected noise can cause a rise in the stress response. And I think that’s what’s going on here with the parenting behaviour," Nedelec tells New Scientist. Indeed, in previous work, she and her colleagues that noise can cause spikes in stress hormones in fish.

The upside to the finding is that it points to an immediate, straightforward way to improve fish survival, experts say. "While we try to tackle the biggest threat of climate change, we need simple solutions that reduce local threats," Steve Simpson, a University of Bristol researcher and coauthor on the paper, tells The Times. "Acoustic sanctuaries can build resilience on coral reefs, and help give reefs more chance of recovery."   

"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," Nedelec tells The Independent. "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."