“Traffic calming” helps coral reefs breed more

Spiny chromis family. Credit: Dr Sophie Nedelec

New research shows that less noise from motorboats helps coral reef fish have more babies.

Scientists did something called “traffic calming” on three reefs for a whole breeding season. They cut the number of boats within 100m and slowed down those that were still close.

Then, they watched how spiny chromis fish bred. At the end of the season, 65 percent of nests on reefs with less motorboat traffic still had babies in them, compared to only 40 percent on reefs with a lot of motorboat traffic.

On reefs with less noise, the babies were bigger, and at the end of the season, each nest had more babies.

Aquarium tests with the same species show that noise makes parents stop doing important things, like “fanning” their eggs with their fins to make sure they have enough oxygen.

The research was done on reefs near the Lizard Island Research Station on Australia’s Great Barrier Reef. The research was led by the universities of Exeter and Bristol.

“Coral reefs around the world face many problems, and the results of our experiment show how to help struggling populations,” said Dr. Sophie Nedelec, the lead author of the study from the University of Exeter.

“Reducing boat noise at reefs gives fish the much-needed rest they need to reproduce successfully.

“Any boat driver can make three easy changes: move boating channels farther away from reefs, drive slowly when getting close to reefs, and don’t anchor next to reefs.

“These solutions give people in the area the power to protect ecosystems that are weak.”

Dr. Nedelec added, “No one has ever tried a field experiment like this before.

“We kept an eye on six reefs (three with traffic calming and three without) where 86 spiny chromis broods were born during the summer breeding season by swimming along each reef every other day.

At the end of the breeding season, 30 of the 46 nests that were seen on reefs where traffic calming was done still had babies in them. On control reefs, where there was no traffic calming, only 16 of the 40 reefs still had young.

Dr. Laura Velasquez Jimenez of James Cook University, who was also a co-author, said, “Since spiny chromis hide their eggs in caves in the reef, it’s hard to find the nests before the babies hatch, so we did a parallel study in aquariums to look at how embryos develop.”

In this aquarium study, some parents and eggs of spiny chromis were kept with natural reef sounds playing through speakers, while others were kept with intermittent boat noise playing through speakers.

When boat noise was played, it stopped the fanning, but when natural sounds were played, it didn’t stop.

Professor Andy Radford from the University of Bristol, who is also a co-author, said, “The complementary lab study showed that these improvements in breeding are really due to limiting noise pollution and not other kinds of disturbance from the boats.”

All of the results show that reducing boat noise could help reef fish populations a lot and make reefs more resistant to the changes that are being caused by people.

Climate change is making cyclones and bleaching happen more often, and when they do, they cause a lot of damage.

After these bad things happen, finding ways to speed up population growth could mean the difference between a decline and a recovery.

But the team is clear that limiting the number of boats won’t be enough to protect coral reefs completely.

Professor Steve Simpson from the University of Bristol, who is the main author, said: “We know that reefs are in trouble all over the world.

“While we try to deal with climate change, which is the biggest threat, we need simple ways to deal with local threats.

“Acoustic sanctuaries can help coral reefs get stronger and give them a better chance of getting better.”

The paper is in the magazine Nature Communications.

Further information: Limiting motorboat noise on coral reefs boosts fish reproductive success, Nature Communications (2022). DOI: 10.1038/s41467-022-30332-5

Journal information: Nature Communications

Source: University of Exeter