Coral likes to make its ocean home in places with noisy neighbours

By Yvaine Ye

diver on coral reef
Pristine reefs are noisy place

Amy Apprill, Woods Hole Oceanographic Institution

Corals seem to appreciate noisy neighbours. Free floating coral larvae are more likely to settle on a surface – where they then begin growing into a stony reef – if the water is alive with the rumbling noise of a healthy fish population. The finding could be useful for efforts to restore damaged reefs to health.

Tiny coral larvae drift with the ocean currents, looking for a place to settle down by sensing multiple environmental cues including light, temperature and the chemicals released by other marine organisms.

Previous research suggests that coral larvae may also be picky about the sound condition underwater. To investigate further, Amy Apprill at the Woods Hole Oceanographic Institution in Massachusetts and her colleagues collected 990 mustard hill coral larvae (Porites astreoides) and placed equal numbers of them in 18 sealed boxes filled with filtered seawater. Nine of the boxes were transparent and the other nine were blackened to prevent light exposure.

Advertisement

The team placed the boxes in the Caribbean: six on a healthy, fish-abundant reef, another six on a less robust reef and the last six at a barren site. All three sites have similar light exposure but differ significantly in the level and quality of sound.

Quiet or noisy?

An environment with a healthy population of large fish and coral has louder low frequency sounds, such as deep grunting and chirping noises. In contrast, the barren site lacks these and is much quieter overall, save for the high-frequency sounds from snapping shrimp.

After two and a half days, the team found at least 50 per cent more larvae had settled in boxes at the healthy reef site compared to those at the other two locations.

It’s still unclear how these larvae listen. Apprill says they may sense the sound through the hair around their bodies.

The finding might help us develop better approaches to conserve or restore coral reefs, Apprill says. “Maybe we can put a speaker in the water on degraded or artificial reefs we are trying to recover and play back healthy reef sounds,” she says.

Journal reference: Royal Society Open Science, DOI: 10.1098/rsos.181358

More on these topics: