Coral Reef Restoration Through Sound: How Healthy Reef Noises Boost Coral Larvae Settlement

Researchers are exploring innovative techniques to support the restoration of coral reefs, with a new study revealing the potential of 'acoustic enrichment.' This method, which uses sounds from thriving coral reefs, has shown promise in attracting coral larvae to settle in degraded reef areas. Healthy coral reefs, teeming with the sounds of feeding fish, territorial grunts, and the snapping noises of shrimp, emit a unique chorus that coral larvae seem to recognize as a suitable habitat.

A study led by the Woods Hole Oceanographic Institution (WHOI) found that playing recorded sounds from vibrant reefs can prompt certain coral species, specifically golfball coral larvae, to settle and grow in degraded reef environments.

Encouraging Coral Settlement with Soundscapes:

In the study, researchers collected larvae of Favia fragum, known as golfball coral, from the U.S. Virgin Islands. The larvae were divided and placed in two quiet bays off St. John's coast. At one site, Great Lameshur Bay, researchers set up solar-powered speakers near the larvae, playing sounds from the nearby healthy Tektite reef. Meanwhile, another site, Grootpan Bay, used either silence or local bay sounds for comparison.

Results indicated that after 24 hours, around 30% of larvae exposed to healthy reef sounds settled, while no larvae settled in the control group without reef sounds. This pattern continued, with settlement rates increasing for both groups over 48 hours, although the initial acoustic boost was most effective within the first 36 hours. However, after this period, the larvae settled at similar rates, regardless of sound.

These findings align with previous research on coral larvae responsiveness to auditory cues, where larval corals, drifting through the water column, rely on environmental cues like chemicals, light, and sound to find suitable places to attach and grow. By enriching soundscapes in degraded reefs, scientists hope to provide coral larvae with the cues needed to recognize a hospitable environment, supporting coral reef restoration at a larger scale.

WHOI researchers, led by doctoral candidate Nadège Aoki, pointed out that golfball coral larvae, like many coral species, have a limited time frame in their larval stage to find a suitable habitat before resources run out. The larvae are most receptive to sound cues during their first 8 to 36 hours. After this critical period, they settle quickly, prioritizing location less as they exhaust their energy reserves.

This research highlights the potential for soundscapes to support coral regeneration, especially in controlled environments like aquariums, where replicating natural coral reproduction can be challenging. Using recorded reef sounds could improve settlement rates in nurseries, enhancing coral populations for restoration projects. WHOI’s marine biologist Aran Mooney noted that this study offers a broader understanding of coral biology and reproductive strategies, as responsiveness to sound cues may vary significantly between coral species.

The potential for this technique to be scaled is promising. While WHOI researchers emphasize that simply broadcasting sound is not a standalone solution, integrating acoustic enrichment with other conservation methods may offer significant gains for reef restoration efforts. As coral reefs face severe threats from climate change, pollution, and other human impacts, such integrative strategies become increasingly valuable for the survival of these essential ecosystems.

Coral reefs, covering less than 1% of the ocean floor, support over a quarter of all marine species and protect coastlines, providing food, shelter, and economic opportunities for millions worldwide. However, approximately 25% of coral reefs have been lost in the past three decades.

Supported by the Vere and Oceankind Foundations, the National Science Foundation, and WHOI's Reef Solutions Initiative, this research points to an exciting frontier in coral restoration, suggesting that with the right approach, acoustic enrichment could become a valuable tool in the ongoing efforts to protect and restore coral ecosystems globally.

(Source: Woods Hole Oceanographic Institution)