Soundscape enrichment enhances recruitment and habitat building on new oyster reef restorations.
Marine soundscapes provide important navigational cues to dispersing larvae in search of suitable habitat. Yet, widespread habitat loss has degraded marine soundscapes and their functional role in recruitment. Habitat restoration efforts can provide suitable substrate for habitat regeneration, such as constructing reefs to facilitate recruitment and habitat growth by oysters, but typically occur where soundscapes are degraded and recruitment is limited. Enhancing marine soundscapes on newly constructed reefs using speaker technology may ensure sufficient recruitment to establish a trajectory of recovery for the desired habitat. Across two of the largest oyster reef restorations in Australia, we deployed low-cost marine speakers at four sites and at three times throughout the recruitment season to test whether soundscape enrichment could boost recruitment and habitat formation by oysters. In the presence and absence of soundscape playback, we compared oyster recruitment rates to settlement panels across space and time, and oyster habitat cover and three-dimensional habitat building on newly constructed boulder reefs. On the settlement panels deployed across the two reef restorations, soundscape playback significantly increased oyster recruitment at 8 of the 10 sites by an average (±1 SE) 5.1 ± 1.9 times (5281 ± 1384 more larvae per m2), and by as much as 18 times. On boulders atop newly constructed reefs, where the restoration goal is for oysters to form three-dimensional habitat, the surface area covered by oysters after 5 months did not differ between speaker and control treatments. However, soundscape playback appeared to influence the earlier recruitment of oysters, resulting in significantly more large oysters per boulder that formed significantly more three-dimensional habitat building by an average 4.3 ± 1.2 times relative to nonspeaker controls. Synthesis and applications. Our results show that using speakers to enrich marine soundscapes at new restoration sites can boost oyster recruitment, resulting in more larger oysters that form more three-dimensional habitat atop reef restorations. In accelerating the formation of these vertical growth forms, which provide the ecological functions that motivate restoration efforts, the early application of speaker technology on new reef restorations may help steer ecological succession on a trajectory of desired habitat recovery, potentially reducing the substantial cost of ongoing intervention.