Soundscape enrichment enhances recruitment and habitat building on new oyster reef restorations

Biogenic 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 restorations can provide suitable substrate for
habitat regeneration, such as reefs constructed to facilitate recruitment
and habitat growth by oysters, but typically occur where soundscapes are
degraded and recruitment 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 speakers at four sites and at three times throughout the
recruitment season to test whether soundscape enhancement could boost
recruitment and habitat building 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 formation 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 (±1SE) 5.1 ± 1.9 times
(5,281 ± 1,384 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 non-speaker controls. Synthesis
and applications. Our results show that using speakers to enhance marine
soundscapes boosts the number of oyster recruits, 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.