Oyster larvae swim along gradients of sound

Abstract

1. Marine soundscapes provide navigational information for dispersing organisms, but with wide-scale habitat loss, these soundscapes are becoming muted.Consequently, dispersing larvae that use soundscapes for navigation may be lost at sea, limiting the success of restoration efforts that rely upon the recruitment of dispersing organisms to restore habitat. Where limited larval supply constrains restoration efforts, using speakers to create gradients in healthy soundscapes could provide the navigational cue that attract larvae and enhances recruitment.2. Combining laboratory and field studies, we test whether broadcasting soundscapes might act as a directional cue for oysters targeted for national-scale reef restoration; the Australian flat oyster Ostrea angasi. In the laboratory, we tested whether settlement of larvae increases along a gradient of increasing sound intensity (8 m laboratory tank) versus a no sound control, and whether settlement increases with soundscapes that approximate healthy reefs.3. In the field, we tested the context dependency and magnitude of using boosted soundscapes for restoration practice in areas of low, medium and high background noise, by observing the settlement rates of naturally recruiting oysters at three restoration sites when exposed to boosted reef sound relative to ambient conditions. 4. In the laboratory, we showed that 83% of larvae swim horizontally towards reef sound to settle in greater densities closer to its source, a near doubling of the larvae (44%) that dispersed in the no sound controls. Larval settlement increased by 300% in the presence of reef sound relative to controls in the laboratory. In the field, speakers increased larval settlement in localities of lower background noise. To our knowledge, this is the first evidence that oyster larvae can swim horizontally and choose to move towards a sound source. Synthesis and applications.We discovered that oyster larvae can swim horizontally towards reef sound and then settle in higher densities, relative to controls.Importantly, this effect of sound on recruitment is enhanced in localities of lower background noise. We propose that where recruitment is limited, restoration practitioners best use acoustic technology in localities of lower background noise to guide larvae to boost recovery.

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

“…Planning to deploy substrate to coincide with known peaks in recruitment may provide a partial solution (Lipcius et al, 2021; McAfee & Connell, 2020), but this still relies on the relative chance encounter of sufficient larvae finding the new habitat, as opposed to their interaction with navigational cues (e.g. Williams et al, 2022). Building on previous observations that speakers can enhance the recruitment of diverse animal groups (reviewed by Williams et al, 2021), our results show that speakers can overcome the functional absence of natural soundscapes to help steer the initial weeks and months of rapid ecological succession on a trajectory towards the target habitat.…”

“…Nevertheless, these speakers (1) enriched soundscapes relative to ambient controls (i.e. increased the root‐mean‐square sound pressure level [SPL rms ] and snaps per minute, discussed below), (2) broadcast a clean snapping shrimp soundscape to the human ear (on land and in water) and (3) demonstrably influenced larval oyster swimming and settlement behaviour in the laboratory (Williams et al, 2022).…”

“…Planning to deploy substrate to coincide with known peaks in recruitment may provide a partial solution (Lipcius et al, 2021;McAfee & Connell, 2020), but this still relies on the relative chance encounter of sufficient larvae finding the new habitat, as opposed to their interaction with navigational cues (e.g. Williams et al, 2022).…”

“…Such larvae are typically considered relatively passive dispersers. However, oyster larvae, for example, actively swim towards and settle in response to habitat-specific sounds (Lillis et al, 2013;Williams et al, 2022), with settlement rates increasing with the 'attractiveness' (health) of the soundscape (Williams et al, 2021).…”

“…Such larvae are typically considered relatively passive dispersers. However, oyster larvae, for example, actively swim towards and settle in response to habitat‐specific sounds (Lillis et al, 2013; Williams et al, 2022), with settlement rates increasing with the ‘attractiveness’ (health) of the soundscape (Williams et al, 2021). In this Decade on Ecosystem Restoration (2021–2030), soundscape enrichment may offer a technological solution to enhance a fundamental component of restoration success; a means for enhancing early successional processes to steer restorations on the desired trajectory of recovery.…”