Anthropogenic noise disrupts acoustic cues for recruitment.

Anthropogenic noise is rising and may interfere with natural acoustic cues used by organisms to recruit. Newly developed acoustic technology provides enriched settlement cues to boost recruitment of target organisms navigating to restoration sites, but can it boost recruitment in noise-polluted sites? To address this dilemma, we coupled replicated aquarium experiments with field experiments. Under controlled and replicated laboratory conditions, acoustic enrichment boosted recruitment by 2.57 times in the absence of anthropogenic noise, but yielded comparable recruitment in its presence (i.e. no boosting effect). Using the same technique, we then tested the replicability of these responses in real-world settings where independently replicated 'sites' are unfeasible owing to the inherent differences in soundscapes. Again, acoustic enrichment increased recruitment where anthropogenic noise was low (by 3.33 times), but had no effect at a site of noise pollution. Together, these coupled laboratory-to-field outcomes indicate that anthropogenic noise can mask the signal of acoustic enrichment. While noise pollution may reduce the effectiveness of acoustic enrichment, some of our reported observations suggest that anthropogenic noise per se might also provide an attractive cue for oyster larvae to recruit. These findings underscore the complexity of larval behavioural responses to acoustic stimuli during recruitment processes.

Repairing recruitment processes with sound technology to accelerate habitat restoration.

Humanity's ambitions to revive ecosystems at large scales require solutions to move restoration efforts beyond the small scale. There are increasing calls for technological solutions to reduce costs and facilitate large-scale restoration through the use of emerging technologies using an adaptive process of research and development. We show how technological enrichment of marine soundscapes may provide a solution that repairs the recruitment process to accelerate the recovery of lost marine habitats. This solution would solve the problems of current practice that largely relies upon natural recruitment processes, which carries considerable risk where recruitment is variable or eroded. By combining the literature with laboratory experiments, we describe evidence for "highways of sound" that convey navigable information for dispersing life stages in search for adult habitat. We show that these navigational cues tend to be silenced as their habitat is lost, creating negative feedbacks that hinders restoration. We suggest that reprovisioning soundscapes using underwater technology offers the potential to reverse this feedback and entice target organisms to recruit in greater densities. Collective evidence indicates that the application of soundscape theory and technology may unlock the recruitment potential needed to trigger the recruitment of target organisms and the natural soundscapes they create at large scales.