Repairing recruitment processes with sound technology to accelerate habitat restoration

Noise pollution causes parental stress on marine invertebrates, the Giant scallop example

In marine invertebrates, abiotic stresses on adults can act directly on gametes quality, which impacts phenotype and development success of the offspring. Human activities introduce noise pollution in the marine environment but still few studies on invertebrates have considered the impacts on adult or larval stages separately, and to our knowledge, never investigated the cross-generational effects of anthropogenic noise. This article explores parental effects of pile driving noise associated with the building phase of offshore wind turbines on a coastal invertebrate, Pecten maximus (L.). Adults were exposed to increasing levels of sound during gametogenesis, then their offspring were also exposed. The results highlight that anthropogenic noise experienced by the parents reduces their reproductive investment and modify larval response in similar conditions. Also, larvae from exposed adults grew 6-fold faster and metamorphosed 5-fold faster, which could be an amplified adaptive strategy to reduce the pelagic phase in a stressful environment.

Soundscape enrichment increases larval settlement rates for the brooding coral Porites astreoides

Coral reefs, hubs of global biodiversity, are among the world's most imperilled habitats. Healthy coral reefs are characterized by distinctive soundscapes; these environments are rich with sounds produced by fishes and marine invertebrates. Emerging evidence suggests these sounds can be used as orientation and settlement cues for larvae of reef animals. On degraded reefs, these cues may be reduced or absent, impeding the success of larval settlement, which is an essential process for the maintenance and replenishment of reef populations. Here, in a field-based study, we evaluated the effects of enriching the soundscape of a degraded coral reef to increase coral settlement rates. Porites astreoides larvae were exposed to reef sounds using a custom solar-powered acoustic playback system. Porites astreoides settled at significantly higher rates at the acoustically enriched sites, averaging 1.7 times (up to maximum of seven times) more settlement compared with control reef sites without acoustic enrichment. Settlement rates decreased with distance from the speaker but remained higher than control levels at least 30 m from the sound source. These results reveal that acoustic enrichment can facilitate coral larval settlement at reasonable distances, offering a promising new method for scientists, managers and restoration practitioners to rebuild coral reefs.

Habitat Restoration Restores Underwater Soundscapes and Larval Recruitment

Habitat degradation alters many ecosystem processes, and the potential for the reestablishment of ecosystem function through restoration is an area of active research. Among marine systems, coastal habitats are particularly vulnerable to anthropogenic degradation and, in response, are the focus of marine ecological restoration. One of the crucial functions of structurally complex coastal habitats (e.g., saltmarshes, seagrass meadows, kelp forests, coral reefs) are as nurseries to coastal and offshore species, many of whose larvae utilize sound to locate suitable nursery habitat. However, the effect of habitat degradation and subsequent restoration on underwater soundscapes and their function as navigational cues for larvae is unexplored. We investigated these phenomena in sponge-dominated hardbottom habitat in the waters surrounding the middle Florida Keys (Florida, United States) that have been degraded in recent decades by massive sponge die-offs caused by harmful algal blooms. One of the consequences of sponge die-offs are dramatic changes in underwater sounds normally produced by sponge-associated animals. We tested whether soundscapes from healthy hardbottom habitat influenced larval recruitment, and then examined how hardbottom degradation and restoration with transplanted sponges affected underwater soundscapes and the recruitment of larval fishes and invertebrates. Larval assemblages recruiting to healthy areas were significantly different than those assemblages recruiting to either degraded or restored hardbottom areas. Fewer larvae recruited to degraded and restored areas compared to healthy hardbottom, particularly during the full moon. Experimental playback of healthy hardbottom soundscapes on degraded sites did not promote larval community differences although some individual species responded to the playback of healthy habitat soundscapes. These results indicate that habitat-associated soundscapes have idiosyncratic effects on larval settlement, which is diminished by the degradation of nursery habitat but can be reestablished with appropriate habitat restoration.

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.