Finding a Restoration Lullaby: Using soundscapes to support oyster reefs

Abstract

Using soundscapes to support larval settlement and enhance oyster reef restoration

Atlantic oysters (Crassostrea virginica) are an iconic, keystone species supporting Massachusetts’ coastal ecosystems, shoreline protection, water quality, and a $30 M/yr aquaculture industry. Yet, a myriad of historical and present-day stressors has diminished oyster populations, severely compromising the ecosystem and in turn its socio-economic and ecological services. New tools and technologies are required to restore this keystone species and build resiliency to increasingly challenging environmental conditions. A key need, identified by town shellfish managers and restoration non-profits alike, is a means to increase oyster larval settlement rates in both aquaculture and field applications. Settlement rates can be extremely variable year-to-year in the field and even between larval sets in aquaculture tanks, limiting efficiency (cost and labor) and effectiveness of restoration and remote setting methods. A novel tool to enhance settlement rates has emerged from the growing field of soundscape ecology. Three species of oyster larvae have demonstrated substantially greater settlement in both lab and field experiments when presented with soundscapes of their natural settlement habitat. This includes the recruitment of wild larvae to restoration sites to support 3-dimenstional habitat creation. However, key knowledge gaps currently limit our ability to apply this powerful restoration tool in MA and New England. First, how generalizable are settlement-enhancing cues? We need to understand if there are broadly applicable settlement cues for the eastern oyster or if there are instead regional ‘dialects’. Second, while key data show southern populations of the eastern oyster settle in response to acoustic cues, there has been no work on northern populations or addressing acoustically mediated settlement with respect to the needs and constraints of oyster restoration and aquaculture. The latter is critical as we seek to develop and scale acoustic enrichment for the eastern oyster in MA and across its range.

We designed our objectives and methodology in collaboration with our industry partners and beneficiaries. Our first objective is to record soundscapes at three sites with high natural recruitment, two in MA and one in ME. Data collected at the MA sites will provide a library of soundscapes to use in settlement experiments. Comparing data from all three sites will broaden our understanding of the potential settlement-enhancing acoustic cues in the Northeast. We will work with project collaborators to deploy acoustic recorders for 2–3 weeks during the period of the first natural set. Our second objective is to determine how the presence of sound from an oyster habitat soundscape affects the setting efficiency of New England eastern oyster pediveligers. We will conduct controlled, calibrated lab experiments with conditions mirroring that of remote setting operations to enhance transferability of our results. Settlement rates of larvae exposed to MA soundscapes will be compared to rates under control conditions. Similar experiments using soundscape data collected from North Carolina addresses our third objective: assess how setting efficiency varies with differences in regional oyster habitat soundscapes. Eastern oysters from southern U.S. populations settled in higher rates to these sounds, but soundscapes differ substantially from NC to MA. These healthy oyster reef sounds may serve as a strong acoustic cue across the species range, or regional differences may support using MA soundscapes for MA restoration. In the second year, we will also integrate trials within a restoration non-profit’s hatchery to explore the transferability of these tools to an industry setting. We will continue to work closely with manger and restoration stakeholders to scale our methods for future field applications to restore wild oyster populations. Our partners have expressed strong interest, with actionable ideas for applying acoustic enrichment tools at their restoration and aquaculture sites to support Massachusetts’ coastal ecosystem and communities.