Identifying sentinel indicators of acoustic propagation conditions using the soundscape codea)

Substrate composition in shallow water environments, including biological communities, strongly impacts transmission loss as propagating sounds are repeatedly reflected, scattered, and absorbed by the air-water interface and seafloor [Farcas, Thompson, and Merchant (2016). Environ. Assess. Rev. 57, 114-122]. The soundscape code (SSC), a technique that implements a collection of metrics to provide rapid, quantitative assessment of soundscape properties, was used to characterize coastal habitats in the Gulf of Maine. To determine whether SSC metrics of amplitude, impulsivity, uniformity, and periodicity serve as sentinel indicators of marine habitat composition and spatial distribution, hydrophones were deployed in three coastal habitat types (sand, macroalgae, and eelgrass) containing varied acoustic propagative properties. Deployments were replicated in four geographic locations along the Maine and New Hampshire coastlines. Hourly metrics were calculated across five frequency bands (low, 10-100 Hz; mid 100-1000 Hz; high1, 10 kHz; ultra-high 10-144 kHz, and broadband 10 Hz-144 kHz) and employed for multivariate statistical analysis to draw direct comparisons among soundscapes. Discriminant analysis revealed that habitats and geographic regions could be differentiated with high accuracy using SSC metrics as predictors. This finding supports the use of these metrics as sentinel indicators of acoustic propagation conditions in coastal Gulf of Maine ecosystems.