Application of geoacoustic inference for ecosystem monitoring of a seagrass meadow

Seagrasses provide a multitude of ecosystem services: they alter water flow, cycle nutrients, stabilize sediments, support the food web structure, and provide a critical habitat for many animals. However, due to threats to seagrass meadows and their associated ecosystems, these habitats are declining globally. Since the biological processes and physical characteristics associated with seagrass are known to affect acoustic propagation due to bubble production, which results in dispersion, absorption and scattering of sound, acoustical methods are proposed to assess the health of seagrass meadows. For this purpose, an experiment was conducted in the Lower Laguna Madre where the seabed was covered by a dense growth of Thalassia testudinum. During the experiment, a combustive sound source was used to produce broadband signals at ranges of 20 m to 1000 m from the receiver location. Three sensors were positioned at the receiver location: two hydrophones located within and above the seagrass canopy, and a single-axis geophone. The data were analyzed for the purposes of inferring environmental parameters in the seagrass meadow and to investigate the feasibility of using acoustical methods to monitor ecosystem health. Initial results indicate that water column void fraction can be inferred. [Work sponsored by ARL:UT IR&D and ONR.]