Acoustic propagation in a seagrass meadow over diurnal and seasonal time scales

Acoustic propagation in seagrass meadows is highly sensitive to oxygen production through photosynthesis. In addition to gas volumes encapsulated within the seagrass, free bubbles are released into the water column as oxygen diffuses through the plant tissue, affecting acoustic dispersion, absorption, and scattering. Because the oxygen production cycle is largely driven by sunlight, these effects exhibit a diurnal dependence. Previous work explored using acoustics to monitor seagrass photosynthetic activity, but this study presents new results that span both diurnal and seasonal time scales. Acoustic propagation experiments were conducted in a seagrass meadow in a shallow bay on the Texas Gulf Coast. A piezoelectric sound source transmitted frequency-modulated chirps (0.1–100 kHz) over several diurnal cycles, and the received acoustic signals were match-filtered to obtain band-limited impulse responses. Water temperature, salinity, depth, dissolved oxygen, and solar irradiance were concurrently measured with oceanographic probes. Measurements were taken both in winter and summer to examine the seasonal dependence of seagrass photosynthesis and its effect on the acoustic propagation environment. Dependence of the received acoustic signal on various environmental parameters will be discussed with the goal of using acoustics to study seagrass photosynthesis and productivity. [Work supported by ARL:UT IR&D and ONR.]