Diurnal measurements of sound attenuation (100 Hz—10 kHz) in a shallow (1-2 m), seagrass (Zostera marina) meadow are impacted by photosynthetic activity and water column height

Abstract

Seagrass meadows are important habitats that provide a variety of ecosystem services. As the seagrasses photosynthesize, they fill their vascular tissues with oxygen which is also released as bubbles into the water column. Measurements of sound attenuation were made in August 2022 in a shallow (1–2 m water depth) Zostera marina meadow in Shinnecock Bay, New York. Sound sources included tones (100 Hz–2 kHz) transmitted over an 8hour period (0800–1600 local time) and a 10 kHz Fishtek pinger operating over a 3 day period. Hydrophones were placed in the seagrass meadow at ranges of 1, 3, and 7 m from the source to determine attenuation. Vertical profiles of temperature, salinity, and dissolved oxygen were measured at the study site during the 8 hour tonal source experiment, and solar irradiance and tide level for Shinnecock Bay were obtained for the 3 day study period. Peak to peak sound pressure levels varied by more than 31 dB over a diurnal period for the 10 kHz signals. Sound attenuation of lower frequency tones varied from 9 to 30 dB both with dissolved oxygen (a proxy for photosynthetic activity of the seagrass) as well as water column height.