Acoustic monitoring of O2 production of a seagrass meadow

• Show the effects of photosynthesis in acoustic propagation over a seagrass meadow
• Discuss the differences in the various signal frequency bands
• Relate acoustic perturbations with oxygen measurements by optodes
• Show the potential of an acoustic system to infer oxygen production at ecosystem level instantaneously
• Suggest that primary production is underestimated by methods that rely on the mass balance of dissolved O2

Acoustic data were acquired in October 2011 over a Posidonia oceanica meadow in the Bay of la Revellata, Calvi, Corsica. The purpose was to develop an acoustic system for monitoring the oxygen (O2) production of an entire seagrass meadow. In a shallow water area (< 38 m), densely covered by P. oceanica, a sound source transmitted signals in 3 different bands (400–800 Hz, 1.5–3.5 kHz and 6.5–8.5 kHz) toward three self-recording hydrophones at a distance of 100 m, over the period of one week. The data show a high correlation between the diel cycle of the acoustic signals' energy received by the hydrophones and the temporal changes in water column O2 concentration as measured by optodes. The results thus show that a simple acoustic acquisition system can be used to monitor the O2-based productivity of a seagrass meadow at the ecosystem level with high temporal resolution. The finding of a significant production of O2 as bubbles in seagrass ecosystems suggests that net primary production is underestimated by methods that rely on the mass balance of dissolved O2 measurements.