This paper discusses the ambient noise acquired during the period of one week, from May 8 to 15, 2013 over a Posidonia oceanica bed in the Bay of la Revellata, Calvi, Corsica. The acoustic receivers were moored at 3 locations with water depth ranging from 2 to 20 m. Simultaneously with acoustic measurements, the dissolved O2 was measured by an array of optodes. The noise field in the band 2-7 kHz was dominant. The noise directionality and bottom reflectivity estimated using a short vertical array show a diurnal variability pattern. The mean noise power measured at all receivers shows also a diurnal variability pattern, which is negatively correlated with the O2 dissolved in the water. Changes in noise power between the night (highest noise power) and day period (lowest noise power) as high as 5 dB were observed at the various locations. These results suggest that the ambient noise power and directionality are correlated with the photosynthetic activity of the seagrass meadow and that a passive acoustic system can be used to monitor the O2 production of the meadow.