Passive acoustics as a tool for assessment of seagrass ecosystems

Abstract

Seagrass meadows are important coastal ecosystems, being the most productive biomes on Earth. The amount of produced oxygen is a key parameter for assessing the seagrass ecosystem metabolism and productivity. Several experiments conducted in Posidonia oceanica seagrass meadows have demonstrated that using active acoustic methods one can monitor the oxygen production. The acoustic method is sensitive to bubbles production and provides estimates at ecosystem level, what is an advantage to other methods. Healthy seagrass ecosystems are populated by several noisy marine taxa such as fishes and crustaceans, therefore the ambient noise can be used to assess the ecosystem metabolism and productivity. During two periods of one week in October 2011 and May 2013, acoustic and environmental data was gathered at several locations over a Posidonia oceanica bed in the Bay of Revellata in Corsica (France). The diurnal variability pattern of ambient noise characteristics (frequency band, power, directivity, and number of noisy sources) shows an evident correlation with oxygen production as measured by independent methods (optodes). The ambient noise data were dominated by impulse like waveforms associated with marine taxa. This work discusses the challenges faced on using these waveforms to invert for oxygen production.