Comparative analysis of fish sounds recorded during an early acoustic experiment in a Mediterranean seagrass meadow

Posidonia oceanica seagrass meadows constitute an important ecosystem of the Mediterranean Sea, providing habitat for many species of invertebrates and fishes, some of which produce sounds with distinctive features. Using such sounds to monitor marine habitats is at the core of passive acoustic monitoring. In the Mediterranean, an arched frequency modulation centred around 747 Hz, which aurally sounds like /kwa/, has been investigated as an environmental proxy. Remarkably, these sounds were already noted as a distinctive feature of the soundscape recorded during an early acoustic experiment, USTICA 99 (Ustica, Sicily, Italy), which simultaneously measured photosynthetic gas exchanges and fish migration at the scale of a Posidonia meadow. In this study, we revisit that dataset to describe the specific characteristics of the early recorded /kwa/ sounds and compare them with more recent field studies conducted in French P. oceanica meadows, approximately 500 km north of Ustica and 15 years later. Our comparative analysis confirms a high degree of homogeneity in the /kwa/ sounds, with some variations that are further examined.