Amsterdam – Underwater acoustic signals can provide insights into the health of the sea. This is the finding of a study published in the international journal Ecological Indicators, conducted by a multidisciplinary team from Italy’s National Research Council (CNR), comprising Pier Francesco Moretti of the Department of Earth System Science and Environmental Technologies (CNR-DSSTTA), Angela Pomaro of the Institute of Marine Sciences (CNR-ISMAR) and Silvano Buogo of the Institute of Marine Engineering (CNR-INM), as part of the PRIN SEAmPhonia project. The research involved deploying several hydrophones – microphones designed to record underwater sounds – during a series of experimental campaigns at the Acqua Alta oceanographic platform in the Adriatic Sea, off the coast of Venice. The work also benefited from the expertise of the Underwater Acoustics Laboratory at the CNR research area in Tor Vergata. “The study proposes an innovative approach based on analysing the underwater soundscape, meaning the acoustic signature produced by the combined physical, biological and human processes that characterise the marine environment. The novelty lies in identifying an integrated characteristic of the marine ecosystem as a whole by observing its acoustic field, rather than analysing the contributions of individual sound sources separately,” explains Angela Pomaro. “The aim is to identify a new indicator capable of assessing ecosystem conditions through the acoustic signals it produces, taking the system as a whole into account and moving beyond traditional approaches based on individual sound sources or the low frequencies associated with shipping traffic.” Using data collected at the Acqua Alta oceanographic platform, the researchers identified a persistent day-night oscillation in high-frequency acoustic signals that could not be explained solely by environmental physical factors. “This pattern could reflect the collective rhythms of the ecosystem’s biological components, acting as a kind of ‘heartbeat’ of the sea that provides information about its health,” Pomaro continues. “More specifically, the discovery concerns the day-night oscillation in the spectral slope at high frequencies. This particular feature of the acoustic spectrum could reflect the overall behaviour of the ecosystem rather than that of any single biological or physical component.” The significance of the finding lies in the fact that this information emerges from a characteristic typical of complex systems: the power law identified at the higher frequencies of the marine acoustic spectrum, which is linked to the concept of scale invariance. “The observed oscillations could provide a new ecological indicator associated with the biological activity of the ecosystem. This indicator can be compared to body temperature, which offers an overall measure of health without describing every individual biological process. Changes in the indicator would therefore signal a change in the system, although further analysis would be needed to identify the specific causes,” says Pier Francesco Moretti of CNR-DSSTTA. The study points towards an approach based on measuring system-level indicators that can continuously describe the overall condition of marine ecosystems in a non-invasive way and allow comparisons between different sites. “An indicator that does not depend on instrument calibration opens the way to an innovative method for monitoring marine ecosystems. Unlike approaches used to date, which often rely on low frequencies associated with shipping traffic and absolute sound intensity levels, as set out in the European Marine Strategy Framework Directive (MSFD), this methodology could make it possible to assess ecosystem health and detect changes at an early stage by listening to the marine soundscape,” Moretti concludes. (9colonne)