The soundscape of Mediterranean shallow water

In the marine environment, acoustic signals are source of information, crucial for inter and intra specific communication, i.e. during territorial and reproductive activities, orientation and habitat recognition. Soundscape analysis highlights the coexistence and the interconnection of all acoustic components, revealing different ecosystem processes. The Mediterranean Sea comprises a plurality of ecosystems and shows a high degree of biological diversity. However, poor studies have been carried out to investigate if this ecological richness is reflected in the acoustic environment. Objective of this work is to investigate the soundscape of Mediterranean coastal habitats in protected and impacted areas, with the aim of improving knowledge for the conservation of shallow waters habitats. Biological signals were described, together with their temporal and spatial patterns, and the impact of anthropogenic noise was estimated. Furthermore, the efficiency of the Acoustic Complexity Index (ACI), developed to study the acoustic complexity of terrestrial environment, was tested for Mediterranean coastal habitats. In order to obtain a baseline of the Mediterranean coastal soundscape, the marine protected area of Lampedusa Island was monitored one year long. The soundscape is dominated over 2 kHz by snapping shrimps activity along all the year, following daily and seasonal patterns. The fish choruses characterize the frequencies below 2 kHz during the summer season. Results show that the presence of a protected zone does not preserve the acoustic space of species, since the boat noise masks during 46% of time sampled the frequency band used by soniferous fish. Moreover, the acoustic complexity index (ACI), applied in this Mediterranean shallow waters, was recognized as a good indicator for biological emissions, even if a major adjustment was needed to be applied to the marine environment. In order to overcome this issue, I tested how ACI efficiency varies by adjusting its temporal resolution, applied during ACI computation, in relation to the different biological signals considered. Compared to terrestrial habitats, the soundscape of marine environment is characterized by manifold biophonical component in terms of type of signals (impulsive, tonal) and of frequency extent (from few Hz to hundreds kHz), that could influence index response. I found that higher temporal resolution was required for pulsed signals than for tonal sounds, while ACI efficiency for boat noise and geophonies did not change when a different temporal resolution was selected. After to have demonstrated the functioning of the acoustic metrics in marine coastal environment, I applied them to study a high impacted area made up of the typical Posidonia oceanica meadow and sandy patches. Results showed that these two different habitats are characterized at the high and medium frequencies by distinct soundscapes and, the meadows have a more complex soundscape. New biological signals have been described for the first time and potentially attributed to both endemic and alien fish species. Finally, a new approach to analyze the impact of noise in a shallow water environment has been carried out. The propagation of particle velocity generated by pile driving in an enclosed and simulated shallow sandy habitat resulted complexly related to the sound pressure transmission. This thesis represents a base study for the future Mediterranean soundscape analysis, describing and characterizing different acoustic environments and their components. This first contribution paves the way for new questions and studies through different approaches. For example, the connection between the health status of the habitat and its soundscape complexity is poorly analyzed, and nowadays totally unknown in the Mediterranean marine system. The full comprehension of this relationship, mostly in key habitats, such as Posidonia oceanica meadows, could make the soundscape approach one of the most powerful tool to monitor of habitat changes under a growing human impact.