This paper describes the lessons learned from the experiment BIOCOM'19 carried out in January 2019, in a shallow water bay off the island of Cabo Frio (RJ, Brazil). A dual accelerometer vector sensor hydrophone was deployed for two days, near a rocky shore covered with a significant benthic fauna. The results show that the frequency band above approximately 1.5 kHz is mostly associated with invertebrate biological noise and that the acoustic and the particle motion fields have a similar behavior, following the usual dawn-dusk activity pattern, and a coherent directivity content. At low frequencies, below ∼300 Hz, the acoustic pressure and the particle acceleration fields have significantly different spectral content along time. Many of these differences are due to anthropogenic noise sources related with nearby boating activity, while during quiet periods, they may be attributed to the biological activity from the rocky shore.
Soundscape ecology has gained prominence in the monitoring of marine ecosystems due to its non-invasive characteristics and spatiotemporal efficiency. However, the development of ecoacoustic indices is a recent field that needs to address many challenges to fulfill its great potential, especially in the context of marine ecology. Here, we reviewed the most recent studies that used ecoacoustic indices in marine ecosystems. The literature search was conducted in the Scopus (Elsevier) database and used the chain referral sampling in the list of references of each publication. In total, we identified 27 publications that used ecoacoustic indices in marine environments such as coral reefs, rocky shores, coastal regions, and offshore regions. A total of four major limitations were identified and addressed, including: the challenge to find adequate acoustic bioindicators; the lack of a universal index or standardized protocol; the issue that most acoustic indices applied to marine environments have been developed to be used in terrestrial environments; and the lack of studies that have tested ecoacoustic indices under different environmental conditions. Once these challenges are addressed, the analysis of marine sound based on the interpretation of ecoacoustic indices has a great potential to become one of the most cost-effective tools for monitoring environments.
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