MEPS 585:31-48 (2017)  -  DOI: https://doi.org/10.3354/meps12370

ABSTRACT: Coastal soundscapes are dominated by broadband transient sounds primarily emitted by benthic invertebrates. These sounds are characterized by a very large dynamic of amplitude. The loudest ones propagate further and interfere with the detectability of benthic sounds by invading other more distant habitats. Acoustic diversity assessment is therefore biased when applying acoustic indices related to the signal’s power. Here, we propose new acoustic indices (IDSS: indices of the diversity of spectral shape) capable of extracting the diversity of the benthic invertebrate biophony (BIB) despite interference from loud and abundant sounds. A passive acoustic ecological survey was conducted in a shallow Mediterranean bay with a small-scale mosaic of biocenosis. The sound pressure level and spectrum of the BIB revealed that the rocky fringe had the most powerful biophony, propagating up to 3680 m, thus ‘invading’ other habitats. However, these power-based indices failed to depict BIB diversity. The IDSS allowed us to discriminate BIB diversity despite the interfering rocky fringe biophony, including low-power sounds not depicted by traditional power-based methods. Four main categories of benthic invertebrates sounds (BIS) spectra were found. Two categories (high-power, peak frequencies ~3 to 4 kHz) were mainly linked to the rocky fringe. Their contribution to the diversity (56%) decreased with increasing distance to the fringe, where low-power BIS (peak frequencies above 15 kHz) predominantly contributed to the BIB (42%) and may be specific to coralligenous reefs. The IDSS enables a better characterization and quantification of BIB diversity and soundscape structure with a fine spatial resolution (~200 m).

KEY WORDS: Soundscape ecology · Mapping biophony · Passive acoustic ecological survey · Benthic invertebrate sounds · Acoustics indices · Diversity of spectral shapes · Acoustic monitoring