Mapping the diversity of spectral shapes discriminates between adjacent benthic biophonies

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).

From the Reef to the Ocean: Revealing the Acoustic Range of the Biophony of a Coral Reef (Moorea Island, French Polynesia)

“…The source level of the barrier reef of Moorea (SPL at 1 m) was estimated to be 147 dB re 1 µPa for the most energetic frequency band 3.5-5.5 kHz and was of 136 dB re 1 µPa for larger BTS band (1-70 kHz). These values are within the range of source levels usually found in coral reefs [84] and healthy temperate rocky reefs [51]. In this study, there was an increase in low frequency sounds emitted by fish (200-500 Hz) during the day and an increase of high frequencies emitted by benthic invertebrates (3.5-5.5 kHz) during the night.…”

“…To assess the temporal variability of the benthic invertebrate biophony (the sum of the many isolated broadband transient sounds (BTS) produced by benthic invertebrates [51] (Figure 2A)) recordings from the fixed station were analysed (Figures 1 and 2). BTS were grouped into four frequency "bands" (3.5-5.5 kHz, 6-8 kHz, 10-13 kHz and 14-17 kHz).…”

Listening forward: approaching marine biodiversity assessments using acoustic methods

“…It is also possible to take different statistical measurements of spectral variation, such as the spectral median or a specific percentile, to emphasize changes in the sources of continuous sounds, such as environmental sounds and biological choruses. Considering only high percentiles (95th or 99th) within specific frequency ranges can be used to characterize transient high-energy sounds [ 205 ]. Collating long-term spectrograms into a single power spectral density probability (PSDP) plot [ 206 ] can provide an overview of the levels of energy likely to occur at a given frequency and are source-specific if the source is significant at a site.…”

Investigating the utility of ecoacoustic metrics in marine soundscapes

“…ACI and H are the most widely used metrics in marine soundscape studies; however, there are dozens of terrestrial soundscape metrics that might be considered in the marine realm (Sueur et al, 2014;McPherson et al, 2016), including some emerging assessment tools that may better represent the time and/or frequency dynamics within a recording (e.g., Eldridge et al, 2016;Lossent et al, 2017). Soundscape synthesis experiments similar to those conducted in this study (and by Gasc et al, 2015 in terrestrial settings) can provide a tool for understanding these metrics.…”