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

Xavier Raick,Éric Parmentier,David Lecchini,Lucia Di Iorio,Julie Lossent,Cédric Gervaise

doi:10.3390/jmse9040420

Abstract

The ability of different marine species to use acoustic cues to locate reefs is known, but the maximal propagation distance of coral reef sounds is still unknown. Using drifting antennas (made of a floater and an autonomous recorder connected to a hydrophone), six transects were realized from the reef crest up to 10 km in the open ocean on Moorea island (French Polynesia). Benthic invertebrates were the major contributors to the ambient noise, producing acoustic mass phenomena (3.5–5.5 kHz) that could propagate at more than 90 km under flat/calm sea conditions and more than 50 km with an average wind regime of 6 knots. However, fish choruses, with frequencies mainly between 200 and 500 Hz would not propagate at distances greater than 2 km. These distances decreased with increasing wind or ship traffic. Using audiograms of different taxa, we estimated that fish post-larvae and invertebrates likely hear the reef at distances up to 0.5 km and some cetaceans would be able to detect reefs up to more than 17 km. These results are an empirically based validation from an example reef and are essential to understanding the effect of soundscape degradation on different zoological groups.

Highlights

Accepted: 9 April 2021A soundscape is a collection of sounds composed of three acoustic sources: geophony, anthrophony and biophony that reflect important ecosystem processes and human activities [1,2]
Since different species have different hearing frequency ranges, the detection distance does not automatically correspond to the propagation distance of the reef sound
The aims of the present study are to describe the biophony of the barrier reef at Moorea Island (French Polynesia) to (1) measure its propagation distance in the ocean empirically, (2) describe how abiotic and anthropic factors interfere with it and (3) estimate the detection distance based on known audiograms

Summary

Introduction

Accepted: 9 April 2021A soundscape is a collection of sounds composed of three acoustic sources: geophony, anthrophony and biophony that reflect important ecosystem processes and human activities [1,2]. Coral reefs are considered to be hotspots of biodiversity [5] and acoustic hotspots [6,7] In these environments, snapping shrimps tend to dominate reef soundscapes at frequencies above 1 kHz [8], while a band attributed to damselfish is found around 400 Hz [9]. Numerous studies have estimated that these soundscapes may offer a reef orientation cue at relatively large distances [10,11,12], but there is a lack of empirical studies on reef sound propagation. Measuring the distance over which reef sounds propagate is necessary to determine their relative importance as cues for long-range orientation and habitat choice. As reef soundscapes are composed of sounds of different frequencies, they propagate over different distances.

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