‘Posidonia meadows calling’: a ubiquitous fish sound with monitoring potential

Abstract

In the Mediterranean Sea, the seagrass Posidonia oceanica plays a key ecological role, and is protected by a range of legislation. Standard Posidonia monitoring programmes generally focus on the plant at different spatial and short temporal scales, without considering the organisms dependent on the ecosystem. Passive acoustic monitoring (PAM) has a high potential to non-intrusively monitor biological activities and biodiversity at high temporal resolution, and to assess ecosystem health. This is particularly relevant considering that Posidonia meadows host numerous sound-producing fish species. In this study, bottommoored hydrophones were deployed in nine Western Mediterranean meadows covering a distance of more than 200 km to identify acoustic features potentially relevant to monitor this critical habitat. Among eight identified fish sound categories, we found a single type of sound (that we will refer to as /kwa/) dominating the soundscape of Posidonia meadows over a time span of 7 months. Compared to other low-frequency sounds, the /kwa/ presented unique characteristics that suggest it is produced by a fish via fast contracting muscles. The /kwa/ was the only sound detectable under anthropogenic noise conditions, and little affected by it. Cluster analyses performed on 13 acoustic features revealed a high degree of call diversity. /Kwa/ diversity, combined with its large-scale (all meadows), long-term (7 months) occurrence and low noise interference, make the /kwa/ a promising candidate for PAM of Posidonia meadows. Furthermore, variability in acoustic features suggests a central role of the /kwa/ in communication. Overall, this work sets the basis for establishing the relevance of the /kwa/ in monitoring P. oceanica meadows and developing PAM techniques for this critical habitat.

The sea chordophones make the mysterious /Kwa/: emitter identification of the dominating fish sound in Mediterranean seagrass meadows

“…Cluster analysis carried out by Di Iorio et al (2018) on a consistent sample of /Kwa/ (i.e. N /Kwa/ =23,566) revealed a high degree of /Kwa/ variability.…”

“…Neptune seagrass meadows are crucial habitats that provide refuge, nursery and food to several fish and invertebrate species (Gobert et al, 2006;Abadie et al, 2018). It is somehow surprising that the first descriptions of the Neptune seagrass soundscape and of its fish biophonical component have been published only very recently (Ceraulo et al, 2018;Di Iorio et al, 2018). Di Iorio et al (2018) recorded the soundscape of nine Western Mediterranean meadows (over a 200 km range) over 7 months (March-October).…”

“…It is somehow surprising that the first descriptions of the Neptune seagrass soundscape and of its fish biophonical component have been published only very recently (Ceraulo et al, 2018;Di Iorio et al, 2018). Di Iorio et al (2018) recorded the soundscape of nine Western Mediterranean meadows (over a 200 km range) over 7 months (March-October). All nine sites were dominated by one particular fish sound type, the /Kwa/, which was 20 times more abundant than any other fish sound.…”

“…All nine sites were dominated by one particular fish sound type, the /Kwa/, which was 20 times more abundant than any other fish sound. The /Kwa/ possesses unique features which set this sound type apart from other Mediterranean fish calls, especially in terms of pulse shape, spectral content (bandwidth, peak frequency, pseudo-harmonic contour) and intrinsic variability (Di Iorio et al, 2018). The /Kwa/ is a fast, amplitude-modulated pulse train of 13±6 pulses repeated every 13± 4 ms with a peak frequency of 747±136 Hz characterized by pseudo-harmonics around the 800 Hz contour in the spectrographic view (Di Iorio et al, 2018;Fig.…”

“…<500 Hz; Desiderà et al, 2019), and only a few show harmonic and pseudo-harmonic contours. The /Kwa/ has been registered over a wide geographical range, from French and Corsican coastlines (Di Iorio et al, 2018) to Sicily (Ceraulo et al, 2018; the /Kwa/ was here called 'medium frequency fish sound') and Ustica Island (Hermand, 2006) and from Crete (M.B., personal observation) to the Azores (Rita Carriço, personal communication), passing through the Balearic islands (M.B., personal observation; Correa et al, 2018, 'croak sound'). None of the 38 currently identified Mediterranean vocal fish species produces the /Kwa/ (Di .…”