Invertebrate sounds from photic to mesophotic coral reefs reveal vertical stratification and diel diversity.

Although mesophotic coral ecosystems account for approximately 80% of coral reefs, they remain largely unexplored due to their challenging accessibility. The acoustic richness within reefs has led scientists to consider passive acoustic monitoring as a reliable method for studying both altiphotic and mesophotic coral reefs. We investigated the relationship between benthic invertebrate sounds (1.5-22.5 kHz), depth, and benthic cover composition, key ecological factors that determine differences between altiphotic and mesophotic reefs. Diel patterns of snaps and peak frequencies were also explored at different depths to assess variations in biorhythms. Acoustic recorders were deployed at 20 m, 60 m, and 120 m depths across six islands in French Polynesia. The results indicated that depth is the primary driver of differences in broadband transient sound (BTS) soundscapes, with sound intensity decreasing as depth increases. At 20-60 m, sounds were louder at night. At 120 m depth, benthic activity rhythms exhibited low or highly variable levels of diel variation, likely a consequence of reduced solar irradiation. On three islands, a peculiar peak in the number of BTS was observed every day between 7 and 9 PM at 120 m, suggesting the presence of cyclic activities of a specific species. Our results support the existence of different invertebrate communities or distinct behaviors, particularly in deep mesophotic reefs. Overall, this study adds to the growing evidence supporting the use of passive acoustic monitoring to describe and understand ecological patterns in mesophotic reefs.

Acoustic and photographic monitoring of coastal maritime traffic: Influence on the soundscape.

Due to the absence of Automatic Identification System data (used by 3.7% of the Calvi bay fleet), the acoustic monitoring of coastal environments presents difficulties. A specific visual monitoring protocol has been set up on a photographic observatory using the wide-angle camera GoPro®. The detection and localization of boats were carried by two image processing algorithms and allowed the creation of a map of maritime traffic for a surface of 3.48 km2. The ocean noise is described through two different scales (the individual scale and the global scale) which are linked to the traffic information. The Sound Pressure Level characterizes the individual sources and correlates with the distance of the nearest ship, whereas the Ambient Noise Level characterizes the background without individual sources and correlates with the number of boats present. A high spatial and seasonal variability due to coastal maritime traffic is observed in the broadband [100 Hz-30 kHz]. Closest to the traffic, the acoustic is punctuated by diel patterns of biological sounds and the use patterns of the boaters. In spite of an important diurnal flotilla (more than 550 boats per day), the nocturnal activity of fish remains an important element on the soundscape (average and median levels higher during the night).

Fish biophony in a Mediterranean submarine canyon.

Although several bioacoustics investigations have shed light on the acoustic communication of Mediterranean fish species, the occurrence of fish sounds has never been reported below -40 m depth. This study assessed the occurrence of fish sounds at greater depths by monitoring the soundscape of a Mediterranean submarine canyon (Calvi, France) thanks to a combination of Static Acoustic Monitoring (three stations, from -125 to -150 m depth, 3 km from coastline) and of hydrophone-integrated gliders (Mobile Acoustic Monitoring; from -60 to -900 m depth, 3-6 km from coastline). Biological sounds were detected in 38% of the audio files; ten sound types (for a total of more than 9.000 sounds) with characteristics corresponding to those emitted by vocal species, or known as produced by fish activities, were found. For one of these sound types, emitter identity was inferred at the genus level (Ophidion sp.). An increase of from 10 to 15 dB re 1 µPa in sea ambient noise was observed during daytime hours due to boat traffic, potentially implying an important daytime masking effect. This study shows that monitoring the underwater soundscape of Mediterranean submarine canyons can provide holistic information needed to better understand the state and the dynamics of these heterogeneous, highly diverse environments.

Sea chordophones make the mysterious /Kwa/ sound: identification of the emitter of the dominant fish sound in Mediterranean seagrass meadows.

The /Kwa/ vocalization dominates the soundscape of Posidonia oceanica meadows but the identity of the species emitting this peculiar fish sound remains a mystery. Information from sounds recorded in the wild indicates that the emitting candidates should be abundant, nocturnal and benthic. Scorpaena spp. combine all these characteristics. This study used an interdisciplinary approach to investigate the vocal abilities of Scorpaena spp.; morphological, histological and electrophysiological examinations were interpreted together with visual and acoustic recordings conducted in semi-natural conditions. All observed Scorpaena spp. (S. porcus, S. scrofa and S. notata) share the same sonic apparatus at the level of the abdominal region. This apparatus, present in both males and females, consists of 3 bilaterally symmetrical muscular bundles, having 3-5 long tendons, which insert on ventral bony apophyses of the vertebral bodies. In all chordophones (stringed instruments), the frequency of the vibration is dependent on the string properties and not on the rate at which the strings are plucked. Similarly, we suggest that each of the 3-5 tendons found in the sonic mechanism of Scorpaena spp. acts as a frequency multiplier of the muscular bundle contractions, where the resonant properties of the tendons determine the peak frequency of the /Kwa/, its frequency spectra and pseudo-harmonic profile. The variability in the length and number of tendons found between and within species could explain the high variability of /Kwa/ acoustic features recorded in the wild. Finally, acoustic and behavioural experiments confirmed that Scorpaena spp. can emit the /Kwa/ sound.

Automatic fish sounds classification.

The work presented in this paper focuses on the use of acoustic systems for passive acoustic monitoring of ocean vitality for fish populations. Specifically, it focuses on the use of acoustic systems for passive acoustic monitoring of ocean vitality for fish populations. To this end, various indicators can be used to monitor marine areas such as both the geographical and temporal evolution of fish populations. A discriminative model is built using supervised machine learning (random-forest and support-vector machines). Each acquisition is represented in a feature space, in which the patterns belonging to different semantic classes are as separable as possible. The set of features proposed for describing the acquisitions come from an extensive state of the art in various domains in which classification of acoustic signals is performed, including speech, music, and environmental acoustics. Furthermore, this study proposes to extract features from three representations of the data (time, frequency, and cepstral domains). The proposed classification scheme is tested on real fish sounds recorded on several areas, and achieves 96.9% correct classification compared to 72.5% when using reference state of the art features as descriptors. The classification scheme is also validated on continuous underwater recordings, thereby illustrating that it can be used to both detect and classify fish sounds in operational scenarios.

Illuminating the binding interactions of galactonoamidines during the inhibition of ß-galactosidase (E. coli).

Several galactonoamidines were previously identified as very potent competitive inhibitors that exhibit stabilizing hydrophobic interactions of the aglycon in the active site of ß-galactosidase (Aspergillus oryzae). To elucidate the contributions of the glycon to the overall inhibition ability of the compounds, three glyconoamidine derivatives with alteration in the glycon at C-2 and C-4 were synthesized and evaluated herein. All amidines are competitive inhibitors of ß-galactosidase (Escherichia coli) and show significantly reduced inhibition ability when compared to the parent. The results highlight strong hydrogen-bonding interactions between the hydroxyl group at C-2 of the amidine glycon and the active site of the enzyme. Slightly weaker H-bonds are promoted through the hydroxyl group at C-4. The inhibition constants were determined to be picomolar for the parent galactonoamidine, and nanomolar for the designed derivatives rendering all glyconoamidines very potent inhibitors of glycosidases albeit the derivatized amidines show up to 700-fold lower inhibition activity than the parent.

A Seaway Acoustic Observatory in Action: The St. Lawrence Seaway.

A setup for measuring spectral source levels (SSLs) of ships transiting along a seaway, the traffic density and shipping noise, is presented. The results feed shipping-noise modeling that reproduces the actual in situ observations to map shipping-noise variability over space and time for investigating its effects on aquatic organisms. The ship's SSL databank allows sorting the different contributors to total shipping noise for assisting in exploring mitigation approaches (e.g., fleet composition, rerouting). Such an acoustic observatory was deployed since November 2012 for a complete annual cycle of measurements in the deep downstream part of the St. Lawrence Seaway.

Wind dependence of ambient noise in a biologically rich coastal area.

The wind dependence of acoustic spectrum between 100 Hz and 16 kHz is investigated for coastal biologically rich areas. The analysis of 5 months of continuous measurements run in a 10 m deep shallow water environment off Brittany (France) showed that wind dependence of spectral levels is subject to masking by biological sounds. When dealing with raw data, the wind dependence of spectral levels was not significant for frequencies where biological sounds were present (2 to 10 kHz). An algorithm developed by Kinda, Simard, Gervaise, Mars, and Fortier [J. Acoust. Soc. Am. 134(1), 77-87 (2013)] was used to automatically filter out the loud distinctive biological contribution and estimated the ambient noise spectrum. The wind dependence of ambient noise spectrum was always significant after application of this filter. A mixture model for ambient noise spectrum which accounts for the richness of the soundscape is proposed. This model revealed that wind dependence holds once the wind speed was strong enough to produce sounds higher in amplitude than the biological chorus (9 kn at 3 kHz, 11 kn at 8 kHz). For these higher wind speeds, a logarithmic affine law was adequate and its estimated parameters were compatible with previous studies (average slope 27.1 dB per decade of wind speed increase).

Analysis and modeling of 255 source levels of merchant ships from an acoustic observatory along St. Lawrence Seaway.

An ensemble of 255 spectral source levels (SSLs) of merchant ships were measured with an opportunistic seaway acoustic observatory adhering to the American National Standards Institute/Acoustical Society of America S12.64-2009 standard as much as possible, and deployed in the 350-m deep lower St. Lawrence Seaway in eastern Canada. The estimated SSLs were sensitive to the transmission loss model. The best transmission loss model at the three measuring depths was an empirical in situ function for ranges larger than 300 m, fused with estimates from a wavenumber integration propagation model fed with inverted local geoacoustic properties for [300 to 1 m] ranges. Resulting SSLs still showed a high variability. Uni- and multi-variate analyses showed weak intermingled relations with ship type, length, breadth, draught, speed, age, and other variables. Cluster analyses distinguished six different SSL patterns, which did not correspond to distinctive physical characteristics of the ships. The broadband [20-500 Hz] source levels varied by 30 dB or more within all four 50-m length categories. Common SSL models based on frequency, length and speed failed to unbiasly replicate the observations. This article presents unbiased SSL models that explain 75%-88% of the variance using frequency, ship speed, and three other automatic identification system ship characteristics.

Whistle source levels of free-ranging beluga whales in Saguenay-St. Lawrence marine park.

Wild beluga whistle source levels (SLs) are estimated from 52 three-dimensional (3D) localized calls using a 4-hydrophone array. The probability distribution functions of the root-mean-square (rms) SL in the time domain, and the peak, the strongest 3-dB, and 10-dB SLs from the spectrogram, were non-Gaussian. The average rms SL was 143.8 ± 6.7 dB re 1 µPa at 1 m. SL spectral metrics were, respectively, 145.8 ± 8 dB, 143.2 ± 7.1 dB, and 138.5 ± 6.9 dB re 1 µPa(2)·Hz(-1) at 1 m.

Mapping probability of shipping sound exposure level.

Mapping vessel noise is emerging as one method of identifying areas where sound exposure due to shipping noise could have negative impacts on aquatic ecosystems. The probability distribution function (pdf) of sound exposure levels (SEL) is an important metric for identifying areas of concern. In this paper a probabilistic shipping SEL modeling method is described to obtain the pdf of SEL using the sonar equation and statistical relations linking the pdfs of ship traffic density, source levels, and transmission losses to their products and sums.

Arctic underwater noise transients from sea ice deformation: Characteristics, annual time series, and forcing in Beaufort Sea.

A 13-month time series of Arctic Ocean noise from the marginal ice zone of the Eastern Beaufort Sea is analyzed to detect under-ice acoustic transients isolated from ambient noise with a dedicated algorithm. Noise transients due to ice cracking, fracturing, shearing, and ridging are sorted out into three categories: broadband impulses, frequency modulated (FM) tones, and high-frequency broadband noise. Their temporal and acoustic characteristics over the 8-month ice covered period, from November 2005 to mid-June 2006, are presented and their generation mechanisms are discussed. Correlations analyses showed that the occurrence of these ice transients responded to large-scale ice motion and deformation rates forced by meteorological events, often leading to opening of large-scale leads at main discontinuities in the ice cover. Such a sequence, resulting in the opening of a large lead, hundreds by tens of kilometers in size, along the margin of landfast ice and multiyear ice plume in the Beaufort-Chukchi seas is detailed. These ice transients largely contribute to the soundscape properties of the Arctic Ocean, for both its ambient and total noise components. Some FM tonal transients can be confounded with marine mammal songs, especially when they are repeated, with periods similar to wind generated waves.

Under-ice ambient noise in Eastern Beaufort Sea, Canadian Arctic, and its relation to environmental forcing.

This paper analyzes an 8-month time series (November 2005 to June 2006) of underwater noise recorded at the mouth of the Amundsen Gulf in the marginal ice zone of the western Canadian Arctic when the area was >90% ice covered. The time-series of the ambient noise component was computed using an algorithm that filtered out transient acoustic events from 7-min hourly recordings of total ocean noise over a [0-4.1] kHz frequency band. Under-ice ambient noise did not respond to thermal changes, but showed consistent correlations with large-scale regional ice drift, wind speed, and measured currents in upper water column. The correlation of ambient noise with ice drift peaked for locations at ranges of ~300 km off the mouth of the Amundsen Gulf. These locations are within the multi-year ice plume that extends westerly along the coast in the Eastern Beaufort Sea due to the large Beaufort Gyre circulation. These results reveal that ambient noise in Eastern Beaufort Sea in winter is mainly controlled by the same meteorological and oceanographic forcing processes that drive the ice drift and the large-scale circulation in this part of the Arctic Ocean.

Automated segmentation of linear time-frequency representations of marine-mammal sounds.

Many marine mammals produce highly nonlinear frequency modulations. Determining the time-frequency support of these sounds offers various applications, which include recognition, localization, and density estimation. This study introduces a low parameterized automated spectrogram segmentation method that is based on a theoretical probabilistic framework. In the first step, the background noise in the spectrogram is fitted with a Chi-squared distribution and thresholded using a Neyman-Pearson approach. In the second step, the number of false detections in time-frequency regions is modeled as a binomial distribution, and then through a Neyman-Pearson strategy, the time-frequency bins are gathered into regions of interest. The proposed method is validated on real data of large sequences of whistles from common dolphins, collected in the Bay of Biscay (France). The proposed method is also compared with two alternative approaches: the first is smoothing and thresholding of the spectrogram; the second is thresholding of the spectrogram followed by the use of morphological operators to gather the time-frequency bins and to remove false positives. This method is shown to increase the probability of detection for the same probability of false alarms.

Shipping noise in whale habitat: characteristics, sources, budget, and impact on belugas in Saguenay-St. Lawrence Marine Park hub.

A continuous car ferry line crossing the Saguenay Fjord mouth and traffic from the local whale-watching fleet introduce high levels of shipping noise in the heart of the Saguenay-St. Lawrence Marine Park. To characterize this noise and examine its potential impact on belugas, a 4-hydrophone array was deployed in the area and continuously recorded for five weeks in May-June 2009. The source levels of the different vessel types showed little dependence on vessel size or speed increase. Their spectral range covered 33 dB. Lowest noise levels occurred at night, when ferry crossing pace was reduced, and daytime noise peaked during whale-watching tour departures and arrivals. Natural ambient noise prevailed 9.4% of the time. Ferry traffic added 30-35 dB to ambient levels above 1 kHz during crossings, which contributed 8 to 14 dB to hourly averages. The whale-watching fleet added up to 5.6 dB during peak hours. Assuming no behavioral or auditory compensation, half of the time, beluga potential communication range was reduced to less than ~30% of its expected value under natural noise conditions, and to less than ~15% for one quarter of the time, with little dependence on call frequency. The echolocation band for this population of belugas was also affected by the shipping noise.

Biogeography of acoustic biodiversity of NW Mediterranean coralligenous reefs.

Monitoring the biodiversity of key habitats and understanding the drivers across spatial scales is essential for preserving ecosystem functions and associated services. Coralligenous reefs are threatened marine biodiversity hotspots that are challenging to monitor. As fish sounds reflect biodiversity in other habitats, we unveiled the biogeography of coralligenous reef sounds across the north-western Mediterranean using data from 27 sites covering 2000 km and 3 regions over a 3-year period. We assessed how acoustic biodiversity is related to habitat parameters and environmental status. We identified 28 putative fish sound types, which is up to four times as many as recorded in other Mediterranean habitats. 40% of these sounds are not found in other coastal habitats, thus strongly related to coralligenous reefs. Acoustic diversity differed between geographical regions. Ubiquitous sound types were identified, including sounds from top-predator species and others that were more specifically related to the presence of ecosystem engineers (red coral, gorgonians), which are key players in maintaining habitat function. The main determinants of acoustic community composition were depth and percentage coverage of coralligenous outcrops, suggesting that fish-related acoustic communities exhibit bathymetric stratification and are related to benthic reef assemblages. Multivariate analysis also revealed that acoustic communities can reflect different environmental states. This study presents the first large-scale map of acoustic fish biodiversity providing insights into the ichthyofauna that is otherwise difficult to assess because of reduced diving times. It also highlights the potential of passive acoustics in providing new aspects of the correlates of biogeographical patterns of this emblematic habitat relevant for monitoring and conservation.

Source motion detection, estimation, and compensation for underwater acoustics inversion by wideband ambiguity lag-Doppler filtering.

Acoustic channel properties in a shallow water environment with moving source and receiver are difficult to investigate. In fact, when the source-receiver relative position changes, the underwater environment causes multipath and Doppler scale changes on the transmitted signal over low-to-medium frequencies (300 Hz-20 kHz). This is the result of a combination of multiple paths propagation, source and receiver motions, as well as sea surface motion or water column fast changes. This paper investigates underwater acoustic channel properties in a shallow water (up to 150 m depth) and moving source-receiver conditions using extracted time-scale features of the propagation channel model for low-to-medium frequencies. An average impulse response of one transmission is estimated using the physical characteristics of propagation and the wideband ambiguity plane. Since a different Doppler scale should be considered for each propagating signal, a time-warping filtering method is proposed to estimate the channel time delay and Doppler scale attributes for each propagating path. The proposed method enables the estimation of motion-compensated impulse responses, where different Doppler scaling factors are considered for the different time delays. It was validated for channel profiles using real data from the BASE'07 experiment conducted by the North Atlantic Treaty Organization Undersea Research Center in the shallow water environment of the Malta Plateau, South Sicily. This paper provides a contribution to many field applications including passive ocean tomography with unknown natural sources position and movement. Another example is active ocean tomography where sources motion enables to rapidly cover one operational area for rapid environmental assessment and hydrophones may be drifting in order to avoid additional flow noise.

On the consideration of motion effects in the computation of impulse response for underwater acoustics inversion.

The estimation of the impulse response (IR) of a propagation channel may be of great interest for a large number of underwater applications: underwater communications, sonar detection and localization, marine mammal monitoring, etc. It quantifies the distortions of the transmitted signal in the underwater channel and enables geoacoustic inversion. The propagating signal is usually subject to additional and undesirable distortions due to the motion of the transmitter-channel-receiver configuration. This paper shows the effects of the motion while estimating the IR by matched filtering between the transmitted and the received signals. A methodology to compare IR estimation with and without motion is presented. Based on this comparison, a method for motion effect compensation is proposed in order to reduce motion-induced distortions. The proposed methodology is applied to real data sets collected in 2007 by the Service Hydrographique et Océanographique de la Marine in a shallow water environment, proving its interest for motion effect analysis. Motion compensated estimation of IRs is computed from sources transmitting broadband linear frequency modulations moving at up to 12 knots in the shallow water environment of the Malta plateau, South of Sicilia.